Hot Extrusion of Alpha Phase Uranium-Zirconium Alloys for TRU Burning Fast Reactors

The development of fast reactor systems capable of burning recycled transuranic (TRU) isotopes has been underway for decades at various levels of activity. These systems could significantly alleviate nuclear waste storage liabilities by consuming the long-lived isotopes of plutonium (Pu), neptunium (Np), americium (Am), and curium (Cm). The fabrication of metal fuel alloys by melt casting pins containing the volatile elements Am and Np has been a major challenge due to their low vapor pressures; initial trials demonstrated significant losses during the casting process. A low temperature hot extrusion process was explored as a potential method to fabricate uranium-zirconium fuel alloys containing the TRU isotopes. The advantage of extrusion is that metal powders may be mixed and enclosed in process canisters to produce the desired composition and contain volatile components. Uranium powder was produced for the extrusion process by utilizing a hydride-dehydride process that was developed in conjunction with uranium alloy sintering studies. The extrusions occurred at 600 degrees C and utilized a hydraulic press capable of 450,000 N (50 tons) of force. Magnesium (Mg) metal was used as a surrogate metal for Pu and Am because of its low melting point (648 degrees C) and relatively high vapor pressure (0.2 atm at 725 degrees C). Samples containing U, Zr, and Mg powder were prepared in an inert atmosphere glovebox using copper canisters and extruded at 600 degrees C. The successful products of the extrusion method were characterized using thermal analysis with a differential scanning calorimeter as well as image and x-ray analysis utilizing an electron microprobe. The analysis showed that upon fabrication the matrix of the extruded metal alloy is completely heterogeneous with no mixing of the metal particle constituents. Further heat treating upon this alloy allows these different materials to interdiffuse and form mixed uraniumz-irconium phases with varying types of microstructures. Image and x-ray analysis showed that the magnesium surrogate present in a sample was retained with little evidence of losses due to vaporization

Repair of the trigeminal nerve: a review

Nerve surgery in the maxillofacial region is confined to the trigeminal and facial nerves and their branches. The trigeminal nerve can be damaged as a result of trauma, local anaesthesia, tumour removal and implant placement but the most common cause relates to the removal of teeth, particularly the inferior alveolar and lingual nerves following third molar surgery.\ud \ud The timing of nerve repair is controversial but it is generally accepted that primary repair at the time of injury is the best time to repair the nerve but it is often a closed injury and the operator does not know the nerve is injured until after the operation. Early secondary repair at about three months after injury is the most accepted time frame for repair. However, it is also thought that a reasonable result can be obtained at a later time.\ud \ud It is also generally accepted that the best results will be obtained with a direct anastamosis of the two ends of the nerve to be repaired. However, if there is a gap between the two ends, a nerve graft will be required to bridge the gap as the two ends of the nerve will not be approximated without tension and a passive repair is important for the regenerating axons to grow down the appropriate perineural tubes.\ud \ud Various materials have been used for grafting and include autologous grafts, such as the sural and greater auricular nerves, vein grafts, which act as a conduit for the axons to grow down, and allografts such as Neurotube, which is made of polyglycolic acid (PGA) and will resorb over a period of time