On the Accident Behaviour of the HTR 500: A Short-Term Analysis

[Automatically extracted and translated] The present estimation of the HTR 500 design concept attempts to filter the risk-relevant accidents out of the whole spectrum of possible accident sequences and to assess the risk they cause using methods of risk analysis. Accidents with loss of forced convection, so-called core heatup accidents, represent the dominant risk; those with additional failure of the liner cooling system account for half of the integral societal risk of late fatalities, which is expected to be below 10-3 per annum despite the still comparatively large uncertainties of the analysis. Maximum late fatalities slightly exceed 3000 persons, no early fatalities are computed for any case. Water ingress and depressurization accidents are of minor significance. The risk therefore keeps clear off figures for a pressurized water reactor of equal power. The selected safety concept proved to be well-balanced; the essential safety systems are acceptable in our view. Radiation exposure from accidents which could be of significance in the licensing procedure due to their relatively large frequency (>10-5 /annum) remains below the limits stipulated in the radiation protection ordinance.