铅铋流体热工力学及安全特性研究进展

Study Progress on Thermal Mechanics and Safety Characteristics of Lead Bismuth Fluid

加速器驱动的次临界反应堆(ADS)是最有前景的嬗变技术之一,铅铋流体作为堆内靶件和冷却剂,其热工安全特性成为广泛关注的热门课题。目前国内外已经开展了一些程序计算、数值模拟和实验研究,也得到了相应铅铋流体热工及安全特性。研究表明:气体注入可在一定范围内增强流体自然循环;气体注入率超过一定范围会降低流体自然循环流量。铅铋自然循环中,热分层最严重的区域存在于变温段;且在回路中,热分层状态不同;回路温差较大时,流速提高,热分层现象较明显。对于流动铅铋介质中的控制棒落棒,正常工况条件下,落棒时间随着铅铋流速的增大而增大;地震工况下,控制棒配重增加,初始加速度比正常工况要大,在曲线上呈现为速度时间曲线斜率较正常工况大。在未来研究中,进一步强化实验研究是应该努力的重要方向;开展多数学方法特别是新数学方法比较研究;要确定论与非确定论结合,发现铅铋流体机理特性,明确其可靠性标准;提升其自然循环能力,强化增重和自凝固等其安全特性。

The accelerator driven subcritical reactor(ADS)is one of the most promising transmutation technologies,in which the lead-bismuth eutectic is used as the coolant and the neutron spallation target.So the thermal hydraulics and safety analysis of lead-bismuth fluid have become a hot issue concerned widely.At present,experimental study and numerical simulation including programming calculation have been carried out for this work at home and abroad.The results show that,a lead-bismuth eutectic loop could gain improved performance of natural circulation by gas-injection with a certain rate in some range,but excessive gas-injection would lead to worse performance with lower natural circulation flow instead.Besides,obvious thermal stratification would take place in the lead-bismuth eutectic loop,while a temperature-variable segment would appear in the most serious thermal stratification region.Thermal stratification shows different features among the loop.And more obvious thermal stratification will appear while higher temperature difference between the hot leg and the cold leg is designed to reach higher velocity of fluid.Besides,for the dropping of the control rod in flowing lead-bismuth eutectic in the designed condition,the higher the velocity of lead-bismuth eutectic is,the longer the drop-time of the control assembly is.Under the seismic condition,the initial falling acceleration would increase as the balance weight of the control rod increases,and bring about a greater slope of speed-time curve.For further study,the experimental investigation should be the focus of effort.A growing number of mathematical methods should be used especially the comparison of new mathematical methods.The investigation of flow and heat transfer mechanism of lead-bismuth eutectic is still needed to continue by deterministic analysis integrated with uncertainty analysis to define the reliability criterion.Performance of natural circulation system and its safety,such as weight gain and solidification,should be improved by more efforts.