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Large Japanese electricity utility Tokyo Electric Power (Tepco) confirmed on Thursday, March 19 that nearly all fuel in one of four damaged nuclear reactors at Fukushima No. 1 nuclear power plant has melted and fallen into the containment building.
With the design of the Fukushima Daiichi plants, the containment building was a very simple shell protecting the reactor from the elements, but provided no real protection in the event of a nuclear accident. Instead, the nuclear reactor was enclosed in primary and secondary containment vessels, which sat atop a thick concrete pad at the base of the containment building.
In the event of a meltdown, the thick concrete pad is the only barrier between highly radioactive molten fuel and groundwater.
While there has been suspicions that nuclear fuel did melt its way through the containment vessel and to the base of the containment building, until Thursday there was no definitive proof meltdown had occurred.
The implication of the findings is that it will be very difficult to remove the highly radioactive molten fuel from Unit 1. As well, the molten fuel must continue to be cooled with water until it is removed.
Holes and fractures in the concrete base of the reactor building also means that groundwater continues to seep in and become irradiated before draining into the Pacific Ocean, causing an ongoing nuclear disaster.
The official decommissioning plan tells us the plant should be fully shut down sometime after 2022.
(Score: 4, Interesting) by Nuke on Tuesday April 07 2015, @04:41PM
As for "needing cooling with water", fuel in a shut-down reactor will emit residual heat for a while (that is what melted it), but the rate of heat output declines rapidly. After 4 years it will be so small as to be absorbed by its immediate surroundings and be conducted away through supports and even insulation. I am a nuclear engineer, and am involved in the off-load refuelling and maintenance of power stations. The residual heat is so little by the end of a four week maintenance period that no special provision is made to disperse it by then - natural convection does it. Let alone four years. Guys like me are even working inside what is normally the cooling circuit - it's just warm enough not to need a woolly jumper under your overalls :-)
The molten fuel will have water over it to stop its radioactive emissions activating the surrounding metalwork any more than necessary. Wonderful stuff for stopping radiation, water is.