池式钠冷快堆堆内自然循环余热排出设计研究

Research on Design of Natural Circulation Decay Heat Removal for Pool-type Sodium-cooled Fast Reactor

  • 摘要: 基于装量功率比约为1 t/MW的较典型池式钠冷大功率快堆的堆内自然循环设计,采用ERAC程序,对两组4种不同事故余热排出系统(DHRS)输入条件下,反应堆在紧急停堆后堆内的自然循环余热排出特性进行分析。结果表明,从DHRS启用到其对堆芯产生显著冷却效应,需要较长时间,在千秒量级。在该段时间内,堆芯余热的排出依靠反应堆固有的热工流体安全特性。随后,在堆内关键温度上升到限值之前启用DHRS带出池内热量,使堆内关键温度处于下降趋势即可满足安全要求;相比将独立热交换器(DHX)布置在冷池,将其布置在热池时,热池温度及主容器壁温相对要低,这有利于主容器的温度控制,其效果要优于布置于冷池。另外,不同布置会对堆芯盒内、盒间流流量产生影响,但总体上对堆芯的冷却效应影响不大;池式钠冷快堆余热排出设计中,要充分利用固有热工流体安全特性,降低对DHRS的时效性要求。可以考虑将全部的DHX都布置在热池,并缩小设备体积、降低散热功率设计值,或在不降低安全性的前提下选用其他更经济便捷的有效方式等,以此大幅降低余热排出设备投入成本,降低反应堆运行成本,提高经济性。本文研究结果可为我国后续的商用快堆、一体化快堆等池式液态金属堆的堆内自然循环设计提供重要参考。

     

    Abstract: Based on the design parameters of the core decay heat removal through natural circulation of the typical high-power sodium-cooled fast reactor, using the system analysis program ERAC, a detailed analysis of the reactor core decay heat removal process characteristics after emergency shutdown was conducted, and comparative analysis was conducted on the cooling effects in the reactor under two sets of four conditions of decay heat removal system (DHRS). The results indicate that enabling DHRS requires thousands of seconds as it has a significant cooling effect on the core. During this period, the removal of core decay heat relies on the inherent thermal-hydraulic safety characteristics of the reactor. In principle, DHRS only needs to carry out the heat inside the reactor before the temperatures at the critical locations reaches its limit value, and keep the temperatures in a decreasing trend. When the independent heat exchanger (DHX) is arranged in the hot pool, the temperatures of the hot pool and the main vessel are relatively lower, which is beneficial for temperature control of the main vessel as the main circuit pressure boundary, and its effect is better than when arranged in the cold pool. In addition, different locating arrangements of DHXs will have an impact on the mass flow in the assembly wrappers and inter-wrappers, but the impact on the overall cooling effect on the core temperature is not significant. In order to reduce the investment and operating costs of nuclear power plants and then improve economic efficiency, it should be optimized on the natural circulation design of the pool-type sodium-cooled fast reactor. The optimization direction is to fully utilize the inherent thermal-hydraulic safety characteristics of the pool-type sodium-cooled fast reactor, reduce the requirements for the start cooling time and the power of heat discharge of DHRS. It is feasible to consider arranging all DHXs in the heat pool, reduce their volume, and lowering their design value of heat dissipation power. Alternatively, without compromising safety, other more economical and convenient effective methods could be selected. These research results will provide important references for the natural circulation design of pool-type liquid metal reactors such as commercial fast reactor and integrated fast reactor in China.

     

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