Dynamic Multiphysics Simulation of the Load-Following Behavior in a Typical Pressurized Water Reactor Power Plant

Abstract

Most Nuclear Power Plants (NPPs) are designed for baseload operations, maintaining a steady power output at 100%, except during planned maintenance and refueling. However, in countries like France, Slovakia, and Korea, where nuclear power is a major source of electricity, integrating nuclear energy with intermittent renewables is crucial for stable power generation. This integration necessitates daily power adjustments by NPPs in response to grid demands, a process known as a Load Follow Operation (LFO). Such a process introduces strong interdependencies between thermal–hydraulic and neutron–kinetic parameters, coupled with the three-dimensional movement of Control Element Assemblies (CEAs) and Xenon dynamics, which pose safety challenges due to shifts in core power distribution. To address these complexities, a multi-physics approach is employed using the multi-physics package RELAP5/3DKIN and implementing two strategies. The first strategy uses a mechanical shim, adjusting the reactor power exclusively through CEAs. The second strategy combines CEA movement with adjustments in soluble boron concentration. Both strategies are evaluated against axial offset and 3D power peaking safety limits to ensure compliance with operational safety requirements.