Nuclear Dogmas.

At the moment South Africa is poised on the edge of a decision to give hundreds of billions of rands to the moribund French nuclear power industry. We were there first with the bad decisions; Obama, who is giving tens of billions of dollars to the moribund American nuclear power industry, definitely came second. But all this is, of course, a load of complete rubbish. If we need nuclear power — a big if, of course — we don’t need to bring in foreigners. It is, in fact, more sensible to do it ourselves.
Do we need to? Perhaps not. On the other hand, we have just elected to borrow R28 billion from the World Bank towards a 4,8 billion watt coal-fired power plant. That’s 5 rand and 80 cents for every watt to be generated — R580 for every 100-watt light bulb — before we factor in the cost of the coal and the environmental destruction arising out of that. If we were to go nuclear, would it really make matters worse?
Well, maybe. However, let’s think about what we would need to do to pursue nuclear energy. Luckily, we have a fair amount of uranium in southern Africa. We can dig it up, at great environmental cost and cost to the people doing the digging. (Uranium is not terribly radioactive, but it is extremely poisonous, being a heavy metal — the heaviest found in nature — and extremely reactive, so it easily gets into your body.)
Then, at considerable expense and difficulty, we combine the uranium metal with fluorine gas to produce uranium hexafluoride and we are able to start enriching the uranium, increasing the proportion of U-235 from a tiny fraction of the body of uranium (which is mostly U-238, essentially useless stuff) to a usable fraction. The simplest way to do this is to pump the gas around a corner. (You can also spin the gas in a centrifuge, which is the American way, but this is a lot more technically complicated.) The gas on the outer edge of the corner will contain more U-238, because it’s heavier and corners less effectively. Separate the outer edge of the cornering stream of gas from the inner edge, and you have a light and heavy stream; discard the heavy stream and repeat with the light stream, and watch it get lighter and lighter over time. The advantage of this process is that all you need is a pipe, a jet-nozzle (admittedly this is a complex piece of equipment) and a gas pump. There are very few moving parts, hence there is little danger of an escape of the poisonous gas. (The biggest problem is that the system sometimes clogs up with uranium tetrafluoride, which is solid at room temperature.)
Why doesn’t everybody do this? Well, that’s easy: if you carry on with the process, eventually you have ninety percent U-235 and you can make the kind of reliable, safe, trustworthy atom bomb which the Americans dropped on Hiroshima. Distributing uranium enrichment plants effectively means distributing the capacity to make nuclear weapons. America wants a monopoly of nuclear weapons because that would enable her to rule the world more cheaply than now.
Once you have your enriched uranium, you can put it in a reactor. The big issue here is the reflection and slowing of the neutrons by the matrix in which the uranium is placed. If you have a mass of heavy water — which is not that hard to produce; essentially you can separate it by evaporation, since heavy water boils at a slightly higher temperature than normal water) you can use natural uranium, since heavy water moderates neutrons very well. (The issue is to keep the neutrons moving slowly enough so that they don’t simply ricochet off the uranium nucleus, but burrow inside and give the U-238 indigestion so that it fissions and gives off more neutrons.) Or you can just use ordinary water, but then you must use enriched uranium.
The nice thing about ordinary water is that it keeps the reaction cool. However, if it boils, the bubbles are places where there is no neutron moderation and no cooling either. Faster neutrons can lead to more rapid reactions, which means that boiling water reactors can be a little dangerous. It is always possible for a reaction to get too fast, and outstrip the cooling capacity, and that could damage the reactor. So what you can use instead is water under pressure, which doesn’t boil; you can then heat it up to a few hundred degrees and pipe in water at normal pressure which turns to steam and can be passed through a steam turbine. This also means that the water in the turbine spends less time in contact with lots of neutrons and is less likely to become radioactive, so that if the steam leaks it’s less of a problem.
“Less” is of course a very relative term here.
Alternatively, you can just use graphite, like the dear old Soviet RBMK reactor or the British Windscale reactor. Both of these have their problems, since graphite catches fire if you heat it up enough — which is essentially what happened at Windscale (now Sellafield) in 1957 and Chernobyl in 1986. Graphite is a good moderator, and you can cool it with water or with high-pressure gas such as carbon dioxide. (Preferably not air, to avoid oxidation.)
Now, those reactors were actually built, not to provide power (although they did, of course) but to provide plutonium. You stick your 95% U-238 into the reactor and there are neutrons flying about. Much of the time when they wallop into the U-238 they don’t make it fission; instead, the neutron changes to a proton and, by degrees, the atom may eventually change into plutonium. The desirable kind of plutonium is Pu-239, which is securely fissionable; unfortunately, this plutonium may absorb another neutron and turn into Pu-240, which is dangerously unstable, so the longer you leave the plutonium in the reactor, the less desirable it becomes. Meanwhile, Pu-239, because it is fissionable, may fission, generating more neutrons. You have to strike a balance between your desire for plutonium and your desire not to have your fuel elements so full of fissionable material that the reaction runs out of control.
Usually, however, what you can then do is take the fuel element out in good time and process it for the plutonium. This is tricky, because you have to dissolve the fuel element (which by this time is far too radioactive for a living human to approach it) in nitric acid and then precipitate the plutonium out of this dangerously radioactive soup, a chemical reaction which must be done with no humans present and without any release of material into the air. This is one of the largest sources of nuclear waste; the corrosive sludge remaining after the plutonium is removed is usually just thrown away. (This was the source of the Urals nuclear disaster in 1957.)
However, if it is done properly you end up with plutonium which is much more enriched with fissionable Pu-239 than uranium is with U-235. You can then melt the plutonium, mix it in with natural uranium, and use it in fuel elements. Probably you will not use the same reactors that you would use for straight uranium (plutonium has different physical properties to uranium) but the end product will be the same; generating power while producing plutonium which can be processed and used for fuel again.
Why doesn’t this happen? The answer is simple: the United States doesn’t want it to happen. The United States wants to ensure that reactors across the world remain uranium-based rather than plutonium-based. Plutonium reprocessing plants are potential sources of nuclear weapons, even more so than uranium enrichment plants (Israel and India both obtained their nuclear weapons through an impeccably legal purchase of a plutonium reprocessing plant, in both cases supposedly for research purposes). Of course there are other reasons; countries with reprocessing plants mostly jealously guard their plutonium for use in precious, precious bombs, and they mostly have uranium enrichment systems to go with their reactors and don’t want to develop new reactors. This is farcical, however, because there is potentially fifty or a hundred times as much plutonium as there is U-235, and it is much cheaper to produce than enriched uranium. A plutonium economy is probably the only way to make a nuclear power system economically viable.
Of course, there are huge dangers. The kind of reactors which are cheap to build are also unsafe. Unsafe is, however a relative term; the catastrophe of Chernobyl did not happen because the reactor was badly built or ill-designed, it happened because the people in control of the reactor were playing games with it (trying to simultaneously reduce the power output and the coolant inflow in order to see what would happen; what happened was that some elements overheated and started a graphite fire which rapidly ruined the whole control system, and before the reactor operators got round to shutting the reactor down, the core exploded, blowing the roof off the building and spraying vapourised nuclear waste across the Ukraine). If you run a nuclear reactor with the same care with which you drive a car, catastrophe is not very likely.
Nuclear waste management, of course, is also problematic. You can stick it in a big hole in the ground and hope it will go away. Alternatively, you can put it in a building with thick walls, padlock the door and put a guard at the gate, and hope it will go away. These are not really solutions to the problem. The only real solution is to recycle high-level nuclear waste through nuclear reactors, changing the dangerously radioactive isotopes either into less radioactive isotopes or into isotopes which are so radioactive that they have a half-life of only a few years. Then stash them somewhere you can draw heat from their decay (such as a pond of boiling water), and put a few guards on the door of the boiler room and the turbine hall. It’s an expensive solution, but effective. Why nobody is doing it is, presumably, because although it’s an effective solution, it’s expensive. (Incidentally, most low-level nuclear waste can be reprocessed in order to remove the high-level content, leaving nuclear waste which is less problematic and comparatively safe to dump down a mine somewhere. But, again, that’s expensive.)
None of this means that we should all drop everything and get going on building a uranium enrichment plant, a couple of plutonium-breeding reactors, a plutonium reprocessing plant, a couple of dozen plutonium-U-238 reactors and a nuclear waste processing reactor with associated boiling-water high-level waste holding plant. However, doing these things locally probably makes more sense than poisoning our air and water with gigantic coal-burning power plants imported from elsewhere. However, that’s not a debate South Africans are liable to encourage.

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2 Responses to Nuclear Dogmas.

  1. Johan Meyer says:

    Just a point of fact – most (70%) of the waste fell out over Byelarus’, not Ukraine. I agree about the design vs operation question – with proper operation, those designs are much more efficient than certain W European designs, but still a damn evil technology.

  2. Nokwindla says:

    Hawu, kwenzekalentoni ngaleya-post yakho yanamhlanje!?

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