Accident analysis for nuclear power plants with graphite moderated boiling water RBMK reactors

Deterministic safety analysis (frequently referred to as accident analysis) is an important tool for confirming the adequacy and efficiency of provisions for the safety of nuclear power plants in accordance with the defence in depth concept. Owing to the close interrelation between accident analysis and safety, an analysis that lacks consistency, is incomplete or is of poor quality is considered a safety issue for a given nuclear power plant. The development of IAEA guidance publications for accident analysis is thus an important step towards resolving this issue. Various IAEA safety publications have provided details of the requirements as well as guidance for accident analysis, in particular for nuclear power plants of Russian design with water moderated, water cooled power reactors (WWERs) and graphite moderated, boiling water reactors (RBMKs). In particular, the IAEA has developed several guidance publications relevant to accident analysis within the Extrabudgetary Programme on the Safety of WWER and RBMK nuclear power plants. Likewise, several of the revised IAEA Safety Standards Series publications, for example the Safety Requirements on Safety of Nuclear Power Plants: Design (NS-R-1) and the Safety Guide on Safety Assessment and Verification for Nuclear Power Plants, address this topic. Consistent with these publications, the IAEA in 2002 issued a detailed report on Accident Analysis for Nuclear Power Plants (Safety Reports Series No. 23) that provides practical guidance for performing accident analysis. That report covers the steps required for accident analyses, i.e. selection of initiating events and acceptance criteria, selection of computer codes and modelling assumptions, preparation of input data and presentation of the calculation results. It also discusses aspects that need to be considered to ensure that the final accident analysis is of acceptable quality. Separate IAEA Safety Reports deal with specific features of individual reactor types, such as pressurized water reactors, boiling water reactors, pressurized heavy water reactors and RBMKs. The present Safety Report provides further guidance by considering specific design features of nuclear power plants with RBMK reactors. In particular, the guidance given focuses on classification of initiating events, on selection of acceptance criteria and on initial and boundary conditions, and specific suggestions are offered for the analysis of different groups of events. This report is aimed primarily at analysts, whether from regulatory bodies or from utilities, who coordinate, perform or review computational analyses of transients and accidents for RBMK reactors. The report is also intended as guidance for IAEA activities in this domain, such as training courses and workshops