Slashdot Mirror
Dismantling a Nuclear Reactor
AmiMoJo sends in a BBC story about the hardware used to decommission a nuclear reactor:
"The device cost £20m to design and build and will operate in highly radioactive conditions inside Dounreay's landmark Dome. Its detachable tool bits cost £100,000 each and weigh between 37-93kg. They will cut and grab 977 metal rods once used to 'breed' plutonium from uranium. ... Once in place, the device will operate in highly radioactive conditions and in a nitrogen atmosphere. Nitrogen prevents any residue of the liquid metal from reacting. Exposure to water or oxygen would cause the metal to catch fire. ... Up to three tool bits will be in use at any one time and can be replaced by another three carried in a special tool box without the need to remove the tool itself from the reactor. The rest of the tool bits will be stored above the reactor and would be fitted into place during service and maintenance breaks."
I have three words for you "positive temperature co-efficient". Someone care to define why this is not desirable in a nuclear reactor? c'mon anyone? I will give you a hint, it involves reactivity and temperature. OK TIMES UP. The answer is : Think back to Chernoblyl. It used a liquid sodium moderator. When the termperature goes up the reactivity goes up. This makes things a little difficult to stop a runaway reaction. PWR's and BWR's have a negative co-efficient meaning that if you overheat the water, it has a tendency to slow the reaction.