On the use of probabilistic safety analysis methods, it was said that these methods had been developed, along with the necessary data bases. A probabilistic analysis had been done for the new RBMK 1500 design. Quantitative safety criteria were included in these. An example was given that the reliability of the reactor protection system was required to be about 10-7 per year.
In the summing up, the Russian delegation again chose to highlight the importance of human error and reconfirmed particularly the benefits to be had by further exchanges in the man-machine interface area.
Session 3B, Working Group 3
Chairman
―
H Rabold
Decision basis for evacuation, sheltering, use of
prophylactics; criteria for medical treatment; control of foodstuff and water; prevention of groundwater contamination; decontamination of people, material, soil etc; radiological conditions for plant re-entry.
The Chairman noted that there had been a proposal from the UK that the IAEA should organise a conference on decontamination matters. Dr Eggleton informed the Conference of relevant Harwell work on decontamination of urban surfaces.
The Russians stressed that loose caesium contamination had been a predominant problem. The spray of decontaminant solutions was widely used and vacuum cleaners were used to clear up loose particles. In some cases pastes were put on walls, establishing a quick-drying film which was peeled off with the active particles sticking to it. Solid wastes are being stored in the waste repository for Unit 5, which had already been built.
In regard to emergency measures Mr Dunster outlined the UK system of indicating the thresholds at which action would be considered. The Russians indicated a similar philosophy, the important whole body dose being 25 rem, below which evacuation would not be necessary and 75 rem by which it certainly should be taking place. Similarly, the Russians have reference levels at which they advise sheltering, iodine distribution etc.
Professor Ilyin pointed out that one factor delaying the need to evacuate Pripyat's population was that the accident occurred at night when the people were indoors. The decision to evacuate was taken at 14.00 hours on 27 April. Iodine had already been given out at 08.00 hours.
It was clear that the military people had been much involved in the evacuation. One particular problem which occurred was having to throw away contaminated clothing and give people clean clothes.
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