Evaluation of Impact of NEK Safety Upgrade Program Implementation on the Reduction of Total Core Damage Frequency

The nuclear accident in Japanese plants in 2011 has initiated a quick response from the countries utilizing a nuclear power. Krsko Nuclear Power Plant (NEK) was required by Slovenian Nuclear Safety Administration (SNSA) to perform consequential actions to reduce the risk of severe accidents and their consequences as low as feasible. NEK have analyzed the response to the severe accidents, and based on the results of this analysis, proposed the measures to be implemented in the shortest possible time. In response to SNSA request NEK has developed the Safety Upgrade Program (SUP) which contains a comprehensive set of measures for plant safety improvements. SUP Phase 1 has been implemented during the Outage 2013. This paper presents the work done on the evaluation of impact of plant modifications planned for implementation in Phases 2 and 3 of NEK Safety Upgrade Program on the quantitative figure of merit for the plant risk significance – total core damage frequency (CDF). A significance of the most valuable measures in terms of contribution to the CDF reduction was determined and a new fractional contribution of initiators categories was obtained. The quantification of total CDF was made by employment of RiskSpectrum PSA code and running a predefined set of analytical cases for all initiator categories covered by the scope of NEK PSA model. The basis for analysis was NEK’s most recent at-power PSA model which reflects the plant status with plant modernization implemented in SUP Phase 1. The analysis was done in two steps. In the first step plant modifications planned for SUP Phase 2 were addressed and in the second step plant modernization measures and upgrades planned in SUP Phase 3 were modeled in addition to those already modelled in the first step