Safety Analysis of WWER-440 Nuclear Power Plants: Potential Consequences of a Large Primary to Secondary Systam Leakage Accident

In 1990 the IAEA initiated a programme to assist the countries of central and eastern Europe and the former Soviet Union in evaluating the safety of their first generation WWER-440/230 nuclear power plants. The main objectives of the programme were to identify major design and operational safety issues; to establish international consensus on priorities for safety improvements; and to provide assistance in the review of the completeness and adequacy of safety improvement programmes. The scope of the programme was extended in 1992 to include RBMK, WWER-440/213 and WWER-1000 plants in operation and under construction. The programme is complemented by national and regional technical cooperation projects. The programme is pursued by means of plant specific safety review missions to assess the adequacy of design and operational practices; Assessment of Safety Significant Events Team (ASSET) reviews of operational performance; reviews of plant design, including seismic safety studies; and topical meetings on generic safety issues. Other components are follow-up safety missions to nuclear plants to check the status of implementation of IAEA recommendations; assessments of safety improvements implemented or proposed; peer reviews of safety studies, and training workshops. The IAEA is also maintaining a database on the technical safety issues identified for each plant and the status of implementation of safety improvements. An additional important element is the provision of assistance by the IAEA to strengthen regulatory authorities. The programme implementation depends on voluntary extrabudgetary contributions from IAEA Member States and on financial support from the IAEA Regular Budget and the Technical Cooperation Fund. For the extrabudgetary part, a Steering Committee provides co-ordination and guidance to the IAEA on technical matters and serves as a forum for exchange of information with the European Commission and with other international and financial organizations. The general scope and results of the programme are reviewed at relevant Technical Cooperation and advisory group meetings. Guidance relevant to water moderated, water cooled WWER-type reactors and graphite moderated, boiling water RBMK type reactors has been developed within the IAEA’s Extrabudgetary Programme on the Safety of WWER-and RBMK nuclear power plants. To a certain extent, accident analysis is also covered in several publications of the IAEA Safety Standards series, for example in the Safety Requirements on Safety of Nuclear Power Plants: Design (NS-R-1) and in the Safety Guide on Safety Assessment and Verification for Nuclear Power Plants (NS-G-1.2). Consistent with these publications, the IAEA also developed a Safety Report on Accident Analysis for Nuclear Power Plants (Safety Reports Series No. 23). A Coordinated Research Project (CRP) on Assessment of the Interfaces between Neutronic, Thermohydraulic, Structural and Radiological Aspects in Accident Analysis was implemented from 2003 to 2005 to comprehensively evaluate a complex accident scenario within the framework of the IAEA subprogramme on Development of Safety Assessment Methods and Tools. Twelve organizations from eight Member States participated in the CRP. This report provides a summary of the CRP. Results, recommendations and conclusions resulting from the IAEA programme are intended only to assist national decision makers who have the sole responsibility for the regulation and safe operation of their nuclear power plants. Moreover, they do not replace a comprehensive safety assessment which needs to be performed in the framework of the national licensing process.