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Kitamura, Akira; Akahori, Kuniaki; Nagata, Masanobu*
Genshiryoku Bakkuendo Kenkyu (CD-ROM), 27(2), p.83 - 93, 2020/12
Direct disposal of spent nuclear fuel (SNF) in deep underground repositories (hereafter "direct disposal") is a concept that disposal canisters stored fuel assemblies dispose without reprocessing. Behavior of radionuclide release from SNF must be different from that from vitrified glass. The present study established a methodology on determination of instant release fraction (IRF) of radionuclides from SNF, which is the one of the parameters on radionuclide release based on the latest safety assessment reports in other countries, especially for IRF values proportional to a fission gas release ratio (FGR). Recommended and maximum values of FGR have been estimated using the fuel performance code FEMAXI-7 after collecting FGR values on Japanese SNFs. Furthermore, recommended and maximum values of IRF for Japanese SNFs used in a pressurized water reactor (PWR) have been estimated using the presently obtained FGR values and experimentally obtained IRF values on foreign SNFs. The recommended and maximum IRF values obtained in the present study have been compared with those of the latest safety assessment reports in other countries.
Nagata, Masanobu; Chikazawa, Takahiro*; Akahori, Kuniaki*; Kitamura, Akira; Tachi, Yukio
Genshiryoku Bakkuendo Kenkyu (CD-ROM), 23(1), p.31 - 54, 2016/06
Although spent nuclear fuel is planned to be disposed after reprocessing and vitrification of high-level radioactive waste (HLW), feasibility study on direct disposal of spent nuclear fuel (SF) has been started as an alternative option to flexibly apply change of future energy situation in Japan. Radionuclide inventories and their release behavior after breaching spent fuel container should be assessed to confirm safety of the SF disposal. However, these detailed studies have not been performed in Japan. Therefore, we investigated some foreign safety assessment reports on direct disposal of spent nuclear fuel by focusing on the source term of the fast release of radionuclides (i.e. instant release fraction; IRF) for the purpose of contributing to the safety assessment of Japanese SF disposal system. As a result of comparison between the safety assessment reports in foreign countries, although some fundamental data have been referred to the reports in common, the final source term dataset (IRF) was seen differences between countries in the result of taking into account the national circumstances (Reactor type and burnup, etc.). We also found the difference of assignment of uncertainties among the investigated reports; a report selected pessimistic values and another report selected mean values and their deviations. It is expected that these findings are useful as fundamental information for determination of the release rates for the safety assessment of Japanese SF disposal system.
Shibata, Atsuhiro; Yano, Kimihiko; Sambommatsu, Yuji; Nakahara, Masaumi; Takeuchi, Masayuki; Washiya, Tadahiro; Nagata, Masanobu*; Chikazawa, Takahiro*
Proceedings of International Conference on Toward and Over the Fukushima Daiichi Accident (GLOBAL 2011) (CD-ROM), 6 Pages, 2011/12
JAEA has been developing a U crystallization process. The development targets were DFs of over 100, confirmation of mechanical performance of crystallizer, and so on. Fundamental data were obtained by beaker-scale experiments with actual dissolver solution. DFs for most of the FPs are improved by washing. However the formation of Pu-Cs double salt causes low DF of Cs. To confirm the mechanical performance of an annular type crystallizer and a crystal separator, some experiments were carried out. The crystallizer and the separator have good performance. However washing of UNH crystals by the separator did not have the intended effect for solid impurities. We discussed the application of crystal purification technology to improve the purity and selected KCP. UNH crystal purification tests were carried out using bench-scale KCP apparatus with simulated solid impurities. The purifier has good performance on the decontamination of not only liquid impurities but also solid impurities.
Washiya, Tadahiro; Tayama, Toshimitsu; Nakamura, Kazuhito*; Yano, Kimihiko; Shibata, Atsuhiro; Nomura, Kazunori; Chikazawa, Takahiro*; Nagata, Masanobu*; Kikuchi, Toshiaki*
Journal of Power and Energy Systems (Internet), 4(1), p.191 - 201, 2010/02
Japan Atomic Energy Agency (JAEA) and Mitsubishi Materials Corporation (MMC) are developing the crystallization process for elemental technology of FBR fuel reprocessing. The uranium (U) crystallization process is a key technology for New Extraction System for TRU Recovery (NEXT) process that was evaluated as the most promising process for future FBR reprocessing. We had developed an innovative crystallizer and fabricated an engineering-scale crystallizer and have carried out continuous operation test to investigate the stability of the equipment at steady and non-steady state conditions by using depleted uranium. As for simulating typical failure events in the crystallizer, crystal accumulation and crystal blockage were occurred intentionally, and monitoring method and resume procedure were tried and selected in this work.
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.
Washiya, Tadahiro; Chikazawa, Takahiro*; Nagata, Masanobu*; Kikuchi, Toshiaki*; Hirasawa, Izumi*
no journal, ,
no abstracts in English
Oyama, Koichi; Katsurai, Kiyomichi; Kondo, Yoshikazu; Washiya, Tadahiro; Myochin, Munetaka; Nagata, Masanobu*; Horiuchi, Nobutake*; Chikazawa, Takahiro*; Kikuchi, Toshiaki*
no journal, ,
no abstracts in English
Shibahara, Takahiro*; Nagata, Masanobu*; Chikazawa, Takahiro*; Kikuchi, Toshiaki*; Morita, Yasuji; Ikeda, Yasuhisa*
no journal, ,
Thermal decomposition of precipitants of U(VI) with pyrrolidone derivatives was investigated for the development of an advanced reprocessing system for spent FBR fuels based only on precipitation method using the pyrrolidone derivatives. It was found that the thermal treatment of U(VI) precipitates at constant temperature of 150 - 170 C before the decomposition of the precipitate at high temperature contribute to the production of the U oxides with low impurities and the recovery of the with pyrrolidone derivatives.
Yano, Kimihiko; Sambommatsu, Yuji; Takeuchi, Masayuki; Washiya, Tadahiro; Nagata, Masanobu*; Chikazawa, Takahiro*
no journal, ,
Crystal purification test was carried out with KCP type testing device for uranyl nitrate hexahydrate including solid impurity. It was confirmed the influences of grain size and density of solid impurities on purification performance.
Takeuchi, Masayuki; Yano, Kimihiko; Sambommatsu, Yuji; Shibata, Atsuhiro; Washiya, Tadahiro; Nagata, Masanobu*; Chikazawa, Takahiro*
no journal, ,
In an uranium crystallization system, a great part of uranium in dissolver liquor with high heavy metal concentration is separated by cooling as uranyl nitrate hexahydrate (UNH) crystal. However, the purity of UNH crystal is not high, so we have discussed the application of crystal purification technology to improve the purity of UNH crystal. In this study, the effects of grain size and density of solid impurities on the purification performance were evaluated in UNH crystal purification tests to discuss the purification mechanism of KCP. From the results, a decontamination factor of smaller grain size of solid impurities was larger than that of bigger one, on the other hand, the density effect was not significant. It is explained that the smaller size of solid impurities is easy to pass through between UNH crystal grains and the decontamination of the solid impurities in the purifier is promoted by pushing down them along the flow of melt.
Nagata, Masanobu; Kitamura, Akira; Tachi, Yukio; Akahori, Kuniaki*; Chikazawa, Takahiro*
no journal, ,
no abstracts in English
Nagata, Masanobu; Akahori, Kuniaki*; Kitamura, Akira; Tachi, Yukio; Chikazawa, Takahiro*
no journal, ,
no abstracts in English