Japan and the United States extended on Tuesday a bilateral nuclear agreement that has served as the basis for Tokyo's push for a nuclear fuel recycle policy.
The pact, which entered into force in July 1988, has authorized Japan to reprocess spent fuel, extract plutonium and enrich uranium for 30 years. As neither side sought to review it before the end of the term, it will remain effective, leaving Japan the only country without nuclear arms that is allowed to reprocess spent nuclear fuel.
(A spent nuclear fuel reprocessing plant in Rokkasho, Japan)
But the passing of the initial 30-year period raises uncertainty over the future of the pact, now that it can be terminated anytime six months after either party notifies the other.
The United States is seen as concerned about Japan's stockpiles of plutonium, though Tokyo has limited its research, development and use of nuclear energy to peaceful purposes.
"Japan will do all it can to maintain the nuclear nonproliferation regime while keeping the (Japan-U.S.) nuclear pact," Foreign Minister Taro Kono told reporters.
"It will be important to make efforts toward reducing the large amount of plutonium that Japan possesses," Kono added.
Japan has around 47 tons of plutonium, which is enough to produce about 6,000 nuclear warheads.
Of the 47 tons, around 10 tons were stored in Japan and the reminder in Britain and France as of the end of 2016, according to government data.
In early July, Japan clearly stated for the first time in its basic energy plan that it will trim the amount.
Spent fuel from nuclear reactors is reprocessed to extract uranium and plutonium, which is then recycled into fuel called mixed oxide, or MOX, for use in fast-breeder reactors or conventional nuclear reactors.
But following the 2011 Fukushima nuclear disaster, most of Japan's nuclear power plants remain offline as they are required to pass newly established safety regulations.
The administration of Prime Minister Shinzo Abe has maintained its pro-nuclear policy, saying that plants that can clear the new stricter safety checks will resume operation. But restarting them seems difficult amid persisting safety concerns.
Nuclear regulators are still assessing the safety of a planned spent nuclear fuel reprocessing plant in northeastern Japan after repeated delays to the start of the plant.
The Rokkasho plant, a key pillar of the country's nuclear fuel recycling policy, will be able to produce around 8 tons of plutonium a year when fully operational.