钠冷快堆熔化事故不同DHX运行响应的ATHLET模拟

ATHLET simulation of different DHX operation responses in sodium-cooled fast reactor melting accidents

摘要:

钠冷快堆 (SFR) 作为一种先进的核反应堆,使用液态钠作为冷却剂,依靠快中子进行核裂变,具有非能动安全特性。但是,当发生严重事故时,可能会导致堆芯熔化。为提高SFR在严重事故下的安全响应性能,文中提出使用ATHLET程序对SFR在严重事故下钠池各位置的温度进行安全分析。首先,对SFR堆芯结构进行合理简化,在模型搭建基础上划分节点图。其次,采用ATHLET程序模拟计算SFR的堆芯熔化事故,输入熔融物衰变热与冷池/热池独立热交换器 (DHX) 功率等关键参数。最后,根据模拟结果分析了分别位于冷池/热池的4台DHX的不同运行状态对SFR主要区域热工参数的影响。结果表明:热池DHX的关闭会使下冷池与下腔室之间的流道出现逆流,下腔室下降段温度大幅升高,而冷池DHX的关闭工况会使SFR各部分区域冷却剂的温度都显著升高。相较之下,冷池失去一台DHX的运行对严重事故下的SFR更为危险,严重事故时应保证冷池的两台DHX都处于运行状态,及时排出堆芯熔化热量。综上,文中针对DHX在堆芯熔化事故下作用的研究结果能够为SFR结构设计优化和热工水力模型验证提供参考价值。

Abstract:

Sodium-cooled fast reactor (SFR) is an advanced nuclear reactor that uses liquid sodium as a coolant and relies on fast neutrons for nuclear fission, with passive safety characteristics. However, it may lead to core melting when a severe accident occurs. In order to improve the safety response performance of SFR in severe accidents, the ATHLET (analysis of thermal-hydraulics of leaks and transients) code is provided to conduct a safety analysis of the temperature of sodium pool in SFR under severe accidents in this article. Firstly, the SFR core structure was reasonably simplified and a nodalization diagram was developed based on the established model. Then, the ATHLET code was used to simulate the core melting accident of SFR, the key parameters including the decay heat of molten matter and the power of decay heat exchangers (DHX) in the cold/hot pools were input. Finally, based on the simulation results, the impact of different operating conditions of four DHXs located in the cold/hot pools on the thermal parameters of the main regions in SFR was analyzed. The results showed that the closure of DHX in the hot pool would cause backflow in the flow channel between the lower cooling pool and the lower chamber, resulting in a significant increase in the temperature of the descending section of the lower chamber. The closure of DHX in the cold pool would cause a severe increase in the temperature of the coolant in various parts of the SFR. In comparison, the closure of one DHX in the cold pool is more dangerous for SFR in severe accidents and it is necessary to ensure that both DHXs in the cold pool are in operation under severe accidents, which can timely remove the heat of core melting. In summary, the results on the role of DHX in core melting accidents in this article can provide valuable references for optimizing structural design and validating thermal hydraulic models of SFRs.