Howard L. Anderson

Reactive barriers for 137Cs retention

137Cs was dispersed globally by cold war activities and, more recently, by the Chernobyl accident. Engineered extraction of 137Cs from soils and groundwaters is exceedingly difficult. Because the half-life of 137Cs is only 30.2 years, remediation might be more effective (and less costly) if 137Cs bioavailability could be demonstrably limited for even a few decades by use of a reactive barrier. Essentially permanent isolation must be demonstrated in those few settings where high nuclear level wastes contaminated the environment with 135Cs (half-life 2.3 x 10(6) years) in addition to 137Cs. Clays are potentially a low-cost barrier to Cs movement, though their long-term effectiveness remains untested. To identify optimal clays for Cs retention, Cs desorption was measured for five common clays: Wyoming Montmorillonite (SWy-1), Georgia Kaolinites (KGa-1 and KGa-2), Fithian Illite (F-Ill), and K-Metabentonite (K-Mbt). Exchange sites were pre-saturated with 0.16 M CsCl for 14 days and readily exchangeable Cs was removed by a series of LiNO3 and LiCl washes. Washed clays were then placed into dialysis bags and the Cs release to the deionized water outside the bags measured. Release rates from 75 to 139 days for SWy-1, K-Mbt and F-Ill were similar; 0.017% to 0.021% sorbed Cs released per day. Both kaolinites released Cs more rapidly (0.12% to 0.05% of the sorbed Cs per day). In a second set of experiments, clays were Cs-doped for 110 days and subjected to an extreme and prolonged rinsing process. All the clays exhibited some capacity for irreversible Cs uptake. However, the residual loading was greatest on K-Mbt (approximately 0.33 wt.% Cs). Thus, this clay would be the optimal material for constructing artifical reactive barriers.

Anion Scavengers for Low-Level Radioactive Waste Repository Backfills

Minimization of 129/− and 99 TcO4 − transport to the biosphere is critical to the success of low level radioactive waste (LLRW) storage facilities. Here we experimentally identify and classify potential sorbent materials for inclusion in LLRW backfills. For low pH conditions (pH 4-5), Cu-sulfides and possibly imogolite-rich soils provide Kds (distribution coefficients) of roughly 103 mL g−1 for /−, and 102 mL g−1 for TcO4 −. At near neutral pH, hydrotalcites, Cu-oxides, Cu-sulfides, and lignite coal possess Kds on the order of 102 mL g−1 for both /− and TcO4 −. At high pH (pH>10), such as might occur in a cementitious LLRW facility, calcium monosulfate aluminate Kds are calculated to be roughly 102 mL g−1 for both both /− and TcO4 −.

Chemical evolution of leaked high-level liquid wastes in Hanford soils

A number of Hanford tanks have leaked high level radioactive wastes (HLW) into the surrounding unconsolidated sediments. The disequilibrium between atmospheric C0{sub 2} or silica-rich soils and the highly caustic (pH > 13) fluids is a driving force for numerous reactions. Hazardous dissolved components such as {sup 133}Cs, {sup 79}Se, {sup 99}Tc may be adsorbed or sequestered by alteration phases, or released in the vadose zone for further transport by surface water. Additionally, it is likely that precipitation and alteration reactions will change the soil permeability and consequently the fluid flow path in the sediments. In order to ascertain the location and mobility/immobility of the radionuclides from leaked solutions within the vadose zone, the authors are currently studying the chemical reactions between: (1) tank simulant solutions and Hanford soil fill minerals; and (2) tank simulant solutions and C0{sub 2}. The authors are investigating soil-solution reactions at: (1) elevated temperatures (60--200 C) to simulate reactions which occur immediately adjacent a radiogenically heated tank; and (2) ambient temperature (25 C) to simulate reactions which take place further from the tanks. The authors studies show that reactions at elevated temperature result in dissolution of silicate minerals and precipitation of zeolitic phases. At 25 C, silicate dissolution is not significant except where smectite clays are involved. However, at this temperature CO{sub 2} uptake by the solution results in precipitation of Al(OH){sub 3} (bayerite). In these studies, radionuclide analogues (Cs, Se and Re--for Tc) were partially removed from the test solutions both during high-temperature fluid-soil interactions and during room temperature bayerite precipitation. Altered soils would permanently retain a fraction of the Cs but essentially all of the Se and Re would be released once the plume was past and normal groundwater came in contact with the contaminated soil. Bayerite, however, will retain significant amounts of all three radionuclides.

A Preliminary Assessment of IE-911 Column Pretreatment Options

The use of a novel molecular sieve, IE-911 is one technology that may be used to recover cesium from liquid radioactive wastes at Savannah River and other DOE sites. Preliminary column tests performed at Savannah River and Oak Ridge National Laboratories indicated that ion exchange columns packed with this material had a potential for plugging. A Two-pronged approach was taken to assess this issue. The key to using this material is that it must be pretreated to neutralize the acid content imparted by the manufacturing process. In addition to duplicating the processes that had historically led to column plugging, we also investigated a variety of other pretreatment options. In general, it was found that when problems arose, they could be traced to the accumulation of particulate matter at the inlet end of a column. Mass-fouling of the pore spaces in the column was not observed. Both the Ie-911 and a hydrous Nb oxided were implicated. However, several column tests were also performed in which plugging was not observed. Based on these results it was concluded that a

Nanofiltration treatment options for thermoelectric power plant water treatment demands.

.......................................................................................................................................3 ACKNOWLEDGEMENTS ......................................................................................................................5 TABLE OF CONTENTS ........................................................................................................................7 LIST OF TABLES ................................................................................................................................9 List of Figures ................................................................................................................................11

pH modification for silica control

ABSTRACT Lowering solution pH slows the polymerization of silica and formation of silica scale. In batch systems, lowering the pH of approximately 200 ppm silica solutions prevents scale formation for over 300 h. Silica scale forms most quickly near pH 8. Solutions with pH 3.6–3.7 can maintain silica levels of 1,000–3,000 ppm for roughly 90 h. Bench-scale membrane testing showed that silica scale formation lag times of approximately 72 h were achievable after lowering the pH to 4.5–4.7, which might allow flushing of silica-laden solutions through, for example, flow reversal, before scale formation occurs during water treatment.

Corrosion of Uranium in Desert Soil, with Application to GCD Source Term M

Uranium fragments from the Sandia Sled Track were studied as analogues for weapons components and depleted uranium buried at the Greater Confinement Disposal (GCD) site in Nevada. The Sled Track uranium fragments originated as weapons mockups and counterweights impacted on concrete and soil barriers, and experienced heating and fragmentation similar to processes thought to affect the Nuclear Weapons Accident Residues (NWAR) at GCD. Furthermore, the Sandia uranium was buried in unsaturated desert soils for 10 to 40 years, and has undergone weathering processes expected to affect the GCD wastes. Scanning electron microscopy, X-ray diffraction and microprobe analyses of the fragments show rapid alteration from metals to dominantly VI-valent oxy-hydroxides. Leaching studies of the samples give results consistent with published U-oxide dissolution rates, and suggest longer experimental periods (ca. 1 year) would be required to reach equilibrium solution concentrations. Thermochemical modeling with the EQ3/6 code indicates that the uranium concentrations in solutions saturated with becquerelite could increase as the pore waters evaporate, due to changes in carbonate equilibria and increased ionic strength.