Efforts to cool the nuclear fuel rods in Fukushima’s No 2 reactor have failed. The rods have become molten and it appears some have melted through the steel reactor core into a concrete layer. Two dangers now arise: radioactive chemicals created by the concrete reacting with the nuclear fuel and the nuclear fuel pooling enough to go critical.
This is what ended up happening to the nuclear fuel in Chernobyl’s No 4 reactor. Lava-like ‘corium‘, which is just a fancy name for ‘substance made from the molten core of a nuclear reactor’, melted through the steel liner and solidified in what was called the ‘elephants foot’ on the concrete basement floor*. The fuel melted through several metres of concrete, creating hydrogen gas and other volatile substances.
Ironically, the water they’re desperately trying to get into the reactors at Fukushima to carry away the heat actually helps to sustain nuclear reactions by slowing down (moderating) the neutrons emitted when an atom decays making them more likely to collide with other unstable atoms. Without the water and with all the reactions with concrete the melting ends. The corium gradually solidifies into what becomes a flaky and still highly radioactive material.
We’re still told that there won’t be a major radiation release from Fukushima as there was from Chernobyl. During that disaster, a graphite fire and multiple explosions after the core was breached sent corium and other irradiated materials high into the atmosphere to be distributed over a wide area. There’s not meant to be any more explosions at Fukushima. They say they are confident they can cool the corium as it comes out.
But a hell of a lot of stuff that wasn’t meant to happen has happened. If the corium is reacting with the concrete creating large amounts of hydrogen and carbon monoxide, then explosions are a real possibility. If the corium comes out all as one glob it could go critical, recreating the self-sustaining chain reaction that powers a nuclear reactor when it’s in action. That’s a hell of a lot more energy then is currently being emitted by the background decay of the fuel rods, which has been enough to cause all these problems. The one bright side is there’s no way it can go supercritical and explode like a nuclear bomb.
It’s not just No 2 reactor. Plutonium has been detected around reactor No 3. This reactor uses MOX fuel, containing plutonium, which is really dangerous stuff. The fact that plutonium seems to be leaking from the reactor suggests a breach in its core too.
With radiation levels rising, it is becoming both evermore vital and evermore difficult for workers to get close to the reactors to try to solve the problems.
I hope they’re drawing up plans for a sarcophagus, and not one like Chernobyl’s that started leaking after a few years.