Cesium remains the most widely dispersed isotope while concerns remain over long-term contamination from strontium and plutonium.
In one significant respect U-233 is better than uranium-235 and plutonium-239, because of its higher neutron yield per neutron absorbed.
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This week they said that Iran would suspend its uranium enrichment and plutonium reprocessing activities, in return for European concessions over trade.
Officials trying to stem nuclear proliferation used to congratulate themselves that only a very few of the known incidences of trafficking involved the sort of uranium and plutonium useful for a bomb.
Ironically, the accident happened only one day before a ship carrying nuclear fuel made up of mixed uranium and plutonium docked in Japan, surrounded by coast guard vessels and greeted by demonstrators.
The Europeans had hoped that Iran might be persuaded to bring a permanent halt to all uranium and plutonium work if it received the right inducements, including trade and other, less proliferation-prone nuclear technologies.
According to papers filed with the Blue Ribbon Commission, the current research involves faster and simpler processes for separating uranium and plutonium from other fission products in spent fuel and from minor elements like americium and curium.
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Given a start with some other fissile material (U-233, U-235 or Pu-239) as a driver, a breeding cycle similar to but more efficient than that with U-238 and plutonium (in normal, slow neutron reactors) can be set up. (The driver fuels provide all the neutrons initially, but are progressively supplemented by U-233 as it forms from the thorium.) However, there are also features of the neutron economy which counter this advantage.
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From a public health perspective, the most important isotopes are short-lived isotopes of iodine (like Iodine-131), Cesium-137, Strontium-90, and possibly Plutonium-239.
"Japan accepts regular and irregular inspections from the IAEA and makes public how it handles and uses plutonium, which proves that Japan makes a peaceful use of it, " he said.
The material that went into Fat Man, the plutonium bomb detonated over Nagasaki, was made at Hanford, which at its peak consisted of nine nuclear reactors and five plutonium reprocessing plants.
That move prompted Britain, France and Germany to discontinue negotiations aimed at persuading the Iranians to abandon for good their ambitions to enrich uranium and make plutonium (another potential bomb ingredient).
The site produced plutonium for the bomb dropped on the Japanese city Nagasaki and continued producing plutonium for the US nuclear arsenal for years.
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The fuel in No. 3 is a blend of plutonium and reprocessed uranium, referred to as MOX (for mixed oxide) and manufactured by the French nuclear company AREVA. MOX fuel rods are also less stable than plutonium-free rods.
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The Mox plant, which processes a blend of plutonium and uranium, was given the go-ahead at the start of this month.
This came close to exploding and blowing the plutonium-fuelled reactor to smithereens.
So a supposedly cheaper option was agreed on: to convert the reactors to use fuel that would produce far less plutonium and would not require subsequent reprocessing.
Mohamed ElBaradei, the head of the International Atomic Energy Agency, wants a worldwide moratorium on enrichment of uranium and reprocessing of plutonium, the two fuels for nuclear weapons.
Supporters of this legislation have implied that our nuclear arsenal is unaffected by the current absence of U.S. production of plutonium and highly enriched uranium for weapons purposes.
And chemists who understand how plutonium ages also develop forensics to track missing nuclear material and catch those trafficking in it.
David Sanderson, a physicist at the Scottish universities' research and reactor centre, says that while this would need heavy investment (and a lot of workers), plutonium can be mixed with waste and vitrified into storable glass blocks, so making it unusable in bombs if any terrorists managed to steal some.
It has a lot of information that needs to be given about all its plutonium production and extraction.
They include Iran's ongoing uranium enrichment program, experiments with small amounts of plutonium, and a possible program that combines work on high explosives, missiles, and uranium.
The fuel, called MOX, takes uranium from spent fuel rods and mixes it with plutonium, creating a less stable fuel, one that is potentially far more dangerous in a meltdown.
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America wants to talk to North Korea about how it might dismantle both its plutonium production and the uranium-enrichment programme whose belated discovery sparked the latest crisis over a year ago.
The answer lies in its plant for reprocessing spent fuel, built partly to take used fuel from Germany and Japan (which largely paid for its construction) and partly to produce the plutonium that was once expected to be needed as fuel for fast-breeder reactors, in Britain and elsewhere.
Alan Stern expects that after the Pluto flyby in 2015 or so, there will be plenty of power left, both electricity from the plutonium generator and fuel, so New Horizons will keep on going to explore other Plutolike objects in this region of the solar system which is known as the Kuiper Belt.
President Obama had also promised to build a modern Chemical and Metallurgy Research Replacement facility for handling plutonium which was included in the Treaty Resolution of Ratification and presented in his message to the Senate upon entry of the treaty into force.
James Acton, an analyst with the Carnegie Endowment for International Peace, said North Korea's plutonium stockpile is small and it would be difficult and expensive for the North to produce more.
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