Ecocentric

Fukushima: Chernobyl Redux?

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Shan Nair is a British nuclear safety expert who was part of a panel that advised the European Commission on its response to the Chernobyl disaster in 1986. For almost twenty years, he worked within the UK nuclear industry for Britain’s national energy supply company analyzing both waste arising from spent nuclear fuel and also the consequences of what are called LOCAs–Loss of Coolant Accidents, which is precisely what officials are battling against at the Fukushima Daiichi power plant in Northern Japan. I spoke to Nair by phone to learn his thoughts on the incident.

Ecocentric: In the aftermath of Chernobyl, Europe faced a radioactive cloud that drifted over the continent. Is that your concern here?

I do not think that a Chernobyl-style cloud is the biggest concern. My main concern is contamination of the water table. If the entire fuel has melted the odds are it will go straight through the pressure vessel and therefore through the ground until it gets to the water table. Then it will cool down, but the problem is that the water table will start leaching actinides and fission products from the melted glob of fuel into the environment. So you will end up with some radioactive contamination of water supplies and ultimately crops and other products. That’s a major problem because radioactive particles are much more dangerous when digested—they cause internal irradiation of organs with resulting increased cancer risks.

How bad a scenario will that be from a public health perspective?

The severity of the water table risk depends on the local topography–it depends on the depth of the water table, which itself moves up and down. I would imagine the water table is quite close to the surface right now because of all the flooding, which is not good. Also, the type of soil is important: the more silica there is in the soil the less likely the leaching will be. The silica will melt at high temperature when it comes into contact with the molten fuel and when it cools it will cause a seal around the glob of radioactive melted fuel. That’s why radioactive waste repositories are often in desert areas–sand is often almost pure silica. It also depends on the ground water flow–is it toward land or the sea?

Watching the Japanese rush to stop a meltdown must feel like a nightmarish deja vu of Chernobyl for you?

Yes and no. This is not Chernobyl. That’s important to know. It can’t be Chernobyl because the Boiling Water Reactors (BWRs) at Fukushima are designed differently than the High Power Channel-type Reactor (RBMK) reactor at Chernobyl. The RBMK was designed so that the hotter the core gets the greater the reactivity–so you have a situation where you are in a vicious cycle and a race to an explosion. The BWRs are designed in such a way that the hotter it gets the less radioactive the core gets so there is a self-shutdown type of mechanism. But the problem is that before you can get to a safe level you might have a complete meltdown. I believe that’s what they are battling against now in Japan.

There are also reports about problems keeping the spent fuel cool at one of the reactors. Did that happen at Chernobyl?

No, that’s a new issue.  Spent fuel is fuel that has been used in the reactor and is still “hot,” still producing decay heat and releasing radioactive particles. The bad news is that the spent fuel pool doesn’t have the same level of containment as the reactor core, so if it overheats or causes a fire there’s a higher risk of leaks, but the good news is that it should be much easier to cool.

At Chernobyl many first responders to the incident knew they faced certain death. There are reports that all but 50 workers at the Japanese plants have been evacuated. Those that have stayed behind, are they on a suicide mission?

The helicopter pilots who dumped sand on the burning core at Chernobyl knew they were going to die, and they did die. We don’t know what the radiation levels are inside the plant but reports of a 400 millisievert figure suggests that it’s not a suicide mission for the 50 workers who have stayed. They can do what is called “dose sharing”—rotating workers so that they don’t receive an unsafe dose for any longer than needed. It is still a risky operation, however.

And the areas around the plant that are almost certainly contaminated, what will need to happen there?

The best thing people can do is stay indoors. Concrete shields a lot of “the nasties” from you when you are indoors. In the longer, term, I remember that after Chernobyl there was a town in Northern Sweden called Gavle. The radioactive cloud went over the town and it started raining heavily and there was a lot of deposition of radioactive particulate material that was caught into surfaces of roads and buildings. There was a high level of cesium-137. When we went there and waved our Geiger counters about the counters maxed out–it was that bad. Now, what that means was that it was high enough so that it exceeded the safe limit for operating a nuclear power plant, but at the same time it wasn’t an immediate health risk. It wasn’t higher than, say, the black sands of southern India, which emits that level of natural back ground radiation because the sands are rich in thorium. In any case, in Gavle, the Swedes sandblasted the surface of roads and buildings to take off the thin exterior layer of the concrete out and put it into low-level radioactive storage. We did that because the tiny radioactive particles had lodged in the lattice of the silica of the concrete. Removing that layer reduced radioactivity a great deal.

What will be the long-term lessons from Fukushima?

When you are designing safety features and counter measures for nuclear reactors you do a PSA—a probabalistic safety analysis— which takes into account a range of accident scenarios and their probabilities. The PSA will consider low probability/high consequence events but at some point you have have to draw the line.  You can’t take into an account a scenario in which an alien race invades from mars, for example. Unfortunately, the size of the earthquake and tsunami exceeded the worst-case scenario that the reactors were designed to handle.  The nuclear industry will need to re-examine how severe its “worst-case” scenario should be and push the envelope on the extreme case/low probability event considered in a PSA; that seems pretty clear.

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