Nuclear Science User Facilities 78 Accomplishments The irradiation engineering challenge in this project is to develop a low-cost “Fire Rabbit” capsule that accom- modates SiC/SiC tube specimens, enabling a radial heat flux relevant to LWR fuel claddings, and maintaining the specimen temperature constant . The heat flux was produced by placing a concentric gamma-absorbing tube as a heat source inside the specimen (Figure 2).The need to maintain the specimen outer-surface temperature is the most significant challenge when SiC swells linearly by ~0.7% while a gap of a few microns causes unaccept- able temperature deviations due to high heat flux. Moreover, any excessive mechanical constraint on the specimen has to be avoided. Our team came up with the idea of using an embossed metallic foil sleeve surrounding the specimen, so that a constant heat conduction from the specimen to the capsule housing is maintained during and after the specimen swelling.Thus, an expand- able thermal homogenizer sleeve was inserted between the foil and the specimen to minimize radial perturba- tion of temperature.The embossing pattern was optimized through a series of ex-pile experiments involving the measurement of heat conduction as a function of the compressive deforma- tion of the foil layer.The actual radial build of the irradiation capsule is shown in Figure 2. Figure 2. Design and construction of the Fire Rabbit irradiation vehicle developed in the project, enabling simultaneous high radial heat flux and neutron exposure for tubular test specimens.