Multiphysics Simulations Of Molten Salt Reactors Using The Moltres Code

The aim of this paper was to model and simulate Molten Salt Reactor (MSR) specific phenomena, to analyzethem on an example of two different MSR designs, and to assess the accuracy of different codes.Although inherent safety features and interesting nuclear properties of MSRs present a number of poten-tial benefits for the field of nuclear energy production, there is an evident lack of experimental data, provenprototypes, and materials being able to withstand extreme conditions. In order to pave the way for MSRs aconsiderable amount of modeling and engineering work must be done. There are only few numerical tools whichare capable of simulating the complex behavior of such reactors properly. One of these codes, Moltres, is anapplication of MOOSE, a C++ based multiphysics simulation environment, and was utilized extensively in thisproject along with a Monte Carlo code called Serpent.The Serpent code was used to generate group constants for the multigroup diffusion equation solver em-bedded in Moltres, which is coupled with delayed neutron precursor (DNP) and thermal hydraulics equations.Simplified models of the Oak Ridge Nuclear Laboratory's Molten Salt Reactor Experiment (MSRE) and ofSeaborg Technologies' Compact Molten Salt Reactor (CMSR) were created in the Serpent and in Gmsh soft-ware which was used to generate a mesh file for Moltres. Moltres simulations took advantage of a symmetryin the two dimensional geometrical models and included only the nuclear reactor core and the effect of heatremoval in the primary heat exchangers. Phenomena such as DNP transport with the moving fuel and crosssection change with the temperature were duly accounted for.Results for the MSRE case were compared to the original design calculations and a good qualitative anddecent quantitative agreement was found. Some propositions to be included in Seaborg Technologies' reactordesign were produced. Two transients, Unprotected Loss Of Flow and Unprotected Loss Of Heat Sink, werelooked into. The Moltres code proved to be a valuable tool to simulate MSRs. However, many uncertaintiesin the input data and numerous model simplifications caused the results to be only preliminary and requiringmore refinemen.