Nuclear Science User Facilities 114 As shown in Figure 2 the as-produced microstructure of the blocks is typical of ~5% cold-working, all traces of which disappear during irradiation. Most importantly, this Row 8 reflector assembly operated over the range of dpa rates that are characteristic of the baffle-former assembly of pressurized water reactors (PWRs). With the exception of the discarded, much longer (395.3 mm) Block 1, located far below the core, each of the four hex-blocks in the NSUF NFML had initial dimensions of 52.2 mm flat-to-flat cross-sectional thickness and a length of either 217.5 (for Blocks 5 and 6) or 243.3 mm (Blocks 2,3,and 4). Block 6 was also discarded and is not in the NFML. Blocks 2–5 are currently maintained in the NSUF NFML, with Blocks 2 and 4 located at INL in fully intact form, with profilometry data available to describe their dimensional changes. Blocks 3 (mid-core) and 5 (far above- core) were shipped to the Westing- house hot cells in Pittsburgh and have since been extensively sectioned into smaller segments with a wide range of sizes and geometries. Large portions of both blocks still remain in Pittsburgh, but various subsets of smaller speci- mens have been shipped to several national laboratories, to the Center for Advanced Energy Studies (CAES) and a number of universities. Some of these previously shipped specimens have been tested to destruction, but others remain intact at Westinghouse or their current location for further use or for shipment to other laboratories. Figure 2. Cold-worked microstructure of an archive block, showing deformation- induced twin bands and dislocation cells existing prior to irradiation.