Japan Prepares to Declare the Fukushima Reactor "Shutdown"

Illustration for article titled Japan Prepares to Declare the Fukushima Reactor Shutdown

Japanese officials are preparing to finally declare the Fukushima power plant in a state of cold shutdown as early as 9am tomorrow (GMT). Now they can begin the estimated 40-year process of dismantling the site and repopulating the area.

Cold shutdown is when the water used to cool the fuel rods is lowered below the boiling point, which brings the reactor subcritical—meaning the nuclear reaction isn't self-sustaining. The reactors at Fukushima have actually been in cold shutdown since September but officials have been hesitant to declare the all-clear on account of occasional temperature spikes in the system. And the fact that an official announcement of that shutdown stipulates some 80,000 residents will be allowed back within the 12-mile exclusion zone.

As for the plant, it's being demolished. Very slowly. Officials believe they'll be able to begin removing intact fuel rods for shipment and storage off-site by next year. The rods that went critical and melted down likely won't be accessible for another decade. An area of 930 square miles around the plant may need decontamination too. The entire cleanup process is expected to last 40 years. And as for TEPCO, the plant's owner, it's being nationalized. The Japanese government is injecting $13 billion dollars into the company to prevent its collapse. [Reuters - Image: The AP]

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Since somebody else wasn't clear, for anybody interested a briefexplanation on what happened:

Inside a Pressurized Water Reactor, the fuel rods are not moved. They need to be in a certain geometry to react, not to mention that moving them would be a safety hazard, and a chance for stuff to go Really Wrong. Instead, 'control rods' which absorb and neutralize Neutrons are inserted and removed to speed up or slow down the reaction. As soon as the Earthquake hit, all control rods were fully inserted to 'shut down'. This is called a SCRAM.

All fine and good, except in an active reactor, the fuel rods aren't the only thing which is undergoing nuclear reaction... the decay products of the atoms which react are also radioactive, also in the reactor, and provide a significant portion of the energy. The two big ones are Iodine-131 and Cesium-137. Iodine has a half-life of 8 days, so is incredibly, absurdly hot, Cesium-137 has a half-life of 30 years, so it's only mostly hot. Even after you shut down a pressurized Water Reactor, you're really only shutting down the main fission reaction, and these reactions continue, which is why you need to keep running the pumps to circulate the coolant.

And, because of the energy and temperature of the reactions, you get a lot of dissociation of water, meaning a lot of H2 and O2 is created when the bonds of the water are broken. There's a recombiner which also runs, to create water from the offgas... if power is lost, you end up with hydrogen and oxygen building up, which they had to vent... which is what led to the hydrogen explosions.

As a side note, I really wish we'd get away from Pressurized Water Reactors for stationary plants, but hey, they keep getting operational extensions because they're absurdly expensive and still work well for the most part... Move to something like a Liquid Fluoride Thorium Reactor, or at least a Molten Salt reactor of some kind... you can actually design those suckers so that they're actually fail-safe, even if they lose all power for the rest of eternity. For a pretty decent presentation on the future of nuclear, check out [thoriumremix.com] (I have no association with anybody related to that site, video, or what have you, just found it well made)