LNT is nonsense

This piece is an experiment. It is not only a highly technical argument; it is a highly abbreviated, highly technical argument. It goes very fast, far too fast. But LNT is at the core of what is wrong with nuclear power. If this post perplexes people enough to check out the extended discussion of radiation harm models in Why Nuclear Power has been a Flop, it will have been a success.

Don't be miffed if you are mystified by the title. You're probably better off for it. LNT stands for Linear No Threshold. It's the hypothesis that radiation harm is strictly proportional to the dose no matter how rapidly or slowly that dose is received. This is like saying taking one aspirin a day for a year is the same as taking 365 aspirins in a day. LNT is the foundation for all our radiation regulation and response. LNT is nonsense.

LNT is a repair denier

Radiation dose is the amount of radioactive energy absorbed by our tissue. It is measured in joules per kilogram of tissue. The shorthand for joules per kg (J/kg) is called a gray(Gy). LNT claims that 1 Gy received in a few minutes is the same as 1 Gy received over 50 years.

In fact, 1 gray received in a few hours will make you very sick. Vomiting, diarrhea. You may lose some hair. Your immune system will be depressed for several weeks. You will almost certainly recover; but your chances of contracting cancer sometime in the future will be increased by roughly 10%. Not good.

1 gray received evenly over 50 years is a dose rate of 0.05 milligrays per day (mGy/day), where a milligray is one-thousandths of a gray. Such dose rates will produce no detectable harm. Spots along the Kerala coast of India have natural background dose rates of 0.16 mGy/d. Nearby districts have natural dose rates of 0.01 mGy/d or less. 117,000 people who live in the region were studied for 15 years. The people who lived in the high dose rate spots, people who received over 500 mGy in that period, had slightly lower cancer rates than the people who live in the low dose rate spots, people who had received less than 50 mGy.¹ Why Nuclear Power has been a Flop lists example after example of very large doses received over extended periods with no detectable harm. We start to see detectable harm only when dose rates get above 20 mGy per day.

The reason for this resilience is nature has equipped us with a very effective repair system. We live in a sea of radiation. Depending on where you are reading this, in the last minute your body has absorbed between 1 and 10 million radioactive particles with enough energy to produce cell damage. Life evolved in an environment where the natural level of radiation was 5 times higher than it is now. Without that repair system, we would not be here.

The details of this repair process have been elucidated by scientists all over the world, including three Nobel Laureates. UC Berkeley even has movies of the process.² This system can be overwhelmed; but only if the dose rate is high enough. In its claim that dose rate is irrelevant, LNT is not just quantitatively wrong, LNT is qualitatively wrong.

LNT is a killer

Despite these facts, LNT is the all important basis for all our radiation regulation and response. LNT leads to horribly tragic policies. In the six months after Chernobyl, 116,000 people were evacuated from the area around the plant, many from villages where the dose rate was less than parts of Kerala. So far they have not been allowed to return to their homes, despite the fact that the dose rates are now well below background in many parts of the planet and have been for a very long time.

Preposterously, four years after the release --- after everything had settled down --- another 220,000 people were forcibly uprooted from areas where the maximum dose rate was about 0.02 mGy/d. This was done on the grounds that, if these souls were allowed to stay where they were, they would receive an extra 100 mGy over a 70 year life. People who move from Florida to South Dakota as children will receive an extra 500 mGy over a 70 year life.³ The evacuees have suffered all sorts of psychological problems. For many, their lives were ruined.

At Fukushima, 160,000 people were evacuated despite the fact that, if there had been no evacuation, no member of the public would have received more than 50 mGy in the first year after the release. The panicked, disorganized, botched evacuation killed more than 50 frail, old people in 48 hours.⁴ People are not allowed to return unless the dose rate at their home is less than one-third the dose rate in parts of Kerala. The Japanese government has adopted a policy of reducing the release related dose rate to less than 0.003 mGy/d, convincing everybody that 0.003 mGy/d must be dangerous. As a result, large numbers of the evacuees have still not returned. Fukushima is a low background dose rate area. This expensive, scarifying mitigation policy requires that the total dose rate be less than the average background dose rate on the planet.

LNT has led to ALARA, which is the regulatory design policy that no amount of radiation exposure is acceptable if the plant can afford to reduce if further. In other words, there are no limits. This policy has resulted in nuclear power costing four or more times what it could and should cost, effectively preventing nuclear power from solving both energy poverty and global warming. The cost to humanity is incalculable.

LNT thrives on a false dichotomy

The ``No Threshold'' in Linear No Threshold is redundant. If harm is strictly proportional to dose, then there can be no dose except zero that causes absolutely no harm. Yet just about everyone, friend and foe, focuses on the No Threshold part of Linear No Threshold. The anti-LNTers claim there is such a threshold, pointing to all the situations in which people have received substantial doses with no detectable harm. The LNTers counter no detectable harm does not mean no harm. Where is your proof that that there is a threshold below which there is absolutely zero harm? No such proof is possible.

In fact, the No Threshold assumption is not unreasonable. If there is a threshold, what is that number? Is it the same for everybody? And what is magic about that particular dose, such that just above this dose there is harm, just below it there is none. The anti-LNTers have no answer. Once you frame the issue as either there is a threshold or LNT, LNT wins.

But this is a false dichotomy. There are an infinity of dose-response curves besides LNT which accept the No Threshold assumption. The classic dose-response curve is S-shaped. Such S-shaped curves are always above zero except at zero dose. But as you approach zero dose, the harm can be many thousands of times smaller than that predicted by LNT. Figure 1 shows an S-shaped curve fitted to the atom bomb survivor solid cancer mortality. Even in a release as large as Fukushima, few members of the public will experience a dose rate higher than 1 mGy per week. At that dose rate, the S-shaped harm is 400 times less than the LNT harm. And in that dose range, the S-shaped curve is above the actual cancer mortality.

Figure 1 S-shaped Curve Fit to Bomb Survivor Cancer Data. Left: 0 to 1000 mGy. Right: 0 to 150 mGy. The S is very lopsided with the low end hook much smaller than the high end. In a nuclear power plant release, it’s only the very low end that is relevant.

LNT cannot survive its no repair claim

The proper way to refute LNT is not to claim there is a threshold; but rather to shine the focus on LNT's assertion that exposure period is irrelevant. Our bodies know how to repair radiation damage. No knowledgeable observer can deny this. But if that is the case, what counts is keeping the damage rate below the repair rate; and the time to repair becomes critical. We know the cellular repair processes operate on time frames of hours; and the higher level repair processes operate on a period of a day or two.

Any realistic model of radiation harm needs to be based on the dose rate through time, the dose profile. One approach is to divide the dose profile into repair periods, estimate the harm in each repair period, and then add up the repair period harms. If turns out that, if your dose-response curve is linear, however you chop the dose up into repair periods, when you add up the harm from each period, you come up with the same number. The only thing that counts is the cumulative dose. Another way of saying LNT implies no repair.

But if your dose-response curve is non-linear, say S-shaped, the dose within each repair period becomes all important. Now the data starts to make sense. The data says, if the dose is received in a few hours or less, we start to see a statistically significant increase in cancer at doses much above 100 mGy. But if the dose rate is below about 10 mGy per day, we see no detectable effect from a cumulative dose of tens of thousands of mGy.⁵ An S-shaped model combined with a repair period has no problem matching both the harm from a dose received in a single spike, and the harm from the same dose spread out over a lifetime. The Flop book has some numerical examples.

LNT cannot come anywhere near replicating both behaviors. LNT is qualitatively wrong. LNT is horribly tragic nonsense. The LNT model of radiation harm must be abandoned if humanity is to enjoy the benefits of nuclear power.

1. Nair, M. and Rajan, B. and Akiba, S. Background radiation and cancer incidence in Kerala, India, Karanagappally cohort study, Health Physics. Vol 96, January, 2009.

2. Neumaier, T. and Swenson, J. and Pham, C. Evidence for formation of DNA repair centers and dose-response nonlinearity in human cells, PNAS Early Edition, November, 2011

3. The background dose rate in Florida is 1.3 mGy/y; in South Dakota, 8.6 mGy/y. Mauro, J. and Briggs, N. Assessment of variations of radiation exposure in the United States, EPA Technical Report, EP-D-05-002, July, 2005.

4. Tanigawa, K. and Hosi, Y. and Hirohashi, N., Loss of Life after Evacuation: Lessons learned from the Fukushima accident, The Lancet, Vol. 379, 2022, pages 889-890.

5. Devanney, J. Why Nuclear Power has been a Flop, Table 5.18.