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山下 拓哉; 下村 健太; 永江 勇二; 永井 英一*; 安松 智博*; 中島 悟*; 荻野 翔矢*; 溝上 伸也*
Proceedings of 11th European Review Meeting on Severe Accident Research Conference (ERMSAR 2024) (Internet), 11 Pages, 2024/05
Internal investigations of the Fukushima Daiichi Nuclear Power Plant (1F) have been conducted, and the internal situation is gradually becoming clearer. In addition, trial debris removal has been conducted and much information is being obtained. The information obtained from the trial debris removal is managed in the decommissioning fundamental research database (debrisWiki), which was established by JAEA and TEPCO. However, it is difficult to understand the entire accident progress only from individual data. Therefore, we developed a 3D view application (debrisEye) for 1F decommissioning. debrisEye was created by Unity. For the CG displayed in debrisEye, pre- and post-accident conditions were constructed. The pre-accident status was created using design information and point cloud data from periodic inspections. The post-accident status was created mainly from the results of the internal investigation. For areas where internal investigations have not yet been obtained, the information in the estimation diagram was reflected. CG displayed on debrisEye can be viewed from any viewpoint and angle using the functionality contained in debrisEye. It is also possible to clipping at any cross section and to show or hide each part. debrisEye can be linked to and used with debrisWiki to write information in any location, thus displaying the analysis results and location of the debris collected. Visual linking of debris analysis results with on-site information is expected to facilitate understanding of accident progress and improve efficiency of decommissioning work.
下村 健太; 山下 拓哉; 永江 勇二
Proceedings of 11th European Review Meeting on Severe Accident Research Conference (ERMSAR 2024) (Internet), 12 Pages, 2024/05
From the results of the internal investigation of Fukushima Daiichi Nuclear Power Station Unit 2, it was confirmed that part of the fuel assembly (upper tie plate) had fallen to the bottom of the pedestal periphery. From this result, it could be presumed that RPV has a hole large enough for the upper tie plate to drop. However, internal investigations have not revealed where the holes are located at the bottom of the RPV. One of failure mode of the RPV lower head would be assumed to be mechanical failure. In this failure, it is assumed that the RPV lower head will be damaged due to the accumulation of creep damage caused by core material above the creep temperature of the RPV substructure materials falling into the lower plenum. Such damage evaluation is performed by thermohydraulic-structure coupled analysis. In the analysis during accident, the RPV lower head is exposed to high temperature conditions. Therefore, the material properties of the RPV material in the high temperature range are required for evaluation by analysis. In this study, we obtained the strength data of RPV material form the creep temperature range to near the melting point and formulated the material property formulas (elastoplastic stress-strain, creep strain, creep rupture) necessary for mechanical failure evaluation.
reaction systemRizaal, M.; 中島 邦久; 鈴木 恵理子; 三輪 周平
Proceedings of 11th European Review Meeting on Severe Accident Research Conference (ERMSAR 2024) (Internet), 11 Pages, 2024/05
The pseudo-binary CsI-MoO reaction system during transportation in the reactor under severe accident conditions has been investigated by using the JAEA-TeRRa semi-integral test facility. An oxygen gas with approximately 10 mbar of partial pressure was given to argon-steam upstream gas flow during the reaction to study its effect on downstream chemistry between CsI and MoO (Mo/Cs molar ratio of 2.13). The product of CsI-MoO reactions both gas and aerosols were analyzed upon their condensation on type-304L stainless steel sampling coupons at respective temperatures (T= 1150-450 K). Post-test analyses revealed that at a low oxygen potential of -192 kJ/mol (i.e. reference case with argon-steam only), most of the CsI reached downstream (T 
400 K) without any reaction with MoO. On the other hand, when oxygen potential was slightly increased to about -144 kJ/mol, the CsI vapor could react with MoO to form cesium polymolybdates (Cs
MoO
and CsMo
O
) and gaseous iodine which predominated the aerosol and gas that reached the downstream region. Particle size at this location was found to be less than 2.7 
m in contrast to the former case having an irregularly large size. The gaseous iodine in the latter case, based on the thermodynamic analyses, was estimated to be hypoiodous acid (HIO) or molecular iodine (I). The results in this study indicated that speciation of both Cs and I with the Mo chemistry during a severe accident could be variedly formed depending on the prevailing oxygen potential.
石田 真也; 田上 浩孝; 岡野 靖; 山野 秀将; 久保 重信; 飛田 吉春
Proceedings of 11th European Review Meeting on Severe Accident Research Conference (ERMSAR 2024) (Internet), 10 Pages, 2024/05
The new detailed fuel pin model has been developed in the SIMMER-V code to simulate thermal and mechanical behavior of the fuel pin from accident initiation to fuel pin failure. The SIMMER code has mainly been developed to simulate the event progression in Transition Phase (TP), and the Initiating Phase (IP) was simulated by the SAS4A code and the results of the SAS4A code were taken over as the initial conditions of the SIMMER code. The transfer of data between codes causes discontinuities due to differences in geometric models and analysis models. There is an additional issue that SIMMER has no analytical model applicable to reactor cores with complex geometry. To solve these issues, the improved SIMMER code, SIMMER-V, is being developed by introducing a detailed and flexible model to simulate fuel pin failure in the IP. This paper describes the development of the new detailed fuel pin model, the construction of the verification matrix, and the results of the verification.
田上 浩孝; 石田 真也; 岡野 靖; 山野 秀将; 久保 重信; Payot, F.*; Saas, L.*; Trotignon, L.*; Gubernatis, P.*; Dufour, E.*; et al.
Proceedings of 11th European Review Meeting on Severe Accident Research Conference (ERMSAR 2024) (Internet), 12 Pages, 2024/05
特殊な炉心設計を有する大型非均質炉心を含む将来的なナトリウム冷却高速炉(SFR)のシビアアクシデント(SA)解析のために、原子力機構はCEAと共同でSIMMER-Vを開発している。SAの事象推移は従来、個々の燃料集合体内で発生するピン破損と鉛直方向燃料分散が主体となる起因過程(IP)をSAS4Aで、炉心損傷領域が全炉心へと拡大する遷移過程をSIMMER-IIIもしくはSIMMER-IVで解析を行ってきた。SIMMER-Vの共同開発の範囲は限定的であるが、SIMMER-Vの計算を他の計算領域や他のコードと連携させるための柔軟なインタフェースを提供すること、また、詳細な燃料ピンモデルや燃料同位体組成を柔軟に扱えるモデルのような新しい先進物理モデルを追加することにより、コードの適用性を大幅に拡大することを目指している。前者はCEAが、後者は原子力機構(JAEA)が担当する。コード開発と並行して、新しいモデルや手法の検証と妥当性確認が実施された。本論文では、SIMMER-Vコード開発プログラムの目的と全体的な枠組み,代表的な新要素,最近の開発の進展について述べる。
Li, X.; 山路 哲史*; 佐藤 一憲*; 山下 拓哉; 永江 勇二
Proceedings of 11th European Review Meeting on Severe Accident Research Conference (ERMSAR 2024) (Internet), 12 Pages, 2024/05
For Fukushima Daiichi Nuclear Power Station (1F) Unit-2, the muon radiography investigation results indicate that the fuel debris are largely retained inside the RPV. The current study focuses on the analysis of metallic melt penetration behavior in the CRD housing with Moving Particle Semi-implicit (MPS) method. A three-dimensional CRD housing model with simplified inner structures was established. The injection of SS-Zircaloy eutectic melt into the CRD housing was simulated and its downstream penetration and freezing behavior under vertically varying temperature boundary conditions was analyzed. It is found that the melt would start to freeze and form channel blockages soon after it enters the region with a relatively cold boundary in the downstream.
