Nuclear Science User Facilities 122 to enable a more comprehensive understanding of in-pile phenomena. The instrumented in-pile irradiation vehicle designed for insertion into BR2 is shown in Figure 2.The test vehicle is comprised of an outer capsule that serves as the housing for individual fuel samples and customizable instrumentation, such as thermocouples or other developmental in-pile instrumentation requiring testing.The in-core portion of the device is shown in Figure 2 (label a). A unique aspect of the device is the customizable internals that keep individual samples isolated from one another in sealed sample enclosures separated by insulators that utilize gas gaps to isolate thermal effects from adjacent specimens, shown in Figure 2 (label b and c).This allows for in-pile conditions, such as atmosphere, temperature, composition, geometry, and power, to vary between samples in a single device. Such a device is able to provide the unique capability to target various phenomena of interest on a per sample basis. It also has the ability to be implemented for future work without a large-scale redesign or qualification. Figure 2 (label d) shows the sample enclosures for the U-Zr alloy foils (top) and the U-Mo alloys disks (bottom). Low-enriched (19–20% weight U-235) U-Mo and U-Zr alloys of varying compositions were selected as the alloy compositions for this Figure 2. a) In-core portion of the test vehicle. b) Enlarged section of vehicle illustrating the stack-up of specimen holders separated by insulators. c) Insulators utilizing gas gaps to isolate specimen holders. d) Specimen holders for the U-Zr alloy foils (top) and the U-Mo alloys disks (bottom).