Radiological incident at IRE
At the time of writing this paper (12/9/2008), the analysis of the incident is still ongoing and some information is still required or has to be confirmed in order to obtain a clear picture of the entire incident scenario. Hence, this information should be viewed accordingly.
Activities of the IRE
The Institute for Radio-elements (IRE) located at Fleurus – Belgium is a nuclear installation producing radioisotopes for the medical sector by extraction of fission products from highly enriched uranium targets irradiated in nuclear reactors (BR-2 Mol, HFR Petten...).
One of the produced radioisotopes is iodine-131 with a half-life of 8 days.
The production is a batch process. Two or three campaigns are performed each week.
Origin of the incident
On Friday the 22nd of August, after production, the contents of three tanks of 50 l, filled with high activity waste from different production units, were transferred to a larger tank of 2700 l, partly filled. At that moment the IRE did not detect any abnormality. However, apparently, an exothermal chemical reaction (not fully characterised at present) started in the 2700 l tank leading to the release of I-131 to the stack through filter batteries. The release lasted for several days.
The increase of I-131 release was not properly noticed by the operators and did not lead to immediate countermeasures by the IRE.
Evolution of the incident
On Monday the 25th of August in the morning, a safety engineer identified the problem and from that moment on, IRE gave full priority to stopping the release. However, the first attempts were not successful. Indeed, the isolation of the tank risked to lead to an overpressure.
On Monday, the IRE informed the TSO (Bel V) about the incident. FANC was notified around 17:30H by the IRE.
The evaluation performed by the IRE gave a total release of 45 GBq I-131, which is approximately equal to the cumulative I-131 releases for 2006 and 2007.
From Monday onwards, the release was still going on but was decreasing by one order of magnitude (see also appendix).
The first conservative evaluations showed that the most critical person was directly exposed to dose levels below the trigger level of the emergency plan.
The Telerad network, which monitors the radioactivity on the entire Belgian territory and particularly around the IRE, could not detect the airborne concentration of the I-131 released. Indeed, the momentary concentration of I-131 in the air remained below the detection limits of the detectors for this radionuclide.
FANC/BEL V actions
After the IRE gave the assurance that no production was ongoing and that no new production batch was planned before Thursday 28th August, a team consisting of a FANC inspector, accompanied by two Bel V experts and an independent expert specialised in ventilation systems was sent on site Tuesday 26th August in the morning. Additional mobile monitors were also installed in the vicinity of the IRE.
The FANC forbade any new production until the following conditions are met:
- The origin of the incident is known and measures are implemented to avoid any other similar incident
- The monitoring system of the ventilation and of the release to the environment is fully operational
- Analysis and implementation of improvement of the safety alarm management system
According to the information provided, none of the workers at IRE received significant additional doses.
The FANC informed the Government and issued communiqués on its web site, as well as to the press on the same day.
On Wednesday the 29th of August, the incident was notified to the IAEA as an INES 3. A provisional short description of the incident was provided together with a rough evaluation of the doses received by the most critical person (160 µSv effective dose).
Also on Wednesday, grass samples were collected by the FANC for measurement. On Thursday the 28th, the results of these measurements and conservative simulations showed an order of magnitude of contamination in specific areas possibly justifying protective measures of the food chain. Hence, the FANC requested to trigger the nuclear emergency plan (U-2 level – events that do not require direct protective measures of the population, actions related to the food chain may be decided).
National emergency management
On Thursday evening information and the first recommendations were issued on the governmental web site and distributed by the press. A full characterisation of a possible water, air, grass, vegetables and milk contamination was further carried out. It was recommended to the population living in a zone of 5 km north east of the IRE not to eat fruits or vegetables from their gardens, nor to use rain water.
Information to be issued by the local police and the city of Fleurus, directly to the concerned population on Friday the 29th, was planned and an information phone line was opened.
On Saturday 30th, further characterisation of the contamination allowed reduction of the area where protective measures were recommended to 3 km-area to the north east of the IRE. In addition, measurements confirmed that no significant contamination of milk had occurred. Recommendations were therefore limited to avoid eating fruits and vegetables from the gardens until Sunday, 7th September.
At no time was there a need to trigger direct protective action for the population (sheltering, evacuation or intake of iodine tablets).
Nevertheless, to reassure the local population, those who wished, were invited to pass a medical examination to measure a possible contamination of their thyroid gland. Those examinations were performed on Monday 1st September and Tuesday 2nd September, with priority to the most sensitive persons, children and pregnant women. 1320 persons were examined, none of them showed signs of contamination. The trigger level of the detector was set at 40 Bq which ensures a sufficiently low detection level and can be performed within a reasonable time frame. Those results are consistent with the diffusion calculations.
FANC and Bel V, on a permanent base, follow-up on the evolution of the situation in situ and work in close contact with the operator. Their priorities are:
- To prevent additional activity release in the environment
- To obtain a full analysis of the incident including the lessons to be drawn
Aware of the significant impact on public health a shortage could have, FANC keeps in mind the importance of a swift resumption of the supply of radioisotopes to the hospitals.
On September 6th, the emergency level was reduced from level 2 to level 1 based on the reassuring results of the analysis of the 252 environmental samples, on the results of the medical examination of the population and on the ongoing securisation of the site. Moreover, all samples taken from fruits or vegetables indicated I-131 contamination below 100 Bq/kg (in fact only four samples were approaching this value). This 100 Bq/kg value is the reference level recommended (although not yet approved) by the WHO, for the consumption of food, by children, on a permanent basis.
The emergency level 1 means that there are no longer any countermeasures in force. Hence, the advice towards the population to refrain from consuming vegetables and fruit from their gardens was lifted. All actors involved in the management of the crisis remained in stand-by till Friday the 12th, when the emergency was lifted.
Further information and results of the sample analysis is to be found on the FANC website www.fanc.fgov.be (although only in FR or NL)