Measurement of post-irradiation stress in irradiated monolithic U-10Mo fuel plates in a shielded Argon hot-cell environment

The fuel system selected by the United States High Performance Research Reactor (USHPRR) program for the conversion of USHPRRs to low-enriched uranium operation consists of monolithic U-10wt%Mo (U-10Mo) fuel foils with a Zr-diffusion barrier and AA-6061 cladding. While residual stresses that result from the fabrication of the fuel plates are anticipated to be relieved early in a reactor cycle, during core shutdown, stresses are added to those introduced by fuel swelling and irradiation assisted creep, mainly due to the differences in thermomechanical properties of the cladding and fuel foil. Measurement of these post-irradiation stresses as a function of fission density is vital to understanding potential fuel system delamination mechanisms and ultimately qualifying the new research reactor fuel system. To perform measurements on radiologically hazardous specimens, a radiation hardened incremental slitting and deflection detection system was developed for use in and recently installed in the Argon atmosphere Hot Fuel Examination Facility hot cell. Following system testing, the first measurements of irradiated U-10Mo fuel plates were gathered on 10 specimens that encompass a range of irradiation conditions. The slit surface cross-sections are currently being characterized to define the interface boundaries and model the stress profiles. Initial results show interesting trends in the stress state with respect to plate geometry and operating conditions in the reactor.