A risk management approach to nuclear waste inventory versus storage capacity

Nuclear waste is presently stored in 177 underground storage tanks at -the U. S. Department of Energy`s Hanford Site in Washington State. The storage tanks are of two construction types, 149 single-shell tanks (SSTS) and 28 double-shell tanks (DSTs). No waste has been added to the SSTs since 1980. However, the DSTs are configured to receive additional waste from site waste generators. The overall waste inventory is time dependent and strongly influenced by present and future tank farm operations. These operations include waste evaporation, retrieval, pretreatment, and processing; waste generated from various site facilities; and SST waste inventory transferred to the DSTS. A risk-based simulation model was developed to replicate the waste inventory through the year 2015. The DST waste,,; were divided into three waste types (aging, complexed, @md non-complexed) that were simulated in the model. For each of the three waste types, statistical analyses were performed and the time-de,Pendent waste volumes at the ``mean`` and ``90% confidence level`` were compared with existing DST capacity. Several ``off-normal`` operation scenarios were also analyzed using the risk-based simulation model. Mitigating actions or fallback positions were modeled where off- normal scenarios indicated that capacity shortfalls could potentially occur. The results indicated that selectedmore » fallback positions were adequate to ensure that the storage capacity exceeded the waste invento0167ry during the affected time periods.« less