Analyzing APR1400 System Response Under Load Follow Operation Using a Multiphysics Approach

The power manuverability of nuclear power plants (NPPs) is becoming more and more important as governments expand the deployment of renewable energy resources in their energy mix. For this purpose, load follow (LF) operation (LFO) schemes are introduced and tested for different types of reactors. Currently, all NPPs in Korea are operated at a baseload, that is, 100% rated power, and do not rely largely on power tracking control except for startup, shutdown, and some anticipated transients without scram. However, as the contribution of NPPs in the total electricity generation exceeds 50%, LFO may be necessary to balance the intermittency of renewable energy resources. However, the execution of LF can be challenging due to the complex interaction of the nuclear system parameters. Therefore, MODE-K was proposed to investigate the feasibility of LFO for OPR1000 and APR1400. Although MODE-K has shown good results in controlling reactor power and core reactivity, analysis has focused on neutronics aspects only and neglected plant response. A multiphysics LF simulation is therefore undertaken in this work using the multiphysics package RELAP5/SCDAPSIM/MOD3.4/3DKIN to accurately represent the impact of the underlying feedback mechanisms on APR1400 system performance. The simulation uses the three-dimensional neutron kinetics module (3DKIN) to model the reactor core by defining up to eight different control rod banks. Compared to the point-kinetics model of the Reactor Excursion and Leak Analysis Program (RELAP5), the use of 3DKIN yields a more realistic simulation by representing the entire core and reflecting the control rod motion in real time without assumptions related to the axial and radial power distributions, or burnup state.