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

6.1.1.1 Concept Summary
6.6
6.1.1 Very Deep Hole
The very deep hole (VDH) concept involves the placement of nuclear waste as much as
10,000 m (32,800 ft) underground, in rock formations of high strength and low permeability.
In this environment, the wastes might be effectively contained by the distance from the
biosphere and the location below circulating groundwater as they decay to innocuous levels
(OWI 1978 and ERDA 1978). To act as a nuclear waste repository, the host rock would have to
remain sealed and structurally stable under the heat and radiation introduced by the wastes.
Potential rock types for a repository of this kind include crystalline and sedimentary rocks
located in areas of tectonic and seismic stability.
An immediate question concerning this concept is: "How deep is deep enough?" The re-
quired depths would place the wastes far enough below circulating ground waters that, even if
a connection develops, transport of materials from the repository to the surface would take
long enough to ensure that little or no radioactive material reaches the biosphere (LBL
1979). The absolute value of this depth is not yet determined.
Defining the necessary depth at a given site requires determining site-specific limits on
the transport of radioactive materials to the biosphere, the site-specific hydrologic regime,
and the heat-source configuration (waste packing). Available data from the literature, pri-
marily from the oil and gas industry, show that some sedimentary rocks are porous and perme-
able and may contain circulating groundwater to depths in excess of 9,000 m (30,000 ft).
Investigations of crystalline rock, although very limited, suggest that at much shallower
depths some such rocks have relatively low porosities and permeabilities. Hence "very deep"
for these crystalline rocks may mean just a few thousand meters instead of the 9,000 m or
more required for sedimentary rocks. Once the required depth has been determined, the tech-
nology for making the hole to that depth and the ability of the surroundings to accept the
heat source become the limiting factors. It is clear that problems of making the hole, hold-
ing it open, emplacing the waste, and sealing the hole must be considered together. Should
shallow depths be determined as adequate, many of the potential problems of the very deep
hole concept (e.g., drilling technology and ambient conditions at depth) would be mitigated.
The concept assumes that disposal in very deep holes would not permit retrieval of
wastes. It would also provide assurance that no climatic or surface change will affect dis-
posal.
Environmental impact considerations for the very deep hole concept are those associated
with drilling a deep well or sinking a deep shaft, constructing the predisposal surface faci-
lities, emplacing the wastes, decommissioning the facilities, and ensuring long-term contain-
ment of the wastes.