About 750 people took part in a rally on 8 December to commemorate the 1995 accident at Monju, Japan's prototype fast breeder reactor (FBR), at Tsuruga City, Fukiui Prefecture. The demonstrators further expressed their opposition to the planned restarting of Monju.
(560.5353) WISE Hiroshima - On 8 December 1995 there was a sodium coolant leakage and subsequent fire at Monju - one of the most feared types of accident, and the subject of repeated warnings from anti-nuclear experts and groups.
The cause was a very simple design mistake: a breaking temperature sensor. In order to control and monitor the operation of the plant, many sodium coolant pipes contain temperature sensors. The design of these is like a long thimble (or "pocket") projecting from the wall of the pipe to near its center. In the 1995 accident the "pocket" had broken off, which started the leaking of the pipe.
The operator was the Power Reactor and Nuclear Development Corporation (PNC), now known as the Japan Nuclear Cycle Development Institute (JNC). PNC stated that the accident was unexpected and tried to pass it off as not serious.
The accident ended the government's plans for further construction of FBRs in Japan, but Monju itself is not permanently closed. It has been under safety review since June 2001, and after the necessary renovations, is supposed to restart in 2003 or 2004.
Before Monju can be put back into operation it will be necessary to replace all the thermocouple pockets of the same type as that which failed. The design of the replacement has not yet been finalized. The faster sodium can be drained from a leaking loop the more quickly any incident can be terminated. The design of the Monju secondary sodium draining system has therefore been re-examined with a view to shortening the drain time.
The information received in the Control Room from leak detection, smoke detection, temperature sensors etc. during the accident was presented to the operators on various panels and displays in such a way that it was difficult to understand and follow. A new dedicated sodium leak panel will be introduced which groups all information relevant to this type of incident.
Opponents filed a civil and administrative lawsuit against the operation of Monju in 1983, which is currently under appeal.
Experts warn that FBRs are more dangerous than conventional commercial reactors. Plutonium is highly toxic and more fissile than uranium, and the possibility of a core explosion is higher than with the other types of reactor. Sodium reacts easily with water and burns fiercely, making it technologically difficult to control safely.
Japan is also located in an earthquake-prone region, and there are several active faults near Monju, yet the structure of Monju FBR is more fragile than conventional reactors.
Before the sodium accident in December 1995, construction of a reprocessing plant for spent fuel from FBRs had been started. If the facility, called Recycle Equipment Test Facility (RETF), which is located in Tokaimura, is completed and goes into operation, it will separate super weapons-grade plutonium of high purity from 17.5 tons of FBR blanket fuel. Greenpeace International has revealed that sensitive technology for this was illegally transferred from five nuclear weapons laboratories in the United States, including the Savannah River site, and Oak Ridge National Laboratory.
It is clear that development of FBRs and continuation of reprocessing will undermine efforts towards non-proliferation, especially in this region of northeast Asia, where military tensions have been high. Moreover, the 11 September disaster in the USA alerted us all to the vulnerability of nuclear facilities to unexpected attack by terrorists.
Anti-nuclear groups, including "Stop Monju" and Citizens Nuclear Information Center, are campaigning for a million petition signatures for the scrapping of Monju FBR, and have so far collected more than 877,000.
On the sixth anniversary of the Monju accident, six citizens of Plutonium Action Hiroshima did a street action at the Atomic Bomb Dome in Hiroshima City. They gave leaflets to passers-by, reminding them of the accident six years ago, and tried to draw public attention to the government's intention to restart Monju FBR.
Sources:
- WISE Hiroshima
- www.jnc.go.jp/zmonju/mjweb/index.htm
Contact: Satomi Oba at WISE Hiroshima (dogwood@muc.biglobe.ne.jp)