The Advanced Gas Reactor (AGR)-3/4 experiment was designed to study fission product transport within graphitic matrix material and nuclear-grade graphite. To this end, this experiment consisted of 12 capsules, each fueled with 4 compacts containing uranium oxycarbide (UCO) tri-structural isotropic (TRISO)-coated particles as driver fuel and 20 UCO designed-to-fail (DTF) fuel particles in each compact. The DTF fuel was fabricated with a thin pyrocarbon layer that was intended to fail during irradiation and provide a known source of fission products. These fission products could then migrate through the compact and into the surrounding concentric rings of graphitic matrix material and/or nuclear-grade graphite. Through post-irradiation examination (PIE) of the rings (including physical sampling and gamma scanning) fission product concentration profiles within the rings can be determined. These data can be used to elucidate fission product transport parameters (e.g., diffusion coefficients within the test materials) which will be used to inform and refine models of fission product transport. After irradiation in the Advanced Test Reactor (ATR) had been completed in April 2014, the AGR-3/4 experiment was shipped to the Hot Fuel Examination Facility (HFEF) at the Materials and Fuels Complex (MFC) for inspection, disassembly, and metrology. The AGR-3/4 test train was received at MFC in two separate shipments between February and April 2015. Visual examinations of the test train exterior did not indicate dimensional distortion, and only two small discolored areas were observed at the bottom of Capsules 8 and 9. Despite slight external discoloration, no corresponding discoloration was found on the inside of these capsules. Prior to disassembly, the two test train sections were subject to analysis via the Precision Gamma Scanner (PGS), which did not indicate that any gross fuel relocation had occurred. A series of specialized tools, including clamps, cutters, and drills, had been designed and fabricated to carry out test train disassembly and recovery of capsule components (graphite rings and fuel compacts). This equipment performed well for separating each capsule in the test train and extracting the capsule components. Only a few problems were encountered. In one case, the outermost ring (the sink ring) was cracked during removal of the capsule through tubes. Although the sink ring will be analyzed to obtain a mass-balance of fission products in the experiment, these cracks do not pose a major concern because the sink ring will not be analyzed for its fission product spatial distribution. In Capsules 4 and 5, the compacts could not be removed from the inner rings using standard methods. An arbor press was modified and used to successfully remove the compacts from the inner rings without damaging the rings. Dimensional measurements were made on the compacts, inner rings, outer rings, and sink rings. The diameters of all compacts decreased by 0.5 to 2.0%. Generally, the extent of compact diametric shrinkage increased with...
Mechanical properties of six depleted uranium-molybdenum (U-Mo) alloys have been obtained using microhardness, quasistatic tensile tests, and scanning electron microscopy (SEM) failure analysis. U-Mo alloy foils are currently under investigation for potential conversion of high power research reactors to low enriched uranium fuel. Although mechanical properties take on a secondary effect during irradiation, an understanding of the alloy behavior during fabrication and the effects of irradiation on the integrity of the fuel is essential. In general, the microhardness, yield strength, Young's modulus, and ultimate tensile strength improved with increasing Mo content. Microhardness measurements were very sensitive to local composition, while the failure mode was significantly controlled by the impurity concentration of the alloy, especially carbon. Values obtained from literature are also provided with reasonable agreement, even though processing conditions and applications were quite different in some instances.
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