Continuous temperature representation in coupled OpenMC/MOOSE simulations

In recent years the use of Monte Carlo methods for modeling reactors has become feasible due to the increasing availability of massively parallel computer systems. One of the primary challenges yet to be fully resolved, however, is the efficient and accurate inclusion of multiphysics feedback in Monte Carlo simulations. The research in this paper presents the application of an existing numerical method for stochastically transporting particles in a material with continuously varying properties for incorporation of multiphysics feedback in Monte Carlo simulations. The implemented continuous material transport method allows for continuous representations of temperature and nuclide density to be used in OpenMC simulations which allows for multiphysics feedback information to be used in OpenMC without needing to discretize the geometry beyond the initial constructive solid geometry (CSG) representation. Functional Expansion Tallies (FETs), also implemented in OpenMC, allow multiphysics data to be efficiently sent to Multiphysics Object-Oriented Simulation Environment (MOOSE) applications through passing of polynomial expansion coefficients, minimizing data transfer between applications. In this paper these methods of incorporating multiphysics feedback are shown to be accurate in correctly calculating Doppler feedback in a light water reactor (LWR) assembly containing an asymmetric loading of burnable poisons. Both the eigenvalue and spatially varying U-238 capture rates are correctly calculated using the continuous material transport method.