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International Hydrolytics Ltd.
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POTENTIAL
APPLICATIONS OF AHC TECHNOLOGY TO NUCLEAR WASTE DISPOSAL
AHC TECHNOLOGY - A BENEFICIAL TOOL FOR HYDROLYTIC
EARTH RESTORATION APPLICATIONS TO NUCLEAR WASTE CLEANUP ACTIVITIES
This Appendix describes recently formulated
concepts, "proof-of-concept" studies, and in-house development activities
which establish the feasibility of incorporating AHC technology as the key
element in a broad range of environmental restoration, waste management,
decontamination / decommissioning projects that are currently scheduled for
Hanford Washington, Rocky Flats Colorado, Savannah River Georgia, and other
Department of Energy (DOE) sites.
SURFACE VITRIFICATION
The Hanford Waste Vitrification (HWV) plant,
as currently designed, will be capable of processing 2.4 tons of high-level
nuclear waste per day, beginning in 1999. In effect, this high temperature
process will transform mixtures of high-level waste slurries, whether
pre-treated or not, and sand-like material into low-grade glass which solidify
in steel tube canister "molds" 2 ft. in diameter by 10 ft. long, for
eventual storage in Federal repositories, e.g., Yucca Mountain, Nevada. In
addition, it is anticipated that, by 2010, the installation of a replacement
melter will boost the high-level nuclear waste processing capability by 300% to
500%. In any event, AHC technology, in its present form, affords a surface
vitrification alternative to achieve drastic increases in processing capacity,
with essentially no change in energy costs. The basic elements of this AHC
alternative include: step 1 - metering, high-level nuclear waste slurries and
hydrolytic cements into a high shear pin mixer; step 2 - casting the pin mixer
effluent into a high speed belt of interconnected mini-briquette plastic molds,
with flexibility in two dimensions; step 3 - accelerating the hydrolytic
setting process with microwave heating; step 4 - surface vitrification of
briquettes in the HWV plant; step 5 - pour casting mixtures of hydrolytic
cement and surface-vitrified briquettes directly into steel canisters to
solidify at ambient temperature; and step 6 - eventual storage in Federal
repositories. An important side benefit of this AHC alternative is that
radioactive gases attendant to normal operation of a HWV plant will effectively
be eliminated in proportion to reduced "dwell times" of nuclear waste
in the high temperature environment, i.e., surface vitrification requires
orders of magnitude less time than volume vitrification.
ALTERNATIVE TO GROUT IMMOBILIZATION
In September of 1993, after nearly 5 years
of intensive technical investigations and the construction of a $29 million
Hanford Grout Immobilization facility, the DOE announced that the "grout
concept," in its present form, was no longer a viable option for
solidification of low-level nuclear waste prior to storage in underground, 123'
x 50' x 34', concrete vaults. Presumably, this decision was based on the
following shortcomings of Portland cement/flyash grout: excessive heat from
exothermic hydraulic cement reactions; thermal stress-induced fractures during
28 day curing cycles; inadequate control of viscosities and set times;
excessive shrinkage during the cure cycle; and inability to reduce leachates to
acceptable levels. In any event, this decision was immediately followed by
successful demonstration that, with appropriate modification to basic
hydrolytic cements and/or judicious selection of dispersed phase additives, AHC
technology can far surpass all grout specifications. In effect, this
demonstration combined modified/unmodified hydrolytic cements with DOE-approved
nuclear waste simulants, i.e., corrosive oxidizer sludges containing 32.3%
sodium nitrate, sodium nitrite, sodium hydroxide, and lead nitrate salts, to
achieve the following, non-optimized, results: simple replacement of Hydrolytic
water components with 40oC sludge water produced dimensionally stable AHC
materials with 10.7% by weight of sludge solids; dispersed phase additives of
carbon black reduced ionic mobilities by 10% (surface absorption); a silicone
copolymer (1 of over 300 different types) reduced ionic mobilities by an
additional 83.8% (permeability reduction); special silicone-glycol surfactants
reduced ionic mobilities by 99.9% (closed cell formation); selective chemical
(silane) and molecular sieve (zeolite) additions to hydrolytic cements allow
AHC-encapsulated nuclear wastes to easily pass EPA's toxic chemical leaching
procedures; a sodium silicate molar ratio of 1.8 (SiO2:Na20) eliminated
shrinkage and maintained viscosities within desired pumping limits; and
Hydrolytic set times were adjustable over a very wide range.
LAND DISPOSAL / PLUME CONTAINMENT
Coincident with
"proof-of-concept" investigations for Westinghouse Hanford Corp.,
laboratory personnel were involved in AHC product development activities that
may have direct or indirect application to plume containment at various DOE
sites. Specifically, these prototype development activities related to
solidification of caustic soil sludges with hydrolytic cements for potential
applications to soil stabilization, oil field cleanup, and low cost,
water-resistant, construction materials (an improved adobe, of sorts). Sludge
parameters for these investigations were limited to the following ranges:
temperature 80oF to 105oF; pH - 12; soil mesh size - 50 to 100; and solids
content - 40% to 72.6%. In addition, variations in hydrolytic cement/dispersed
phase components included: sodium silicate molar ratio - 1.8 to 3.22; oil
additives - 5% to 15%; and kerosene additives - 2% to 13.5%. Relevant data from
these studies, i.e., initial set times, gelation times, water loss, etc.,
indicate that the optimized Hydrolytic mixing parameters and dispersed phase
additives which result from "tailored AHC alternatives to grout
immobilization of low-level wastes" are directly applicable in preventing
ground water contamination from leaking underground storage tanks, piping
systems, etc., at DOE sites.
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