An analytical model is developed to derive diffusion coefficients from the element profiles of the most mobile glass elements. Congruent dissolution is considered as a transient phenomenon and neglected. In the model, altered glass consists of two sublayers: a gel layer at the solution side, and a diffusion layer at the pristine glass side. In both layers, mobile glass elements diffuse towards the solution, while hydrogen/water diffuses towards the pristine glass.

Fitting the element profiles of boron, sodium and lithium leads to diffusion coefficients in the diffusion layer, which at 90°C are typically of the order of 10-22 m2/s to 10-21 m2/s. At 40°C, these diffusion coefficients are typically a factor ten lower. The diffusion coefficients in the gel are by less than a factor two hundred larger than those in the diffusion layer.

The diffusion coefficients derived from the profiles in this way are used to predict the dissolution behavior. These predictions, for which a constant value (representing congruent dissolution) is added to the predicted diffusive release, agree reasonably well with the measured dissolution data. Those results support the idea that diffusion determines the long term release of glass matrix elements in synthetic interstitial clay water. Flux conservation at the interface between the gel and the diffusion layer is not consistent with a constant (as a function of time) width of the diffusion layer. Some experimental evidence supports that this width increases with time.

An iron phosphate base glass and a simulated Hanford Tank Farm B (TFB) waste loaded iron phosphate glass were reacted under both Product Consistency Test (PCT) and Vapor Hydration Test (VHT) conditions. Solution aliquots were collected following reaction of the TFB glass after the completion of a PCT at 90°C for time periods of 7, 49, 185, 274, and 365 days. Normalized element release patterns for sodium were highest of all the elements present, with values initially decreasing between 7 and 182 days and then increasing thereafter. Normalized release values for phosphorous declined between 49 and 182 days but increased thereafter, whereas calcium contents declined to and remained below the analytical detection limit after 182 days. Normalized element release patterns for Ce, Nd, and Fe were below 0.00045 g/m2 for all time periods tested. Amorphous iron oxide and elongate crystals (possibly apatite?) were noted as alteration products in both long-term PCT and short-term VHT formats.

The VHT samples were reacted at 150°C for time periods of 3, 7, and 35 days for the base glass and 3, 7, 35, 91, 185, and 300 days using the TFB glass. Reacted samples were examined for alteration products, with an emphasis on identifying phases that could potentially occur during geologic disposal. The base glass reacted quickly under the VHT conditions. Phosphorous released from the base glass apparently formed phosphoric acid, which quickly lowered the solution pH to a value of one. The acidic nature of the fluids, in turn, led to an accelerated rate of glass corrosion. The addition of alkali and alkaline earth elements in the TFB glass prevented the low pH excursion seen in the base glass; possibly by ion exchange processes that remove hydrogen ions from solution, sequestering of phosphorous in alteration phases to prevent phosphoric acid formation, or both. This change led to a dramatic decrease in TFB glass reaction rates relative to the base glass composition. Alteration products included an amorphous iron precipitate and several crystalline phases.

We report results from ultra small angle x-ray scattering (USAXS) and transmission electron microscopy (TEM) of dilute silicate colloids that occur naturally in groundwater from the USGS J-13 well, located near the Yucca Mountain Site in Nevada. We also examined a separate sample of this groundwater that had been treated by heating to 90 degrees C in contact with crushed Topopah Spring Tuff from the Yucca Mountain. The USAXS measurements were done at the UNICAT undulator beamline at the Advanced Photon Source at the Argonne National Laboratory. Power-law plots (scattering intensity verses momentum transfer) were fitted to the USAXS data. Colloids in the untreated J-13 groundwater were shown to have a fractal dimension of nearly 3, whereas colloids in the treated groundwater (“EJ-13”) have a dimensionality of approximately 2.4 over a length scale of approximately 3 to 300 nm. Similar power-law plots with dimension 3 characterized concurrent SAXS measurements from aqueous suspensions of Na-montmorillonite and NIST Brick Clay (NBS-67). We attribute these results to the sheet silicate layered structure of the clay colloids present in J-13 well water, montmorillonite, and “brick clay” systems. The differences between EJ-13 and as-received J-13 are perhaps owing to exchange of calcium for sodium with the tuff. Radionuclide incorporation into, adsorption onto, or ion exchange with existing groundwater colloids may promote colloidal transport of radionuclides in groundwater. Such radionuclide-bearing colloids could thereby increase the concentrations of actinides in groundwater and enhance migration into human-accessible aquifers. Our results demonstrate the first application of USAXS to study the physical nature of such groundwater colloids, and represent perhaps one of the most dilute systems ever studied by small angle scatering.

Samples of groundwater are often found to be close to saturation with respect to some minerals. A common approach to modelling of groundwater chemistry is to assume that such minerals control some chemical property of the groundwater. As an example, calcite is often supposed to control the pH value (in addition to concentrations of calcium and carbonate). Here, three models have been used to investigate the control of chemical properties of a groundwater from the Äspö site at the Swedish East Coast.

In the first model, a set of minerals has been selected, in which all minerals are close to saturation with respect to the groundwater. Then an attempt has been made to model formation of the groundwater from rain by letting PHREEQE equilibrate the rain with the minerals.

The second model is similar, but the mineral set used is similar to the one observed at Äspö, and includes also minerals that are far from saturation. To handle the complex situation with numerous minerals and spatial variability, the CRACKER program was used to simulate formation of groundwater from rain.

In the third model, the CRACKER program has been used with the observed groundwater. In the simulation, the water has been disturbed locally, and the relaxation of water chemistry has been studied.

Results from all three kinds of models show that no conclusions on regulation of chemical properties in groundwater can be drawn from saturation properties of minerals. Rather, most properties are controlled by complicated interactions, including spatial variability, irreversible reactions and mixing.

Glass undergoes various corrosion mechanisms during burial. The state of deterioration and corrosion phenomena are deciding factors in the choice of conservation materials and techniques. Among the conservation treatments reviewed for ancient, archaeological glass are pre-treatment storage, cleaning, consolidation of weakened and de-vitrified glass, adhesives for reconstruction, and fill materials for restoration. The most recent materials and techniques used by conservators are presented. The concepts of permanence and reversibility with regard to conservation methods and materials are examined.

An approach, assuming that co-precipitation on the surface of the cement phase dominates ‘sorption’, is proposed and discussed to interpret the sorption behaviour of the cement-complex system. This model takes account of the mineralogical composition of Ordinary Portland Cement (OPC) and assumes that Calcium Silicate Hydrates (C-S-H) dominates the sorption (fixation) of actinide onto OPC and that a small amount of surface co-precipitation of actinides with calcium hydroxide in the structure of C-S-H is formed during the late period of the fixation process. Therefore, this will be referred to as the ‘Surface Co-Precipitation Model (SCPM)’. The modelling results show generally good agreement between the predicted and measured distribution ratios of plutonium, thorium and neptunium, of which the dominant species in high pH solution are neutral species, on OPC.

An important attribute of the high-level waste (HLW) disposal program in the United States (U.S.) is the estimated long life of waste packages (WPs). The outer container of the WP is proposed to be constructed of a nickel-based alloy, Alloy 22 (58Ni-21Cr-14Mo-3W-4Fe), which is highly corrosion resistant. Under nominal conditions of the proposed repository at Yucca Mountain (YM), Nevada, WPs are anticipated to have a long life because of their extremely slow uniform corrosion rate. The technical basis for this expected long life of geological scale is still subject of discussion. In this paper, the NRC Total-system Performance Assessment (TPA) Code is used to evaluate uncertainties associated with the WP performance within a 10,000-year period. Early WP failure may occur due to localized corrosion or high frequency of manufacturing defects. Localized corrosion may occur under mixed salt deposits on the WP surface at temperatures above 100°C. High frequencies of WP juvenile failure are considered to account for the limited industrial experience with Alloy 22 and uncertainty in the long-term performance of Alloy 22 as container material. The localized corrosion and the high frequency of manufacturing defects were simulated with the TPA code by lowering the critical relative humidity for the onset of aqueous corrosion, RHc, and increasing the fraction of initially defective WPs. By sampling RHc from various normal distributions, the mean annual total effective dose equivalent (TEDE) approached 1 mrem/year at 10,000 years. Assuming a fixed fraction of initially defective WPs (1 percent), the mean annual TEDE approached 0.07 mrem/year at 10,000 years.

The passive corrosion rate of Alloy C-22 is exceptionally low in a wide range of aqueous solutions, temperatures and electrochemical potentials. Alloy C-22 contains approximately 22% chromium (Cr) by weight; thus, it forms a Cr-rich passive film in most environments. A study of the composition, thickness and other properties of the passive film was undertaken to better understand the role of the protective oxide in preventing corrosion. In general the oxide film is expected to be a function of solution pH, temperature and applied electrochemical potential. In this work we focus on the oxide films that form at pH=8.

Zirconolite (formally CaZrTi2O7) is a crystalline phase particularly well adapted to actinide immobilization because of its excellent long-term behavior and its good containment capacity. Most of the French studies on zirconolite deal with minor actinides that are mainly responsible for the long-term radiotoxicity of high-level radioactive wastes. For these kind of studies, trivalent minor actinides (Am3+, Cm3+) can be simulated by a lanthanide ion with an ionic radius similar to that of Nd3+. Thus, several materials having the composition Ca1-xNdxZrTi2-xAlxO7 (0 ≤ x ≤ 0.8) were prepared by solid state reaction. These polycristalline materials were first characterized by X-ray diffraction and scanning electron microscopy associated with energy dispersive X-ray analysis in order to determine the nature of the crystalline phases formed. For low neodymium content (x ≤ 0.1), electron spin resonance of Nd3+ ions revealed that a significant proportion of these ions entered into trace amounts of perovskite. Nevertheless, all Ca1-xNdxZrTi2-xAlxO7 samples with x ≤ 0.6 can be considered as almost single phase zirconolite-2M. Structure refinement by the Rietveld method of Ca0.7Nd0.3ZrTi1.7Al0.3O7 showed that Nd3+ and Al3+ ions mainly entered respectively into the calcium site and into the split five-fold coordinated titanium site. Structural characterization of Ca0.3Nd0.7ZrTi1.3Al0.7O7 and Ca0.2Nd0.8ZrTi1.2Al0.8O7 samples confirmed that these compositions led to the crystallization of almost single phase zirconolite-3O, an orthorhombic polytype of zirconolite, whose structure was also refined by the Rietveld method. Results concerning neodymium location in Ca0.7Nd0.3ZrTi1.7Al0.3O7 and Ca0.3Nd0.7ZrTi1.3Al0.7O7 were qualitatively confirmed by optical absorption spectroscopy at low temperature.

Most fission products and actinides in spent nuclear fuel (SNF) are trapped in the uranium dioxide (UO2) crystal structure and cannot escape until the UO2 is oxidized. Oxidation destroys the crystal structure, exposes the radionuclides to groundwater, and creates the potential for dissolution. For a repository in an oxidizing geochemical environment, the potential exists to delay the release of radionuclides for hundreds of thousands to millions of years by using a combination of excess depleted uranium dioxide and iron in the waste package (WP) to locally maintain chemically reducing conditions. This approach limits the rate of oxygen transport to the SNF after WP failure. Alternative methods of oxygen transport to the SNF were investigated, including transport by groundwater, diffusion through air, and diffusion through water.

The dissolution behavior of the ceramic waste form (CWF) is being investigated to support its qualification for disposal in the proposed repository at Yucca Mountain. The CWF consists of sodalite and glass phases and has been consolidated either by hot isostatic pressuring (HIP) or by pressureless consolidation (PC). In this paper we compare the dissolution behavior of the two materials using in MCC-1 type tests at 90°C in a simulated silicate groundwater. The test solutions were periodically exchanged limit feedback effects. The solid surface area to volume ratio was 10 m-1. Five types of samples were tested: (1) HIP CWF, (2) binder glass vitrified by HIP, (3) PC CWF, (4) binder glass vitrified by PC, and HIP sodalite. Boron releases were used to monitor glass dissolution; these were similar in tests with HIP CWF, HIP glass, and PC CWF, but about 3X higher in tests with PC glass. At the end of the tests, the surfaces of the reacted materials were examined with scanning electron microscopy for signs of preferential dissolution. Differences in the dissolution behaviors of the materials are described and the implications of the test results regarding the performance of the CWF in the disposal system are discussed.

We are investigating the evaporation of pore water representative of the designated high-level-nuclear-waste repository at Yucca Mountain, NV to predict the range of brine compositions that may contact waste containers. These brines could form potentially corrosive thin films on the containers and impact their long-term integrity. Here we report the geochemistry of a relatively complex synthetic Topopah Spring Tuff pore water that was progressively evaporated in a series of experiments. The experiments were conducted in a vented vessel in which HEPA filtered air flowed over the 95°C solution. Samples of the evaporating solution and the condensed vapor were taken and analyzed to determine the evolving water chemistry and gas volatility. The final solid was analyzed by X-ray diffraction.

The synthetic Topopah Spring Tuff water evolved towards a complex brine that contained about 45 mol % Cl, 7 mol% NO3, 43 mol% Na, 4 mol % K, and less than 1 mol % each of SO4, Ca, Mg, HCO3 and Si. Trends in the solution data and identification of CaSO4 solids suggest that fluorite, carbonate, sulfate, and Mg-silicate precipitation minimize the corrosion potential of “sulfate type pore water” by removing F, Ca, and Mg during the early stages of evaporation.

Ceramic waste forms based on garnet, (Y,Gd,An‥)3(Al,Ga,An‥)5O12, and zircon, (Zr,An‥)SiO4, where An=U, Pu, Np, Am, and Cm have been proposed for the immobilization of weapons-grade plutonium and other actinides. The lattice capacity of these materials depends on the valence state and ionic radius of the substitute ions. The method of cathodoluminescence (CL) allows the determination of the valence state of different ions (e.g., some transition metals, lanthanides, and actinides) in ceramic. There is a lack of information in the literature concerning CL properties of actinide ions. Cathodoluminescence images and emission spectra of synthetic yttrium-aluminum garnet, gallium-gadolinium garnet and zircon doped with Am were studied. Americium ion has three groups of lines of CL in visible region at 1.6eV, 1.9eV and 2.3eV. The interpretation of these lines has been done using the results of absorption spectra of Am in solution and in crystal LaCl3. There are f-f transitions of Am3+ ion. The ratio of intensities and the structure of these lines depend on the matrix. However, the spectral positions of these lines in two types of garnets and in zircon coincide. It was conclude that these lines can be used for identification of Am3+ ion in different crystalline matrices.

Spent sealed radiation sources containing Ra-226 are immobilised either by the embedding into metal matrix materials or by welding enclosure in metal hermetic capsules. Encapsulation of sources ought provide safe conditions for storage for a long time period. Gaseous products (helium and radon) are generated due to the decay of Ra-226. The gas generation of Ra-226 sources can cause their rupture and consequent leakages of radionuclides. The higher the radioactivity of sources the higher the intensity of gas generation. The pressure of accumulated gas depends on many other factors therefore necessary limitations ought be determined for the encapsulation procedures. The process of gas generation is described herein in order to reveal the conditions of safe immobilisation of radium sources. A simple model describing immobilisation of sources in a metal host is proposed. Both helium and radon generation is considered followed by accumulation of gases near sources. Partial pressures of helium and radon are found depending on time. The diffusion of helium in the metal and decay of Rn-222 are taken into account. It is shown that the pressures of both radon and helium increase until some maximum values, after that the pressures slowly fall down. The maximum radon pressure being not very high is achieved during 65 days after immobilisation whereas helium increases its pressure during an extended period of time lasting for tens of years (137 years in the glass matrix) reaching very high magnitudes for powerful sources (137.5 MPa for a 100 GBq source in a glass capsule). Safe conditions of immobilisation of radium sources can be determined on the base of obtained data.

Field and laboratory studies have been underway at the INEEL and BYU to investigate the effect of atmospheric pressure fluctuations on the migration of contaminant plumes.

In the field, two vadose-zone piezometer nests were instrumented to measure soil-pressures and carbon tetrachloride concentrations at depths of roughly 78-ft, 112-ft., and 150-ft., below ground surface in wells 25-ft. apart. At land surface, a manifold was constructed to systematically rotate from port to port at 15-minute increments of time. Contaminant concentrations were measured at each rotation, and soil pressures were measured at all ports at 15-minute increments. Atmospheric pressures were also recorded. Results showed that atmospheric pressure changes propagated downward lagged in time and dampened in amplitude. Carbon tetrachloride concentrations were observed to decrease with pressure increases at each port, suggesting that pressure increases pushed the plume downward. Increases in concentration were observed with decreases in pressure. Concentrations were observed to change at a port by as much as an order of magnitude. Modeling is underway to assist in isolating the transport mechanisms involved and assist in quantifying the effect of varied pneumatic permeability on pressure propagation.

Laboratory work is underway at BYU to more carefully isolate the mechanisms of diffusive transport and pressure fluctuation in unsaturated conditions. A sealed soil column has been packed with sand and instrumented with a contaminant reservoir at one end and concentration sensor at the other. A mechanical syringe is used to vary the pressure within the tube, and pressure sensors have been emplaced.

An affiliation has been established with researchers at the DOE Sandia laboratory to utilize a novel non-invasive vapor detector in our sealed-column laboratory work.

The dissolution behavior and fission-product release from irradiated thoria-urania fuel was studied by immersing fuel samples in J-13 well water at 90°C. The samples are from the Shippingport Light Water Breeder Reactor and consist of binary solid solutions of (U,Th)O2 with UO2 contents varying from 2.0 to 5.2 Wt.%. The post-irradiation U isotopic composition of the samples used in our experiments is: 87.3% 233U, 10.4% 234U, 1.8% 235U, and <0.5% 238U, 236U, 232U. Burn up values for the samples range from 22.3 to 40.9 megawatt-days per kg-metal. Our tests were performed on polished disks and on crushed and sieved samples in stainless-steel reaction vessels with air-filled head-space. After 196 days of reaction, samples showed no evidence for corrosion at the micrometer scale. Concentration ranges (μgL-1) of key radionuclides in filtered (∼5 nm pore size) leachates were: 0.1 – 15 90Sr, 0.9 – 7.0 99Tc, 0.1 – 35.2 137Cs,<0.2 – 0.8 233U, <0.1 – 0.7 232Th. Concentrations of 237Np, 239Pu, 240Pu and 241Am were all <0.2 μgL-1. The relatively high concentrations of the fission products 90Sr and 137Cs occur early during leaching and decrease for later samplings. Matrix dissolution rates for the irradiated thoria-urania samples range from ∼3x10-3 to <3×10-5 mg m-2day-1 and are at least two orders of magnitude lower than those measured for UO2 spent fuels under similar experimental conditions.

Perovskite-based ceramics ABO3 (A = La or Gd; B = Al or Fe) and a pseudobinary system: LaAlO3 + CaZrTi2O7 are promising matrices for immobilization of actinide fraction of HLW. The ceramic samples containing 241Am, 238Pu or 147Pm were prepared by cold pressing in pellets at 100–300 MPa and sintering at 1300–1500 °C. Leach rates of radionuclides and matrix elements (La, Gd, Al and Fe) from powders were measured using Soxhlet unit. Sintered ceramics in the series: LaAl1-xFexO3 were composed of perovskite phase. Ceramics in the compositional series xLaAlO3 + CaZrTi2O7 (0.4 ≤ x ≤ 6) consisted of perovskite, zirconolite, and baddeleyite at x = 0.4 and x = 0.7, and perovskite and baddeleyite at higher x values. Leach rate of radionuclides and matrix elements from all the ceramics were lower than 10-8 g·cm-2·day.

Halogenation of phenolic moieties is one of the most important reactions between humic substances (HS) and iodine or chlorine. These reactions were studied in order to assess the importance of these interactions with reduced (I−) and oxidised (I2) form of iodine. I− was fixed by the addition of Na2S2O3. After separation of HS and I− by ultrafiltration, no significant uptake was evidenced in the time framework of this study. The consumption of I2(aq) by HS was followed by the decay of I−3 absorbance (351 nm). It comes out that (i) when I− is fixed by Na2S2O3, no interaction with HS could be quantified; (ii) I2(aq) does react with HS but the kinetics cannot be linearalised. This study confirms the significance of iodine-organic matter interactions as a governing process for iodine migration in surface environment. More studies are on going to develop predictive models of iodination kinetics.

In-diffusion experiments for Cs+ and I- in sandstone were performed as a function of ionic strength of porewater ([NaCl] =0.01, 0.51M) and tracer concentration ([Cs1] =7.5E-5, 1.5E-2M) together with the measurements of the fundamental properties of sandstone, and apparent diffusivities (Da) and rock capacity factors (α) for Cs+ were obtained. The obtained Da-values for Cs+ were scarcely dependent on [NaCl], but increased with increasing [Cs+]. This trend is consistent with that of α-values, indicating that although effective diffusivity and distribution coefficient scarcely depend on [NaCl], those depend on [Cs+]. The concentration profiles of I- were all in breakthrough. Although this indicates that I- diffusion is faster than that of Cs+, the concentration profiles of I- may have been lower than those for blank samples.

Results on the chemical behavior of Fe(0) and UO2(s), as well as the interaction between fresh and corroded iron with U(VI) in simulated cement contacting alkaline solution are reported. Batch experiments were conducted under anoxic conditions at different alkalinities and salt concentrations to investigate: (a) the corrosion of iron foils (b) the U(VI) removal by fresh, aged and pre-treated (with FeS or Fe3O4 layers) iron surfaces in a simulated cement pore fluid, (c) the dissolution rates of newly reduced UO2.00 slices in simulated cement pore fluid and KOH solutions (pH 12.7) and (d) the isotope exchange reactions between dissolved 235U(VI) and 238UO2(s). The reacted iron and UO2(s) surfaces were analyzed by X-ray diffraction (XRD), scanning electron microscopy-energy dispersive spectra (SEM-EDS), laser Raman spectroscopy and X-ray photoelectron, spectroscopy (XPS).