150 MWt熔盐堆(SM-MSR)反应性引入事故后果的不确定性及参数敏感性分析

Uncertainty and sensibility analysis of reactivity insertion transient accident of a 150 MWt molten salt reactor(SM-MSR)

熔盐反应堆是第四代核反应堆的6种候选堆型之一,具有良好的安全特性。反应性引入事故是熔盐堆重要的设计基准事故之一,通过对150 MWt模块化熔盐堆(Small Modular Molten Salt Reactors,SM-MSR)反应性引入事故的分析和研究有利于深入了解熔盐堆的安全特性。研究150 MWt熔盐堆反应性引入事故分析结果的不确定性和参数的敏感性,为熔盐堆设计和安全分析提供重要的支持。采用RELAP5-TMSR程序建立瞬态分析模型,并采用基于蒙特卡罗方法的输入不确定性传递方法研究反应性引入事故的不确定性,通过多元线性回归法分析参数的敏感性。分析结果表明:反应性引入事故堆芯出口温度最高值为727.4℃,低于安全限值(800℃),燃料盐出口最高温度分布符合正态分布。熔盐堆具有良好的固有安全特性,在反应性引入事故下,影响反应堆安全最敏感的5个因素分别为燃料盐密度、堆芯阻力系数、堆芯功率、一回路阻力系数、停堆深度。

[Background]Molten salt reactors have been selected as one of the promising candidate Generation IV reactor technologies,due to the advantages of inherent safety and high economic efficiency.The small modular molten salt reactor(SM-MSR),which utilizes low-enriched uranium and thorium fuels,is regarded as a wise development path to speed deployment time.Uncertainty and sensibility analysis of accidents possess a great guidance in nuclear reactor design and safety analysis that can be performed to obtain the safety boundary and through sensitivity analysis,thereafter to obtain the correlation of the accident consequence and input parameters.Reactivity insertion transient accident represents a type of hypothetical accidents of SM-MSR,and the study of reactivity insertion transient accident can offer useful information to improve physics thermohydraulic and structure designs.[Purpose]This study aims to investigate the uncertainty and sensibility of MSR reactivity insertion accident and provide supports for the design and safety analysis of the small modular molten salt reactor.[Methods]RELAP5-TMSR code was employed to establish a transient behavior analysis model for SM-MSR,and the model consisted of four coupled parts,including the primary circuit,2nd circuit,air cooling system modules and passive residual heat removal system.Then,propagation of input uncertainty approach on the basis of Monte Carlo methods was employed to analyze the uncertainty of reactivity insertion transient accident consequence.Uncertain parameters for the reactivity insertion transient accident were selected by the phenomena identification and ranking table(PIRT).Subsequencely,a list of input parameters along with their associated density functions was adopted by using a probabilistic methodology to establish the code run times and sets of uncertain input parameters that was propagated through the RELAP5-TMSR code,and then obtain the upper and lower uncertainty bands of the reactivity insertion transient consequence.Finally,the sensibility of input parameters was analyzed by performing Multiple Linear Regression(MLR)method,and the F-test was used to assess whether the MLR models comply with statistical laws.If the linear model was strong collinear,a significance test of the semi-partial correlation coefficient(SPC)was used for the ranking of input uncertainty parameters,otherwise,the standardized regression coefficient(SRC)would be used for the significance test.[Results]The uncertainty analysis results show that the maximum fuel salt temperature of SM-MSR is 727.4℃which is lower than the acceptance criteria(800℃).Through statistical analysis,the maximum value of reactor outlet fuel salt temperature is normally distributed.[Conclusions]The molten salt reactor has good safety characteristics,and the 5 important parameters are density of fuel salt,local resistance coefficient of reactor core,reactor power,local resistance coefficient of primary circuit and reactor shutdown margin.