Quantitative Analysis of Safety Margin Reduced by Power Uprate in SBLOCA

Abstract

Nuclear Energy Agency of OECD has developed a methodology in the Safety Margin Action Plan (SMAP) to quantify the reduction of safety margin due to power uprate. The methodology combines the probabilistic and deterministic approaches of safety analyses. In the present study, the SMAP methodology is adopted to quantify the reduction of safety margin of a 5% power uprate of Maanshan nuclear power plant (NPP) of Taiwan Power Company. The sequence selected to demonstrate the methodology is small break cold leg loss of coolant accident. An evaluation model code, RELAP5-3D/K is used in the LOCA analysis. The plant specific probabilistic safety assessment (PSA) model is used to determine the accident scenario analysed. Uncertainty of the predicted peak cladding temperature (PCT) during the accident is quantified using the rank statistics. Phenomenon Identification and Ranking Table (PIRT) for parameters that are important for the small break LOCA analyses and their distribution are identified. Two sets of calculations are performed to determine PCT of the 95th percentile with 95% of confidence at 102% and 105% power cases. The results demonstrate that, statistically, the safety margin for the particular accident scenario analysed is not reduced due to power uprate from 102% to 105% power.