The ANS Position Statement on Radiation Harm

Periodically the American Nuclear Society, the professional society of nuclear engineers and scientists, issues Position Statements. The ANS Position Statement on radiation harm is here. It's a committee written compromise which fails to say much of anything. Recently, the ANS decided to update the statement. An attempt was made to radically alter the statement's failure to call out LNT. Unsurprisingly this failed. The updated statement will merely call for still more research.

ANS position statements by fiat can be no longer than two pages. They are usually accompanied by a longer Backgrounder. Here's the radiation harm statement the ANS should have issued.

We live in a sea of radiation. Every minute of every day each of us is bombarded with 1 to 10 million penetrating radioactive particles which have enough energy to damage our DNA. But radiation damage is the not the only problem our DNA faces. In fact, it's far from the biggest problem. We use oxygen based metabolism. In metabolism most of the O2 ends up as CO2. But about 5% is converted to Reactive Oxygen Species (ROS) such as OH-. These chemically active ions react with and damage our DNA. Each of our cells produces about one billion ROS microbombs per day.\cite{feinendegen-2012} The information in our DNA must be preserved. Nature had to come up with a repair system to handle this onslaught.

DNA damage can take two forms: Single Strand Breaks (SSB) where one side of the double helix is still intact, and Double Strand Breaks (DSB) where both sides are broken. SSB's are repaired almost automatically using the intact strand as a template. The repair is effectively errorless. The problem is DSB's which are subject to viable misrepair which could lead to cancer.

Metabolic damage creates 10 to 50 DSB/cell-day.\cite{vilenchik-2003, bouwman-2018, lieber-2010, costes-2021} Radiation creates 0.01 to 0.05 DSB/mSv.\cite{vilenchik-2003, white-2016, bissell-2011} Metabolic damage is equivalent to 200 to 5000 mSv/d. Looking at these numbers, 20 mSv/d might stress our repair system, but 2 mSv almost certainly will not. In fact, we have never reliably detected an increase in cancer from dose rates of 2 mSv/day, even when that dose rate is experienced for decades. The most compelling example is the radium dial painters.\cite{rowland-1994} We do start to see significant increases at dose rates much above 20 mSv/d.

In a nuclear power plant release, the dose to the public will be incurred over a period of months and years. To estimate the harm, we must have a model that convert's each person's dose rate profile to the corresponding cancer incidence. Any model which does not recognize our dose rate dependent ability to repair DNA damage is bound to be qualitatively wrong.

LNT, the Linear No Threshold hypothesis, on which our radiation protection regulation is based is such a model. LNT assumes cancer incidence is proportional to cumulative dose, regardless of how slowly or rapidly that dose is experienced. This hypothesis is contradicted by

1) everything we know about DNA repair, and

2) the data.

When essentially all the radiation is incurred in less than a day, as in the case of the atom bomb survivors, we start to see statistically significant increases in cancer at cumulative doses of 100 to 200 mSv. But when the dose is received more or less evenly over years and decades, we cannot detect significant increase in cancer as long as the dose rate is less than 20 mSv/day even at cumulative doses of 100,000 mSv.¹ LNT claims such doses should have killed these people many times over.

We must have a model that recognizes our amazing repair ability. It should be consistent with the fact that the repair process is essentially complete in a day.\cite{bissell-2011} The model should be conservative, but reasonably accurate. The bulk of any uncertainty should be resolved in favor of the over-estimation of harm. But too conservative will lead and has led to gross misallocation of resources and an overall decrease in societal welfare, including disruptive, deadly evacuations and fossil fuel related sickness and deaths. The ANS believes we cannot be certain that any dose, however small, might not cause cancer. Therefore, the model should accept the No Threshold hypothesis.

Sigmoid No Threshold (SNT) is a harm model which complies with these criteria.² SNT does just as good a job as LNT in predicting the response to acute doses, and a far, far better job in estimating the harm associated with chronic dose rate profiles. The ANS recommends that LNT be replaced by SNT as the basis for our radiation protection regulation.

1. See Green Table in accompanying Backgrounder

2. See description in accompanying Backgrounder.