Cold Cap Grout Formulation for Waste Containment at DOE Site, Hanford, Washington
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COLD CAP GROUT FORMULATION FOR WASTE CONTAINMENT AT DOE SITE, HANFORD, WASHINGTON LILLIAN D. WAKELEY AND JAMES J. ERNZEN Concrete Technology Division, Structures Laboratory, U.S. Army Engineer Waterways Experiment Station, 3909 Halls Ferry Road, Vicksburg, MS 39180
ABSTRACT WES developed a grout to be used as a cold (non-radioactive) cap or voidfill material between the solidified low-level waste and the cover blocks of near-surface disposal vaults at the U.S. Department of Energy (DOE) Hanford Facility. The project consisted of formulation and evaluation of candidate grout, followed by a physical scale-model test to verify grout performance under project-specific conditions and provide data to verify numerical models of stresses and isotherms inside the Hanford demonstration vault. Evaluation of unhardened grout included segregation, bleed, flow, and working time. For hardened grout, strength, volume stability, thermal heat rise, and geochemical compatibility with surrogate wasteform grout were examined. The grout was formulated to accommodate unique environmental boundary conditions (vault temperature = 45 °C) and exacting regulatory requirements (mandating less than 0.1% shrinkage with no expansion and no bleeding); and to remain pumpable for a minimum 2 hr. A grout consisting of API Class H cement, an ASTM C 618 Class F fly ash, sodium bentonite clay, and a natural sand from the Hanford area met all performance requirements in laboratory studies.
BACKGROUND Radioactive wastes at the DOE Hanford Facility have been in temporary storage for up to 40 years. These wastes include chemically hazardous and radioactive salts created during decades of processing nuclear weapons materials. For permanent disposal of some of these wastes, the DOE initiated the Hanford Grout Vault Program, during which large volumes of low-level wastes will be grouted into concrete vaults within a subsurface multiple3 barrier system. Most of the volume of the 5000-m vaults will be filled with the wasteform grout, which is the first-line physical and only chemical barrier to waste mobility. A non-radioactive or "cold" cap grout will fill the upper 1.2 m of each vault, between the wasteform and the precast cover blocks. This cold cap grout will be placed on top of the wasteform grout in at least three lifts, sometime after the wasteform grout has hardened, to form a load-bearing barrier between the covering layers and the hazardous materials contained below them. The Waterways Experiment Station (WES) developed the cold cap grout for the first concrete vault (Figure 1) and demonstration of this disposal system at Hanford.
Mat. Res. Soc. Symp. Proc. Vol. 245. ©1992 Materials Research Society
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Figure 1.
Grouted Waste-Disposal Vault
PERFORMANCE REQUIREMENTS There are three categories of performance requirements: 1) pumping and placement properties, 2) properties of unhardened grout after placement, and 3) properties of hardened grout.
Pumping and Placement The location of existing ports in the cover blocks dictates that the grout will
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