TNAG-1776-FCO40-2530-Daya-Bay-nuclear-power-station-project-safety-concerns-in-Ho-1988 — Page 166

8

EMERGENCY MONITORING OF ENVIRONMENTAL RADIOACTIVITY

8.1 Introduction

Normal operation of a nuclear reactor gives rise to the release of only very small quantities of radioactivity to the environment. Such releases in gaseous or liquid form are controlled at a level where the consequent average radiation dose to the population is a minute fraction (less than 0.1 percent) of the natural background radiation which the public receives from cosmic rays, the rocks and soil, and from building materials.

World-wide experience of the operation of other nuclear reactors indicates that normal operation of the Daya Bay reactor would not result in any significant increase in the radiation dose to the population of Hong Kong. Nevertheless the Government of Hong Kong is implementing a programme to monitor background radiation levels in Hong Kong. This programme has started prior to the Daya Bay reactor becoming operational in order to measure the base line of natural radiation background, (see Figure 8.1). Continued routine monitoring will provide assurance that radiation levels are not significantly increased by operation of the reactor, or, possibly, provide information on long term trends in radiation levels during operation of the reactor and demonstrate compliance, or otherwise, with the recommendations of international bodies concerning dose limits to the public.

A major accident at one of the Daya Bay reactors could lead to an uncontrolled release of radioactivity into the atmosphere. (However even a serious accident may not produce a large release; in the case of the accident at the Three Mile Island PWR in the USA the release of radioactivity was not sufficient to cause serious health effects even to the public living immediately outside the site). In the event of an accidental release at Daya Bay an intensive monitoring programme should immediately be put into effect in Hong Kong, so that an assessment could be made of the need to implement countermeasures to protect the public. This intensive monitoring programme would be based on an enhancement of the routine background radiation monitoring programme, with trained and experienced personnel using equipment with which they were familiar to monitor the same pathways of radiation dose to the public as were measured in the routine background monitoring programme. These experienced personnel would be supplemented and assisted by other staff who had been trained and exercised in these emergency duties.

8.2 Pathways of Exposure to the Public

An accidental atmospheric release of radioactive fission products from the Daya Bay reactor could expose the population of Hong Kong to increased radiation dose by a number of different pathways as illustrated in Figure 4.1. The most important routes are:

(i)

direct radiation from the airborne plume;

(ii)

inhalation of airborne materials;

(iii)

direct radiation from ground deposition;

(iv)

ingestion of contaminated food and water;

(v)

contamination of skin and clothing.

The contribution to the total dose from each of these routes would have to be assessed, although it is likely that some of the routes would be insignificant.

Any accident which results in a discharge of radioactivity to the sea will in general have less significant consequences than an accidental release to the atmosphere.

The timescale after the release at which these individual routes became important would vary. For instance, radiation from the plume would be the most immediate route, although it would be transitory. On the other hand, radioactive material would enter the foodchain only after many hours or perhaps several days. Only then would the ingestion route become significant. These timescales determine the order of priority in implementing an emergency

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