Minutes from SAGE update meeting 13 March 2011
Held in 70 Whitehall at 14.30
PRESENT
Professor John Beddington, Government’s Chief Scientific Advisor and SAGE Chair
Hillary Walker (Department for Health)
Nick Gent Health (Protection Agency)
Peter Tallantire (Cabinet Office)
Colin Potter (Health and Safety Executive)
BY TELEPHONE
Paul Howarth (National Nuclear Laboratory)
Sue Ion (Independent)
Pat Boyle (Met Office)
Mat Hort (Met Office)
Mike Griffiths (Rimnet)
Elizabeth Surkovic (GO-Science)
SECRETARIAT
Chris McFee (GO-Science)
Andy Gregory (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 provide 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. There are six reactors at the Fukushima plant. It was reported that three of these are shut down for planned maintenance and provide no threat. Work is currently ongoing at the plant to mitigate the risks from the other three reactors.
4. A second plant (Onagawa) is reported to be experiencing similar issues. This plant is 70 km north of Fukushima. It is of broadly similar design to Fukushima and so the scenarios below are valid for that plant as well.
AGENDA ITEM 3: SCENARIOS
5. The group discussed likely scenarios for the current situation in JAPAN.
Most likely worst case
6. It was agreed that the most likely scenario is that current cooling mechanisms were likely to ensure that current emissions are relatively modest and will not require any additional evacuation measures other than those currently being undertaken by the Japanese authorities.
7. However, the group cautioned that they do not currently have good information about the efficiency of the cooling methods and the corresponding potential damage to the reactor cores. They are currently getting information from international organisations and web sites and are not getting direct information from the Japanese Authorities. The group agreed that there is merit in approaching the Japanese authorities directly to request further information.
ACTION: THE CHAIR to seek further information from Japan.
Reasonable worst case
8. The group agreed that, should the cooling mechanisms break down or fail, then the next scenario is likely to be an increase in pressure which will need to be contained leading to additional releases of material which will be more radioactive than those hitherto. This material is unlikely to go beyond the current exclusion zones already established (20km). The group heard that any emissions will be monitored in real time by the Japanese authorities.
9. The group agreed that the reasonable worst case scenario is that current cooling mechanisms fail, the increase in pressure cannot be contained and pressure build up leads to a failure of the reactor pressure vessel. The core material released into the containment vessel would rapidly heat up and react with the concrete base of the vessel.
10. An initial explosive reaction would 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, release of material would occur over a significantly longer timescale.
11. If this reasonable worst case from a nuclear perspective is coupled with unfavourable meteorological conditions then the combination is the reasonable worst case. 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 is maximised. Some radioactive material may therefore reach as far as Tokyo but this will be very limited.
12. The group agreed that lessons learned from similar incidents (at level 6 and beyond) is that a maximum exclusion zone (currently 20 km) will be effective. There was a 30km zone in place following the Chernobyl fire (level 7) and there is no evidence to suggest that a larger evacuation zone would have led to any significant reduction in health effects from direct exposure to radiation. Tokyo is around 250 km away from Fukushima.
13. If this reasonable worst case scenario occurs, then it will be possible to take mitigating action – taking shelter within buildings. This will be necessary whilst the plume passes over.
14. The group also agreed that there are second order health effects in terms of food and water, which will need to be monitored but is unlikely to be significant in the Japan context.
AGENDA ITEM 4: CONCLUSIONS
15. The CHAIR summed up. He said that unanimous view of SAGE is that there is no need for UK nationals to have to evacuate the vicinity of Tokyo, even in the likely reasonable worst case of a nuclear incident plus unfavourable weather conditions.
16. Lessons learned from more significant incidents, such as Chernobyl, are that a exclusion zone (currently 20 km) will be effective - even in the event of a more substantial release - in minimising the health effects from direct radiation exposure. Any emissions will be monitored in real time by the Japanese authorities which should enable appropriate advice to be issued.
