Monju Fast-Breeder Reactor Set for Decommissioning

Science Technology

At a September 21 ministerial meeting, the Japanese government took a step toward decommissioning the Monju fast-breeder reactor in Tsuruga, Fukui Prefecture. Cabinet members involved in nuclear power policy agreed to draw up plans within the year for the development of a new fast reactor to replace Monju, operated by the Japan Atomic Energy Agency. The formal decision to decommission the reactor will be made after the plans are complete. The government will maintain its fuel-recycling policy, though, and establish a committee, headed by the minister of economy, trade, and industry and comprising government and business representatives, to discuss the road ahead.

Japanese media sources indicate that Japan is likely to pursue joint research with France on its planned ASTRID fast-breeder reactor. Despite the colossal investment of more than ¥1 trillion to date, Monju has been inoperative for most of its lifetime, being plagued by accidents and technical difficulties. Its decommissioning represents a major turning point in Japan’s energy policy.

Only 250 Productive Days

In the nuclear fuel cycle, used fuel from nuclear plants is reprocessed to extract uranium and plutonium so it can be recycled as fresh fuel. Fast-breeder reactors, which produce more fuel than they consume while simultaneously generating power, are a key part of the government’s fuel cycle strategy. Dubbed “dream nuclear reactors,” they have been under development since the 1960s.

Construction of the first-stage experimental reactor Jōyō began in 1970, and it reached criticality in 1977 but is no longer in operation. This was followed by the start of work on the second-stage prototype reactor Monju in 1980, and there were two further planned stages that would have ultimately led to a practical-use reactor.

However, just four months after Monju started generating electricity in August 1995, a sodium leak in the cooling system caused a fire, and the reactor was shut down. It did not come into operation again until 2010, but another accident soon took it offline. It has since faced numerous issues and has only notched up 250 productive days in its 22 years of existence.

Monju Timeline

1968 Power Reactor and Nuclear Fuel Development Corporation (now Japan Atomic Energy Agency) begins preliminary design of a fast-breeder reactor.
1970 Tsuruga in Fukui Prefecture is selected as the construction site for the new reactor, which will be named Monju.
1985 Construction begins.
1991 Test run begins.
April 1994 Criticality reached.
August 1995 Starts generating power.
December Sodium leak causes fire, and the reactor is shut down.
August 2007 Design changes to improve safety is completed and verification tests begin.
May 2010 Reactor restarts after more than 14 years.
July Scheduled suspension of operations.
August Restart put off after a fuel transfer device falls into the reactor vessel.
2012 JAEA is revealed to have failed to conduct many required equipment safety checks.
May 2013 The Nuclear Regulation Authority orders the indefinite suspension of operations.
November 2015 The NRA advises the Ministry of Education, Culture, Sports, Science, and Technology to replace JAEA as the operator of Monju.

Cost of Meeting New Regulations Too Great

There are two major factors behind the decommissioning decision: the systematically inadequate implementation of safety management and the astronomical costs of maintaining the reactor if restarted.

In 2012, it emerged that 9,679 equipment checks required by safety regulations had not been performed at Monju. When the Nuclear Regulation Authority inspected the facility the following year, it found further cases in which some of the most important equipment for ensuring safety had not been properly checked. Then in 2014, it came to light that more than 50 cameras for monitoring the facility did not actually work. In November 2015, the NRA advised the Ministry of Education, Culture, Sports, Science, and Technology to replace the operator of Monju, but the ministry failed to take concrete measures.

New regulations introduced following the March 2011 accident at Fukushima Daiichi Nuclear Power Station also meant that restarting Monju would require major reconstruction work, including increased earthquake resistance. The government estimated that improvements would cost an additional ¥580 billion, and that it would take 10 years before the reactor could go online again. As ¥20 billion is needed for annual maintenance alone, increasing calls from within the government for decommissioning paved the way for the end of the Monju experiment.

(Banner photo: The Monju reactor in Tsuruga, Fukui Prefecture, on November 11, 2015. © Jiji.)

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