Squirrel: A MOOSE-Based App for Solving Point Kinetics in Molten Salt Reactors

This paper presents Squirrel, a point-kinetics (PK) solver for calculating transients in a liquid-fueled nuclear reactor. Squirrel is developed within the Multiphysics Object Oriented Simulation Environment (MOOSE) framework. The modified PK solver accounts for reactivity changes due to changes in the spatial delayed neutron precursor (DNP) distribution by weighting the importance of the position of the delayed neutrons with the adjoint shape function of the reactor, expanding MOOSE PK capabilities to account for the spatial change in the DNP. Squirrel approximates the temperature feedback by weighting the impact of a local variation in temperature with the shape function to estimate the global effect on reactivity. In combination with the MOOSE internal Navier-Stokes module, Squirrel is tested on the National Center for Scientific Research benchmark. The results show that the solver can accurately calculate the change in reactivity induced by the movement of DNPs and the dynamic power change due to the temperature feedback. Squirrel is validated on a simple model of the Molten Salt Reactor Experiment. The results agree with the existing literature, showing that the chosen approach can capture the key aspects of reactor dynamics in a molten salt reactor under the assumption of a time-independent shape function.