Salt Disposal of Heat-Generating Nuclear Waste

and DHLW over-test were designed to identify how the host rock and the disposal
room respond to the excavation itself and then to the heat generated from waste
placed in vertical holes in the drift floor. These tests imparted a relatively modest
thermal load in a vertical borehole arrangement and did not use crushed-salt
backfill or explore reconsolidation of salt. They primarily focused on the
mechanical response of the salt under modest heat load. The results can be used,
for example, to validate the next-generation high-performance codes over a
portion of the multiphysics functionalities. The Heated Axisymmetric Pillar test
involved an isolated, cylindrically shaped salt pillar and provides an excellent
opportunity to calibrate scale effects from the laboratory to the field, as well as a
convenient configuration for computer model validation (Matalucci 1987).
1985–1990. A set of moisture transport and release tests were part of the
borehole plugging and sealing test series at WIPP and were designed to measure
moisture release associated with heated boreholes and to evaluate transport
mechanisms. Each borehole contained a nitrogen flow and a water vapor
collection and measurement system. Water vapor flowing in the nitrogen was
collected and weighed (Nowak and McTigue 1987). These data characterizing
brine movement and accumulation were interpreted in terms of a model for flow
in a saturated porous medium. Comparisons between model calculations and brine
inflow rates showed order-of-magnitude agreement for permeability in accord
with independent in situ determinations of permeability in the salt. Expected
accumulations of brine in typical WIPP waste disposal rooms were calculated by
numerical methods using a mathematical description for the brine inflow model.
Brine accumulation in a disposal room was calculated to be in the range of 4 m 3 to
43 m 3 in 100 years. The maximum expected accumulation, 43 m 3 , is 1.2% of the
initial room volume, about the same as the quantity of brine in the salt that was
removed by mining the room (Nowak, McTigue, and Beraun 1988).
1986–1991. An in situ test of simulated HLW glass and other waste package
components was conducted at WIPP beginning in 1986 in a program known as
the Materials Interface Interactions Test (MIIT). The MIIT involved
approximately 1,900 samples in 50 test boreholes, with specimens that included
16 variations of simulated HLW glass, 11 potential canister metals, rock salt, and
two brine solutions (Wicks and Molecke 1988). The MIIT included a 5-year study
of the burial of simulated waste glasses and the resulting long-term waste-glass
leaching behavior. Brine analyses were performed on samples from selected
boreholes containing simulated waste-glass specimens, resulting in release rates
of less than one part in 100,000 for all elements investigated (Wicks 2001).
1.4 Analogues for Salt Disposal
As this report acknowledges, some key issues pertaining to HLW disposal in salt
need attention if a salt disposal option is selected. These remaining issues should
not be misconstrued to imply the scientific basis for salt disposal is weak. It is
not. Salt disposal remains a very favorable option for the U.S. The most likely
future for HLW salt disposal includes permanent, dry encapsulation.
10