Thermal analysis of the 450 MW(t) modular high-temperature gas-cooled reactor under depressurized conduction cooldown

As a part of a recent plant cost reduction study, the Modular High-Temperature Gas-Cooled Reactor (MHTGR) design was reevaluated to improve its economic potential. Preliminary safety analyses were performed with a range of core configurations and core powers to ensure they met the MHTGR safety goals. Safety assessments were performed for selected off-normal events. The off-normal events were selected to be the most challenging events where all forced cooling is assumed lost with only the safety related systems, structures and components assumed working. Based on plant cost study results an 84 column fuel core configuration at 450 MW(t) module power level was the recommended design. This paper discusses the results of the safety analysis for a selected off-normal event, the depressurized conduction cooldown with a small primary coolant leak. 3 refs. 9 figs