THE HAGUE - Japan will turn over hundreds of kilograms of sensitive atomic material of potential use in bombs to the United States to be downgraded and disposed of, the two countries' leaders said ahead of a nuclear security summit on Monday.
China had voiced concern earlier this year about Japan's holding of plutonium but Washington and the United Nations nuclear agency in Vienna have made it clear they are not worried about the way Tokyo is handling the issue.
US President Barack Obama and Japanese Prime Minister Shinzo Abe said in a joint statement that all highly enriched uranium (HEU) and separated plutonium would be removed from the Fast Critical Assembly at the Japan Atomic Energy Agency.
Like uranium, plutonium is used to fuel nuclear power plants and for research purposes, but can also provide material for nuclear weapons. A Fast Critical Assembly is used for studying the nuclear physics of so-called fast reactors.
"This effort involves the elimination of hundreds of kilograms of nuclear material, furthering our mutual goal of minimizing stocks of HEU and separated plutonium worldwide, which will help prevent unauthorized actors, criminals, or terrorists from acquiring such materials," said the joint statement released by the White House.
"This material, once securely transported to the United States, will be sent to a secure facility and fully converted into less sensitive forms."
The announcement was made in The Hague shortly before leaders from 53 countries, including Obama and Abe, were due to hold a two-day summit aimed at preventing al Qaeda-style militant groups from acquiring nuclear bombs.
It will be the third such summit since 2010, when it was held in Washington at Obama's initiative. Minimizing civilian uses of HEU or plutonium is seen as vital in reducing the threat of nuclear terrorism.
CHINESE "EXTREMELY CONCERNED"
The plutonium, the statement said, would be prepared for "final disposition" and the HEU would be downblended to low-enriched uranium for civilian purposes.
Last month, China said it was "extremely concerned" by a report that Japan has resisted returning to the United States more than 300 kg (660 lb) of mostly weapons-grade plutonium.
Japan's Kyodo news agency at the time said the United States had pressed Japan to give back the nuclear material, which could be used to make up to 50 nuclear bombs. Japan had balked, but finally given in to US demands, Kyodo said.
The material was bought for research purposes during the 1960s. An official at Japan's Education Ministry said in mid-February that the two governments would probably reach an official agreement on its return at summit in The Hague.
Nuclear-armed China is involved in a bitter territorial dispute with Japan. It denies Japanese accusations that it is a threat to peace and in turn has accused Japan of trying to rearm and failing to learn the lessons of its brutal behaviour during World War Two, when Japanese forces occupied China.
Japan, the world's only target of atomic bombs in the final stages of World War Two, does not have nuclear weapons and says it will not seek to obtain them.
Chen Kan, secretary general of the China Arms Control and Nuclear Disarmament Association, said before the US-Japanese announcement that Japan "in recent years" has been stockpiling a large amount nuclear material, including HEU and plutonium.
"Experts believe such Japanese stockpiling activities have far exceeded the normal necessity of its domestic use of nuclear energy," he told a news conference on the sidelines of the summit in the Netherlands.
Japan also has plutonium contained in spent nuclear fuel at civil reactor and reprocessing sites, totaling 159 tones at the end of 2012, according to Japanese data on the website of the International Atomic Energy Agency (IAEA).
A White House fact sheet said Japan's Fast Critical Assembly came online in 1967 when HEU and plutonium were believed to be required for the type of experiments it was involved in.
But recent advancements have changed that and it will now become the world's first "major fast critical facility to convert from HEU and separated plutonium fuels, marking a significant milestone for global nuclear security," it said.