Multiphysics simulations for LWR analysis

Accurate prediction of the neutron and temperature distributions within an operating nuclear reactor requires the solution of multiple coupled physics equations. In a light water reactor (LWR), there is a very strong coupling between the power distribution (described by the radiation transport equation) and the temperature and density distributions (described by a thermal diffusion equation in combination with a fluid flow model). This study aims to begin to quantify the impact of such feedback mechanisms as well as identify numerical difficulties associated with such multiphysics problems. A description of the multiphysics model and current solution strategy within the Exnihilo code package for coupling between 3-D radiation transport and 3-D heat transfer is given. Numerical results detailing the effects of varying the nature of the coupling and the impact of mesh refinement for a representative 3×3 pressurized water reactor (PWR) "mini-assembly" are presented.