Issues of Safety Assessment of New Russian NPP Projects in View of Current Requirements for the Probability of a Large Release

This paper considers the issues of safety assessment of new nuclear power plant (NPP) projects with VVER Generation III+ reactors in relation to the probability target for large release, which is subject to verification in the development of a full-scale Probabilistic Safety Assessment (PSA) Level 2. The design solutions implemented in Generation III+ reactors allow reducing the probability of a severe accident (SA) due to internal initial events to a level of 10⁻⁷/year. Exceeding the radioactive release criterion may thus be related mainly to the consequences of beyond-design external events. This places special demands both for the selection of SA scenarios to consider and the methods for modeling the accident progression and consequences. The paper presents a method for selecting the representative SAs in the frame of PSA of new VVER NPP projects and a practical example of radiological analysis for two bounding accidents at an arbitrary NPP using an advanced integrated computer code system.