Corrosion behavior of extra-high-purity Type 316 austenitic stainless steel in a liquid lead-bismuth eutectic with oxygen saturation or low oxygen concentrations

入澤 恵理子; 加藤 千明

Corrosion Science, 256, p.113173_1 - 113173_16, 2025/11

https://doi.org/10.1016/j.corsci.2025.113173

This study investigates the corrosion behavior of extra-high-purity Type 316 austenitic (316EHP) stainless steel with reduced impurity segregation at the grain boundaries in a liquid lead-bismuth eutectic (LBE) at 530C to evaluate (1) the resistance of the steel to intergranular oxidation in the LBE with oxygen saturation and (2) its dissolution corrosion resistance at lower oxygen concentrations than the equilibrium oxygen potential of magnetite. Under oxygen saturation conditions in the LBE, 316EHP generated protective uniform oxide layers without severe intragranular oxidation. Compared with the case of the conventional 316L stainless steel, enhanced Cr diffusion along the grain boundaries in 316EHP considerably improved the intergranular-oxidation resistance of the steel. However, in the LBE with a low oxygen concentration, 316EHP exhibited high susceptibility to dissolution corrosion, thus undergoing a rapid intergranular attack particularly for short exposure durations, and island-like ferritic particles were formed for long exposure durations. Future studies should explore the optimal oxygen concentrations for oxide scale formation and the long-term corrosion behavior of the steel in dynamic LBE systems.

First freezing experiments with a molten mixture of boron carbide and stainless steel in core disruptive accidents of sodium-cooled fast reactors

江村 優軌; 松場 賢一; 菊地 晋; 山野 秀将

Proceedings of 13th Korea-Japan Symposium on Nuclear Thermal Hydraulics and Safety (NTHAS13) (Internet), 8 Pages, 2024/11

Assuming the CDA of SFRs, the eutectic melting between BC as a control rod material and stainless steel (SS) as a structural material could occur below their melting points. After that, the mixture produced by eutectic melting between BC and SS (BC-SS mixture) would relocate inside or outside of the original core region. From the viewpoint of core reactivity changes, the relocation behavior of BC-SS mixture induced by its melting/freezing behavior, is one of the key elements to evaluate the CDA consequences. Many experimental studies on freezing behavior using core materials and its simulants, including molten UO, SS, tin, wood's metal have been reported in the past. Based on these experimental findings, the freezing/blockage model for the severe accident simulation code was established and discussed through analyses of freezing process. Specifically, it has been considered that the experimental correlation of melt-penetration length was a key indicator to quantitatively describe freezing behavior. However, there was no experimental data for the freezing behavior of actual BC-SS mixture. Therefore, the freezing experiments of BC-SS mixture were conducted to investigate the freezing and blockage behavior inside a flow path such as fuel pin bundle. In the freezing experiments, BC powder and SS block were heated up to around 1,750 K using a graphite heating furnace, then BC-SS mixture flowed down into an SS pipe for cooling below 750 K. The experimental results showed that the BC-SS mixture solidified and resulted in the blockage in the SS pipe with 4 mm or 6.7 mm in inner diameter, respectively. Furthermore, the observations for cross section of SS pipe suggested that the BC-SS mixture penetrated deeper than molten SS. This difference is considered to be influenced by decrease of the melting point.

Study on eutectic melting behavior of control rod materials in severe accidents of sodium-cooled fast reactors, 3; Material analysis of boron carbide immersed in molten stainless steel

高井 俊秀; 江村 優軌; 山野 秀将

Proceedings of 14th International Topical Meeting on Nuclear Reactor Thermal-Hydraulics, Operation, and Safety (NUTHOS-14) (Internet), 11 Pages, 2024/08

Interest in eutectic reaction between boron carbide, which used as control rod material and stainless steel, which used as cladding tubes, etc. is growing from a perspective to improve analysis accuracy of severe accidents analysis codes. Immersion experiment of boron carbide pellet into molten stainless steel were carried out in the temperature range between 1773 and 1973 K. The eutectic melting behavior of the pellet were investigated by observing the cross section of the pellet using an optical microscope, a scanning type electron microscope. And elemental distribution in there and crystal structure were analyzed to clarify the eutectic reaction behavior. Based on the thickness reduction of the pellet cross section, the reaction rate constants between boron carbide and stainless steel were evaluated under various conditions of contact temperature and contact time.

Impact of uncertainty reduction on lead-bismuth coolant in accelerator-driven system using sample reactivity experiments

方野 量太; 大泉 昭人; 福島 昌宏; Pyeon, C. H.*; 山本 章夫*; 遠藤 知弘*

Nuclear Science and Engineering, 198(6), p.1215 - 1234, 2024/06

https://doi.org/10.1080/00295639.2023.2246779

京都大学臨界集合体A架台で測定された鉛ビスマスサンプル反応度を用いたデータ同化によって加速器駆動システムの冷却材ボイド反応度の鉛ビスマス非弾性散乱断面積に起因した不確かさを低減できることを実証した。サンプル反応度について、データ同化の式中に現れる実験不確かさと相関を再評価し、結果を明示した。不確かさ評価に用いる感度係数はMCNP6.2で評価し、データ同化はMARBLEを用いて実行した。鉛ビスマスに対してサンプル反応度は感度係数が大きいため、加速器駆動システムの冷却材ボイド反応度の断面積起因不確かさを6.3%から4.8%まで減少させ、本研究で設定した暫定的な目標精度5%を達成できることを示した。さらに、ADJ2017に使用された積分実験データを用いることで、マイナーアクチニドや鉄など他の支配的な核種に起因する不確かさを効果的に低減できることを示した。

Development and validation of analysis code for spallation products behavior in LBE coolant system of ADS comparing with the distribution data in MEGAPIE spallation target

宮原 信哉*; 有田 裕二*; 中野 敬太; 前川 藤夫; 佐々 敏信; 大林 寛生; 武井 早憲

Nuclear Engineering and Design, 403, p.112147_1 - 112147_17, 2023/03

https://doi.org/10.1016/j.nucengdes.2022.112147

通常運転時と事故時の両方の場合における放射線障害の安全性研究のために、加速器駆動システム(ADS)の鉛ビスマス共晶(LBE)冷却システムにおけるポロニウム210を含む核破砕生成物(SP)のインベントリと放出および輸送挙動を評価することが重要である。福井大学と日本原子力研究開発機構(JAEA)は、多様な運転状況におけるADSのLBE冷却システム内のSPの時間依存挙動を予測するコンピューター解析コードTRAIL(Transport of Radionuclides In Liquid metal systems)を開発している。LBE冷却材中の放射性SPと安定SPの両方のソースタームが入力として与えられ、放射性SPの放射性崩壊連鎖モデルがコードに実装され、SPの移動性が評価される。本論文では、最近のコード開発の進捗状況と検証結果を、MEGAPIE破砕ターゲットにおける揮発性SPの分布データと比較して示す。

BWR lower head penetration failure test focusing on eutectic melting

山下 拓哉; 佐藤 拓未; 間所 寛; 永江 勇二

Annals of Nuclear Energy, 173, p.109129_1 - 109129_15, 2022/08

AA2022-0018.pdf:8.64MB

https://doi.org/10.1016/j.anucene.2022.109129

Decommissioning work occasioned by the Fukushima Daiichi Nuclear Power Station (1F) accident of March 2011 is in progress. Severe accident (SA) analysis, testing, and internal investigation are being used to grasp the 1F internal state. A PWR system that refers to the TMI-2 accident is typical for SA codes and testing, on the other hand, a BWR system like 1F is uncommon, understanding the 1F internal state is challenging. The present study conducted the ELSA-1 test, a test that focused on damage from eutectic melting of the liquid metal pool and control rod drive (CRD), to elucidate the lower head (LH) failure mechanism in the 1F accident. The results demonstrated that depending on the condition of the melt pool formed in the lower plenum, a factor of LH boundary failure was due to eutectic melting. In addition, the state related to the CRD structure of 1F unit 2 were estimated.

France-Japan collaboration on thermodynamic and kinetic studies of core material mixture in severe accidents of sodium-cooled fast reactors

Quaini, A.*; Goss, S.*; Payot, F.*; Suteau, C.*; Delacroix, J.*; Saas, L.*; Gubernatis, P.*; Martin-Lopez, E.*; 山野 秀将; 高井 俊秀; et al.

Proceedings of International Conference on Fast Reactors and Related Fuel Cycles; Sustainable Clean Energy for the Future (FR22) (Internet), 10 Pages, 2022/04

CEAと原子力機構は、現在の実施体制の下で新しいサブタスク、炉心混合物質における相互作用の動力学、炉心混合物質の物性、UO-Fe-BC系の高温熱力学データ、BC-SS速度論およびBC-SS共晶材料の再配置(凍結)に関する実験的研究、SIMMERコードシステムのBC/SS共晶および動力学モデル、混合物の液相化速度をモデル化するための方法論を定義した。この論文は、以前の実施協定の下での日仏協力で得られた主要な研究開発結果と、現在の協定の下での実験的および分析的ロードマップについて説明する。

加速器駆動核変換システムビーム窓とLBEの核解析

中野 敬太; 岩元 大樹; 西原 健司; 明午 伸一郎; 菅原 隆徳; 岩元 洋介; 竹下 隼人*; 前川 藤夫

JAEA-Research 2021-018, 41 Pages, 2022/03

JAEA-Research-2021-018.pdf:2.93MB

加速器駆動核変換システム(ADS: Accelerator-Driven System)の構成要素の一つであるビーム窓の核特性を粒子・重イオン輸送計算コードPHITS及び誘導放射能解析コードDCHAIN-PHITSを用いて評価した。本研究では日本原子力研究開発機構が提案するADSの運転時にビーム窓内部に生成される水素やヘリウム等の量、高エネルギー粒子により引き起こされるビーム窓材の原子弾き出し数、ビーム窓内部の発熱量及び分布を導出した。また、中性子源標的及び冷却材として用いられる鉛ビスマス共晶合金(LBE)中の生成核種、発熱密度及び放射能分布を求めた。ビーム窓解析の結果、300日間のADSの運転によりビーム窓中に最大で約12500appmのH及び1800appmのHeの生成と62.1DPAの損傷が発生することが判明した。一方で、ビーム窓内の最大発熱量は374W/cmであった。LBEの解析では、BiやPoが崩壊熱及び放射能の支配的な核種であることが判明した。さらに、陽子ビームによるLBE中の発熱はビーム窓下流5cm付近が最大であり、945W/cmであることがわかった。

Effect of BC absorber material on melt progression and chemical forms of iodine or cesium under severe accident conditions

日高 昭秀

Insights Concerning the Fukushima Daiichi Nuclear Accident, Vol.4; Endeavors by Scientists, p.341 - 356, 2021/10

https://doi.org/10.15669/fukushimainsights.Vol.4.341

Boron carbide (BC) used for BWR or EPR absorbers could cause phenomena that never occur in PWR with Ag-In-Cd absorbers during a severe accident (SA). BC would undergo a eutectic interaction with stainless steel and enhance core melt relocation. Boron oxidation could increase H generation, and the change of liberated carbon to CH could enhance the generation of CHI. HBO generated during BC oxidation could be changed to CsBO by combining it with cesium. This may increase Cs deposition into the RCS. There could be differences in the configuration, surface area, and stainless-steel to BC weight ratio between the BC powder and pellet absorbers. The present task is to clarify the effect of these differences on melt progression, and the iodine or Cs source term. Advancement of this research field could contribute to further sophistication of prediction tools for melt progression and source terms of the Fukushima Accident, and the treatment of CHI formation in safety evaluation.

鉛ビスマス冷却型加速器駆動核変換システムにおける酸素消費量の評価

菅原 隆徳; 小松 篤史

JAEA-Research 2020-016, 44 Pages, 2021/01

JAEA-Research-2020-016.pdf:2.94MB

液体鉛ビスマス共晶合金(LBE)を用いた原子炉システムでは、酸素濃度を制御することにより、LBEによる鋼材腐食を防ぐ必要がある。本研究では、LBE冷却型加速器駆動核変換システム(ADS)について、そのプラントで用いられる酸素消費量の評価を行った。評価は、実験に基づく酸化被膜厚さの評価式を用い、その厚さから酸素消費量を評価した。その結果、燃料集合体の発熱部については、2サイクルの炉内滞在で、最大で約35[m]の酸化被膜が作られ、ビーム窓については、1サイクルの運転で約20[m]の酸化被膜が作られることがわかった。これらの結果から求めたサイクルあたりの酸素消費量は、燃料集合体全体とビーム窓それぞれで、25[kg]と0.3[kg]となり、プラント全体としては約30[kg]となった。最終的な結果として、JAEA-ADSでは、定格運転時3-4[g/h]、ピーク時約150[g/h]の酸素を供給でき、1サイクル(=1年間)約30[kg]、40年間で約1200[kg]を供給できる酸素供給装置が必要となる。