engleski

Upgrade to NPP Krško Internal Flooding PSA

The existing internal flooding probabilistic safety analysis (PSA) study of Krško NPP was upgraded in response to the Krsko Periodic Safety Review (PSR) issues concerning the screening criteria for internal floods, residual risk from screened out areas and propagation of scenarios to plant damage states and Level 2. The area screening process was revisited in order to cover also the areas with relevant risk potential, although without automatic reactor trip equipment, which may have been screened out in the original study. Through the screening process, the residual core damage frequency (CDF) from screened out areas was systematically estimated in order to demonstrate that its combined value is acceptably low as compared to the total estimated internal flooding CDF. In the next step, the internal flooding PSA model was extended to Level 2 in order to address the corresponding PSR issue. All Level 1 core damage sequences from the internal flooding event trees in the PSA model were extended to Level 2. Frequencies of release categories were quantified. The plant area screening process was repeated at Level 2 in a manner equivalent to the screening at Level 1. Residual Level 2 risk was estimated in terms of large early release frequency (LERF). The paper describes the overall process of upgrading the internal flooding PSA study and model, and presents its results.

NPP Krško; Internal Flooding PSA

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