Alternatives for Implementing Bumup Credit the Design and Operation of Spent Fuel Transport Casks*

The traditional assumption used in evaluating criticality safety of a spent fuel cask is that the spent fuel is as reactive as when it was fresh (new). This is known as the \"fresh fuel assumption.\" It avoids a number of calculatiOnal and verification difficulties, but could take a heavy toll in decreased efficiency. The alternative to the fresh fuel assumption is called \"burnup credit.\" That is, the reduced reactivity of spent fuel that comes about from net depletion of fissile radionuclides and net increase in neutron absorbers (poisons) is taken into account. It is recognized that the use of burnup credit will in fact increase the percentage of unacceptable or non-specification fuel available for misloading. This could reduce individual cask safety margins if current practices with respect to loading procedures are maintained. As such, additional operational, design, analysis, and validation requirements should be established that, as a minimum, compensate for any potential reduction in fuel loading safety margin.