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Kobayashi, Fuyumi; Fukaya, Hiroyuki; Izawa, Kazuhiko; Kida, Takashi; Sono, Hiroki; Suyama, Kenya
Proceedings of 12th International Conference on Nuclear Criticality Safety (ICNC2023) (Internet), 7 Pages, 2023/10
In the criticality experiment in the new STACY, pseudo fuel debris samples are used to acquire data for validation of the system used for 1F debris criticality safety assessment. The pseudo fuel debris is a pellet with a diameter of 8 mm and a height of 10 mm containing uranium oxide and structural materials (iron, silicon, zirconium, etc.). The pellets are made by mixing, pressing and sintering uranium dioxide powder and structural materials powder. The UO powder uses the same composition of uranium as the STACY driver fuel rods, in order to reduce the errors in fuel composition. The pseudo fuel debris fabrication devices and analysis equipment are installed at the BECKY in order to evaluate the critical properties of fuel debris with high accuracy in dimension and analysis. This equipment is located in the same laboratory and can quickly respond to experimental needs such as preparation of the pseudo fuel debris and analysis before and after irradiation.
Araki, Shohei; Gunji, Satoshi; Arakaki, Yu; Yoshikawa, Tomoki; Murakami, Takahiko; Kobayashi, Fuyumi; Izawa, Kazuhiko; Suyama, Kenya
Proceedings of 12th International Conference on Nuclear Criticality Safety (ICNC2023) (Internet), 8 Pages, 2023/10
New experiments simulating fuel debris in the new criticality assembly, STACY, are designed to contribute to the validation of criticality calculations for criticality control of the fuel debris in the Fukushima Daiichi Nuclear Power Plant accident. In the new STACY experiment, a two-region core consisting of a driver region and a test region was investigated in order to configure a debris-simulated core with under-moderation condition (lattice pitch 1.27-cm) having the constraint of available fuel rod number. The test region with a 1.27-cm lattice pitch is surrounded by the driver region, in which fuel rods are arranged in a checkerboard pattern on a 1.27-cm lattice plate, with a 1.80-cm lattice pitch. Neutron spectra and sensitivity were calculated by using MCNP6 and ENDF/B-VII. The core which has a 1717 test region with 373 fuel rods is the largest two-region core under the constraint. It was found that the core which has a 17
17 test region can simulate the neutron spectra of under-moderation condition in a 13
13 region inside the test region with the root-mean square percentage error of less than 5%. It was also confirmed that the sensitivity of
Si and
Ca (n,
) reactions when the concrete simulant, was loaded could be simulated.
Araki, Shohei; Gunji, Satoshi; Tonoike, Kotaro; Kobayashi, Fuyumi; Izawa, Kazuhiko; Ogawa, Kazuhiko
Proceedings of European Research Reactor Conference 2020 (RRFM 2020) (Internet), 7 Pages, 2020/10
Critical experiments of thermal neutron system are still expected to be playing an important role for wide technical issues. The Japan Atomic Energy Agency (JAEA) is renovating the Static Experimental Critical Facility (STACY) to maintain the experimental capability. The new STACY is designed as a general-purpose criticality facility. Its core mainly consists of low enriched UO fuel rods, grid plates, and light water moderator. The first experiment campaign in the new STACY aims to obtain criticality characteristics of fuel debris, which will be used in validation of criticality analysis methods. The designs of the experimental core configurations are in progress.
Kobayashi, Fuyumi; Sumiya, Masato; Kida, Takashi; Kokusen, Junya; Uchida, Shoji; Kaminaga, Jota; Oki, Keiichi; Fukaya, Hiroyuki; Sono, Hiroki
JAEA-Technology 2016-025, 42 Pages, 2016/11
A preliminary test on MOX fuel dissolution for the STACY critical experiments had been conducted in 2000 through 2003 at Nuclear Science Research Institute of JAEA. Accordingly, the uranyl / plutonium nitrate solution should be reconverted into oxide powder to store the fuel for a long period. For this storage, the moisture content in the oxide powder should be controlled from the viewpoint of criticality safety. The stabilization of uranium / plutonium solution was carried out under a precipitation process using ammonia or oxalic acid solution, and a calcination process using a sintering furnace. As a result of the stabilization operation, recovery rate was 95.6% for uranium and 95.0% for plutonium. Further, the recovered oxide powder was calcined again in nitrogen atmosphere and sealed immediately with a plastic bag to keep its moisture content low and to prevent from reabsorbing atmospheric moisture.
Kobayashi, Fuyumi; Ishii, Junichi; Shirahashi, Koichi; Umeda, Miki; Sakuraba, Koichi
Kakuhan, Kongo Gijutsu To Toraburu Taisaku, p.341 - 344, 2014/10
The silver mediated electrochemical oxidation (Ag/MEO) process with the ultrasound agitation has been developed for the purpose of the mineralization of organic wastes containing transuranium nuclides at the nuclear fuel reprocessing process. In the Ag/MEO process, organic solvents are decomposed by divalent silver cations under the relatively low temperature and the ambient pressure condition. The ultrasound agitation is effective in mixing the electrolytic solutions and the organic solvents, and is expected to promote the oxidation of the organic solvents. Therefore, the Ag/MEO process with the ultrasound agitation could be a candidate for the treatment of organic solvents. Destruction tests of TBP and dodecane by the Ag/MEO process were conducted to optimize some treatment conditions. Under optimized conditions, the destruction tests of kerosene and TODGA were carried out. It was confirmed that the Ag/MEO process is effective for the mineralization of these organic solvents.
Kokusen, Junya; Sumiya, Masato; Seki, Masakazu; Kobayashi, Fuyumi; Ishii, Junichi; Umeda, Miki
JAEA-Technology 2012-041, 32 Pages, 2013/02
Uranyl nitrate solution fuel used in the STACY and the TRACY is adjusted in the Fuel Treatment System, in which such parameters are varied as concentration of uranium, free nitric acid, soluble neutron poison, and so on. Operations for concentration and denitration of the solution fuel were carried out with an evaporator from JFY 2004 to JFY 2008 in order to adjust the fuel to the experimental condition of the STACY and the TRACY. In parallel, the solution fuel in which some kinds of soluble neutron poison were doped was also adjusted in JFY 2005 and JFY 2006 for the purpose of the STACY experiments to determine neutron absorption effects brought by fission products, etc. After these experiments in the STACY, a part of the solution fuel including the soluble neutron poison was purified by the solvent extraction method with mixer-settlers in JFY 2006 and JFY 2007. This report summarizes operation data of the Fuel Treatment System from JFY 2004 to JFY 2008.
Ishii, Junichi; Kobayashi, Fuyumi; Uchida, Shoji; Sumiya, Masato; Kida, Takashi; Shirahashi, Koichi; Umeda, Miki; Sakuraba, Koichi
JAEA-Technology 2009-068, 20 Pages, 2010/03
At Nuclear Fuel Cycle Safety Engineering Research Facility, the cerium mediated electrolytic oxidation method which is a decontamination technique to decrease the radioactivity of TRU wastes to the clearance-level has been developed for the effective reduction of TRU wastes generated from the decommissioning of a nuclear fuel reprocessing facility and so on. This method corrodes the oxide layer and the surface of metallic TRU metal wastes by the strong oxidation power of Ce in nitric acid. In this study, parameter tests were conducted to optimize the solution condition of Ce
initial concentrations and nitric acid concentrations. The target corrosion rate of metallic TRU wastes set to be 2
4
m/h for the practical use of this method. Under the optimized solution condition, a dissolution test of stainless steel simulating wastes was carried out. From the result of the dissolution test, the average corrosion rate was 3.3
m/h during the test time of 90 hours. Based on the supposition that the corrosion depth of metallic TRU wastes was 20
m enough to achieve the clearance-level, the treatment time for the decontamination was about 6 hours. It was confirmed from the result that the decontamination could be performed within one day and the decontamination solution could repeatedly reuse 15 times.
Kobayashi, Fuyumi; Ishii, Junichi; Shirahashi, Koichi; Umeda, Miki; Sakuraba, Koichi
JAEA-Technology 2009-056, 16 Pages, 2009/11
The silver mediated electrochemical oxidation (Ag/MEO) process with the ultrasound agitation has been developed for the purpose of the mineralization of organic wastes containing transuranium nuclides at the nuclear fuel reprocessing process. In the Ag/MEO process, organic solvents are decomposed by divalent silver cations under the relatively low temperature and the ambient pressure condition. The ultrasound agitation is effective in mixing the electrolytic solutions and the organic solvents, and is expected to promote the oxidation of the organic solvents. Therefore, the Ag/MEO process with the ultrasound agitation could be a candidate for the treatment of organic solvents. Destruction tests of TBP and dodecane by the Ag/MEO process were conducted to optimize some treatment conditions. Under optimized conditions, the destruction tests of kerosene and TODGA were carried out. It was confirmed that the Ag/MEO process is effective for the mineralization of these organic solvents.
Sugikawa, Susumu; Umeda, Miki; Kobayashi, Fuyumi; Nagata, Masanobu*; Dojiri, Shigeru; Amano, Masae*
Proceedings of International Conference on Nuclear Energy System for Future Generation and Global Sustainability (GLOBAL 2005) (CD-ROM), 4 Pages, 2005/10
The mineralization of radioactive contaminated organic wastes by mediated electrochemical oxidation process has some attractive features as alternative to incineration process: The process operates safely at low temperatures and ambient pressures. JAERI has been investigated the process since 1996 and confirmed complete mineralization of this organic solvent. In order to greatly improve current efficiency for the oxidation reaction, further experiments were performed under condition of strong mixing of organic solvent and anolyte with an aide of ultrasonic wave. The current efficiencies for the oxidation reaction by ultrasonic agitation between organic solvent and anolyte were twice to that by mechanical agitation. On the basis of these results, two processes, one for destruction of a small amount of TBP/dodecane and the other for destruction of intermediate compounds following alkaline hydrolysis of a large amount of TBP/dodecane, were proposed.
Ishii, Junichi; Kobayashi, Fuyumi; Uchida, Shoji; Sumiya, Masato; Umeda, Miki
no journal, ,
no abstracts in English
Araki, Shohei; Izawa, Kazuhiko; Gunji, Satoshi; Suyama, Kenya; Ishii, Junichi; Seki, Masakazu; Kobayashi, Fuyumi; Fukaya, Hiroyuki
no journal, ,
To measure critical characteristics of fuel debris, the Static Experiment Critical Facility (STACY) is being converted to the heterogeneous thermal system using fuel rods and light water moderator from the homogeneous system using solution fuel. This report presents an overview and progress of the modified STACY.
Kobayashi, Fuyumi; Ishii, Junichi; Kimura, Akihiro; Sugikawa, Susumu
no journal, ,
no abstracts in English
Kobayashi, Fuyumi; Sumiya, Masato; Kida, Takashi; Izawa, Kazuhiko; Ogawa, Kazuhiko
no journal, ,
Towards the decommissioning of the Fukushima Daiichi Nuclear Power Stations (1F), Japan Atomic Energy Agency (JAEA) has designed fabrication equipment of a pseudo fuel debris for the evaluation of the criticality characteristics of 1F fuel debris. In order to confirm the feasibility of the fabrication-method in designing, some fuel pellets mixed with uranium oxide and structural materials (iron, silicon, zirconium, etc.) were manufactured. The properties such as pressing and sintering condition were obtained by the prototyped fuel debris. The pseudo fuel debris fabricating equipment reflecting these properties is designed in 2016 and now constructed. The equipment will be installed in 2018 to start the fabrication.
Maekawa, Tomoyuki; Seki, Masakazu; Sumiya, Masato; Araki, Shohei; Murakami, Takahiko; Hasegawa, Kenta; Yoshikawa, Tomoki; Mori, Takashi*; Ishii, Junichi; Kobayashi, Fuyumi; et al.
no journal, ,
As previously reported, to clarify critical characteristics of fuel debris, the Static Experiment Critical Facility (STACY) is being converted to the heterogenous thermal system using fuel rods and light water moderator from the homogenous system using solution fuel. Seismic reinforcement of the support structure of the core tank started in 2022. This report presents progress on manufacture and construction of the modified STACY in 2021 and 2022.