Abstract The Organisation for Economic Co-operation and Development (OECD)/Nuclear Energy Agency (NEA) Benchmark Study of the Accident at the Fukushima Daiichi Nuclear Power Station (BSAF), which started in 2012 and continued until 2018, was one of the earliest responses to the accident at Fukushima Daiichi. The project, divided into two phases, addressed the investigation of the accident at Units 1, 2, and 3 by severe accident (SA) codes until 500 h, focusing on thermal hydraulics, core relocation, molten corium concrete interaction (MCCI), and fission product release and transport. The objectives of the BSAF were to make up plausible scenarios based primarily on SA forensic analysis, support the decommissioning, and inform SA code modeling. The analysis and comparison among the institutes have brought up vital insights regarding the accident progression, identifying periods of core meltdown and relocation and reactor pressure vessel (RPV) and primary containment vessel (PCV) leakage/failure through the comparison of pressure, water level, and containment atmosphere monitoring system (CAMS) signatures. The combination of code results and inspections (muon radiography, PCV inspection) has provided a picture of the current status of the debris distribution and plant status. All units present a large relocation of core materials and all of them present ex-vessel debris with Unit 1 and Unit 3 showing evidence of undergoing MCCI. Uncertainties have been identified, in particular on the time and magnitude of events such as corium relocation in the RPV and into the cavity floor and RPV and PCV rupture events. Main uncertainties resulting from the project are the large and continuous MCCI progression predicted by basically all the SA codes and the leak pathways from the RPV to the PCV and the PCV to the reactor building and environment. The BSAF project represents a pioneering exercise that has set the basis and provided lessons learned not only for code improvement but also for the development of new related projects to investigate in detail further aspects of the Fukushima Daiichi accident.

中文翻译：

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OECD/NEA BSAF 项目的主要发现、剩余不确定性和经验教训

摘要 经济合作与发展组织 (OECD)/核能机构 (NEA) 对福岛第一核电站 (BSAF) 事故的基准研究始于 2012 年，一直持续到 2018 年，是最早的研究之一。对福岛第一核电站事故的反应。该项目分为两个阶段，根据严重事故 (SA) 规范对 1、2 和 3 号机组的事故进行调查，直至 500 小时，重点是热力水力学、堆芯搬迁、熔融真皮混凝土相互作用 (MCCI) 和裂变产物的释放和运输。BSAF 的目标是构建主要基于 SA 取证分析的合理场景，支持退役，并为 SA 代码建模提供信息。各研究所之间的分析和比较得出了关于事故进展的重要见解，通过比较压力、水位、水位，确定堆芯熔毁和搬迁以及反应堆压力容器（RPV）和主安全壳（PCV）泄漏/故障的时期，和安全壳大气监测系统 (CAMS) 签名。代码结果和检查（μ子射线照相、PCV检查）的结合提供了碎片分布和工厂状态的当前状态。所有单元都出现了大量的核心材料搬迁，并且所有单元都出现了前船碎片，其中单元 1 和单元 3 显示了进行 MCCI 的证据。确定了不确定性，特别是关于事件的时间和幅度，例如 RPV 中的真皮重新定位并进入腔底以及 RPV 和 PCV 破裂事件。该项目产生的主要不确定性是基本上所有 SA 规范预测的大而连续的 MCCI 进展以及从 RPV 到 PCV 和 PCV 到反应堆建筑和环境的泄漏路径。BSAF 项目代表了一项开创性的工作，它不仅为规范改进，而且为开发新的相关项目以详细调查福岛第一核电站事故的进一步方面奠定了基础并提供了经验教训。该项目产生的主要不确定性是基本上所有 SA 规范预测的大而连续的 MCCI 进展以及从 RPV 到 PCV 和 PCV 到反应堆建筑和环境的泄漏路径。BSAF 项目代表了一项开创性的工作，它不仅为规范改进，而且为开发新的相关项目以详细调查福岛第一核电站事故的进一步方面奠定了基础并提供了经验教训。该项目产生的主要不确定性是基本上所有 SA 规范预测的大而连续的 MCCI 进展以及从 RPV 到 PCV 和 PCV 到反应堆建筑和环境的泄漏路径。BSAF 项目代表了一项开创性的工作，它不仅为规范改进，而且为开发新的相关项目以详细调查福岛第一核电站事故的进一步方面奠定了基础并提供了经验教训。