[en] The Sodium-Water reaction test facility, SWAT-3, was disassembled at the O-arai Engineering Center of JNC. It was the first experience in Japan to disassemble the large-scale sodium facilities containing sodium-water reaction products. This report describes some special techniques (extracting the sodium from the damp tank, treatment of the sodium-water reaction products, disassembly of the damp tank) obtained through the disassembly work of the SWAT-3 dump tank, which contained a large amount of sodium-water reaction products deposits. Information is also presented on the corrosion of the structural material of the dump tank, whose inner surface had come into contact with the sodium-water reaction products over a long period. (author)

[en] ⁹⁹Tc is produced in a high yield of 6% upon nuclear fission of ²³⁵U, ²³⁹Pu and so on. It is one of the important nuclides in existence around nuclear facilities because it has an extremely long half-life of 214,000 years and various chemical forms in soils. Based on the results of tracer experiments that have been conducted by research organizations in various laboratories, it was thought that the transfer velocity of ⁹⁹Tc in soils would be high. However, it was found from the results of analysis of actual soil samples that the transfer factor of ⁹⁹Tc from soil to plants was about 100 times smaller than that of the reported value. The vertical transfer of TcO₄^- (7 valences) is faster than that of TcO₂ (4 valences). These results suggest that an environmental assessment on a long-term scale in connection with the environmental assessment of low-level waste from nuclear facilities and an environmental assessment of contaminated areas should be based on parameters from field data. (author)

[en] The JNC conducted R and D projects on uranium exploration in Japan from 1956 to 1987. Several mine facilities, such as waste rock yards and a mill tailing pond, were retained around Ningyo-Toge after the projects ended. Thus, JNC's Ningyo-Toge Environmental Engineering Center proposed a reclamation plan for these facilities with fundamental policy, an example of safety analysis and timetables. Although the plan is primarily based on the Japanese Mine Safety Law, it also refers to ICRP recommendations, IAEA reports, measures implemented overseas, etc. because this is the first such case in Japan. This plan was evaluated and validated from the technological viewpoint by the Technological Advisory Board on the Reclamation of the Ningyo-Toge uranium mining and milling facilities, in the 4th Meeting on April 11, 2002. The Board was established on January 29, 2001 and composes 10 experts regarding nuclear energy, radiology, mining, civil engineering, etc.; its chairperson is Dr. M. Nakano, a professor emeritus of Univ. of Tokyo. This report illustrates the reclamation plan mainly concerning waste rock yards and a mill tailing pond. (author)

[en] The decontamination method of scraping off contaminated depth mechanically was developed for the equipment of uranium enrichment facilities whose surface was contaminated by uranium. The ''Cylinder Scraping Machine,'' made as an experiment, can scrape off a constant depth of cylinder-shaped equipment along the surface of equipment made of carbon steel or aluminum alloy. The depth of scraping was set at 0.5mm in accordance with the contamination depth of the uranium enrichment equipment, and examination of the processing condition, which makes the scraps into a suitable form for suction collection, and of the processing precision was conducted and the decontamination effect was gauged by a scraping test of the body with simulated contamination. As a result, the validity of the basic function of the 'Cylinder Scraping Machine' and the processing conditions suitable for scraping decontamination were confirmed and the subjects to apply it to the processing of the actual used materials regarding the scraps collection mechanism, cooling of the scraping part and others were extracted. (author)

[en] To observe the airborne gamma radiation dose rate, monitoring posts are set up at the border of a supervised area of JNC-OEC. Measurement values of some ionization chambers set at monitoring posts were increased by signals of unknown origin occurring at random times. To probe the cause, measurement of electric field intensity at the ionization chamber and immunity test at anechoic chamber were carried out. Result of examination made clear that measurement values are increased by a specific frequency band electromagnetic wave. There were also clear indications that ferrite cores and shield tube are effective in eliminating electromagnetic wave noise. When attaching ferrite cores to cables of ionization chambers, unknown increase of measurement values can be stopped. (author)

No abstract available

[en] This paper presents the development of fault diagnosis using statistical method. We apply the fault diagnosis to the process data of the uranium enrichment demonstration plant. A uranium enrichment plant is structurally stable and there is a little change in the process data. It is necessary to detect the microscopic fluctuation in the process data before the serious fault. First we apply the auto-regressive model (AR model) to the process data, and estimate the validity of the AR model. Next we attend the cross-correlation in the process data, and construct the physical model using the simple law of the physics in the plant. We estimate the validity of the physical model. As a result we confirm that the fault diagnosis using statistical method is valid in the stable plant. (author)

[en] QUALITY (Quantitative Assessment Radionuclide Migration Experimental Facility) was constructed to investigate the radionuclide migration behavior under an aerobic condition. The construction commenced on Jan. 22, 1998 and completed on July 30, 1999. The operation was started on Aug. 18, 1999. This facility contains atmosphere controlled glove boxes to obtain basic data of radionuclide migration in engineered barrier materials and rocks on a laboratory scale. Various analytical equipments is available in this facility. This report presents the objectives, the outline and the data use. (author)

[en] The Mizunami Underground Research Laboratory (MIU) is planned to be constructed at the research site of JNC in Mizunami, Gifu prefecture. A wide range of geoscientific research and development activities which have been performed in and around the Tono mine for these years, is planned to extend in the laboratory. The MIU consists of surface and underground facilities down to a depth of about 1,000 meters. This report describes the overall layout and the basic construction method of the underground facility, including the composition of the overall research program which is necessary to design the underground facility and to select its construction method. (author)

[en] Each year, maintenance work is carried out for about 10,000 pieces of equipment, including mechanical devices, electric equipment and instruments, at the Tokai Reprocessing Plant. Ninety percent of such maintenance work is preventive maintenance. In order to manage the information about the maintenance work, a computer support system was developed between 1985 and 1992. Twenty-seven thousand pieces of equipment and 180,000 maintenance histories have already been registered in the system. The system has been used for planning inspections and replacement of equipment as well as checking their maintenance histories. Actual usage of the system has shown that some auxiliary functions need to be added. The system will therefore be improved and extended. (author)