Abstract Micro reactors are increasingly being considered for utilization as distributed power sources. Hence, the probabilistic safety assessment (PSA) of a direct supercritical–CO2–cooled fast reactor, called micro modular reactor (MMR), was performed in this study; this reactor was developed using innovative design concepts. It adopted a modular design and passive safety systems to minimize site constraints. As the MMR is in its conceptual design phase, design weaknesses and valuable safety insights could be identified during PSA. Level 1 internal event PSA was carried out involving literature survey, system characterization, identification of initiating events, transient analyses, development of event trees and fault trees, and quantification. The initiating events and scenarios significantly contributing to core damage frequency (CDF) were determined to identify design weaknesses in MMR. The most significant initiating event category contributing to CDF was the transients with the power conversion system initially available category, owing to its relatively high occurrence frequency. Further, an importance analysis revealed that the safety of MMR can be significantly improved by improving the reliability of reactor trip and passive decay heat removal system operation. The findings presented in this paper are expected to contribute toward future applications of PSA for assessing unconventional nuclear reactors in their conceptual design phases.

中文翻译：

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概念设计阶段超临界二氧化碳冷却微型模块化反应堆的 1 级概率安全评估

摘要 微型反应堆越来越多地被考虑用作分布式电源。因此，本研究对称为微模块化反应堆 (MMR) 的直接超临界 CO2 冷却快堆进行了概率安全评估 (PSA)；该反应器是采用创新设计理念开发的。它采用模块化设计和被动安全系统，以最大限度地减少场地限制。由于 MMR 处于概念设计阶段，因此可以在 PSA 期间识别设计弱点和宝贵的安全见解。1 级内部事件 PSA 的执行涉及文献调查、系统表征、起始事件的识别、瞬态分析、事件树和故障树的开发以及量化。确定对堆芯损坏频率 (CDF) 有显着影响的起始事件和场景，以确定 MMR 的设计弱点。对 CDF 有贡献的最重要的起始事件类别是电源转换系统最初可用类别的瞬变，因为其发生频率相对较高。此外，重要性分析表明，通过提高反应堆跳闸和被动衰变热去除系统运行的可靠性，可以显着提高 MMR 的安全性。预计本文中提出的研究结果将有助于 PSA 在概念设计阶段评估非常规核反应堆的未来应用。对 CDF 有贡献的最重要的起始事件类别是电源转换系统最初可用类别的瞬变，因为其发生频率相对较高。此外，重要性分析表明，通过提高反应堆跳闸和被动衰变热去除系统运行的可靠性，可以显着提高 MMR 的安全性。预计本文中提出的发现将有助于 PSA 在概念设计阶段评估非常规核反应堆的未来应用。对 CDF 有贡献的最重要的起始事件类别是电源转换系统最初可用类别的瞬变，因为其发生频率相对较高。此外，重要性分析表明，通过提高反应堆跳闸和被动衰变热去除系统运行的可靠性，可以显着提高 MMR 的安全性。预计本文中提出的研究结果将有助于 PSA 在概念设计阶段评估非常规核反应堆的未来应用。