Decommissioning of the Plutonium Research Building No.1 (Plan and Present Status)

Komuro, Michiyasu; Kanazawa, Hiroyuki; Kokusen, Junya; Shimizu, Osamu; Honda, Junichi; Harada, Katsuya; Otobe, Haruyoshi; Nakada, Masami; Inagawa, Jun

JAEA-Technology 2021-042, 197 Pages, 2022/03

JAEA-Technology-2021-042.pdf:16.87MB

Plutonium Research Building No.1 was constructed in 1960 for the purpose of establishing plutonium handling technology and studying its basic physical properties. Radiochemical research, physicochemical research and analytical chemistry regarding solutions and solid plutonium compounds had been doing for the research program in Japan Atomic Energy Agency (JAEA). In 1964, the laboratory building was expanded and started the researching plutonium-uranium mixed fuel and reprocessing of plutonium-based fuel, playing an advanced role in plutonium-related research in Japan. Since then, the research target has been expanded to include transplutonium elements, and it has functioned as a basic research facility for actinides. The laboratory is constructed by concrete structure and it has the second floor, equipped with 15 glove boxes and 4 chemical hoods. Plutonium Research Building No.1 was decided as one of the facilities to be decommissioned by Japan Atomic Energy Agency Reform Plan in September 2014. So far, the contamination survey of the radioactive materials in the controlled area, the decontamination of glove boxes, and the consideration of the equipment dismantling procedure have been performed as planned. The radioisotope and nuclear fuel materials used in the facility have been transfer to the other facilities in JAEA. The decommissioning of the facility is proceeding with the goal of completing by decommissioning the radiation controlled area in 2026. In this report, the details of the decommissioning plan and the past achievements are reported with the several data.

Decommissioning of the Uranium Enrichment Laboratory

Kokusen, Junya; Akasaka, Shingo*; Shimizu, Osamu; Kanazawa, Hiroyuki; Honda, Junichi; Harada, Katsuya; Okamoto, Hisato

JAEA-Technology 2020-011, 70 Pages, 2020/10

JAEA-Technology-2020-011.pdf:3.37MB

The Uranium Enrichment Laboratory in the Japan Atomic Energy Agency (JAEA) was constructed in 1972 for the purpose of uranium enrichment research. The smoke emitting accident on 1989 and the fire accident on 1997 had been happened in this facility. The research on uranium enrichment was completed in JFY1998. The decommissioning work was started including the transfer of the nuclear fuel material to the other facility in JFY2012. The decommissioning work was completed in JFY2019 which are consisting of removing the hood, dismantlement of wall and ceiling with contamination caused by fire accident. The releasing the controlled area was performed after the confirmation of any contamination is not remained in the target area. The radioactive waste was generated while decommissioning, burnable and non-flammable are 1.7t and 69.5t respectively. The Laboratory will be used as a general facility for cold experiments.

Conceptual study on parasitic low-energy RI beam production with in-flight separator BigRIPS and the first stopping examination for high-energy RI beams in the parasitic gas cell

Sonoda, Tetsu*; Katayama, Ichiro*; Wada, Michiharu*; Iimura, Hideki; Sonnenschein, V.*; Iimura, Shun*; Takamine, Aiko*; Rosenbusch, M.*; Kojima, Takao*; Ahn, D. S.*; et al.

Progress of Theoretical and Experimental Physics (Internet), 2019(11), p.113D02_1 - 113D02_12, 2019/11

AA2019-0315.pdf:1.37MB

https://doi.org/10.1093/ptep/ptz120

An in-flight separator, BigRIPS, at RIBF in RIKEN provides each experiment with specific nuclides separated from many nuclides produced by projectile fragmentation or in-flight fission. In this process, nuclides other than separated ones are discarded on the slits in BigRIPS, although they include many nuclides interested from the view point of nuclear structure. In order to extract these nuclides for parasitic experiments, we are developing a method using laser ion-source (PALIS). A test experiment with Se beam from RIBF has been performed by using a gas cell set in BigRIPS. Unstable nuclides around Se were stopped in the gas cell in accordance with a calculation using LISE code. The stopping efficiency has been estimated to be about 30%. As a next step, we will establish the technique for extracting reaction products from the gas cell.

Crack formation in cementitious materials used for an engineering barrier system and their impact on hydraulic conductivity from the viewpoint of performance assessment of a TRU Waste disposal system

Hirano, Fumio; Otani, Yoshiteru*; Kyokawa, Hiroyuki*; Mihara, Morihiro; Shimizu, Hiroyuki*; Honda, Akira

Nihon Genshiryoku Gakkai Wabun Rombunshi, 15(2), p.97 - 114, 2016/06

https://doi.org/10.3327/taesj.J15.015

A mechanical analysis code MACBECE2014 has been developed at the Japan Atomic Energy Agency to make realistic simulations of the physical integrity of the near-field for performance assessment of geological disposal of TRU waste in Japan. The MACBECE2014 code can be used to evaluate long-term changes in the mechanical behavior and any subsequent changes in the permeability of engineering barrier components, including crack formation in cementitious materials caused by expansion due to metal corrosion. Simulated results of the TRU waste disposal system with a bentonite buffer using the MACBECE2014 code demonstrated that the low permeability of the engineering barrier system could be maintained for long time periods after disposal because the physical integrity of the bentonite buffer remained intact. Simulated results of the disposal system with a concrete backfill, showed that crack formation leads to a significant increase in permeability of the system.

Numerical simulations and analysis for the SP pillar stability experiment, 2; Discontinuum based approaches using distinct element method

Shimizu, Hiroyuki*; Koyama, Tomofumi*; Chijimatsu, Masakazu*; Fujita, Tomoo; Nakama, Shigeo

Dai-13-Kai Iwa No Rikigaku Kokunai Shimpojiumu Koen Rombunshu (CD-ROM), p.443 - 448, 2013/01

DECOVALEX-2011 is an international cooperation project for enhancing the numerical models of radioactive waste repositories. In Task B of DECOVALEX-2011 project, the failure mechanism during excavation, heating and destressing processes observed in the sp pillar stability experiment (APSE), which carried out at the sp Hard Rock Laboratory by the Swedish Nuclear Fuel and Waste Management Company (SKB), were simulated using two dimensional Distinct Element Method. As a result, it is found that the simulated crack generation and propagation during the destressing process by 2D-DEM agree qualitatively well with the observation at site.

The Distinct element analysis for swelling pressure test of bentonite; Discussion on the effects of wall friction force and aspect ratio of specimen

Shimizu, Hiroyuki*; Kikuchi, Hirohito; Tanai, Kenji; Fujita, Tomoo

JAEA-Research 2011-024, 74 Pages, 2011/10

JAEA-Research-2011-024.pdf:7.23MB

For geological isolation systems for HLW, due to the lack of standardization of swelling test method for bentonite as a buffer material, the accuracy and reproducibility of the results are not sufficiently proved. In this study, bentonite swelling pressure test were simulated by newly developed distinct element method, and the effects of wall friction force and aspect ratio of bentonite specimen were discussed.

Distinct element approach for the analysis of coupled thermal-mechanical processes in the near field of the HLW repository

Koyama, Tomofumi*; Shimizu, Hiroyuki*; Chijimatsu, Masakazu*; Nakama, Shigeo; Fujita, Tomoo

Proceedings of 2011 World Congress on Advances in Structural Engineering and Mechanics (ASEM '11plus) (USB Flash Drive), p.3759 - 3782, 2011/09

In this paper, the coupled thermal-mechanical processes in the sp pillar stability experiments (APSE) carried out by the Swedish Nuclear Fuel and Waste Management Company (SKB) were simulated using 2 dimensional Distinct Element Method (2-D DEM) with particles. The main objective for large scale in-situ experiment is to investigate the yielding strength of crystalline rock and the formation of the excavation disturbed/damaged zone (EDZ) during excavation of two boreholes, pressurizing in one of the borehole and heating processes. For the simulations, the heat flow algorism was newly introduced into original DEM code to consider heating processes in the APSE. For the DEM simulations, one of the borehole cross sections (in 2-D) was selected and modeled as an assemblage of many particles bonded each other to investigate the failure mechanism during excavation and heating processes in detail including crack propagation at the borehole surface. The microscopic parameters used in the DEM simulations were determined by the calibration using the laboratory uniaxial/triaxial compression testing results. The calculated stress distribution, displacements and temperature distribution were compared with the ones obtained from in-situ measurements and 2-D, 3-D FEM simulations. The simulated crack propagation during the excavation, pressurizing and heating processes by DEM with particles agrees qualitatively well with the observation. The parametric study for initial microcracks was performed to reproduce the spalling phenomena observed in the APSE.

Numerical simulations for the coupled thermal-mechanical processes in sp Pillar Stability Experiment; Continuum and discontinuum based approaches

Koyama, Tomofumi*; Shimizu, Hiroyuki*; Chijimatsu, Masakazu*; Kobayashi, Akira*; Nakama, Shigeo; Fujita, Tomoo

Proceedings of 4th International Conference on Coupled T-H-M-C Processes in Geosystems: Fundamentals, Modeling, Experiments and Applications (GeoProc 2011) (CD-ROM), 11 Pages, 2011/07

In this paper, the coupled thermal-mechanical processes in the pillar stability experiments carried out at the sp Hard Rock Laboratory by the Swedish Nuclear Fuel and Waste Management Company (SKB) were simulated using both Finite Element Method (FEM) and Distinct Element Method (DEM) with particles. The main purpose for in-situ experiment is to investigate the yielding strength of crystalline rock and the formation and growth of the excavation disturbed/damaged zone (EDZ) during excavation and heating processes. For the 3-D numerical simulations using FEM (called THAMES), the measured in-situ stress and its time evolutions (stress re-distribution) due to the tunnel and two borehole excavations, pressurize in one of the borehole as well as heating process were considered. On the other hand, in 2-D DEM simulations, one of the borehole cross sections (in 2-D) was selected and modeled as an assemblage of many particles bonded each other to investigate the failure mechanism during excavation and heating processes in detail including crack propagation at the borehole surface (spalling phenomena). The microscopic parameters used in the DEM simulations were determined by the calibration using the laboratory uniaxial/triaxial compression testing results. The calculation results such as stress distribution, displacements as well as temperature distribution were compared with the in-situ observation and measurements. The simulation results from 3-D FEM shows good agreement with the data obtained from the measurements. The simulated crack propagation during the excavation, pressurizing and heating processes by DEM with particles agrees qualitatively well with the observation. The findings obtained from two different types of numerical simulations can be used for the performance and safety assessment of nuclear waste disposal.

Discrete and continuum approaches for the analysis of coupled thermal-mechanical processes in the near field of a HLW repository

Shimizu, Hiroyuki; Koyama, Tomofumi*; Chijimatsu, Masakazu*; Fujita, Tomoo; Nakama, Shigeo

Dai-40-Kai Gamban Rikigaku Ni Kansuru Shimpojiumu Koen Rombunshu (CD-ROM), p.248 - 253, 2011/01

This paper reports on the results of the numerical simulations for the analysis of coupled thermal-mechanical processes in the near field of a HLW repository using Finite Element Method (FEM) and Distinct Element Method (DEM). The FEM approach provides quantitative information of the change of stress and strain during excavation and heating process. On the other hand, the DEM approach shows the crack propagation process at the borehole surface, and this result agrees qualitatively well with the experimental observation. By comparing these results obtained from both approaches, quantitative and qualitative insights into various aspects of the processes occurred in the near field can be obtained.

Overview of national centralized tokamak program; Mission, design and strategy to contribute ITER and DEMO

Ninomiya, Hiromasa; Akiba, Masato; Fujii, Tsuneyuki; Fujita, Takaaki; Fujiwara, Masami*; Hamamatsu, Kiyotaka; Hayashi, Nobuhiko; Hosogane, Nobuyuki; Ikeda, Yoshitaka; Inoue, Nobuyuki; et al.

Journal of the Korean Physical Society, 49, p.S428 - S432, 2006/12

To contribute DEMO and ITER, the design to modify the present JT-60U into superconducting coil machine, named National Centralized Tokamak (NCT), is being progressed under nationwide collaborations in Japan. Mission, design and strategy of this NCT program is summarized.