The AGR-5/6/7 irradiation test train was sectioned at ATR and sent to HFEF for examination and disassembly. Visual examinations of the test train exterior did not indicate any notable damage or degradation. Prior to disassembly, the two test train sections were subjected to analysis via gamma scanning and neutron radiography, and those non-destructive exams did not indicate that any fuel relocation or significant internal test train damage had occurred. A series of specialized tools were used to disassemble the test train and recover the fuel and capsule components. This equipment generally performed as intended, but some additional tooling was required for removing burrs from some of the stainless-steel capsule shells to allow removal of some graphite holders. The Capsule 2 graphite holder was damaged during cutting its shell. Some light damage occurred in other holders when the throughtubes were removed. One compact from Capsule 2 was broken during disassembly, and the identities of five compacts from Capsule 1 were lost. It appears likely that the cause of the fuel failure in Capsule 1 (evident from online fission gas measurements) was precipitated by issues related to the capsule design and not by subpar performance of the fuel itself. When the Capsule 1 holder was removed from the stainless-steel Capsule 1 shell, three columns of well-defined deposits were visible along the TC channels between Fuel Stacks 7, 8, 9, and 10. The locations of the three columns of deposits coincided with the three longest Ni-sheathed, Nb-sleeved, Cambridge Type N TCs, and they were generally located in the axial portion of the holder that had the highest temperatures. The apparent thicknesses of these deposits further confirm that the holder was not centered in the shell and that the gas gap on the side of the holder with these deposits was larger than the gas gap on the opposite side of the holder. This larger gap would have increased temperatures near Fuel Stacks 7–10 to promote substantial Ni transport and possibly high enough to melt the TCs. Some portions of these deposits appeared to have bright, reflective specks in them. Compacts recovered from the fuel stacks adjacent to these deposits (i.e., Stacks 7–10) had dark splotches and bright reflective specks not seen on compacts from other stacks. It is hypothesized that overheating these TCs resulted in the transport of Ni to the holder (forming deposits on its surface) and to the fuel, causing some visual variations on the compacts’ surfaces and a chemical reaction between the Ni and the SiC to form Ni-silicides that ultimately led to fuel failure in Capsule 1. Initial examinations of the deposits confirm the presence of elements from the TCs, such as Ni. Examinations of the compacts themselves are in progress. Most compacts appeared pristine when examined through the hot cell window; however, most will be re-imaged with enhanced in-cell capabilities. Some compacts had minor chipping on their edges commensurate with similar chipping observed in prior AGR campaigns. Some unexplained marks were observed on a minority of compacts from Capsules 2, 3, and 4. Some of these marks appear deep enough to have exposed underlying particles. It is not clear what could have caused these marks, and additional exams and analyses are in progress to understand them. Dimensional measurements were made on the fuel compacts and graphite holders. Generally, the IDs of the holders increased, and the ODs decreased, giving an overall reduction in the thicknesses of the holders. This would also result in increases to the width of the gap between the holder and the stainless-steel shell. The extent of the fuel channel diameter change, ID change, and OD change did not seem to be strongly related to the irradiation temperature and fluence. These dimensional changes are generally consistent with what has been observed in prior AGR campaigns. The final dimensions of these components of the AGR-5/6/7 test will be used to refine the thermal calculations for this irradiation experiment. Substantial additional PIE is in progress on AGR-5/6/7 to collect data on fuel performance and compare those data to results obtained in the earlier AGR campaigns. This includes comprehensive gamma scanning of the graphite holders and compacts and enhanced visual examinations of compacts. Destructive fuel exams (including but not limited to deconsolidations and ceramography) are in progress. A host of post-irradiation fuel heating tests in inert and oxidizing atmospheres are also planned.
