Future of Japan's Monju plutonium breeder reactor under review

Masafumi Takubo and Frank von Hippel

On 29 August 2016, Mainichi Shimbun reported on an ongoing review by Japan's Cabinet Secretariat of options for the future of Monju. According to Mainichi, the Secretariat estimates that it would cost ¥600 billion (~$6 billion) to operate Monju for ten years. Japan's Atomic Energy Agency (JAEA) estimated in December 2012 that decommissioning the reactor would cost ¥300 billion (~$3 billion).

JAEA completed construction of its 350-MWe Monju prototype fast-neutron reactor and connected it to the grid in August 1995 but the reactor was shut down four months later by a fire caused by leakage of its molten sodium coolant. It was restarted again 15 years later, in May 2010, but was shut down again three months later by a refueling accident. Since 2012, it has been impossible to restart the plant because of safety inspection violations. The plant therefore has operated a total of only 250 days in two decades. In November 2015, Japan's Nuclear Regulation Authority called for new (non-JAEA) management but none of Japan's nuclear utilities has been willing to take the project on.

With the huge projected costs for restarting the plant and no operator in sight, it would be natural for the Shinzō Abe Administration to consider cancelling Monju - as France, Germany, the United Kingdom and the United States cancelled their prototype breeder reactors in the 1980s and 1990s.

Cancelling Monju would bring Japan's whole plutonium program into question, however. The Abe Administration's new reprocessing law, discussed below, suggests that it is unwilling to accept such a prospect.

The price for restarting Monju would include the cost of upgrading it to post-Fukushima-accident safety standards for fast-breeder reactors. Those standards have yet to be established. It also would include the cost of upgrading the safety of Japan's Tokai Plutonium Fuel Production Facility (PFPF) so that it could produce fuel for Monju at an estimated cost of nearly ¥100 billion(~$1 billion). Japan's Ministry of Education, Culture, Sports, Science and Technology (MEXT), which funds Monju, says some of its fuel would have to be replaced even before startup because of the loss of reactivity due to decay of the 14-year half-life isotope Pu-241. Sixty percent of the 1995 core had to be replaced in 2010 for this reason.

The ¥1.2 trillion (~$12 billion) spent on Monju thus far already makes it comparable in cost to France's much larger (1240 MWe) Superphénix breeder reactor, which was shut down in 1998 after operating for 13 years at an average capacity factor of only 5.5 percent. (The global average capacity factor for water-cooled power reactors was 74 percent in 2015.)

The total failure of the Monju project creates an opportunity for Japan to reconsider the future of Japan's Rokkasho Reprocessing Plant (RRP), now the only remaining plant dedicated to separating nuclear-weapon-usable plutonium in a non-nuclear-weapon state. Although the commercial operation of the RRP has been repeatedly delayed - cumulatively for 20 years at this point - the Abe Administration's plan is to start operations as soon as possible.

Japan's fast-neutron breeder-reactor program, with Monju as its flagship, was the original and is still the ultimate rationale for the reprocessing program. In the 1960s and 1970s, the purpose of civilian plutonium separation in Japan and other countries was to supply startup plutonium fuel for breeder reactors that, thereafter, would supply their own plutonium fuel by "breeding" it out of the abundant non-chain-reacting uranium isotope, U-238. But the liquid-sodium-cooled breeder reactors proved economically uncompetitive with water-cooled reactors fueled with uranium enriched in natural chain-reacting U-235.

Due to the economic failure of their breeder programs and the resulting accumulation of separated plutonium in France and Japan, the near-term rationale for their fast-neutron reactor development programs shifted to fissioning separated plutonium and other long-lived transuranic elements (reactor-produced elements heavier than uranium) so as to remove them from radioactive waste to be placed in final geological disposal sites. The slow neutrons in water-cooled reactors can only fission some of these isotopes. Breeder-reactor advocates promoted fast-neutron reactors to fission transuranics despite the fact that those responsible for radioactive management in both countries had concluded that doing so would not significantly reduce the danger to surface waters from deeply buried radioactive waste.

Despite the loss of the rationale for reprocessing, Japan's Government recently buttressed the RRP financially by passing a law to create an organization authorized to collect funds from Japan's nuclear utilities for reprocessing spent fuel at the time it is generated. The purpose of the law is to guarantee that all of Japan's low-enriched power reactor fuel will be reprocessed and the recovered plutonium fabricated into MOX fuel, even if the utilities owning the power plants producing the spent fuel go bankrupt when Japan fully liberalizes its electricity market.

According to a 2011 estimate by Japan's Atomic Energy Commission, operating the RRP will cost about ¥200 billion (~$2 billion) per year to produce plutonium with a fuel value that is less than the cost of fabricating it into fuel. The economics of reprocessing in France are similarly irrational. One therefore needs to find other explanations than those stated for the persistence of reprocessing in France and Japan. Partial explanations include:

  • The thousands of jobs and government subsidies to local and regional governments associated with reprocessing and related facilities have become important to the rural areas where they are located;
  • Abandoning the pursuit of a plutonium economy would be seen by elite nuclear technocrats as an admission that they had wasted the equivalents of tens of billions of taxpayers' dollars;
  • Reprocessing is government policy and therefore not responsive to market economics; and
  • In Japan, some see its reprocessing capability as providing a virtual nuclear deterrent.