Subseabed Disposal: Systematic Application of the Site Qualification Plan

Two criteria, geologic stability and barrier effectiveness, form the basis of the Subseabed Disposal Program´s site qualification plan to evaluate the ocean basins and identify those regions having characteristics most favorable for containment of radioactive waste. Stability criteria are used to define those regions least likely to be disturbed by tectonic forces or oceanographic changes during the lifetime of a waste repository. Barrier criteria define those lithologies most likely to form an effective barrier to the release of radionuclides. A systematic investigation of successively smaller areas of the seafloor has begun, initially using archived data but gradually becoming more detailed to include reconnaissance, swath-mapping and deep-tow seismic surveys and sampling. Two north Pacific regions and three north Atlantic regions (PAC I and II and ATL I, II, and III, respectively) have thus far been selected for further investigation based on the site qualification plan. The PAC I region, centered on the Shatsky Rise in the northwest Pacific, has been subdivided into areas and locations on the basis of an exhaustive review of data available in the archives of national and international agencies and institutions. Results from three locations surveyed and sampled within the PAC I region (VEMA cruise 36-12) suggest some variability in seismic reflector character and lithology, attributable partially to the effects of the North Pacific current. PAC II, located northeast of Hawaii, represents a generic study region characteristic of the Pacific pelagic, abyssal hill environment. Seismic reflection surveys and sampling indicate uniform sediment properties and processes, both laterally and vertically, within the PAC II region. Initial investigation of Regions ATL I, II, and III, located within the distal Nares abyssal plain, the distal Sohm abyssal plain, and the Cape Verde region, respectively, suggests certain smaller areas within these regions warrant more detailed - - study.