Coolant system mishap at Japan’s long-stalled Monju fast breeder sends cautionary note to other nations pursuing same technology

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Publish date: April 28, 2010

Written by: Charles Digges

NEW YORK – The Monju prototype fast breeder nuclear power reactor, which has been gearing up for an early May restart after a 15-year stoppage, suffered a temporary glitch in a coolant leakage detector Tuesday that the Japan Atomic Energy Agency reported had no impact on the environment, Japanese media reported.

However, one Japanese nuclear industry source familiar with the Monju project was quoted as saying in Japan Today that malfunctions of this type – and worse – are “inevitable” in such reactors.

The government-affiliated agency said the sodium detector, housed in an auxiliary building to the reactor at the Monju centre in Tsuruga, Fukui Prefecture, came to a halt after a fan motor overheated, triggering an alarm at 11:59 p.m. Monday.

A fire accompanying a sodium leak shut down the reactor in December 1995, and the project has not been restarted since. Another restart date for the reactor had been scheduled for March 2009.

That the reactor would still be ailing in its sodium coolant detection system should give pause not only to Japanese authorities but other nations that are considering adding fast breeders cooled by liquid metal sodium to their nuclear power production fleets – most notably the Russia and the United states.

Early in April, Russian Prime Minister Vladimir Putin said the Russian government would set aside $2 billion to push forward with  sodium cooled fast breeder  units of about 800 MWw, and the construction of a 100MWe lead-bismuth-cooled fast reactor called the SVBR by 2015.  Russia is currently operating the BN-600 fast breeder near Beloyarsk.

The United States, in the wake of the Obama administration’s decision to close down the flawed Yucca Mountain spent nuclear fuel repository, has appointed a Blue Ribbon Commission to examine different methods of storing spent nuclear fuel and reactors that produce less of it. One item on the commission’s agenda, according to US Energy Department officials close to the talks, is the use of fast breeders in America’s nuclear mix.

The dangers of fast neutron or breeder reactors

The theory behind fast breeders is their ability to produce more fuel than they consume during operation – most commonly plutonium or plutonium and uraniam mixed oxide (MOX) fuel. The spent fuel can easily be refabricated into new fuel, creating something of a nuclear perpetual motion machine.

But as much as officials in many governments, especially in Russia, say that fast breeders are key to reducing proliferation, environmental groups say the spent fuel generated by such reactors is far more than needed to keep them running, and poses a risk of adding to the worldwide plutonium stockpile.

Environmentalists also assert that the process to refabricate the fuel for reuse is extremely dangerous to the environment, and that accidents at plutonium powered reactors could be several times more catastrophic than accidents at current uranium water cooled reactors.

Nuclear industries throughout Europe and Japan have furthermore been trying to get the science of breeder reactors down for dozens of years and with costly research and development – and are still, as exemplified by the Tuesday’s glitch at Monju, far from a safe resolution.

Progress on these and traditional reactors, however, continues as many countries have been persuaded that nuclear power, with its zero emissions during power production, will turn the tides of climate change – a point Bellona vociferously refutes.

Miwako Ogiso, a member of a local anti-nuclear group, told Japan Today the incident was ‘‘an alarm against the resumption of operation. Monju, which has sat idle for 15 years, is never safe.’‘

The incident was revealed just one day after a local government expressed the intention to allow the resumption of the reactor’s operation in exchange for pledges for subsidies and incentives from the central government.

Japanese authorities sorting out incident

The Japan Atomic Energy Agency said it is investigating the cause of overheating of the sodium coolant unit at the Monju reactor. But the nature of the cause could impact the Monju reactor’s resumption, expected in early May at the earliest.
On the possible impact for the restart, Japanese nuclear industry minister Masayuki Naoshima fell short of making a clear-cut statement, saying, ‘‘It could or could not have’’ an impact.
Science and technology minister Tatsuo Kawabata, whose ministry oversees the atomic energy agency, told Japan Today that the agency responded aptly in communicating the incident to the local community and in handling the restoration.
The troubled unit, among 614 detectors, was repaired by 4:58 a.m. Tuesday after replacing components, and normal function was restored by 5:24 a.m., the atomic energy agency said, according to Japan Today, adding that no leakage was detected.

Monju’s hazardous history   

The Monju reactor has been idle since December 1995 after a fire that was caused by a sodium leak. Sodium is used as a coolant in most typical fast breeder designs, but it is far more prone to leakage, and reacts quickly with oxygen in the air, causing flames.
Following the 1995 fire at Monju, more detectors have been installed. But these detectors have been a source of concern because of the ensuing malfunctions. Such malfunctions “are inevitable in a way because their sensitivity level is increased for early detection of leakage,” an industry source told the Japan Times anonymously.

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