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D.2 DOSE TO WORLDWIDE POPULATION
0.7
Worldwide population doses were calculated for the three radionuclides that are consid-
ered to be the major contributors to total-body dose rates and long-term dose commitments:
3 H, 14 C, and 8 5 Kr. A constant world population of 6.4 x 109 persons was used for this
analysis. This value, which is based on a United Nations projection, was reported by
Killough (1977) for the year 2000. It agrees with the value of 6.3 x 10 9 derived from the
method of the Environmental Protection Agency (EPA) (1973) using projections based on a
1970 population of 3.56 x 109 persons and an annual growth rate of 1.9%.
A different method was used to determine the quantity of each of the radionuclides to
which the population was exposed. For 3 H, dispersion was calculated using a seven-
compartment model that considered diffusion into and out of latitudinal bands. The expo-
sure of the population was calculated using assumed diets whose concentrations of 3 H were
related to those in local surface waters. A specific activity approach was used for 14C
in which the concentration of 14C per gram of carbon in people was assumed to be equal to
that in atmospheric carbon dioxide. It was assumed that 8 5 Kr diffused readily across lat-
itudinal bands so that in a few years the concentration was uniform throughout the world's
atmosphere. The dosimetry for 85 Kr is based on external exposure of the body to a semi-
infinite cloud containing this radionuclide, with no accumulation within the body or in any
environmental reservoirs other than the air.
Although the method for each radionuclide is different, each probably estimates the
population dose to within an order of magnitude. Additional uncertainty is therefore intro-
duced when doses from all three radionuclides are totaled. Moreover, care must be exercised
in comparing the relative contributions of these three radionuclides because of the dif-
ferent methods and because of the uncertainty inherent in each.
Each of the three methods is discussed below.
D.2.1 Tritium
Tritium (3H) and tritium oxide released to the environment mix rapidly with the
ambient water and become part of the hydrologic cycle. Tritium rains out or is washed out
of the atmosphere almost entirely in the hemisphere in which it is released. Transport
across latitudinal bands even in the same hemisphere is slow (Renne et al. 1975). As a
result, the tritium released from facilities in the United States will reach peak environ-
mental concentrations in the 300 to 500 latitude band of the northern hemisphere, where
most of the world's population resides.
Baker (1976) has calculated the radiation doses received by local (50-mile radius),
regional (eastern United States), and worldwide populations from a continuous release of
1 Ci/yr of 3H to the atmosphere using the "box" model of Renne et al. (1975). The facil-
ity releasing the 3 H was assumed to be located in the Midwest. Although the magnitude of
the dose to the local population is sensitive to the specific site chosen, the regional pop-
ulation dose should be similar for most midwestern sites. In addition, the world population
dose depends upon the latitude band and not the longitude of the release point.