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The pertinent equations, using the symbols introduced in the last section, then are: (14) s(t) = 3.2 x 102 4 0 t2 (15) t = 0.18 x 102 PPc l/s ppc 2.2 x 1014 1.2 x 1013 (16) N < M / M \3/2 â ,Si* (â) ppc \ ppc / Tables 9 and 10 present the pertinent computations. The proba- bility is extremely small that there will be, on the average, more than 30 of the potential 300 nuclear-powered ships outbound through a single such harbor approach per month. Since the weighted mean ppc, for coastal waters, for the isotope mix in the primary coolant is approxi- mately 10'8, it is evident from a comparison of Table 10 with Tables 3 and 5 that this segment of the continental shelf can safely receive the discharge of warm-up expansion volumes which may have been stored in tanks aboard ship, due to restrictions on the release of this waste into the inshore environment. Since it is considered undesirable to average over a period longer than one month, the maximum permissible amount of activity in a single discharge, even if less than one such discharge were to be made into the subject area per month, is about 5 curies. An inspection of Tables 4 and 6 then indicates that this segment of the continental shelf would be unsuitable as a receiver of spent ion exchange resins. EVALUATION OF THE OUTER CONTINENTAL SHELF (ZONES 3a AND 3b) For the region of the shelf from 12 miles seaward to the 200 fathom line, diffusion on a pertinent scale would be unrestricted by horizontal boundaries. Within this area a mixing layer depth of 40 meters may be assumed. Though there are significant areas of this shelf region which are not fished commercially, migratory fish traverse the whole of the continental shelf, and it is not possible to assume that any segment is biologically unimportant, though some parts of the shelf contribute significantly less to the total fisheries than others. The continental shelf off the east coast of the United States is uti- lized here as the subject area for our computations of the safe rate of discharge of radioactive wastes from nuclear-powered ships into this type of marine environment. The region of this shelf from 12 miles seaward to the 200 fathom line averages about 100 miles in width over 40
TABLE 9 Sample computations for a section of the continental shelf 10 miles long extending seaward from 2 miles offshore to 12 miles offshore, giving the time (t. ) for the maximum concentration resulting from a single release of M curies to be reduced to ppc values for the en- vironment (*PBc), and the permissible number of such discharges per month (N) for various values of s in tic/ml. M, in curies, for fppc (days) N sppe Sppc SPPe (curies/uc/ml) (sees) (per month) =10'' = 10'8 =io'7 10Â« 1. 8x IO4 2 .1 x I0'1 1. 2 x 10* io'2 io'1 1 IO7 5. 8x \0* 6 .7x IO0 3. 7x IO2 io'1 1 10 IO8 1. 8x 10s 2 .1 12 1 10 IO2 10' 5. 8 x 105 .7 3. 7x 10'1 10 JO2 IO3 TABLE 10 Permissible total activity per discharge into a section of the con- tinental shelf 10 miles long extending seaward from 2 miles off- shore to 12 miles offshore, as a function of the number of such discharges per month and the partial permissible concentration for the coastal waters. 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 coastal waters (Uc/ml) io'9 5.2 x 10Â° 5.3 x 10'2 1.2 x 10'2 10'8 5.2 5.3 x 10'1 1.2x 10'' io'7 52 5.3 1.2 41
the 1,200 mile length of the Atlantic seaboard of the United States. It has been estimated that the average retention time for waters on this shelf is about one year. Hence a conservative estimate of the "new" water area available each month is 1/ 10th of the total area, or 4 x 10 10 m2. For unrestricted horizontal mixing, the value of n in equations 5 through 8 is 1.0. The value of the diffusion velocity is taken as 1.0cm/ sec, as found by Joseph and Sender (1958). The pertinent equations for the required computations then become (17) s (t) = 0.40 x 102 0 t ppc (19) N < 2'3 * 1016 - 3'6 * 3/2 t s PPc ppc Tables 11 and 12 present the pertinent computations. A compari- son of the predicted activities in the primary coolant for the SAVANNAH, given in Table 3, with permissible total activity per discharge, given in Table 11, indicates that no undue risk to man would result from the discharge of several thousand gallons of such effluent as a single re- lease into the waters of the continental shelf seaward of a line 12 miles from the coast. In fact, if each of the potential 300 nuclear-powered ships were to make one such release per month into the waters of the continental shelf off the east coast of the United States, the permissible environmental levels would still not be exceeded. Table 4 shows that the total activity on the spent ion exchange resins of the SAVANNAH is predicted to be about 400 curies after 50 days of operation. Since the ppc value for continental shelf waters, in known fishing areas, for the mix of isotopes shown in Table 4, is about 2 x 10'8 nc/ml, it is evident that not even one such discharge per month into known fishing areas of the continental shelf would be suitable. Even for those areas of the shelf which do not contribute materially to fisheries, and where a weighted mean ppc value of 1 x 10'7 \ic/ml ap- plies, the discharge of 400 curies at one time is not advisable. On the other hand, Table 6 shows that the total activity on the spent ion exchange resins on the NAUTILUS amounts to about 12.5 cu- ries. The ppc value for fishing areas on the continental shelf for the isotope mix listed in Table 6 is about 6 x 10'9 nc/ml. Setting M equal to 12.5 curies and sppc equal to 6 x 10'9 |ic/ml in equation 19 gives a maximum permissible number of releases per month of 36, or about 42
TABLE 11 Sample computations for the segment of the continental shelf ex- tending seaward from 12 miles offshore to the 200 fathom depth contour, giving the time (t ) for the maximum concentration from a single release of M curies to be reduced to ppc values for the environment(s), and the permissible number of such discharges per month (N) for various values of s in , c, ml. M, in curies, for M/sppe fppe (sees) 'PPe N sppc sppc = 10'8 sppc (curies '[ic, ml) (days) 7.3 x IO'' (per month) = 10'' = 10'7 10Â» 6.3 x 104 3.6 x 103 10' 1 10 10Â» 2.0 x 105 2.3 1.1 x 102 1 10 IO2 10'Â° 6.3 x 10s 7.3 3.6 10 102 10s 10" 2.0 x 106 23 1.1 x 10'1 102 103 104 TABLE 12 Permissible total activity per discharge into the segment of the continental shelf extending seaward from 12 miles offshore to the 200 fathom depth contour, as a function of the number of such discharges per month and the partial permissible concentration for the coastal waters. ppc for Permissible activity for 1 discharge per month (curies) Permissible activity for 1 discharge per day (curies) Permissible activity for 10 discharges per day (curies) coastal waters (ue/ml) 10'' 23 2.4 5.1 x 10'' 10'8 2.3 x IO2 24 5.1 io'7 2.3 x IO3 2.4 x IO2 51 43