Design and characterization of the fission signature assay instrument for nuclear safeguards

Rossi, F.; 小泉 光生; Rodriguez, D.; 高橋 時音

Proceedings of INMM & ESARDA Joint Annual Meeting 2023 (Internet), 5 Pages, 2023/05

Since 2015, the Integrated Support Center for Nuclear Nonproliferation and Nuclear Security (ISCN) of the Japan Atomic Energy Agency has been working on the development of the Delayed Gamma-ray Spectroscopy non-destructive assay technique for the quantification of fissile-nuclide content in mixed nuclear materials. Thanks to the efforts and lessons learned from past experiments, the ISCN has successfully designed and fabricated a final integrated instrument. The instrument is composed of a moderator and dose shield where different neutron sources, like Cf-252 and neutron generators, can be inserted to irradiate the sample. Within the moderator, a series of neutron detectors are installed for perform prompt neutron analysis and continuous monitoring of the neutron source emission. Thanks to an innovative transfer system, the sample is then moved to the gamma-ray detector in less than 1.5s providing a fast and reliable movement while being safe from possible contamination. In this work, we will describe the design details of this new instrument. This work is supported by the Japanese Ministry of Education, Culture, Sports, Science, and Technology (MEXT) under the subsidy for the "promotion for strengthening nuclear security and the like".

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.

Sorption of Cs and Eu ions onto sedimentary rock in the presence of gamma-irradiated humic acid

Zhao, Q.*; 齊藤 毅*; 宮川 和也; 笹本 広; 小林 大志*; 佐々木 隆之*

Journal of Hazardous Materials, 428, p.128211_1 - 128211_10, 2022/04

https://doi.org/10.1016/j.jhazmat.2021.128211

令和2年度以降の幌延深地層研究計画において原子力機構が取り組んでいる課題の1つである「実際の地質環境における人工バリアの適用性確認」では、坑道周辺の掘削損傷領域において物質移行に関するデータの取得が必要である。本研究では、地下水中に含まれる腐植物質であるフミン酸に着目し、放射線によるフミン酸の分解反応がCsイオンとEuイオンの収着能へ与える影響について、幌延地域の堆積岩を例として調べた。放射線を照射していないフミン酸の存在下では、Euはフミン酸と錯体を形成することで、岩石への収着能は低下する。一方で、放射線の照射によりフミン酸が分解されると、岩石へ収着するEuイオンが増加することが確認された。また、Csの岩石への収着能はフミン酸の影響を受けることが無く、また、放射線により分解されたフミン酸の影響も見られないことが分かった。以上のことから、廃棄体の近傍ではフミン酸の放射線分解により、岩石への収着するEuイオンの割合が大きくなることが考えられる。

Development and testing of a delayed gamma-ray spectroscopy instrument utilizing Cf-252 neutrons evaluated for nuclear safeguards applications

Rodriguez, D.; Abbas, K.*; 小泉 光生; Nonneman, S.*; Rossi, F.; 高橋 時音

Nuclear Instruments and Methods in Physics Research A, 1014, p.165685_1 - 165685_10, 2021/10

https://doi.org/10.1016/j.nima.2021.165685

Under the MEXT subsidy on research for improving nuclear security related development, we designed the Delayed Gamma-ray Californium Test (DGCT) instrument. From He-3 count-rate experiments performed in collaboration with the European Commission Joint Research Centre, we show the effective neutron flux entering the sample space. Further, we show delayed gamma-ray spectra of both U and Pu samples as well as a comparison to the background from Cf activation of the environment. Finally, we make comparisons to earlier spectra obtained using PUNITA, including relative fission capability, spectral signature, and mass correlations.

Development of delayed gamma-ray spectroscopy for nuclear safeguards, 2; Designing a compact DGS instrument

Rossi, F.; Abbas, K.*; 小泉 光生; Lee, H.-J.; Rodriguez, D.; 高橋 時音

Proceedings of INMM & ESARDA Joint Virtual Annual Meeting (Internet), 7 Pages, 2021/08

The Japan Atomic Energy Agency is developing the Delayed Gamma-ray Spectroscopy (DGS) non-destructive assay technique to quantify the fissile-nuclide content in small samples of mixed nuclear materials. One of our primary goals is to develop a compact and efficient DGS instrument to be easily installable into analytical laboratories. The instrument should include an external neutron source and a gamma-ray detection system along with other supporting systems like sample transfer and neutron monitoring. One of the challenges is to design a compact and efficient moderator for commercial neutron sources (e.g. neutron generators or sealed radioactive sources) that emit neutrons with high energy. However, to be able to enhance the gamma-ray signal from fissile materials, thermal neutrons are best due to their higher fission cross-sections. The choice of viable neutron source (neutron spectrum and strength) depends on several considerations (e.g. sample type and interrogation pattern), but also affect the gamma-ray measurement and the consequence analysis. In this work, we will first describe the evaluation results of our Delayed Gamma-ray Test Spectrometer using a Cf source (DGTS-C) from the first experiment carried out in PERLA in collaboration with the European Commission, Joint Research Centre. In association, we will describe how it provided guidance for our demonstration irradiator. Further, we will present our final moderator design concept for a deuterium-deuterium (D-D) neutron generator and present the latest results of data-model comparisons, including those with our PUNITA results. This work is supported by the Japanese Ministry of Education, Culture, Sports, Science, and Technology (MEXT) under the subsidy for the "promotion for strengthening nuclear security and the like". This work was done under the agreement between JAEA and EURATOM in the field of nuclear material safeguards research and development.

3D position and radioactivity estimation of radiation source by a simple directional radiation detector combined with structure from motion

佐藤 優樹; 峯本 浩二郎*; 根本 誠*

Radiation Measurements, 142, p.106557_1 - 106557_6, 2021/03

https://doi.org/10.1016/j.radmeas.2021.106557

It is important to visualize radioactive substances' position and distribution and estimate their radioactivity levels to reduce the exposure dose of workers in radioactive areas (such as decommissioning worksites of nuclear power stations) and improve nuclear security functions. To visualize the radioactive substance's three-dimensional (3D) location, a directional radiation detector with a cylindrical shield on a simple single-pixel gamma-ray detector was applied to the structure from motion (SfM) technology using an ordinary digital camera. Verification was performed by a system that combines SfM with a CdTe sensor probe having narrow directivity. Am radiation source's position was visualized by drawing the radiation source's image acquired by the gamma-ray detector on the work area 3D model reconstructed through SfM. Furthermore, as SfM is a simultaneous localization and mapping technology, the system measures the gamma rays while measuring the gamma-ray detector's dynamic position and posture information. The measurements can be acquired while the gamma-ray detector is freely moving in the work area. These methods visualized the radiation source's position and quantitatively estimated the radiation source's radioactivity.

Simulation analysis of the Compton-to-peak method for quantifying radiocesium deposition quantities

Malins, A.; 越智 康太郎; 町田 昌彦; 眞田 幸尚

Proceedings of Joint International Conference on Supercomputing in Nuclear Applications + Monte Carlo 2020 (SNA + MC 2020), p.147 - 154, 2020/10

Compton-to-peak analysis is a method for selecting suitable coefficients to convert count rates measured with in situ gamma ray spectrometry to radioactivity concentrations of Cs & Cs in the environment. The Compton-to-peak method is based on the count rate ratio of the spectral regions containing Compton scattered gamma rays to that with the primary Cs & Cs photopeaks. This is known as the Compton-to-peak ratio (RCP). RCP changes as a function of the vertical distribution of Cs & Cs within the ground. Inferring this distribution enables the selection of appropriate count rate to activity concentration conversion coefficients. In this study, the PHITS Monte Carlo radiation transport code was used to simulate the dependency of RCP on different vertical distributions of Cs & Cs within the ground. A model was created of a LaBr(Ce) detector used in drone helicopter aerial surveys in Fukushima Prefecture. The model was verified by comparing simulated gamma ray spectra to measurements from test sources. Simulations were performed for the infinite half-space geometry to calculate the dependency of RCP on the mass depth distribution (exponential or uniform) of Cs & Cs within the ground, and on the altitude of the detector above the ground. The calculations suggest that the sensitivity of the Compton-to-peak method is greatest for the initial period following nuclear fallout when Cs & Cs are located close to the ground surface, and for aerial surveys conducted at low altitudes. This is because the relative differences calculated between RCP with respect to changes in the mass depth distribution were largest for these two cases. Data on the measurement height above and on the Cs & Cs activity ratio is necessary for applying the Compton-to-peak method to determine the distribution and radioactivity concentration of Cs & Cs in the ground.

ナノ粒子を用いた透明遮へい材の開発研究(委託研究); 平成30年度英知を結集した原子力科学技術・人材育成推進事業

廃炉国際共同研究センター; 九州大学*

JAEA-Review 2019-039, 104 Pages, 2020/03

JAEA-Review-2019-039.pdf:5.57MB

日本原子力研究開発機構(JAEA)廃炉国際共同研究センター(CLADS)では、平成30年度英知を結集した原子力科学技術・人材育成推進事業(以下、「本事業」という)を実施している。本事業は、東京電力ホールディングス福島第一原子力発電所の廃炉等をはじめとした原子力分野の課題解決に貢献するため、国内外の英知を結集し、様々な分野の知見や経験を、従前の機関や分野の壁を越えて緊密に融合・連携させた基礎的・基盤的研究及び人材育成を推進することを目的としている。平成30年度の新規採択課題から実施主体を文部科学省からJAEAに移行することで、JAEAとアカデミアとの連携を強化し、廃炉に資する中長期的な研究開発・人材育成をより安定的かつ継続的に実施する体制を構築した。本研究は、研究課題のうち、平成30年度「ナノ粒子を用いた透明遮へい材の開発研究」について取りまとめたものである。本研究は、燃料デブリ取り出しや分析における作業員の被ばく低減や遠隔カメラの光学系・電子系の劣化低減を目的として、遮へい材料をナノ粒子化してエポキシ樹脂に分散・固化することにより透明な遮へい体を開発する。BCやWをナノ粒子化して中性子とガンマ線を同時に遮へいし、中性子から生じる二次ガンマ線も抑制する遮へい体を開発する。

Calculation of gamma and neutron emission characteristics emitted from fuel debris of Fukushima Daiichi Nuclear Power Station

Riyana, E. S.; 奥村 啓介; 寺島 顕一

Journal of Nuclear Science and Technology, 56(9-10), p.922 - 931, 2019/09

https://doi.org/10.1080/00223131.2019.1621781

Determination of fuel debris location and distribution inside primary containment vessel of Fukushima Daiichi Nuclear Power Station is important to decide further decommissioning step and strategy. We calculate neutron flux produced from fuel debris and secondary particles photon resulted from neutron reaction with nuclides inside fuel debris, including direct photon emission from FPs in fuel debris. Neutron and gamma characteristics resulted from calculation could be use as basis for determination suitable spectrometer system or detector for searching, localizing and treatment of fuel debris.

Development of remote sensing technique using radiation resistant optical fibers under high-radiation environment

伊藤 主税; 内藤 裕之; 石川 高史; 伊藤 敬輔; 若井田 育夫

JPS Conference Proceedings (Internet), 24, p.011038_1 - 011038_6, 2019/01

https://doi.org/10.7566/JPSCP.24.011038

東京電力ホールディングス福島第一原子力発電所の原子炉圧力容器と格納容器の内部調査への適用を想定して、光ファイバーの耐放射線性を向上させた。原子炉圧力容器内の線量率として想定されている~1kGy/hレベルの放射線環境に適用できるよう、OH基を1000ppm含有した溶融石英コアとフッ素を4%含有した溶融石英クラッドからなるイメージ用光ファイバを開発し、光ファイバをリモートイメージング技術に応用することを試みた。イメージファイバの本数は先行研究時の2000本から実用レベルの22000本に増加させた。1MGyのガンマ線照射試験を行った結果、赤外線画像の透過率は照射による影響を受けず、視野範囲の空間分解能の変化も見られなかった。これらの結果、耐放射線性を向上させたイメージファイバを用いたプロービングシステムの適用性が確認できた。