Referring to my Sunday post about the events in Japan, a friend in the US has asked me “Are you still this non-apocalyptic after the latest explosion?”. And given what has been reported about the situation at the Fukushima reactors since Sunday I feel I should update my opinions.

So where are we? Well it’s really difficult to tell. There have now been three explosions, and a further significant release of radioactivity. Albeit the radioactivity appears to be relatively short-lived nucleotides. But we now really don’t know enough about what is actually happening in Fukushima. In fact nobody knows exactly what’s happening apart from the engineers on the ground. All we are getting is the third- or fourth-hand account which the Japanese government are putting out and which is then being spun every which way by the media.

Do I trust what we’re being told? Again it is hard to say. All nuclear authorities (and governments) have a poor track record of owning up to bad news; the Japanese are no better or worse that anyone else. That means I am very skeptical about what’s being admitted to. What is being said may be true, but it may not be the whole truth and nothing but the truth. But as I say, we really don’t know, and cannot know.

However as I understand it, and despite the latest reports, the worst case scenario still cannot be as bad as Chernobyl due to the design of the reactors. Of course that doesn’t mean it couldn’t still be really very nasty. Remember that these nuclear plants have three or four levels of containment between the fuel rods and the open air. A full meltdown and fire, as happened at Chernobyl, would require all the levels of containment to be breached, all the cooling to have failed and at least some of the control rods to not be in place between the fuel rods. Given that we are told the reactors shutdown correctly, all the control rods should be inserted amongst the fuel rods which, if I have understood correctly, makes the worst case Chernobyl scenario highly unlikely.

Let’s also be clear. This situation has not obviously been caused by the earthquake – the facility appears to have withstood a quake some 5 times more severe than its design limit. (I have read that the design limit was to withstand a quake of magnitude 8.2, so this 9.0 quake is way above that design threshold; remember the Richter Scale is logarithmic.) It was the subsequent tsunami taking out the nuclear plant’s backup power generators which triggered the problems, and that clearly was not designed for. One has to question the wisdom of building nuclear facilities so close to such an active geological fault, especially one know to trigger tsunamis.

It’s undoubtedly a nasty situation, and extremely scary for the local population. But as far as one can tell the Japanese authorities are probably handling this as well as anyone could. We just have to hope that the authorities and the engineers are doing enough.

But we just don’t know (and may never know) enough about what’s really happening inside those reactors – no-one does except the engineers on site.

if you want to know more technical details there are good posts here, here and here, and regular technical updates here.