Multiphysics Modeling and Adjoint-based Sensitivity Analysis of Molten Salt Reactor

Liquid state fuel brings lots of advantages from its characteristics in terms of inherent and passive safety, as well as waste management or resource utilization. In case of MSR, a circulating liquid fuel system, transport of the delayed neutron precursors from fuel salt flow influences neutron flux distribution and overall power distribution due to their decay at different location in the reactor core. In addition, small variation of temperature affects thermophysical properties of salt, for instance, density, which determines a reactivity feedback coefficient as well. From its strongly coupled physics behavior; i.e. neutronics and thermal-hydraulics, Multiphysics approaches is required for design and analysis of the MSR. In this paper, Multiphysics modeling and adjoint-based sensitivity analysis method for the molten salt reactor are introduced. With many advantages of the adjoint method, sensitivity of 3 types of system responses to the 39 model parameters are evaluated for MSFR case, including temperature dependencies of nuclear data and salt properties, calculated values of kinetic constants for precursors, and reactor design parameter. Adjoint method can predict within 10% accuracy for all data with 77.3 times less computational time, compared to method of recalculating system response. Adjoint method has strong advantages for its applicability based on the straightforward mathematical background, such that it can be applied to any system involving multiple and interacting physics: turbulenct reacting flows, combustion problems, or thermomechanics are just few examples.