On-going R&D program at JAEA on the Advanced Technology Fuels; An Update on the Cr-coated Zry cladding research

Mohamad, A. B.; 山下 真一郎; 根本 義之; 阿部 陽介; Pham, V. H.; 井岡 郁夫; 相馬 康孝; 石島 暖大; 佐藤 智徳; Rizaal, M.; et al.

Proceedings of TopFuel 2025; Nuclear Reactor Fuel Performance Conference (Internet), 8 Pages, 2025/10

https://www.ans.org/pubs/proceedings/issue-3431/

In parallel with the Advanced Technology Fuel (ATF) development program in Japan, Japan Atomic Energy Agency has established an R&D program on the ATF to provide more scientific support to the ATF fuel vendors in Japan. Based on the identified phenomenological issues, the R&D program covers the issues mainly on the light water reactors conditions such as normal operation, loss of coolant accident, beyond design basis accident, and severe accident. The R&D program such as irradiation test, corrosion test, LOCA test, and etc. are proposed. By acquiring the data from the experiment, the final goal is to implement the experimental data and model into the simulation code in order to predict the fuel performance behaviour at high burn-up. In 2024 TOPFUEL, the introduction of the R&D has been presented. In 2025, the update on the Cr-coated research to simulate normal operation and accident conditions will be given. For example, tests are currently underway to understand the in-reactor environment, such as ion irradiation, gamma irradiation and proton irradiation tests. In addition, a loss-of-coolant accident is being simulated for accident conditions, and the chemical effects of fission products on the cladding are being studied.

福島第一原子力発電所廃炉作業への貢献とソースターム予測技術向上におけるFP挙動に関する技術課題に対する取り組み

勝村 庸介*; 高木 純一*; 宮原 直哉*; 内田 俊介*; 駒 義和; 唐澤 英年; 三輪 周平; 佐藤 志彦; 永井 晴康; 倉田 正輝; et al.

日本原子力学会誌ATOMO, 67(2), p.128 - 132, 2025/02

https://doi.org/10.3327/jaesjb.67.2_128

本研究専門委員会では、東京電力ホールディングス株式会社福島第一原子力発電所(1F)事故後の核分裂生成物(FP)挙動を予測可能な技術に高めて廃炉作業に貢献することと、1F事故進展事象の把握で得られた情報をソースターム(ST)の予測技術の向上に反映させ、原子炉安全の一層の向上に繋げることを目標とした活動を実施している。最初の2年間は、1F廃炉における燃料デブリやFP挙動の予測、およびST予測精度向上に必要な、今後取り組むべき技術課題を摘出した。2023年度からは、本専門委員会を延長し、取り組むべき技術課題に対応した3つのワーキンググループを結成し、技術課題の解決に向けた検討を進めている。本報告では2023年度の活動での検討内容について報告する。

Updating fission product chemistry database based on recent investigation in Fukushima-Daiichi Nuclear Power Station, 2; Temperature effects on the deposition behavior of CsOH aerosols on concrete main phase-CaCO

Luu, V. N.; 中島 邦久; Rizaal, M.; 三輪 周平

Proceedings of International Topical Workshop on Fukushima Decommissioning Research 2024 (FDR2024) (Internet), 4 Pages, 2024/10

The trapping behavior of cesium (Cs) on concrete, such as pedestal and shield plugs, was assessed through multiple deposition tests of CsOH aerosols on concrete phase-CaCO within a temperature range of 170C to 570C under humid conditions. The deposition rate of CsOH aerosols on CaCO as a function of temperature was examined. X-ray diffraction analysis revealed the presence of water-soluble CsCO on CaCO samples up to 420C, but negligible detection above this temperature. This finding is supported by quantitative analyses of Cs weight gain and chemical analysis, demonstrating an increase in deposition rate up to 420C, followed by a decline thereafter. The increased deposition rate is attributed to the chemical interaction between CsOH and CaCO, while the diminished rate beyond 420C may result from the decomposition of CaCO under steam, thereby reducing the available reactant for the chemical reaction with CsOH.

Gaseous and aerosol formations in the pseudo-binary CsI-MoO reaction system

Rizaal, 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

https://doi.org/10.5445/IR/1000174165

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 (CsMoO and CsMoO) 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.

福島第一原子力発電所廃炉作業効率化とソースターム予測精度向上への貢献に向けたFP挙動に関する技術調査; 本専門委員会の2年間の活動報告

勝村 庸介*; 高木 純一*; 細見 憲治*; 宮原 直哉*; 駒 義和; 井元 純平; 唐澤 英年; 三輪 周平; 塩津 弘之; 日高 昭秀*; et al.

日本原子力学会誌ATOMO, 65(11), p.674 - 679, 2023/11

https://doi.org/10.3327/jaesjb.65.11_674

本委員会では、東京電力ホールディングス株式会社(東電)福島第一原子力発電所(1F)事故後の 核分裂生成物(FP)挙動を予測可能な技術に高めて廃炉作業に貢献することと、1F事故進展事象の把握で得られた情報をソースターム(ST)の予測技術の向上に反映させ、原子炉安全の一層の向上に繋げることを目標とした活動を実施している。この2年間では、これまでの12年間の1F実機調査や1F関連研究で得られた情報を調査し、1F廃炉における燃料デブリやFP挙動の予測、及びST予測精度向上に必要な課題として「FPの量・物質収支と化学形態」「サンプリング目的とデータ活用」「環境への移行経路」を摘出した。今後、これらの課題の解決に向けた道筋の議論を進める。

Improvement of model for cesium chemisorption onto stainless steel in severe accident analysis code SAMPSON (Joint research)

三輪 周平; 唐澤 英年; 中島 邦久; 木野 千晶*; 鈴木 恵理子; 井元 純平

JAEA-Data/Code 2021-022, 32 Pages, 2023/01

JAEA-Data-Code-2021-022.pdf:1.41MB
JAEA-Data-Code-2021-022(errata).pdf:0.17MB

東京電力福島第一原子力発電所の原子炉内におけるセシウム分布のより正確な予測に向けて、核分裂生成物の化学挙動データベースECUMEに格納されているステンレス鋼へのセシウム化学吸着モデルをシビアアクシデント解析コードSAMPSONに組み込んだ。改良モデルを組み込んだSAMPSONにより、当該モデルを構築した実験の結果を再現し、コードに誤りが無いことを確認した。また、SAMPSONに組み込まれた改良モデルのセシウム化学着挙動解析への有効性を確認するため、温度勾配管を有する装置を用いた実験の解析を実施した。改良モデルを組み込んだSAMPSONにより、実験の結果を再現し、SAMPSONにおけるノードジャンクションの設定方法、エアロゾル生成モデル、CsOH蒸気の飽和蒸気圧等の計算方法等の解析方法、そして改良モデルがセシウム化学吸着挙動解析に適用可能であることを確認した。また、セシウムがシビアアクシデント後に水相を介して移行したことから、原子炉内におけるセシウム分布を予測するためには、セシウム沈着物の水への溶解性の評価が前提となる。このため、ステンレス鋼へのセシウム化学吸着生成物の水への溶解性を調べた。ステンレス鋼304へのセシウム化学吸着生成物は、873Kから973Kで水溶性の高いCsFeO、973Kから1273Kで水溶性の低いCsFeSiO、1073Kから1273Kで水溶性の低いCsSiOであることが分かった。これらの結果から、セシウム化学吸着量に影響を与える原子炉内温度やCsOH蒸気種濃度のようなシビアアクシデント解析条件に応じて、セシウム化学吸着生成物の水への溶解性を予測できる可能性を得た。

A New method of measuring ruthenium activity in ruthenium-containing alloys by using thermogravimetric analysis

Liu, J.; 中島 邦久; 三輪 周平; 白数 訓子; 逢坂 正彦

Journal of Nuclear Science and Technology, 59(4), p.484 - 490, 2022/04

https://doi.org/10.1080/00223131.2021.1979432

A new method named TG calibration curve method has been proposed to evaluate the Ru activity in the Ru-containing alloys by using the kinetic relationship between oxidative evaporation rate of Ru atom and overall vapor pressures of various RuOx gases in the experimental system constructed by the authors. The experimental results show that the oxidative evaporation rate of Ru atom from experimental powders is approximately proportional to the overall vapor pressures over powders. By using their specific quantitative relationship, we determined the Ru activity in RuPd alloy in the temperature range from 1523 to 1673 K. The obtained values of Ru activity agree well with those theoretically calculation, and indicated the reliability of this new method.

Revaporization behavior of cesium and iodine compounds from their deposits in the steam-boron atmosphere

Rizaal, M.; 三輪 周平; 鈴木 恵理子; 井元 純平; 逢坂 正彦; Goullo, M.*

ACS Omega (Internet), 6(48), p.32695 - 32708, 2021/12

https://doi.org/10.1021/acsomega.1c04441

This paper presents our investigation on cesium and iodine compounds revaporization from cesium iodide (CsI) deposits on the surface of stainless steel type 304L, which were initiated by boron and/or steam flow. A dedicated basic experimental facility with a thermal gradient tube (TGT) was used for simulating the phenomena. The number of deposits, the formed chemical compounds, and elemental distribution were analyzed from samples located at temperature range 1000-400 K. In the absence of boron in the gas flow, it was found that the initial deposited CsI at 850 K could be directly re-vaporized as CsI vapor/aerosol or reacted with the carrier gas and stainless steel (CrO layer) to form CsCrO on the former deposited surface. The latter mechanism consequently gave a release of gaseous iodine that was accumulated downstream. After introducing boron to the steam flow, a severe revaporization of iodine deposit at 850 K occurred (more than 70% initial deposit). This was found as a result of the formation of two kinds of cesium borates (CsBO5HO and CsBO4HO) which contributed to a large release of gaseous iodine that was capable of reaching outlet of TGT ( 400 K). In the case of nuclear severe accident, our study have demonstrated that gaseous iodine could be expected to increase in the colder region of a reactor after late release of boron or a subsequent steam flow after refloods of the reactor, thus posing its near-term risk once leaked to the environment.

Synthesis of simulated fuels containing CsI under gas-tight condition

Liu, J.; 三輪 周平; 中島 邦久; 逢坂 正彦

Nuclear Materials and Energy (Internet), 26, p.100916_1 - 100916_6, 2021/03

https://doi.org/10.1016/j.nme.2021.100916

A new synthesis method of simulated fuel containing highly volatile compound of cesium iodide (CsI) was established based on a gas-tight sintering technique. This method can enhance the grain growth of the SIMFUEL pellets by increasing sintering temperature and time. The CsI content in the simulated fuel did not significantly decrease even for 10 hours sintering time and its final value can be quantitatively controlled by adjusting its vaporization amount. A slower heating rate after the melting of CsI can promote the dispersion of liquid CsI on the grain boundaries and give a very small CsI particle size.

Experimental study on transport behavior of cesium iodide in the reactor coolant system under LWR severe accident conditions

宮原 直哉; 三輪 周平; Goullo, M.*; 井元 純平; 堀口 直樹; 佐藤 勇*; 逢坂 正彦

Journal of Nuclear Science and Technology, 57(12), p.1287 - 1296, 2020/12

https://doi.org/10.1080/00223131.2020.1782281

主にガス状ヨウ素の生成メカニズムに着目して原子炉冷却系におけるCsIの移行挙動を明らかにするため、温度勾配管を用いたCsIの移行再現実験を実施し、沈着物及び浮遊物の詳細分析を行った。その結果、ガス状ヨウ素が高温領域におけるCs-I-O-H反応体系の気相反応により生成し、速度論の効果によって化学形態を大きく変化させずに下流の低温領域に移行すること、凝縮したCsIの化学反応、すなわち、CsCrO化合物が生成する壁面への沈着CsIとステンレス鋼の化学反応、またはエアロゾルとなったCsIと水蒸気との化学反応により、ガス状ヨウ素が生成することを明らかにした。