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Aomori Shi, Japan

Japan Nuclear Fuel Ltd. is a nuclear energy company based in Rokkasho, Aomori Prefecture, Japan involved in the production of nuclear fuel, as well as the reprocessing, storage and disposal of nuclear waste. The mission of Japan Nuclear Fuel Limited is to establish a nuclear fuel cycle infrastructure in Japan.In uranium enrichment JNFL plans to provide for an ultimate capacity of 1,500 ton-SWU/year, enough to meet one third of the nuclear fuel needs of all nuclear power plants in Japan. Currently, the Uranium Enrichment Plant in Rokkasho, Aomori, is operating with a capacity of 1,050 ton-SWU/year, which is equivalent to the nuclear fuel used by 8 or 9 reactors at 1,000 MW-class nuclear plants.Rokkasho Reprocessing Plant, Japan's first commercial reprocessing plant, began reprocessing in 2007, however complications have delayed full commercial operation until 2012. The plant has a design reprocessing capacity of 800 tonnes-U/year, enough to reprocess the spent fuel produced by 30 reactors at 1,000 MW-class nuclear power stations, though full capacity has yet to be realized. Responding to a December 1998 request from The Federation of Electric Power Companies, JNFL has been conducting technological studies regarding MOX fuel fabrication technology. According to the current plan, Japanese electric power companies will be implementing Plutonium-Thermal utilization with 16 to 18 of the nuclear reactors operating in Japan. In late October 2010, work formally got under way on a 130 tonne/year J-MOX fuel fabrication plant, which is located on the same site as the Rokkasho Reprocessing Plant.JNFL also operates low and high level nuclear waste long-term storage facilities which will accommodate 2,880 canisters of vitrified high level waste and the ultimate capacity of the Low-Level Radioactive Waste Disposal Center now under construction will be 600,000 m3. Wikipedia.

Kitashiba N.,Japan Nuclear Fuel Limited
International Conference on Nuclear Engineering, Proceedings, ICONE

In recent years, high burn-up fuel (∼55GWd/t (Assembly)) experienced some fuel leakages in Japanese PWRs. Grid-to-Rod fretting (GTRF) wear at the bottom grid position in some fuel assemblies was observed through fiberscope in onsite inspection and GTRF was considered to be cause of leakage issues. As a countermeasure to these fuel leakages, Mitsubishi Nuclear Fuel (MNF) has developed ZDP-1 fuel assembly. ZDP stands for "Zero Defect Performance". ZDP-1 is MNF's first design of ZDP fuel series. ZDP-1 fuel assembly is designed to make more margins against GTRF wear at the bottom grid. In this paper, the improvements of ZDP-1 and the wear evaluation results of ZDP-1 are explained, together with the situation of the wear issue and results of root cause analysis on the fuel leakages. Copyright © 2015 by JSME. Source

Yasuda Y.,Japan Nuclear Fuel Limited | Takahashi M.,Tohoku University
International Conference on Nuclear Engineering, Proceedings, ICONE

In the present study, the concept of Generalized Failure Mechanism Knowledge (GFMK) has been proposed and applied practically to Rokkasho reprocessing plant. GFMK is a knowledge scheme that describes failure mechanism independent of particular subject. In this scheme, sets of conditions leading to specific failure are generalized, which allows us to apply to different equipment. Once GFMK have been constructed, it is possible to estimate the likelihood of the failure without expert judgments. Following two issues have been studied in this study. 1) Building a GFMK knowledgebase based on previous troubles cases 2) Application of GFMK to specific plant sub-systems to derive failure mechanism For issue 1), the GFMK knowledgebase has been constructed based on the previous failures cases in Rokkasho reprocessing plant with emphasis on the events related to aging. For issue 2), it has been confirmed that the possible failure mechanism can be obtained by applying GFMK to the realistic scale sub-system of Rokkasho reprocessing plant. The derived failure mechanism has been compared with the ones on the design specification and has been confirmed that most of the derived failure mechanism are feasible. Copyright © 2015 by JSME. Source

Yoshida Y.,Hokkaido University | Oosawa K.,Hokkaido University | Oosawa K.,Japan Nuclear Fuel Limited | Watanabe S.,Hokkaido University | And 5 more authors.
Applied Physics Letters

We have studied nanopatterns induced by nanosecond pulsed laser irradiation on (111) plane surfaces of a polycrystalline iron-aluminum alloy and evaluated their magnetic properties. Multiple nanosecond pulsed laser irradiation induces a wavelength-dependent surface transformation of the lattice structure from a B2-type to a supersaturated body centered cubic lattice. The selective formation of surface nanopatterns consisting of holes, stripes, polygonal networks, and dot-like nanoprotrusions can be observed. Furthermore, focused magneto-optical Kerr effect measurements reveal that the magnetic properties of the resultant nanostructured region changes from a paramagnetic to a ferromagnetic phase in accordance with the number of laser pulses. © 2013 AIP Publishing LLC. Source

Yamamoto S.,Obayashi Corporation | Kumagai M.,Japan Nuclear Fuel Limited | Koga K.,Obayashi Corporation | Sato S.,Obayashi Corporation
Geological Society Special Publication

The 'subsurface disposal' concept has been proposed for relatively higher-activity low-level waste (LLW) in Japan. This concept includes a low-permeability layer (LPL) made of bentonite material and a low-diffusion layer (LDL) made of dense cementitious material. The influence of gas generation and migration on the mechanical stability of the engineered barrier system (EBS) is one of the issues for long-term performance assessment of the disposal facility. In this study, coupled hydromechanical modelling and analyses are carried out in order to evaluate the mechanical stability of the system. Two gas generation rate cases are simulated: (1) a reference case; and (2) a conservative case. It is found from the analyses that the tensile stress developed in the cementitious components due to accumulated gas pressure is lower than the tensile strength of the materials, and that stress developed in the LPL remains compressive apart from at the interface between the LPL and the LDL, which suggests that opening could occur at the interface. These results indicate that the gas pressure would not mechanically damage the EBS of the subsurface disposal even if a relatively high gas generation rate were assumed. © The Geological Society of London 2015. Source

Sugawara T.,Akita University | Shiono T.,University of Shiga Prefecture | Yoshida S.,University of Shiga Prefecture | Matsuoka J.,University of Shiga Prefecture | And 2 more authors.
Physics and Chemistry of Glasses: European Journal of Glass Science and Technology Part B

The densities of two simulated radioactive waste glasses and melts were determined between 298 and 1278 K by the Archimedean immersion method for annealed glasses at room temperature, dilatometric measurements for glasses in the temperature range from 373 K to the glass transition region and Archimedean densitometry using a molten chloride salt for liquids above 825 K. At temperatures above 1079 K the density of a stable liquid can be measured with a precision of 0·3%. The molar volume of the waste glass melt between 1079 and 1278 K is consistent with both the high temperature extrapolation of the molar volume at the glass transition temperature and the value estimated using partial molar volumes reported previously, which has been obtained using double-bob Archimedean densitometry. The temperature dependence of the molar volume (dV/dT) between the glass transition temperature and 1278 K is significantly larger than that calculated using partial molar thermal expansivities in the previous model. This suggests that the thermal expansivity of borosilicate melts is temperature dependent. Source

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