The Linear-No-Threshold Hypothesis

In a recent article we discussed the BEIR VII report's conclusion with respect to the linear-no-threshold (LNT) hypothesis concerning low-level radiation's possible health effects. It's worthwhile to compare it with other reports' findings, all from professional organizations in the US.

First, here's the pertinent statement in BEIR VII

"At doses of 100 mSv or less, statistical limitations make it difficult to evaluate cancer risk in humans. A comprehensive review of available biological and biophysical data led the committee to conclude that the risk would continue in a linear fashion at lower doses without a threshold and that the smallest dose has the potential to cause a small increase in risk to humans." [A typical person in the US receives 3 milliSieverts per year.]

That's a tepid justification for retaining LNT, but compare that with the statement from the National Institutes of Health:

"It is very difficult to detect biologic effects in animals or people who are exposed to small doses of radiation. Based on studies in animals and in people exposed to large doses of radiation such as the atomic bomb survivors, scientists have made conservative estimates of what might be the largest doses that would be reasonably safe for a person over a lifetime. But these calculations are estimates only, based on mathematical models. Low-level exposures received by the general public have shown no link to cancer induction. Even so, the U.S. Government uses these estimates to set the limits on all potential exposures to radiation for workers in jobs that expose them to ionizing radiation. International experts and various scientific committees have, over the years, examined the massive body of knowledge about radiation effects in developing and refining radiation protection standards."

And with the statement from the Health Physics Society"

"There is substantial and convincing scientific evidence for health risks following high-dose exposures. However, below 5–10 rem (which includes occupational and environmental exposures), risks of health effects are either too small to be observed or are nonexistent."

"In view of the above, the Society has concluded that estimates of risk should be limited to individuals receiving a dose of 5 rem in one year or a lifetime dose of 10 rem in addition to natural background." [5 rems would be 50 milliSieverts.]

Professor Bernard Cohen goes on to estimate what would be the health effects of low-level exposures and compares them with other health risks, using the LNT model even though he shows in his analyses that it overstates the adverse effects and probably understates the beneficial (hormesis) effects of low-level radiation.

As an exercise we'll do something simple here. The BEIR report says ten million mSv would cause 1140 deaths. And it says that, on average, 304 million Americans receive 3 mSv per year, so the total would be 912 million mSv. So all of the radiation-induced deaths add up to 104,000 per year. Of that number, according to the report, 0.2% are due to nuclear energy, the rest mainly being due to natural radiation. If the LNT hypothesis is right, 208 deaths per year can be attributed to nuclear energy.

In comparison, every study done shows that tens of thousands of Americans die every year from the pollution generated by coal-fired power plants. The most comprehensive study done so far puts the range between 33,000 and 121,000 per year, just counting adults over 25. In 2006, according to DOE, coal generated 1930 billion KWH of electricity and nuclear generated 787 billion KWH, so if nuclear replaced coal an additional 510 deaths would take place, but at least 50,000 lives would be saved.

And all of the radiation-related deaths depend on a hypothesis that hasn't been proved and which specialized professionals don't believe.

Here's the kicker: Coal plants emit more than ten times as much radioactivity as nuclear power plants. If the LNT hypothesis were true, 5000 of the coal-related deaths would be avoided by converting to nuclear energy just because of reducing radioactive emissions.

If some form of renewable energy could provide full-time power, this might be a harder decision to make. As we saw in an earlier article, though, there aren't any that could.

So those are the two options. We can let over 50,000 Americans die every year from coal or we can switch to nuclear energy and start cleaning up the environment while minimizing the threat of global warming. What to do, what to do.

Bernard L. Cohen

This is the easiest to write of the articles on this blog. The only important part is a link to Prof. Bernard L. Cohen's website, THE NUCLEAR ENERGY OPTION. Here you'll find the most authoritative treatment anywhere of all aspects of nuclear energy as it relates to the public, and it's written clearly enough that any reasonably well-educated person can understand it perfectly.

This article could end right here, but maybe it's worthwhile to offer one example of his explanations. Since safety is the one place where most people's knowledge of nuclear energy is dodgy, what follows makes a good sample.

RISKS OF NUCLEAR ENERGY IN PERSPECTIVE

With the benefit of this perspective, we now turn to the risks of nuclear energy, and evaluate them as if a large fraction of the electricity now used in the United States were generated from nuclear power. The calculations are explained in the Chapter 8 Appendix, but here we will only quote the results.

According to the Reactor Safety Study by the U.S. Nuclear Regulatory Commission (NRC) discussed in Chapter 6, the risk of reactor accidents would reduce our life expectancy by 0.012 days, or 18 minutes, whereas the antinuclear power organization Union of Concerned Scientists (UCS) estimate is 1.5 days. Since our LLE from being killed in accidents is now 400 days, this risk would be increased by 0.003% according to NRC, or by 0.3% according to UCS. This makes nuclear accidents tens of thousands of times less dangerous than moving from the Northeast to the West (where accident rates are much higher), an action taken in the last few decades by millions of Americans with no consideration given to the added risk. Yet nuclear accidents are what a great many people are worrying about.

The only other comparably large health hazard due to radiation from the nuclear industry is from radioactivity releases into the environment during routine operation (see Chapter 12). Typical estimates are that, with a full nuclear power program, this might eventually result in average annual exposures of 0.2 mrem (it is now less than one-tenth that large), which would reduce our life expectancy by another 37 minutes (see Chapter 8 Appendix). This brings the total from nuclear power to about 1 hour (with this 37 minutes added, the UCS estimate is still about 1.5 days).

If we compare these risks with some of those listed in Table 1, we see that having a full nuclear power program in this country would present the same added health risk (UCS estimates in brackets) as a regular smoker indulging in one extra cigarette every 15 years [every 3 months], or as an overweight person increasing her weight by 0.012 [0.8] ounces, or as in raising the U.S. highway speed limit from 55 miles per hour to 55.006 [55.4] miles per hour, and it is 2,000 [30] times less of a danger than switching from midsize to small cars. Note that these figures are not controversial, because I have given not only the estimates of Establishment scientists but also those of the leading nuclear power opposition group in this country, UCS.

I have been presenting these risk comparisons at every opportunity for several years, but I get the impression that they are interpreted as the opinion of a nuclear advocate. Media reports have said "Dr. Cohen claims . . ." But there is no personal opinion involved here. Deriving these comparisons is simple and straightforward mathematics which no one can question. I have published them in scientific journals, and no scientist has objected to them. I have quoted them in debates with three different UCS leaders and they have never denied them. If anyone has any reason to believe that these comparisons are not valid, they have been awfully quiet about it.