Applicability of DYMOS Code for Daily Load-following Analysis of Molten Salt Reactors

Abstract

This paper demonstrates the applicability of a simple plant transient analysis code, DYMOS (Dynamic Analysis of Molten Salt Reactors), to daily load-following of a Molten Salt Reactor (MSR). It models the reactor core with one-point kinetics equations, incorporating molten salt circulation and transit time, and includes major lumped plant components such as heat exchanger, steam generator, and turbine-generator. DYMOS has previously been validated against transient tests of the U.S. experimental thermal reactor MSRE, and against accident analyses of a 700 MWt molten salt fast reactor using coupled 3D thermal-hydraulic model and one-point kinetics model. As an additional verification, a shorter load-following operation was compared with a previous study, showing good agreement. Based on these results, daily load-following between 100% and 50% power was simulated for MSR-FUJI. The reactor operates at 100% output for 14 hours during the daytime, reduces output to 50% for 8 hours at night, and transitions linearly between these states in a 1-hour period (“14-1-8-1" mode). The results demonstrate that MSR-FUJI can achieve load-following solely by adjusting the fuel salt flow rate, without control rod movement. Moreover, due to the negligible effect of xenon poisoning in MSR-FUJI, the flow rate adjustment pattern remains straightforward. Thus, DYMOS can be applied to load following operations of MSRs.