John Beddington (JB): Let me now talk about what would be a reasonable worst case scenario. If the Japanese fail to keep the reactors cool and fail to keep the pressure in the containment vessels at an appropriate level, you can get this, you know, the dramatic word "meltdown". But what does that actually mean? What a meltdown involves is the basic reactor core melts, and as it melts, nuclear material will fall through to the floor of the container. There it will react with concrete and other materials … that is likely… remember this is the reasonable worst case, we don't think anything worse is going to happen. In this reasonable worst case you get an explosion. You get some radioactive material going up to about 500 metres up into the air. Now, that's really serious, but it's serious again for the local area. It's not serious for elsewhere even if you get a combination of that explosion it would only have nuclear material going in to the air up to about 500 metres. If you then couple that with the worst possible weather situation i.e. prevailing weather taking radioactive material in the direction of Greater Tokyo and you had maybe rainfall which would bring the radioactive material down do we have a problem? The answer is unequivocally no. Absolutely no issue. The problems are within 30 km of the reactor. And to give you a flavour for that, when Chernobyl had a massive fire at the graphite core, material was going up not just 500 metres but to 30,000 feet. It was lasting not for the odd hour or so but lasted months, and that was putting nuclear radioactive material up into the upper atmosphere for a very long period of time. But even in the case of Chernobyl, the exclusion zone that they had was about 30 kilometres. And in that exclusion zone, outside that, there is no evidence whatsoever to indicate people had problems from the radiation. The problems with Chernobyl were people were continuing to drink the water, continuing to eat vegetables and so on and that was where the problems came from. That's not going to be the case here. So what I would really re-emphasise is that this is very problematic for the area and the immediate vicinity and one has to have concerns for the people working there. Beyond that 20 or 30 kilometres, it's really not an issue for health.

And:

[Q] Good morning. Couple of days ago the Japanese authorities predicted a 70% chance of another aftershock exceeding magnitude 7, and potentially another tsunami. If that were to happen and the emergency procedures that are taking place now, how does that affect your worst case scenario?

[JB] I think the worst case scenario would remain. The issue is basically that if they can't, if for example, their attempt to cool fails, and if their attempts to keep the pressure in the containment vessel fails, then you would get an explosion. What I suppose, you know, in a reasonable worst case that that would happen in a single reactor, if you had a massive new influx of tsunami and so on, you move into a sort of relatively low probability event, but you might get more than one, but the point still remains that you would actually have no real concerns even if there were two rather than one explosions, they don't multiply it up, it doesn't mean that it goes up to 1,000 metres or anything like that. It's still up to about 500 metres, it still is a relatively short duration and the key thing here also is wind direction. When does it happen? If the wind is taking material, is going out into the Pacific, it is not going to be a problem. It's the combination, as it were, unhelpful weather, and an explosion that is twice that reasonable worst case scenario. If you had this sort of second tsunami so that people could not work and actually operate on the core then you would have a problem. But that would probably mean that you might get all three reactors go up. But again, I'd emphasise this would not affect the advice we are giving

David Fuller's view Assuming Sir John is correct in his assessments, there is little need for people in Tokyo, let alone China, to panic. However, there is the serious problem of ongoing radiation leakage in the Fukushima region, albeit at what are still described as 'low levels'. Perhaps, but they are having a cumulative effect. This will increase the risks of soil and water table pollution, and make the eventual cleanup process very expensive. Meanwhile, nuclear technicians are still struggling to prevent Sir John Beddington's 'worst case' scenario described above.