This potential project will develop and test cost effective high-silica
cementitious materials. These high-silica cementitious materials
will be evaluated on their ability to buffer the pH and Eh of the
groundwater, to slow corrosion of waste packages (WP), and to retard
radionuclide migration. While being compatible with YM repository
systems, these materials are expected to be less expensive to produce,
and as strong, and more durable than ordinary Portland Cement (OPC).
Therefore use of these cementitious materials in the YM repository
(e.g., inverts, drift liners, bulkheads)may significantly reduce
these costs and may reduce uncertainty in repository performance.
Both laboratory development and natural analog studies are anticipated
using a unique combination of expertise at ORNL, UT, UC Berkeley,
and Minatom to develop and test high-silica hydraulic, cementitious
binders . The major tasks of this project are to (1) formulate and
make candidate cementitious materials using high-silica hydraulic
binders, (2) measure the physical and chemical properties of these
materials, (3) expose combinations of these materials and WP materials
to static and flowing YM groundwater at temperatures consistent
with the expected repository conditions, (4) examine specimens of
both the cementitious materials and WP materials periodically for
chemical and mineralogical changes to determine reaction mechanisms
and kinetics, and (5) predict the long-term performance of the these
material by thermodynamic and transport modeling and by comparisons
with natural analogs.
High-silica binders have a number of advantages for YM applications.
Evidence from archaeological and geological samples shows that high-silica
cement binders are extremely durable. These cements, used by the
Greeks and Romans, have survived for hundreds of years in hot water
and for thousands of years in marine environments. As an additional
benefit, high-silica binders are as strong as OPC, while suppressing
the formation of free calcium hydroxide that elevates the pH in
OPC.
High-silica binders also cost 30-50% less. Furthermore, stoichiometric-excess
silica in these binders seals stress cracks in structures by forming
alteration-minerals. Leachates from these cementitious binders are
nearly saturated in orthosilicates [SiO4Hxx-4]
that passivate metal surfaces. These silicate minerals are also
very strong radionuclide absorbers, resulting in very insoluble
silicates of actinides, fission products, and uranium.
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