Medical exposure and natural background are not counted. The guidance limits for strictly partial-body dosage are higher.48 Since proper use of the guidance limits involves the ALARA principle (exposure to be as low as reasonably achievable), almost no one receives the maximum under ordinary circumstances, and the average for the exposed population is far below it. However, as standards are driven lower and lower by regulation, protection tends to become more costly, and cost-benefit considerations become important. It may well be that unnecessarily costly environmental restrictions would lead suppliers to use alternative technologies that have greater risks. Any fresh evidence of effects—or lack of effects—in the low-dosage range (relative to the standards) would therefore be of the greatest value.

A recent highly publicized study based on death certificates49 claimed that cancer mortality associated with employment at an atomic plant was significantly increased in that segment of the working population that had received cumulative doses of less than 10 rem. The doses to the entire population ranged from below 1 rem to above 25 rem (with 75 percent below 5 rem), accumulated over periods up to 20 years and more.

The same statistical data have been reinvestigated by others,5052 who employed better methods of analysis, and the whole issue has been reviewed.53 No increase in leukemia was observed, including myelogenous leukemia, the hallmark of radiation-induced cancer. No increase in cancer from doses below 10 rem was noted. For doses above 10 rem, small excesses of cancer of the pancreas and of multiple myeloma were noted, but they could not be shown to have been caused by occupational exposure to radiation. Further and more refined study is to be undertaken.

In the case of fission products from the present generation of light water reactors, the principal sources of public exposure are radioactive gases and emissions into the atmosphere—radon-222 (222Rn) in uranium mines and mills, and krypton-85 (85Kr), tritium, iodine-129 (129I), and carbon-14 (14C) in other parts of the fuel cycle. Inhalation makes the lung a primary target. The target for iodine is the thyroid gland. Other agents include bone seekers.

In the routine operation of light water reactors, the general population is exposed to radiation by emissions into the atmosphere and by the cooling water discharged into local water (Figure 9–3). Spent fuel is handled separately, for eventual reprocessing or long-term storage. For regulatory purposes, the dose to an individual member of the population is maximized by estimation for a hypothetical individual who spends all his or her time at the plant boundary and obtains all his or her food and water from the immediate area. Such an individual is subjected to airborne radioactive gases, receives external exposure from radioactive particulates deposited



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