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The Monju accident fall-out

Nuclear Monitor Issue: 

(January 19, 1996) The official in charge of investigating the cover-up of Japan's worst nuclear power accident committed suicide on January 13, by leaping from the roof of a Tokyo hotel, police said.

(445.4402) WISE-AmsterdamThe victim is Shigeo Nishimura, 49, deputy general manager of the general affairs department of the Power Reactor and Nuclear Fuel Development Corp. (PNC), the government corporation that runs the country's prototype fast-breeder reactor Monju. Nishimura leaped to his death the day after attending a news conference where officials revealed that the cover-up had extended from plant officials to company head-quarters in Tokyo.

He was tormented both by failure to get to the bottom of the cover-up and by the harm his inquiries would do to colleagues and the government corporation for which he worked for 26 years. "They (PNC staff) were confident in their technical ability. But they may have found it difficult to explain their panic and confusion from the accident. It is most difficult for people to judge others and discover the truth," Nishimura said in one of three suicide notes. He was investigating why plant officials took one hour to notify authorities about the leak and why video film of the incident was both edited and concealed from the press and government agency charged with determining what caused the leak.

The shock suicide was the latest fallout from the December 8 accident involving a massive coolant leak at Monju, Tsuruga, 320 km (200 miles) west of Tokyo (see WISE NC 444.4392).

Leak from defective weld? On December 11, the Fukui prefectural officials and, separately later, STA (Science and Technology Agency) officials together with PNC (Power Reactor and Nuclear Fuel Development Corp.) staff entered the secondary sodium piping room where the leakage took place, in order to conduct a short survey of the spot. According to the reports of the survey, the leak seemed to have occurred from a defective weld of a tube for temperature measurement attached to one of the 55 cm main secondary lines (loop C). The welding of the tube was carried out in 1991 when PNC had to remodel the whole loop due to design fault. At this time the old thermometer tube was removed for ease of reconstruction works and after the works a new one was welded. This process is regarded to be the cause of the defect.

Heap of Rubble
The video pictures taken by the Fukui officials as well as by NHK TV team showed that the room is like a heap of rubble. The observation of the survey teams made clear that:

  1. Sodium oxide and sodium hydroxide deposited most intensively around the defective tube and the area directly under the tube. But they were observed in a wide range of areas, suggesting the sodium-water reaction lasted for hours vigorously, filling the room with fumes and spreading the reaction products all over the room.
  2. Some steel structures including the thermometer tube, ventilation duct inlet and floor directly under the breached part showed the evidences of melting, indicating that the burning of sodium gave rise to a very high temperature of over 1500 C.
  3. The video pictures of the room together with theoretical considerations strongly suggest that the spay fire, one of the most feared type of sodium reactions, actually took place, contrary to the initial PNC statement: "a minor leakage in the secondary sodium loop caused some fumes."

PNC Cover Up
In the first few days quite a few malfunctions, failures and controversial PNC practices were revealed:

  1. The sodium leakage detectors did not work as expected
  2. The thermometer at the very spot of leakage first showed a sharp rise to 600§C and then failed due to excessive heat
  3. The first signal of leakage came from the sharp temperature rise and the fire alarm was actuated almost at the same time at 7:47 p.m. In addition the operators observed fumes in the room. One minute after, the leakage detector responded. In spite of these clear evidences of sodium leakage, the operators took another 12 minutes to conclude that it was a sodium leakage. They started to coast down the reactor power at 8:00. And as it was a slow coast down of power, the reactor was brought to complete halt only at 21:20. This is a violation of the operation manual which provides that the reactor be shutdown immediately when a sodium leak is detected.
  4. PNC behaved scandalously in this accident, too. On the second day after the leakage, PNC team entered the room and took video pictures. What they released to TV networks as the "pictures of the spot" were mostly pictures of intact pipes and clean floors, and the only picture related to the leakage was a picture of a corner of the room with a lump of reaction products. It was a trick to play down the seriousness of the accident. The actual scene of the disastrous damages with molten steel structures and reaction products spreading all through the room were made public only after the prefectural survey team took video pictures two days after and released them. The first two videos released by PNC were 1 minute and 4 minutes long. PNC claimed that was all the footage they had, but later it came out that there was an 11- and a 4-minute video made. On Dec. 22, the STA discovered a third PNC video during it's investigations.
  5. The third video showed that the workers entered the room at 6 a.m. Dec. 9 and not 10 a.m. (4 hours later) as reported by PNC.
  6. The report of the accident to the local governments was delayed by an hour, which made the local residents extremely angry.
  7. The air conditioning was not stopped at the time of the accident, but only three hours later. Under the regulations, PNC must shut down the air conditioning ducts if fire alarms sound. Some nuclear experts say the negligence might have helped enlarge the scope of fire.

Interim report on accident
On Dec. 26 an interim report issued by the Fukui prefectural government. One conclusion of the report: "There are serious faults with basic issues at the plant, issues which are indispensable in winning residents' trust in nuclear power". Warning systems and written instructions at Monju were not adequate and pointed out the following:

  • Gauges measuring volume of leaking sodium were not in the same room where the alarms were located
  • there were no television cameras to monitor the portion of the plant where liquid sodium circulated
  • air ducts were located directly beneath pipes where the leak occured
  • the instruction manual did not give the duty director the authority to stop the reactor.

Bleak Outlook of Pu Program
PNC and STA started an investigation of the cause of the accident, after taking out the primary and secondary sodium from the loop C and then cleaning up the room. If it is found that the defective weld was really the cause, it will take a long time to inspect all the other welds in the primary and secondary sodium lines as well as in water lines before restarting. But a main problem is obviously that the corrosive coolant (sodium) is too dangerous. According to Jinzaburo Takagi of the Nuclear Citizens Information Center, luck prevented a real disaster. The reactor was only running at 40 percent of its capacity when the accident took place in a secondary cooling system relatively far from the reactor core. If this had occurred on a larger scale, it might have affected the core and could have caused a radioactive release or even an explosion of the whole reactor. It is highly likely that the Fukui Prefectural Government and other local governments will strongly resist the restart of Monju.

On december 12, Tukio Kurita, the governor of Fukui Prefecture, lodged a protest with Prime Minister Tomiichi Murayama over the unfaithful attitudes of the central government and PNC, demanding the government to suspend all the experiment plans on Monju. The anti-nuclear movement, which is already active and persistent, particularly against Monju and Japan's plutonium policy, will surely gain ground. On Sunday December 17, 600 demonstrators took part in a rally in Turuga.

Now that PNC and STA have lost the confidence of the public completely, the outlook for restart is bleak. On December 12, the Japanes daily newspaper Asahi Shimbun predicted that it would take, "in the worst case", two years for Monju to restart. In a reverse sense, restart after two years may be a worst-case scenario for the anti-nuclear movement, who have to bring it into a scrap before two years. After being stored for two to three years, plutonium, the fuel for Monju, can no longer be used; it degrades. According to PNC officials the fuel can be used in other Japanes reactors.

The plan to build a 600 MW class demonstration FBR should be frozen. In the current long-term nuclear energy program, construction of this demonstration reactor is due to start in the beginning of the next century. But this reactor is supposed to be constructed on the basis of the experiences with the prototype FBR Monju, which has now clearly proven to be big failure.

There is now good reason to scrap the whole FBR program and review Japan's plutonium policy thoroughly.


  • Information Updat, CNIC, 12 Dec.
  • Japan Times, 13, 19 and 23 Dec.
  • reuter, 26 Dec. 1995, 13 and 14 January 1996

Contact: Citizens' Nuclear Information Center, 1-59-14-302 Higas-hi-nakano, Nakano-ku, Tokyo 164, Japan. Tel: +81-3-5330-9520; Fax: +81-3-5330-9530