Tokai (Japan)

Map of Tokai

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JPDR: BWR 15 MW shut-down 1982
GCR 150 MW by GEC, shut-down 1998
BWR 1100 MW grid connection 1978, by GEC
Reprocessing plant

Facilities in Tokai

plantreactor typconstruction startoperation startshut down
Tokai reprocessing plantreprocessing plant

"18 kg of uranium powder was carried in a powder handling box in the pellet fabrication room in the uranium fuel fabrication facility. This exceeds the box's 15 kg nuclear limit. The limit was exceeded on 3 occasions."


During start-up operation in Tokai-2, the outlet valve stem broke in the motor-driven feedwater pump. The valve stem had become brittle due to cracks along the crystal grain boundary, a feature of grain boundary type stress corrosion cracking. The stem broke when a load was applied.


"recirculation flux control valve component lapsed and missed at Tokai-II"


"Reactor Tokai II manually shut down due to feedwater stopped during test operation; one control rod failed to insert into reactor core."


"Reactor automatically shut down due to transmission line stoppage caused by lightning; one of 185 control rods failed to insert into reactor core."


In March 1998, Japan`s first commercial nuclear power plant, Tokai plant was shut down after being operated for 32 years.

After the reactor was shut down, the spent fuel was taken out of the reactor over a period of three years, and was sent to the reprocessing plant in Sellafield. U. K.
In December 2001 the Japan Atomic Power Company (JAPC) has started the dismantling of the plant. JAPC´s plan is to complete the decommissioning within about 17 years. The schedule consist of three stages. The first and second stages are termed the "safety storage period" since the reactor itself will be left untouched. The reactor core, heavily contaminated with radioactivity, will finally be dismantled about 13 years after its shut down. However, this 13 years period is extremely short compared to the decommissioning plans of other countries which have gas-cooled reactors (GCR).

JAPC expects about 177,000 tons of waste to be produced by the decommissioning process, they consider that 90 % of this waste does not need to be treated as radioactive materials according to the "clearance level" set by the government.

However, there is great uncertainty about the amount of waste that is likely to be produced. For example, when the Japan Atomic Energy Research Institute (JAERI)´s Japan Power Demonstration Reactor (JPDR) was decommissioned, the amount of generated waste far exceeded the original estimation. Accordingly, the amount of waste treated as radioactive material exceeded the estimate.

It is assumed that the total cost of the decommissioning process will be about 93 billion yen, with the cost for treating the waste at about 58 billion yen. The JAPC has said that the cost of about 6,7 billion yen for the first period will be paid "from their own assets (including the reserve fund)" but it is unclear where the money is going to come from for the second and third decommissioning periods.


The dismantling started and is due to finish in 2017. Since workers must wear heavy protective clothing, their work is limited to 30-minute shifts. The amount of waste is expected to total 177,000 tons, nearly 90 percent of which will be generated in the final dismantling stage after 2010. All the waste from nuclear power plants is currently kept on-site.


Worst NPP accident in history of Japan
A nuclear accident at a test facility in the JCO Ltd.'s uranium processing plant, Tokai took place in 10:35 am Japanese Standard Time (+900) on 30 SEP 99.

The uranium processed on September 30 at the plant was enriched to 18.8% of uranium-235, rather than the 3-5% used for commercial light water reactor fuel. Material of this high enrichment grade was being produced for the experimental Joyo Fast Breeder reactor. The uranium was of French military origin, this was confirmed by JCO Co. spokesman, Norimichi Mori, to the French daily Le Monde. French sources indicated that the 18.8% enriched uranium was exported in December 1997. The 420 kg of uranium had been enriched by Cogema in its military enrichment plant in Pierrelatte (shut down in 1996). The deal had been organized by the German nuclear fuel broker Nukem. Cogema stressed directly after the accident that it had no agreement with JCO Co. In fact, Cogema's client is JNC Co., operator of the Joyo experimental fast breeder reactor, which subcontracted the conversion work to JCO.

According to the Japan Atomic Industrial Forum (JAIC), the JCO's Tokai plant is able to process 715 ton uranium for light-water reactor fuel, and three tons of uranium for FBR fuel. The conversion of fuel for Joyo was the first operation of that kind in three years and only began on September 22. JCO employs 154 persons.

The criticality condition ceased at 6:30 a.m. October 1. At 4:30 p.m. the same day, the request to the residents (310,000 people) within a 10-km radius of the plant to stay indoors was lifted. At 6:30 p.m. on October 2, the evacuation advice to the residents within a 350-m radius of the plant was lifted and which was essentially saying that the government had made its "Safety Declaration". However, that did not mean that the situation became free of danger. As already mentioned, there is a precipitation basin full of radiation in the plant and it has been left untouched. Radiation was still being released from the complex by an air-conditiong system, which was only shut down on Monday, October 11, so nearly two weeks after the accident.

Criticality incidents occurred in the early history of nuclear energy in America and in Russia at military facilities and some research institutes, however, there have been no such incidents recently. Furthermore, there has never been an incident like this one in which the criticality condition continued for so long. This is the worst accident ever in the history of nuclear power development in Japan. The number of exposed people continues to increase and reached 63 as of October 9.
It has been reported that the criticality explosion accident happened during a refining process for highly-enriched uranium for the fast breeder test reactor, Joyo. Sixteen kg of highly-enriched uranium was filled into a settling basin designed for no more than 2.4 kg, an amount almost 6.5 times more than it should have been.

According to the Science and Technology Agency, three Japanese experts were sent to a special meeting of International Atomic Energy Agency (IAEA) to report on the criticality accident for IAEA staff members and representatives of various nations to IAEA. This meeting was held in Vienna in the morning of October 18th local time.

INES level 4 or 5?
The accident has been provisionally rated Level 4 on IAEA's 7-level International Nuclear Event Scale (INES). But on October 8, the Japan Atomic Industrial Forum have "unofficially" upgraded the accident at Tokai-mura to INES level 5; an "accident with off-site risk". The new rating has been agreed in principle by the relevant authority, the Science and Technology Agency. The new INES rating is not yet "official", and has not been reported to the IAEA in Vienna.

The chain reaction caused heavy releases of gamma and neutron radiation. Three workers were exposed to doses of up to 17 Sv, causing severe radiation sickness. Sixty others were irradiated at lower levels. Radiation levels remain high inside the plant building, preventing inspection of the damage inside the plant. First reports that an explosion had blown a hole into the roof of the facility have not been confirmed.

At the boundary of the facility, atmospheric gamma dose rates of 0.84 mSv/h (milliSievert per hour) and neutron dose rates of 4.5 mSv/h were recorded. The dose limit for members of the public is 1 mSv per year. Actual figures may have been higher, since recording started only several hours after the start of the chain reaction.



PNC admits Tokai incident report false:

The operator of Japan's nuclear fuel reprocessing complex at Tokai has admitted that an official report on last month's fire and explosion at the plant contained false information.
A spokesman for the state-run PNC said company officials had submitted a report to the Japanese government, stating that a fire at the Tokai plant had been extinguished. In fact, PNC officials had failed to verify that this was the case.
It is not yet clear when the fire was actually put out, but it is possible that it continued to smolder for several hours after it had been reported to be extinguished. The failure to douse the fire is believed by many analysis to have been the root cause of the subsequent explosion.


Tokai fire, explosion exposures reach 37, highest ever in Japan
The Asphalt Bituminization Treatment Facility is a peripheral part of the spent fuel reprocessing complex. It handles relatively high-end LLW liquids such as water used for rinsing equipment and off-gas. They are boiled to reduce their volume by evaporating water, and then mixed with asphalt and stored in drums.
The fire began at 10:06 a.m. on the conveyor line for asphalt-filled drums on the first floor. Alarms kicked in at 10:10, the sprinkler was manually activated at 10:12, and was shut off at 10:13. At 8:04 p.m. that evening, a massive explosion jolted the building, blowing out 30 windows and at least two doors and hatches. Radioactive material leaked outside and into the Low-Level Radioactive Liquid Waste Evaporation Facility.
There were a total of 112 workers in the two buildings at the time of the first fire and the later explosion. They were checked and 37 workers were found to have received some contamination, with the highest exposure 7,3 Bq cesium-137, PNC said. Himeno said nine of the 37 were found exposed after the fire and the rest from aerosols spread by the explosion, but he said doses were all from 10-4 to 10-3 of allowable limits.

The incident on March 11, has been classified as the worst nuclear accident in the nation's history.
The sprinkler system to put out the fire was left on for only one minute. It is believed that failure to extinguish the blaze completely led to the subsequent explosion.
Containment systems did not function effectively, so that radiation from the room with the fire leaked into an adjacent building, exposing workers, who were not evacuated until 24 minutes after the fire was noticed.
The fire started shortly after 10 a.m. in a chamber in which low-level liquid waste from the plutonium extraction process is mixed with asphalt and poured into metal drums for eventual disposal. The waste is so dangerous, that people are not allowed in the chamber and all of the work is done by remote-controlled machines.
The explosion, 10 hours later, blew out most of the windows in the four story concrete building, as well as some thick shutters and doors, allowing radiation to escape.
The cause of the fire is still not known.

Increases in radiation levels have reportedly been observed south-west of the Tokai Mura reprocessing plant following the recent fire and explosion. Tokai operator PNC admitted that there had been a five hour delay following the incident before authorities had been informed of the radiation release. The incident has now been officially confirmed as INES Level 3.

Workers in charge of plant repairs at the nuclear fuel processing plant in Tokaimura began a four-day golf tournament on the day of the accident. They continued playing the next day although it was clear that damage was more serious than initially thought.
Investigator's findings of official indifference and mishandling of emergency procedures in the aftermath of the accident have provoked widespread criticism.
Officials published that, the radiological health effects of the incident for workers on-site at the time were negligible. As said last week, 37 workers did inhale some airborne radioactivity, but in no case did any individual radiation dose exceed 1/2100 (less than 0,05%) of the permissible annual dose limit.
With regard to off-site releases, the document reproduces measurements taken around the period of the incident at an off-gas stack. However, there is no indication of the overall environmental impact of the releases, and PNC officials say investigations are still continuing. There have been recent media reports of significant temporary increases in airborne radioactivity levels at some distance from the plant, but even the reported levels would in no way be harmful to human beings.
There has been no official reaction by the PNC to media reports that the bituminisation facility at the Tokai reprocessing plant may remain shut indefinitely following the incident. However, one nuclear official in Tokyo said that if the facility were to remain shut down for a prolonged period it would be for political, not technical, reasons.
The maximum radioactivity dose was still reaching 1.200 µSv per hour in the asphalt-solidification facility of the Tokai Mura reprocessing plant. The maximum safe limit of dose rate for workers at NPPs is 50.000 µSv a year.


On June 28, the JAPCO formally decided that it will end commercial operation of the Tokai nuclear plant, probably at the end of March 1998 and begin decommissioning it. It will be the first of Japan's commercial reactors to go. The company plans to decommission the plant, by first removing the spent fuel over four or five years, allowing the reactor to cool down for five to ten years, and then dismantling the plant over about five years.
From the beginning of commercial operation in July 1966, the Tokai plant has had an average capacity factor of 62%. Last year problems occurred on seven occasions. It was out of service for the whole of 1993 to replace a low-pressure TU, which shows how aged the facility is. Decommissioning a 30 year old plant makes good sense but dismantling and disposal present a plethora of problems.
The company thinks that it will cost 25 billion yen to dismantle the plant, excluding the cost of managing the wastes (construction costs were 46,5 billion yen at 1966´s value).


Generator tripped due to sea water leak to main condenser.


Jaeri November 27 launched a test program of shallow underground disposal methods, utilizing some 2.000 metric tons of low-level radioactive waste (LLW) from Japan's decommissioned first power reactor.
The LLW to be disposed of its largely concrete chunks of reactor shields and contaminated structures from the Japan Demonstration Power Reactor (JPDR) in Jaeri´s Tokai Research Facility. The BWR was commissioned in 1963, and dismantling started in 1986.
Jaeri has just completed excavating a 45-by-16-meter pit at the reactor site, officials said. LLW will be placed in the pit, in a tier 3,5-m thick. This phase is scheduled to run through March 1996. Then the LLW will be covered by a 2,5-m-thick layer of landfill, they said. The surface will be covered with grass, the site will be fenced, and a management building built at the edge. The LLW disposal area will be covered by special tents to prevent rainwater from penetrating, engineers said.


Radioactive leak in sampling operation room.


Tokai-1 control rod rope cut. A rope that supports a control rod was severed due to friction caused by a wrongly-placed cutter, slamming the control rod into the reactor core of the 166-MW gas cooled reactor Tokai-1 of Japan Atomic Power Co., the Ministry of International Trade & Industry (MITI) reported. The incident, which took place October 24, reduced the reactor output.
A rope cutter is a device to chop off the rod-supporting rope hydraulically if the control rod drive fails to function in a scram. The cutter which caused the trouble was placed too close to the rope, officials said. Engineers were inspecting all the other rods, ropes, and cutters, they added.


Radioactive leak into steam piping in evaporator.


Graphite sleeve damaged during fuel transfer


Generator stopped due to sea water leakage into main condenser. The same failure ocurred again on April 21.


Spent fuel feeder shearing device failed


Three workers exposed to radiation. Residue solvent with 1 Bq alpha and 84 Bq beta activity contaminated their work clothes and boots.


Shutdown as solid residual glass was found stuck near the melter - 3 days after the facility produced its first vitrified HLW. It was the first acident in the brandnew (US$ 380 million) facility.


Start of construction of the advanced Recycle Equipment test facility (RETF) - designed to develop seperation technologies; cost: 1200 million US$; project is based partly on US DOE technology;


CR drive mechanism failure.


CR malfunctioned, reactor manually stopped.


Increase of containment floor drain water. Reactor manually stopped.


Fuel rod dropped during replacement.


Failure in fuel handling due to loosening of fuel assembly handle. Reactor stopped manually.


Radioactivity level of coolant CO2 increased due to pinhole in fuel cladding (recurrent)


Many washers found corroded and lost in auxiliary sea water cooling pump.


Difficulty in fuel replacement; Reactor manually shutdown, UNLOADING OF THE FUEL ELEMENT