TNAG-1776-FCO40-2530-Daya-Bay-nuclear-power-station-project-safety-concerns-in-Ho-1988 — Page 186

lifted when the levels of radioactivity fall below the appropriate derived emergency reference level. Following the lifting of any

interdictions the relevant foodstuffs should still continue to be monitored to ensure that the levels of radioactivity in the foodstuffs remain acceptably low, (see Chapter 8).

Major accidents at the Daya Bay plant which are large enough to require countermeasures in Hong Kong are unlikely to cause any significant levels of ground contamination such that major decontamination of streets and buildings would be required. Accidents which are large enough to cause levels of ground contamination, such that major decontamination should be considered, are so unlikely that detailed planning and in particular purchase of expensive specialised equipment is not justifiable. It is, however, worth considering the principles to be applied when deciding what, if any, actions would be justifiable if a very large accident had occurred.

Following a very large beyond design-basis accident, which it must be emphasised is highly unlikely, the decision-maker could be faced with a number of situations where the doses likely to be received by the public could be reduced by taking some action which will cost money and perhaps also involve some social costs. He or she will therefore have to consider whether or not some protective measure will be cost-effective. This situation is similar to the optimization of radiation protection. Much has been written on this topic but in particular the decision-maker should consider the advice giving in the International Commission on Radiological Protection's Publication 37 (ref 39). In such circumstances the decision maker will have to balance the 'cost' of the potential health detriment against the cost of some countermeasure. Taking an extreme example, if following a very large accident at the Daya Bay plant some people had been relocated from their homes due to localised high levels of ground contamination a decision must be made concerning the timing of the return of these people to their homes. As time progresses, the dose rate in the affected area will decrease due to natural processes together with any decontamination processes

FIG 9.3

OPTIMIZATION

OF DOSE RATE

AT WHICH

PUBLIC MAY BE

ALLOWED TO

RETURN TO

HOME

TOTAL

COST

68

HEALTH DETRIMENT

PROTECTION MEASURES

OPTIMUM

DOSE RATE