Nek5000-Pronghorn-SAM multiscale modeling of pool-type Molten Salt Reactors

Molten Salt Reactors (MSRs) are an attractive Generation-IV reactor concept, which propose using a liquid molten salt as fuel. As a result, multiphysics modeling of MSRs involves the coupling across multiple space and time scales in the fuel salt. Regarding thermal hydraulics, the solvers should ideally be able to capture the mixing effects at the smallest eddies in the reactor core to system level transients that can last minutes or hours. These multiple scales in thermal hydraulics complicates the usage of a single tool for modeling and simulation of MSRs. This work will present recent progress in coupling the NEAMS thermal-hydraulics codes Nek5000 (high-fidelity CFD code), Pronghorn (intermediate-fidelity CFD code), and SAM (system code) for multiscale modeling and simulation of MSRs. Coupling between Nek5000 and Pronghorn is conducted offline, where Nek5000 high-fidelity simulation are harvested to improve RANS turbulence model closures in Pronghorn via a regularized turbulence approach. Pronghorn and SAM are then coupled online via a domain-overlapping approach in which thermal fields and fission-generated power is transferred between both codes. In this coupling, the power computed in the reactor core with spatial dynamics in Pronghorn is passed to SAM; simultaneously, the cold primary heat exchanger temperature computed with SAM from the whole balance of plant model is passed to Pronghorn's heat exchanger model. This yields a simulation of the whole MSR power plant with higher fidelity in the reactor core. Demonstration of this coupling is presented the example case of the Molten Salt Fast Reactor.