General Considerations 



19 



evaluations must, of necessity, be conservative. 

 Under some circumstances this necessity could 

 involve considerable cost to society. Those sites 

 and methods of disposal, both on the land and 

 in the sea, that provide the least hazard may 

 also involve the greatest disposal costs, so that, 

 to the extent we must include a safety factor be- 

 cause of ignorance, there can be economic loss. 

 In disposing of radioactive materials in the 

 sea, we aim at two things: (1) isolation of the 

 materials, so that their entry into the part of the 

 sea and its contents used by man is limited, (2) 

 dispersal of the materials that do enter the 

 domain important to man, to keep the concen- 

 trations of radioactive elements at tolerable 

 levels. Depending on the quantity of materials 

 to be dealt with, we may need to consider either 

 or both of these possibilities. 



Introduction in the upper mixed layer 



Radioactive materials introduced into the up- 

 per mixed layer will, because of the rapid 

 transport and large horizontal and vertical mix- 

 ing within this layer, be carried away from the 

 site of introduction and rapidly dispersed. Dis- 

 persion may be more rapid in coastal areas than 

 in the open sea, but in some situations there may 

 be a net transport inshore, particularly in or 

 near estuaries, if the materials are introduced 

 below the surface. 



Direct evidence of near-surface transport and 

 dispersion of fission products in the open sea has 

 been obtained by the surveys of the "Shunkotsu 

 Maru" (Miyake, Sugiura and Kameda, 1955) 

 and the "Taney" (Harley, 1956), respectively 

 four and thirteen months after the Pacific weap- 

 ons tests of March 1954. The indicated trans- 

 port of these products was in good agreement 

 with current velocities measured by conven- 

 tional means. These data from the open sea and 

 earlier measurements on the partially confined 

 waters of Bikini Lagoon (Munk, Ewing and 

 Revelle, 1949) demonstrate the rapid dispersal 

 of fission products in the surface layer. 



Dispersion in an inshore situation (the Irish 

 Sea) was measured with fluorescein by Selig- 

 man (1955) as a preparatory study for the dis- 

 charge of low-level wastes from a power reactor 

 installation. Subsequent experience with libera- 

 tion of the radioactive wastes (Anon., 1956) 

 confirmed that they were rapidly dispersed. 



Radioactive materials introduced into coastal 

 waters enter directly into that part of the ocean 



most utilized by man, from which he removes 

 the greater share of his harvest of marine food 

 organisms. The sessile algae, bottom living in- 

 vertebrates, and fishes of these waters heavily 

 concentrate certain of the elements, such as 

 strontium, cesium, zinc, and cobalt that has 

 radioactive isotopes most hazardous to man. 

 While dispersion due to physical transport and 

 dispersion in these waters is high, they are 

 usually shallow, so that the volume is limited 

 and there can also be considerable accumula- 

 tion in shallow bottom sediments from which 

 the isotopes can be again taken up by man's 

 food organisms. 



In some coastal areas the combination of 

 physical and biological processes can result in 

 local concentrations of radioactivity in the wa- 

 ters themselves (Ketchum, Chapter 5 ) . 



Because of the above considerations, the 

 quantity of radioactive materials that can be in- 

 troduced safely into coastal waters near shore 

 is very limited, of the order of a few hundred 

 curies per day. The particular physical, chemi- 

 cal, and biological factors vary so widely from 

 one coastal area to another, that careful study 

 is required to determine the safe amount in any 

 particular locality, and continuous monitoring 

 should be conducted to guard against efi^ects of 

 unforeseen variability in environmental factors. 



The rather low level of discharge of radioac- 

 tive products that can be tolerated in coastal 

 waters imposes the necessity of providing ade- 

 quate safeguards against discharge of high-level 

 atomic wastes from accidents to power reactors, 

 either at locations on the shore or shipborne 

 reactors. 



The quantity of radioactive material that can 

 be safely deposited in the mixed layer in the 

 open sea depends on such local characteristics 

 as the direction and rate of transport, the rate 

 of horizontal dispersion, the rate of uptake by 

 organisms, and the contiguity of fishing areas. 

 However, in general, the quantities will be 

 much greater than those permissible for coastal 

 waters. An idea of the order of magnitude of 

 mixed fission products that can be safely intro- 

 duced in a fairly typical situation is given by the 

 results of weapons tests in the Pacific where a 

 quantity of mixed fission products of the order 

 of half a ton was introduced into the mixed 

 layer in a short time period. That this was near 

 the limit of safety is evidenced by the capture in 

 adjacent areas of specimens of tunas and other 

 fishes with sufficient radioactivity to be doubt- 



