Validating an adaptive time step scheme for the neutron diffusion equation with the UMass-Lowell Research Reactor kinetics data

Abstract

Currently, most reactor simulation codes use predefined constant or variable time steps for simulation, which is inefficient. Available adaptive time step methods in the area of neutron transport and reactor kinetics are rather based on multistep and multistage integration methods, which could be time expensive. In this work, an adaptive time step scheme that takes advantage of a single integration per time step is evaluated for linear and non-linear reactor kinetics problem, using the point kinetics model of the UMass-Lowell Research Reactor. The time step selection scheme requires no solution evaluations or operator inversions beyond those already performed in the adaption-free solution, and requires no modifications to the solution algorithm. The solution accuracy from an inverse matrix method implementing the adaptive time step scheme is compared to an analytical solution for the linear problem. And for the nonlinear problem, the comparison is made with a numerical solution from an automated ordinary differential equation solver and the reactor experimental data.