An assessment of issues related to determination of time periods required for isolation of high level waste Page: 2 of 18
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The question of determining required isolation periods has again been raised
in regard to the projected emplacement of spent nuclear fuel at the Yucca
Mountain Project Facility. This study is intended to address that question.
Long-term isolation requirements for the disposal of HLW in a deep
geologic repository were developed by the Environmental Protection Agency
(EPA) (9). These criteria establish that projected releases of radioactivity
be limited for a period of 10,000 years. The EPA release criteria were based
on the assumption that if the repository could provide adequate containment
of the material for 10,000 years, it is reasonable to assume that it would
provide adequate containment for periods beyond this time.
For the geologic repository, the two primary release pathways are 
the long-term movement of nuclear- material to the repository boundary and
beyond by groundwater; and  human intrusion into the repository horizon.
In effect, the second pathway is very scenario-specific and the risk is of
very low probability. Therefore, this study will focus on the groundwater
In 40 CFR 191, EPA states that radioactivity release from the waste
disposal facility should be such that "risks to future generations will be no
greater than the risks that would have existed if the uranium ore used to
create the wastes had not been mined to begin with." To make such a
determination requires a comparative assessment of the SNF or HLW repository
against a typical uranium ore deposit. The objective of this study is to
make such an assessment using the most recent data on radionuclide
inventories and dose consequences.
To compare the potential hazard of the repository against that of the
uranium ore deposit from which the nuclear fuel was originally extracted
requires the determination of a sound basis for comparison. Some
possibilities include comparative evaluation of hazard per unit mass
(repository vs. ore body) or per.unit volume. Such evaluation, however,
would involve use of relatively subjective assumptions regarding dimensions
and other properties. A more objective basis would involve comparison per
metric ton of heavy metal (MTHM) considering the uranium ore quantities and
components required to produce 1.0 MTMH of nuclear fuel against those in the
corresponding quantity of spent fuel. That is the basis for comparison
applied in this study.
Radioactivity in Uranium Ore
Determination of the quantity of ore required to produce 1.0 MTHM must
consider all losses in processing the ore into nuclear fuel. For purposes of
this evaluation, it is assumed that: 90% of the U308 is recovered from the
ore, 1.0% is lost in conversion of U308 to UF6, the uranium is enriched from
natural uranium to 3.2% U-235 with a 1.0% material loss in the enrichment
process, and other small losses in the processes of conversion to and
fabrication of nuclear fuel. Table I summarizes the radionuclide content of
the uranium ore required to produce 1.0 MTHM of nuclear fuel. For purposes
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Cohen, J.J.; Daer, G.R.; Smith, C.F.; Vogt, D.K. & Woolfolk, S.W. An assessment of issues related to determination of time periods required for isolation of high level waste, article, June 1, 1989; Las Vegas, Nevada. (digital.library.unt.edu/ark:/67531/metadc624089/m1/2/: accessed July 18, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.