Radioactivity estimation of multiple radiation sources using a Compton camera to investigate radioactively contaminated objects

佐藤 優樹

Applied Radiation and Isotopes, 203, p.111083_1 - 111083_9, 2024/01

https://doi.org/10.1016/j.apradiso.2023.111083

At the Fukushima Daiichi Nuclear Power Station (FDNPS), radioactive substances released during the accident were deposited on various equipment and building structures. During the decommissioning work, an investigation of the deposition of radioactive substances inside the contaminated equipment and structures can provide information on the cause and progression of the accident. This study introduces a quantitative evaluation method of radioactivity using a Compton camera, a type of gamma-ray imager, to investigate the deposition and contamination level of radioactive substances on contaminated objects at the FDNPS. Multiple Cs radiation sources with varying radioactivity were placed horizontally in one dimension within the field of view of the Compton camera, and a proof-of-principle study was conducted to evaluate the radioactivity of each source quantitatively.

JRR-3、JRR-4及び再処理特別研究棟から発生した放射性廃棄物に対する放射化学分析,2

飛田 実*; 後藤 勝則*; 大森 剛*; 大曽根 理*; 原賀 智子; 青野 竜士; 今田 未来; 土田 大貴; 水飼 秋菜; 石森 健一郎

JAEA-Data/Code 2023-011, 32 Pages, 2023/11

JAEA-Data-Code-2023-011.pdf:0.93MB

日本原子力研究開発機構の研究施設等から発生する放射性廃棄物は、放射能レベルに応じて将来的にトレンチとピットに分けて浅地中埋設処分される予定であり、埋設処分を開始するまでに、廃棄体の放射能濃度を評価する方法を構築する必要がある。そこで、原子力科学研究所バックエンド技術部では、研究施設等廃棄物に対する放射能濃度評価方法の検討に資するため、JRR-3、JRR-4及び再処理特別研究棟から発生した放射性廃棄物よりコンクリートを試料として採取し、放射化学分析を実施した。本報告書は、令和3年度から令和4年度に取得した23核種(H、C、Cl、Ca、Co、Ni、Sr、Nb、Ag、Cs、Ba、Eu、Eu、Ho、U、U、U、Pu、Pu、Pu、Am、Am、Cm)の放射能濃度データについて整理し、放射能濃度評価法検討のための基礎資料としてまとめたものである。

Evaluation of thermal expansion reactivity feedback effect in water-moderated fuel-particle-dispersion system

福田 航大

Proceedings of 4th Reactor Physics Asia Conference (RPHA2023) (Internet), 4 Pages, 2023/10

水減速燃料粒子分散体系(例:燃料デブリ体系)における熱膨張フィードバックが即発超臨界時の出力ピーク値や放出エネルギーに与える影響を定量的に明らかにすることを目的とした解析を行った。熱膨張を考慮する場合/しない場合の燃料温度反応度係数を仮想的な体系に対して計算し、Nordeheim-Fuchモデルを用いた評価を行った。その結果、熱膨張の影響を無視することで出力ピーク値や放出エネルギーに数十パーセントの誤差が生じうることが明らかとなった。この誤差は臨界事故解析の多くの場面では問題となる大きさではないものの、解析の目的によっては(例えば、事故後の被ばく量やRI放出量の検証のため精度よく結果を得たい場合)熱膨張反応度フィードバックの影響を考慮すべきであることが示された。

Radiation imaging of a highly contaminated filter train inside Fukushima Daiichi Nuclear Power Station Unit 2 using an integrated Radiation Imaging System based on a Compton camera

佐藤 優樹; 寺阪 祐太

Journal of Nuclear Science and Technology, 60(8), p.1013 - 1026, 2023/08

https://doi.org/10.1080/00223131.2022.2159894

The Fukushima Daiichi Nuclear Power Station (FDNPS) suffered a meltdown in the aftermath of the large tsunami caused by the Great East Japan Earthquake that occurred on 11 March 2011. A massive amount of radioactive substance was spread over a wide area both inside and outside the FDNPS site. In this study, we present an approach for visualizing a radioactive hotspot on a standby gas-treatment system filter train, a highly contaminated piece of equipment in the air-conditioning room of the Unit 2 reactor building of FDNPS, using radiation imaging based on a Compton camera. In addition to fixed-point measurements using only the Compton camera, data acquisition while moving using an integrated Radiation Imaging System (iRIS), which combines a Compton camera with a simultaneous localization and mapping device and a survey meter, enabled the three-dimensional visualization of the hotspot location on the filter train. In addition, we visualized the hotspot and quantitatively evaluated its radioactivity. Notably, the visualized hotspot location and estimated radioactivity value are consistent with the accident investigation report of the FDNPS. Finally, the extent to which the radioactivity increased the ambient dose equivalent rate in the surrounding environment was explored.

Development of transient behavior analysis code for metal fuel fast reactor during initiating phase of core disruptive accident

太田 宏一*; 尾形 孝成*; 山野 秀将; 二神 敏; 島田 貞衣*; 山田 由美*

Proceedings of 30th International Conference on Nuclear Engineering (ICONE30) (Internet), 8 Pages, 2023/05

The experimental analyses of the U-Pu-Zr fuel pin behavior during transient overpower (TOP) tests were performed by CANIS, and the residual cladding wall thickness and molten region of the fuel alloy after the tests, and the reactivity inserted by molten fuel extrusion before the fuel pin failure were compared with the experimental results. On the basis of these analysis results, detailed calculation models were developed for and implemented into CANIS to be made it possible to consider changes in the local properties of the fuel alloys due to redistribution of fuel constituents during steady-state irradiation and in the cladding thinning rate depending on the fuel-cladding interface temperature. The modified CANIS properly predicted fuel behavior and resulting reactivity changes before fuel pin failure in TOP events.

JAEA-JRC collaborative development of delayed gamma-ray spectroscopy for nuclear safeguards nuclear material accountancy

Rodriguez, D.; Abbas, K.*; Bertolotti, D.*; Bonaldi, C.*; Fontana, C.*; 藤本 正己*; Geerts, W.*; 小泉 光生; Macias, M.*; Nonneman, S.*; et al.

Proceedings of INMM & ESARDA Joint Annual Meeting 2023 (Internet), 8 Pages, 2023/05

Under the MEXT subsidy to improve nuclear security related activities, we present the overview of the JAEA-JRC delayed gamma-ray spectroscopic analysis project. We describe past results, recent joint experiments, and the final goals for this project.

Iron-induced association between selenium and humic substances in groundwater from deep sedimentary formations

寺島 元基; 遠藤 貴志*; 紀室 辰伍; 別部 光里*; 根本 一昭*; 天野 由記

Journal of Nuclear Science and Technology, 60(4), p.374 - 384, 2023/04

https://doi.org/10.1080/00223131.2022.2111376

For better understanding of impact of natural organic matters (NOM) on facilitating migration of Se in underground environments, association mechanism between Se and humic substance (HS) in groundwater was investigated by incubation experiments using groundwater sample under abiotic and biotic conditions and speciation analyses by an isolation technique with DAX-8 resin and a size exclusion chromatography coupled on-line to UV-Vis and ICP-MS detection (SEC-UV-ICP-MS). Selenite added into the groundwater was reduced to elemental Se only when microbial activity was stimulated by a nutrient. The speciation analysis by the isolation technique showed the presence of Se associated with HS and that proportion of the associate to total dissolved Se is highest in the reducing condition. The SEC-UV-ICP-MS analyses of alkaline extracts from the DAX-8 resin showed that Se was coeluted with Fe as well as HS, regardless of microbial activity and redox conditions. Logarithmic peak areas of Se and Fe coeluted with HS in the SEC chromatograms was linearly correlated in the moderately oxidizing condition (r = 0.947, p 0.01 with addition of Se; r = 0.995, p 0.01 without the addition of Se). The SEC chromatogram of Se coeluted with HS in the reducing condition was well matched with those of Se-Fe-HS ternary complex in the moderately oxidizing condition. Therefore, these suggest that the association between Se and HS in groundwaters can be dominated by a formation of Se-Fe-HS ternary complex.

Urban factors and mental health symptoms in children of the Tokyo Early Adolescence Survey; Impact of proximity to railway stations

Davies, S. J. C.*; Bolea-Alamanac, B.*; 遠藤 香織*; 山本 優*; 山崎 修道*; Malins, A.; Evans, J.*; Sullivan, S.*; 安藤 俊太郎*; 西田 淳志*; et al.

Journal of Transport & Health, 28, p.101564_1 - 101564_11, 2023/01

https://doi.org/10.1016/j.jth.2022.101564

The study tested the hypothesis that proximity of home to railway stations is a positive predictor of mental health at age 10 years. Using the Tokyo Early Adolescence Survey we examined relationships between distance from home to the nearest railway station and SDQ (Strengths and Difficulties Questionnaire) scores for hyperactivity/inattention, prosocial behaviour and emotional symptoms. Greater distance to the nearest railway station was associated with SDQ-derived hyperactivity/inattention scores in the unadjusted analysis across all 4052 analyzable children, and in the fully adjusted analysis in boys ( = 0.198, 95% C.I. 0.009 to 0.386, p = 0.040) but not in girls ( = 0.007, 95% C.I. -0.164 to 0.177, p = 0.940). There were no associations with other SDQ-based outcomes. If replicated, these findings suggest that access to high-quality transit may be associated with improved hyperactivity/inattention outcomes in children living in urban environments.

Numerical study of initiating phase of core disruptive accident in small sodium-cooled fast reactors with negative void reactivity

石田 真也; 深野 義隆; 飛田 吉春; 岡野 靖

Journal of Nuclear Science and Technology, 13 Pages, 2023/00

https://doi.org/10.1080/00223131.2023.2243949

To improve the safety of future SFRs, the development of SFRs with low void reactivity has been promoted. Small SFRs can have a negative void coefficient of reactivity, so the analysis of the CDA event sequence in small SFRs is valuable for the investigation of the reactor characteristics for the future research and development of SFRs. In this study, the typical initiating events of a CDA in small SFRs were evaluated with the computational code, SAS4A. The event progression of ULOF and UTOP in the low void reactivity reactor is found to be slow due to the effective operation of the negative reactivity feedback and the absence of significant positive reactivity insertion. No power excursion occurs in the initiating phase. In ULOF, the cladding melt and relocation behavior becomes more important for the evaluation of the event progression due to its positive reactivity.

JRR-3、JRR-4及び再処理特別研究棟から発生した放射性廃棄物に対する放射化学分析

飛田 実*; 今田 未来; 大森 剛*; 生天目 勉*; 鬼澤 崇*; 黒澤 勝昭*; 原賀 智子; 青野 竜士; 水飼 秋菜; 土田 大貴; et al.

JAEA-Data/Code 2022-007, 40 Pages, 2022/11

JAEA-Data-Code-2022-007.pdf:1.99MB

日本原子力研究開発機構の研究施設等から発生する放射性廃棄物は、放射能レベルに応じて将来的に浅地中埋設処分される予定であり、埋設処分を開始するまでに、廃棄体の放射能濃度を評価する方法を構築する必要がある。そこで、原子力科学研究所バックエンド技術部では、研究施設等廃棄物に対する放射能濃度評価方法の検討に資するため、JRR-3、JRR-4及び再処理特別研究棟から発生した放射性廃棄物よりコンクリート、焼却灰、セラミックフィルタ及び耐火レンガを試料として採取し、放射化学分析を実施した。本報告書は、令和2年度から令和3年度に取得した24核種(H、C、Cl、Ca、Co、Ni、Sr、Nb、Tc、Ag、I、Cs、Ba、Eu、Eu、Ho、U、U、Pu、Pu、Pu、Am、Am、Cm)の放射能濃度データについて整理し、放射能濃度評価法検討のための基礎資料としてまとめたものである。