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Equations 6, 7 and 10 then become (20) s (t) = 16 â 0 tz 'M (21) t PPc i/s ppc (22) ppc The resulting computations are summarized in Tables 13 and 14. Table 3 shows that the predicted activity on the spent ion exchange res- ins for the SAVANNAH* is about 400 curies. The weighted mean ppc value for fishing areas of the open sea, for the isotope mix on the ion exchange resins of the SAVANNAH, is about 5 x 10**. Applying this value to the subject open sea area, equation 22 gives a limiting value of over 10' for the permissible number of releases, per month, of 400 curies each. This corresponds to about 30 such discharges per day. In those large areas of the open sea which do not contribute materially to the commercial fishery harvest, the appropriate value for the corre- sponding environmental ppc is 3 x 10'7 . The permissible number of releases into the subject open sea area would for this case be over 104 per month, or 300 per day. Thus, if each of the 300 potential nu- clear-powered ships should discharge spent ion exchange resins, con- taining 400 curies each, into the subject open sea area once each 2 months, the permissible limit of radioactivity in the environment would not be exceeded. CONSERVATIVE AND NON- CONSERVATIVE ESTIMATES USED IN THIS REPORT As a result of the many gaps in our basic knowledge of the per- tinent phenomena in the sea which enter into the problem evaluated in this report, it has been necessary for the working panel to include many estimated parameters in the evaluation. Because we are treating a problem which is potentially very dangerous to man and to man's utilization of the natural environment, we have in general made con- servative (safe) estimates of the uncertain factors. An additional rea- son for making conservative approximations is that the nuclear ship â¢Since completion of this report, subsequent re'evaluation of the probable character and activity of the primary coolant and the ion exchange resins has been issued by the Oak Ridge National Laboratory (1959). While this ORNL report includes somewhat different values for the activity in these potential wastes, the general conclusions arrived at here remain unchanged. 45
TABLE 13 Sample computations for a selected trade route area of the open sea, giving the time (*p c) 'or the maximum concentration result- ing from a single release of M curies to be reduced to ppc values for the environment (*_pc), and the permissible number of such discharges per month (N) for various values of s in ..c ml, ppc M, in curies, for M/.ppe 'PPe fppc (days) N (per month) sppc sppc = 10'8 SPPe (curies/uc/ml) (sees) =10'' = 10'7 10Â» 1.3x 10s 1.5 2.7 x 104 1 10 102 1010 4 x 10s 44 8.8 x 102 10 102 10* 10" 1.3 x 10* 15 2.7 x 10 ID2 103 10< 1012 4 xlO6 46 8.8 x 10'' 10> 10Â« 10s TABLE 14 Permissible total activity per discharge into a selected trade route area of the open sea, as a function of the number of such discharges per month and the partial permissible concentration for the open sea. Permissible activity for 1 discharge per month (curies) Permissible activity for 1 discharge per day (curies) Permissible activity for 10 discharges per day (curies) ppc for open sea waters (ne/ml) 10'9 9.4 x 102 9.5 x 10 2.0 x 10 IO'8 9.4 x 103 9.5 x 102 2.0 x 102 lO'7 9.4 x 104 9.5 x 103 2.0 x 103 46
is not fixed and may travel into marine waters which are most restric- tive from the standpoint of dispersion, exchange and biological uptake, as well as being heavily utilized by man. The following summarizes the conservative approximations made in this evaluation. 1. It is assumed, for coastal areas and fishing areas of the con- tinental shelf, that a selected segment of the population receives all its protein requirement from seafood harvested from the marine area subject to waste disposal. This assumption is not overly cautious for a country such as Japan, but is quite conservative for the United States. This restrictive assumption is relaxed when considering those areas of the outer continental shelf and open sea which contribute little to the fisheries harvest. 2. In computing the distribution of activity with time resulting from a given discharge, the radioactive decay was not included. 3. In computing the effect of discharge of spent ion exchange res- ins, it was assumed that all the activity was immediately released by the resin to the sea water. This is a conservative assumption only if the resins sink. 4. The effect of initial mechanical dilution on the distribution of activity after release to the marine environment was not included in the computations. This factor would be significant only during the very early stages of dispersion, since the point source solution and the fi- nite source solution to the diffusion equations converge with increasing time. The major importance of initial mechanical dilution would be the reduction of any density difference between the effluent and the re- ceiving waters. The assumption is made that no such density difference exists; hence the major effect of initial mechanical dilution is in fact indirectly included in the evaluation. 5. In the computations for the outer continental shelf and for the open sea, the possible transport of activity out of the surface layer by settling of particulate material was not included. In inshore waters it is possible that this process would be detrimental, since activity could be concentrated onto bottoms where important shellfish and bottom feeding fin fish occur. 6. The highest measured concentration factors for the uptake of a specific isotope by the biota were employed in the calculations, ex- cept that where concentration in the skeleton was important, one-tenth of the concentration factor from sea water to bone was used, since bone makes up about one-tenth of the edible portion. Possible non-conservative features of our estimates include the following. 47