ATWS accident analysis of rod withdrawal in small modular molten salt reactor

Abstract

[Backgrounds] Among all kinds of accidents beyond the design basis of molten salt reactor (MSR), the ATWS accident of rod withdrawal is the most typical one, which is the test of the safety capability limit of the reactor. Therefore, it has important research significance in the field of accident analysis for MSR. Purpose This study aims to assess the safety limits of the liquid MSR during postulated transients. Methods First of all, the RELAP5-TMSR (reactor excursion and leak analysis program-thorium molten salt reactor) code was employed to conduct a preliminary analysis of ATWS accident of the control rod withdrawal in 125 MW liquid MSR, and the equivalent hydraulic components of this reactor were modeled. Then, the changes of key parameters such as reactor power and molten salt temperature of three shutdown strategies were analyzed. Finally, the sensitivity analysis of some important factors such as reactivity introduction value, rod lifting speed and temperature coefficient was carried out. Results The shut-down strategy of keeping the primary loop pump operation, shutting down the secondary loop pump and the third loop fan keeps the lowest core molten salt temperature among the three shutdown strategies. In the case of only maintaining the operation of the primary loop pump, the temperature extremum is closely related to the reactivity introduction value, introduction rate and temperature reactivity coefficient. Thermal peak of ATWS accident of rod withdrawal increases with the increase of reactivity introduction value and rod lifting speed. Requirements for the design of regulation rod worth and temperature reactivity coefficient of MSR. Conclusions This study provides reference value for design requirements of regulation rod worth and temperature reactivity coefficient of MSR.

Keywords

• molten salt reactor
• atws
• safety analysis
• relap-tmsr