小型模块化熔盐堆误提棒ATWS事故分析

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

误提棒未能紧急停堆(Anticipated Transient Without Scram,ATWS)事故是熔盐堆的超设计基准事故之一,以125 MW液态熔盐堆为研究对象,采用RELAP5-TMSR(Reactor Excursion and Leak Analysis Program Thorium Salt Reactor)程序,针对误提棒ATWS事故,选取三种停堆策略分析反应堆功率和熔盐温度等关键参数的变化。此外对反应性引入价值、提棒速度和温度系数等若干重要因素也开展了相应的敏感性分析。分析结果表明:维持一回路主泵运行、关闭二回路主泵和三回路风机的停堆策略是三种策略中堆芯熔盐温度最低的;在仅维持一回路主泵运行的情况下,温度极值与反应性引入价值、引入速率及温度反应性系数密切相关,温度峰值随反应性引入价值和提棒速度的增加而增大。

[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.