PROBABILISTIC SAFETY ASSESSMENT PAST, PRESENT AND FUTURE - AN IAEA PERSPECTIVE

Despite the high level of development that probabilistic safety assess ment (PSA) methods have reached, a number of issues place constraints on its use in supporting decision making on safety matters. A recent p ublication of the International Nuclear Safety Advisory Group (INSAG) represents an important step in reaching international consensus on th e use of PSA. PSA is ''strongly encouraged'' by INSAG; however, it is noted that ''PSA methodology is not sufficiently mature for its presen t status to be frozen''. The main aspects of the report are discussed in this paper. The paper next discusses three main categories of PSA a pplication, namely the adequacy of design and procedures, optimization of operational activities and regulatory applications. For each of th e applications, the objectives, specific modelling requirements and th e prospects for implementation are presented. Consistent with its stat utory functions, an important aspect of the work of the IAEA is to rea ch international consensus on the possibilities of and limitations on the use of PSA methods. Whereas past efforts have been concentrated on promotion and assistance to perform Level 1 PSAs, work is now extendi ng with emphasis on PSA applications, Level 2 and Level 3 analysis, ex ternal events and shutdown risks. The main elements of IAEA's PSA Prog ramme are discussed. Finally some challenges related to the use of PSA in the backfitting of nuclear power plants in Eastern Europe and coun tries of the former USSR are addressed.