Radiolytic Gas Generation Rates from Hanford RHO-CAW Sludge and Double-Shell Slurry Immobilized in Grout

摘要

Cement-based grouts will be used to immobilize low-level waste solutions at the Rockwell Hanford Operations (RHO) in Richland, Washington. The radioactivity in these aqueous encapsulated waste solutions can cause decomposition of the pore water in these grouts. Concern has been expressed over the potential for pressurizing the waste packages used to contain this material and the flammability and explosion hazards from hydrogen gas from this decomposition. Oak Ridge National Laboratory (ORNL) undertook the task of establishing the radiolytic gas production rates for the two types of RHO waste streams - current acid waste (CAW) and double-shell slurry (DSS) - and determining the composition of the generated gases, the effects of surface-to-volume ratio of the samples, waste slurry particle sizes, and the water content of the waste form. The alpha exposure of the grouts containing RHO-CAW sludge (with NO sub 3- ) produced H sub 2 and O sub 2 at almost a 2:1 ratio, with a trace of N sub 2 O. The alpha irradiation of the grouts containing the DSS solution (with both NO sub 3- and NO sub 2- ) produced mainly N sub 2 O, H sub 2 , and a trace of CH sub 4 . In this case, O sub 2 and N sub 2 were either produced or consumed, depending upon when the sample was collected. During the gamma radiolysis of the grouts containing the DSS solution, N sub 2 O, H sub 2 O, N sub 2 , and a trace of CH sub 4 were produced. In this case, O sub 2 from the air in the system was consumed. The average G/sub t/ value for the grout containing the RHO-CAW sludge exposed to alpha irradiation was 0.42 molec/100 eV, which is close to that for the gamma exposure of pure water (0.45 molec/100 eV). A G/sub t/ value of 0.12 molec/100 eV was obtained for the grout containing the DSS solution from the alpha exposure. As expected, a smaller G/sub t/ value of 0.018 molec/100 eV was obtained for the gamma exposure of the grout with DSS solutions. (ERA citation 10:031576)