熔盐快堆Th-U燃料循环增殖性能分析

Analysis of Th-U breeding in molten salt fast reactor

熔盐快堆是当前国际上关注的热点之一,本文基于堆芯结构双流体方案,即裂变熔盐燃料和增殖熔盐介质各自独立冷却循环,利用氟化或氯化熔盐中钍铀重金属盐高温下的高溶解度特性,获得熔盐快堆的高增殖。通过比较钍铀燃料循环熔盐快堆的三种可行性熔盐燃料方案(LiF+ThF4+UF4、NaF+ThF4+UF4和NaCl+ThCl3+UCl3),采用基于反应堆安全分析和设计的综合性模拟程序SCALE(Standardized Computer Analyses for Licensing Evaluation),计算了中子能谱、反应性温度系数,分析了增殖比BR(breeding ratio)受反应堆裂变区、增殖区和ZrC中子反射层的尺寸影响、熔盐中6Li和35Cl同位素丰度的影响,以及熔盐密度误差对BR计算值的准确性影响、易裂变核素随反应堆运行时间演化等。在钍铀燃料循环熔盐快堆中,通过优化处理得到三种熔盐燃料方案的增殖比BR约为1.2。

[Background]Because of its superior performance,molten salt reactor has been selected as one of the candidates for the fourth-generation reactors,and has become the focus of international attention.[Purpose]In the molten salt fast neutron reactor,we try to find the most suitable molten salt fuel scheme to achieve the purpose of high proliferation of fissile nuclides.[Methods]Based on the two-fluid cooling cycle scheme,independent cooling cycles of fission molten salt fuel and breeding molten salt,a comprehensive simulation program SCALE(Standardized Computer Analyses for Licensing Evaluation)was employed to achieve high breeding ratio(BR)in the molten salt fast reactor by utilizing the high solubility characteristics of thorium and uranium heavy metal salts in fluorinated or chlorinated molten salts at high temperatures.Three feasible molten salt fuel schemes(LiF+ThF4+UF4,NaF+ThF4+UF4,and NaCl+ThCl3+UCl3)were compared by calculating the neutron energy spectrum and the reactivity temperature coefficient.Influence factors of BR,such as the sizes of fission zone,breeding zone and ZrC reflective layer,the isotopic abundance of 6Li and 35Cl in the molten salt,molten salt density error on the calculation accuracy,and the evolution of fissile nuclides with reactor operating time,were computationally analyzed.[Results]The breeding ratio(BR)of reactor reaches about 1.2 in all three molten salt fuel schemes when the diameter and height of the fission zone are both 260 cm.[Conclusions]With optimization of the reactor geometry,and the composition and isotopic abundance of the molten salt fuel,a high breeding ratio of the reactor is achievable for the thorium-uranium fuel cycle of molten salt fast reactor.