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allied
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Page 12
7
th
International Conference on
Recycling and Waste Management
October 03-04, 2019 | Melbourne, Australia
Journal of Environmental Waste Management and Recycling | Volume: 02
Deep Isolation – Development of the safety case for disposal of Radioactive wastes
in horizontal boreholes
James Voss
and
Rodney Baltzer
Deep Isolation, USA
N
uclear power is likely to be a low-carbon source of
baseload energy for decades to come. One challenge
remains vexing to the continued use of nuclear power, this
being the safe management of radioactive wastes.
Deep Isolation has developed a safe, secure, and
permanent deep geological disposal method for high-
level waste, including spent nuclear fuel as well as sealed
sources and other highly radioactive materials. The
method uses horizontal drilling techniques and emplaces
the disposal canisters in a horizontal orientation. This
provides additional safety factors to those found in deep
mined repositories or deep vertical boreholes.
The innovative solution uses established directional drilling
technology from the oil and gas industry to drill a vertical
drill hole hundreds to thousands of meters deep and then
transition to a horizontal drill hole that is thousands of
meters in length. The target geologic media for our disposal
solution is in or below formations that have been out of
contact with surface waters for hundreds of thousands to
millions of years. These formations are present at various
depths throughout much of the world and will ensure the
suitability of the geologic environment prior to considering
any location.
Work by Deep Isolation has focused on the development
of the safety case for its disposal system. This paper will
address the dominant features of the Deep Isolation
system that establish the demonstrable case for disposal
safety.
Siting: Deep Isolation is establishing a list of criteria that
are necessary for the candidate site to be acceptable.
The criteria include stability, the age of the water in the
disposal horizon, the isolation of the water at the disposal
horizon from water above and below (determined by
isotopic age dating methods), and geochemistry. It should
be noted that Deep Isolation is no longer focused on shales
and other sedimentary rocks. After being convinced of
the drilling and emplacement technology, Deep Isolation
is actively considering emplacement locations in deep
basement rock, provided all siting conditions are met.
Elimination of Pathways: In other disposal concepts, the
process of emplacing nuclear wastes creates a pathway for
its release to thebiosphere. Deep Isolation is addressing this
with horizontal emplacement a considerable distance from
the vertical borehole. In addition, the horizontal portion of
the borehole is inclined a few degrees above horizontal.
These design facets eliminate two pathways for transport
of radionuclides in disposal. The first is that analyses have
shown that there is essentially no thermal gradient present
at the vertical portion of the emplacement borehole, thus
eliminating the energy source to move contaminants to
the surface. These analyses have considered very high
burnup fuel with minimal cooling. The slight incline of the
horizontal emplacement borehole creates a preferential
path for any gases evolved during the disposal process,
noting that the preferential pathway is to a “dead end” –
the end of the horizontal emplacement borehole. Analyses
are ongoing to determine the quantity of gases expected
once wastes are emplaced.
Engineered Barriers: Deep Isolation is mindful of regulatory
requirements for engineered barriers as well as the cases
for excluding them. Alternative canister materials are
being considered for the various geologic environments
that might be present in disposal conditions. In addition,
Deep Isolation is evaluating alternative backfill and
seal materials that would be used to close the disposal
boreholes.
A comprehensive safety case is being prepared by Deep
Isolation and its progress will be reported in this paper. The