578 



sediments is that they are structurally a very simple geologic formation. The sedi- 

 ments are uniform over a great horizontal extent and are free from faults, fissures 

 or cracks. This means that the models that are developed to predict the behavior of 

 waste movement (beyond the heated zone) in the far field will be relatively simple 

 and less difficult to verify. The far field will be the barrier after a cannister fails 

 and will be the barrier for perhaps 90 percent of the lifetime of a repository. Fourth, 

 the maximum temperature that the sediment will experience occurs within about 2 

 years after emplacement and the heat will begin to dissipate into the ocean after 15 

 years allowing us to experiment and monitor in real time the worst case conditions 

 that will exist in the repository. This is a result of the relatively short distance 

 between the heat source of the waste cannister and the heat sink of the ocean's 

 waters and the high thermal conductivity of the sediments. The deeper a heat 

 source is placed in a geologic media the longer it takes for the heat pulse to pass 

 through the surrounding media. 



Land based disposal offers the advantage that it can be done completely within 

 the U.S. making the disposal operations free from international consideration of 

 control. Since man has been mining for thousands of years the engineering neces- 

 sary for mined repositories will probably require less development than the engi- 

 neering necessary for a subseabed disposal. Although there is considerable scientific 

 technology to draw upon there has never been a commercial scale operation on the 

 deep sea floor. 



4. The necessary depth of emplacement of containers cannot be stated precisely at 

 this time. The depth will depend in part on the exact physical and chemical 

 properties of the sediments at a given site in the ocean. Thus the burial depth could 

 well be different at various regions in the oceans. The necessary depth will also be 

 in part determined by the requirements for safety. The shallowest burial presently 

 considered as a reference case for calculation is burial of 30 meters. For most of the 

 major radionuclides this would be a very adequate barrier. Plutonium for example 

 would migrate (based on present model predictions) only about 10 meters in 100,000 

 years. The lifetime of a repository will probably be required to be 10,000 years. 

 Other isotopes that absorb less strongly to the sediments may make it desirable to 

 have a deeper burial. If emplacement of cannisters is done by a drilling operation 

 they would probably be placed deeper into the sediments, perhaps to depth of a few 

 hundred meters. 



There probably would be a trade-off between depth and ease of retrievability. We 

 assume that with present technology cannisters placed 30 to 100 meters into the 

 sediment should be relatively easy to recover. The emplacement, recovery, and 

 other engineering considertations have not been major areas of research of the 

 program to date. It is not planned to pursue these topics in earnest until the 

 fundamental scientific question of the deep sea sediments ability to contain radioac- 

 tive waste is more adequately answered. 



5. Researchers in the project have for the first time collected and cultured in the 

 laboratory bacteria that are native to the deep sea. It can safely be stated that they 

 are native to the deep sea since they can only be grown at deep sea temperatures 

 and pressures. These organisms, with very reasonable doubling times of a few hours 

 are being tested for their radiosensitivity. Deep sea amphipods, apparently ubiqui- 

 tous in the deep oceans, have also been captured and maintained in the laboratory 

 are also useful experimental organisms. Although there appears to be nothing 

 unique about the biochemistry of dep sea organisms except that their enzymes may 

 function optimally at deep sea pressures, it has been hypothesized that the organ- 

 isms have evolved at different background radiation levels and thus may have 

 radiosensitivity different from terrestrial or shallow water organisms. For example, 

 their capacity to repair sublethal radiation damage may be different from non- 

 barophilic organisms. The organisms isolated from the deep sea will be used to test 

 that hypothesis. The deep sea organisms maintained in the laoratory will also be 

 used to see if the uptake of radioisotopes is different from similar shallow water 

 organisms. 



Another area of biological research within the project is to determine any possible 

 biological pathways in the ocean that could transport radioisotopes to the surface 

 waters and to man. A second part of this research is to build models that will allow 

 as to quantify the rates of transfer. The first half of the research has to date 

 involved studying the mobile near-bottom scavenging organisms. We wish to know 

 their abundance, their vertical and horizontal range, their life history, and their 

 metabolism. For the second half of the project models are presently being construct- 

 ed that should allow us to make the necessary calculations of biological transport of 

 nuclides. 



In an effort to obtain the best possible guidance for the program's biological 

 research, the program is funding a biological oceanography workshop. About 50 



