Thursday April 17 , 2014
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Lessons learned from incidents

Many ALARA Newsletters include an article on a radiological incident. These articles first describe the incident and the circumstances to finish by lessons to be learned. The aim of these article is to encourage good practices (especially the implementation of the ALARA principle) within different sectors. The incidents reports are anonymous and have been selected on the basis of those which provide interesting and useful lessons, to help others prevent such incidents and/or mitigate the consequences. Most of the articles published in the ALARA Newsletters were taken from the OTHEA/RELIR database.

This section includes all the incident cases presented in the different Newsletters.

Study case n°25: Incident involving stainless steel sheets contaminated with cobalt 60 in Italy
Study case n°24: Analyse of unintended overexposure during palliative treatment and the development of a critical incident reporting system in Switzerland
Study case n°23: Radiological incident during treatment of a breast cancer in Germany
Study case n°22: Retrieval of a fire damaged gauge containing a radioactive source in Ireland
Study case n°21: Radiological Incident involving a Tc-99m generator in Ireland
Study case n°20: Transport case prompts reminder on the importance of RP controls
Study case n°19: Radionuclide gauges in rough industrial environments
Study case n°18: Incident involving Radioactive Lightening Conductors (Croatia)
Study case n°17: Incident involving a gauge system
Study case n°16: Incident in a textile treatment plant (France)
Study case n°15: Radiography incident (Spain)
Study case n°14: Transport of gauges from a refurbished brewery
Study case n°13: Radiological incident involving contaminated scrapyards (Macedonia and Italy)
Study case n°12: Contamination of workers during dismantling of glove boxes (Czech Republic)
Study case n°11: A radiography incident at a research reactor (Sweden)
Study case n°10: Radiography incident (Sweden)
Study case n°9: Radiography incident (Italy)
Study case n°8: Radiography incident (Italy)
Study case n°7: Radiography incident (France)
Study case n°6: Radiography incident (Sweden)
Study case n°5: Gammagraphy incident (Spain)
Study case n°4: Radiography incident
Study case n°3: Incident in a university laboratory
Study case n°2: Radiography incident

Study case n°1: Incident in a research laboratory

The radioactive incident of ACINEROX in Spain

25. Incident involving stainless steel sheets contaminated with Co-60 in Italy

European ALARA Newsletter - Issue 23

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Description of the incident
Between January and February 2008, the Carabinieri of Environmental Care Command – Radioactive Materials Pollution Unit, supported by APAT (Italian Environmental Protection Agency) and other Competent Authorities, seized 3 hot rolled stainless steel sheets in coils contaminated by cobalt 60. Each coil weighs about 10 tons and is made of sheets 6 mm thick (see figure below). Probably they are part of a single casting. Fortunately, they were destined for industrial applications (like tanks, chimneys, pulleys) not for domestic use.

The shipment was a combined transport of many containers from China to an Italian plant through a South Korean export society. The same ship carried more than 180,000 tons of steel, but only these 3 coils were contaminated. The other coils had different thickness or different identification number.

The dose-rate at contact was about 20 mSv/h (52 mSv/h inside the coils) and 4 mSv/h at one meter.

In steel factories, cobalt sources are used in the blast furnace to check the thickness of the walls. If the maintenance works are not adequate, the sources can fall in contaminating all the melt.

In Italy, radiometric checks are compulsory only on  metal scraps and not on other metallic products. In some harbours not all the imported containers are investigated by portal monitor or handhold instruments. For these reasons, the contamination was discovered later, only after the radiometric check of metal scraps coming out from the steel works in the factories. At the end of the investigations, more than ten persons were reported to the public persecutor for many offences against the environment and all the contaminated steel were seized in Italy and the others countries where it has been exported (Croatia, Turkey, Egypt and Poland).

Lessons learned
The seizure of contaminated steel and other similar events that have happened in Italy in the past, clearly demonstrate that the problem of orphan sources involves not only scrap metal but the semi-finished products, too. In conclusion, radiometric checks should be compulsory on all metal products. The Italian law is changing in this way.

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24. Unintended overexposure during palliative radiation therapy treatment in Switzerland

European ALARA Newsletter - Issue 22

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Legal provisions
In Switzerland, the use of ionising radiation in medicine is regulated by several ordinances. Whilst the Radiological Protection Ordinance gives a general framework, more detailed requirements are specified in technical Ordinances, such as the “Use of unsealed sources”, the “Use of sealed sources in medicine” and the “X-ray” Ordinances. The Ordinance on medical accelerators is particularly relevant to radiation therapy, and in particular, requires overdoses to be notified to the surveillance authorities (Art. 27) (as is also required in Germany – see ALARA Newsletter Issue 21, October 2007).

Incident summary
In 2006 an incident took place in a radiation therapy unit whereby an elderly patient was overexposed during a palliative treatment. The incident was discovered shortly after the final dose fraction had been administered, whilst undertaking routine checks of calculations. As required by law, the surveillance authority (SFOPH – Swiss Federal Office of Public Health) was informed by the medical physicist in charge.
The circumstances which led to the incident were investigated and fully clarified. An error was made in the hand-calculation whereby the fraction dose was not divided by the number of fields (2 fields: pa/ap), resulting in the wrong number of monitor units. None of the staff involved in the treatment noticed the unusually high number of monitor units. Fields are normally thoroughly checked one day after treatment starts. However, this treatment consisted of 3 fractions and, due to a lack of time, the monitor units were not re-calculated before the end of the final fraction which was 2 days after the start of treatment. As a consequence, the patient received a dose higher than intended.
Following the incident the overexposure of the patient was investigated; the calculation mistake had resulted in the patient being treated with 30 Gy instead of 15 Gy. It was decided to closely observe the patient during their palliative care. Sadly, the patient passed away a few weeks later. A post-mortem was undertaken, and the cause of death was found to be multifactorial with several findings unrelated to the overexposure.

Lessons learned / Measures
Several measures were identified in order to avoid such mistakes in the future:

  • The definition of a stop-dose in the record and verify (R&V) system, which halts further treatment after the first session until the calculation check is performed,
  • The calculation check has to be signed, and thus documented,
  • The used data parameters, which are important for monitor unit calculation, correct delivery and documentation, have to be verified and listed prior to the second treatment.

Radiation therapy critical reporting system
Following discussions with relevant professional bodies, a working group comprising members of the Swiss Society of Radiobiology and Medical Physics (SSRMP) and the Swiss Association of Radiation Oncology (SASRO) was brought together to analyse future cases and propose measures in order to avoid future incidents. This group has been working on a CIRS (Critical Incident Reporting System) with the aim of making such a system available to each radiation therapy department in Switzerland. In collaboration with the SFOPH, they have been defining rules and content of this national CIRS database called ROSIS_CH. One issue specific to Switzerland relates to the use of different languages in different areas and it is planned to include the ability to enter the text of the input in the local language in the local expandable database with a translation to the different languages appearing in the national database, thus avoiding speculations about the source of the data. It is hoped the system will be available sometime in 2008.

   

23. Incident during treatment of a breast cancer

European ALARA Newsletter - Issue 21

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Legal provisions
General provisions for the exposure of patients to radiation are laid down in the Radiation Protection and the X-Ray Ordinances. Detailed requirements are given in the Guideline Radiation Protection in Medicine. Here the responsibilities of the medical practitioner, the medical physics expert and paramedical personnel are specified, in particular concerning dose prescription, therapy planning and application of radiation to the patient. In case of any unusual event, the radiation protection officer has to immediately inform the competent authority.

Incident summary
In 2004, a patient was overexposed during treatment for breast cancer. The incident was discovered two weeks after the end of the radiation treatment, when the patient experienced severe skin reactions.

Three medical practitioners were involved in the treatment of this patient and some of the changes in the treatment were not coordinated within the medical team. The patient received a complex treatment at an electron linear accelerator that covered seven fields and intended a total energy dose of 50 Gy in the target volume. A proper field simulation took place on two days before the therapy began. Due to lack of information, the team from the second day did a wrong field simulation, which was erroneously verified by a medical practitioner. Consequently, the patient received a dose significantly higher than intended.

After the patient worried about difficulties in breathing and skin burns on her back, fibrotic changes of the lung were found it was discovered that she had been overexposed. The wound on the back disappeared some months later.

The authority was immediately informed about the incident. As a result of several examinations, the medical practitioners were instructed:
  • To improve internal communication and documentation of the treatment planning; and
  • To verify treatment parameters more often during the different stages of treatment.

 

Dose to the patient
The overexposure of the patient could not be investigated precisely afterwards. The additional dose in a worst-case scenario was estimated to be about 90 Gy, but the observed injuries indicated, that the real overexposure was significantly lower. It was assumed, that the patient received about double the intended dose.

 

Lessons learned
Precise documentation, measures for training of personnel, and an overall quality assurance system have to be implemented in the working practice of radiotherapy. Additional control steps to verify the treatment procedure should be established on a random basis, accompanying the course of the therapy. In order to enforce these requirements, every state authority, that issues licenses for radiotherapy, has to prove, that the licensee complies with these requirements.

Finally, every person involved in radiotherapy procedures should be aware of the responsibility that is necessary for a proper treatment of patients.

   

22. Retrieval of a fire damaged gauge containing a radioactive source (Ireland)

European ALARA Newsletter - Issue 21


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Introduction
On the 16th January 2006 the Radiological Protection Institute of Ireland (RPII) (the Regulatory Authority) learned from media reports that a fire had destroyed part of a factory situated in the midlands of Ireland. It was reported to have started on the 15th January and firemen fought throughout the night and into the next morning to contain the fire. As the company who owned the factory held a licence from the RPII for the custody and use of a gauge containing a radioactive source, plans were initiated to visit the scene.

As preparations were underway, the assistant chief fire officer for the area and a representative of the licensee contacted the RPII and requested assistance regarding the detection and retrieval of the gauge. After a brief discussion it was decided that the RPII would assist in assessing any possible radiological implications of the fire arising from possible damage to the gauge and would also assist and advise on its recovery and removal from the factory.

The gauge formed part of a Heuft fill-height detection system (Model – Basic 4) (Figure 1) and it contained a 1.67 GBq Americium-241 (Am-241) source.  The system was used on a production line as part of a quality control process to determine the volume of contents in metal cans. The Am-241 source and the associated radiation detector are contained within a ‘bridge unit’.

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Figure 1. Heuft fill-height detection system (Model Basic 4) on the production line of the plant (pre-fire)

RPII Inspectors arrived at the factory on the afternoon of the 17th January and immediately met with representatives of the Emergency Services (fire officers and crew) and the licensee to assess the situation on the ground. The building housing the production line was gutted in the fire and all existing access routes were considered by the fire officers to be unsafe. However, the fire crew managed to cut an opening in the side of the building as close as possible to the known location of the fill-height detection system (Figure 2). This subsequently allowed safer access to the vicinity of the bridge unit.

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Figure 2. Portion of galvanised sidewall that was cut through by fire crew to facilitate access to the production line area


Initial efforts focused on assessing if any contamination or damage to the integrity of the sealed source had occurred, and efforts were then concentrated on locating and removing the bridge unit from the building.

Recovery Operation – Part 1
Measurements of ambient dose equivalent rates (dose rate) were undertaken at the improvised entry location using a hand held Mini-Instruments / Thermo Electron Corporation Mini-Rad 1000 Radiation Survey Meter and a Telepole (telescopic GM Tube). A number of back-up instruments with various scales and contamination monitors were also available for use as required. No dose rates above background were measured at the improvised entry location using the hand held survey meters, and at locations 4m distance inside the factory using the Telepole instrument. Based on these measurements the RPII Inspectors advised the fire crew to cut a pathway through the galvanized panels and other debris into the production line area.

On entering the production line area the remnants of the fill-height detection system were identified (Figure 3). The environment in the area around the remains of the level system was completely destroyed and the array of galvanized metal and debris made access and working conditions very difficult. The bridge unit was located at the base of the fill height detection system.  As no dose rates above background were detected using the hand held instruments the bridge unit was removed by a fire officer for closer inspection (see Figure 4).

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Figure 3. Remnants of the Heuft fill-height detection system

 

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Figure 4. Damaged bridge unit being surveyed outside the building


Once outside the building further measurements and wipe tests were undertaken on the surface of the bridge unit. No levels above background were detected using the field contamination monitor (Berthold LB 1210 B). The wipes which were analysed the next morning by the RPII’s Measurement Services confirmed that no traces of Am-241 were present.

Given the damage to the unit it wasn’t possible to confirm the presence of the source and it was considered necessary to send photographs (Figure 4) to the manufacturer in England (Heuft UK) for their assessment of the bridge unit. Heuft UK advised that the source block was missing from the bridge unit and provided a description of the source block to facilitate the recovery operation.

A second recovery operation was then arranged. In the interim the building was secured by the licensee and the fire crew.

Recovery Operation – Part II
Once the production line area was confirmed as being relatively stable, an RPII Inspector along with the licensee’s radiation protection officer entered the building through the opening created earlier in the week by the fire crew. They were suitably attired and equipped with Electronic Personal Dosimeters, TLD’s, Finger TLD’s and radiation survey meters. A small stepladder made access to the remains of the production line area easier, and the ground directly beneath their feet was scanned with a contamination monitor prior to dismounting from the bottom rung of the ladder.

The floor in the production line area was covered in debris, and after, scanning with the contamination monitor, items of debris were sifted through using a long handled tweezers and then set aside if no radiation was detected above background. At a location close to the fill-height detection system the contamination monitor registered a deflection of 300 cps (background 6 cps) and a metal component was recovered (Figure 5). This component was set aside and the surrounding area scanned to determine if there had been any contamination or leakage. No readings above background were detected.

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Figure 5. Front view of the recovered component which included the source block containing the Americium-241 source.


The component was removed from the building for further examination. A dose rate of approximately 10 µSv/hr was detected at the front face, and approximately 2-3 µSv/hr at the rear face, and it was therefore assumed to be the missing source housing. On further inspection the shutter mechanism was identified and, although loose, it was confirmed to be closed. Wipes were taken of all exposed surfaces. No contamination was found on the wipes using the contamination monitor. The wipes were subsequently given to the RPII Measurement Services for analysis, which confirmed that there was no contamination present and therefore no leakage from the source had occurred. 

With the component pointing away from all personnel the RPII Inspector opened the shutter with a long handled tweezers and the measured dose rate reached approximately 200 µSv/hr. This confirmed that the recovered component was in fact the Am-241 source contained within its protective housing

The shutter was fixed in a closed position and the component was put in a secure metal container.  This container was labelled as containing radioactive material and placed in secure storage on site along with the previously recovered bridge unit. Dose rates around this container were less than 1 µSv/hr.

The licensee is storing the device until arrangements for its disposal with Heuft or its agents can be made.

Findings
The metal source block and the metal bridge unit used by Heuft in this model of fill-height gauge are very robust as they survived a significant fire (estimated to be greater than 1000 °C for several hours), and prevented any leakage or contamination of the source.

However, this incident has identified one potential flaw in the safety design of this model of Heuft fill-height gauge. The mounting plate which holds the Am-241 source block inside the bridge unit is made of aluminium, and during this fire the mounting plate melted which resulted in the source block detaching from the bridge unit and falling out onto the floor.

The metal radiation warning labels riveted to the outside of the bridge unit were also destroyed in the fire. These labels were subsequently found to be located on the detector end of the bridge unit rather than the source end.

Lessons Learned and Actions Taken
This incident highlights the importance of involving the manufacturers of measurement systems containing radioactive sources at an early stage. In this case the information provided by Heuft UK was instrumental in recovering the source.

The manufacturer, the RPII and other licensees with a similar fill-height detection system have consulted on the findings of this incident and the aluminium mounting plate in all units has been replaced by one made of stainless steel. Heuft UK has also indicated that all fill-height detection systems being currently manufactured now have a stainless steel mounting plate.

The question of fire proof radiation warning labels and engraved trefoil signs is being pursued by Heuft UK.

All licensees in Ireland with fill-height detection systems, irrespective of the manufacturer or model have also been advised of the findings from this incident and asked to incorporate them into their Safety Plans and / or to contact their manufacturers for further advice.

   

21. Radiological incident involving a Tc-99m generator in Ireland

European ALARA Newsletter: Issue 19


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Introduction
During 2004 the Dosimetry Service of the Radiological Protection Institute of Ireland measured a penetrating dose of 11.3 mSv on a TLD assigned to a van driver employed by a licensed distributor of radioactive sources in Ireland. The TLD was issued on 1st September 2004 and received back on the 18th October 2004. The exposure period for the TLD is taken to be between 4-6 weeks.

On Saturday morning of each week the driver collected six Technetium generators (from a licensed depot at Dublin Airport) for delivery to hospitals in Cork city to the south and Galway city to the west. Cork city is about a 3 hour drive from Dublin and Galway city is about a further 3 hour drive from Cork.

In accordance with their licence conditions the Distributor carried out an incident investigation into this recorded dose of 11.3 mSv, and in their Incident Report they stated that, during the exposure period of this TLD, the van driver had carried the Technetium generators into the hospitals as on-going construction work at the hospitals had prevented trolley access. The van driver was wearing his TLD on his trousers pocket/belt during each days work.

During the exposure period in question it was estimated that the van driver would have physically carried the generators for a total of about 120 to 180 minutes, and the Distributor concluded in their Incident Report that physically carrying the Technetium generators into the hospitals was responsible for the high recorded dose on the van driver’s TLD. It is worth noting that carrying the Technetium generators into the hospitals was a clear breach of the Distributor’s own stated work procedures.

As part of the Regulatory Services Division investigation into this recorded high dose it was decided to conduct a series of exposure/dose measurements on live Technetium generators following their arrival into Dublin Airport on one Saturday morning. These measurements would be used as part of a dose reconstruction.

All radiation measurements were therefore conducted on Saturday 15th January 2005 in the car park of one of the Cargo Depots at Dublin Airport.

Measurements
One of the Technetium generators with a designated TI of 2.5, based on a facility production date of 14th January 2005, was isolated for analysis from the rest of the consignment.

A series of radiation measurements were made at the top surface (lid) and at the side walls of the outer container using Mini-Rad 1000 Series instruments. Additional measurements were made at a distance 1 m from the container in order to validate the TI value.

TLDs were placed on the lid of the container, and attached to the side walls of the container for a period of 11 minutes.

Radiation measurements were made in the driver’s seat at the front of the vehicle in order to estimate the dose received by the driver during transport with the full consignment of 6 generators securely stowed in the back of the Ford Transit transport vehicle.

Radiation measurements were also made at a point c.5 cm distance from the load in order to replicate the exposure situation of the generators being securely stowed in the front of the transport vehicle i.e. directly behind the driver’s seat.

Results
The Technetium generator in question indicated a dose rate of c.500 µSv/hr along the vertical sides of the container and a dose rate of c.600 µSv/hr across the lid. The TI recorded, with a Min-Rad 1000, was between 2 and 3 consistent with a designated TI value of 2.5 as of the 14th January 2005.

When all the generators were securely stowed at the back end of the transport vehicle the dose rate at the driver’s seat in the front end of the vehicle was 5-10 µSv/hr. The dose rate at a point c.5 cm distance from the load was c.500 µSv/hr, and this was taken as representing the maximum dose rate that could possibly be received by the driver if the generators were stowed directly behind the driver’s seat and not to the rear of the vehicle.

Discussion of results
The van driver explained that during the period in question he wore his TLD on his trousers pocket/belt and he carried the generators at arms length down by his side. At the end of each Saturday the TLD was left in the transport vehicle until the following Saturday. The transport vehicle was not involved in transporting radioactive sources from Sunday to Friday.

A typical Saturday trip for the driver was to deliver 3 generators to Hospitals in Cork and 3 generators to hospitals in Galway. This would entail about 6 hours of travelling with a diminishing number of generators on board. The return journey from Cork or Galway would entail an empty van.

On the basis of the information supplied by the van driver and the results of the radiation measurements made on the Technetium generator in Dublin Airport a maximum dose of the order of 1 to 1.5 mSv could possibly have been received by the van driver from carrying the generators. An additional dose of c.400 µSv could have accrued from transporting the generators giving rise to a maximum dose of the order of 2 mSv over the exposure period. An estimated dose of this magnitude is not consistent with a recorded TLD dose of 11.5 mSv over the exposure period.

In the course of further discussions with the van driver it transpired that the Technetium generators were, more than likely, stowed directly behind the driver’s seat in the front of the vehicle, as this allowed easier access to the generators by the driver.

Stowing the generators directly behind the driver’s seat could have given rise to dose rates of the order of 500 µSv/hr over several hours each Saturday. If we assume 3 hours at 500 µSv/hr and a further 3 hours at 200 µSv/hr then the van driver could have received a dose of the order of 2 mSv per week from transporting the generators giving rise to a total dose from transporting and carrying the generators of the order of 12 mSv.

Conclusions and lessons learned
It is the opinion of the Regulatory Services Division that the high dose received by the van driver was as a consequence of a lack of understanding of the radiation hazard associated with the products he is transporting, and of a deficiency of appropriate training and supervision by the Distributor. Stowing the generators in the front end of the vehicle is not consistent with the “Notes for Drivers” issued by the Regulatory Service, and is also a clear breach of the Distributor’s own stated work procedures. The Distributor was asked to update/amend their Radiation Safety Procedures or Local Rules and to revise their staff training to emphasise that:
  • Technetium generators should always be stowed in the rear of transport vehicles in order to ensure that the radiation dose rate at the driver’s seat is less than 20 µSv/hr when the transport vehicle is fully loaded.
  • Once outside the transport vehicle the Technetium generators should only be moved around on a designated trolley provided by his employer. Drivers should not, under any circumstances, physically carry generators into client’s premises.

This incident highlighted:
  1. The merits of drivers wearing TLDs as it was through this practice that the circumstances giving rise to unacceptable radiation doses to this particular van driver was discovered.
  2. The benefits of conducting dose reconstructions following incidents of high recorded doses.
  3. Inspections carried out by Regulatory Authorities on licensed Distributors should always include field inspections of the transport side of things.
   

20. Transport case prompts reminder on the importance of RP controls

European ALARA Newsletter: Issue 19

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Description and analysis of the incident
The UK Health and Safety Executive (HSE) have issued a reminder to companies working with radiation on the importance of protection control measures, including basic monitoring. The reminder follows the conclusion of a prosecution case brought jointly by HSE and the UK Department for Transport (DfT) against specialist contractor, AEA Technology plc (AEAT).

The court fined the company a total of £250,000 (approx Euro 343,000) and ordered to pay £151,323 (approx Euro 205,000) prosecution costs. The company pleaded guilty to criminal charges under health and safety and road transport law, of:
  1. Failing to ensure, so far as reasonably practicable, the health safety and welfare at work of employees during work associated with the removal and transport of the radiation source;
  2. Failing to conduct the transport and management of radioactive materials in such a way as to ensure, so far as was reasonably practicable, that persons not in its employment who may be affected thereby were not exposed to risks to their health or safety;
  3. Failing to take all necessary steps to restrict, so far as reasonably practicable, the extent to which employees and others were exposed to ionising radiation;
  4. Failing to ensure that ionising radiation levels were adequately monitored;
  5. Failing to ensure that requirements for package inspection were satisfied before shipment, and;
  6. Causing a package containing a radioactive source to be transported without determining the Transport Index of that package. A further charge of failing to adequately consult a Radiation Protection Adviser (qualified expert) was held on file.
The prosecution followed an incident in March 2002, when AEAT were contracted to remove a 129 TBq cobalt-60 tleltherapy source, previously used in cancer treatment, from a Leeds hospital and transport it 3.5 hours by road to Windscale, Cumbria, for disposal. At Windscale, radiation levels of up to 3.5 Sv/h were discovered coming from underside of the specialist container used to transport the material.

Investigation revealed that a vital shieldielding bar was missing from the inside of the transport container and that this allowed a beam of radiation to emit from its base. It was also found that the packaging inside the container was wrongly configured and the source was able to mover around inside the container. Although radioation monitoring had been performed around the container, measurements were not routinely carried underneath and the high dose rates had therefore gone unnoticed.

A primary cause of the incident was the company’s failure to supervise and support their staff properly in the use and preparation of the transport containers.

Fortunately although there is no evidence that anyone received a significant exposure during the preparation and transport of this material, there was clearly the potential for an extremely serious incident. Anyone exposed to the beam coming from the container could have exceeded the legal dose limit within seconds and suffered radiation burns within minutes.

Lessons Learned
The case highlights the need for proper preparation and monitoring of transport packages. Adhering to approved contaner preparation procedures would have detected the omission of the shielding bar before the radioactive material was loaded to the package. Whilst passing sentence, the court remarked that the incident had arisen because of poor management, no oversight, and poor relationships between key personnel. Employees involved were substantially remiss, indefferent to the fact that the wrong transport contaner was used, made assumptions that were wholly unjustified, failed to follow their own procedures, were cavalier and indifferent to their duties, and  their failure to obtain advice from their RPA demonstrated a degree of arrogance. The court also commented that the risk was considerable, was deeply concerned that had there been a road traffic accident during the journey grave risk of radiation injury could have resulted, and that it was not impressed by the suggestion that the employees involved had been misslead by the numbering of the flasks. It concluded that anyone involved in the radiation industry had to be meticulosly caerful and that there was no room for carelessness, making assumptions and not following procedures.

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19. Radionuclide gauges in rough industrial environments

European ALARA Newsletter: Issue 18

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Introduction
Industrial gauges for permanent installation using radioactive sealed sources are widely used in Norway, as in the majority of other developed countries. The gauges are used to measure thickness and density of many materials and also used as level gauges. Such gauges are often well-suited and are the preferred choice when working in rough environments where other options fail due to a number of reasons; primarily heat, cold, pressure, corrosive agents, dust, dirt or vibration.

Frequently used isotopes in industrial gauges are caesium-137, cobalt-60 and americium-241. Depending upon the specific application, industrial gauges in some instances contain relatively small quantities of radioactive material, however in some cases activity levels can be as high as several hundred giga becquerels.

Even though the gauges are designed for many years of use in harsh environments, heat, cold, pressure, corrosive agents, dust, dirt and vibration can be a serious threat to the radiation safety and integrity of the device. From our experience in Norway during inspections, some examples of such cases are described which might give special radiation protection challenges.

Example 1: worn out because of vibration – lost source
In 2005, two industrial gauges supposed to contain Co-60 sources were found with serious defects. In one of them the radioactive source was missing, and has not yet been recovered. The particular gauge model (see Figure 1), which is commonly used with no problem, was found to fail in dusty and vibratory environments after about 10 years of use.
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Figure 1: The pin (~ 5mm) securing the locking mechanism to a slit in the source housing was grinded off.

When the pin securing the locking mechanism is grinded off, only the sealing will hold the shutter mechanism in place. The thin metal wire of the sealing is not meant for holding the gauge together, and is easily snatched off (e.g. by vibration).

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Figure 2: For security reasons the gauge is not usually padlocked in open position, and with the pin grinded off the source holder is easily removed from the shielding.

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Figure 3: The gauge with the missing source also missed the screw keeping the spring-loaded plate in place.

These serious incidents happened to a well-known gauge model. The gauge is of a so-called “Scandinavian” or “Swedish” design, and the use of this model outside Scandinavia is unknown to us. The manufacturer is now making a model specially made for vibratory environments.

Example 2: corrosive environment
Some radionuclide gauges are installed in corrosive environments and rust might in turn lead to problems with the opening/ closing/ shutter mechanism. In figure 4 an extended handle has been welded on the shutter mechanism in such a way that extra force might be used to open and shut the rusty gauge (for example with the use of a hammer). There are examples where this has led to shutter damage and the gauge has no longer been able to be put in shut position.

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Figure 4: Rusty radionuclide gauge with extended handle

Example 3: covered and worn-out markings and signs
In some industrial environments chemical agents might wipe out the labels and markings, or they are covered with production waste.

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Figure 5: The labelling of open and shut position is worn-out.

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Figure 6: Challenging environment, but in this case the gauge is protected by a mudguard and a trefoil warning sign was placed to the right of the picture.

Production waste covering the warning labels is also a safety threat, and procedures for cleaning labels regularly are important to have in place.

Lessons learned
The lesson learned from inspections is first of all that the undertakings should prepare instructions and work procedures which ensure proper cleaning and maintenance of the radionuclide gauges.

Radionuclide gauges exposed to particularly rough environments should be inspected more frequently. With the registration regime we have today, we have little information on the environment where the gauges are installed. With the introduction of electronic webbased notification of radionuclide gauges, the Norwegian Radiation Protection Authority plan to introduce questions about the installation environment.

With an enhanced inspection frequency, last but not least, information to the undertaking will also be an important contribution to radiation safety.
   

18. Incident involving Radioactive Lightening Conductors (Croatia)

European ALARA Newsletter: Issue 18

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Description of the incident
Radioactive lightning conductors (RLC) have been used in a number of countries for several decades because it was believed that radioactive attachments improve the effectiveness of the lightning conductors. Even though these types of RLC have not been manufactured in last 10 years, many are still in regular use in Croatia and have created a number of specific radiation protection and regulatory problems. RLCs represent the largest homogenous group of radioactive sources in Croatia. These devices were classified as consumer products. The consumer products are usually covered by the general license concept with little or no regulatory control. The general license concept enables persons with minimal or no training in radiation safety to possess and use licensed radioactive sources or devices. The RLC installed in Croatia used cobalt-60 or europium-152 and 154 with activity 10 – 20 GBq, which exclude them from the consumer products category. They are treated as sealed radioactive sources.

As time has gone by, warning labels and signs on RLC often became obliterated as a result of exposure to adverse environments and improper maintenance. Also, personnel knowledgeable about the RLC retire, are discharged or otherwise leave the licensee’s plant.

Not surprisingly, as a consequence of these developments and the absence of control and inspection, some of these RLC entered the public domain, most frequently by being discarded with scrap metal.

In August 2005 two radioactive sources in original lead container (open on upper side) were dismantled from RLC installed on the roof of one hotel and sold as scrap metal. During transfers of the devices two 15 GBq europium-152 and 154 sources were dislodged from the containers. Scrap metal was exported to Italy. It was transported from Croatia via Slovenia to Italy by truck.

At the Italian border during routine monitoring of the cargo on the truck transporting this scrap metal, according to Italian law procedures, the presence of radioactive material was detected. Two intact sealed radioactive sources were discovered (1 cm x 1.5 cm). No leakage of radioactive content was detected. The sources were placed in an interim storage and after some time with the consent of the regulatory authority of Croatia they were returned to Croatia and stored in the recognised storage facility.

The State Office for Radiation Protection asked for an investigation, dose reconstruction and evaluation of the consequences. Direct measurements at the source gave 5 mSv/hr maximum at a distance of 10 cm; and 1 mSv/hr at a distance of 1 m. The driver and passenger were exposed to the sources as were workers who were handling the scrap metal in the scrapyard. However, only the driver and his companion were identified. They had no radiation monitor during transport. It was estimated that the dose at the driver’s position was 100 µSv/hr. Based on the transport time, average distance and simulation of the transport it was estimated that they received an effective dose of about 3 mSv. They were sent for a medical examination including chromosomal aberration analysis.

Conclusions and lessons learned
Lost and unwanted sources can cause safety and security problems such as radiation exposures to workers and members of the public and radioactive contamination. The described incident has not resulted in especially significant radiation exposures and no contamination occurred. Nevertheless it should be stressed that prevention of radioactive sources from entering the public domain in an uncontrolled manner has become an international challenge to authorities responsible for regulating the safe use and disposal of radioactive sources. A new specific safety problem had appeared during the 1991-95 war in some newly independent countries formed after the disintegration of Yugoslavia. Investigation showed that many RLC in war-affected areas were displaced, and some were even found buried under the ruins. These damaged RLC became available for unauthorised uses or subject to unsafe handling by the local population. Furthermore, radioactive materials could be collected by local scrap merchants and sold to scrap processing facilities. For these reasons over the past years Croatian authorities mounted campaign to locate, recover and dispose of all RLC that had been damaged, lost or abandoned. After successful completion of the campaign some specific lessons were learned from this experience that served as a basis for further actions in this field. RLCs represent the largest homogenous group of radioactive sources in Croatia but with the least regulatory control of all radioactive sources and they frequently enter the public domain in an uncontrolled manner from time to time. In order to maintain and regain full control over all radioactive sources in the country and because of some doubts about their operational effectiveness, there is now consensual decision that about 250 RLC still installed in Croatia have to be dismantled and properly stored as soon as possible. With the assistance of IAEA this project would be completed in 2006 and hopefully incidents of the type described will not happen in future.

The scrap metal recycling industries should be concerned as well, because of more and more experiences with sources becoming mixed with scrap metals destined for recycling. If the owner or the manufacturer of these sources cannot be identified or is no longer in existence, the source is considered to be an "orphan source" and the unlucky finder may be held responsible for long-term security and eventual disposal of the unwanted source. The metal scrap dealers are encouraged to establish monitoring system for radioactivity at the entrance to their scrap-yards.

In conclusion, an important lesson to be learned from the incident is that periodic contacts by regulators (for example via more frequent inspections) with users of radioactive sources serve as reminders to them of the need to maintain control and accountability of the sources, to properly dispose of the sources when they are longer needed, and to otherwise provide for their safe use. It is also necessary to give higher priority to an ongoing review of general license policies and procedures especially taking into account Directive 2003/122/Euratom on the control of high-activity sealed radioactive.
   

17. Incident involving a gauge system

European ALARA Newsletter: Issue 17

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Description of the incident
The incident occurred in the UK, and involved a level gauge system containing a 1 GBq caesium-137 source. The source assembly fell out of the shielded housing onto the ground below. An employee subsequently picked it up and took it to a control room where it remained for almost 2 days. The presence of an unshielded source was eventually recognised by a supervisor, who was investigating the non-operation of the gauge. He immediately threw the source assembly out of the window, after which he buried it in a soft mud bank around which he set up an appropriate exclusion zone. The source was subsequently recovered (by NRPB) and placed in a shielded container.

Doses to workers
Workers did not wear personal dosimeters. Consequently, a reconstruction of the incident, and dose rate measurements were used to estimate the doses received by the employee and the supervisor. The results are given in the table below.

Person
Estimated whole body effective dose
Estimated equivalent dose to finger
Employee
2 - 3 mSv
300 mSv max
Supervisor
0.05 mSv
0.04 mSv max

It is worth noting that the doses received could have been considerably higher.

Lessons learned
  • Gauging systems are a very common application, and it is extremely rare for the source to fall out under normal operating conditions. In this case, the source housing was subject to constant vibration, and this certainly was a major factor in a securing bolt becoming loose. This problem can readily be addressed at the design stage, for example through the addition of a locking pin. Operators should also ensure that regular checks on the integrity of source housings are undertaken, especially where harsh environmental factors exist.
  • An early indication of the loss of the source was provided by the failure of the gauge system itself. Operators should be aware of this and put procedures in place to immediately check the location of the source in the event of such a failure.
  • Providing employees with suitable information, instruction and training is important - even for those who do not directly work with radiation sources. In this case, simple radiation awareness training (location of the sources on site, what they look like inside and outside their containers, basic precautions, who to contact, etc) could have helped avoid any radiation exposures.
   

16. Incident in a textile treatment plant (France)

European ALARA Newsletter - Issue 16

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Description of the incident
In 1995, at 1.30 a.m. in the depollution department of a textile treatment plant, Mr A notices that the machine which measures the density of detergents to be released into the environment is dirty. He undertakes the cleaning of it. This machine is situated in a noisy, cramped location on an extremely hot pipe. It is located at a height of 3.5 m and is not accessible except with a ladder. There is a warning sign making the risks due to the sealed caesium source (activity 7.4 GBq - 06/30/1989) clearly visible at 2 m from the ground.

Indications relating to the source are written on an engraved plaque, fixed on the container housing this source. To clean the machine, Mr A takes the container completely apart and removes the source. He wedges a piece of paper in the collimator tube and then decides to take it off and to unplug it with compressed air. For this, he takes the tube in his right hand and brings it into another workshop. Suspecting then the presence of the source at the end of the tube, he searches for a dosimeter pen which confirms this presence. He then decides to replace the source in the "source carrier" with a pair of tweezers.

At the end of this operation, he feels a burning sensation in his right hand and is accompanied to the nearest hospital. A few days later he goes to the Institut Curie at the request of the labour physician.
Exposure duration of his hand was 30 to 45 minutes. During the whole operation, Mr A was not wearing any dosimeter.

Radiological consequences
Mr A was the only exposed person. An erythema appeared immediately at the end of his period of work, together with a burning sensation (first degree burn). This was followed by an oedema and the development over the course of 2-3 weeks of a large lesion, about 5 cm in diameter. The final result was local necrosis.

Taking into account clinical observations, the dose delivered to the patient’s right hand was most likely above 30 Sv. Furthermore, Mr A had a biological “dosimetry” (searching chromosomal aberrations) revealing a whole body dose of 200 mSv.

Lessons learned
  • The installation of the source in noisy, cramped location, situated on a inaccessible very hot pipe, does not allow for normal surveillance and maintenance and led to the unfortunate initiative of Mr A.
  • Mr A’s behaviour denotes a poor knowledge of the risks linked to the presence of the source in the machine. The one-week training he received was too basic and it did not make clear the incurrent risks.
  • Before undertaking the cleaning of a machine, one must make sure that the radioactive source is properly shielded using a dose-rate meter. In this example, Mr A failed to check the dose rate before cleaning the machine. All of this clearly demonstrates a lack of “radiation protection culture” on the part of the employee who was otherwise a “competent person”.
  • The wearing of an electronic dosimeter with alarm could have compensated for forgetting to use a dose rate meter and could have avoided the incident.
   

15. Radiography incident (Spain)

European ALARA Newsletter - Issue 15

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Description and radiological consequences of the incident
On the 28th April, 2004 the Spanish Regulatory Authority (CSN) was notified of an event resulting in the overexposure of two radiographers because they were working near to radioactive source while it was in unsafe position. There were no personnel dosimetry records but estimated doses were 158 mSv and 79 mSv. The device involved in the event was a Technical Operations, model TO-660 serial number 653, with a 19.79 Ci (733 GBq) iridium-192 source.

The incident took place because the operator failed to follow the required operational procedures on radiation protection for mobile gammagraphy activities. This produced the following deviations:
  • The operator did not receive from his supervisor a prior assessment of the work to be carried out describing the associated risks and specific requirements on radiological protection, including the need to optimising doses. Such prior assessments have been required by law in Spain since 2001;
  • The operator worked all the time without a radiation monitor, so it was not possible for him to know whether the radioactive source was in a safe or unsafe position;
  • Both the operator and the assistant were not wearing an individual dosimeter, so it was not possible to determine the doses received.

Lessons learned
CSN considers that special attention is needed on the following issues, to prevent similar incidents occurring:
  1. The radiological protection supervisor responsible for each job (mobile gammagraphy) shall prepare a prior assessment to inform the operators of the associated risks and specific radiation protection requirements to be followed;
  2. Operators and assistants shall carry out every job in accordance with well-established operational procedures;
  3. These operational procedures shall include provisions to prohibit starting any work until equipment for detecting and measuring radiation (radiation monitor and personal dosimeters), are fully operable;
  4. An additional effort shall be made to improve refresher training on radiological protection for operators and assistants, in order to assure they understand and recognize the importance of carrying out the work in a safe manner, to protect not only themselves but also the general public.
   

14. Transport of gauges from a refurbished brewery

European ALARA Newsletter - Issue 14

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Description of the incident
As part of a refurbishment programme in a brewery, four liquid level gauges, each containing a 3.7 GBq americium–241 source, were removed from a production line to safe storage prior disposal. The sources were beyond their useful working life and as a consequence were no longer covered by a Special Form Certificate, thus requiring a Type B container to transport them. The Am-241 source assembly of each gauge was sandwiched between stainless steel plates, attached to which were a shutter mechanism and mounting bracket. The radioactive material was incorporated within a thin-walled, stainless steel tube.

The company that was contacted to dispose of the sources brought only one Type B container to site. The contractor intended to dismantle the gauges on the site and transport all four Am-241 sources in one trip. It was discovered that source assemblies, which were each about the size of a 13-amp fuse, were fixed in place with adhesive. The contractor's employee prised them out of their housing using screwdriver and placed them in the Type B container. The sources were damaged in the process. The work was carried out in the back of a small van in the visitors' car park of the brewery, adjacent to a busy main road. The van driver then went to a second location about 100 miles away to collect some more equipment for disposal before returning to base. A few days later, it was discovered that both the container and the van itself were contaminated with Am-241. Subsequent monitoring revealed that the contamination was rather more extensive, and included other vehicles and properties. The company reported the incident and a detailed investigation commenced. The investigation showed:
  1. The contractor did not discuss the job with the brewery or their RPA and had inaccurate information about the size of the gauges;
  2. Alternative methods of work had not been considered; and
  3. There was doubt about whether the available radiation monitoring instrument was capable of being used – when the specialist batteries of the radiation monitor were checked some days later these were found to be flat.

Radiological Consequences
The doses involved were primarily from intakes of americium-241 and the committed effective dose equivalents were estimated to be 20 mSv and 2 mSv for employees of the disposal contractor and less than 1 mSv for the wife of the former.

Lessons learned
  1. Equipment holding radioactive sources should, wherever possible, be transported with the source undisturbed to suitable facilities before dismantling takes place;
  2. Where removal of sources on the site is unavoidable, close liaison between the companies (and their respective RPAs) should take place with a view to ensuring that adequate facilities are available for the work to proceed safely;
  3. Local rules should clearly and unambiguously state what should be done (or not done) if conditions change during the work;
  4. Contingency plans should be incorporated into local rules, made known to relevant employees, and practiced;
  5. After source manipulations appropriate monitoring should be undertaken. In situations such as this, contamination should always be considered possible; not just from the manipulation procedure, but also due to degradation of the source integrity due to the environment.
  6. Means should be provided for the checking of radiation monitoring instruments on-site before each use (e.g. check source). Spare batteries should be carried with equipment.
   

13. Radiological incident involving contaminated scrapyard (Macedonia and Italy)

European ALARA Newsletter - Issue 13

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The event and its radiological consequences
On June 2001, a foundry in Skopje (Macedonia) sent 32 steel slabs of different sizes (total amount about 65 tons) to three shipyards in Italy, as follows:
  1. 12 slabs were sent to the harbour of Ancona;
  2. 19 slabs were sent to the harbour of Palermo;
  3. 1 slab was sent to the harbour of Livorno.
All the slabs were contaminated with detectable quantities of cobalt-60. Surveys carried out with a portable multichannel analyser showed that the contamination was due to 60-cobalt, with a concentration of about 1 Bq/g. Direct measurements gave 3 µSv/h at maximum at a distance of a few cm; at a distance of 1 m, 1 µSv/h; at a distance of 3 m, the equivalent of the background was measured. The contamination was detected because of the following events:
  1. The Ancona shipyard used 12 slabs to build two fishing boats;
  2. On October 2001 the shipyard sent its metal scraps to a firm that usually gathers scraps to be sent to a foundry;
  3. This firm monitored these scraps, according to Italian law procedures, and detected some radioactive contamination;
  4. The firm notified the local Police Body.
The contaminated slabs were traced and found to be produced in Skopje (Macedonia) and traded in Italy through a trading firm to the shipyards referred above. The slabs sent to the harbour of Palermo were simply stored; the slab sent to the shipyard of Livorno was used in the same period. Surveys were performed in all three harbours according to criteria and procedures agreed among the involved surveyors. Information about the contamination was obtained by the foundry in Skopje:
  1. In two castings, of about 100 tons each, 60-cobalt contamination was detected with activity concentrations of 0.831 Bq/g and of 0.609 Bq/g, respectively;
  2. The preceding five castings were reported free of contamination. No information could be obtained concerning the five following castings. The total production of contaminated steel amounted to 200 tons, of which 35 tons were sent to Italy. No information is available concerning where the other 135 tons were sent.
The trading firm considered the detected contamination in perfect compliance with the Italian legislation. However, the Italian laws for radiation protection state that the exemption level of 1 Bq/g is not valid for recycling and waste management. For components with a contamination lower than 1 Bq/g, their use is allowed only if the annual dose to any member of the public is less than 10 µSv/y and the collective dose is less than 1 Sv/y.

At Ancona, surveys and measurements were performed by the relevant Regional Authorities for Environmental Protection (ARPA) in co-operation with the police and a surveyor from ANPA (the National Agency for Environmental Protection). At Livorno, surveys and measurements were performed by the relevant Regional Authorities for Environmental Protection (ARPA) in cooperation with the police. At Palermo, the local laboratory for Hygiene and Public Health co-operated with the police body. At the harbour of Ancona:
  1. Almost all the slabs had already been used to build two fishing boats; the contaminated components of the two boats were readily identified; the affected areas were identified and declared “restricted areas”;
  2. Powders and scraps produced during the building of the boats were identified, collected and removed from the areas normally occupied by workers, in a sealed container. No removable contamination was left in these last areas;
  3. The remaining slabs were put in the same containers;
  4. The relevant workers were likely to have been exposed to doses less than 1 mSv, but in any case their exposures are to be considered as not justified;
  5. As for internal contamination, carpenters and welders (25 workers) immediately underwent whole body monitoring at the ENEA Centre of Bologna. No internal radioactive contamination was detected.
At the harbour of Livorno, 1 slab was used in the building of a boat; this boat was seized and measurements were carried out on scraps and powders. The same criteria as for Ancona were adopted. At Palermo, the 19 slabs have not been used yet. All the slabs were seized and set away from any unauthorised access.

On March 2002, the judge in Ancona responsible for the case stated that all the remaining slabs in Palermo, powders and scraps gathered in Ancona and Livorno should be sent back to the foundry in Skopje. Components of relevant sizes were cut into smaller parts in restricted areas; all the areas were covered with plastic sheets; air samplers were used to monitor air contamination during all the procedures. All the involved areas were left free of radioactive contamination. The work was completed and all contaminated materials were sent to Skopje by October 2002.

Lessons learned and conclusion
In conclusion, this event is not thought to have resulted in significant radiation exposures to either workers or members of the public. Nevertheless it should be stressed that small doses could be delivered to a large number of members of the public, if metal tools or consumer goods with a very low contamination are distributed among the population. In this case the missing 135 tons of contaminated steel surely will cause some exposure to some people somewhere in the world.

A further consideration is that EC Directives and the national legislations focus on the problem of contaminated scrap metal. Il this case, the contamination was associated with freshly manufactured material. In order to avoid such events, newly manufactured materials should be controlled in the same way as scrap metal, when crossing every checkpoint at any European border.

   

12. Contamination of workers during dismantling of gloves boxes (Czech Republic)

European ALARA Newsletter - Issue 11

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Description of the incident
During June and July 2001, three dry glove boxes, which served before as part of a line for manufacturing radioactive sources (smoke detectors) from pulverised 241-AmO, were dismounted and processed as radioactive waste. This operation was carried-out in the Nuclear Research Institute, plc at Rez (NRI), the Czech Republic. The manufacturing company declared the activities in glove boxes prepared for waste process as 150, 180 and 50 MBq of 241-Am respectively. Before the transport from the manufacturing factory in Prague to the NRI at Rez, where boxes were processed as radioactive waste, the contamination on the walls and the inside installation was fixed by lacquer. All dismounting procedures took place in the Fragmentation and Decontamination Centre (FDC) of NRI in three time periods; the data critical operations being June 21st, July 3rd and 10th of July 2001. On the beginning of the operations, the boxes were separated from each other and the external and internal surfaces were monitored. The operations comprised the removal of the covering foil, the opening of the box and its dismounting. The material was then fragmented, i.e. cut in pieces by hydraulic shears and saw machine. The fragmented radioactive waste was put into steel drums and conditioned by cementing as radioactive waste.

Before the daily operations started the system for monitoring the volume activity of air in the working area was switched on and the locally adaptable exhaustion for FDC area was put in operation. At particular steps the surface contamination was measured using both wipes and direct measurement. The workers should use the protective aids appropriate to the character and hazard of this working activity, including respirators.

In the course of dismounting operations the dust particles with 241-Am were incidentally released and due to violation of the radiation protection requirements (non-systematical use of personal protective aids, no full observance, keeping off approved radiation protection procedures) several workers were internally contaminated. Subsequently this contamination spread through the whole building. On 10th July after the dismounting operations concerning the third box and subsequent waste treatment were finished, the chief of the FDC was informed about the result of the evaluation of the filter of the device for volume activity measurement in air in the FDC. The value of filter activity exceeded the monitoring programme determined intervention level and the chief of the FDC ordered to immediately stop all the working activities in FDC area. On 11th July the measurement of respirators used by workers revealed a considerable contamination, reaching in the worst case 1 kBq of 241-Am (later amended to 2,7 kBq). The chief of the FDC evaluated the situation and declared at 16.30 an extraordinary event of the 1st grade (in the terms of the Decree of SUJB No. 219/1997 Coll.).

On 12th July the notification of as extraordinary event was transmitted to the State Office for Nuclear Safety (SUJB) and the media were informed. The worker suspected of the highest internal contamination (W1) was directed to the National Radiation Protection Institute (NRPI) for where the first in vivo investigation was performed and the data were reported as preliminary results to SUJB. The necessity for highly conservative estimate was considered because it should serve as a guide for possible remedial steps. From the first two in vivo measurements the body burden of 241-Am was estimated at about 5 kBq and considering the date July 10th as the time of intake, the committed effective dose (E50) was assessed in the order of 1 Sv. The evaluation was based on the presumption that inhalation (with particles of AMAD 5 É m, class M) was the main mechanism of internal contamination and that the deposit was located in lungs only.

In addition in other seven people similar internal contamination of 241-Am was ascertained. It was, however, recognised that the first obtained results of measurements were overestimated due to the contamination which remained on the body surface in spite of thorough showering before measurements and absence of positive response of surface monitors. The collection of stool and urine was carried-out. The repeated in vivo investigations (WBC, head and knees) and evaluation of the first excreta results reduced the doses initially estimated, so that at the time of notification of the event to IAEA on 17th July the maximal committed effective dose was quantified as 350 mSv.

The follow-up of the workers with measurable contamination continued. The decrease of the results in vivo measurements below detection limits during several weeks confirmed the interference of early findings with surface body contamination. Eighteen other employees were screened on WBC. Whole body counting, measurement of head and also measurement of knee in some cases were performed. No measurable internal contamination was found in this screened group.

A final evaluation in January 2002 was based on excretion data and points to the committed effective dose (E50) of 50 mSv in W1, and to E50 in the range of 5 to 185 mSv in W3-W8. The excretion analysis suggested, that in some workers repeated intakes might occur, e.g. partly already on June 21st and July 3rd (in the two first operations). This uncertainty complicated the interpretation of excretion results. The worker W2 did not fit fully with the patterns typical for subjects presented above. In this case clearly measurable activity was found with lung measurement and this activity did not decrease considerably in the course of time so that it was supposed that no external contamination was present on the trunk. The committed effective dose in this case was calculated by combining the in vivo (lung) results and the excretion data. The estimated E50 of the worker W2 was 130 mSv. The whole body measurements in the event involved workers will be continue with the half year period to precise the present time obtained results.

On the basis of first results, some workers seemed to be qualified for treatment by DTPA infusions. The worker W1 was hospitalised on July 13th and was treated by two doses of 1 g Ca-DTPA. Five more workers (W2-W6) were given two doses of Ca-DTPA on 20th and 22nd July. The tolerance of the treatment was good, no adverse effects were observed. After the assessment of the intakes had been amended, no continuation of the treatment seemed to be justified.

Lessons learned
  • After any hazardous operation with open sources it is necessary to control daily the personal clothing and protective aids, including respirators and change them as frequent as appropriate – the obligation to use such personal protection during hazardous operation is self evident.
  • Very important input data on calculation of a possible release of radioactive material at the workplace could be obtained from the activity measurements of the filters of ventilation system, together with the record of ventilation rate and precise intervals of collecting period. The results must be available before the next task at the workplace is started.
  • Contamination of the body surface may considerably interfere with the in vivo measurements of alpha emitters. The sensitivity of a portable alpha monitor may be to low to detect any activity which is latter ascertained with a long term whole body measurement in shielded conditions. In this respect the role for early onset of collecting stool and urine in suspected subjects could not be overlooked, as well as the preparedness to apply express methods which are able to differentiate surface and internal contamination in event involved workers.

Point of view of the State Office for Nuclear Safety
The inspection of SUJB concluded that the considerable underestimation of the hazard of the dismantling and fragmentation of dry glove boxes contaminated by 241-Am caused this extraordinary event first of all. This working task should have been prepared in more detail especially as radiation protection procedures were concerned. Besides some important elements of the periodic safety control were lacking including the thorough and regular documentation of all indices and circumstances important for protection. Some gaps in the responsibility of the Radiation Protection Officer of the plant could be identified. Based on these findings the SUJB decided to penalise the NRI by a fine amounting to 150,000 Czech Crowns (about 5000 US $). SUJB preliminary classified that event on the INES Scale at level 2 and notified it to IAEA. Final classification from the point of view of released activity should correctly correspond to level 1. The estimated effective dose in one radiation worker exceeded (more than two times) the annual dose limit and in some others reached just this level which corresponds to INES level 2. SUJB conservatively confirmed former event classification on the INES Scale at level 2.
   

11. Radiography incident at a research center (Sweden)

European ALARA Newsletter - Issue 10

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Description of the incident
One researcher entered an experimental area at a high-energy electron-beam research facility, accompanied by his son. The operator in charge of the accelerator, who had no information about their presence, directed a 100 MeV electron beam to a photon production target in a neighbouring room with the resulting well-collimated photon beam directed through the experimental set-up in the room where the two persons were located. A reconstruction indicated that they had been exposed to whole body dose rates of 30 to 60 mGy/h and 3 to 8 mGy/h respectively for the two beam currents used during the exposure. The possible exposure times were 10 minutes for the researcher and 5 minutes for the son according to their recollection. The estimated doses are of the order of 10 mGy with large uncertainties. No personal dosimeter was used.

The prime cause of the incident was that the operator had beforehand disabled the interlock system at the request of the researcher, although he was not entitled to give such an order. Underlying this was the fact that the management had shown no clear commitment to radiation protection, and in particular had not set down rules that should have given the operator clear responsibilities and the power to refuse such a request. The same research group did not want to switch-off some bending magnets that were part of the interlock system since it would have made it difficult to regain the same beam quality. Instead, another “home made” interlock arrangement was used and this proved inadequate. Together with other deficiencies such as: unclear internal responsibilities, illogical warning lights/instructions, lack of personal/warning dosimeters, lack of functional information channels and the presence of a non-authorised person (the son), this made this incident possible. There were probably no intentions to break the law, but the series of mistakes and poor decisions have to be interpreted as a consequence of a non-functional radiation protection organisation and a lack of radiological protection culture among the research team.

Lessons learned
  • Laboratory managers should be sensitise to their legal and judicial responsibilities in terms of radiation protection. Their commitment should rely on adequate information and training on radiological risks and their management.
  • The responsibilities and information channels of the radiation protection organisation have to be clearly defined.
  • The disabling of an interlock system should be allowed only in clear-cut cases where special procedures, approved by designated senior managers, should be put in place to ensure that the radiation incidents are avoided.

Point of view of the Swedish regulatory body
By chance, the exposures and therefore the doses were quite low; though they should have been much more important with such a device, and then leading to a serious accident.

This event points out a crucial lack of radiation protection culture, both at the management of the installation and at the researcher levels. In such a case, a prosecution should be performed as a way to sensitise these stakeholders, to modify their behaviour and to avoid a future accident.
   

10. Radiography incident (Sweden)

European ALARA Newsletter - Issue 7

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Description of the incident
During one evening of May 1999, two radiographers, using a portable X-ray unit, examined welds on a large pipe of a steam extraction system at a Swedish nuclear power plant. Between exposures, which each took about 1.5 minutes, they moved their apparatus around, handled plates and prepared for the subsequent exposure. The used X-ray unit produces a rather narrow beam. The work was performed in a closed area, with a collimated beam, and with full control over all entrance doors. The radiographers were not aware of the cleaning work mentioned below, and they did not foresee that someone could enter the area inside of the pipe! At the same time, another work team had been ordered to perform clean-up work at the steam extraction system. One person, P, was to remove debris left inside of the pipe as the result of grinding work. P, equipped with the tube of a suction system, entered the pipe through a man-hole and two of his colleagues, positioned at the man-hole, fed him tube as he moved along. P started cleaning the inside and advanced about 20 meters forward. At that point he reached the place were the radiography work was performed. At this section the pipe opens up and P stood up, turned around, and reverted to the place were he entered the pipe. P did not hear or notice anything unusual during the 15 minutes he stayed in the pipe.

It is difficult to estimate exactly how long time P has spent at the section of the pipe were the radiography work was performed. He estimated himself that he was standing up for about 15 seconds before he again crouched down and crawled back to the man-hole. P was equipped with a thermoluminescence dosimeter (TLD) but he had removed his electronic dosimeter since he thought it would hinder his movements inside of the pipe. The radiation level at the place where the work was performed is usually neither high nor changing. P and his colleagues were not aware of the radiography work.

At one point of time, while the radiographers were rearranging their equipment, vibrations were noticed from the pipe system. They tapped on the pipe but P, inside the pipe, did not hear this. They stopped their work and when they went around the corner they saw the two workmates of P who were busy feeding the tube. Everyone now realised the seriousness of the situation and the radiation protection unit was contacted.

The X-ray plates were checked for disturbances or shadows but such were not found. The TLD belonging to P was promptly evaluated and exhibited a total dose of 0.5 mSv which compared well with the 0.75 mSv of P’s electronic dosimeter. P was sent for blood tests to the nearby hospital during the same night and the result of the analysis showed normal values. A test set-up with several dosimeters was exposed at the place were the radiography work was done. It was estimated that the maximum dose received by a person situated in the collimated beam during one exposure of 1.5 minutes would be in the order of 30 to 40 mSv.
The Swedish Radiation Protection Institute and the Swedish factory inspection were informed about the incident in the morning of the following day. Debriefing was offered to the involved personnel.

Lessons learned
The incident was quickly reported and the follow-up work was performed well.

The routines for management of work permits at the power plant must be improved. Radiography work and/or clean-up work must be governed by work permits which are coupled to the work permit for the main work (construction, repair work) so that all activities can be fully co-ordinated and controlled. In the present case, the lack of information to the involved persons and the missing co-ordination was evident.

A firm which performs X-ray examinations must take full responsibility for their radiography work, regardless of whether it is performed at a nuclear power plant or not.

The radiographers should have ensured that nobody could be exposed. The assumption made, unconsciously or not, that no one would enter into the beam inside of the pipe was apparently wrong.
   

9. Radiography incident (Italy)

European ALARA Newsletter - Issue 6

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Description of the incident
In September 1997, firm A asked firm B to carry out some non-destructive testings on its behalf in the installation of firm A. According to the contract, firm A was to supply its gammagraphic apparatus, whereas firm B would supply its personnel and its radiation protection organization.

On September 29th, 1997 some radiography had to be carried out on a very large 15 cm thick vessel. Since the exposure was expected to last seven hours, workers of firm A and B agreed that the two operators of firm B would return the source to the shielded position at the end of the exposure, collect all the exposed films and leave them in the radiographic laboratory. The next morning a worker of firm A was to replace the apparatus in the source store. The exposure was carried out with a cobalt-60 source of 1221 GBq (33 Ci) between 9 p.m. of September 29th and 4 a.m. of September 30th. At 5.30 a.m. Mr BM of firm A was the first who went to the installation and, as agreed, worked to replace the gammagraphic apparatus in the source store. While collecting the projection sheath, he noticed a metallic noise and he immediately understood the significance and danger. He hurried towards the entrance of the installation and stopped the incoming workers. In a few hours all normal operating conditions were restored. The doses of Mr BM were estimated as follows:
  • Whole body dose: 890 mSv;
  • Hand dose: 3.56 Gy;
  • Eye lens: 3.56 Gy.

Mr BM was immediately admitted to a hospital; some symptoms of a radiation dermatitis were present but soon faded away. With regard to the radiation protection organization, both firms A and B had a very good record: apparatuses were frequently checked, safety procedures were adequate and available on site, all the workers had been given good quality portable monitors and were normally used to record the dose rates. Furthermore, all the workers of the two firms had been adequately informed about risks associated with radiations; in particular, the workers of firm B had attended a refresher course just three months before.

It was concluded that the two workers of firm B misconnected the remote control cable with the source holder, so that the source was pushed to the working position, but it could not be returned to the safety position at the end of the irradiation. Further they did not switch on their portable dose rate monitor. When they collected the exposed films at the end of the irradiation, they had to be in a position quite close to the source, but the vessel thickness shielded the two workers from significant irradiation, as none was detected by their personal dosimeters.

Lessons learned
Cable-source holder connection: All the overexposures were triggered by a misconnection between the source and the remote control cable. It is evident that this is the weakest point of the gammagraphic apparatus. Researches should be stimulated to design new systems. Furthermore, this problem is not limited to the Italian situation, since all the apparatuses used are produced abroad.

Periodic safety controls: Firms operating with such apparatus should be more careful with the periodic checks on the safety systems of their apparatus.
   

8. Radiography incident (Italy)

European ALARA Newsletter - Issue 6

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Description of the incident
In May 1992, a 19-year-old radiographer, on the first day of his employment, received a significant overexposure, while performing his first radiography on a part of a gas duct in an open site. The source he was using was an iridium-192 source of about 1480 GBq (40 Ci). He was working completely alone and had been given almost no training and extremely poor information by his employer. At some stage the source became disconnected from the drive cable and he found it on the ground. He was not able to immediately recognize it as the source, picked it up to examine it and tried to insert it in the projection sheath. All these actions lasted 2 to 3 minutes.

The evening of the same day, his hands grew swollen and red. The young radiographer was admitted to the nearest hospital with radiation dermatitis. His doses were estimated as follows:
  • Whole body dose: 499 mSv;
  • Eye lens dose: 151 – 517 mSv;
  • Hand dose: 74 – 113 Gy.

The events that caused the overexposure can be summarized as follows:
  1. The radiographer was left alone by the person in charge of his training during the exposure with a gammagraphic apparatus, whose operating conditions had not been regularly checked;
  2. He had inadequate training, and no accurate information about the risks connected with the use of ionizing radiations;
  3. He had never seen a diagram, nor a picture of a source;
  4. He was not aware that he should use his portable monitor, nor did anyone tell him to switch it on.

Lessons learned
Training and Information for workers: This is a duty on the responsible administrators of the firms, at least in Italy. Usually they transfer this task to the qualified expert; but it is not always the case; they sometimes disregard this task, with heavy consequences. It is absolutely essential that appropriate training is provided.

Management: Providing training is one aspect of radiological protection but this is just one part of an overall approach to managing radiation protection.
   

7. Radiography incident (France)

European ALARA Newsletter - Issue 5

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Description of the incident
In February 1995, a team of two radiographers was executing the inspection of welds on a construction site, by night. The equipment being inspected was an upright gas tank, with a diameter of 8 m and open at both the bottom and the top. This base was 1 m above the ground on temporary supports, so that the radiographers could move easily from outside to inside of the structure. The weld to be inspected was at 10 m above the ground which called for scaffolding and safety ladder. The exposure device, containing 2.7 TBq iridium-192 was manually remote controlled from outside the base of the tank. For greater convenience, it was tightly fixed onto the scaffolding hand rail with a rope and 4 or 5 knots! The 3 m projection sheath was positioned at the correct distance from the weld with a specially adapted rigid tool (2 magnets, each of 80 kg magnetic strength!). At the start of the exposure, the radiographers heard the noise of the magnetic support falling on the scaffolding floor. It was 2 a.m, pitch dark and they had only portable lamps and usual radiationmonitors. There was no operating phone on the site, and after study of the situation, the two radiographers, without the possibility of ready contact with their management, decided to retract the source. This was not successful as the projection sheath was severely bent. So, they decided to take down the radiographic system in its totality, to straighten the sheath and finally to retract the source into the exposure device. One of the radiographer had to go up and down 3 times for this purpose. It took about 30 minutes to recover the source. A subsequent investigation by the radioprotection safety manager assessed the doses to be approximately 38 mSv for the operator who went up and down the ladder 3 times (the last time with the equipment in his hand), and 8 mSv for the second one who had remained down stairs. These results are in agreement with the films badge results (which were a little bit higher, but included the exposures for the rest of the month).

Lessons learned
  1. The high dose in this incident resulted from poor planning, both in respect of how the work was undertaken (without due consideration of what could go wrong and the implications) and of the actual recovery operations. Management instructions should require the radiographers to estimate doses from proposed recovery operations and should set an action level above which the advice of management should be sought – however difficult this may be.
  2. Magnet fixing systems must be easily and automatically disconnected from the ejection sheath in case of accidental situation (the system is now developed).
  3. No rope nor knot for fixing the gamma source equipment.
  4. Mobile phone should be available on the site (especially at night) to summon assistance.
   

6. Radiography incident (Sweden)

European ALARA Newsletter - Issue 4

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Description of the incident
At the site of a Swedish nuclear power station, some radiography companies had installed X-ray equipment in a building, which was not within the supervised area of the power station. In this incident a weld on a non-radioactive pipe was to be radiographed with an X-ray set to approve the welding method. The radiography equipment and the pipe were installed in a lead-shielded temporary radiography room, 3 x 3.5 m. The operator put the tube voltage to 155 kV and the exposure time to 5 minutes and checked, from the operators place (a panel outside of the room), that the required values were achieved. He then left the area for a few minutes.

A big warning sign was posted at the entrance to the temporary radiography room. However, this sign was also there when no radiography was effected and the people working in the area had got accustomed to this. The doors to the temporary radiography room were kept closed but not locked when radiography was performed.

Three persons entered the building looking for the operator but cannot find him. They wanted to have a look at the weld on the pipe. They looked at the operator panel and drew the incorrect conclusion that the radiography equipment was not in use. They subsequently open the door to the radiography room and called out for the operator. When no answer was received they entered into the room and inspected the weld on the pipe. The TLDs were worn at the height of their pockets because they also functioned as identity cards. However in the accident this meant that they were not in the useful beam of the X-ray set. The later reconstruction of the radiation field and the position of the three persons, together with the information from their dosimeters, showed that fortunately the incurred doses were in fact quite low; the effective dose equivalents were 0.5 mSv, 0.9 mSv, and 3 mSv respectively.

Lessons learned
  1. The incident provides a classical example of warning signs eventually being neglected if they are up all the time, even when no radiation source or radiation field is present.
  2. A temporary radiography room of this type should always be monitored when radiography work is performed and a flashing lamp or some other clear signal should inform people that the radiography equipment is in use.
   

5. Gammagraphy incident (Spain)

European ALARA Newsletter - Issue 4

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Case N° 5a
In 1993 a radiographer was working with a remote exposure device containing 1.6 Tbq of iridium-192. After the operation, he retracted the source, but he proved with his survey meter that the source really was not retracted. The analysis of the accident showed that the male connector end of the crank was broken. That piece had been changed some days before the operations by the manufacturer and the new one had a manufacturing defect.

In summary, the accident happened due to incorrect manufacture and quality control of a very important safety piece of the device. Regulatory authorities inspected the manufacturer and required corrective actions. The radiographer had communicated the accident to his radiation safety officer and they correctly carried out the emergency plan to recover the source. Nobody received significant doses (0.5 mSv whole body dose).

Case N° 5b
In 1994 a radiographer was working at night with an exposure device containing 0.8 Tbq of iridium-192 and had difficulties when trying to lock it in the safe position. He saw his electronic dosimeter off-scale, but his survey meter was malfunctioning and did not detect radiation. He struck the lock assembly with a hammer to reach the lock position. Then he left the exposure device in the client’s facility without any supervision and went to his office to get another survey meter. He returned to the operation site and started to work again, but he had the same problems with the lock assembly. Moreover, his electronic dosimeter was off-scale again and the new survey meter neither worked correctly. He returned to his facility again, took a new survey meter and decided to leave there his TLD and went back to continue the operations.

In summary, the survey meters did not work correctly and the radiographer did not verify them previously. Although he detected a failure on the device he continued working and did not communicate the problems to his radiation safety officer and did not use his TLD. Anyway the TLD showed a dose of 8.5 mSV.

Case N°5c
In 1995 an individual without qualification was ordered by his company to do radiographs at night with an iridium-192 source of 1.9 Tbq. During the operations this person was not able to retract the source into the safe position. Recognising that a problem existed he tried unsuccessfully to contact the radiation safety officer of the facility. Finally, he contacted personnel of the competent authority and the accident was solved without radiological consequences. The analysis of the accident showed that the operator did not know the emergency plan arrangements.

In summary, although this person was not qualified or well trained, fortunately he did recognise the problem and took appropriate actions and therefore avoided to receive an overexposure (the operator received a whole body dose of 2.11 mSv). The company acted imprudently in having an untrained person perform radiography.

Lessons learned
In order to diminish the occurrence of this kind of incidents, the CSN led a campaign with the following features:
  • Review the operational and radiation protection procedures of all gammagraphy companies and require some significant modifications,
  • Press the radiation protection responsible for an appropriate control of the procedures performance by operators,
  • Insist that training is the cornerstone for the excellence in this type of work, as many others,
  • But, in some cases, the need for sanctions was inevitable.
   

4. Radiography incident

European ALARA Newsletter - Issue 3

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Description of the incident
One type of industrial radiography exposure equipment uses a pneumatic system to transfer the radioactive source from the shielded container to the exposure position. These systems are installed in purpose built radiography facilities with interlocks on the access doors that are linked to installed gamma alarm monitors. Over a two-year period two very similar incidents occurred in the same facility. They involved an iridium-192 source of about 7 TBq giving a dose rate of approximately 0.9 Sv.h-1 at 1 m. In both incidents the source became stuck in the pneumatic exposure tube. In the first incident the end cap of the tube had been slightly deformed due to repeated impact from the source and it eventually jammed the source when it was exposed. It was noted that there was a lack of routine maintenance. In the second incident a piece of metal swarf in the tube jammed the source. In both incidents the safety systems worked and prevented uncontrolled access. At this point it is worth comparing how the sources were actually recovered and the safety culture that would have been applied in the nuclear industry. In the latter case there would have been detailed planning, written procedures would have been produced, portable shielding used and probably some sophisticated handling equipment made available. In reality the source recoveries were treated as simple engineering problems that needed to be resolved quickly but with only limited consideration of radiation protection aspects. Long handling tongs were used to ensure the hand doses were not excessive, but control of the whole body doses was less successful; the doses being 29 and 40 mSv from the first incident and 16 and 52 mSv from the second incident.

Lessons learned
  1. Routine inspections of equipment before use and a programme of routine maintenance can significantly reduce the probability of sources becoming stuck in an exposed position.
  2. The incidents display the value of installed safety systems, including a gamma alarm monitor interlocked to access routes. Without these, such incidents would have probably resulted in radiation burns and possibly fatalities.
  3. The design of the facility and equipment should have taken into account means for the recovery of a source that is stuck or cannot be returned by the normal means. For example after the second incident a mechanical means of pushing the source back to the shielded position, that could be operated from outside the facility, was installed.
  4. The planning of source recoveries is essential to implementing ALARA. Industrial radiography could benefit from learning from the safety culture of the nuclear industry.
   

3. Incident in a university laboratory

European ALARA Newsletter - Issue 3

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Description of the incident

A university department had, for quite a number of years, a stock of caesium-137, in the form of caesium chloride solution. This was originally obtained for use in a teaching experiment, but this was discontinued many years ago and the solution retained for other possible uses. During a programme of disposing of old sources an incident occurred which gave rise to a significant intake. At the time of the accident the activity of the solution was 150 MBq. The solution was kept in a standard multidose vial with a rubber septum cap. The work was being undertaken on a shelf bench behind lead bricks. This was contrary to the local rules, which required the work to be done in a fume cupboard. The user reported that when a pressure relief needle was used, the force necessary to push through the age hardened rubber system was such that when it penetrated it went further and entered the solution. This gave rise to an unexpected spurt of liquid from the vial, which contaminated the face of the user. It is possible that through ageing or being left in the sun the vial had become slightly pressurised. The user decontaminated himself and the laboratory, but did not report the incident to the University authorities until several days later. Subsequently whole body monitoring measured the intake to be 10 MBq and the committed effective dose equivalent was estimated to be 140 mSv. It was thought that ingestion was the main intake route, but inhalation or absorption through the skin would not have altered the assessed dose. The intake amounted to a remarkably high 7 % of the original activity, which suggests the users face was close to the vial or other things also went wrong.

Lessons learned
  1. The retention of radioactive solutions beyond their useful life provides an ongoing potential for accidents, especially where ageing of the containment is relevant.
  2. The incident provides a classic example of why manipulations of this type and using this amount of activity were required to be, and should have been, carried out in a fume cupboard.
  3. All incidents should be reported as soon as possible so that appropriate measures can be taken. Although it did not occur here, poor monitoring after the decontamination could have left a situation where the contamination was allowed to spread.
   

2. Radiography incident

European ALARA Newsletter – Issue 2


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Description of the incident

A radiography remote exposure container, housing a 550 GBq iridium-192 source, was being used to examine a circumferential weld on a steel vessel under ‘open shop’ conditions, ie. a barriered off area of a factory. On completion of the exposure, the winding mechanism was used to return the source to its container. During this procedure the portable dose rate meter located at the winding position recorded a drop in the dose rate, and this was assumed to mean that the source had been safely returned to the container. However, when the equipment was used five days later the resulting radiographs were all blank, revealing that the source was missing from the radiography container; obviously the source had been lost. After a search the source was found near the location at which it was last used. Later investigation showed that the source had become detached from the drive cable, for some unknown reason, and had fallen unnoticed from the guide tube during dismantling.  The dose rate meter had not been used correctly to ascertain that the source had fully returned to its container. The noted drop in dose rates at the winding position had arisen because the source had become detached from the drive cable close the source container, which shielded the dose rate meter from direct radiation from the source. The source was recovered in a controlled manner by the RPS. It was found that during the five days since the source had been lost 78 workers had been irradiated to some degree. Their estimated doses are given below. The source was in a readily accessible position and had it been picked up during the five days that it was missing this would have led to radiation burns and, possibly, fatalities.


Number of staff
Dose range (EDE - mSv)
2
100 - 150
4
30 - 100
9
11 - 30
63
< 11

Lessons learned
  1. The monitor should have been taken up to the container to verify the source was fully in the safe position.
  2. Monitoring should have been carried out when the container was returned to the source storage location. This would have identified much sooner that the source was missing.
   

1. Incident in a research laboratory

European ALARA Newsletter – Issue 2

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Description of the incident

A researcher working in a laboratory used for handling unsealed radioactive materials was manually dispensing, in a fume cupboard, a routine delivery of what he believed to be 74 MBq phosphorus-32. When the stock solution was removed from its shielding the portable radiation monitor placed in the fume cupboard by the researcher went off scale; he expected this because the monitor could only measure the much lower dose rates from diluted material. It was then switched off. The appropriate beta shielding was used for the activity concerned. The containers into which the material was dispensed were placed behind Perspex shielding and the monitor switched back on. The expected drop in dose rate was not observed and the RPS was contacted. Investigations revealed that the activity that was delivered was, in fact, 1000 times greater than was ordered, invoiced for, and that stated on the package. A packaging note did, however, state the correct activity but had not been noticed. Although a few spots of contamination, up to 480 Bq.cm-2, were found on a laboratory coat, significant levels of contamination were limited to the fume cupboard. The researcher’s film badge recorded a penetrating radiation dose of 0.04 mSv. An investigation and reconstruction concluded that any intake of activity had been negligible but that his fingers had received doses of around 120 mSv.

Lessons learned
  1. A radiation dose rate monitor capable of measuring all expected dose rates should always be used.
  2. Whenever any radioactive source is purchased and received on the premises all paperwork must be examined in order to ensure that the activity and nuclide delivered are as expected. If there is any doubt or conflicting information is given, further advice should be sought. A radiation monitor should be used in order to ensure that the associated dose rates are as expected for the quantity and type of material concerned.
  3. Suppliers of radioactive materials must continually ensure that all quality assurance procedures are effective.
   

The radioactive incident of ACINEROX in Spain

J.T. Ruiz, J.M. Campayo (LAINSA)
European ALARA Newsletter – Issue 8

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Introduction
At the end of May of 1998 a caesium-137 source was melted accidentally in one of the stainless steel production plant furnaces of the company ACERINOX in Cadiz (Spain).

Once the presence of radioactive contamination was detected, a number of organisations provided assistance. These included LAINSA, an expert company in decontamination and dismantling of radioactive and nuclear facilities with experience in radioactive emergencies, the regulatory body, CSN, and the waste management utility, ENRESA. They have evaluated the situation and implemented first radiological protection measures:
  • Evaluation of the contamination in the plant;·
  • Control of the access of people, vehicles and materials to the contaminated zones;
  • Delineation and signing of all areas where radioactivity was detected;
  • Control of radiation in the gases extracted by the smoke clearing system.

The recovery operation for the affected facilities began immediately: even before the formal approval from CSN of a Performance Plan, to decontaminate the affected facilities.

Decontamination took 5 months, and 50.000 man.hours were necessary to perform the whole work (20 % corresponding to radiological protection activities). The total collective dose was about 60 man.mSv.

Objectives
The objectives established in the Performance Plan, previously mentioned, were:
  • To avoid contamination outside of the Plant;
  • To guarantee the radiological protection of the professionally exposed workers, the personnel of ACERINOX and the public in general;
  • To control the decontamination activities according to the Radiological Protection standards;
  • To ensure that the generated radioactive wastes remained in safe conditions as far as their manipulation, storage and transport are concerned.

Affected facilities

Since the very beginning the contamination had affected the smoke dust that circulates through the conduits of the gas extraction system of the electrical arc furnace nº 1 and to the shared clearing system for furnaces n° 1 and n° 2 (Figure 1).

Table 1 summarises the detected values of radiation in the affected systems. The measured activities in samples taken in the smoke dust, before the beginning of the operations of decontamination were in the range 800 to 2000 Bq/g.

Figure 1. Contaminated facilities
incident0.jpg












Table 1. Levels of initial radiation in the main areas

System
Average dose rate
(mSv/h)
Maximum dose rate
(mSv/h)
Electrical arc furnace n° 1 and gas ducts extractions
0.5
1.8
Natural cooler and stark arrester
0.02
0.05
Bag filter n° 1
0.05
0.1
Bag filter n° 2
0.02
0.03
Silos A and B
0.03
0.1

 

Radiological Criteria
According to the Performance Plan approved by the CSN the final state of the facilities would be such that:
  • The maximum permissible dose in any zone of the factory did not exceed the value 1 mSv in an annual period;
  • The derived values from surface contamination were such that they did not exceed 4 Bq/cm2, in those areas where their measurement was possible.

Due to the dimensions of the facility and the great number of affected zones it was not easy to establish a strict and unique access control. Thus, in the first phase those zones with higher dose rates and requiring greater movements of people were identified. The measures adopted were based on two general approaches:
  • Immediate Intervention: action to remove radioactive material, decontaminating the zone, remove systems, equipment… or;
  • Isolation of these areas, by establishing alternative access and routes.

Works development

The objective established for the final state of the facilities had to fulfil two requirements; the production of the Steel Works had to continue and it was necessary to cope with the radiological protection principles.

Therefore, in the first phase decontamination was limited to clearing line n° 1, allowing normal production to continue on the other clearing line. In that phase most of the very low activity contaminated wastes were generated.

Next decontamination of the electrical furnace nº1 was undertaken, followed by the bag filter nº 2 and silos. In these phases, less smoke dust wastes were extracted but metallic wastes, refractory bricks of the furnace… were generated. Dry decontamination techniques (vacuum cleaning, grinding…) were used to avoid the generation of liquid wastes that would have been difficult to treat in that facility.

Radiological control
The main activities of LAINSA were as follow:

Control of effluents
Isokinetic samples were taken from the gas evacuation systems. The results show that the values, prior to dispersion and diffusion in the atmosphere, were less than the lower limit of detection: 0.6 mBq/L. This monitoring was continuous until the decontamination of the smoke clearing systems was completed.

Radiological control of decontamination work
The criteria for radiological protection control of the programme are summarised in the Table 2.
The radiological state of area, equipment or systems were described in the corresponding Radiation Work Permit, where a dose estimation was also made.


Table 2. Radiological protection criteria

Individual dose constraints
0.3 mSv per day; 1 mSv per week; 3 mSv per month

ALARA studies
If anticipated collective dose is higher than 10 man.mSv

Use of electronic dosimeters
Works with dose rate greater than 30 µSv/h
Control of exposed time
If an ambiant dose rate higher than 150 µSv/h
Control of environmental contamination
Before and during the execution of the works with risk of producing dust.
With values betwen 3.75 % and 37.5 % of the LDCA, face mask will be used.
With values greater than 37.5 % of the LDCA, air-fed equipment will be worn, the ventilation conditions will be improved.
Control of surface contamination
Surface contamination limit in zones in which the measurement is feasible < Bq/cm2

 

Controls of access
RP technicians from the UTPR – a specialised radiation protection company authorised to perform radiation protection tasks and provide specific activities such as decontamination – monitored the entrance and exit of personnel, materials and wastes, and controlled the accesses to the work zones. The controlled zones in thee work places and the waste storage areas were periodically monitored, to assure that the established radiological conditions were fulfilled.

Occupational exposure
All the personnel involved in decontamination operations in ACERINOX were classified as Professionally Exposed Personnel to ionizing radiation and used TLDs. The total collective dose was 60 man.mSv. For the 5 months period, the average individual dose was 0.6 mSv and the maximum individual dose was 3.5 mSv.

Table 3 shows the results of the operational dose (electronic dosimeters) for the critical tasks. 40 % of the total collective dose was associated to the operations of decontamination of the electrical arc furnace nº 1 and of the gas ducts, where doses rates were the highest. The next critical group consists of the individual dedicated to the wastes segregation and preparation (23 % of total collective dose). In this case, the number of people and the time used were more significant than the dose rates. As far as the internal dosimetry was concerned, two programs of monitoring were set up (whole body monitoring), the first a few days after the start of works, to verify the suitability of the adopted protection measures. The second at the end of the work to confirm the absence of contamination. In all the cases, the results were less than the recording level, 0.5 mSv.

Table 3. Operational dose for critical tasks
Task
Doses (man.mSv)
Electrical arc furnace n° 1 and gas ducts extractions
16.1
Natural coolers
3.1
Bag filter n° 1
5.3
Bag filter n° 2
2.3
Scaffolding installation and stripping
3.4
Silos
0.5
Wastes handling
9.7
Total
40.4

Waste management
The wastes produced were put into two types of containers. The smoke dust was put into 1 m3 big-bags, whereas metallic, plastic wastes, paper… were put into 220 litres drums. Each waste was identified, labelled and measured. The parameters registered for each container were the content, weight, size, origin, specific activity... These wastes were stored within the facility in a place with the suitable radiological and physical security conditions. A significant percentage of the waste was checked with spectrometrical measures to determine the specific activity and to evaluate the decontamination process.

Conclusions
The incident in ACERINOX in May 1998 did not involved illegal risks of exposure to ionizing radiation for the workers, or for the public, nor for the environment. The adopted radiological protection measures in the decontamination work were effective (no internal contamination). Also, the external doses remained at very low levels, thanks to the strict application of the established criteria of radiological protection from the beginning of the works.

Finally we would like to note that the immediate intervention made in ACERINOX, has demonstrated the capacity of response and co-ordination between companies and institutions in an incident without precedent in Spain.

Approximately 2000 tons of low level activity wastes were produced in the decontamination operation at ACERINOX (smoke dust: 91 %, fibre cement panel: 4 %, refractory bricks 2 %, compressible waste 2 %, metallic waste 1 %).