A quantitative analysis of a risk impact due to a starting time extension of the emergency diesel generator in optimized power reactor-1000

Abstract

An emergency diesel generator (EDG) is the ultimate electric power supply source for the operation of emergency engineered safety features when a nuclear power plant experiences a loss of off-site power (LOOP). If a loss of coolant accident (LOCA) with a simultaneous LOOP occurs, the EDG should be in the state of a full power within 10 s, which is a prescribed regulatory requirement in the technical specifications (TS) of the Optimized Power Reactor-1000 (OPR-1000). Recently, the US nuclear regulatory commission (NRC) has been preparing a new risk-informed emergency core cooling system (ECCS) rule called 10 CFR 50.46. The new rule redefines the size for the design basis LOCA and it relaxes some of the requirements such as the single failure criteria, simultaneous LOOP, and the methods of analysis. The revision of the ECCS rule will provide flexibility for plant changes if the plant risks are checked and balanced with the specified criteria. The present study performed a quantitative analysis of the plant risk impact due to the EDG starting time extension given that the new rule will be applied to OPR-1000. The thermal-hydraulic analysis and OPR-1000 probabilistic safety assessment (PSA) model were combined to estimate the whole plant risk impact. Also, sensitivity analyses were implemented for the important uncertainty parameters.