Neutrons do not, so they escape and go thudding into the shielding material around the reactor.

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In addition to driving the turbines to create electricity, the steam generators are "one of the barriers between the radioactive material in the reactor core and ultimately the external environment, " Jaczko noted.

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The United States and other leading nations have been negotiating with Iran to send low-enriched uranium abroad to be turned into material for use in medical research and treatment at a reactor in Tehran.

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Some of the suggestions include using molten lead as the coolant for the system, but the reactor would run at a temperature above 700 degrees C. when the material becomes corrosive.

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When the Chernobyl reactor in the Ukraine melted down, an entire reactor with virtually no containment system exploded, spewing huge amounts of radioactive material into the air, where they were blown by the wind into habitable areas.

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Hence presumably reprocessing is involved in the final stage, since if the protactinium-233 is left in the reactor it will be at least partly converted to protactinium-234, which is not a useful fissile material.

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