Washington has urged Tokyo to return storage of nuclear materials

Washington's demand that Tokyo return 331 kg of weapons-grade plutonium demonstrates that, in addition to concerns over nuclear terrorism, the United States is monitoring Japan's capacity to develop nuclear weapons, observers said.

Kyodo News Agency quoted government sources on Sunday as saying that Japan has given in to strong demands from the administration of US President Barack Obama to return the plutonium provided for research purposes during the Cold War.

"Washington hopes to reduce Tokyo's storage of nuclear materials at a time when the potential is growing for Japan — a nation swinging to the right politically — to further its nuclear development," said Xia Liping, dean of the School of Political Science and International Relations at Tongji University in Shanghai.

Since 2010, the US has urged Tokyo to return the plutonium to prevent nuclear materials from falling into the hands of terrorists, the news report said.

But Tokyo has resisted, saying the plutonium is needed for researching fast reactors.

The batch of plutonium, which could be used to produce 40 to 50 nuclear weapons, is now supplied for use as nuclear fuel at the Japan Atomic Energy Agency's fast critical assembly in Tokaimura, Ibaraki prefecture.

The facility, which attained criticality in 1967, is Japan's only critical assembly designed to study the fast reactors.

Xia said that aside from the concern over terrorists, the US, which dropped two atomic bombs on Japan's Hiroshima and Nagasaki in 1945 during World War II, also wants to prevent Japan from becoming a country capable of producing nuclear weapons.

He suggested that Tokyo may have been accumulating nuclear materials over the years to prepare for nuclear programs, and that even holding nuclear materials served as a potential threat to Japan's neighbors.

Kyodo cited an unnamed Japanese expert as saying that Japan has another estimated 44 tons of plutonium, but its quality is not on a par with the plutonium used for research purposes.

"The materials that Japan currently possesses could produce 1,000 atomic bombs," Xia said.

"According to some Japanese experts, Japan could even produce nuclear weapons within a month," he added.

Zhai Dequan, deputy secretary-general of the China Arms Control and Disarmament Association, said the US will limit Tokyo's such moves.

"Washington is by no means equivocal on this issue," he said.

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