Management of Commercially Generated Radioactive Waste - U.S. ...

6.59
Radionuclides might be sorbed by the host rock, which would substantially retard the
waste transport within the lens. Sediments that might exist at the shoreline in the dis-
charge zone could have useful sorption properties and retard radionuclides prior to dis-
charge and dilution in the seawater.
Ground-water Transport, Saline Zone Location. It has been suggested that offshore
islands may have essentially static saline ground water at depth, due to the absence of
hydraulic gradients at sea level. However, the residual or continuing effects of oceano-
graphic, geothermal, climatological , or other changes may create flow. These effects would
need to be examined prior to siting a repository in such a location (see Figure 6.1.11).
Flow transport in the saline zone may be accompanied by dispersion and diffusion, which
would result in reduced concentrations at a distance from the repository. The amount of
sorption of radionuclides in the host rock or on seabed sediments would depend on the parti-
cular radionuclide, ground-water, and rock or sediment chemistry.
Seawater Contamination. It appears that the principal discharge of wastes from an island
repository would be into the seawater, possibly through sediments. Discharge might occur in
a relatively concentrated near-surface zone if the waste were located in the freshwater lens.
This could cause contamination of littoral and near-surface aquatic systems.
Discharge from wastes located in the saline ground-water zone would likely be dispersed
through the seabed if the thermal-convection effects were insufficient to distort the flow
patterns significantly.
Volcanism. Some islands, particularly those in island arcs and to a lesser extent oce-
anic islands, are frequently highly active seismically and volcanically. Such activity could
discharge the waste in either lava flows or into the atmosphere. Geologic data for the most
recent volcanic event would be relied upon to establish inactivity before an island was
selected as a disposal site.
Potential Impacts
In determining the potential impacts of island disposal over the long term, the follow-
ing factors would be considered:
* Corrosion, leaching, and transportation of radionuclides to the biosphere by the ground
water
* The influence of thermal effects on flow
* Thermal/mechanical effects on permeability and porosity
* Retardation of radionuclides on rock fractures and seabed sediments
* Sediment and current movements
* Pathways to man via marine organisms, typical marine activities, and island
considerations.