Earthquakes and nuclear power just don’t mix. You can’t build nuclear facilities in safe areas in Japan – there aren’t any. You can’t safely store spent fuel in a land with volcanoes and earthquakes. Obvious stuff really…
And, yet here we are. There are nuclear power plants all over Japan. Some of them built on fault lines. Many on the coast (with subsequent access to water for cooling) and therefore liable to swamping by tsunamis.
Building a nuclear plant to survive Magnitude 8.2 quakes, and n meter tsunamis is just an invitation to nature to make you look stupid. Oddly enough, that’s what happened. Quakes of roughly five times the power (magnitude is a log scale…), and tsunamis of 10m swamped Fukushima.
Surviving the quake itself is quite an achievement, but it’s a hollow victory when the plant is subsequently swamped by the sea. Being confident in your defenses, to the point of locating your emergency power in a low lying area, with power switching in a basement liable to flooding, is just asking to be humbled by nature.
Consequently, here we are with three nuclear reactors that have gone into meltdown. Since late on Friday the situation has pretty much gone from bad to worse. One by one the emergency cooling of the reactors has gone offline. This has caused the fuel rods to be partially, or in the case of reactor 2, completely out of coolant water.
Even with control rods inserted this increases the temperature and pressure in the containment vesselsis raised to the point where it has been impossible to pump in sea water (the only reliable source of cooling). In order to relieve this pressure steam from containment vessel has been vented, releasing radioactive materials (Caesium 137, Iodine 131) from the high temperature fuel, into the atmosphere.
Mixed in is also Hydrogen (released when the Zirconium alloy that is used to house the Uranium fuel pellets is heated above something like 1500ºC) that when mixed with Oxygen is highly explosive. This is what has caused the two explosions that blew away the buildings surrounding the secondary containment. What we’ve been told is that neither of these explosions has damaged the primary of secondary containment of the reactors.
As things stand two of the three reactors have been bought under control. They are being cooled with sea water and poisoned with Boric Acid. This indicates that they are going to be decommissioned, as the corrosive effects on anything other than de-ionised water render the reactor vessel unusable.
The third reactor came very close to boiling dry last night, and was still at an elevated pressure this morning. Unless they have been extremely lucky this means the fuel has completely melted down, and is lying at the bottom of the primary containment. This is going to make the task of cooling it a lot harder.
As long as the operators have control over the mechanisms for releasing pressure the situation can probably be maintained. However, if the fuel is now lying in a heap at the bottom of the containment vessel it seems likely that it’ll eventually get to a temperature when it melts through the steel primary containment and leaks out into the secondary containment. The design is presumably such that the fuel is spread out, but with each line of defense that falls we get a little closer to disaster situation of Uranium getting out into the environment.
This morning the government has announced that it will be working more closely with Tepco. The implication is that Tepco hasn’t been sufficiently forthcoming with information, which given their record isn’t entirely surprising.
Rather surprisingly i’ve managed to stay somewhat doggedly optimistic that the situation will be resolved. At this point we’re teetering on the edge a little. In any other situation having two out of three stabilized would be good sign, but this last one is making me extremely nervous.
[Edit: this was written purely as an exercise in calming down. Saying all this stuff, attempting to stay rational, and digest what i’ve read, is my way of coping.
If you have questions you’re probably better off asking them elsewhere. I’m by no means a nuclear expert, and remain a committed sceptic of the entire industry.
Update: things have again got worse and an explosion in the secondary containment of reactor 2 has released more radiation into the environment. It’s no longer clear if the primary containment retains intact (at least nobody seems to have very much information) but there was some talk in a confused Tepco press conference that the pressure was still ‘within parameters’. The area in which people should stay inside, or take precautions if they are outside has been widened to 30km.]