NORTH-AMERICAN STUDIES ON LEAD MOBILITY IN SIMULATED NUCLEAR WASTE REPOSITORY ENVIRONMENTS

The potential mobility of lead, a candidate waste package material, un der conditions simulating possible U.S. and Canadian nuclear waste dis posal-vault environments, was investigated by conducting a series of c orrosion and sorption experiments combined with geochemical calculatio ns. The corrosion rates of lead in these environments never exceeded 4 0 mu m/yr. The corrosion products were moderately soluble in the host geologies and groundwaters. Apparent diffusion coefficients for lead r anged from 10(-15) to 10(-11) m(2)/s, and the distribution coefficient s ranged from 95 to 378 mL/g. These results indicate both low mobility and high sorption behavior in these environments. Because these value s for lead are in the same range as those of some radionuclides, the t ransport time for both lead and radionuclides are expected to be simil ar. Lead would be expected to react strongly with natural rock materia ls in the far field in both geologies. The low corrosion rate of lead and low rate of transport of corrosion products, together with lead's excellent gamma shielding properties that reduce groundwater radiolysi s, are properties warranting consideration for enhanced disposal perfo rmance of waste packages in both the U.S. and Canada.