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

215
GEOLOGIC CONSIDERATIONS
Draft p. 3.1.14--The ratings contained in the Table on p. 3.1.14 of the draft State-
ment, are suspect. If they were redone, taking containment/isolation into account, the
relative merits of salt and granite should increase. (154)
Draft p. 3.1.16-17--"Uncertainties" cited in the USGS Circular 779 relate only to con-
tainment and not to isolation and thus are important for only a few hundred years.
"Uncertainties" should be placed in the proper perspective. (154)
Draft p. 3.1.24--Geochemical aspects of repository isolation (containment) have not yet
been adequately studied. "Engineered barriers ... will probably have negligible permanence
compared to lifetime of the repository," but not for the limited time period for which con-
tainment is required. (154)
Draft p. 3.1.52--If the role of containment versus isolation is properly reflected,
there is no need for precise predictions of geologic events over hundreds of thousands of
years. (154)
Response
The presence of younger rock is not an absolute requirement. Much geologic history has
been deduced from the gaps or absences in the stratigraphic column. The Canadian Shield has
pre-Cambrian rocks at the surface and is considered one of the most stable parts of North
America.
The draft table on p. 3.1.14 summarizes the properties of the four media by assigning
a numerical value to the property in terms of its potential for isolation (Statement usage)
for each medium. All have potential for isolation of waste -- this draft table compares
them by their properties. Three items have been added to the table: Plasticity, Ion
Exchange Capacity and Absence of Linear Discontinuities.
Density of sampling to adequately represent the rock mass is a problem that will depend
on the specific conditions at a site and can be considered after exploration and testing
have begun. Also, see item 3, draft p. 3.1.51.
There is some ambiguity and perhaps confusion between the terms "isolation" and "con-
tainment." In the Statement, containment is used in a retention sense for both containers
and host rock. This usage is commensurate with the definitions for "isolation" and "con-
tainment" given by the recent DOE Position Paper to the NRC rulemaking hearings on nuclear
waste storage disposal (DOE 1980a).
The following definitions for isolation and containment are taken directly from this
DOE Position Paper. "Isolation means segregating wastes from the accessible environment
(biosphere ) to the extent required to meet applicable radiological performance objectives.
Containment means confining the radioactive wastes within prescribed boundaries, e.g.,
within a waste package."