7
ACCIDENT ASSESSMENT
7.1 The Incident Assessor
The job of the assessor is vital to the successful operation of the Contingency Plan. He or she will have to advise the MAC controller and hence the CCC on the magnitude of the potential radiological hazards and on what countermeasures should be taken.
How successful the assessor is will depend upon a number of important factors:
(i)
his or her knowledge and understanding of reactor accidents;
(ii)
the quality and quantity of the data being supplied to him or her;
(iii)
the format in which the data is presented to him or her;
(iv)
the calculational tools available to him or her.
The most able incident assessor with a complete understanding of reactor accidents and their potential radiological hazards would find it extremely difficult to rapidly analyse a post-accident situation without suitable aide-memoires and means of quickly performing a number of calculations. As part of preparing for his or her role in the event of an accident at Daya Bay the designated incident assessor must consider how he or she will perform the task and prepare whatever pro forma, etc., he or she will need. This will involve considering what information will be available at each stage of the accident and deciding how best to use that information as discussed in the following
section.
7.2 The Incident Assessment
The assessment may best be described in four stages. In the first stage actions may need to be taken prior to any release of radioactive material based upon plant conditions. In the second stage, the assessment will be a prediction of the likely radiological consequences of a release. This is likely to be based on limited data available from the reactor operators and from installed monitoring equipment. As such a number of conservative assumptions will have to be made. In the third stage monitoring data will become available from teams sent out to monitor the plume and in the fourth stage deposition data will become available.
First Stage
Certain abnormal plant conditions may indicate that a release of radioactive material into the environment is possible within the next few hours. Such conditions will require the reactor operators to declare an ‘Emergency Standby' or some higher category of emergency situation. This situation should be notified to the Hong Kong Authorities, (see Chapter 5). At this early stage the incident assessor should consider whether meteorological conditions are such that any release could potentially affect Hong Kong. Studies have shown that if certain abnormal plant conditions arise it may be prudent to take some off-site actions before any release of radioactivity has taken place, (ref 18). In general these actions will be restricted to an area close to the reactor site, for example, if a core melt has occurred consideration should be given to precautionary evacuation of people living within 5-8 km of the reactor. If however a core melt event has occurred at Daya Bay and the meteorological conditions are such that Hong Kong could be affected by a release, the incident assessor should advise the MAC controller and hence the CCC that a small possibility exists that sheltering could be required in the north-eastern area of Hong Kong closest to the Daya Bay site, at sometime within the next few hours.
Second Stage
The first alert of any actual release of radioactivity from Daya Bay should be from the reactor operators, and they
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