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

Draft P. 3.1.71
Issue
253
GEOLOGIC CONSIDERATIONS
Sorption of radionuclides is controlled by the site-specific geology. It seems
unlikely that radionuclide behavior data from one site can be applied to another site.
(113-EPA)
Response
Radionuclide behavior data from one site cannot be applied to another site with preci-
sion; however, they appear adequate for use in a generic statement.
Draft p. 3.1.104
Issue
A major deficiency in the design of the repositories in granite, shale, and basalt is
that they have been designed as if the host rock were salt. The repositories in the four
geologic media should not be of similar design. For instance, the inherent structural
characteristics of granite have not been taken into consideration. The design of a mine in
hard rock is substantially different from that in salt. Where, by the nature of the mate-
rial, a repository in salt is confined to a single level, a repository in massive granite
need not be. The long term stability of large rooms in granite is well known. (208-NRC)
Response
Room and pillar mining provides for efficient use of the rock formation for the
emplacement of nuclear wastes. The concept of room and pillar mining was tailored to the
rock structural characteristics of the four.rock types shale, salt, basalt and granite as
plainly indicated in Table 7.4.2. The multiple level concept for room and pillar mining in
repositories is constrained only by the physical dimensions of the geology. No technical
basis is known to disavow multiple levels. In the case of bedded salt, multiple levels may
be physically impossible since it is a horizontally layered geology. Room height may be of
the same order dimensionally as the geologic layer thickness, thus restricting a repository
to one-level thickness does not entirely rule out multiple levels though. With a thinly
layered geology multiple levels may be possible if multiple thin layers exist as in the case
of the WIPP site.
Domal salt has a potential for providing for multilevel emplacement since its geologic
vertical dimension is a couple magnitudes of order greater compared to the room height
dimension. Therefore salt repository design is not confined to a single level.
Rooms in granite may be extremely stable. Thermal/mechanical analysis for the precon-
ceptual design stages has been performed. Thermal/mechanical models are presently being
developed to address the impact of the heat generated by nuclear wastes upon room stability
in granite repositories.