Designing injectable colloidal silica barriers for waste isolation at the Hanford Site

Conference · Sat Dec 31 04:00:00 EST 1994

OSTI ID:400689

Persoff, P; Moridis, G J; Apps, J; Pruess, K ^[1]; Muller, S J ^[2]

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1. Lawrence Berkeley Lab., CA (United States). Earth Sciences Div.
2. Univ. of California, Berkeley, CA (United States). Dept. of Chemical Engineering

Injectable barriers can be formed from colloidal silica, a gelling colloidal suspension. A particular problem associated with emplacement of colloidal silica barriers is uncontrolled rapid gelling due to chemical interactions between the grout and divalent ions in the soil. The authors discuss three techniques for solving this problem. Gel-time control can be achieved in Hanford sand by displacing the divalent ions away from the injected grout. This can be done by preceding the grout injection with a preflush of 4% NaCl brine. For cases where preflushing is not permitted, displacement of divalent ions can also be achieved by starting the grout injection with diluted colloidal silica, which eventually gels due to its colloid content and accumulation of displaced divalent ions. Preliminary laboratory results support this strategy. A 13% solids colloid displaced divalent ions and did not gel during the injection period, while colloids with 20% or greater solids content gelled too rapidly. A second strategy to avoid preflushing is to use NaF, rather than NaCl, brine (or a mixture) to cause gelling of the first grout injected. The sodium ions caused displacement of divalent cations. The fluoride ion precipitates or complexes the major divalent cations, preventing premature gelling, but leaving enough cations to gel slowly. Hanford sand accelerates gelling of colloidal silica grout that has been prepared with NaCl, but preliminary laboratory results show that if NaF is used instead of NaCl, the Hanford sand delays gelling.

• DOE Contract Number: AC03-76SF00098
• OSTI ID: 400689
• Report Number(s): CONF-941124--; ISBN 0-935470-85-9
• Country of Publication: United States
• Language: English

Related Subjects

05 NUCLEAR FUELS
COLLOIDS
CONTAINMENT SYSTEMS
DESIGN
HANFORD RESERVATION
RADIOACTIVE WASTE DISPOSAL
RADIONUCLIDE MIGRATION