Rheological Characterization of Cementitious Grouts Used to Dispose of Intermediate-Level Radioactive Waste By Hydrofrac
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RHEOLOGICAL CHARACTERIZATION OF CEMENTITIOUS GROUTS USED TO DISPOSE OF INTERMEDIATE-LEVEL RADIOACTIVE WASTE BY HYDROFRACTURING AT OAK RIDGE NATIONAL LABORATORY
E. W. MCDANIEL AND J. G. MOORE Chemical Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37830, USA
P. 0. Box Y,
ABSTRACT The hydrofracturing process is a waste disposal process in use at the Oak Ridge National Laboratory for the permanent disposal of locally generated waste solutions. This process is now being modified for use in the disposal of sludge that results from the sodium hydroxide neutralization of acid waste solutions. In this process, the sludges will be slurried in a bentonite clay suspension and mixed with a solids blend of cement and other additives. The amount of dry solids required for each liter of waste slurry will be determined from a rheogram that relates the viscosity of the slurry with the grams per liter recommended for grouts with desirable flow properties. A description of the process and the development of rheograms are included. Data are presented on the use of chemical additives to control the flow properties of grouts.
INTRODUCTION
At Oak Ridge National Laboratory (ORNL), intermediate-level waste (ILW) solutions (wastes with a specific activity between 1.5 x 104 and 2.0 x 1010 Bq/L) are currently being disposed of by the hydrofracturing process. In this process, the waste solution is mixed with cement and injected into an impermeable shale formation at a depth of abeut 300 m. Here the waste grout sets, fixing the radionuclides in the cement matrix. Subsequent injections form new grout sheets adjacent and parallel to the earlier grout sheets. This process is described in refs. 1 and 2. The existing hydrofracturing disposal facility was built in 1963 for a series of four experimental injections. It was modified in 1966 for the routine disposal of the Laboratory's ILW solutions and has since been used for the disposal of over one million gallons of waste solution containing about 500,000 Ci of various radionuclides. This facility has worked quite well for the disposal of ILW but cannot handle either slurries or wastes with a specific activity higher than 2.0 x 1010 Bq/L. A disposal system for these types of waste has been designed and is being built. When the new facility has been completed, the sludge that is now in the Gunite waste tanks at ORNL will be suspended and pumped to the new ILW storage tanks in Melton Valley. Subsequently, this suspended sludge will be pumped to the new fracturing facility and mixed with a cement mix base to form a grout. This grout will then be injected underground by the hydrofracturing technique (Fig. 1).
558 SUSPENSION OF
DRY SOLIDS
SLUDGE IN BENTONITE
GROUT
HYDROFRACTURE FACIITYSLURRY/
GUNITE GUIETNSSLUDGE-SLURRY TANKS SSESO SUSPENSION
INJECTION
(
SLD +R
WELL
Fig. 1. Flow diagram of sludge disposal process.
The grout-containing sludge must have properties not greatly dissimilar from those of current shale fracturing grouts.3 It must be fluid an
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