Abstract Reactor system which applies supercritical carbon dioxide(s-CO2) Brayton Cycle as its direct power conversion system has advantages of high thermal efficiency and high compactness. Due to the high coolant outlet temperature (around 500 °C) and the less effective heat transfer capacity of S-CO2 compared to water or metal liquid, which are commonly used in GEN IV reactor concepts, the safety performance of this kind of newly developed reactor system needs to be carefully evaluated. Preliminary safety assessment of loss-of-flow accident (LOFA) for a s-CO2 Brayton cycle cooled reactor system is carried out in this paper. The safety analysis methodology is proposed firstly and three types of LOFA are investigated to clarify the unique safety characteristics of s-CO2 Brayton cycle cooled reactor system, including partial LOFA with reactor scram, partial LOFA without reactor scram and total LOFA. The short term analysis results demonstrate that the reactor core can survive these three types of LOFA without safety system in the very first 10 to 20 s. A hybrid passive/active emergency core cooling system is designed to remove the decay heat for a long time. Results indicate that the hybrid passive/active emergency core cooling system designed in this paper can help the reactor system safely go through these three types of LOFA. This study will be benefit for the core design and safety system design for s-CO2 direct cooled rector system.

中文翻译：

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失流事故下超临界二氧化碳布雷顿循环冷却反应堆系统的初步安全评价

摘要 采用超临界二氧化碳(s-CO2)布雷顿循环作为直接功率转换系统的反应堆系统具有热效率高、结构紧凑等优点。由于第四代反应堆概念中常用的冷却剂出口温度高（约 500 °C）和 S-CO2 的有效传热能力低于水或金属液体，因此这种新开发的安全性能反应堆系统需要仔细评估。本文对s-CO2布雷顿循环冷却反应堆系统的失流事故（LOFA）进行了初步安全评估。首先提出了安全分析方法，并研究了三种类型的 LOFA，以阐明 s-CO2 布雷顿循环冷却堆系统的独特安全特性，包括部分 LOFA 与反应堆紧急停堆，无反应堆紧急停堆的部分 LOFA 和总 LOFA。短期分析结果表明，反应堆堆芯可以在没有安全系统的情况下在最初的 10 到 20 秒内经受住这三种类型的 LOFA。混合被动/主动紧急堆芯冷却系统旨在长时间去除衰变热。结果表明，本文设计的混合被动/主动应急堆芯冷却系统可以帮助反应堆系统安全地通过这三种类型的 LOFA。本研究将有利于 s-CO2 直冷反应堆系统的堆芯设计和安全系统设计。混合被动/主动紧急堆芯冷却系统旨在长时间去除衰变热。结果表明，本文设计的混合被动/主动应急堆芯冷却系统可以帮助反应堆系统安全地通过这三种类型的 LOFA。本研究将有利于 s-CO2 直冷反应堆系统的堆芯设计和安全系统设计。混合被动/主动紧急堆芯冷却系统旨在长时间去除衰变热。结果表明，本文设计的混合被动/主动应急堆芯冷却系统可以帮助反应堆系统安全地通过这三种类型的 LOFA。本研究将有利于 s-CO2 直冷反应堆系统的堆芯设计和安全系统设计。