The answer is to get it out of Japan so that China and other S E Asia countries won't think it could be used to make nuclea weapons. See summary and reference URL below.
Japan will send a huge cache of plutonium -- enough to produce 50 nuclear bombs -- to the United States as part of a deal to return the material that was used for research, reports and officials said Tuesday.
The plutonium stockpile, provided by the US, Britain and France decades ago, has caused some disquiet given that Japan has said it has the ability to produce a nuclear weapon even if it chooses not to.
Some 331 kilograms (730 pounds) of the highly fissionable material will be sent by ship to a nuclear facility (SRS) in South Carolina by the end of March, Kyodo News reported in a dispatch from Washington that cited unnamed Japanese government sources.
The shipment, which comes ahead of a nuclear security summit in Washington in March, is meant to underscore both countries' commitment to nuclear non-proliferation and is part of a deal they made in 2014.
It will be one of Japan's most significant overseas movements of plutonium since it transported one tonne from France in 1993 to be used in nuclear reactor experiments.
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