The most widely used and versatile medical radioisotope today is technetium-99m. Roughly 30 million people depend on this radioisotope for diagnostic procedures each year, and this demand is expected to grow. Although there are numerous ways of procuring this isotope, the most common and most practical, for reasons to be stated later, comes from fission product molybdenum. Molybdenum is produced in all nuclear reactors 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 to Tc-99m 87% of the time.
In 1978, the Reduced Enrichment for Research Test Reactors (RERTR) program was established at Argonne National Laboratory to investigate technology that would aid in converting High Enriched Uranium (HEU) facilities to use Low Enriched Uranium (LEU) fuel. Since the majority of all Mo-99 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 (SA) Mo-99. Approximately three years ago the Oregon State TRIGA Reactor (OSTR) switched from HEU to LEU fuel elements in compliance with the RERTR program, and recently, a novel LEU target design has been developed for use in TRIGA reactors for production of Mo-99. Preliminary analysis has already been carried out with targets replacing several fuel elements, and it does not appear to negatively affect the reactor behavior.
The current supply capability of Tc-99m cannot keep pace with the growing demand. There are few, if any, new production facilities of Mo-99
slated for the future, and many of those presently operating will shutdown in the coming decades. Factoring in the time needed to license and construct new reactors, and the always pressing political and public wariness towards nuclear power, action must be taken immediately to ensure the future supply of this invaluable radioisotope. This research will analyze the viability of operating a low-power research reactor using the newly developed target design as the only source of fissile material. The normal TRIGA fuel will be offloaded and replaced with the new target elements for some optimal amount of time to produce molybdenum. After Mo-99 production reaches saturation, the normal fuel will be loaded back into the reactor, where normal operation can continue. MCNP5 will be the primary simulation tool used to analyze the behavior of the reactor and verify compliance with all safety limitations set forth in the OSTR Safety and Analysis Report as stated by the U.S. Nuclear Regulatory Commission.