Theoretical verification of test results for self-powered radiation detectors; Comparison of Co gamma irradiation test results with calculated results

Takeda, Ryoma; Shibata, Hiroshi; Takeuchi, Tomoaki; Nakano, Hiroko; Seki, Misaki; Ide, Hiroshi

JAEA-Testing 2024-007, 33 Pages, 2025/03

JAEA-Testing-2024-007.pdf:1.63MB

Japan Materials Testing Reactor (JMTR) in Oarai Research and Development Institute of the Japan Atomic Energy Agency (JAEA) has been developing various reactor materials, irradiation techniques and instruments for more than 30 years. Among them, the development of self-powered neutron detectors (SPNDs) and gamma detectors (SPGDs) has been carried out, and several research results have been reported. In this report, we compare and verify these test results with the theoretical output results obtained by the calculation code created in the JAEA report (JAEA-Data/Code 2021-018). The comparison was made with the irradiation test results of SPGD, a cobalt-60 gamma irradiation facility. As a result, it was found that the calculation results reproduced the test results well when the emitter diameter was relatively small compared to the range of Compton scattered electrons by the gamma rays. On the other hand, when the emitter diameter is relatively large, the output current in the test results is only about half of the calculated output current. The self-shielding effect of the emitter may be one of the reasons for the difference in the emitter diameter, and a new formulation, such as incorporating the effect of self-shielding caused by a larger emitter diameter or a non-isotropic -ray field as a change in the mean electron range or mean minimum energy in the calculation code, is necessary. The new formulation is necessary.

Modelling transport pathways of faults with low hydraulic connectivity in mudstones with low swelling capacity

Ono, Hirokazu; Ishii, Eiichi; Takeda, Masaki

Geoenergy (Internet), 2(1), p.geoenergy2023-047_1 - geoenergy2023-047_10, 2024/12

https://doi.org/10.1144/geoenergy2023-047

Large spontaneous Hall effect with flexible domain control in the antiferromagnetic material TaMnP

Kotegawa, Hisashi*; Nakamura, Akira*; Huyen, V. T. N.*; Arai, Yuki*; To, Hideki*; Sugawara, Hitoshi*; Hayashi, Junichi*; Takeda, Keiki*; Tabata, Chihiro; Kaneko, Koji; et al.

Physical Review B, 110(21), p.214417_1 - 214417_8, 2024/12

https://doi.org/10.1103/PhysRevB.110.214417

Study on public exposure risk assessment for dismantling of radioactive components in decommissioning phase of nuclear reactor facilities

Shimada, Taro; Kabata, Kazuhiko*; Takai, Shizuka; Takeda, Seiji

Proceedings of Probabilistic Safety Assessment and Management & Asian Symposium on Risk Assessment and Management (PSAM17 & ASRAM2024) (Internet), 10 Pages, 2024/10

Nuclear regulatory inspections during the decommissioning phase of nuclear power plants need to be conducted based on risk information, but a method for quantitatively evaluating this risk has not been developed. Therefore, in this study, an event tree of accident events that may occur in the decommissioning phase has been developed, and a code DecAssess-R has been developed to evaluate the exposure risk, which is expressed as the product of the exposure dose and probability of occurrence according to the accident sequence for each equipment to be dismantled. In particular, we have taken into account that the amount of mobile radioactivity that may accumulate in HEPA filters and be released all at once during an accident varies temporally and spatially with the progress of dismantling work. The event tree was constructed based on the results of the survey of domestic and international trouble information in the decommissioning phase and similar dismantling and replacement operations. The event frequencies are based on information from general industries, and the event progression probabilities are based on the equipment failure probabilities in the operation phase. The safety functions to be reduced with the progress of decommissioning were taken into account according to the dismantling work schedule. As a result of the exposure risk assessment for dismantling operations of BWRs and PWRs in Japan, the exposure risk for fire events was the largest. In particular, the exposure risk was greater for the dismantling of components in the reactor building by airborne cutting than for the dismantling of reactor internals, which has the greatest radioactivity in underwater dismantling.

Procedure on confirmation of completion of decommissioning of nuclear facilities (Contract research)

Shimada, Taro; Shimada, Asako; Miwa, Kazuji*; Nabekura, Nobuhide*; Sasaki, Toshihisa*; Takai, Shizuka; Takeda, Seiji

JAEA-Research 2024-004, 115 Pages, 2024/06

JAEA-Research-2024-004.pdf:6.02MB

We have studied the confirmation method for the termination of decommissioning of nuclear facilities based on the site release flow presented at the Nuclear Regulation Authority (NRA) study team meeting in 2017, and organized it as a procedure for the site soil. First, the effects of radionuclides released by the Fukushima Daiichi Nuclear Power Station accident are excluded as background radioactivity, and the distribution of radioactivity concentration of facility origin on the site is evaluated using geostatistical method kriging. Then, considering the downstream transport of sediment by surface runoff generated by rainfall that exceeds the infiltration capacity of the ground surface, a series of evaluation procedures are presented to evaluate the exposure dose reflecting future changes from the evaluated radioactivity concentration distribution, and a comparison method with the assumed 0.01 mSv/y as a dose criterion is proposed. Furthermore, an example of the procedure for evaluating the distribution of contamination in the subsurface was also presented for the case where groundwater is affected.

Joint clarification of contaminant plume and hydraulic transmissivity via a geostatistical approach using hydraulic head and contaminant concentration data

Takai, Shizuka; Shimada, Taro; Takeda, Seiji; Koike, Katsuaki*

Mathematical Geosciences, 56(2), p.333 - 360, 2024/02

https://doi.org/10.1007/s11004-023-10084-8

To enable proper remediation of accidental groundwater contamination, the contaminant plume evolution needs to be accurately estimated. In the estimation, uncertainties in both the contaminant source and hydrogeological structure should be considered, especially the temporal release history and hydraulic transmissivity. Although the release history can be estimated using geostatistical approaches, previous studies use the deterministic hydraulic property field. Geostatistical approaches can also effectively estimate an unknown heterogeneous transmissivity field via the joint data use, such as a combination of hydraulic head and tracer data. However, tracer tests implemented over a contaminated area necessarily disturb the in situ condition of the contamination. Conversely, measurements of the transient concentration data over an area are possible and can preserve the conditions. Accordingly, this study develops a geostatistical method for the joint clarification of contaminant plume and transmissivity distributions using both head and contaminant concentration data. The applicability and effectiveness of the proposed method are demonstrated through two numerical experiments assuming a two-dimensional heterogenous confined aquifer. The use of contaminant concentration data is key to accurate estimation of the transmissivity. The accuracy of the proposed method using both head and concentration data was verified achieving a high linear correlation coefficient of 0.97 between the true and estimated concentrations for both experiments, which was 0.67 or more than the results using only the head data. Furthermore, the uncertainty of the contaminant plume evolution was successfully evaluated by considering the uncertainties of both the initial plume and the transmissivity distributions, based on their conditional realizations.

Evaluation of the remaining spent extraction solvent in vermiculite after leaching tests via PIXE analysis

Arai, Yoichi; Watanabe, So; Hasegawa, Kenta; Okamura, Nobuo; Watanabe, Masayuki; Takeda, Keisuke*; Fukumoto, Hiroki*; Ago, Tomohiro*; Hagura, Naoto*; Tsukahara, Takehiko*

Nuclear Instruments and Methods in Physics Research B, 542, p.206 - 213, 2023/09

https://doi.org/10.1016/j.nimb.2023.07.003

Study on borehole sealing corresponding to hydrogeological structures by groundwater flow analysis

Sawaguchi, Takuma; Takai, Shizuka; Sasagawa, Tsuyoshi; Uchikoshi, Emiko*; Shima, Yosuke*; Takeda, Seiji

MRS Advances (Internet), 8(6), p.243 - 249, 2023/06

https://doi.org/10.1557/s43580-023-00528-y

In the intermediate depth disposal of relatively high-level radioactive waste, a method to confirm whether the borehole for monitoring is properly sealed should be developed in advance. In this study, groundwater flow analyses were performed for the hydrogeological structures with backfilled boreholes, assuming sedimentary rock area, to understand what backfill design conditions could prevent significant water pathways in the borehole, and to identify the confirmation points of borehole sealing. The results indicated the conditions to prevent water pathways in the borehole and BDZ (Borehole Disturbed Zone), such as designing the permeability of bentonite material less than or equal to that of the host rock, and grouting BDZ.

Fact-finding survey on the competencies and literacy of radiological technologists regarding radiation disasters

Arai, Tomohiro*; Murata, Sho*; Watanabe, Yuichi*; Ishihara, Toshihiro*; Fukamizu, Yoshiya*; Takeda, Satoshi*; Ebata, Kiyokadzu*; Watanabe, Yuki; Takashima, Yoshio*; Kaneko, Junichi*

Journal of X-Ray Science and Technology, 31(2), p.237 - 245, 2023/03

https://doi.org/10.3233/XST-221341

Radiological technologists have received specialized education about radiation and serve as risk communicators who aim to lessen patients' anxiety about radiation exposure, in addition to performing radiological examinations in routine clinical practice. Also, Radiological technologists across Japan were dispatched to the affected area to conduct an essential procedure-screening the belongings and body surfaces of evacuees for contamination at the nuclear disaster at the Fukushima Daiichi Nuclear Power Plant operated by Tokyo Electric Power Company in March 2011. In this study, we conducted a fact-finding survey on knowledge and awareness of radiation disasters among radiological technologists at National Hospital Organization facilities in Japan to reveal their literacy and competencies regarding radiation disasters. Also, we compared the knowledge and awareness of radiation disasters among Japanese radiological technologists between nuclear power station areas and non-nuclear power station areas and discuss ideal human resource development for radiological technologists to be ready to serve during a radiation disaster.

Evaluating the effectiveness of a geostatistical approach with groundwater flow modeling for three-dimensional estimation of a contaminant plume

Takai, Shizuka; Shimada, Taro; Takeda, Seiji; Koike, Katsuaki*

Journal of Contaminant Hydrology, 251, p.104097_1 - 104097_12, 2022/12

https://doi.org/10.1016/j.jconhyd.2022.104097

When assessing the risk from an underground environment that is contaminated by radioactive nuclides and hazardous chemicals and planning for remediation, the contaminant plume distribution and the associated uncertainty from measured data should be estimated accurately. While the release history of the contaminant plume may be unknown, the extent of the plume caused by a known source and the associated uncertainty can be calculated inversely from the concentration data using a geostatistical method that accounts for the temporal correlation of its release history and groundwater flow modeling. However, the preceding geostatistical approaches have three drawbacks: (1) no applications of the three-dimensional plume estimation in real situations, (2) no constraints for the estimation of the plume distribution, which can yield negative concentration and large uncertainties, and (3) few applications to actual cases with multiple contaminants. To address these problems, the non-negativity constraint using Gibbs sampling was incorporated into the geostatistical method with groundwater flow modeling for contaminant plume estimation. This method was then tested on groundwater contamination in the Gloucester landfill in Ontario, Canada. The method was applied to three water soluble organic contaminants: 1,4-dioxane, tetrahydrofuran, and diethyl ether. The effectiveness of the proposed method was verified by the general agreement of the calculated plume distributions of the three contaminants with concentration data from 66 points in 1982 (linear correlation coefficient of about 0.7). In particular, the reproduced large spill of organic contaminants of 1,4-dioxane in 1978 was more accurate than the result of preceding minimum relative entropy-based studies. The same peak also appeared in the tetrahydrofuran and diethyl ether distributions approximately within the range of the retardation factor derived from the fraction of organic carbon.