11 February 2014, 16:20

'Small earthquake right under Fukushima reactor could be very destructive' - expert

'Small earthquake right under Fukushima reactor could be very destructive' - expert

Two magnitude-5 earthquakes struck off the coast of Japan’s Fukushima prefecture. This is the site of the 2011 tsunami and earthquake that killed more than 18,000 people and triggered the world’s worst nuclear disaster since Chernobyl. The Voice of Russia talked to Kevin McCue, Director of the Australian Seismological Center.

The first quake hit 34 kilometers off the city of Namie, on Friday. The US Geological Survey measured its magnitude at 5.1. The tremor caused no serious damages, and no tsunami warning was issued in its wake, the Japan Meteorological Agency said. The second quake, measured magnitude 5.0, and struck 34 kilometers from Iwaki on Saturday. Like the previous quake, no tsunami warning was issued, though they posed stark reminders of the chronic insecurity at the crippled Fukushima Daiichi Nuclear Power Plant. 

Kevin, how will the latest earthquakes that we’ve seen past couple of days affect the radiation situation in and around the Fukushima plant? What do you think?

These are fairly small earthquakes, Dmitry. They are about 150 kilometers offshore and nearly 200 kilometers from Sendai or from Fukushima. I think that these are very small earthquakes but there is a possibility of a much bigger earthquake happening there again.

Exactly. As far as I understand this is an active seismological area that Japan is in.

Yes, it is a very active part of the Pacific plaques, so you have an active earthquake zone right around the Pacific. And it comes within 100 kilometers of the coast of Honshu, the east coast of Honshu. So the earthquake that destroyed the Daiichi reactors was a very rare event. This is a problem for buildings of reactors and any other buildings for that matter. Engineers are kind of playing a game of chance when they build a building, it is like having a game of poker. There is no possibility for designing for the worst possible earthquake. So they designed for something else. Let’s say the reactor has a lifetime of 100 years, I believe they are about 48-years-old now so they are about nearly half way through their lifetime that had one earthquake. And we know Japan has a very good record of earthquakes, perhaps as long as 1,000-year record. In that time we had this one grade magnitude 9 earthquake. Let’s say it had a return period of 1,000 years. Let’s pretend it happens every 1,000 years on average. Then the reactor in its lifetime of 100 years has a 10%-chance of having one of those earthquakes. That is the designed earthquake will be far exceeded with a probability of about 10%, that is what I mean about taking a chance. If we are wrong about this 1,000 years frequency of these earthquakes, let’s say it is 10,000 years. Then in their 100-year lifetime they have only a 1%-chance of being enswathed. So it is never zero, there is always a risk here. And the law doesn’t take risk into account. After the earthquakes happened, then of course they are trying to find somebody to blame for the earthquake - the engineers and building owners have taken the risk and they know they are taking a risk when they build them and they just got unlucky I think.

Kevin, just for future reference, you say that these two earthquakes which were 5.1 and 5.0 of magnitude were barely felt at the side of the Fukushima plant and they were something like 34-40 kilometers away from it. What kind of magnitude should worry us then that may actually have some kind of effect on the situation which is already predier?

These earthquakes from looking at the screen in front of me they are about 150 kilometers of the coast so that is kind of deep. I’m not sure, they are off Miyako, my Japanese is not very good, they are about 150 kilometers off shore, so they are a long way away relatively. But I would imagine that a relatively small earthquake could give the Fukushima plant a very bad fright if they happened right under the reactor, say an earthquake like the one that happened in Christchurch in New Zealand in February of the same year as the Tohoku earthquake, just a month before – 6.2. The ground shaking there was incredibly strong, much stronger than those nuclear reactors had been designed for. So you could easily had a magnitude 6 earthquake right under the reactor and that would be very destructive even now.

Alright. What if the same earthquakes happen where they actually happen? What kind of magnitude would you need to actually feel some damage at the Fukushima plant?

Well, I think that has to be upper around magnitude 6 before you would even feel them, and that has to be over 7 before you would start getting any damage, I think. So, fairly large earthquakes but they can happen at any time. And even another Tohoku earthquake – there is about a 6% probability of having two of those in 100-year lifetime of the reactor- a small chance but still a chance of having another very great earthquake off the Japanese coast.

So if I understand correctly, Kevin, though you say that there is a probability for everything which is, well, philosophically absolutely true for anything, you think that at the moment TEPCO, Fukushima has not much to worry about in terms of having to upgrade security at the power plant?

No, I think they ought to be doing it as we speak. You know, I think the Japanese public wouldn’t find it acceptable for the damage at the plants and I imagine that they ought to be getting on with not only stabilizing the reactors but making sure that any other tsunami or any strong ground shaking doesn’t cause additional damage at those plants. I think that is a matter of high priority and I’m sure that is what they are doing.

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