Circulating fuel reactor (CFR) kinetics are characterized by delayed neutron precursor (DNP) drift in addition to the neutronic and thermal hydraulic phenomena typical of other reactor types. This environment can be computationally challenging to model, given that the multiphysics phenomena generally have non-linear interdependencies requiring the use of iterative solution techniques. In this work, a multilevel nonlinear projective method in RZ geometry is presented which calculates a transport solution to the CFR kinetics problem. This approach offers computational savings by coupling the multiphysics phenomena to low-order quasi-diffusion equations. The method is verified with the method of manufactured solutions. A residual-balanced algorithm for multilevel coupling is presented and shown to mitigate oversolving when compared to a standard fixed point iteration scheme.
Transient and steady-state simulations demonstrating the influence of the DNP drift phenomena are shown, as well as a comparison to results from the Molten Salt Reactor Experiment.
The importance of capturing transport effects when simulating channel-type CFRs is also investigated, and are found to produce average variations of 2-3% in the two-group fluxes when compared to the P1 approximation.