2018 | AFC ACCOMPLISHMENTS 106 Figure 1. Mini fuel design concept. Qualification of new nuclear fuel materials requires a thorough scientific understanding of fuel behavior including irradiation performance.Traditionally, irradiation performance data has been acquired through many integral fuel irradiation experiments where full-size fuel pellets are tested under conditions that closely match those of the intended application. While this approach is logical, it is very expensive and time consuming, particularly when considering a large test matrix. Furthermore, the large number of variables that affect fuel performance make it difficult to develop fundamental models of various phenomena from integral fuel tests, which often have many independent variables that cannot be well-controlled. The ability to perform well-controlled separate effects irradiation testing would allow for evaluation of a wide range of new fuel concepts within a reasonable time and cost. This goal of this project is to implement a new capability for performing accelerated separate effects irradiation testing of miniature (“mini”) fuel specimens in the High Flux Isotope Reactor (HFIR) at Oak Ridge National Laboratory (ORNL).The design concept places the mini fuel specimens inside individually sealed sub-capsules inside steel targets in the reflector of the reactor.Temperature is controlled by sizing an insulating gas gap between the sub-capsules and the target housing. Reducing the size of the fuel allows for very high fission rates (on a per unit mass basis) without prohibitively large temperature gradients. Furthermore, the small fuel mass results in the total heat generated in each sub-capsule being dominated by gamma heating in the structure instead of fission in the fuel itself.This essentially decouples the fuel temperature from the fission rate. The benefit of this work to the nuclear community is that advanced fuel concepts can now be evaluated early in their development process under very controlled conditions, and in a much more economical manor. Using the mini fuel capability, several fuel performance variables can be explored under a single irradiation campaign including temperature, burnup, composition, geometry, enrichment, grain size, impurities, and non-stoichiometries. Separate Effects “Mini Fuel” Irradiation Testing Principle Investigator: Christian Petrie Collaborators: Joseph Burns, Annabelle Le Coq, Alicia Raftery, Jake McMurray, Robert Morris, Kurt Terrani