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

3-29 3-30
Comment .. Comment
"'umber Number
3..h.9 pp. 3.1.24, 3.1.33, 3.1.235 .h.11 p. 3.1.33
Several comments.have been.made about the "self-healing" properties of The GEIS states that "Mines in Canadian Shield Granite appear to be tight
3.h.1O p. 3.1.26
salt: and free from circulating groundwater below depths of about 3000 ft." We
p. 3.1.33 - "Fractures tend to self-heal, thus reducing...water ingress..." recognize that granite has a low hydraulic conductivity and that seepage
rates are low enough to appear negligible by visual inspection. However,
p. 3.1.24 - "A key problem will be preservation of low permeability, it is likely that groundwater inflow into operating mines is evaporated by
Preliminary thermal loading analyses indicated that tensile ventilation airflow. In the long time frame of a repository, this inflow
forces will be induced near the outer margins of the repos- is expected to be significant.
itory. Thus, thermal expansion could create potential
pathways for work migration by fracturing or by opening 3.h.12 p. 3.1.41
pre-existing fractures. For salt strata this is not a Groundwater nuclide transport is not included among the issues needed to
problem; salt is expected to deform plastically and heal be resolved to determine post-operational impact of the repository (p. 3.1.41).
Internal fractures. However, the problem is that if the On page 3.1.48 and 49 it states that groundwater movements that are insignif-
surrounding strata were breached by fracturing, salt could icant over the short term could be a problem where considered over the
be vulnerable to rapid solution by groundwater. Therefore, long term. Groundwater movement in a salt repository is considered to be
it appears that th ermally induced permeability will be an negligible.
important consideration for all host rock media."
Table 3.1.49 on page 3.1.164 implies that.there could be an unacceptable
p. 3.1.235 - "...generally accepted...salt tends to heal any opening" 50 year body dose as a result of the groundwater transport of radionuclides
by the year 2050. Is this in contradiction to other passages discounting
It may not be realistic to depend on this "self-healing behavior" to the effects of mass transport?
produce an impermeable seal around the repository. The repository design
should consider worst case behavior. Worst case behavior would be the 3.h.13 p. 3.1.41
opening of thermally or mechanically induced fractures around the repository Operational difficulties which may prevent sealing the repository have not
to water flow from an overlying aquifer. The water under greater pressure been discussed. It is difficult to see how one could do an adequate job
due to depth could keep the fractures open and increase the dimensions of of either backfilling or retrieving if a repository becomes flooded. The
the fractures as a result of the flow. point to emphasize is that operational problems may impact long-term
The great deficiency in the hydrogeologic data base is actual field studies not addressed.
and methods for obtaining rock dispersivities. Also lacking are in-situ
sorption studies for a variety of geologic, hydrologic and geochemical 3.ýh.14 p. 3.1.47 to 3.1.76
performance. The effects of contaminating the repository in an accident,
which may affect both occupational safety and long-term performance, are
environments. (Note: The Canadians are doing work in this area at the For a repository in salt, a discussion of brine migration is missing.
Chalk River Nuclear Laboratories (CRNL)). There was no mention of the possibility that sorption of the effluent of a