Pacific Northwest Laboratory conducted experiments to produce empiricalleach rate data for phosphate-sulfate waste (PSW) grout. Effective diffusivities were measured for various radionuclides (90Sr, 99Tc, t4c, 129J, t37cs, "Co, 54 Mn, and U), stable major components (N~, SOl·, H 3 B0 3 , K and Na) and the trace constituents Ag, As, Cd, Hg, Pb, and Se. Two types of leach tests were used on samples of actual PSW grout and synthetic PSW grout: the American Nuclear Society (ANS) !6.1 intermittent replacement leach test and a static leach test.Grout produced from both synthetic and real PSW showed low leach rates for the trace metal constituents and most of the waste radionuclides. Many of the spiked trace metals and radionuclides were not detected in any leachates. None of the effluents contained measurable quantities of 137 Cs, 60 Co, 5 4 Mn, 109Cd, stcr, 2 1 0Pb, 203Hg, or As. For those trace species with detectable leach rates, T~J appeared to have the greatest leach rate, followed by 99Tc, 75 Se, and finally U, 14C, and ttc.nAg. Leach rates for nitrate are between those for I and Tc, but there is much scatter in the nitrate data because of the very low nitrate inventory. contained measurable quantities of 137 Cs, 60 Co, 54 Mn, 109 Cd, 51 cr, 210 Pb, 203 Hg, or As.For those trace species with detectable leach rates, 1~1 appears to have the greatest leach rate, followed by 99 Tc, 75 Se, and finally U, 14 C, and 110 "Ag. leach rates for nitrate are between those for I and Tc, but there is much scatter in the data because of the very low nitrate inventory. Particular attention was placed on studies that address the effect of sample size on the effective diffusion coefficient (D,), the effect of initial inventory on the effective diffusion coefficient, and comparison of actual PSW and synthetic PSW grout. The comparisons of results with standard-sized grout specimens (35 ml) and large-sized {142 ml} specimens was not conclusive. For a few species {K, Na, U) the calculated De values are indistinguishable, but for other species (B, I, Tc) size appears to have an effect. The B and I data suggest that D, values are lower for larger specimens, while the Tc data suggest the opposite (the larger specimen yielded a larger D,). For many of the trace metals the • larger specimen led to lower De limiting values when detection limits were observed. Thus, from a practical standpoint, for the slow-leaching constituents present in low inventories, greater sensitivity can be achieved by leaching larger samples. v The comparison of leach tests where the original inventory varied from a baseline value to about 10 times baseline is used to differentiate diffusion-controlled from solubility-controlled leaching. The only data set with variable inventory that gives conclusive results is that for U. Increasing the U content of the grout led to much lower D, values. Regardless of the amount of U placed in the grout, its concentration in the leachates was very low, implying solubility control. The scatter ln the Tc and I data in replicates o...

No abstract