원자로 정지를 방지하는 소외전원상실 관리

Abstract

A loss of offsite power event in a nuclear power plant resulting from the loss of connections to the electrical grid can be effectively managed without resulting in an unscheduled reactor trip, provided the reactor operates at a reduced power level and the heat is dissipated properly through steam generators operating with the auxiliary feedwater system. We have developed effective procedures for managing such house load operations that will maintain a stable steam generator water level using the auxiliary feedwater system. The procedures are based on a first-principle energy balance with the heat flux from the primary to the secondary side represented through an average primary system temperature. The reduced order model has been validated through actual simulations of steam generator dynamics with the MARS-KS code. With the help of the reduced order model, various scenarios or tracks involving judicious combinations of reactor power, reactor coolant flowrate and steam generator feedwater flowrate that could support stable house load operations are simulated and summarized as an operating procedure in a multi-path event tree structure. In order to apply our method to real nuclear power plants, we need to account for statistical fluctuations in the MARS-KS data together with uncertainties in the reduced order model prediction of the water level. A Kalman filtering algorithm has been developed to generate an optimal estimate of steam generator water level as part of an operational support system. For the stable house load operation cases and simple transient cases, the linear Kalman filtering formulation was applied to yield sufficiently accurate system estimates for the management of loss of offsite power without reactor trip.