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中村 勇気*; 小島 良洋*; 山下 拓哉; 下村 健太; 溝上 伸也
Journal of Nuclear Science and Technology, 62(12), p.1226 - 1230, 2025/12
被引用回数：0 パーセンタイル：0.00(Nuclear Science & Technology)In 2011, at the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident, it has been reported that several Units of containment vessel had failed, and large quantity of radionuclides had been released into the environment, however, the detail of accident progression with core melt, reactor and containment vessel failure, has still large uncertainties. Especially for the Unit 2 and Unit 3, even they had succeeded in the initial core cooling, at last lost cooling system and fell into severe accident into large release of the fission product into the environment. To clarify these uncertainties in accident scenario, considering the latest information and several insights, the latest accident scenario for Unit 2 and Unit 3 are studied using the severe accident analysis code in this study. It is shown that both Units would result in the thermal stratification in the containment water which encouraged the containment pressure increase at the early phase of the accident. On the other hand, it would be also possible that containment leakage happened to decrease the containment pressure at the later phase of the accident.
Li, X.; 佐藤 一憲; 山路 哲史*
Annals of Nuclear Energy, 133, p.21 - 34, 2019/11
被引用回数：6 パーセンタイル：41.56(Nuclear Science & Technology)This study aims at identifying the modeling uncertainties and addressing the sensitivity parameters in Fukushima NPP Unit 3. A more detailed Control Volume (CV) division model of the reactor core region has been developed to better simulate the thermal-hydraulic behavior in the core region. The current study suggested that the local vapor heatup behavior could influence the core melting and relocation behavior, which can lead to different core degradation scenarios. With the current modeling assumptions in MELCOR, the best estimate conditions for RPV pressure history of Unit 3 suggested that 6 SRVs could have remained open when the major core slumping took place at 12:00, March 13 with 50 to 80 tons of water inventory in the lower plenum. The current analysis also suggested that the efficiency of the AWI to the reactor core could have been only 0.15 as of reported by TEPCO with the current modeling conditions if debris dryout was assumed to have occurred at around ca. 54.0 h.
Zheng, X.
no journal, ,
The severe accident researches, of both experiment and simulation, are active to assess the potential risk of a nuclear reactor. The results of the risk assessment, however, include significant uncertainties as a result of its innate complexity. The author introduces methods of how to quantify the uncertainties during the severe accident simulation. Integral severe accident codes have been developed to simulate accident progression and determine the consequences. Various accident scenarios are modeled within the probabilistic risk assessment (PRA) framework, which specifies the progression and probability of each accident scenario. Numerical models are generally the simplification of severe accidents, which diverges from the reality and causes the uncertainties. Methods of parameter and scenario uncertainty analysis are introduced in detail, including Monte-Carlo-sampling-based method, global sensitivity analysis, dynamic event tree, and surrogate models.
