The U.S. Department of Energy (DOE) is conducting in situ closures (entombment) at a large number of facilities throughout the complex. Among the largest closure actions currently underway are the closures of the P and R Reactors at the Savannah River Site (SRS), near Aiken, South Carolina. In these facilities, subgrade open spaces are being stabilized with grout; this ensures the long term structural integrity of the facilities and permanently immobilizes and isolates residual contamination. The large size and structural complexity of these facilities present a wide variety of challenges for the identification and selection of appropriate fill materials. Considerations for grout formulations must account for flowability, long term stability, set times, heat generation and interactions with materials within the structure. The large size and configuration of the facility necessitates that grout must be pumped from the exterior to the spaces to be filled, which requires that the material must retain a high degree of flowability to move through piping without clogging while achieving the required leveling properties at the pour site. Set times and curing properties must be controlled to meet operations schedules, while not generating sufficient heat to compromise the properties of the fill material. The properties of residual materials can result in additional requirements for grout formulations. If significant quantities of aluminum are present in the facility, common formulations of highly alkaline grouts may not be appropriate because of the potential for hydrogen generation with the resultant risks. SRS is developing specialized inorganic grout formulations that are designed to address this issue. One circum-neutral chemical grout formulation identified for initial consideration did not possess the proper chemical characteristics, having exceptionally short set times and high heat of hydration. Research efforts are directed toward developing grout formulations that can meet operational requirements for chemical compatibility, extended set times and reduced heat generation.

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