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

5.1
CHAPTER 5
GEOLOGIC DISPOSAL
In this chapter, the concept of a conventionally mined deep underground repository for
disposal of spent fuel and/or fuel reprocessing wastes is described. The status of the
technology is described as are uncertainties that require resolution and additional informa-
tion that would improve confidence in the concept. A description of a conceptual repository
for spent fuel or for fuel reprocessing wastes is given. An analysis is presented of the
environmental impacts associated with construction and operation of repositories in repre-
sentative media. Several types of failures of repositories in the long term have been
hypothesized to assess societal risk. A description of dollar costs of repositories is also
presented. The concern for safeguards is reviewed. Finally, the environmental impacts are
summarized in terms of the irreversible and irretrievable commitment of resources and in
terms of unavoidable adverse impacts.
5.1 DESCRIPTION OF THE GEOLOGIC DISPOSAL CONCEPT
Geologic disposal of radioactive wastes, as used in this Statement, is the disposal of
radioactive wastes in conventionally mined repositories deep within the geologic formations
of the earth. Included is the concept of multiple barriers to provide a series of indepen-
dent barriers to the release of radionuclides to the biosphere.
The multiple barriers that could contain nuclear waste in deep mined repositories fall
into two categories: 1) geologic or natural barriers and 2) engineered barriers. Geologic
barriers are expected to provide isolation of the waste for at least 10,000 years after the
waste is emplaced in a repository and probably will provide isolation for millenia there-
after. Engineered barriers are those designed to assure total containment of the waste
within the disposal package during an initial period during which most of the intermediate-
lived fission products decay. This time period might be as long as 1000 years in which case
the radiation levels and heat generation rates of the total waste would drop by factors of
approximately 1,000 and 100, respectively. Engineered barriers must be designed to with-
stand the more severe radiation and thermal conditions encountered initially.
Two important components of the geologic barrier to be considered in siting are the
host rock itself and the geologic surroundings. Properly chosen rock structures provide
physical and chemical properties that contribute to repository strength. Sufficient repos-
itory depth and lateral extent of the rock mass contribute to the isolation capability of
the repository. Tectonic stability and a noncommunicating hydrologic regime combine with
rock properties to maintain repository strength and isolation integrity. The geologic bar-
riers can be selected through the site-selection process to provide a stable long-term envi-
ronment for the waste that is not likely to be disturbed by natural events or human
activities.