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complex history of the continents. We can observe the processes by which the sea 

 floor is being made, transported, and subducted in various areas; this allows us to 

 make sound predictions about the future of sites in the oceans. 



The plastic sediments of the ocean floor are also without faults or fissures, and 

 can easily be studied with acoustic techniques. In the areas under consideration, 

 these sediments are uniform over wide areas. This simplicity greatly increases our 

 ability to make accurate models. 



The ocean itself presents an unsurpassed barrier to human intrusion, whether 

 deliberate or accidental, to the repository. The areas of the sea floor under consider- 

 ation are perhaps the least valuable property on the earth. There is little reason for 

 anyone to visit the area. 



The canisters could be placed individually, or in stacks a few canisters high. A 

 single disturbance, from whatever cause, should affect only one or a few canisters. 

 The remainder of the repository would not be jeopardized. 



The populations in the area floor under consideration are very sparse (Fig. 13). 

 The emplacement of canisters would temporarily disturb about 0.01 percent of the 

 disposal area. 



For these reasons among others, the seabed is being considered for the disposal of 

 HLW by a number of nations which may lack suitable land-based areas available 

 for safe disposal of nuclear wastes. The SDP cooperates with these nations in an 

 international working group (Fig. 14) to share information and avoid unnecessary 

 duplication of effort. 



SITE STUDIES 



The ocean is clearly too immense for detailed study over large areas. It is possible 

 to use existing data and exclusion criteria, however, to narrow down the oceans to 

 areas for detailed study. This process has led to the selection of midplate, mid-gyre 

 regions as the most promising for our studies. 



The areas under consideration are away from plate boundaries where seismic 

 activity is concentrated (Fig. 15). They are away from the coastal regions, which 

 have productive waters where fishing activity is concentrated (Fig. 16) and which 

 may also have valuable hydrocarbon deposits or manganese nodule deposits having 

 high copper content (Fig. 17). 



The low primary production in mid-gyre regions allows the deposition of sediment 

 types that provide the best barrier to nuclide migration. The sediments at locations 

 within these areas are uniform over a wide lateral extent. Cores from different 

 locations may have the same features even though their deposition rate may differ 

 (Fig. 18). The mid-gyre regions also provide areas of very stable environment which 

 are insensitive to global climatic changes (Fig. 19). Locations have been found where 

 deposition has been continuous for many millions of years (Fig. 20), and is most 

 unlikely to stop in the next million years. Thus, these areas of the ocean appear to 

 offer a predictable, simple environment that is remote from man's activities. 



In summary, we are cautiously optimistic about the possibilities for subseabed 

 disposal of high level wastes and spent fuel, in that to date we have not identified 

 anything which makes the concept infeasible. 



