Regulation by Statistics

The U.S. Nuclear Regulatory Commission was established by the Energy Reorganization Act of 1974.  This Act abolished the Atomic Energy Commission, splitting its promotional and regulatory functions. The promotional and development activities were vested in the Department of Energy; the regulatory functions were transferred to the NRC. The NRC’s responsibilities are fourfold: protecting public health and safety, protecting the environment, protecting and safeguarding nuclear materials and nuclear power plants in the interest of national security, and assuring conformity with antitrust laws.

In furtherance of the first of these responsibilities, the NRC in 1986 published “safety goals” to “broadly define an acceptable level of radiological risk” as the result of the commercial operation of nuclear powered plants to generate electricity. These goals were “based on the principle that nuclear risks should not be a significant addition to other societal risks”:

  • Individuals should bear no significant additional risk to life and health as the result of nuclear power plant operation.
  • Societal risks to life and health should be comparable or less than the risks of generating electricity by other technologies, and should not be a significant addition to other societal risks.

These two goals were then defined quantitatively: less than a 0.1% increase in risk (one more chance in a thousand) of prompt fatality and less than 0.1% increase in risk of latent cancer fatality. Since these goals were established, the NRC has developed a risk-informed regulatory approach by which it seeks to accomplish these goals using probabilistic risk models—estimating the probability of certain reactor accidents, estimating the dose effects these accidents would have on the population surrounding the reactor facilities, and estimating the health effects these doses would cause. The NRC then implements a regulatory framework that ensures operators of reactor facilities maintain their accident probabilities some margin below the thresholds that would exceed these 0.1% increases.

However, when these goals were established (and still today), there was little information on what the long-term effects of radiation exposure might be. Nuclear technology as an energy source was relatively new, having been developed only thirty years prior. And while there was plenty of data to understand the severe physiological effects of extreme radiation doses, very little was available on moderate levels of exposure, either acute or over time.

Most of the information available today is based on long-term monitoring of people in the vicinity of four nuclear events: the bombs dropped on Hiroshima and Nagasaki in 1945, the Windscale reactor accident in the UK in 1957, cleanup efforts following the SL-1 accident in Idaho in 1961, and the Chernobyl accident in 1986 in what is now Ukraine.

The body of data from the bomb victims is the most complete, as the majority of the long-term survivors have by now died, but the actual doses are unknown, are much higher than could be expected from a commercial reactor accident, and cannot be accurately modeled. The exposure of those involved in the SL-1 cleanup was relatively low and was received over time, so those data too are of limited use in modeling the health effects of acute exposures.

Epidemiological studies following the Windscale accident followed 470 male employees through 1997. These studies indicated no change in mortality rate and no change in the overall rate of cancer.  There were excess deaths noted due to diseases of the circulatory system and heart disease, but these were compensated for by an over-70% decrease from the expected rate of genitor-urinary tract cancers.

Similarly, in the population affected by the Chernobyl accident—for which we have much better dose information—there was no statistically significant change in the cancer rate among those exposed to moderate levels of ionizing radiation (10 rem or less over a short period of time).  For comparison purposes, the maximum permitted annual dose (total effective dose equivalent or TEDE) for a trained radiation worker in the United States is 5 rem; the maximum permitted dose for a member of the public is 100 mrem (0.1 rem) TEDE at a rate of no more than 2 mrem in any one hour.  (On an airline flight from NY to LA, you get about 4 mrem.)  For a nifty comparison of radiation doses received from various things, see this chart (1 Sv = 100 rem).

Current plans are underway to conduct similar long-term epidemiological studies of Fukushima residents exposed to ionizing radiation from the reactor accidents caused by the March 2011 tsunami.  They promise to be more accurate than previous studies.

The point of all this is that the modeling of the physiological effects of radiation is very conservative.  The popular fear of radiation has driven the regulatory entity to take extreme steps to minimize the possibility of mishaps which may expose the population.  It is likely that an objective study could lead to some relaxing of regulatory requirements.  But that is not necessarily prudent.  As a result of the current regulatory scheme, there has never been an incident in the United States in which a member of the public received an elevated dose due to a commercial reactor accident.  Regulators of other industries should take note.

References:

NRC mission & background: 10 C.F.R. § 1.1, 1.11 (2012)

Safety goals:  51 Fed. Reg. 28044 (Aug. 21, 1986)

Dose limits:  10 C.F.R. § 20.1201, 20.1301 (2012)

Fukushima study plans:  Suminori Akiba, Epidemiological studies of Fukushima residents exposed to ionising radiation from the Fukushima Daiichi Nuclear Power Plant prefecture—a preliminary review of current plans, 32 J. Radiol. Prot. 1 (2012)

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