The general population’s actual external radiation exposure from nuclear power plants does not approach the so-called permissible dose rates, because of certain inherent factors. For example, the heavy shield­ing required to protect the utility employees in the normal course of their activities gives assurance that the external radiation dose to the public will be undetectable. I know of no case in which radiation from the plant proper has caused a perceptible change in the levels of radiation exposure beyond the property boundary. This means that the dose to people at the property boundary from direct radiation from the plant is less than 10 mrem/yr, which is the approximate lower limit of measurement.

In the case of a boiling water reactor (bwr), the principal way in which the general population would be exposed to external radiation would be by direct irradiation from the cloud of passing radioactive gases discharged from the plant. For example, consider a hypothetical situation in which a bwr stack is located 100 meters from a 360° fence at which the dose is assumed to be 500 mrads/yr. Thus, people living right on the fence would receive the aec maximum permissible dose to individuals. From known rates of diffusion of gaseous effluents from point sources, it can be calculated that the dose rate beyond the fence would on the average diminish inversely with the 1.8 power of distance from the stack. The per capita doses have been calculated for populations of 105, 10e, and 107 people uniformly distributed around the fence at a density of 1,000 people per square kilometer. The annual per capita doses for the three popula­tions turns out to be 1.9 mrad, 0.28 mrad, and 0.04 mrad. This, in fact, overestimates the per capita dose because a dose of 500 mrad would be occurring only in the direction of maximum wind direction which would perhaps be one-eighth of the plant circumference. For seven-eighths of the plant circumference, the dose would be much less than 500 mrad/yr. It should also be noted that the radioactive gases emit mostly beta radia­tion, which will not penetrate to the blood-forming bone marrow or to the gonads. This illustrates the kind of built-in conservatism that exists in the aec regulations — even under the worst conceivable conditions, 10 million people distributed around a boiling water reactor would receive a total of 400 man rads instead of the 1.7 million man rads permitted under a literal interpretation of current regulations.

We have seen earlier that 106 man rads may produce 20 cases of leukemia in the lifetime of an exposed population of a million; 400 man rads may on this basis cause 0.008 cases per million exposed people. Assuming the mean sensitive life span to be 60 years, 400 man rad/yr could produce 0.5 cases per million people per generation. As explained earlier, this is an upper limit of risk, and the true risk will be somewhere between zero and this probability. Since the normal incidence of leukemia in the general population is about 70 cases per million per year, the 0.5 cases in 60 years would occur against a normal background of 4,200 cases.

With respect to genetic effects, if the doubling dose for spontaneous mutations is a per capita exposure of 2 rad/yr, 0.17 rad/yr delivered over many generations would result in about an 8 per cent increase in the spon­taneous mutation rate. However, since the man at the fence can receive no more than.5 rad, the external radiation dose from the plume would, at the limit of permissible exposure, result in a per capita annual dose of 0.04 mrad in a population of 10 million people, as previously shown. On the improbable assumption that these 10 million people constitute a closed breeding population for as many generations as it takes to reach equilibrium, the spontaneous mutation rate would eventually be raised by about 0.05 per cent. This is equivalent to the change in radiation ex­posure that might be expected from living at a difference in altitude of about 10 feet.

To place all of this in further perspective, it should be noted that temperature, like ionizing radiation, can cause genetic mutations and that as much as 50 per cent of the mutations that occur normally in con­temporary man might be due to the increase in testicular temperature caused by the male practice of wearing trousers. Although this observa­tion appeared in the literature in 1957 (Ehrenberg et al., 1957), I am unaware of any subsequent popular movement to prescribe kilts in place of the more mutagenic habit of dress of the American male.