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Miura, Takatomo; Kudo, Atsunari; Koyama, Daisuke; Obu, Tomoyuki; Samoto, Hirotaka
Proceedings of 12th International Conference on Nuclear Criticality Safety (ICNC2023) (Internet), 10 Pages, 2023/10
Tokai Reprocessing Plant (TRP) had reprocessed 1,140 tons of spent fuel discharged from commercial reactors (BWR, PWR) and Advanced Thermal Reactor "Fugen" from 1977 to 2007. TRP had entered decommissioning stage in 2018. In order to reduce the risk of High Active Liquid Waste (HALW) held at the facility, the vitrification of HALW is given top priority. HALW generated from reprocessing of spent fuel contains not only fission products (FPs) but also trace amounts of uranium (U) and plutonium (Pu) within the liquid and insoluble residues (sludge). Under normal conditions, concentrations of U and Pu in HALW are very low so that it can not reach criticality. Since FPs with high neutron absorption effect coexists in HALW, even if the cooling function is lost due to serious accident and HALW evaporates to dryness, it is considered that criticality would not been reached. In order to confirm this estimation quantitatively, criticality safety evaluations were carried out for the increase of U and Pu concentrations by evaporation of HALW to the point of dryness. In this evaluation, infinite multiplication factors were calculated for each of solution system and sludge system of HALW with respect to the concentration change through evaporation to dryness. It is confirmed it could not reach criticality. The abundance ratios of U, Pu and FPs were set conservatively based on analytical data and ORIGEN calculation results. Multiplation factors for two-layer infinite slab model of solution and sludge systems of HALW were also calculated, and it was confirmed it could not reached criticality. In conclusion, the result was gaind that there could be no criticality even in the process through evaporation to dryness of HALW in TRP.
Kuroda, Yasuji; Kurabayashi, Kazuaki; Otani, Takehisa; Tomiyama, Masahiro; Miura, Takatomo; Namatame, Toshihiro
no journal, ,
It was based on teachings of the Fukushima Daiichi Nuclear Power Plant accident, and the view and concrete measure against security were arranged supposing major accidents, such as all the power supply loss by the earthquake and tsunami, about decay heat removal, such as highly radioactivity waste fluid in the Tokai reprocessing facility, and plutonium solution, and the measure against hydrogen exhaust gas. Moreover, while verifying the validity of safety measures, an example of verification of the data used for safety evaluation was shown.
Miura, Takatomo
no journal, ,
Tokai Reprocessing Plant (TRP) shifted to the decommissioning stage in 2018 and the process of TRP decommissioning is planned to continue for approximately 70 years until the release of controlled areas of approximately 30 facilities. As preliminary to decommissioning process, clean-up is ongoing (1st step). Prior to a dismantling planned to start within a few years as the 2nd step, we need to investigate a situation in cells in detail, and 3D cloud data and 3D As-Built are expected to utilize for equipment dismantling at 2nd step. But Regarding 3D As-built at TRP, there are some issues (e.g. Several cells are narrow and under high-radioactive condition, it is limited access to inside of a cell, and so forth). In this study, we considered how to get 3D cloud data in response to the characteristics of TRP based on these issues. As a result, considering structure of reprocessing plant like TRP, it is effective for scanning to use the remote jig combined guide rail and cable bear. Furthermore, we confirmed making new hole in the cell wall makes it possible to get data for 3D As-Built. From these studies, we have some good prospect on how to establish 3D As-Built at TRP cells.