Development of Coupled PROTEUS and SAM Code System for Multiphysics Analysis of Advanced Reactors

Abstract

In order to meet the growing worldwide electricity demand while reducing the environmental impacts from CO2-emission energy sources, the next-generation nuclear reactor systems are being developed under the goals of sustainability, safety, reliability, economic competitiveness, proliferation resistance, and physical protection. The molten salt reactor (MSR) with liquid fuel is one of these reactors, which is receiving growing interest from the industry worldwide. Various micro-reactor concepts are also being developed to enable flexible siting to support applications for remote areas and integration into micro-grids in populated areas and to provide resilient power for emergency operations related to natural disasters. The design and safety analyses of these advanced nuclear reactors require multiphysics simulations. In particular, the liquid fuel of MSRs results in a strong coupling of neutronics and thermal-hydraulics. The core reactivity is directly correlated with the velocity of flowing fuel because of the precursor decay outside the core and the large negative reactivity due to the thermal expansion of liquid fuel. Meanwhile, diverse micro-reactor designs in irregular geometries with non-conventional heat removal systems such as heat pipes make the conventional analysis tools based on the diffusion theory inadequate. Therefore, this work aimed to develop coupled neutronics and thermal-hydraulics multiphysics analysis capabilities for advanced reactors, focusing on MSRs and micro-reactors, using the neutronics code PROTEUS and the system analysis code SAM of the U.S. DOE’s Nuclear Energy Advanced Modeling and Simulation (NEAMS) program. For accurate and efficient simulation of the steady-state and transient behaviors of MSRs, the nodal solver of PROTEUS (PROTEUS-NODAL) has been coupled with SAM under the MOOSE framework. The coupling was made by developing a MOOSE wrapper of PROTEUS-NODAL and a master application that controls PROTEUS-NODAL neutronics and SAM thermal-fluidic calculations. The coupled code system was verified and validated with the Molten Salt Fast Reactor (MSFR) benchmark problem and the available experimental data of the Molten Salt Reactor Experiment (MSRE). The solutions for the MSFR problem agreed well with the open literature results. The validation test results for the pump start-up, pump coast-down, and natural circulation tests of MSRE agreed well with the measured values. These results indicate the reliability of the coupled code system of PROTEUS-NODAL and SAM for steady-state and transient analyses of MSRs. To model diverse micro-reactor designs of irregular geometries, the MOC transport solver of PROTEUS (PROTEUS-MOC), which can solve 3-D heterogeneous problems with complicated geometries, has been coupled with SAM under the MOOSE framework. A MOOSE wrapper of PROTEUS-MOC was developed as the master application to control the simulation process with the sub-application SAM. A unit-cell and one-sixth core problems of a heat-pipe cooled micro-reactor design (HP-MR) were analyzed with the coupled code system to demonstrate the developed capabilities. The results confirm the applicability of the coupled PROTEUS-MOC and SAM code system to steady state and transient analyses of micro-reactors.