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Japan Nuclear Cycle Development Institute (JNC) operated a small uranium refining and conversion plant, as well as a small centrifuge enrichment demonstration plant, at Ningyo Toge, Okayama prefecture. The Nuclear Fuel Processing Business Activity at the Ningyotoge Environmental Engineering Center of the Japan Nuclear Cycle Development Institute is responsible for the Prototype Uranium Enrichment Plant.
PNC (Power Reactor and Nuclear Fuel Development Corp.) built a small demonstration enrichment plant at Ningyotoge [Ningyo-toge] in Kamisaibara Village of Okayama Prefecture. In 1997 the Japanese government decided to transfer the enrichment research and development (R&D) from the PNC to the utility owned by the Japan Nuclear Fuel Ltd. (JNFL).
A wide range of technology development by the PNC made Monju become what it is. Uranium with a 0.2-0.3% content of uranium 235 -- a level much lower than for natural uranium -- is the basis of fuel for the fast breeder reactor. It had uranium supplied from Ningyo-toge.
Enrichment work at the JNC's Ningyo-toge enrichment facility in Okayama Prefecture was wound up in the spring of 2000. The dismantling and removal, started in FY 2000, of installations of refining and conversion facilities that have completed commercialization tests of recovered uranium conversion will be conducted, whereas the buildings themselves will be used as waste storage facilities. As this decommissioning preceded other decommissioning, engineering data on this decommissioning were compiled through the decommissioning work.
Between 1956 and 1988, the Power Reactor and Nuclear Fuel Development Corporation (PNC) and its predecessor undertook domestic exploration for uranium, resulting in the discovery of deposits at two locations on the island of Honshu. Total discovered reserves, reported as recoverable at US$ 80-130/kgU, are some 6,600 tonnes.
By 2001 cumulative production of uranium in Japan amounted to only 87 tonnes, the bulk of which (84 tonnes) was produced by a test pilot plant operated by PNC at the Ningyo-Toge mine between 1969 and 1982. Uranium had been mined on a small scale from 1969 to 1982, with total reserves estimated at 2,000 tonnes U3O8. The deposit consists of nine major bodies. Those are distributed in an area of 4 km (NS) by 6 km (EW) and occur in a paleochannel. Main body, Nakatsugawa body, is 700 m long and 600 m wide and 1.2 thick. The sedimentary rock is deposited on the Late Cretaceous to Paleogene granitoids. Primary deposit minerals are ningyoite, coffinite and uraninite. Secondary deposit minerals are autunite and carnotite.
In 1988, the existence of a high radiation area was disclosed around the Ningyo-toge mine, which was closed in 1982. The origin of radiation is mining residues that were discarded and left as they were since closing of the mine.
The JNC conducted R&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.
JNC placed top priority on determining the management of Katamo debris pile sites at the Ningyo-toge Environmental Engineering Center. Based on the overall plan for abandoned mine measures formulated at the end of FY 1999, specific measures were examined. On the basis of this plan, essential technologies were developed for stabilizing and permanently managing slag. In addition, every facility was provided with safety maintenance and supervisory activities.
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