Working for a Nuclear Free Japan -- Green Action


FAQs on Japan's prototype fast breeder reactor MONJU

May 29, 2005 (Revised)


Monju (280MW) is Japan's prototype fast breeder reactor located at the tip of the Tsuruga Peninsula in Fukui Prefecture. On January 27, 2003, the Nagoya Court of Appeals (Kanazawa Branch) handed down a verdict in favor of Fukui citizens suing to stop the reactor from operating. The court found the license issued by the national government for Monju illegal due to serious deficiencies in the government's safety review. On January 31, 2003, the national government appealed the decision.

The Supreme Court verdict on Monju is to be handed down May 30, 2005 in Tokyo.

Monju has been shut down since December 8, 1995 because of a sodium leak and fire accident. The accident occurred while the reactor was undergoing testing at low output before attaining full power.

The Japanese government and Monju's owner and operator, Japan Nuclear Cycle Development Institute (JNC) sought an early re-start of the reactor, and on February 6, 2005 Governor Nishikawa of Fukui gave approval for refurbishment work necessary for re-start. Construction work is underway.

Japan currently has 54 commercial nuclear power plants (light water reactors). These reactors use uranium for fuel and supply approximately 34% of Japan's electricity demand. Fast breeder reactor technology which uses a mixture of plutonium and uranium fuel has been under development in Japan since the 1960's with the aim of replacing the current inefficient nuclear technology. Plutonium, an element non-existent in nature, is created in conventional nuclear reactors as the uranium fuel fissions, and is extracted for use by reprocessing.

Advocates of the fast breeder claim that the technology would create a never-ending source of energy because it can convert uranium 238, an abundant isotope of uranium that could not be used as fuel in conventional reactors, into plutonium, thus breeding even greater quantities of plutonium than was put into the reactor.

However, in spite of being the main pillar of the Japanese government's nuclear energy long-term development plan for decades, and costs exceeding 2 trillion yen, the fast breeder program has to date produced only one hour of electricity (at Monju in September 1995). (The ﹍Long Term Program for the Research, Development and Utilization of Nuclear Energy﹎ is reviewed once every 5 years. The fast breeder program has to date been a part of nine Long Term Programs.)

Commercialization of the fast breeder is nowhere in site. The Japanese government's Long Term Program [November 2000] now makes no mention of specific goals for commercialization. The current program nevertheless calls for the early re-start of Monju.

Nuclear weapon states such as the USA, Britain, and France spent decades developing fast breeder technology as part of their nuclear weapons and energy programs. However all three countries have since abandoned their programs. Germany also constructed a prototype fast breeder reactor at Kalkar but abandoned the program before the reactor went into operation.


Fast breeder reactor technology is dangerous because it uses immense quantities of plutonium. In addition the fast breeder is vulnerable to reactivity accidents (explosions). Monju requires 1.2 tons of plutonium. The half-life of plutonium is 24,000 years (i.e. it takes 24,000 years for plutonium's radioactivity to halve). One millionth of 1 gram of plutonium entering the lungs can cause lung cancer.

Fast breeder reactors, unlike conventional nuclear reactors that use water as a source of coolant, use sodium to cool the reactor and transfer the heat for electricity generation. Sodium burns and explodes when it comes into contact with air and water. In Monju, the thickness of the pipes separating the sodium from the water is only 3.8 mm thick. Many fast breeder reactors that were under development in the world have suffered accidents involving sodium.

Although proponents state that the plutonium that fast breeder reactors would breed would provide a virtually never-ending source of energy, it is highly doubtful whether fast breeders could ever operate long enough without technical difficulties or accidents to produce enough plutonium to be worthwhile as an energy source.

Fast breeder reactors are particularly vulnerable to earthquakes since the high heat generated by the reactor has made it necessary for the pipes to be bent in many locations in order to absorb the expanding and shrinking of pipe materials, and pipes are strung up in this configuration. Monju is located in an area with several earthquake faults.

Commercial use of plutonium involves the handling of massive quantities of this nuclear weapon capable material. Only a few kilograms of plutonium are necessary to make a nuclear weapon. (The IAEA considers 8 kilograms to be an SQ, significant quantity, enough to make one nuclear weapon.) One commercial breeder would require approximately 10 tons of plutonium, five tons approximate in the reactor and an additional five tons approximate for refueling. If fast breeder reactors were to supply the same amount of nuclear energy as is currently supplied in Japan by conventional nuclear power plants, they would require more than twice the plutonium as is in all the nuclear weapons worldwide today.

The plutonium Monju would breed if operated, although not great in quantity, is super weapons-grade plutonium. One of the reasons nuclear weapon states developed fast breeder technology was to obtain this type of plutonium. Possession and development of such technology by Japan would be a detriment to Asian regional security.


Even if development of the fast breeder were to proceed according to hopes of advocates, the technology would not be capable of supplying 1% of Japan's energy needs in the mid-21st century. (Five full size fast breeder reactors operating at capacity would supply little more than 1% of Japan's total energy needs based on current demands. Commercialization by 2050 is considered to be difficult even by fast breeder advocates.)


Without a fast breeder program or use of MOX (mixed plutonium and uranium) fuel at conventional nuclear power plants in Japan, the Japanese government and electric utilities would need to admit that there is no need to extract plutonium from the spent nuclear fuel of nuclear power plants. If there is no need for plutonium to be extracted from the spent nuclear fuel, it would become unnecessary to ship this fuel to the Rokkasho Reprocessing Plant in Aomori for reprocessing. Without being able to ship the fuel to Rokkasho, the fuel would "overflow" at nuclear power plant sites and utilities would be forced to shut down their nuclear power plants because there would no longer be space to store the spent fuel.

The breeder program is a hoax energy program, and one of the reasons for continuing the program is to defer dealing with the nuclear waste problem. There is also concern that Japan continues the fast breeder program because the Japanese government wants to maintain and develop its plutonium technology with the intent of keeping the options open to some day possess nuclear weapons. Another reason given for the program continuing is bureaucratic stagnation and Diet inaction.


Citizens nationwide have submitted more than one million signatures calling on the Japanese government to initiate a moratorium on Monju. The civil and administrative lawsuit against Monju filed in September 1985 by Fukui Prefecture citizens although ending in plaintiffs' defeat in March 2000, was reversed by victory in the Court of Appeals as mentioned above.

More than 200,000 Fukui Prefecture citizens are on record signing a petition seeking permanent closure of Monju. Another national petition drive is on-going demanding complete closure of Monju, and 980,000 signatures have been gathered to date.

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