Abstract The accident occurred in Japan on 11 March 2011 has revived the interest for the analysis of severe accidents. The scarce and sometimes unreliable data concerning boundary conditions, effectiveness of accident management measures and equipment performance, pose a tough challenge in modelling the accident scenarios. Throughout an analysis of the challenges posed by the Fukushima Daiichi Unit 1 data recorded, this paper describes the major postulates proposed by CIEMAT concerning the equipment and component responses, the effectiveness of accident management actions and the MELCOR model applied. Among most influencing assumptions are those related to the reactor pressure vessel (RPV) leaking pathways and failure mode, the water flow rate entering the reactor, the potential leaking pathways and failure mode and location from the primary containment vessel (PCV) to the reactor building, the corium relocation from RPV to the cavity and its distribution in the PCV, the potential stratification of the suppression pool and the hypotheses made a priori concerning fission product release and transport. Based on the postulated scenario and model, a remarkable agreement of the thermal footprints in terms of RPV and PCV pressures during 500 h has been achieved, in which the RPV and PCV leaks/failures as well as venting played a determining role in the short run of the accident and water injection heavily conditioned the long one. As for the scarce data related to fission products (FP), a consistent agreement is found in the suppression chamber, but estimates in the Dry-Well are about an order of magnitude below measurements despite showing the observed trend. A number of factors might affect FP comparisons to data, from the approximate method to derive dose rates (measurements) from FP masses (MELCOR results) to the RPV and PCV postulated failures. Anyway, based on the data available the set of hypotheses and approximations made seem to make up a defensible scenario for Fukushima Daiichi Unit 1. The studies and results presented in this paper have been achieved under the frame of the OECD/BSAF projects through the CSN-CIEMAT collaboration agreement on severe accidents research.

中文翻译：

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使用 MELCOR 2.2 展开的福岛第一核电站 1 号机组建模中的挑战和敏感性

摘要 2011年3月11日发生在日本的事故重新引起了对严重事故分析的兴趣。关于边界条件、事故管理措施的有效性和设备性能的稀缺且有时不可靠的数据对事故场景建模提出了严峻的挑战。在对福岛第一核电站 1 号机组数据所记录的挑战进行分析的过程中，本文描述了 CIEMAT 提出的关于设备和部件响应、事故管理措施的有效性和所应用的 MELCOR 模型的主要假设。影响最大的假设包括与反应堆压力容器 (RPV) 泄漏路径和故障模式、进入反应堆的水流量、从主安全壳 (PCV) 到反应堆厂房的潜在泄漏路径和失效模式和位置​​，从 RPV 到空腔的真皮迁移及其在 PCV 中的分布，抑制池的潜在分层和假设关于裂变产物的释放和运输。基于假设的场景和模型，在 500 小时内 RPV 和 PCV 压力方面的热足迹已经实现了显着的一致性，其中 RPV 和 PCV 泄漏/故障以及排气在短期内发挥了决定性作用事故和注水严重影响了长期的工作。至于与裂变产物（FP）相关的稀缺数据，在抑制室中找到了一致的协议，尽管显示了观察到的趋势，但干井中的估计值仍比测量值低一个数量级。许多因素可能会影响 FP 与数据的比较，从从 FP 质量（MELCOR 结果）导出剂量率（测量值）的近似方法到 RPV 和 PCV 假定故障。无论如何，根据可用数据，假设和近似值集似乎构成了福岛第一核电站 1 号机组的合理假设。 本文中提出的研究和结果是在 OECD/BSAF 项目框架下通过 CSN 实现的-CIEMAT 关于严重事故研究的合作协议。从 FP 质量（MELCOR 结果）推导出剂量率（测量值）的近似方法到 RPV 和 PCV 假定故障。无论如何，根据可用数据，假设和近似值集似乎构成了福岛第一核电站 1 号机组的合理假设。 本文中提出的研究和结果是在 OECD/BSAF 项目框架下通过 CSN 实现的-CIEMAT 关于严重事故研究的合作协议。从 FP 质量（MELCOR 结果）推导出剂量率（测量值）的近似方法到 RPV 和 PCV 假定故障。无论如何，根据可用数据，假设和近似值集似乎构成了福岛第一核电站 1 号机组的合理假设。 本文中提出的研究和结果是在 OECD/BSAF 项目框架下通过 CSN 实现的-CIEMAT 关于严重事故研究的合作协议。