Stability of High-Level Waste Forms

The objective of the proposed effort is to use a new approach to develop solution models of complex waste glass systems and spent fuel that are predictive with regard to composition, phase separation, and volatility. The effort will also yield thermodynamic values for waste components that are fundamentally required for corrosion models used to predict the leaching/corrosion behavior for waste glass and spent fuel material. This basic information and understanding of chemical behavior can subsequently be used directly in computational models of leaching and transport in geologic media, in designing and engineering waste forms and barrier systems, and in prediction of chemical interactions

Phase equilibria of advanced technology uranium silicide-based nuclear fuel

The phases in uranium-silicide binary system were evaluated in regards to their stabilities, phase boundaries, crystal structures, and phase transitions. The results from this study were used in combination with a well assessed literature to optimize the U-Si phase diagram using the CALPHAD method. A thermodynamic database was developed, which could be used to guide nuclear fuel fabrication, could be incorporated into other nuclear fuel thermodynamic databases, or could be used to generate data required by fuel performance codes to model fuel behavior in normal or off-normal reactor operations. The U3Si2 and U3Si5 phases were modeled using the Compound Energy Formalism model with 3 sublattices to account for the variation in composition. The crystal structure used for the USi phase was the tetragonal with an I4/mmm space. Above 450°C, the U3Si5 phase was modeled. The composition of the USi2 phase was adjusted to USi1.84. The calculated invariant reactions and the enthalpy of formation for the stoichiometric phases were in agreement with experimental data

Compatibility/Stability Issues in the Use of Nitride Kernels in LWR TRISO Fuel

The stability of the SiC layer in the presence of free nitrogen will be dependent upon the operating temperatures and resulting nitrogen pressures whether it is at High Temperature Gas-Cooled Reactor (HTGR) temperatures of 1000-1400 C (coolant design dependent) or LWR temperatures that range from 500-700 C. Although nitrogen released in fissioning will form fission product nitrides, there will remain an overpressure of nitrogen of some magnitude. The nitrogen can be speculated to transport through the inner pyrolytic carbon layer and contact the SiC layer. The SiC layer may be envisioned to fail due to resulting nitridation at the elevated temperatures. However, it is believed that these issues are particularly avoided in the LWR application. Lower temperatures will result in significantly lower nitrogen pressures. Lower temperatures will also substantially reduce nitrogen diffusion rates through the layers and nitriding kinetics. Kinetics calculations were performed using an expression for nitriding silicon. In order to further address these concerns, experiments were run with surrogate fuel particles under simulated operating conditions to determine the resulting phase formation at 700 and 1400 C

Deep Burn Develpment of Transuranic Fuel for High-Temperature Helium-Cooled Reactors - July 2010

The DB Program Quarterly Progress Report for April - June 2010, ORNL/TM/2010/140, was distributed to program participants on August 4. This report discusses the following: (1) TRU (transuranic elements) HTR (high temperature helium-cooled reactor) Fuel Modeling - (a) Thermochemical Modeling, (b) 5.3 Radiation Damage and Properties; (2) TRU HTR Fuel Qualification - (a) TRU Kernel Development, (b) Coating Development, (c) ZrC Properties and Handbook; and (3) HTR Fuel Recycle - (a) Recycle Processes, (b) Graphite Recycle, (c) Pyrochemical Reprocessing - METROX (metal recovery from oxide fuel) Process Development

Summary Report Documenting Status of the Rare Earth Oxide Investigation

The goal of this work is to enhance the understanding of ceramic nuclear fuel thermochemistry through a coordinated modeling and experimental approach. This work supports the Advanced Fuels Campaign Feedstock and Fabrication Technology R&D Program and is focused on the following tasks: (1) use existing compound energy formalism-based models to support Los Alamos National Laboratory (LANL) fuel development activities, (2) assess rare earth (RE) oxide systems and begin development of thermochemical representations of U-RE-O systems, and (3) develop a U-Ce-O thermochemical model for the fluorite-structure phase. In support of the experimental efforts at the LANL, an assessment of temperature-oxygen potential conditions for preparing stoichiometric U{sub 1-y}Ce{sub y}O{sub 2} at relatively low values of y (< 0.4) was performed. There is significant agreement in the literature that both the independent urania and ceria phases, and the urania-ceria solution phase are stoichiometric at oxygen-to-metal (O/M) ratios of 2 at 850 C and an oxygen potential of -368 kJ/mol. The oxygen potential value is obtained at a partial pressure of CO/CO{sub 2} ratio of unity at 1 bar total pressure. This information was successfully applied in thermogravimetric analysis experimental efforts at LANL investigating urania, ceria, and blended powders of the two oxides. Data reported in the literature for oxygen potential-temperature-composition for U{sub 1-y}Ce{sub y}O{sub 2-x} was extracted manually and used to generate a data file. Assessment of the data showed both wide error ranges within sets of data as well as inconsistencies between data sets of different investigators. Figure 1, a plot of the extracted data, illustrates the paucity of experimental data with respect to composition, temperature, and O:M space. For example, as shown in Figure 1, the data as a function of temperature are limited to the range 873 K to 1273 K and higher O:M ratios. Furthermore, the compositions studied have focused on higher uranium fractions and very little work has been done at corresponding lower O:M ratios. A compound energy formalism representation has been developed for the (U,Ce)O{sub 2+x} utilizing developed models for the UO{sub 2+x} from Gueneau et al. (2002) and CeO{sub 2-x} of Zinkevich et al. (2006). A three sublattice approach was used to allow for uranium of valences up to +6. Vacancies are considered only on the anion sites. The ionic species are introduced in the sublattice as follows: (U{sup 6+},U{sup 4+},U{sup 3+},Ce{sup 4+},Ce{sup 3+}){sub 1}(O{sup 2-},Va){sub 2}(O{sup 2-},Va){sub 1} Gibbs free energy expressions for each of the derived constituents can be determined from standard state values. Optimizations using all available thermochemical information, e.g., oxygen potentials and phase equilibria, can thus yield the necessary corrections to the Gibbs free energies for the non-standard constituents and derived interaction parameters (L values). While a model is available that includes all the interactions separately among the urania and ceria species, determination of any possible non-ideal interactions between the urania and ceria cations requires optimization from first principles (if possible) and experimental data for the system. Utilizing the best set of data for oxygen potential-temperature-composition for U{sub 1-y}Ce{sub y}O{sub 2-x} the FactSage thermochemical computational software code was used to optimize the system for selected Gibbs free energy functions and interaction parameters. While it was possible to obtain optimized solutions, the resulting parameters did not allow adequate reproduction of the data, as can be seen in Fig. 2. As noted above, the quality of the data among the various investigators is poor and that is a likely cause for the lack of a reasonable representation. The focus for the remainder of the fiscal year will be twofold. There will be collaboration with LANL on the collection of experimental data to resolve inconsistencies in the literature data and to fill some of the gaps in the experimental space. Next the thermochemical data will be used to optimize model parameters in an attempt to achieve a better fit to the data, in particular at higher ceria concentrations and at the lower and upper range of O:M

Deep Burn: Development of Transuranic Fuel for High-Temperature Helium-Cooled Reactors- Monthly Highlights November 2010

During FY 2011 the DB Program will report Highlights on a monthly basis, but will no longer produce Quarterly Progress Reports. Technical details that were previously included in the quarterly reports will be included in the appropriate Milestone Reports that are submitted to FCRD Program Management. These reports will also be uploaded to the Deep Burn website. The Monthly Highlights report for October 2010, ORNL/TM-2010/300, was distributed to program participants on November 29, 2010. This report discusses the following: (1) Thermochemical Data and Model Development; (2) TRU (transuranic elements) TRISO (tri-structural isotropic) Development - (a) TRU Kernel Development, (b) Coating Development; (3) LWR Fully Ceramic Fuel - (a) FCM Fabrication Development, (b) FCM Irradiation Testing

Coated Particle Fuel and Deep Burn Program Monthly Highlights April 2011

The baseline change proposal BCP-FCRD-11026 submitted to change the due date for M21AF080202 'Demonstrate fabrication of Transuranic kernels of Plutonium-239/3.5at%Neptunium-237 using newly installed glove box facilities in ORNL 7930 hot cell complex' from 4/25/11 to 3/30/12 was approved this month. During FY 2011 the CP & DB Program will report Highlights on a monthly basis, but will no longer produce Quarterly Progress Reports. Technical details that were previously included in the quarterly reports will be included in the appropriate Milestone Reports that are submitted to FCRD Program Management. These reports will also be uploaded to the Deep Burn website. The Monthly Highlights report for March 2011, ORNL/TM-2011/96, was distributed to program participants on April 8, 2011. As reported previously, the final Quarterly for FY 2010, Deep Burn Program Quarterly Report for July - September 2010, ORNL/TM-2010/301, was announced to program participants and posted to the website on December 28, 2010. This report discusses the following: (1) Thermochemical Data and Model Development - (a) Thermochemical Modeling, (b) Thermomechanical Behavior, (c) Actinide and Fission Product Transport, (d) Radiation Damage and Properties; (2) TRU (transuranic elements) TRISO (tri-structural isotropic) Development - (a) TRU Kernel Development, (b) Coating Development; (3) Advanced TRISO Applications - Metal Matrix Fuels for LWR; (4) LWR Fully Ceramic Fuel - (a) FCM Fabrication Development, (b) FCM Irradiation Testing; (5) Fuel Performance and Analytical Analysis - Fuel Performance Modeling; and (6) ZrC Properties and Handbook - Properties of ZrC

Deep Burn: Development of Transuranic Fuel for High-Temperature Helium-Cooled Reactors- Monthly Highlights September 2010

The DB Program monthly highlights report for August 2010, ORNL/TM-2010/184, was distributed to program participants by email on September 17. This report discusses: (1) Core and Fuel Analysis - (a) Core Design Optimization in the HTR (high temperature helium-cooled reactor) Prismatic Design (Logos), (b) Core Design Optimization in the HTR Pebble Bed Design (INL), (c) Microfuel analysis for the DB HTR (INL, GA, Logos); (2) Spent Fuel Management - (a) TRISO (tri-structural isotropic) repository behavior (UNLV), (b) Repository performance of TRISO fuel (UCB); (3) Fuel Cycle Integration of the HTR (high temperature helium-cooled reactor) - Synergy with other reactor fuel cycles (GA, Logos); (4) TRU (transuranic elements) HTR Fuel Qualification - (a) Thermochemical Modeling, (b) Actinide and Fission Product Transport, (c) Radiation Damage and Properties; (5) HTR Spent Fuel Recycle - (a) TRU Kernel Development (ORNL), (b) Coating Development (ORNL), (c) Characterization Development and Support, (d) ZrC Properties and Handbook; and (6) HTR Fuel Recycle - (a) Graphite Recycle (ORNL), (b) Aqueous Reprocessing, (c) Pyrochemical Reprocessing METROX (metal recovery from oxide fuel) Process Development (ANL)

Communication: First-Principles Evaluation of Alkali Ion Adsorption and Ion Exchange in Pure Silica Lta Zeolite (Vol 149, 131102, 2018)

Using first-principles calculations, we studied the adsorption of alkali ions in pure silica Linde Type A (LTA) zeolite. The probability of adsorbing alkali ions from solution and the driving force for ion exchange between Na+ and other alkali ions at the different adsorption sites were analyzed. From the calculated ion exchange isotherms, we show that it is possible to exchange Na+ with K+ and Rb+ in water, but that is not the case for systems in a vacuum. We also demonstrate that a solvation model should be used for the accurate representation of ion exchange in an LTA and that dispersion interactions should be introduced with care

COIVF-9 %Ob 6Y-- N EAR-N ET-SHAPE FABRICATION BY FORCED-FLOW, THERMAL-G RAD1 ENT CVI*

Forced-flow, thermal gradient chemical vapor infiltration (FCVI) has been developed for the rapid densification of ceramic matrix composites. For preforms of >3 mm thickness FCVl can produce a near-net-shape part in less than one day as opposed to isothermal, isobaric CVI which requires several weeks to densify such a component. Efforts at ORNL and elsewhere have resulted in capability to produce prototypical thick-walled heat exchanger tubes and turbine disk blanks. This paper will review recent modeling and experimental efforts related to the FCVl of cylindrical forms