LIFE EXTENSION OF THE 9975 PACKAGE AS A STORAGE CONTAINER: THERMAL ANALYSIS

摘要

The 9975 shipping package is used to store plutonium bearing material with a heat release of up to 19 Watts at the Department of Energy (DOE) Savannah River Site (SRS). Individual 9975 packages have been used to store these materials for nearly 15 years. The 9975 package contains non-metallic components such as the elastomeric dual O-ring seals, used to ensure containment at the vessel closures, and a fiberboard over pack which provides impact and fire resistance to the containment vessels. These non-metallic components degrade during long term storage, particularly when higher heat generating contents are packaged. Degraded fiberboard properties result in higher peak internal 9975 package material temperatures during a fire accident event. The thermal performance of the 9975 shipping package was evaluated for a sequential accident consisting of a fire and drop which locally ruptures the outer drum. The package is exposed to an off-normal 58.3°C (137F) ambient temperature prior to being fully engulfed in a fire for 1.5 hours at 815.6°C (1500°F). Subsequently the fiberboard smolders for 1.0 hour at 760°C (1400F) at the location of drum rupture, followed by cool down to the ambient temperature. The thermal evaluation considered both the beginning-of-life (as-designed) condition and after 20 years of service as a plutonium material storage container. The results of the evaluation demonstrate that the 9975 shipping package maintains containment during initial and after 20 years of service. The maximum Primary Containment Vessel dual O-ring temperatures during the facility fire-drop-smoldering accident are 163.9°C (327°F) and 186.1°C (367°F) for beginning of life and after 20 years of service, respectively, which are within the allowable accident temperature limit of 204.4°C (400°F). Thus, the 9975 shipping package meets its intended function to provide containment.