Level 1 and 2 probabilistic safety assessment for designing a 300 MW NPP

The software for Level 1, 2 and 3 probabilistic safety assessments (PSA) was developed based on the PSA code by the US Nuclear Regulatory Commission and independent research. It was applied to integrating the design of a 300 MW nuclear power plant, unit 2 (C-2). It includes the analysis of initiating events, event trees, fault trees,dependency analysis, human reliability analysis, database analysis, event sequence quantification, plant damage state analysis, accident progression and containment response analysis, source term analysis, large early release frequency (LERF) analysis, uncertainty analysis, importance/sensitivity analysis, applications during design phase, etc. The model of Level 1 and 2 PSA was established for the C-2 unit.Several design improvements based on the PSA were implemented in the design, such as the isolation valves on the mini-flow line of the safety injection pump and spray pump, reciprocating charging pump in chemical and volume control system, essential service water system, etc. The unit's internal events at power generation were assessed as 7.25 x 10-6/ry for core damage frequency (CDF) and 3.24 x 10-7/ry for LERF. The C-2 PSA has not only justified the balance of its design, but also provided the probability assessment information for optimizing C-2 design and operation strategies, reducing the risk of severe accidents efficiently. (authors)