IMPACT OF BWR EXTENDED POWER UPRATE ON SAFETY MARGIN DURING STATION BLACKOUT

摘要

This paper describes the results of research into the feasibility of applying the risk-informed safety margin characterization (RISMC) methodology to a boiling water reactor (BWR) extended power uprate (EPU). Only station blackout (SBO) sequences at an 1100 MWe (nominal) BWR/4 with Mark Ⅰ containment is considered in this investigation. The methodology builds upon previous EPRI-sponsored work that developed the RISMC framework for a pressurized water reactor (PWR) loss of main feedwater (LOMFW) event. This BWR EPU investigation first identified, through a rigorous process, those key parameters that impact core damage probability. Distributions were constructed to represent the uncertainties associated with the parameter values. These distributions were sampled using a Latin Hypercube Sampling (LHS) technique to generate sets of sample cases to simulate using the MAAP code. Simulation results were first benchmarked against the reference plant PRA SBO sequences, with excellent agreement. The changes to thermal-hydraulic safety margins which would occur due to the uprated power conditions were then compared to those for the current nominal full power. The impact on SBO conditional core damage probability (CCDP) and core damage frequency (CDF) were also assessed. Sensitivity studies were performed to evaluate the effect of uncertainties in battery life, crediting early diesel generator operation before run failure, and diesel generator repair. Results to date show that thermal-hydraulic safety margins would be reduced with power uprate. However, the impact in terms of increase in CDF is found to be small. Additional studies of the potential impacts on large early release frequency and non-core damage plant impact states are anticipated.