A copy of the assembly used in the NRU reactor at Chalk River for the production of molybdenum 99. The assembly has a total length of almost 7.9 m and is 7.5 cm in diameter, a dimension designed to fit in a fuel channel location in the reactor. It has been dismantled in two parts in the display. The isotope production section has a four-fold symmetry. Each water-cooled segment contains four, 18 cm long, aluminum-finned, pencils. The individual pencils consist of a central rod, 5.5 mm in diameter, of enriched uranium alloyed with aluminum which is then clad with a 2 mm coating of aluminum. High water flow along the pencils provides the required cooling.
Following irradiation for typically 13 days, the rod is disassembled into two sections, the irradiated pencils are removed and are mechanically and chemically disassembled to extract molybdenum 99 – a fission product. During NRU operation, as much as 67% of the global supply of molybdenum was being produced at NRU.
