令和4年度原子力発電所周辺における航空機モニタリング(受託研究)

普天間 章; 眞田 幸尚; 長久保 梓; 川崎 義晴*; 岩井 毅行*; 平賀 祥吾*; 萩野谷 仁*; 松永 祐樹*; 圷 雄一郎*; 新井 仁規*; et al.

JAEA-Technology 2023-027, 146 Pages, 2024/03

JAEA-Technology-2023-027.pdf:18.12MB

2011年3月11日に発生した東北地方太平洋沖地震による津波に起因した東京電力福島第一原子力発電所事故によって、大量の放射性物質が周辺環境に飛散した。事故直後より、放射線の分布を迅速かつ広範囲に測定する手法として、航空機等を用いた空からの測定方法が適用されている。日本原子力研究開発機構では、有人ヘリコプターを使用した航空機モニタリングを福島第一原子力発電所周辺において継続的に実施してきた。本報告書では、令和4年度に実施した福島第一原子力発電所周辺におけるモニタリング結果について取りまとめると共に、過去のモニタリング結果から空間線量率等の変化量を評価し、その変化要因について考察した。また、航空機モニタリングによる空間線量率の換算精度向上に資するために、航空機モニタリングデータを用いて地形の起伏を考慮に入れた解析を行った。地形の起伏を考慮に入れる前後での解析結果を比較し、本手法による精度向上効果を評価した。さらに、空気中のラドン子孫核種の弁別手法を測定結果に適用して、空気中のラドン子孫核種が航空機モニタリングに与える影響について評価した。

プルトニウム廃棄物処理開発施設 第2難燃物焼却工程設備の更新

山下 健仁; 牧 翔太; 横須賀 一裕; 福井 雅裕; 家村 圭輔

JAEA-Technology 2023-023, 97 Pages, 2024/03

JAEA-Technology-2023-023.pdf:8.21MB

プルトニウム廃棄物処理開発施設第2難燃物焼却室に設置されている第2難燃物焼却工程設備は、混合酸化物燃料製造等に伴い発生する放射性固体廃棄物のうち塩化ビニル(主にビニルバッグ)、RI用ゴム手袋等の難燃性廃棄物の減容処理技術開発を目的に2002年から焼却処理実証運転を行ってきた。しかし、難燃性廃棄物を処理する際に発生する塩化水素等による設備内部の腐食が進むとともに、焼却炉内壁の耐火物に亀裂の発生、進展が確認されたため、2018年から2022年に運転停止期間を設け、焼却炉等の更新を行った。本設備は廃棄物供給工程、焼却工程、廃ガス処理工程、灰取出工程により構成されており、このうち2020年3月から2021年3月にかけて廃ガス処理工程のスプレー塔の更新を、2021年1月から2022年2月にかけて焼却工程の焼却炉の更新を実施した。また、更新機器の腐食・劣化状況調査のため既設機器の撤去・解体作業中に焼却炉、スプレー塔から試料採取を行い、走査型電子顕微鏡/X線マイクロアナライザーによる観察とX線回折による分析を行った。本報告書ではスプレー塔・焼却炉の撤去・解体に係るグリーンハウスの設営方法、更新手順、更新対象機器の腐食・劣化状況の分析結果について報告する。

廃棄体製作基準類整備に関する活動; 令和4年度活動報告書

バックエンド推進部; 埋設事業センター

JAEA-Review 2023-037, 162 Pages, 2024/02

JAEA-Review-2023-037.pdf:2.66MB

日本原子力研究開発機構では、研究施設等廃棄物の浅地中処分に向けて、廃棄物確認における技術基準への対応方法等の検討を進めている。令和4年度から「廃棄体製作基準検討委員会」を設置し、埋設事業センターにて検討中の廃棄物埋設施設を想定した暫定の廃棄物受入基準、廃棄体確認要領等の廃棄体製作に関する基準類の整備を進めていくこととした。令和4年度は、液体廃棄物のセメント固化体及び固体廃棄物の充填固化体に関する基準類を策定することとし、検討を進めた。また、廃棄物確認の方法が確立されていない課題の検討、解体廃棄物の合理的な処理方法の実証等を進めた。本報告書は、それらの内容についてまとめたものである。

Development of an integrated non-destructive analysis system, Active-N

土屋 晴文; 藤 暢輔; 大図 章; 古高 和禎; 北谷 文人; 前田 亮; 米田 政夫

Journal of Nuclear Science and Technology, 60(11), p.1301 - 1312, 2023/11

https://doi.org/10.1080/00223131.2023.2192529

An integrated active neutron non-destructive analysis (NDA) system, Active-N, was developed to gain knowledge of active neutron NDA techniques that are applicable to measurements of nuclear materials in highly radioactive nuclear fuels. Active-N, equipped with a D-T neutron generator, combines three complementary active neutron NDA techniques: Differential Die-away Analysis (DDA), Prompt Gamma-ray Analysis (PGA), and Neutron Resonance Transmission Analysis (NRTA). In this paper, we provide an overview of Active-N and then demonstrate that the compact NRTA system in Active-N can quantify nuclear materials. Monte Carlo simulations were conducted to determine the design of the compact NRTA system including a moderator, flight tubes, and a detector shield. To investigate how accurately the compact NRTA system determines areal densities in a sample, measurements were performed with a Pu pellet-type sample as well as metallic plate samples of In and Ag. The experimental areal densities of Pu, In and Ag were consistent with those calculated for the individual nuclei. These results show that it is feasible to develop a compact NRTA system capable of determining the contents of nuclear materials in nuclear fuels. This research was implemented under the subsidy for nuclear security promotion of MEXT.

Development of a DDA+PGA-combined non-destructive active interrogation system in "Active-N"

古高 和禎; 大図 章; 藤 暢輔

Nuclear Engineering and Technology, 55(11), p.4002 - 4018, 2023/11

https://doi.org/10.1016/j.net.2023.07.015

An integrated neutron interrogation system has been developed for non-destructive assay of highly radioactive special nuclear materials, to accumulate knowledge of the method through developing and using it. The system combines a differential die-away (DDA) measurement system for the quantification of nuclear materials and a prompt gamma-ray analysis (PGA) system for the detection of neutron poisons which disturb the DDA measurements; a common D-T neutron generator is used. A special care has been taken for the selection of materials to reduce the background gamma rays produced by the interrogation neutrons. A series of measurements were performed to test the basic performance of the system. The results show that the DDA system can quantify plutonium of as small as 20~mg and it is not affected by intense neutron background up to 4.2~TBq and gamma ray of 2.2~TBq. As a result of the designing of the combined system as a whole, the gamma-ray background counting rate at the PGA detector was reduced down to s even with the use of the D-T neutron generator. The test measurements show that the PGA system is capable of detecting less than 1~g of boron compound and about 100~g of gadolinium compound in~30 min. This research was implemented under the subsidy for nuclear security promotion of MEXT.

Local electronic structure of interstitial hydrogen in MgH inferred from muon study

門野 良典*; 平石 雅俊*; 岡部 博孝*; 幸田 章宏*; 伊藤 孝

Journal of Physics; Condensed Matter, 35(28), p.285503_1 - 285503_13, 2023/07

https://doi.org/10.1088/1361-648X/acccc7

Magnesium hydride has great potential as a solid hydrogen (H) storage material because of its high H storage capacity of 7.6 wt%. However, its slow hydrogenation and dehydrogenation kinetics and the high temperature of 300 C required for decomposition are major obstacles to small-scale applications such as automobiles. The local electronic structure of interstitial H in MgH is an important fundamental knowledge in solving this problem, which has been studied mainly based on density functional theory (DFT). However, few experimental studies have been performed to assess the results of DFT calculations. We have therefore introduced muon (Mu) as pseudo-H into MgH and investigated the corresponding interstitial H states by analyzing their electronic and dynamical properties in detail. As a result, we observed multiple Mu states similar to those observed in wide-gap oxides, and found that their electronic states can be attributed to relaxed-excited states associated with donor/acceptor levels predicted by the recently proposed ambipolarity model. This provides an indirect support for the DFT calculations on which the model is based via the donor/acceptor levels. An important implication of the muon results for improved hydrogen kinetics is that dehydrogenation, serving as a reduction for hydrides, stabilises the interstitial H state.

A Study on convection in molten zone of aluminum alloy during Fe/Al resistance spot welding

伊與田 宗慶*; 松田 朋己*; 佐野 智一*; 茂田 正哉*; 菖蒲 敬久; 湯本 博勝*; Koyama, Takahisa*; Yamazaki, Hiroshi*; 仙波 泰徳*; 大橋 治彦*; et al.

Journal of Manufacturing Processes, 94, p.424 - 434, 2023/05

https://doi.org/10.1016/j.jmapro.2023.03.032

Aluminum alloys are increasingly being applied to automobile bodies to reduce the weight of automobiles. In joining steel materials and aluminum alloys using resistance spot welding (RSW), it is important to control the state of intermetallic compounds due to the temperature at the joining interface. In other words, in RSW of Fe/Al dissimilar materials, it is necessary to clarify the heating and cooling phenomena of the interface temperature during joining. Although the convection behavior of the molten aluminum alloy is thought to influence the temperature distribution at the joining interface, there are no studies that have directly observed this phenomenon. In this study, convection in molten zone of aluminum alloy during RSW of steel and aluminum alloy is discussed. Direct observations were attempted in order to clarify the convection behavior of the molten aluminum alloy in RSW of steel and aluminum alloy. The main feature of this experiment is that a real-scale test piece and an RSW apparatus used in actual production were used to observe convection during actual production. The observation experiments were conducted using synchrotron radiation X-ray at SPring-8. During welding, the specimens were irradiated with synchrotron radiation X-ray, and convection was observed from the behavior of tracer particles placed on the specimens. As a results, three types of convection were observed: radial outward convection from the center of the molten zone at the joining interface, convection from the edge of the molten zone toward its center, and weak circulating convection at the edge of the molten zone. And, small convection velocities were generated at the edge of the molten zone. Furthermore, the convection velocity inside the molten zone was calculated to be approximately 1.75 m/s. In addition, it was shown that there is a correlation between convection behavior and the shape of the molten zone.

JAEA/ISCN delayed gamma-ray spectroscopy inverse Monte Carlo development status

Rodriguez, D.; Rossi, F.

Proceedings of INMM & ESARDA Joint Annual Meeting 2023 (Internet), 9 Pages, 2023/05

Under the MEXT subsidy for the improvement of nuclear security related activities, we will present on the current and future progress of the delayed gamma-ray spectroscopic analysis development. We highlight a paper soon to be released and the plan for finalizing the project goal.

Short-range spin order in paramagnetic AgCrSe

中村 惇平*; 川北 至信; 岡部 博孝*; Li, B.*; 下村 浩一郎*; 末益 崇*

Journal of Physics and Chemistry of Solids, 175, p.111199_1 - 111199_8, 2023/04

https://doi.org/10.1016/j.jpcs.2022.111199

Muon spin rotation (SR) experiments were performed to directly investigate the temperature dependence of the short-range order or correlations of chromium spins in the paramagnetic phase of AgCrSe. The detailed investigation of the SR spectra over a wide temperature range from low to high temperatures revealed that the short-range spin correlations developed below about 184 K. It also confirmed no short-range correlations at high temperatures, which had been controversial in previous quasi-elastic neutron scattering studies. In addition, the muon spin relaxation was qualitatively changed and showed large missing asymmetry below about 89 K, where the correlation clearly implied short-range spin order. There could be a preparative phenomenon of the phase transition or an anisotropic short-range spin correlation.

Covariance of resonance parameters ascribed to systematic uncertainties in experiments

遠藤 駿典; 木村 敦; 中村 詔司; 岩本 修; 岩本 信之; Rovira Leveroni, G.

EPJ Web of Conferences, 281, p.00012_1 - 00012_5, 2023/03

https://doi.org/10.1051/epjconf/202328100012

In resonance analysis, experimental uncertainties affect the accuracy of resonance parameters. A resonance analysis code REFIT can consider the statistical uncertainty of the experimental data in evaluation of the resonance parameter uncertainty. On the other hand, since the systematic uncertainties of the sample thickness and normalization, which is proportional to the cross-section, are not independent at each measurement point, they must be treated differently from the statistical uncertainty. However, their treatment has not been discussed in detail so far. In this study, we evaluated the effect of the systematic uncertainties of experimental data on deduced resonance parameters by varying sample-thickness values used for the REFIT code. Covariance of resonance parameters ascribed to systematic uncertainties were evaluated from the neutron transmission data of natural zinc measured at the J-PARC MLF ANNRI. We will introduce this evaluation method and discuss the feature of obtained correlations.