Thermal Hydraulic Analysis for Accidents in OPR1000 and Evaluation of Uncertainty for PSA

Probabilistic Safety Assessment (PSA) is a mathematical tool to evaluate numerical estimates of risk for nuclear power plants (NPPs). For the last couple of years, PSA has been put to practical use for verification of safety in research and industrial fields. However, PSA still has the problems about the quality and reliability. The significant one of the problems is that the quantification of uncertainties from thermal hydraulic (TH) analysis has not been included in the quantification of overall uncertainties in PSA. Since TH phenomena are directly concerned with the accidents occurred in the NPPs, the uncertainties from TH analysis should be treated in PSA. The aim of the present study is to develop a best-estimate thermal hydraulic analysis methodology applicable to PSA and capable to quantify uncertainty from TH analysis. Through the research, the best-estimate TH analyses for large break loss of coolant accident (LBLOCA) of optimized power reactor 1000 MWth (OPR1000) were conducted and probabilistic density function (PDF) of peak cladding temperature (PCT) was obtained using statistical methods. The result of this research can be used to assess the core damage frequency (CDF) from the PSA which was already performed.