The NRC regulates the operation of the civilian nuclear power plant fleet by establishing and enforcing regulatory requirements for their design, construction, and operation. To protect the health and safety of the public and environment, the NRC requires all nuclear power plants to have a spent fuel pool where the used reactor fuel assemblies are allowed to cool for a number of years before being moved to interim or permanent storage. Spent fuel pools (SFP) are robust structures with an extremely low likelihood of a complete loss of coolant under traditional accident scenarios. However, in the wake of the terrorist attacks of September 11, 2001, the SFP accident progression was reconsidered and reevaluated using best-estimate accident codes.