铅铋快堆单盒环形燃料组件典型堵流事故分析

Analysis of typical flow blockage accidents of single annular fuel assembly for lead-bismuth cooled fast reactor

铅铋冷却环形燃料组件具有许多安全性优势,但在其运行过程中由于铅铋冷却剂的腐蚀作用,易发生堵流事故而导致传热恶化,从而危及第一道屏障的完整性,为此,亟须开展铅铋快堆环形燃料组件堵流事故研究。建立5×5单盒环形燃料组件模型,基于计算流体力学(Computational Fluid Dynamics,CFD)软件Fluent对内外通道不同堵塞面积、堵块厚度,以及堵块轴向位置下的堵流工况进行模拟分析,分析了内外包壳温度分布、堵块附近流场的轴向速度分布、通道质量流量变化、堵塞处燃料元件径向温度分布以及热量分配,并与正常工况下计算结果进行对比。结果表明:随堵塞面积增加,堵塞区域包壳温度显著上升,回流区域范围扩大,燃料芯块最高温度点位置向堵块侧偏移,堵块侧热流密度减小;当堵塞份额较大时,随堵块厚度增加,各参数变化与上述结论类似;堵块位于入口处时包壳局部温升较堵块位于中心处时更小;且随堵塞面积、厚度的增加以及堵块位置向活性区入口的不断靠近,内通道流量损失程度明显增大,而外通道流量几乎不受影响,因此,内通道发生堵流事故时危害更为严重。

[Background]The annular fuel assembly of lead-bismuth cooled fast reactor has many safety advantages,but during its operation,due to the corrosive effect of lead-bismuth coolant,it is prone to blockage accidents,resulting in deterioration of heat transfer and jeopardizing the integrity of the first barrier.Therefore,it is urgent to research and analyze the blockage accident for the annular fuel assembly of the lead-bismuth-cooled fast reactor.[Methods]A 5×5 single annular fuel assembly model was established,and numerical simulations for blockage of the inner and outer channel were carried out with different blockage areas,blockage thicknesses,and axial position of the blockage based on the computational fluid dynamics(CFD)software Fluent.The temperature distribution of the claddings,the flow field distribution near the blockage,the mass flow change of the channel,the radial temperature distribution,and the heat distribution of the fuel element at the blockage are compared with the result in no-blockage case.[Results]Simulation results indicate that the increase in the blockage area leads to a significant increase in the cladding temperature of the blockage area,an expansion of the scope of the recirculation area expands,the position of the highest temperature point of the fuel pellet shifts to the blockage side,and the heat flux density on the blockage side decreases.When the blockage fraction is large,the changes of parameters are similar to the above conclusions as the blockage thickness increases;when the blockage is located at the entrance,the local temperature rise of the cladding is smaller than that when the blockage is located at the center;with the increase of the blockage area and thickness and as the blockage position gets closer to the entrance of the active zone,the flow loss of the inner channel increases significantly,while the flow of the outer channel is almost unaffected.[Conclusions]Therefore,the damage is more serious when the blockage accident occurs in the inner channel.