2018 | AFC ACCOMPLISHMENTS 162 Idaho National Laboratory (INL) is working with an international partner to develop and test metallic nuclear fuel systems that will enable a closed fuel cycle that is both cost- effective and proliferation. In terms of in-reactor fuel performance, a key objective is to design the fuel system to such that it can achieve high burnup, which in turn will reduce the amount of reprocessing of fuel required per unit of energy produced.A challenge in this regard is to reduce the attack of the cladding by lanthanide fission products; in these experiments different barrier materials were placed between the fuel and the cladding so that the structural integrity of the cladding will be maintained. Project Description Fuel rods for advanced fast-spectrum reactors are typically irradiated within cylindrical capsules; a narrow gas-filled gap between the rodlet and capsule serves to raise fuel and cladding temperatures from levels in the AdvancedTest Reactor (ATR) coolant to values that are prototypical for a sodium-cooled reactor.A challenge in this project was that the irradiation times were constrained to be relatively short. Given the abbreviated irradiation times and that the objective of the experiments was to assess the ability of different barrier materials to protect the cladding, there was a strong desire to accelerate diffusion processes by running the tests at relatively high temperatures. However, the small gas-filled gap between the rodlet and the capsule and the fabrication tolerances of these components lead to high uncertainties in the temperatures that will actually develop in-reactor.The task at hand for the team was to provide best-estimate power levels for every fuel rod for the duration of the experiments and to choose gas compositions (mixtures of helium and argon) that would strike a balance between the desire to accelerate the interdiffusion of constituents and the perceived risk of running the test at too high a temperature given the uncertainties that are inherent in the design. Design of the Integrated Recycle Test Principal Investigator: Gary Povirk Collaborators: Dan Chapman, Doug Dempsey, Randall Fielding, Nate Oldham, Emily Swain Among other objectives, the Integrated Recycle Test has experiments comprised of a number of different barrier materials that, if successful, have the potential to dramatically increase the burnup and high temperature capabilities of fast reactor fuel systems.