定位格架对铅铋堆燃料组件热工水力影响的数值研究

Numerical Study on the Effect of Grid Spacer on Thermal-Hydraulics of LBE Fast Reactor Fuel Assembly

铅铋合金(LBE)作为冷却剂的快堆是第四代核能系统的主要堆型之一。燃料组件的定位格架是燃料棒束的定位结构,同时对燃料组件的热工水力性能也有重要的影响。本研究首先对板翼型格架组件的热工水力特性进行数值模拟,并通过与实验对比,验证了模拟方法的有效性;其次对板翼型、双翼型、单板型三种定位格架组件的热工水力特性进行了数值模拟。结果表明:流经不同格架造成LBE的最高温度位置不同,双翼型、单板型格架组件LBE温度分布更为均匀;格架的翼和板(翼)的中间区域会使对LBE温度均匀起到一定作用的横向速度叠加抵消,单板型格架无此情况;对于格架造成的局部压降,单板型格架阻力系数最小。综合考虑,单板型格架组件的热工水力性能最佳。

As one of the main types of the fourth-generation nuclear power system,the lead-cooled fast reactor has a wide development prospect,which can be applied in the nuclear powered submarine,the small power grid,and other power supply areas.The lead-bismuth eutectic(LBE)is one of the best coolants in the lead-cooled fast reactor.The grid spacer is not only used to support and position the fuel assembly,but also has a certain effect on the thermal-hydraulics of reactor core.However,there are many studies on thermal-hydraulics characteristics of fuel assembly positioned by wire spacer, but there are few relative studies onthe grid spacer, and some existing numerical studies lack experimental verification. In order tostudy the effect of the spacer structure on thermal-hydraulics in the LBE fast reactor core, In a19-rod fuel assembly with three grid spacers, the flow and heat transfer of coolant LBE in thehexagonal flow channel and spacer-positioned fuel assembly were numerically simulated andanalyzed by the CFD method. Firstly, the numerical simulation was carried out for the fuelassembly of the plate-airfoil spacer, and the effectiveness of the simulation method wasverified by comparing with the experimental results. Secondly, the thermal -hydrauliccharacteristics of fuel assemblies with the three grid spacers of the plate-airfoil spacer, thedouble airfoil spacer and the single plate spacer were compared. The results show that there issome difference in the effect of the three spacers on heat transfer, but great difference on theflow. In particular, the highest temperature of coolant of the plate-airfoil spacer assembly islocated in the corner subchannel after flowing through the spacer, and the highest temperatureof coolant of the other two assemblies are located near the exit of the internal subchannel.Meanwhile, the coolant temperature of the single plate spacer assembly is higher in all threesubchannels. In the middle area of the plate (airfoil) and airfoil of the spacer, the transversevelocity in two directions caused by disturbance will appear superposition cancellingphenomenon. But this is not the case for the single plate spacer, and the transverse velocity ofcoolant for the single plate spacer assembly is also larger. With the increase of Re, the pressuredrop through the three kinds of spacers increases nonlinearly. Of the three types of spacers, thesingle plate spacer caused the least pressure drop. In a word, the comprehensivethermal-hydraulic characteristics of the single plate spacer assembly is the best among theplate-airfoil spacer, double airfoil spacer and single plate spacer assembly. The single platespacer can be used as the first choice in the spacer design of lead-cooled fast reactor. Theresults of this study can provide a reference for the spacer design of lead-cooled fast reactor.