20 



Atomic Radiation and Oceanography and Fisheries 



ful for human consumption (Kawabata, 1956, 

 and Hiyama and Ichikawa, 1956). 



Deep water introduction 



The only place in the ocean in which we can 

 be confident at this time that radioactive wastes 

 of the order of some tons a year can be safely 

 deposited is in the depths of the sea. Knowl- 

 edge is, however, insufficient to determine 

 whether radioactive materials of the order of 

 the expected production from power reactors in 

 the next few decades could be disposed of in 

 this way. 



Radioactive materials introduced into the 

 deeper layers will be partially isolated from the 

 upper layer for time periods related to the resi- 

 dence time of the water in the deeper layer. 

 During this time there will be a decrease of 

 radioactivity due to decay, and dilution due 

 to dispersion. Since, as we have noted above, 

 the residence times are variable in different 

 depths and different locations, a much greater 

 time of isolation will be obtained in some places 

 than others. 



The longest average time of isolation will be 

 obtained in deep nearly enclosed basins such as 

 the Black Sea. It has been suggested by Wiist 

 (1957) that there may also be a long isolation 

 period in the abyssal trenches of the central 

 equatorial regions, such as the Romansch Deep 

 or the Tonga Trench, but no data on currents in 

 these deeps are now available. 



Craig (Chapter 3 of this report), assuming 

 an estimated average residence time in the deep 

 sea of 300 years, the introduction into the deep 

 sea of 1,000 tons per year of fission products 

 after 100 days cooling, and complete uniform 

 mixing within the deep water, has calculated the 

 activity in the deep and surface layers at secular 

 equilibrium. This calculation indicates that the 

 total fission product activity in the mxed layer 

 would be about equal to that at present from 

 natural sources (primarily K*°) . The concentra- 

 tion of Sr 90 would, however, be about 6.5 x 

 10"^ microcuries per liter, or 0.16 microcuries 

 per kilogram of calcium in solution in sea water. 



Studies of the uptake of strontium by marine 

 fishes indicate a discrimination against strontium 

 with respect to calcium approximately by a fac- 

 tor between 3 and 10. Thus for human popula- 

 tions such as the Japanese (Hiyama, 1956), in 

 which much of the dietary calcium is obtained 

 from marine fishes (including the bones and 



skin of some species), the amount of strontium 

 90 ingested per unit weight of calcium would 

 be of the order of .04 microcuries per kilogram 

 of calcium. A human population that obtained 

 all its calcium from marine fishes after equilib- 

 rium was established with about 1,000 tons of 

 fission products per year (1.1 x 10^ megacuries 

 of strontium 90) in the deep sea would have a 

 burden, primarily in the bones, of approxi- 

 mately .005 microcuries of strontium 90 per 

 kilogram of calcium. This is 5 per cent of the 

 maximum permissible concentration for the 

 population at large, estimated by the National 

 Bureau of Standards (1955). 



Weapons tests resulted in an average amount 

 of .025 microcuries of strontium 90 per kilo- 

 gram of calcium available to growing plants in 

 the United States in 1955. By 1970, the amount 

 will be .08 microcuries per kilogram of calcium 

 even in the absence of further weapons tests 

 (Kulp, Eckelmann, and Schulert, 1957). Be- 

 cause of discrimination against strontium with 

 respect to calcium in food grains and grasses, 

 and the additional discrimination in cows' milk 

 and in human beings, it is expected that by 

 1970 an average of about .002 microcuries of 

 strontium 90 per kilogram of calcium will 

 exist in the United States population, 2 per cent 

 of the maximum permissible concentration. 



From the above considerations it is uncertain 

 whether reactor-fuel wastes of the order of 

 1,000 tons a year could be deposited safely in 

 the deep sea. Craig's calculation is most useful 

 in orienting our thinking, but is, of course, 

 very much oversimplified. No account is taken 

 of the removal of activity from the sea by sedi- 

 mentation. On the other hand, it does not take 

 into account any biological transfer of material 

 across the pycnocline, nor can we assume that 

 effective concentration of Sr 90 per unit weight 

 of calcium for some commercially important or- 

 ganisms will not be greater than the values we 

 have taken. 



Moreover, such a calculation assumes even 

 distribution of the radioactive materials through- 

 out the deep layer. This could only occur if they 

 were evenly distributed when introduced, or if 

 there were uniform and complete mixing in all 

 parts of the deep layer. 



A priori we should expect that neither the 

 physical circulation and mixing in the deep sea 

 nor the transfer between the deep layer and 

 the mixed layer would be uniform. There is 



