Main Results of a Level 2 PSA Study Completed for Paks NPP

摘要

A Level 2 PSA study of the Paks NPP has been performed recently. The main aim of the study was to define the strategy and means of mitigating the consequences of severe accidents resulting in reduction of risk caused by potential large radioactive release from the containment. The current paper addresses the objectives and scope of the study, as well as the main results achieved. The approach used for severe accident progression and probabilistic event sequence modeling is described within. The objectives of the study were to provide a basis for the development of plant specific accident management strategies and for the evaluation of risk reduction options through system backfits, to gain insights into the progression of severe accidents and containment performance, to identify major containment failure modes and to estimate related radioactivity releases. The scope of the study was mainly determined by the scope of the existing Level 1 PSA studies of the plant, i.e. it covers accident sequences induced by internal initiating events, internal fire and flood hazards assumed at nominal power level, and by internal initiating events emerging during planned shut-down states. Seismic hazards has not been considered within the current Level 2 PSA. The numeric results indicate that in the present plant configuration hydrogen burn and accidents occurring in shut down states and failures of the spent fuel storage pool (SFSP) represent the largest challenge. The results demonstrate that the potential mitigative strategies for accidents starting from the nominal plant operational states are able to reduce the corresponding risk so that Paks NPP could meet the probabilistic objectives defined by different international guides.