Validity of batch sorption data to describe selenium transport through unsaturated tuff

As part of project for characterizing Yucca Mt. as a potential site for high-level nuclear waste respository, we used UFA {trademark} technology (centifuge-induced flow) to directly measure selenite retardation coefficients and hydraulic conductivity under unsaturated conditions on two tuff samples from Yucca Mt. Retardation factor for the selenite species was 2.5 in both Yucca Mt. vitric tuff at 62.6% saturation and zeolitic nonwelded tuff from G-tunnel at 52.8% saturation. For these column experiments, we prepared a solution, using J-13 well water from NTS, with a Se conc. of 1.31 mg/L(ppM). The retardation factor of 2.5 measured for both tuffs translates into a sorption distribution coefficient K{sub d} of 0.9 mL/g for the vitric tuff and 0.8 mL/g for the zeolitic tuff. For batch sorption experiments, using the same zeolitic tuff as for the column experiments and solutions of J-13 well water with a Se conc. of 1.1 mg/L(ppM), the average K{sub d} was determined to be 0.1{+-}0.2 mL/g. Given the small K{sub d} values for Se sorption, general agreement between batch and column measurements (obtained under unsaturated conditions) was observed. Unsaturated hydraulic conductivities during the experiments were 2.5x10{sup -8} cm/s for the Yucca Mt. vitric tuff and 1.2x10{sup -8} cm/s for the zeolitic nonwelded tuff from G- tunnel

Effect of natural organic materials on cadmium and neptunium sorption

In a batch sorption study of the effect of naturally occurring organic materials on the sorption of cadmium and neptunium on oxides and tuff surfaces, the model sorbents were synthetic goethite, boehmite, amorphous silicon oxides, and a crushed tuff material from Yucca Mountain, Nevada. An amino acid, 3-(3,4-dihydroxypheny)-DL-alanine (DOPA), and an aquatic-originated fulvic material, Nordic aquatic fulvic acid (NAFA), were used as model organic chemicals. Sorption isotherm results showed that DOPA sorption followed the order aluminum oxide > iron oxide > silicon oxide and that the amount of DOAP sorption for a given sorbent increased as the solution pH was raised. The sorption of cadmium and neptunium on the iron oxide was about ten times higher than that on the aluminum oxide. The sorption of cadmium and neptunium on natural tuff material was much lower than that on aluminum and iron oxides. The sorption of cadmium on iron and aluminum oxides was found to be influenced by the presence of DOPA, and increasing the amount of DOPA coating resulted in higher cadmium sorption on aluminum oxide. However, for iron oxide, cadmium sorption decreased with increasing DOPA concentration. The presence of the model organic materials DOPA and NAFA did not affect the sorption of neptunium on tuff material or on the iron and aluminum oxides. Spectroscopic results indicate that cadmium complexes strongly with DOPA. Therefore, the effect of the organic material, DOPA, on the cadmium sorption is readily observed. However, neptunium is possibly complexed weakly with organic material. Thus, DOPA and NAFA have little effect on neptunium sorption on all sorbents selected for study

Selenite transport in unsaturated tuff from Yucca Mountain

Direct measurements of unsaturated selenite retardation coefficients and unsaturated hydraulic conductivity were obtained on two tuff samples from Yucca Mountain using the UFA{trademark} technology. The retardation factor for the selenite species was only 2.5 in both Yucca Mountain vitric member at 62.6% saturation and zeolitized nonwelded tuff from G-tunnel at 52.8% saturation with respect to J-13 well water from the Nevada Test Site contaminated with selenium at 1.31 mg/l (ppm). In batch tests on the same material using 1.2 mg/l (ppm), the average K{sub d} was determined to be 13, giving retardation factors higher than the UFA column breakthrough tests by an order of magnitude. The difference could result from preferential flow paths in the UFA column as might occur in the field or differences in residence times between the two types of test. The unsaturated hydraulic conductivities during the experiments were 2.49 {times} 10{sup {minus}8} cm/s for the Yucca Mountain vitric member and 1.16 {times} 10{sup {minus}8} cm/s for the zeolitized nonwelded tuff

Sorption Behavior of Strontium-85 Onto Colloids of Silica and Smectite

Strontium-90 is one of the sizable radioactive contaminants found in DP Canyon at Los Alamos, New Mexico. Radioactive surveys found the {sup 90}Sr is present in surface and groundwater in DP Canyon and Los Alamos Canyon. Colloids may influence the transport of this radionuclide in surface water and groundwater environments in both canyons. In this study, we investigated the sorption/desorption behavior of Sr on colloids of smectite and silica. Laboratory batch sorption experiments were conducted using {sup 85}Sr as a surrogate to {sup 90}Sr. Groundwater, collected from DP Canyon and from Well J-13 at Yucca Mountain, Nevada, and deionized water were used in this study. Our results show that 92% to 100% of {sup 85}Sr was rapidly adsorbed onto smectite colloids in all three waters. The concentrations of Ca{sup 2+} significantly influence the adsorption of {sup 85}Sr onto silica colloids. Desorption of {sup 85}Sr from smectite colloids is much slower than the sorption process. Desorption of {sup 85}Sr from silica colloids was rapid in DP groundwater and slow using J-13 groundwater and deionized water

Radionuclide sorption in Yucca Mountain tuffs with J-13 well water: Neptunium, uranium, and plutonium. Yucca Mountain site characterization program milestone 3338

We studied the retardation of actinides (neptunium, uranium, and plutonium) by sorption as a function of radionuclide concentration in water from Well J-13 and of tuffs from Yucca Mountain. Three major tuff types were examined: devitrified, vitric, and zeolitic. To identify the sorbing minerals in the tuffs, we conducted batch sorption experiments with pure mineral separates. These experiments were performed with water from Well J-13 (a sodium bicarbonate groundwater) under oxidizing conditions in the pH range from 7 to 8.5. The results indicate that all actinides studied sorb strongly to synthetic hematite and also that Np(V) and U(VI) do not sorb appreciably to devitrified or vitric tuffs, albite, or quartz. The sorption of neptunium onto clinoptilolite-rich tuffs and pure clinoptilolite can be fitted with a sorption distribution coefficient in the concentration range from 1 X 10{sup -7} to 3 X 10{sup -5} M. The sorption of uranium onto clinoptilolite-rich tuffs and pure clinoptilolite is not linear in the concentration range from 8 X 10{sup -8} to 1 X 10{sup -4} M, and it can be fitted with nonlinear isotherm models (such as the Langmuir or the Freundlich Isotherms). The sorption of neptunium and uranium onto clinoptilolite in J-13 well water increases with decreasing pH in the range from 7 to 8.5. The sorption of plutonium (initially in the Pu(V) oxidation state) onto tuffs and pure mineral separates in J-13 well water at pH 7 is significant. Plutonium sorption decreases as a function of tuff type in the order: zeolitic > vitric > devitrified; and as a function of mineralogy in the order: hematite > clinoptilolite > albite > quartz

Preparation of the First Shipment of Transuranic Waste by the Los Alamos National Laboratory: A Rest Stop on the Road to WIPP

The Los Alamos National Laboratory (LANL) achieved a national milestone on the road to shipping transuranic (TRU) waste to the Waste Isolation Pilot Plant (WIPP) when it received certification authority on September 12, 1997. Since that time, LANL has been characterizing a non-mixed TRU waste stream and preparing shipments of this TRU waste for disposal in the WIPP. The paper describes the TRU waste identified as waste stream TA-55-43 Lot No. 01 from LANL Technical Area-55 and the process used to determine that it does not contain hazardous waste regulated by the Resource Conservation Recovery Act (RCRA) or the New Mexico Hazardous Waste Act (HWA). The non-mixed determination is based on the acceptable knowledge (AK) characterization process, which clearly shows that the waste does not exhibit any RCRA characteristics nor meet any RCRA listing descriptions. LANL has certified TRU waste from waste stream TA-55-43 Lot No. 01 and is prepared to certify additional quantities of TRU waste horn other non-mixed TRU waste streams. Assembly and preparation of AK on the processes that generated TRU waste is recognized as a necessary part of the process for having waste ready for shipment to the WIPP