One of the current priorities within the Department of Energy (DOE) complex is the stabilization, packaging and storage of plutonium-bearing materials. The packaging is key to the safe long-term handling and storage of these materials. Packaging consists of placing the stabilized materials into a set of two nested stainless steel containers. Each container is seal-welded, providing double containment of the plutonium materials. The outer container is designated as the primary barrier to the release of the materials to the environment. An initial, full scope diagnostic analysis of the equipment, welding materials / consumables and process conditions identified the primary cause of the porosity to be related to geometry at the root of the weld joint preparation. A volume of gas is trapped between the advancing weld puddle and the start of the weld, at weld tie-in, and incorporated into the weld during puddle solidification. Figure 5 illustrates the basic geometric conditions contributing to the porosity. This paper describes the efforts to analyze and understand / quantify the interaction between the weld-joint geometry and formation of porosity.

The transformation of gibbsite to boehmite in strongly caustic solutions was studied using quantitative X-ray diffraction, Fourier transform infrared spectroscopy, and transmission electron microscopy techniques. Under hydrothermal conditions we identified two transformation mechanisms; dehydration and in-situ nucleation and dissolution and nucleation. If the reaction container was not completely sealed, dehydration of gibbsite followed by in-situ nucleation of boehmite was the preferred mechanism. Boehmite produced fibrous boehmite particles within the amorphous matrix of the decomposed gibbsite particles, which exhibited a poorly crystalline structure and smaller size than the initial gibbsite particles. In a closed environment, the preferred mechanism was the dissolution of gibbsite along (001) planes. The final boehmite particles were not morphologically related to the initial gibbsite particles and could be many times larger than the gibbsite particles.

Transport mirrors within the National Ignition Facility, a 192-beam 4-MJ fusion laser at 1053 nm, will be exposed to backscattered light from plasmas created from fusion targets and backlighters. This backscattered light covers the UV and visible spectrum from 351-600 nm. The transport mirror BK7 substrates will be intentionally solarized to absorb >95% of the backscattered light to prevent damage to the metallic mechanical support hardware. Solarization has minimal impact on the 351- and 1053-nm laser-induced damage threshold or the reflected wavefront of the multilayer hafnia silica coating. Radiation sources of various energies were examined for BK7 darkening efficiency within the UV and visible region with 1.1 MeV gamma rays from a Cobalt 60 source ultimately being selected. Finally, bleaching rates were measured at elevated temperatures to generate a model for predicting the lifetime at ambient conditions (20 C), before solarized BK7 substrates exceed 5% transmission in the UV and visible region. Over a 30-mm thickness, BK7 glass will bleach in 10 years to 5% transmission at 600 nm, the most transmissive wavelengths over the 351-600 nm regions.

Solute effect on the creep resistance of two-phase lamellar TiAl with an ultrafine microstructure creep-deformed in a low-stress (LS) creep regime [where a linear creep behavior was observed] has been investigated. The resulted deformation substructure and in-situ TEM experiment revealed that interface sliding by the motion of pre-existing interfacial dislocations is the predominant deformation mechanism in LS creep regime. Solute segregation at lamellar interfaces and interfacial precipitation caused by the solute segregation result in a beneficial effect on the creep resistance of ultrafine lamellar TiAl in LS creep regime.

The capsule targets for ignition experiments at the National Ignition Facility must meet very exacting requirements. Primary among them is an extremely high degree of symmetry at all length scales for the 2-mm-diameter 150-{micro}m-walled capsule. At LLNL work is in progress to produce both polyimide and sputtered beryllium targets that meet these specifications. Both of these targets require a thin-walled spherical-shell plastic mandrel upon which the beryllium or polyimide ablator is deposited. In this paper we report on recent progress in developing NIF capsules that meet the demanding design requirements.

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 closed vessel, heated to 95 C, and purged with atmospheric CO{sub 2}. Aqueous samples of the evaporating solution were taken and analyzed to determine the evolving water chemistry, and the final solid precipitate was analyzed by X-ray diffraction. The synthetic Topopah Spring Tuff water evolved towards a complex brine that contains about 3 mol% SO{sub 4}, and 2 mol% Ca, 3 mol% K, 5 mol% NO{sub 3}, 40 mol% Cl, and 47 mol% Na. Trends in the solution data and identification of CaSO{sub 4} solids (anhydrite and bassanite) 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.