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The Linear No Thought model or LNT

Page history last edited by Andrew Alder 3 years, 2 months ago Saved with comment

A page on energy issues.


The Linear No Threshold model (LNT) for estimating the risks of exposure to radioactive material and other nuclear radiation has its uses, but it also has misuses, and lately it's the misuses that have been far more common in the popular media.


Take the Three Mile Island meltdown for the best example. It killed nobody. But there are hysterical claims, based on the LNT, that the cancer rates of the surrounding population will have increased, and that these extra deaths are therefore due to the accident. The argument is, if such-and-such a dose of radiation gives one person in a thousand cancer, then one-thousandth of that dose will obviously give one person in a million cancer. That's how the LNT is being applied here.


Let us put it into perspective. If we were to similarly apply the LNT to motoring, we might say, if one person in ten dies in a head-on collision at such and such a speed, then obviously one person in a thousand will die in an incident that gives them one hundredth of that force.


And we would make it illegal to stop at a yellow traffic light, because of the enormous number of implied fatalities to the motorists who do stop and to their passengers. Now we do not do that, because we have data. People don't often get killed stopping at yellow lights, and on the other hand they sometimes do get killed when they don't stop. The risk of stopping is hypothetical, and in this case that means pure rubbish. It has no place in public debate on public policy. To try to apply it as I have suggested would be quite simply incompetent.


Or in other words, to apply the LNT to this sort of prediction would, in the case of the injury caused by a sudden stop in a motor vehicle, be just plain ridiculous. Well, to apply it to the whole population in the fallout area of TMI, or any other nuclear accident, or any other small radiation exposure at all, is equally ridiculous.  The LNT was developed to set an upper bound on the risk, and health physicists do apply it, competently, to this day and for that purpose. But it does not predict that this is the level of danger... or at least, not if it is competently used. It predicts that the level of danger is equal to or less than this.


And we now have data on the TMI accident as well. And nobody got cancer. But that spectacular failure hasn't stopped similar hysterical and incompetent application of the LNT to Chernobyl (which did kill people) and Fukushima Daiichi (which is unlikely to kill anyone, while the knee-jerk shutdown of all Japanese power reactors including those of different design which weren't aren't anywhere near the coast is estimated to have killed many thousands by electricity shortages and poor air quality).


And we have other data on the LNT for nuclear radiation as well, which indicates that for very small doses the risk is not just less than this upper bound, not just much much less, but may even be negative (this theory is called radiation hormesis). But this doesn't fit the political agendas of most of those who cite the LNT.  So they continue (often in good faith and ignorance) to cite similar rubbish. And why not? The voices of those who know better are not all that obvious.


We might term this greenwashing. In fact that's a very good name for it.


Nuclear accidents do have the potential to kill people (as does atmospheric pollution and dam collapse and many other consequences of the alternative technologies) and have done so. The SL-1 accident in the USA killed three people. But the risk is not nearly so great as some would have you think! And that is the problem for anti-nuclear activists. If the figures are done competently, nuclear turns out to be far less dangerous than fossil or even hydro. (And they have a similar problem with greenhouse gases and hydro... dams that flood forests release methane.)


So instead of science, they feed this low-level mass hysteria. And it's easy to do. Newspapers have always used their morgue files as their primary sources of information, and there was a hidden danger there. Once something was published, however false it might be, it took on a life of its own.


The Internet has supercharged this process. Urban myths, once published in cyberspace, become part of the public thoughtspace. This is called citeogenesis or circular_reporting and is an acknowledged problem at Wikipedia. But at least there the problem is recognised and addressed as we can. The world of journalism may someday follow our lead. The world of politics never will. Why would they even want to?


Any corrections are often not nearly as exciting as the falsehoods, and so even if they are made they don't get the same coverage. We can't fix that here. But we can have a look at the LNT, at least. It has its uses and abuses.


I hope you might find the above helpful in determining which is which!


See also


nuclear homework





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