25.47 (19) W. B. Silker and M. R. Peterson have evaluated and rated as minimal the possibility of loss at sea of high-level radioactive waste containers during transit to the sea disposal site if adequate precautions were taken. In the event of a loss at sea, the task of locating and recovering single or multiple waste canisters is rated as very good with current levels of technology and experience. In the matter of emplacement, as with transportation, research and development lags behind engineering. This is vividly exemplified by the fact that the ability to drill kilometers into the crystalline rock beneath the unconsolidated and liquified sediments has been demonstrated. Drill hole reentry has been achieved in the deep ocean. Accuracy of bottom positioning in 5 km (20) of water has been quoted as less than one inch. The capability exists for retrieving large objects and for doing detailed engineering work on the floors of the oceans 5 or more thousands of meters below the surface. (19,20) Since we do not as yet have sufficient data and understanding to specify the sediment types and emplacement depths for containment of the radionuclides for the time period required, only conceptual designs of the emplacement methodologies have been developed. Figure 25.16 shows these five subseabed emplacement concepts. Estimates of times, relative costs, and number of canisters per site are given for each concept. The free-fall penetrometer concept obviously is the least expensive in both construction and facilities cost, whereas placement of canisters only in the basalt is estimated to be the most expensive concept by a factor of 40. Holes containing canisters only in the liquified sediment and holes into the crystalline rock with canisters through the column are intermediate in cost. Recovery of the waste from any one of the five emplacement schemes is possible with existing engineering technology, but it would be costly; in our estimation, compared with other options costs of recovery (assuming the necessity of remote operation) would be very nearly equivalent. Recovery of material from the upper sediments (penetrometer emplacement) would obviously be less expensive than from basalt. As indicated in both the Emplacement and the Transportation sections, the engineering capabilities for carrying out oceanic operations are far ahead of the research required to identify the critical emplacement parameters and (19) breachment modes. Silker states, "... series of gigantic grapples were lowered and attached to the (Russian submarine) hull with the aid of a closed circuit television system. Just the idea of retrieving an object of this size is mind boggling. It just emphasizes the fact that, given the sufficient impetus, current technology and engineering capabilities can be scaled to accomplish the near impossible." In the continuing effort since 1973 to assess the oceans as potential sites for radioactive waste disposal, the Seabed Disposal Program participants have arrived at the following conclusions: 1. Several ocean provinces meet the criteria which have been identified as important. Research and development feasibility studies of two of these areas have begun: (a) a midplate/midgyre region in the Pacific and (b) a midocean ridge-flank/midgyre region in the Atlantic. 2. Recent current meter data covering 19 months for the bottom water of the North Pacific midplate/midgyre region shows a concentration of energy in the lower 100 meters with a net flow of 2 to 4 centimeters per second. These data indicate that even in these supposed "tranquil" ocean basin areas, water is moving with sufficient advective energy to rule out the ocean water itself as a principal barrier to the migration of long-lived waste. 3. A positive "buffering" aspect of the ocean water in the midplate/ midgyre Pacific regions is evident from the fact that the various glacial cycles have had no obvious effect on the bottom environment. About 4 million years of history can be read from 10-meter-long core samples. 4. Data from these cores also reveal extreme uniformity of sedimentation uring the last four million years. This record of environmental constancy from the present backwards in time is not found in many other places on earth. 5. Rock samples recovered a few hundred meters below the sediment/rock interface by the Deep Sea Drilling Project (IPOD) in semirelated areas of other ocean basins have revealed a fractured vein structure. Chemical studies of these samples suggest that fluids may percolate through this upper layer of crust. Information from the current IPOD activities, which will drill much deeper holes into the basement rock, will yield additional data on the barrier properties of the upper crust. No holes have been drilled in the North Pacific area and thus any extrapolation from holes drilled elsewhere should be done with extreme caution. No near-term studies are planned for the rock regime. 6. Preliminary calculations using an ion transport model and conservative estimates of upward water movement and sorption coefficients suggest that several tens of meters of sediment are sufficient to contain the ion for approximately ten half-lives. Next years' effort will include the verification of the assumed flow ratio of water and sorption coefficients as well as develop a better understanding of ion movement through a chemical gradient. 25.50 7. Physical property measurements on 10-meter cores obtained from the Pacific indicate that the sediments to those depths are sufficiently plastic to flow into an emplacement hole and close it in relatively short times, thereby filling the hole with material having properties very similar, if not identical, to the surrounding media. Thus, no man-made sediment bypasses should be left to short-circuit the sediment container. 8. Using existing engineering technology, we have begun a preliminary study of methodology in sediment emplacement. Four methods have been identified and their relative rates and costs compared. 9. During the engineering emplacement study it became very apparent that at the present time, the engineering capabilities of working in the deep ocean or ocean floor far surpass the current understanding of the ion transport phenomena. 10. Under the direction of the Nuclear Energy Agency (NEA), the U.S. in February 1976 was host to an International Seabed Disposal Workshop to address all aspects of seabed disposal. From this, a report will be prepared which will give recommendations to the NEA and prepare future cooperative research and development activities. REFERENCES 1. 2. 3. 4. 5. Assessing Potential Ocean Pollutants, a report of the Study Panel on D. R. Anderson and D. M. Talbert, "The Programatic Outline of the Seabed B. C. Heezen and C. D. Hollister, The Face of the Deep, Oxford University H. U. Sverdrup, M. W. Johnson, and R. N. Fleming, The Oceans, Prentice- High-Level Radioactive Waste Management Alternatives, Section 6, "Seabed 6. W. P. Bishop and C. D. Hollister, "Seabed Disposal 7. 8. 9. W. P. Bishop and C. D. Hollister, A Program on the Ocean Basin Floors D. R. Anderson and D. M. Talbert, Submarine Geologic Disposal of High S. K. Runcorn, Continental Drift, Academic Press, New York, 1962. 25.51 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. R. R. Hessler, "The Structure of Deep Benthic Communities From Central D. R. Anderson, et al., Release Pathways for Deep Seabed Disposal of - W. P. Bishop, Seabed Disposal Program A First-Year Report, D. W. Pritchard, R. O. Reid, A. Ohubo, and H. H. Carter, "Physical A. DeFant, Physical Oceanography, vol. I, Pergamon Press, 1961. W. P. Bishop and C. D. Hollister, "Nuclear Wastes Beneath the Deep Sea D. H. Lester, G. Jonsen, and H. C. Burkholder, "Migration of Radio- R. D. Klett, Deep Rock Nuclear Waste Disposal Test: Design and J. D. Gaski, D. R. Lewis, and L. R. Thompson, Chrysler Improved Numerical W. B. Silker and M. R. Peterson, Implications of Seabed Disposal of High Capabilities Brochure, "Deep Ocean Seabed Waste Disposal Technical |