TOKYO, Jan. 26 (Xinhua) -- Japan's key ally the United States has been pressing the country to return more than 300 kg of mostly weapons-grade plutonium that exported to Japan for research purposes during the Cold War, reported local media.
The plutonium that stored at a fast critical assembly in Tokaimura in Japan's Ibaraki Prefecture could be used to produce 40 to 50 nuclear weapons, reported Japan's Kyodo News, citing unnamed Japanese and U.S. government officials.
Japan has strongly resisted the demand raised by U.S. President Barack Obama's administration, but it finally gave in to repeated demands, Kyodo said.
The two countries since last year have been seriously discussing the issue as the United States plans to reach an accord with Japan at the third nuclear security summit in March in the Netherlands, according to the report.
The fast critical assembly belonged to the Japan Atomic Energy Agency is Japan's only critical assembly designed to study characteristics of fast reactors.
The Japanese Ministry of Education, Culture, Sports, Science and Technology and other researchers have argued that the plutonium in question is needed for research and vital for producing good data, said Kyodo.
At present, Japan has another estimated 44 tonnes of plutonium, but its quality is not on par with the plutonium used for research purposes, Kyodo quoted a Japanese expert as saying.