Production of simulated high-burnup used fuel cladding in the HFIR

There is a need to establish the link between the behavior and performance of unirradiated cladding and actual irradiated cladding. ORNL has begun to address part of the testing component of this linkage with an experimental concept to simulate high-burnup used fuel cladding by irradiating cladding material in the High Flux Isotope Reactor (HFIR). Fast neutron irradiation of pre-hydrided zirconium-alloy cladding in the HFIR at elevated temperatures is being carried out to simulate the effects of high burnup on used fuel cladding in order to gain a more complete understanding of the material properties relevant to very long-term storage. Irradiated pre-hydrided metallic materials will generate data to benchmark hot-cell testing of high-burnup used fuel cladding. Additionally, samples free of alpha contamination can be provided to researchers/students in universities without hot cell facilities to support the Department of Energy Office of Nuclear Energy Used Fuel Disposition Campaign (UFDC). This approach is designed to provide well-controlled neutron irradiation of pre-hydrided materials in the desired temperature range (200-350°C) similar to the service temperatures of boiling water reactors (BWRs) and pressurized water reactors (PWRs). The hydrogen content is in the range of 400-800 weight parts per million (wppm), which is similar to what has been observed for high-burnup used fuel cladding in PWRs. Some of the pre-hydrided specimens will be irradiated up to a fast fiuence of 1.3×10²² neutrons/cm² (>1 MeV), corresponding to a burnup level of 65 GWd/MTU. The Zircaloy-4 specimens in this design are placed in the flux trap of HFIR. The clad tubing is fitted with a molybdenum rod, which acts as a heater for the cladding. Finite-element calculations were performed to establish design diameters for the molybdenum heater rods to provide a sufficient mass to bring hydrided cladding specimens to a desired temperature of 330°C at the cladding surface.