小型轻量化铅铋反应堆燃料组件几何结构研究

Geometric configuration of fuel assembly for small lightweight lead-bismuth reactor

燃料组件的几何结构和栅格参数显著影响铅铋反应堆的物理/热工特性,采用不同几何结构燃料组件的堆芯在相同换料周期、热工限值约束下的临界尺寸、燃料装载量存在差异。本文开展小型轻量化铅铋反应堆的燃料组件几何结构研究,通过建立铅铋反应堆堆芯模型,选取棒束型、环形、蜂窝煤型燃料组件方案,比较分析了3种方案在堆芯尺寸、燃料装载量、冷却剂流通面积、包壳和气隙体积相同和在换料周期为10 a、稳态热工安全裕量基本一致条件下堆芯的燃耗特性、反应性系数、稳态热工特性参数。结果表明:相比于棒束型与环形燃料组件,蜂窝煤型燃料组件良好的稳态热工特性与较硬的中子能谱,采用蜂窝煤型燃料组件的堆芯可以实现更小的堆芯尺寸及燃料装载量,具备显著的膨胀负反馈,同时能够有效展平功率分布和降低堆芯压降,是有利于铅铋反应堆小型化及轻量化的燃料组件方案。

[Background]The neutronics and thermal-hydraulic characteristics of lead-bismuth cooled reactors are significantly affected by the geometric configuration of fuel assembly and lattice parameters.Reactor cores loaded with different geometry type fuel assemblies have different critical dimensions and fuel loadings under the same refueling cycle and thermal-hydraulic constraints.[Purpose]This study aims to analyze these key factors and select a geometric structure of fuel assembly that is conducive to miniaturization and lightweight of lead-bismuth reactor.[Methods]First of all,the core model of a 4 MWt small lead-bismuth reactor was established,and simulation analysis of reactor physical characteristics was conducted using the RMC Monte Carlo program developed independently by the Reactor Engineering Calculation and Analysis Laboratory of Tsinghua University and the nuclear database ADS-2.0 released by the International Atomic Energy Agency(IAEA)in 2008.Then,three fuel assembly schemes of rod bundle type,annular type and honeycomb coal type were selected for comparison and analysis in term of fuel consumption characteristics,reactivity coefficient and steady-state thermal parameters under the same core size,fuel loading,coolant flow area,cladding and air gap volume,10-year refueling cycle and basically consistent steady-state thermal safety margin.[Results&Conclusions]The results show that compared with the rod bundle fuel assembly and the annular fuel assembly,the honeycomb coal fuel assembly has good steady-state thermal characteristics and hard neutron spectrum.The core of the honeycomb coal fuel assembly can realize smaller core size and fuel loading,and has obvious expansion negative feedback,and can effectively flatten the power distribution and reduce the core pressure drop.It is a fuel assembly solution that is conducive to the miniaturization and light weight of lead-bismuth reactors.