It is building a facility in South Carolina to transform excess weapons-grade plutonium into fuel for nuclear reactors.

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In a major and welcomed development, Russia announced that it will close its last weapons-grade plutonium production reactor.

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Russia and America finalised a decade-old deal to eliminate 68 tonnes of weapons-grade plutonium, enough for nearly 17, 000 nuclear devices.

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That reactor type is not ideal for producing weapons-grade plutonium, but all reactors produce plutonium that could be used in a nuclear explosion.

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In the midst of the mayhem, they must also shut down an unexpected threat in the nick of time - prevent five tons of weapons-grade plutonium from falling into the wrong hands.

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In softening its demand for a full declaration from North Korea, the United States concluded it is more important to get North Korea to surrender its weapons-grade plutonium than risk the deal fall apart all together, officials said.

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Nuclear weapons, too, can be produced using either uranium enriched to weapons-grade or plutonium.

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