Management Of Fissionable Equivalent Mass Materials At Oak Ridge National Laboratory

The US Department of Energy (DOE) manages an inventory of materials that contains a range of long-lived radioactive isotopes that were produced from the 1960s through the 1980s by irradiating targets in production reactors to produce special heavy isotopes for DOE programmatic use, scientific research, and industrial and medical applications. Since the production reactors and enrichment facilities that produced many of these materials have been shut down, they are considered unique materials that are not likely to be produced again. Oak Ridge National Laboratory (ORNL) uses these materials in DOE’s center for production, storage, and distribution of transuranium isotopes (plutonium through californium) and other related nuclear research programs. ORNL also operates the High Flux Isotope Reactor, which provides a high neutron source for production of isotopes for medical, industrial, and nuclear research programs. As a result, ORNL has an inventory of radioisotopes that are being managed for ongoing research programs and being held for reuse because they have potential intrinsic value to DOE. ORNL has an initiative underway to better manage these materials, particularly focusing on those with high fissionable equivalent mass that could impact the ability to perform ongoing or new research projects. This paper describes the actions ORNL is taking to manage high fissionable equivalent mass materials including implementing an improved reuse program, crediting unmoderated materials in nuclear criticality safety evaluations, and developing new special purpose nuclear criticality safety evaluation subcritical mass limits for select ORNL hot cell facilities.