Minutes from SAGE update meeting 15 March 2011
Held in 35 Great Smith Street at 14.00
PRESENT
Professor John Beddington, Government’s Chief Scientific Advisor and SAGE Chair
Hillary Walker (Department for Health)
Nick Gent (Health Protection Agency)
Colin Potter (Health and Safety Executive)
John Simpson (Health Protection Agency)
Mike Weightman (Health and Safety Executive (Chief Nuclear Inspector))
Paul Howarth (National Nuclear Laboratory)
Arwyn Davies Defra)
David Makay (CSA DECC)
Peter O (CPNI)
BY TELEPHONE
Sue Ion (Independent)
Pat Boyle (Met Office)
Mat Hort (Met Office)
Mike Griffiths (RIMNET)
Kevin Hesketh (National Nuclear Laboratory)
Robin Grimes (Imperial College)
Brian Baptie (British Geological Survey)
Phil Robinson (British Energy)
SECRETARIAT
Chris McFee (GO-Science)
Andy Gregory (Cabinet Office)
Miles Elsden (GO Science)
Elizabeth Surkovic (GO-Science)
Catherine Finney (Cabinet Office)
Elizabeth Moore (Cabinet Office)
AGENDA ITEM 1: WELCOME AND REVIEW OF MINUTES
1. THE CHAIR welcomed the group and thanked them for attending at short notice.
2. The purpose of this meeting was to review the current advice to COBR with a reasonable worst case scenario and a most likely scenario to inform guidance to UK nationals in the Tokyo area.
AGENDA ITEM 2: SITUATION UPDATE
3. The group agreed that information remains uncertain with often contradictory media reporting.
AGENDA ITEM 3: SCENARIOS
4. The group discussed likely scenarios for the current situation in JAPAN.
Most likely worst case
5. The group agreed that the most likely scenario remained that current manual cooling mechanisms were likely to ensure that radioactive emissions are relatively modest. The additional advice for those within a zone between 20 and 30km of the site to remain indoors was a proportionate response to the situation and the group agreed that UK citizens should be strongly urged to follow the advice of the local authorities.
6. However, the group emphasised that the caveat remained that there was poor information about the efficiency of the cooling methods, and the corresponding potential damage to the reactor cores. The capability to effectively cool the reactor’s cores and ponds remained the key factor in limiting the impact of the current situation. The group agreed to continue to use contacts within international organisations such as the IAEA and our links with international partners to increase the understanding of issues on the ground. Members of the group were also working with the UK embassy in Tokyo to approach the Japanese authorities directly to request further information.
Reasonable worst case
7. The group agreed that should these cooling mechanisms break down or fail, then it was likely the reasonable worst case scenario would be reached. The group expressed the view that recent events at reactor two mean there is an increase chance of this occurring. The group heard that recent unconfirmed information had also indicated that cooling mechanisms could be beginning to fail.
8. However, the group agreed that any future release of material remained unlikely to provide a need for similar counter measures beyond the exclusion zones already established (20-30km). The group agreed that any emissions would be monitored in real time by the Japanese authorities, which would enable appropriate advice to be issued.
9. The group agreed that the Reasonable Worst Case scenario remained that the current cooling activities would fail, and the increase in pressure could not be contained and a pressure build up would lead to a failure of the reactor pressure vessel. Activity would then be released into the containment vessel. Furthermore, the fuel elements would continue to build up and ultimately melt, potentially melting through the bottom of the reactor pressure vessel and liner of the outer containment vessel, and react with the concrete base of the vessel.
10. The group agreed that an initial explosive reaction could occur, taking radioactive material up to 500 metres. Following this explosion both the height of the plume and the amount of the material released would decline rapidly. However, the release of material would continue to occur over a significantly longer timescale.
11. The group agreed that an additional concern was that, should a failure occur at one of the three vulnerable units, it would interrupt the cooling activities at the neighbouring plants leading to multiple meltdown failures. If one unit fails it was therefore likely that there would be failures at the two remaining plants. The group could not say how long failure of these other reactors would take, but estimates were that it was likely to be of the order of a day.
12. The group also expressed concern on the ability to maintain integrity of the elevated cooling ponds that are associated with reactor buildings. The group agreed that, whilst the exact make-up of the contents of these ponds was unclear, there were concerns that should the spent fuel rods in these pools be exposed to the air (normally cooled and shielded under approximately 6m of water) they could give a similar event to a meltdown of the reactor cores.
13. The group agreed that there was also a concern that exposure of the material in the pool to the atmosphere could give rise to fires that could give a similar effect to the core meltdown. The group agreed that these pools could contain significantly more material than the reactor cores which could give rise to additional local effects, including direct radiation effects.
14. The group agreed that failure of containment within the ponds could therefore result through a similar scenario to the Reasonable Worst Case to an external core with the meltdown of multiple cores, but taking account of appropriate release fractions.
Enhanced reasonable worst case
15. The group agreed that an enhanced Reasonable Worst Case should be considered where there is a release from all three cores and the equivalent of six reactor cores in cooling ponds. The additional effects from this type of event were unclear, as the make-up of the material in the ponds was unknown. The hazard close to the facility and within the exclusion zone should be increased considerably.
16. The group agreed that current weather predictions suggest the prevailing wind would move around to the North West in the next few hours, taking any radiological material released out over the Ocean. The group heard that these conditions are expected to continue for the next few days.
17. The group heard that it was expected that current cooling activities will need to continue at, or close to, current levels for of the order of 10 days before the cores would have been cooled sufficiently and controlled to lower the current risk.
18. The group agreed that it was therefore possible that wind conditions could again become unfavourable before the risk of release had been removed. In this situation of winds taking material in the direction of Tokyo and rainfall ensuring deposition on the ground the level of deposition to effect human health would be maximised. The group agreed that some radioactive material would be likely to reach as far as Tokyo but this would be very limited.
19. The group agreed that lessons learned from similar incidents (at level 5 to 6) were that a maximum exclusion zone (currently 20-30 km) should normally be effective. There had been a 30km zone in place following the Chernobyl fire (level 7) and there was no evidence to suggest that a larger evacuation zone would have led to any significant reduction in health effects from direct exposure to radiation.
20. The group agreed that even if this enhanced reasonable worst case scenario occurred, then it would be possible to take mitigating action in Tokyo – taking shelter within buildings. This would be necessary whilst the plume passes over. Tokyo is around 220km away from Fukushima.
21. The group agreed that there would be second order health effects in terms of food and water, but mitigation advice would be issued over a longer timescale.
22. The group agreed that even if containment was successful there would be significant long term clean-up issues in and around the Fukushima facility.
AGENDA ITEM 4: CONCLUSIONS
23. Summing up, the CHAIR said that that the unanimous view of SAGE remained that there was no need for UK nationals to have to evacuate the vicinity of Tokyo. Recent events had not significantly affected this advice.
