The government’s Basic Energy Plan, updated last week after its first review in four years, features a pledge to reduce the nation’s stockpile of plutonium extracted from spent nuclear fuel. Today, the plutonium stockpile has reached 47 tons, including 37 tons stored in Britain and France, which have been commissioned to reprocess spent fuel from Japan’s nuclear power plants. The goal of reducing the unused plutonium stockpile was apparently made in view of a concern expressed by the United States, which under a bilateral nuclear pact authorizes Japan to reprocess spent nuclear fuel. Japan is the only non-nuclear weapon state with this authority.

A significant reduction over the short term is expected to be difficult. Behind the accumulation of unused plutonium is the government’s long-standing but stalemated policy of seeking a nuclear fuel cycle, which should be reviewed to reach a fundamental solution to the problem.

Under the elusive nuclear fuel cycle policy, plutonium extracted from spent fuel removed from nuclear reactors is to be converted into plutonium-uranium mixed oxide (MOX) fuel to be used either in fast-breeder reactors or in conventional nuclear plants. But Monju, the nation’s sole fast-breeder reactor and once deemed a prototype for a dream technology for this resource-scarce country because it produces more plutonium than it consumes as fuel, remained mostly idle after it reached criticality for the first time in 1994. It suffered a sodium coolant leak and fire in 1995 and a subsequent series of other problems, until the decision was made in 2016 to finally pull the plug for good.

The use of MOX fuel in conventional reactors, deemed a substitute way to consume the plutonium stockpile, has also not proceeded as expected. The government earlier planned to have MOX fuel used at 16 to 18 reactors across the country by 2015. But the restart of nuclear power plants idled in the wake of the 2011 meltdowns at Tokyo Electric Power Co.’s Fukushima No. 1 plant remains slow. Only four of the nine reactors that have so far been brought back online are capable of using the costly MOX fuel, and only in small amounts.

While the consumption of plutonium as reactor fuel stagnates, the reprocessing of the spent fuel to extract plutonium has also hit a snag. Completion of a reprocessing plant in Rokkasho, Aomori Prefecture — on which more than ¥2 trillion has already been spent — has been delayed for years due to a series of technical glitches. But once completed, the reprocessing plant supposedly will be able to produce up to 8 tons of plutonium annually, raising the specter of further increasing the stockpile of unused plutonium if its use does not pick up.

According to an outline reportedly compiled by the Atomic Energy Commission on a plan to “reduce or manage so as not to exceed the current levels” of Japan’s plutonium stockpile, the government will limit reprocessing of spent fuel at the Rokkasho plant to the volume that would be consumed as MOX fuel at conventional nuclear power plants.

The government will also prod power companies whose nuclear power plants have not yet been restarted to transfer their overseas plutonium stockpiles to other Japanese power firms whose reactors have been put back online, so that the plutonium can be consumed as fuel at the latter’s power plants. But how much such measures will help reduce the overall plutonium stockpile remains to be seen, given that the use of MOX fuel at restarted nuclear power reactors remains low.

The 1988 Japan-U.S. nuclear pact, which authorized Japan to reprocess spent nuclear fuel for 30 years based on the nuclear materials and technology provided earlier by the U.S. for the peaceful use of nuclear energy, will be automatically renewed this month after neither side sought to review the pact. Once the pact is renewed, it can be terminated six months after either party gives notification.

It has been reported that the U.S. recently requested Japan to account for the management and use of its plutonium stockpile. Earlier, the government maintained the position that Japan will not possess plutonium for which it has no purpose. In the new energy plan, it went a step further to include a pledge to try to reduce the stockpile — apparently in light of the concerns expressed by the U.S.

Now this pledge will provide a new challenge for the nation’s nuclear energy policy. The effort to follow through on it should involve reviewing the state of the elusive nuclear fuel cycle policy and whether it is still feasible.

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