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

more »

... iation 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 increasing neutron fluence until exhibiting a turn-around at fluences above about 4.2 × 10 25 n/m 2 . Most compact lengths also decreased. Compact lengths decreased with increasing fluence, reaching maximum shrinkage of about 0.9% at a fast fluence of 4.0 × 10 25 n/m 2 (E > 0.18 MeV). Above this fluence, the extent of length reduction appeared to turn around and decrease as fluence increased. Most compacts from Capsules 4 and 5 and two compacts from Capsule 7 had length increases between 0.1% and 0.5% after a fluence of 4.8 × 10 25 n/m 2 . The inner rings exhibited a decrease in the outer diameter (OD) and an increase in the inner diameter (ID) with increasing fluence. This indicates that the ring wall thickness decreased with fluence. A nearzero change was observed for the lowest-fluence capsules (Capsules 1 and 12 at a fluence of approximately 1.5 × 10 25 n/m 2 ). For Capsule 7, the highest fast fluence capsule (5 × 10 25 n/m 2 ), the ID increased by 2.3%, and the OD decreased by 2.8%. A subtle turn-around in the direction of the dimensional change may exist, beginning at a fluence of 4.8 × 10 25 n/m 2 .