Transient Characteristics of Small Molten Salt Reactor During Blockage Accident

摘要

This paper reports the results from a transient core analysis of a small molten salt reactor (MSR) when a duct blockage accident occurred. The focus of this study is a numerical model employed in order to consider the interaction among fuel salt flow, heat transfer, and nuclear reactions. The numerical model comprises continuity and momentum conservation equations for fuel salt flow, two-group neutron diffusion equations for fast and thermal neutron fluxes, transport equations for six-group delayed neutron precursors, and energy conservation equations for fuel salt and graphite moderators. The analysis results show the following: (1) the effect of the self-control performance of the MSR on the effective multiplication factor and thermal power output of the reactor after the blockage accident is insignificant, (2) fuel salt and graphite moderator temperatures increase drastically but locally at the blockage area and its surroundings, (3) the highest fuel salt temperature after the blockage accident is 1,363 K; this value is lower than the boiling point of fuel salt and the melting temperature of the reactor vessel, (4) the change in the distributions of fast and thermal neutron fluxes after the blockage accident when compared with the distributions at the rated condition is very slight, and (5) delayed neutron precursors, especially the first delayed neutron precursor, accumulate at the blockage area due to its large decay constant. These results imply that the safety of the MSR is assured in the case of a blockage accident.