324 



Site studies to investigate areas of the oceans which may have a predictable 

 geologic future and to determine the properties of the sediments in these areas. This 

 is being done in cooperation with a number of nations. 



Environmental studies to investigate the transport mechanisms, both physical 

 and biological, by which nuclides could be transported back to man. This research 

 includes studies of mixing rates in the ocean and an assessment of life in the deep 

 sea. 



Multibarrier identification and quantification to investigate the natural and man- 

 made barriers that could be interposed between buried wastes and mankind. This 

 includes material corrosion studies, migration of nuclides through sediments, and 

 the physics and chemistry of a heat source in the sediments. 



Safety analyses to use all available information to predict the safety parameters 

 and the amount of environmental impact expected from all phases of the subseabed 

 program. 



Emplacement of wastes in sediments, transportation, and social-scientific issues 

 are all areas which will receive more attention in the future. 



Much of the research in these areas done for the SDP is conducted by researchers 

 at major oceanographic institutions and universities in the United States. Selection 

 of researchers with established interest and expertise in areas important to the SDP 

 has permitted an efficient use of effort and funds. Other research is carried out at 

 various private and government-supported laboratories (Fig. 4). 



The SDP work schedule is divided into four phases (Figs. 5 and 6). Phase 1, 

 completed in 1976, was the estimation of technical and environmental feasibility on 

 the basis of historical data. Phase 2, to be completed about 1987, is the determina- 

 tion of technical and environmental feasibility from newly acquired oceanographic 

 and effects data. Phase 3, to be completed about 1995, is the determination of 

 engineering feasibility and legal and institutional acceptability. Phase 4, to be 

 completed about 2010, is the demonstration of disposal facilities. 



At the end of each phase of the program, concept feasibility is assessed. This 

 assessment requires both internal and external review. At each of these reviews, a 

 comprehensive report will be prepared summarizing the results of that phase. If 

 results indicate that the subseabed disposal concept is unacceptable, the program 

 will be terminated and emphasis thereafter will be placed on demonstrating this 

 unacceptability to other nations which are considering using the seabed for HLW or 

 spent fuel disposal. 



SOME PREUMINARY RESULTS 



High-level waste must be isolated from the biosphere for tens of thousands of 

 years. Since it is impossible to conduct experiments on this time scale, it is neces- 

 sary to construct models to predict the behavior of canisters and radioisotopes in the 

 sediments. The models are developed by using a reiterative plan (Fig. 7) that 

 requires them to pass a field verification test before they can be accepted. 



Research to date indicates that the highly absorptive nature of oceanic clays 

 provides an effective barrier to radioactive cations. The results of predictions from a 

 model developed in the program indicate that plutonium would have migrated only 

 a few meters 100,000 years after emplacement (Fig. 8). 



The models to predict nuclide migration must take into account the heat produced 

 by the waste. The heat production of the waste is the major complicating factor in 

 subseabed disposal. For a specific waste package, the temperature of the sediment 

 reaches a maximum shortly after emplacement, then begins to decrease (Fig. 9). 

 This heat curve points out that it is possible to do experiments, perhaps of 15 years' 

 duration, during the worst case — highest temperature — time after emplacement. A 

 related area of research concerns the resistance of sediment to movement induced 

 by the heat (Fig. 10). 



Corrosion experiments indicate that it will be possible to build containers that 

 will last longer than the thermal period of the waste (Fig. 11), and that these 

 containers will not be excessively costly (Fig. 12). For the last ten years, oceanogra- 

 phers have had the technology to routinely drill in deep sea depths and the ability 

 to re-enter such holes. With this technology, we assume that canisters could be 

 retrieved if it were desirable. 



These selected examples have yet to be verified in the field. Some technical 

 questions, such as canister retrievability, will have to await further engineering 

 studies for definitive answers. The research to date, however, seems to be promising. 



WHY CONSIDER SUBSEABED DISPOSAL 



Areas of the ocean floor have a number of features that make them quite 

 attractive for technical reasons. The seafloor and its covering of sediment is a very 

 simple geological environment. It is geologically young and has not undergone the 



