R. Matthew Asmussen

Getters for improved technetium containment in cementitious waste forms

A cementitious waste form, Cast Stone, is a possible candidate technology for the immobilization of low activity nuclear waste (LAW) at the Hanford site. This work focuses on the addition of getter materials to Cast Stone that can sequester Tc from the LAW, and in turn, lower Tc release from the Cast Stone. Two getters which produce different products upon sequestering Tc from LAW were tested: Sn(II) apatite (Sn-A) that removes Tc as a Tc(IV)-oxide and potassium metal sulfide (KMS-2) that removes Tc as a Tc(IV)-sulfide species, allowing for a comparison of stability of the form of Tc upon entering the waste form. The Cast Stone with KMS-2 getter had the best performance with addition equivalent to ∼0.08wt% of the total waste form mass. The observed diffusion (Dobs) of Tc decreased from 4.6±0.2×10-12cm2/s for Cast Stone that did not contain a getter to 5.4±0.4×10-13cm2/s for KMS-2 containing Cast Stone. It was found that Tc-sulfide species are more stable against re-oxidation within getter containing Cast Stone compared with Tc-oxide and is the origin of the decrease in Tc Dobs when using the KMS-2.

Silver-based getters for 129I removal from low-activity waste

Abstract A prominent radionuclide of concern in nuclear wastes, 129I, is present in low-activity wastes (LAW) at the Hanford site. Several Ag-containing materials were tested as immobilization agents, or “getters”, for I (as iodide, I−) removal from deionized (DI) water and a liquid LAW simulant: Ag impregnated activate carbon (Ag–C), Ag exchanged zeolite (Ag–Z), and argentite. In anoxic batch experiments with DI water, the Ag–C and argentite were most effective, with maximum Kd values of 6.2 × 105 mL/g for the Ag–C and 3.7 × 105 mL/g for the argentite after 15 days. Surface area and Ag content were found to influence the performance of the getters in DI water. In the anoxic batch experiments with LAW simulant, Ag–Z vastly outperformed the other getters with Kd values of 2.2 × 104 mL/g at 2 h, which held steady until 15 days, compared with 1.8 × 103 mL/g reached at 15 days by the argentite. All getters were stable over long periods of time (i.e. 40 days) in DI water, while the Ag–Z and argentite were also stable in the LAW simulant. Ag–Z was found to have consistent I removal upon crushing to a smaller particle size and in the presence of O2, making it a strong candidate for the treatment of LAW containing I.

Silver-functionalized silica aerogels and their application in the removal of iodine from aqueous environments

One of the key challenges for radioactive waste management is the efficient capture and immobilization of radioiodine, because of its radiotoxicity, high mobility in the environment, and long half-life (t1/2 = 1.57 × 107 years). Silver-functionalized silica aerogel (AgAero) represents a strong candidate for safe sequestration of radioiodine from various nuclear waste streams and subsurface environments. Batch sorption experiments up to 10 days long were carried out in oxic and anoxic conditions in both deionized water (DIW) and various Hanford Site Waste Treatment Plant (WTP) off-gas condensate simulants containing from 5 to 10 ppm of iodide (I-) or iodate (IO3-). Also tested was the selectivity of AgAero towards I- in the presence of other halide anions. AgAero exhibited fast and complete removal of I- from DIW, slower but complete removal of I- from WTP off-gas simulants, preferred removal of I- over Br- and Cl-, and it demonstrated ability to remove IO3- through reduction to I-.

Element mobilization and immobilization from carbonate rocks between CO 2 storage reservoirs and the overlying aquifers during a potential CO 2 leakage

Despite the numerous studies on changes within the reservoir following CO2 injection and the effects of CO2 release into overlying aquifers, little or no literature is available on the effect of CO2 release on rock between the storage reservoirs and subsurface. This is important, because the interactions that occur in this zone between the CO2 storage reservoir and the subsurface may have a significant impact on risk analysis for CO2 storage projects. To address this knowledge gap, relevant rock materials, temperatures and pressures were used to study mineralogical and elemental changes in this intermediate zone. After rocks reacted with CO2-acidified 0.01 M NaCl, liquid analysis showed an increase of major elements (e.g., Ca and Mg) and variable concentrations of potential contaminants (e.g., Sr and Ba); lower aqueous concentrations of these elements were observed in N2 control experiments, likely due to differences in pH between the CO2 and N2 experiments. In experiments with As/Cd and/or organic spikes, representing potential contaminants in the CO2 plume originating in the storage reservoir, most or all of these contaminants were removed from the aqueous phase. SEM and Mössbauer spectroscopy results showed the formation of new minerals and Fe oxides in some CO2-reacted samples, indicating potential for contaminant removal through mineral incorporation or adsorption onto Fe oxides. These experiments show the interactions between the CO2-laden plume and the rock between storage reservoirs and overlying aquifers have the potential to affect the level of risk to overlying groundwater, and should be considered during site selection and risk evaluation.