Tokai-mura is located about 110 km northeast of Tokyo in Ibaraki prefecture. Tokai-mura, as the birthplace of Japan's peaceful uses of nuclear energy, possesses a string of facilities for nuclear energy R&D and utilization, and, namely, is a Mecca for Japan's nuclear energy. Tokai-mura newly incorporated the two villages of Ishigami and Muramatsu. In 1957, JRR-1, an experimental reactor at the nuclear research institute, went critical and lighted the torch for the peaceful uses of nuclear energy in Japan.
Mitsubishi Nuclear Fuel Co Ltd operates a major fuel fabrication facility at Tokai, which started up in 1972. Further fuel fabrication plants are operated by Nuclear Fuel Industries (NFI) in Tokai and Kumatori, and JNC has some experimental mixed oxide (MOX) fuel facilities at Tokai for both the Fugen ATR and the FBR program. Also at Tokai, JNC has operated a 90 t/yr pilot reprocessing plant. JNC operates spent fuel storage facilities at Tokai and is proposing a further one. It has also operated a pilot high-level waste (HLW) vitrification plant at Tokai since 1995. Tokai is the main site of JNC's R&D on HLW treatment and disposal.
Tokai Power Station
The original Tokai-1 power station, a British Magnox reactor which closed down in 1998, will be decommissioned over 17 years, the first ten as "safe storage" to allow radioactivity to decay. The Japan Atomic Power Company (JAPC) was established in November 1957, funded by several electric power companies and electrical equipment manufacturers in an effort to develop nuclear power, aimed to generate electricity on a commercial basis. The history of the JAPC represents the history of the introduction, development, and progress of nuclear power in Japan. The pioneer was Japan's first commercial nuclear power station, the graphite-moderated, carbon dioxide gas-cooled reactor (GCR) at the Tokai Power Station, followed by the construction and operation of the Tokai Daini Power Station BWR, a larger light water reactor. Construction of the GCR nuclear reactor, with an electric output of 166MW, started on January 16, 1960 at Tokai Power Station, with commercial operation beginning six years later, on July 25, 1966. The construction of Tokai Daini Power Station, with its large-scale BWR producing 1,100MW electric output, started in June 1973, and commercial operations began five years later in November 1978.
Conversion Testing Facility - JCO Co. Ltd.
On 30 September 1999 a criticality accident - an unplanned chain reaction - occurred at the Conversion Testing Facility of JCO Co. Ltd. in in the village of Tokai-mura, Ibaraki Prefecture. The accident was in a very small fuel preparation plant operated by Japan Nuclear Fuel Conversion Co. (JCO), a subsidiary of Sumitomo Metal Mining Co. It was not part of the electricity production fuel cycle, nor was it a routine manufacturing operation where operators might be assumed to know their jobs reasonably well. The JCO plant at Tokai was commissioned in 1988 and processes up to 3 tonnes per year of uranium enriched up to 20% U-235, much more than for ordinary power reactors. The plant supplied various specialised research and experimental reactors. It uses a wet process.
The accident happened during the process of manufacturing fuel for the Experimental Fast Reactor "Joyo", when three workers, in violation of the rules, had been dealing with the solution containing 16kg of uranium (18.8% enrichment) and pouring the solution into the precipitation tank. The tank has a cooling jacket which contained water. At the point of criticality, the nuclear fission chain reaction became self-sustaining and began to emit intense gamma and neutron radiation, triggering alarms. There was no explosion, though fission products were progressively released inside the building.
Calculations showed that the water in the cooling jacket acted as a neutron reflector, causing the criticality to continue. As the solution boiled vigorously, voids formed and criticality ceased, but as it cooled and voids disappeared, the reaction resumed.
The criticality continued on and off for some 17-20 hours, until it was stopped on the following morning. The reaction was stopped when cooling water surrounding the precipitation tank was drained away, since this water provided a neutron reflector. In order to bring the situation under control, the water in the cooling jacket was flushed by opening the valve in the line that sends water into the jacket, and by blowing argon gas into the cooling system. The criticality became significantly lower around 6.00 AM on October 1. Furthermore, in order to eliminate the possibility of re-criticality, borate solution was poured into the tank around 8:30 AM, which terminated the criticality.
Evacuation of families within 350 meters of the perimeter was implemented. A decision to shelter the population out to a radius of about 10 kilometers was put in effect until it was lifted on the folowing day.
Three workers were exposed to a large amount of neutron radiation, and were taken to the Mito National hospital first, and then transferred to the National Institute of Radiological Sciences, where they received medical treatment. Other than these three workers, 46 people (36 workers of JCO and other companies, 7 local people, and 3 fire fighters) were exposed to radiation, though the dose level was not serious.
On the morning of 01 October 1999, the radiation level in the area returned to the normal level, and the Nuclear Safety Commission confirmed the safety based on the analysis of radiation data and their trends. At 3:00 PM, October 1, the Government declared that it had confirmed the termination of criticality. Accordingly, the post-accident decision to shelter the population within the radius of about 10 kilometers was lifted.
The Japanese authorities gave a provisional rating for the accident at Level 4 on the IAEA's International Nuclear Event Scale, which runs from a minimum of Level 0 to a maximum of Level 7. A Level 4 accident, classified as an "accident without significant off-site risk," involves an external release of radioactivity resulting in a dose to the critical group of the order of a few millisieverts. With such a release, the need for off-site protective actions would be generally unlikely, except, possibly, for local food control. A Level 4 accident also involves a significant damage to the installation. Such an accident might include damage leading to major on-site recovery problems, such as partial core melt in a nuclear power reactor, which the affected Tokaimura facility is not, and comparable events in non-reactor installations.
Hisashi Ouchi died on 21 December 1999, less than three months after the criticality accident. Masato Shinohara died seven months later, also a victim of lethal radiation exposure. The third employee, Yutaka Yokokawa, was hospitalized for several months then released. The three had apparently received full-body radiation doses of 10-20,000, 6-10,000 and 1-5000 millisieverts (about 8000 mSv is normally a fatal dose).
The company conceded that it violated both normal safety standards and legal requirements, and criminal charges were filed. The fact that the plant is a boutique operation outside the mainstream nuclear fuel cycle reduced the level of scrutiny it attracted. The work procedure had been modified three years earlier, without permission from the regulatory authorities.
Tokai Reprocessing Plant (TRP)
The Tokai Reprocessing Plant is capable of handling about 90 tons of spent fuel per year, which is approximately 10% of the total volume from domestic light-water reactors. It had reprocessed around 1,010 tons of spent fuel as of November 2002. The technology development from this plant is reflected in the design of the new Recycle Equipment Test Facility.
JNC provides comprehensive technical assistance to JNFL for the construction of the commercial-scale reprocessing plant, including: technical information, on-site design consultants and cooperation in research and development.
The Tokai Reprocessing Plant (TRP) in Tokai-mura, Ibaraki prefecture in Japan, was built in the early 1970s, using 1960s-era design and technology. The IAEA began inspecting the facility in 1977 and the facility begun reprocessing spent fuel in 1981, though its operation was temporarily halted by a fire and explosion in March 1997. In its annual evaluation of safeguards implementation, as reported to the IAEA's Board of Governors in the Safeguards Implementation Report, the IAEA Secretariat has regularly noted the need for strengthening safeguards implementation at TRP, particularly with respect to procedures used for the measurement of nuclear material in the waste produced.
In 1996, Japan and the IAEA reached agreement on IAEA sampling, on a random basis, of the high active liquid waste transferred in the past to TRP's storage tanks. The results of the sampling activities, which were conveyed to the Japanese authorities in 1998, indicated differences between IAEA measurements of the material and the operator declarations. During the period in which TRP was shut down (1997-2000), studies were undertaken by the IAEA, State authorities and JNC, resulting in further improvements in the techniques used by the operator for sample preparation and analysis to more accurately measure the plutonium content of the material transferred to the HALW storage tanks. JNC began implementing these improved techniques in March 2002. On January 28, 2003, the IAEA announced that, as a result of the introduction of more precise sampling and analytical measurement techniques for measuring plutonium in the high active liquid waste at the TRP's storage tanks, it would be correcting the amount of plutonium declared in past accountancy reports to the IAEA. The corrected accountancy reports on the inventory of the HALW were expected to be in line with IAEA verification data. In November 2002, a group of IAEA experts performed a six-week review of historical data including a detailed analysis of operator declarations since 1977 to further increase the Agency's confidence in its conclusion that no nuclear material has been diverted from the facility.
Recycle Equipment Test Facility
A technology to reprocess the spent fuel from fast breeder reactors, which has high plutonium content and burn-up than light-water reactor fuel, has been developed. Tests have been conducted to improve the conventional reprocessing techniques and the operation of full-scale equipment. The Recycle Equipment Test Facility is now under construction at Tokai to test new types of equipment and processes on an engineering scale.
The Recycle Equipment Test Facility [RETF] is designed to reprocess plutonium produced in Monju and Joyo, Japan's two fast breeder reactors. Approval for construction was given by the Science and Technology Agency and announced on 13 December 1994. Japan Nuclear Fuel Ltd. (JNFL) announced that initial operation of the reprocessing plant being constructed in Rokkasho-mura, Aomori Prefecture has been delayed to July 2005. The previous plan called for operations to begin in January 2003.
|Join the GlobalSecurity.org mailing list|