Nuclear Meltdowns 101
I am no nuclear expert, and that is probably a good thing. I did do a lot of reading about Chernobyl back when it happened. And now I am, as I was then, and as I am sure many of you are, getting really fed up with incomplete, inaccurate, misleading and generally unsatisfactory explanations that are being offered for what is going on at Fukushima. Either information is not available, or it is a flood of largely irrelevant technical minutia designed to thrill nuclear nerds but bound to bamboozle rather than inform the general reader. And so, for the sake of all the other people who aren’t nuclear experts and have no ambition of ever becoming one, here’s what I have been able to piece together.
What do they mean when they say “hydrogen explosions”? The hydrogen gas is being vented from inside the reactors and from spent fuel pools that are directly above them. Since it is very hot, it explodes as soon as it mixes with the outside air. It is formed from the rapid oxidation of the zirconium pipes that hold in the pellets of nuclear fuel. At Fukushima, some of the fuel pellets are made with uranium, while others are made with plutonium from reprocessed nuclear weapons. Zirconium is a metal which, like aluminum, instantly forms a thin, protective layer of oxide on contact with air, but doesn’t oxidize further—unless it is heated up, that is. The zirconium-clad fuel rods must be kept submerged in water at all times, or they do heat up, and then the zirconium cladding oxidizes (burns) very rapidly and disintegrates into a powder. This is already enough information to tell us that a lot of the “fuel rods” at Fukushima are no longer rod-shaped, because the zirconium cladding has disintegrated, and that the fuel pellets must have fallen out and accumulated at the bottoms of the reactor vessels, where they are packed close together and heating up further. How much further they heat up will determine whether they will melt through the bottoms of the reactors. If they do, they would probably melt into the ground below and form a large pancake of hot, molten slag, which will slowly crumble into radioactive dust over many years, as has happened at Chernobyl. There is also a small chance that the fuel pellets will “go critical,” if the mass of them becomes sufficiently compact to restart the nuclear chain reaction; if that happens, the telltale tall brown cloud should be easy to spot from as away as Tokyo. This seems unlikely, but then nobody seems to be able to definitively rule it out either.
What do they mean when they say that they are cooling the reactor with seawater? Seawater is corrosive, and is probably the worst coolant imaginable. Normally, nuclear reactors are cooled with fresh, filtered, deionized water. The crew at Fukushima used seawater because they had no other choice. When the cooling pumps failed because the tsunami caused a blackout, they called in the fire brigade, and the fire engines there apparently use seawater. The reactor cooling systems are plumbed with stainless steel pipes, which degrade rather rapidly on contact with sea water because of the chlorine in it, especially if they are hot (which they are). At Fukushima, “containment” has already become a relative term, since the reactors are vented to the outside air in any case to keep them from bursting, but once these pipes disintegrate (a process that might take a few days to a few weeks) the containment vessels will become riddled with holes, letting in outside air and, if by then there is any zirconium left to burn, possibly causing hydrogen explosions inside the reactors, compromising them further. Their radioactive contents will then be carried to the atmosphere in aerosol form. We will probably know when that happens because the Geiger counters in the area will peg out. Nothing has been said about the destination of the copious amounts of now contaminated seawater that is being pumped through the damaged reactors and spent fuel pools. At Chernobyl, the water that that was used to “cool” the by then nonexistent reactor formed a large radioactive lake which threatened to poison Pripyat river. At Fukushima, we must suspect, all of that contaminated seawater is draining straight back into the Pacific, where tidal currents will carry it up and down the coast, contaminating the entire coastline with long-lived radioactive elements. Which brings us to a very general question:
What is the difference between radiation and radioactivity? This is a basic enough distinction, but, listening to the news coverage, I have observed a great deal of confusion. (Some of it seems intentional, if not malicious: I heard some nuclear expert/twit (a retired Oxford don, I think) on NPR explain how “wadiation” can be “thewapeutic” and never once did he mention “wadioactivity,” and it made me quite mad.) Do not use the two terms interchangeably unless you want to sound like you don’t know what you are talking about. Radiation, of a non-lethal kind, is what you get from a light bulb, an X-ray machine, at the beach or in a tanning booth. Radioactivity, or radioactive contamination, is what you get when a nuclear bomb or a nuclear power plant explodes, and it stays around and produces radiation for years. Both radiation and radioactivity are invisible and hard to measure, but that’s where the similarity ends. Radiation consists of subatomic particles that generally go in straight lines at close to the speed of light. Given enough radiation, initially non-radioactive materials can in turn become radioactive. Radioactivity, on the other hand, is caused by radioactive materials, which decay into other materials, some also radioactive, some stable, plus some radiation, at some rate, either quickly or not so quickly. Uranium and plutonium hang around for many thousands of years. Radioactive substances can be pulverized and carried up into the atmosphere by explosions (not necessarily nuclear ones) in which case they drift with the wind for thousands of kilometers and pollute huge stretches of land and ocean. Exposure to excessive levels of radiation causes radiation poisoning, from which people can fully recover, while the various radioactive elements pollute the environment and are taken up by living organisms in a wide variety of ways, many of them not yet understood by science, poisoning them and causing a wide assortment of cancers and genetic defects. Some may be flushed out, while others become lodged in the lungs or in the bones for the life of the individual, where they remain radioactive, weakening immune systems, causing cancers and birth defects and shortening lifespans. I once spent a few hours at the airport in Minsk, waiting for a flight to Frankfurt with a group of “Chernobyl children” being flown out for treatment. They were quite a sight!
What about these “spent fuel pools” that keep catching on fire? Well that’s probably the most insane thing about the nuclear power industry. They haven’t figured out what to do with the spent fuel rods, so they store them tightly packed in pools of water directly at the site, or, in the case of Fukushima, since land in Japan is at such a premium, stacked directly on top of the reactor itself. The reactors at Fukushima are quite old, and so their spent fuel pools are packed full. The spent fuel rods, which accumulate over the entire lifetime of the power plant, have to be kept submerged to keep them cool, or the zirconium cladding burns away (causing hydrogen explosions) and the fuel pellets accumulate at the bottom of the pool, burning through it if the fuel is fresh enough (which, in some cases, it might be). The result is the same as with the fuel rods disintegrating inside the reactor itself, except that here there is no containment vessel to keep (at least some of) the radioactive material out of the environment.
Why do we have nuclear energy in the first place? This all sounds completely insane, doesn’t it? Well, if it weren’t for the nuclear bomb, anyone who proposed building a commercial fission reactor would have been laughed out of the room. But having nuclear bombs (which are by far the scariest things on the planet) makes nuclear fission reactors that much less scary, relatively speaking. And the reason we have nuclear bombs is because the only thing scarier than a nuclear bomb is not having one, since that opens you up the possibility of having one dropped on you by someone who does, such as the USSR (in theory) or the USA (as an historical fact). Compared to nuclear bombs, nuclear reactors seem “peaceful,” although this is clearly not the case. Compared to nuclear reactors, nuclear bombs are as safe as houses, because they don’t start a chain reaction until somebody pulls the trigger, whereas nuclear reactors maintain a controlled chain reaction during most of their existences. It’s like comparing having a gun safely in your possession to heating your house with ammo, in which case, surely enough, accidents will happen.
What do people mean when they say that nuclear power is “safe” when compared to planes, trains and automobiles? What they mean is that the nuclear power industry has so far killed many fewer people per unit time. They have no data on how many people it will kill eventually, although by now they know that, unlike planes, trains and automobiles, which do crash and burn with some regularity, but cause limited damage, nuclear disasters do not have any definable upper bound on their destructive potential. I am pretty sure that there is enough above-ground radioactive material sitting in spent fuel pools and inside reactors to kill just about everyone. It will stay dangerous for over a million years, which is a lot longer than the expected lifetime of the nuclear power industry, or any industry, or any human civilization, or perhaps even the human race. When nuclear experts say that a nuclear reactor is safe, they can only mean that it is safe for the rest of the afternoon; beyond that they can’t possibly have any actual data to support their claim. All they can do is extrapolate, given a rosy “everything will always remain under control” scenario, and that is not a valid approach. When they say that nuclear power is safe, what they are really saying is that it is safe given their perfect ability to accurately predict that the indefinite future will remain economically and socially stable, and we already know this to not be the case.
If we give up on nuclear energy, what will replace it? Nothing, probably. Let me try an example: if your lucrative murder-for-hire business suddenly runs afoul of a few silly laws (even though it has so far killed many fewer people than planes, trains or automobiles) that doesn’t mean that you should keep killing people until you find another source of income. Same thing with electricity: if it turns out that the way you’ve been generating it happens to be criminally negligent, then you shut it all down. If you have less electricity, you will use less electricity. If this implies that economic growth is over and that all of your financial institutions are insolvent and your country bankrupt, then—I am sorry, but at this point in time that’s not even newsworthy. Don’t worry about that; just keep the nuclear accidents to a bare minimum, or you won’t have anything else left to worry about.