The most widely used and versatile medical radioisotope today is 99m Tc. Roughly 30 million people depend on this radioisotope for diagnostic imaging procedures each year, and this demand is expected to grow. Although there are numerous ways of producing this isotope, the most common is from fission product 99 Mo, which is produced in all nuclear reactors fueled with 235 U as a fission fragment with a yield of around 6.1%. Molybdenum-99 has a half-life of just over 2.5 days, and it will decay

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... 99m Tc 87% of the time. The Reduced Enrichment for Research Test Reactors program was established at Argonne National Laboratory in 1978 to investigate technology that would aid in converting highly enriched uranium (HEU) facilities to low-enriched uranium (LEU) fuel. Since the majority of all 99 Mo produced currently comes from the irradiation of HEU fuel targets, there has been a growing effort to design LEU targets that can yield comparable quantities of high specific activity 99 Mo. Recently, a novel LEU target design has been developed for use in TRIGA reactors for the production of 99 Mo. The simulation tool MCNP5 was used to examine the neutronic behavior of multiple core configurations fueled solely with this new target.