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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: 2) by HiThere on Tuesday April 07 2015, @06:24PM
Different power sources have different modes of collapse. E.g., the Hoover Dam has two possible modes of collapse:
1) The lake behind the dam fills up with silt, and the dam becomes useless.
2) The dam breaks, and floods the downstream area with an immensely destructive flood.
2a) Well, the dam breaks, but it's only a small crack, so the water drains slowly.
2a1) Well, the dam breaks, but it's only a small crack that can be patched, so the water doesn't drain, but the water leaking into the dam gets into the re-bar, rusts it, and the entire dam starts crumbling over a period of decades.
I could have added a bunch more, but I want to call your attention to failure mode 2 (without the subheads). This can easily be more destructive than the Fukishima disaster was...if you don't include the tidal wave. If you include the tidal wave its' about the same. The difference is that it's over more quickly. The main problem with fission piles is that there is no planning for recovery. This would entail reprocessing nuclear wastes, which nobody seems willing to do. And the only way to get rid of them is to burn them in a reactor designed to burn them. Which can probably be done fairly easily, but nobody is willing to build even one to test the design. So even if we don't have nuclear disasters, every time a pile is decommissioned we effectively have a disaster. I believe the name of the design of reactor that burns radioactives to harmless is fast-breeder, but it might be a slightly different design. There are reasons why they are discouraged, but if we won't build them, then fission reactors are a bad idea. (IIRC, they make it too easy to build plutonium, which is much easier to purify out than a uranium isotope, and that's the reason they are discouraged. Not a bad reason.)
Javascript is what you use to allow unknown third parties to run software you have no idea about on your computer.