425 Predictions of Actinide Solubilities Under near-Field Conditions Expected in the WIPP

Friday, November 6, 2009: 2:40 PM
Hereford (Camino Real Hotel)
Christi D. Leigh , Sandia National Laboratories, Carlsbad, NM
Laurence H. Brush , Sandia National Laboratories, Carlsbad, NM
Yongliang Xiong , Sandia National Laboratories, Carlsbad, NM
The Waste Isolation Pilot Plant (WIPP) is a U.S. Department of Energy (DOE) repository in southeast New Mexico for defense-related transuranic waste.

The WIPP actinide source term model used for performance assessment (PA) comprises dissolved and suspended submodels.  This presentation will describe the solubilities.

Anoxic corrosion of Fe- and Al-base metals and microbial consumption of cellulosic, plastic, and rubber materials will produce gas and create strongly reducing conditions.  The use of MgO to consume microbial CO2 will result in low fCO2 and basic pH.  Th, U, Np, Pu, and Am will speciate as Th(IV), U(IV), Np(IV), Pu(III), and Am(III); or Th(IV), U(VI), Np(V), Pu(IV), and Am(III).

The DOE has developed solubility models for +III, +IV, and +V actinides in brines.  These models include organic ligands.

For the WIPP Compliance Recertification Application PA Baseline Calculations, we calculated actinide solubilities with fCO2 buffered by the brucite-hydromagnesite carbonation reaction, with pH maintained by the brucite dissolution-precipitation reaction, and with organic ligands.  The +III, +IV, and +V solubilities are 1.56 × 10‑6, 5.64 × 10‑8, and 4.07 × 10‑7 M, respectively, in Salado brine; and 1.51 × 10‑6, 6.98 × 10‑8, and 8.75 × 10‑7 M in Castile brine.  The U(VI) solubility estimated for both brines is 1 ´ 10‑3 M.

This research is funded by WIPP programs administered by the U.S. Department of Energy.

Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000.