2017 | AFC ACCOMPLISHMENTS 61 / zirconium systems in certain scenarios. However, uncertainties are inherent in the assessment of new technologies. Fuel behavior across a complete range of reactor conditions and possible operating occurrences must be established.The Advanced Fuels Campaign (AFC) has invested in development of test capabilities to study the behavior of candidate fuel materials in environments as they would be experience during opera- tion. Autoclave testing in chemistry- controlled environments is a key component of qualification. Autoclave testing of cladding materials is available at multiple institutions, but assessment of actinide materials under similar conditions poses operational challenges; flow through autoclaves would have to accommo- date testing of little known materials that may fully pulverize and result in distribution of uranium powder throughout the loop. A buffered autoclave capability for uranium materials was therefore developed to facilitate assessment of new proposed fuel materials.Testing can be performed to characterize the stability of fuels under exposure to pressurized water at chemistries that can be matched to either Pressurized Water Reactor (PWR) or Boiling Water Reactor (BWR) conditions. A range of uranium silicide, uranium nitride, and ceramic fissile composite materials have been assessed using this technique.While results have found that U3Si2 is more stable than other fuel materials tested with the exception of UO2, it does suffer hydriding which governs pulveriza- tion under these conditions. Efforts are underway to better understand this behavior and assess its impact on use of U3Si2 as an LWR fuel. The basic behavioral investigations of U3Si2, U3Si5, UN, UN/U3Si2 composites, and UO2 were previously completed at Los Alamos National Laboratory (LANL). Uranium dioxide was included as a reference material, as its behavior under pressurized water is relatively well known and can therefore be used to validate system performance.These studies proved that, while still inferior to UO2, U3Si2 performed the best of the above materials as it largely resisted pulverization through over 30 days of exposure to 300C water.Testing of U3Si5 found rapid pulverization after only two days and led to the termination of work on UN compos- ites shielded by U3Si5.