Study on the evaluation method of radioactivity for dismantling wastes generated from test and research reactors using ORIGEN attached to SCALE6.2.4

Tomioka, Dai; Kochiyama, Mami; Ozone, Kenji; Nakata, Hisakazu; Sakai, Akihiro

JAEA-Technology 2024-023, 38 Pages, 2025/03

JAEA-Technology-2024-023.pdf:1.54MB

Japan Atomic Energy Agency is an implementing organization of near-surface disposal for low-level radioactive wastes generated from research, industrial and medical facilities in Japan. Information on the radioactivity concentration of these radioactive wastes is dispensable for the design and conformity assessment of the waste disposal facilities for the licensing application of the disposal project and its safety review. Radioactive Wastes Disposal Center has been improving the radioactivity evaluation procedure for the dismantling waste generated from the research reactors based on the activation calculation. In order to investigate the applicability of the ORIGEN code (included in SCALE6.2.4), which enables more accurate activation calculations using multigroup neutron spectra, we performed activation calculations with the ORIGEN-code and the ORIGEN-S code (included in SCALE6.0), which has been widely used in the past, for the dismantled wastes from the Rikkyo University Research Reactor, where radioactivity analysis data for the structural materials around the reactor core were compiled. As a result, the calculation time difference between ORIGEN and ORIGEN-S was small and the evaluated radioactivity concentrations of the former were in the range of 0.8-1.0 times those of the latter, which was in good agreement with those of radiochemical analysis in the range of 0.5-3.0 times. The applicability of ORIGEN was confirmed. In addition, activation calculations assuming trace elements in structural materials of nuclear reactor were performed with ORIGEN and ORIGEN-S and the results were compared. The causes of the large differences among 170 nuclides that are important for dose assessment in near-surface disposal were assessed each nuclide.

Development of gas entrainment evaluation model based on distribution of pressure along vortex center line; Application to a gas entrainment experiment with traveling vortices in an open water channel flow?

Matsushita, Kentaro; Ezure, Toshiki; Tanaka, Masaaki; Imai, Yasutomo*; Fujisaki, Tatsuya*; Sakai, Takaaki*

Nuclear Engineering and Design, 432, p.113785_1 - 113785_16, 2025/02

https://doi.org/10.1016/j.nucengdes.2024.113785

Establishing an evaluation method for the gas entrainment (GE) of argon cover gas due to surface vortices is required in terms of safety design of sodium-cooled fast reactors. To modify the evaluation model in an in-house evaluation tool for GE, StreamViewer, a modified evaluation model on the pressure distribution along the vortex center line (PVL model) was proposed to identify the vortex center lines by connecting continuous vortex center points from the suction port to the surface and evaluate gas core length based on the balance between the hydrostatic pressure and the pressure decrease distribution along the vortex center line. PVL model was applied the three-dimensional numerical analysis results for the experiments where a plate induced unsteady traveling vortices in the open channel flow. Consequently, the GE evaluation using StreamViewer with PVL model could reproduce the relation between the inlet flow velocity and the gas core length in the unsteady vortex flow experiments.

Assessment of individual external exposure doses based on environmental radiation in areas affected by the Fukushima Daiichi Nuclear Power Station accident

Sato, Rina; Yoshimura, Kazuya; Sanada, Yukihisa; Mikami, Satoshi; Yamada, Tsutomu*; Nakasone, Takamasa*; Kanaizuka, Seiichi*; Sato, Tetsuro*; Mori, Tsubasa*; Takagi, Marie*

Environmental Science & Technology, 194, p.109148_1 - 109148_8, 2024/12

https://doi.org/10.1016/j.envint.2024.109148

Assessment of individual external doses from ambient dose equivalents is used for predictive and retrospective assessments where personal dosimeters are not applicable. However, it tends to contain more errors than assessment by personal dosimetry due to various parameters. Therefore, in order to accurately assess the individual dose from ambient dose equivalents, a model that estimates effective doses considering life patterns and the shielding effects by buildings and vehicles, were developed in this study. The model parameters were examined using robust datasets of environmental radiation measured in the areas affected by the Fukushima Daiichi Nuclear Power Station accident in 2020 to 2021. The accuracy of the model was validated by comparison with 106 daily personal doses measured in Fukushima Prefecture in 2020. The measured personal dose was well reproduced by the model-estimated effective dose, showing that the model can be used to assess the individual exposure dose, similar to personal dosimetry. Furthermore, this model is an effective tool for radiation protection, as it can estimate the individual dose predictively and retrospectively by using environmental radiation data.

Nuclear fuel storage container opening inspection and metal inner container repacking

Licensing Application Group, Fuels and Materials Department

JAEA-Testing 2024-002, 20 Pages, 2024/08

JAEA-Testing-2024-002.pdf:1.46MB

The contamination accident occurred at Plutonium Fuel Research Facility (PFRF) in Japan Atomic Energy Agency (JAEA) Oarai Research and Development Institute on June 6, 2017. During the work of opening the fuel storage container and checking the properties of the contents, the plastic bag that double-packed the inner container burst. The scattering of the fuels contaminated the work room and exposed the worker. The cause of the plastic bag burst was that the enclosed epoxy resin was decomposed by -rays and the internal pressure increased due to the generated hydrogen gas. The 54 storage containers containing plutonium held at PFRF also at risk of increasing internal pressure. Therefore, an opening inspection was conducted to confirm the contents of the storage container in the hot cell. In addition, the contents of storage containers that may generate gas were stabilized. We are planning to transport the fuel storage containers out to another facility for the decommission of PFRF. The other 9 storage containers include oxide raw material powder: Pu + U in excess of 220 g. In order to decrease to less than 220 g (the limit of transport cask), the metal inner containers in the storage container were taken out and repacked in another storage container. This report describes advance measures such as permit application and the details of about storage container opening inspection and metal inner container repacking.

Study on the evaluation methodology of the radioactivity concentration in low-level radioactive concrete wastes generated from JPDR

Aono, Ryuji; Haraga, Tomoko; Kameo, Yutaka

JAEA-Technology 2024-006, 48 Pages, 2024/06

JAEA-Technology-2024-006.pdf:1.77MB

In the future, radioactive waste which generated from nuclear research facilities in Japan Atomic Energy Agency are planning to be buried for the near surface disposal. It is necessary to establish the method to evaluate the radioactivity concentrations of the radioactive wastes. In this work, we studied the evaluation methodology of the radioactivity concentrations in concrete waste generated from JPDR. In order to construct the evaluation methodology of the radioactivity concentration, the validity of the evaluation methods was confirmed by mainly theoretical calculation and using the result of radiochemical analysis. Correcting the theoretical calculations using results of nuclide analysis, it is possible to evaluate the radioactivity concentrations of nuclides preliminary selected.

Perpendicular magnetic anisotropy of thin films

Takanashi, Koki; Seki, Takeshi*

Magune, 19(3), p.100 - 106, 2024/06

Perpendicular magnetic anisotropy of thin films currently plays an important role in spintronics as well as magnetic recording. Regarding perpendicular magnetic anisotropy, in this article, the fundamentals, the research history, and the recent research trends are reviewed, showing specific examples with perpendicular magnetization such as magnetic multilayers, ordered alloy films, rare earth-transition metal amorphous alloy films, and inhomogeneous or granular films. The physical origins for perpendicular magnetic anisotropy, including interface anisotropy due to structural symmetry breaking, magnetoelastic anisotropy due to strain, bulk-type magnetocrystalline anisotropy, and directional pair ordering of atoms, are discussed in each example.

In-situ neutron diffraction study of serration-involved ultra-cryogenic deformation behavior at 15 K

Kim, Y. S.*; Chae, H.*; Lee, D.-Y.*; Han, J. H. *; Hong, S.-K.*; Na, Y. S.*; Harjo, S.; Kawasaki, Takuro; Woo, W.*; Lee, S.-Y.*

Materials Science & Engineering A, 899, p.146453_1 - 146453_7, 2024/05

https://doi.org/10.1016/j.msea.2024.146453

Archie's cementation factors for natural rocks; Measurements and insights from diagenetic perspectives

Yuan, X.*; Hu, Q. H.*; Fang, X.*; Wang, Q. M.*; Ma, Y.*; Tachi, Yukio

Sedimentary Geology, 465, p.106633_1 - 106633_14, 2024/05

https://doi.org/10.1016/j.sedgeo.2024.106633

Investigations and consideration on contamination inspection and decontamination criteria at a nuclear emergency

Togawa, Orihiko; Hokama, Tomonori; Hiraoka, Hirokazu; Saito, Shota

JAEA-Research 2023-011, 78 Pages, 2024/03

JAEA-Research-2023-011.pdf:2.09MB

When radionuclides are released into the atmospheric environment at a nuclear emergency, protective measures such as evacuation and temporal relocation are carried out using motor vehicles such as private cars and buses to reduce radiation exposure to residents. To confirm conditions of contamination for the evacuated/relocated residents and the used motor vehicles, contamination inspection is conducted in the middle of the route from border areas of Nuclear Emergency Planning Zone to evacuation shelters. In the present inspection in Japan, a value of OIL4 = 40,000 cpm is used as decontamination criteria. For the details and derivation methods of the value, however, no official documents are found which give systematically detailed descriptions and explanation. It is also recognized that even few experts on nuclear emergencies can explain these subjects in detail as a whole. In order to explain scientifically and technically the OIL4 value of decontamination criteria used in contamination inspection in Japan, this report aims at investigating and estimating the deviation methods of OIL4, and examining and considering these results. To achieve the objectives, we show the bases for decontamination criteria, and investigate and estimate the derivation methods for limits of a surface contamination density corresponding to the generic criteria for each exposure pathway. Moreover, we give the OIL4 value some consideration and suggestions from a viewpoint of positioning and feature of OIL4 in Japan, and cautionary points at revising the value.

Preparation of waste standards; Annual report 2022

Project Promotion Department; Radioactive Wastes Disposal Center

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

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

For near surface disposal of radioactive wastes generated from research, industrial and medical facilities, Japan Atomic Energy Agency has discussed methods for corresponding to the technical standards on confirmation related to waste disposal, etc. From FY2022, we have established Waste Standards Committee and interim Waste Acceptance Criteria, Waste Package Confirmation Procedure, etc. have been considered. In FY2022, Waste Package Confirmation Procedures of solidified liquid waste and cement filled waste and related standards were discussed. In addition, issues of preparation of Waste Package Confirmation Procedure and rational treatment method for decommissioning wastes were considered. This annual report summarizes the results of discussion in FY2022.