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

6.54
6.1.3.3 Status of Technical Development and R&D Needs
Present State of Development
In general, conventional mining techniques would be applicable to island repository con-
struction. Transportation, storage, and handling requirements would be similar to those for
the conventional mined geologic disposal concept, with the addition of the sea transportation
link. Construction methods for ports would employ standard engineering practice.
Because the island disposal concept is so similar to the mined geologic repository op-
tion, the state of development is about the same. The ship loading and unloading require-
ments are similar to those described in the subseabed alternative, so again, the state of de-
velopment is about the same.
Technical Issues
Technical issues that differ from those for mined geologic repositories lie in the areas
of unique island hydrology and the resultant impacts of fresh or saline water on the package
materials and the waste formulation.
For example: Is the waste form proposed for conventional mined geologic disposal appro-
priate for island disposal? Are the canisters that encapsulate HLW or the canisters of spent
fuel compatible with the island repository environment? Should emplacement be in the fresh-
water zone or the saline ground-water zone?
Because a major incentive for considering island sites is a particular hydrological re-
gime that frequently exists beneath them, efforts would be needed to:
* Verify the existence of a freshwater lens at various sites and determine its size.
* Determine the flow patterns and velocities of saline ground water at depths beneath the
freshwater lens.
* Verify the stability of the freshwater lens in terms of the equilibrium between deep
groundwater flows, salinity diffusion, precipitation and surface hydrology, the effects
of sea level slopes, and other relevant processes in the natural state.
* Examine the perturbation to the lens caused by construction of the repository shafts and
underground facilities, using simulation models and field evidence, if available. The
shafts and facilities will tend to provide a sump that will drain either the freshwater
or the saline ground water, depending on the location and depth of the repository.
* Examine the effects of heat generation on lens stability using simulation models. Heat
may cause thermal convection cells that could flow counter to the freshwater circulation
and modify the discharge pattern into the seawater.
R&D Requirements
To resolve these technical issues, specific R&D programs would be directed toward:
* Development of a system data base
e Study of hydrogeological aspects of island sites