George W. Griffith

Synthesis and Analysis of Alpha Silicon Carbide Components for Encapsulation of Fuel Rods and Pellets

The chemical, mechanical and thermal properties of silicon carbide (SiC) along with its low neutron activation make it an attractive material for encapsulating fuel rods and fuel pellets. The alpha phase of SiC has particularly attractive thermal properties. Unfortunately, it requires very high temperature processing and continuous alpha SiC fiber is not available commercially. This paper describes a method for fabricating continuous, composite (SiC/C) fibers as well as monolithic SiC fibers by direct conversion of carbon fibers using SiO vapor at ∼ 1600°C. EDS analysis indicates the converted SiC product contains 1:1 stoichiometric amounts of C and Si. Hexagonal (α) SiC was found to be the dominant crystal structure by x-ray diffraction.Copyright

Tritium Production and Permeation in High-Temperature Reactor Systems

Tritium (Display FormulaH13) is a radioactive isotope of hydrogen formed by ternary fission events (rare emissions of three nuclides rather than two during a fission) and neutron absorption (and subsequent decay) of predecessor radionuclides, particularly 6Li and 7Li. Also in fusion, the concept of breeding tritium during the fusion reaction is of significance for the future needs of a large-scale fusion power plant. Tritium is of special interest among the fission products created in next-generation nuclear reactors such as gas cooled reactors and molten salt reactors, because of the large quantities produced when compared with conventional light-water reactors (LWR) and the higher temperatures of operation for these systems enhances permeation. To prevent the tritium contamination of proposed reactor buildings and surrounding sites, this paper examines the root causes and potential solutions for mitigation of permeation of this radionuclide, including materials selection and inert gas sparging. A model is presented that can be used to predict permeation rates of hydrogen through metallic alloys at temperatures from 450–750°C. Results of the diffusion model are presented along with mitigation strategies for tritium permeation.Copyright

Lighting Studies for Fuelling Machine Deployed Visual Inspection Tool

Under subcontract to James Fisher Nuclear, Ltd., INL has been reviewing advanced vision systems for inspection of graphite in high radiation, high temperature, and high pressure environments. INL has performed calculations and proof-of-principle measurements of optics and lighting techniques to be considered for visual inspection of graphite fuel channels in AGR reactors in UK.