An Adaptive Time-Stepping Control Algorithm for Molten Salt Reactor Transient Analyses

This paper presents an adaptive time-stepping (ATS) control algorithm developed for transient analyses of Molten Salt Reactors (MSRs) with flowing fuel. To enhance the computational efficiency while maintaining a targeted accuracy, an ATS algorithm with the proportional-integral-derivative (PID) controller and error monitoring was developed and implemented into the PROTEUS-NODAL code. The performance of the ATS algorithm was tested for a wide range of the Molten Salt Fast Reactor (MSFR) numerical benchmark and the Molten Salt Reactor Experiments (MSRE). The test results show over 20 times speedups for very rapid transients and very slow, long-time transients relative to the reference solution obtained with a small time-step size. In addition, extensive parametric studies were performed on the local error estimates and controller parameters and derived a set of recommended values of initial time step, tolerance and gain for four different transient categories.