A Code-Agnostic Driver Application for Coupled Neutronics and Thermal-Hydraulic Simulations

Abstract

While the literature has numerous examples of Monte Carlo (MC) and computational fluid dynamics (CFD) coupling, most are hardwired codes intended primarily for research rather than as stand-alone, generalpurpose applications. In this work, we describe an open source application, the Exascale Nuclear Reactor Investigative COde (ENRICO), which enables coupled neutronic and thermal-hydraulic simulations between multiple codes that can be chosen at run time (as opposed to a coupling between two specific codes). The application has been designed such that the control flow logic, domain mapping, nonlinear fixed-point iteration, solution transfers, and convergence checks are all agnostic to the underlying physics solvers used. Special emphasis has also been placed on enabling efficient execution on distributed-memory computing environments. The transfer of solution fields between solvers is performed in memory rather than through filesystem input/output. Additionally, solvers can be configured to run on overlapping or disjoint sets of processes. To date, coupling with the OpenMC and Shift MC codes, the Nek5000 CFD code, and a simplified heat diffusion and subchannel solver has been implemented in ENRICO. We present results for coupled simulations of a single light water reactor fuel assembly based on the NuScale reactor using various combinations of the physics solvers. For this problem, the coupled simulations are shown to converge in about four Picard iterations. A comparison of the heat source and temperature distributions computed by ENRICO using OpenMC coupled with Nek5000 and Shift coupled with Nek5000 illustrates remarkable agreement between the codes.

Unbiasedness and Optimization of Regional Weight Cancellation

“…The concentration N i (r ) of nuclide i is a function of position, and the total microscopic cross section σ i (r , E ) is a function of position and energy. 5 The total macroscopic cross section is…”

“…This high-fidelity simulation method comes at the cost of requiring extensive computer resources. Because of this computational cost, multi-physics simulations of a full-core nuclear reactor model, using Monte Carlo neutronics codes coupled with other state-of-theart thermal-hydraulics and fuel performance codes, have become possible only very recently, mainly thanks to the increase in available computer power and to the development of efficient variance-reduction techniques [5,6].…”