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Modern risks: nuclear power

Nuclear power: the most natural risk of all
A health warning: I researched these pieces in the mid and late 90s: people quoted may have changed their views since. I haven't. The evidence, too, may have moved on without my spotting it. This entire site is a work in progress: its evidence is offered in good faith and comments are welcome.

The wider picture
Everyone "knows" Sellafield glows. It's the butt of a hundred jokes - or rather, the same joke re-worked hundreds of times. Making jokes about people suffering radiation burns or leukaemia - even if they are imaginary sufferings, or their connection to Sellafield is imaginary - is of course tasteless as well as alarmist.

The difficulty is that every attempt to explain radiation is open to charges of being deliberately misleading. At the average doses allowed by the regulator, there is scant evidence of any damage at all. They are well below doses which produce what are called "deterministic" effects, namely, very obvious ones. But if one stresses this fact, people feel you are opening a door to the idea that radiation is not bad for us. If one concentrates on the people who get the greatest dose, their being few is forgotten. If one concentrates on the many whose dose is miniscule, one may be thought to be distracting attention from those few who have much bigger doses.

How do you draw attention to this source of radiation, which matters because it exposes many people to a dose; or to that, which matters because its effects are long-lasting?

Enter, the idea of the "collective dose". Definitions, first. A collective dose is the sum total of all the doses to all the people over all time who are exposed to a radiation source. It's derived from one assumption: that any radiation dose however small carries with it a proportional risk however small. This is called the linear dose relationship. If you use that assumption then the dose received by a population will be proportional to the health effect. And for radiation purposes, a "health effect" is regarded as a death.

This is where the devilry begins. Since it's assumed that radiation causes cancer (in big doses it obviously does) and since we boldly assume there will be a cancerous effect even at small doses (which is open to dispute, but assuming it is so is likely to lead us to usefully cautious behaviour), then collective dose theory (and it's only a theory) has it that somewhere in all the crowd of people who receive their portion of a collective dose, there will be some deaths.

This is scary. But it flows out of the business of multiplying a small individual average dose by a lot of people and multiplying that number by a lot of years. The result gives you large numbers. That is, it gives a seemingly large amounts of dose given to a crowd which is "virtual" in the sense that it is composed of a changing cast of people, amongst whom are the dead, the living and the unborn. Somewhere in that crowd, it must be assumed there must be an individual who gets cancer from this dose. It might well not be true, of course, because the real doses to real people are in fact small. Collective dose assessment is certainly a way of magnifying the sense of risk: it assumes a real and large effect from exposures which may have none, and then starts multiplying large numbers all over the place. It is prone, like much statistical work, to the exaggeration which comes from making heroic assumptions and then adding noughts.

Actually, this quite fits the way we think about cancer causation. We do not know as much as we would like about this set of diseases. We know about a third of people die from them, and that that number has increased because people grow to become older now than they used to. We know that various sorts of chemical exposure, and exposure to radiation, do at differing doses cause some cancers and might be assumed to increase the likelihood of people getting others - usually after a long period of time (hence the increase of cancer-death in an ageing population). It is fair to think of most cancers as having many causes which accumulate to generate the disease. These include genetic susceptibility, time, and probably a cocktail of exposures to chemicals and radiation. In both chemical and nuclear cases, most exposures come from "natural" and more or less unavoidable sources whose main effects, especially in the case of chemicals, may even be benign.

A fair way of looking at this picture is to suggest that cancer-causation is a little like a shove ha'penny board. Each contributory factor is a coin which plays its part in the queue of coins which will eventually push one of their number over the edge. This approach allows that each coin is only a small contributory factor; but the role of each in the final outcome cannot be ignored: each was a necessary part of the downfall of the coin which toppled over the end of the board. We think we ought to reduce the exposure of the crowd of us to any additional burden or radiation because in the case of any one of us, any new factor compounding cancer-causation ought to be avoided. Just because we can't see why or how an exposure to radiation of low dose can be a problem does not mean it is sensible to overthrow the generally precautionary logic.

However, there is a further odd complication. If we know many people will die from cancer and that this is the case as the result of a cocktail of effects, then probably the most we can say of any particular new exposure is that it will bring forward the time when someone contracts a cancer. In other words, it may not by itself kill anyone. It may have "only" contributed to a fatal cancer rather than caused it; it may have induced a cancer a little earlier than the cancer would have happened anyway; it may have killed someone at 70 who would otherwise have lived to 75.

Campaigners leap on collective dose data and have argued that it implies that, for instance, the next decade's-worth of Sellafield's radiation will cause 2000 deaths over the rest of time. But it is as true to say that the individual risks of a fatal cancer are very, very small. It is something like one in 1000 million per year. That is the risk to anyone, anywhere in the world, for all time of getting a fatal cancer from the plant. That is many times less than the annual risk of dying in a car crash. The risk is utterly trivial.

It is harder to gauge how much a risk such as is posed by Sellafield's routine radiation really rates. How much does it prey on people's minds? Many of the people who live near the plant have the acceptance of familiarity, stiffened by knowing people whose livings are had at the plant. And people who live further away are pleased not to think too deeply about the place.

The naturalness of nuclear risk
Eighteen hundred million years ago, there was an entirely natural, spontaneous nuclear power station in the earth's crust. Nuclear scientists are pleased that creation made several of its own reactors at Oklo, in Africa's Gabon (and elsewhere), partly because it shows man did not introduce the splitting of atoms in a chain reaction to this planet. Besides, the radioactive "wastes" from that reaction seem to have stayed put, just as the scientists hope to persuade us that modern nuclear wastes can be made to.

Oklo, a reactor for thousands of years, reminds us of our origins. We and our planet are wastes from a fusion reactor, the sun. Nuclear fusion is the collision and combination of lighter elements, as opposed to fission which is the fragmentation of heavier elements; both release some of the prodigious energy contained in atoms. The fusion process produces both stable and unstable elements or isotopes. These unstable elements from our origins in the sun form the basis of the present nuclear industry and contribute to the natural background of radioactivity.

The radioactivity of the earth's elements is decaying, but at different rates (expressed in half-lives), with different intensities of energy, and by a number of different routes, including electron-like fragments called beta-particles and the heavier alpha-particles; and gamma rays. Alpha, beta and gamma radiation have ascending powers to penetrate materials, including human tissue, but all can damage cells.

Plantlife on earth is now dependent, as is our climate, on the heat of the sun's continuing fusion reaction, and the discussion of how that heat passes through lifeforms is the very heart of the fashionable science of ecology. Yet the widely distrusted technology of nuclear physics is doing something elegant, too. Scientists have found ways of restoring to its former vigour some of the dying radiation from the nuclear explosion which formed our world, so that it can reproduce the Oklo process. As a power-generating technique, it has the merit over traditional fossil-fuel burning that it adds very little to atmospheric pollution.

There is good and bad news about the radioactive wastes and emissions from the nuclear industry. Even during its relatively unsophisticated infancy, they did not add significantly to the amount of radiation the average citizen received from the radioactive rocks beneath his or her feet and from continued bombardment from outer space. Hospitals and surgeries contributed far more to the average dose. More recently, the industry's discharges have been reduced, in some cases tenfold, and in the case of Sellafield's emissions to the sea, a hundredfold.

In any case, because we know a good deal about man's response to really large extra doses of radiation, we can be fairly confident that radiation doses have to be a hundred or hundreds of times average background levels to cause us measurable harm. This strong guess is in part derived from the effects of the radiation from atomic bombs used at the end of the second world war: the bombs' radiation - about a hundred times background - caused about an eighth more people to die of cancer than would been expected in an equivalent non-exposed population [1]. Yet the nuclear industry does not multiply the dose most people receive by tens or hundreds, but only increases them by a few thousandths. Even to the 1000 UK nuclear workers most exposed (with doses about ten times average background), the industry poses little more exposure to radiation than Concorde's flight crews experience by spending their working lives high enough in the atmosphere to be less shielded from cosmic radiation than the rest of us. [2] Nuclear workers do not have elevated cancer rates.[3] There is epidemiological - in effect, circumstantial - evidence that the children of the most exposed nuclear workers are, like workers in a wide range of industries, slightly more than usually prone to leukaemia. Some non-nuclear cause makes more obvious sense than that these cases overturn our understanding about radiation, about which we are nonetheless right to be deeply cautious.

Whilst nuclear fission is in principle natural, it creates local concentrations of radioactivity not seen on earth for billions of years. The process of turning uranium into fuel does not create more radiation than man began with, but it does concentrate the radiation in a much smaller bulk. Then, in using it in a reactor we produce a little more, and more problematic radioactivity than was in the original uranium. If this were not so, reactor waste could, in principle, simply be returned to the mines whence it came, and the earth's crust would be no more radioactive than before.

We have gone further than creation. Man has developed chemical techniques for recycling the spent fuel from nuclear reactors into new fuels: a form of uranium, and plutonium. The latter is useful for bomb-makers, and its potential value to terrorists means that it has to be accounted for very carefully (though the plutonium from dismantled Soviet ballistic missile warheads would make a far more likely source of mischief). The recovery process at the moment redistributes most of the radioactivity of spent fuel into bulkier, though much less potent, radioactive wastes. But it also creates a very small amount of highly active, "high" level waste of which it is the only source. New developments promise to recover waste fuels whilst reducing the radioactivity of by-products. The recovered materials may one day provide a fuel source for fast breeder reactors, which have the advantage of generating their own fuel, though their development is stalled partly because uranium is cheap. The recovered fuel can be treated so as to be useful in conventional reactors.

In Britain, recycling of spent fuel is done at Sellafield, including a new reprocessing plant, THORP. The industry insist the profit from the operation more than justifies the marginal increase in radioactivity emissions it involves.

The vast bulk of nuclear wastes (most of what the industry categorises as "low" level wastes) are such that a dustbin load would be no more problem to have around the house than a dustbin of domestic waste. You would not handle it and then lick your fingers, but you would not need a shield. A couple of dustbin loads in one's house wouldn't approach the natural background levels of radiation.

There is a smaller quantity of wastes, called "intermediate" level, which require a sealed container and a few inches of concrete shielding to protect us against exposure to gamma radiation and ingestion of toxic dust. Only about a thousandth of the radioactive wastes is high level and it is this material which must be treated as a very toxic substance requiring several feet of concrete to protect us from the intense gamma radiation.

There is a double-decker load of high level waste in the UK, and its danger comes from its very active decay processes, which lead to the relatively short period of its intense radioactivity (in other words, its short half-life). However, the activity in high level waste will fall over about 500 years, to a thousandth of its present level and be equivalent to our intermediate level waste.

High level waste will become as radioactive as low level waste in 10 million years, or as radioactive as the original uranium from the earth's crust, in about a million years. However, we can draw some comfort from the fact that highly penetrating radioactivity will substantially reduce much quicker: after less than a thousand years a sheet of paper would stand as sufficient barrier between us and the emission of the waste's radioactivity, though we would still have to guard against eating or inhaling it.

The curent intention, for which permission is currently being sought by the industry, is to bury the intermediate nuclear wastes 650 metres deep in the earth's crust. If this sounds like dumping, one should remember that the waste will be in containers designed to delay corrosion, and these will be sealed in caverns backfilled with material chosen to have a benign chemical effect on the waste. The whole will then be housed in an area which will have to pass tough tests as to the likelihood of any radioactivity getting into water which could reach the biosphere.

Even so, it is proposed to delay the disposal of the high level wastes. They generate heat, so it is deemed wise to store them above ground for a generation, until they have cooled and decayed somewhat, before some sort of deep burial.

Nuclear technology involves dangerous material and processes. So do the coal and oil technologies, which have killed and diseased far more employees and customers in accidents, smogs and mines. Even a very bad nuclear accident, such as extreme folly induced at Chernobyl did not kill nearly as many people as died in the Piper Alpha oil field accident, whose death toll was 167. However, there will be hundreds and perhaps thousands of cancers because of Chernobyl: radiation doses kill most of their victims after a delay of a couple of decades. But then, there are health risk associated with burning the oil which Piper Alpha wsproducing, as well.

Why take the risks associated with even well-managed nuclear power? Sometime half way through the next century, and barring accident, there will be 10 billion energy-hungry people in the world. Of these, many will live on bits of the earth's crust which are rich in coal and to a much lesser extent oil. Both these are the product of the arrested and modified decay of plantlife orginally fueled by the heat of the sun's fusion reactions. Niether will last indefinitely, and in any case their use is expensive if limiting or adjusting to their pollution is taken into account. If global warming becomes a prime factor, we will have an additional motive to shift towards non-fossil fuels. True, solar power technologies can do a good deal with the present warmth of the sun, but they are expensive.

We may yet be very glad that we know how to use the radioactivity which remains from the earth's creation.

[1] In the Japanese case, 42,000 people were exposed to an average dose of 300 mSv (average UK exposure 2.5 mSv); by 1986, 3291 of that population died of cancer, about 400 more than would have been expected in a non-exposed population. 1991, KSU Analysis Group, S-611, 82 Nykoping, Sweden.
[2] In 1987 4 workers receieved in excess of legal limit of 50 mSv. 1000 received doses above 15 mSV. Annual average worker does 2mSv. Subsonic aircrew are exposed to about 2mSv and supersonic crews to 2.5 mSv-17 mSv. Coalminers average 1.2 mSv. Radon-exposed miners recieve about 14 mSv. pp 33-34, Living With Radiation, National Radiological Protection Board, 1990, London, HMSO.
[3] p 24 Radiation: Effects and Control, UKAEA, Feb 1993.

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