Sorption Database for Selected Radionuclides on Sedimentary Rocks in Saline Conditions

Abstract

The Nuclear Waste Management Organization’s (NWMO) Adaptive Phased Management (APM) Technical Program is intent on advancing the understanding of solute migration in deep-seated sedimentary and crystalline groundwater systems. In these systems, matrix porewaters and groundwaters have been observed to contain Na-Ca-Cl brine solutions with total dissolved solids (TDS) ranging between 200 and 400 g/L. A database of sorption distribution coefficients (K_d) for 28 elements (C, Cl, Ca, Ni, Cu, As, Se, Zr, Nb, Mo, Tc, Pd, Ag, Cd, Sn, I, Cs, Eu, Hg, Pb, Bi, Ra, Th, Pa, U, Np, Pu and Am) has been developed as relevant to Canadian sedimentary rocks (shale and limestone) and bentonite clay in saline, near neutral pH environments. The database was compiled following extensive reviews of the open literature and international sorption databases, and has been augmented by measuring sorption values for 15 elements including Ni, Cu, Eu, Pb, As, Se, Zr, Cs, Tc, Pd, Sn, U, Th, Np and Pu with Canadian sedimentary rocks (shale and limestone) and bentonite in a range of high salinity solutions that include a synthetic porewater brine (with a TDS of 275 g/L). The sorption measurements for elements Ni(II), Pb(II), Cu(II), Zr(IV), U(VI), Cs(I), Pd(II), Sn(IV) and Th(IV) were performed by both batch sorption tests and long-term diffusion tests. The sorption measurements for redox sensitive elements As, Se, Tc, U, Np and Pu were conducted under reducing conditions.