Since the mid-1980s, a significant number of studies have been directed at understanding the phenomena and
parameters important to implementation of burnup credit in out-of-reactor applications involving pressurizedwater-
reactor (PWR) spent fuel. The efforts directed at burnup credit involving boiling-water-reactor (BWR)
spent fuel have been more limited. This paper reviews the knowledge and experience gained from work
performed in the United States and other countries in the study of burnup credit. Relevant physics and analysis

This paper reviews validation issues associated with implementation of burnup credit in transport, dry storage,
and disposal. The issues discussed are ones that have been identified by one or more constituents of the
United States technical community (national laboratories, licensees, and regulators) that have been exploring the
use of burnup credit. There is not necessarily agreement on the importance of the various issues, which
sometimes is what creates the issue. The broad issues relate to the paucity of available experimental data

Criticality safety analysis devoted to spent-fuel storage and transportation has to be conservative in order to be sure no accident will ever happen. In the spent-fuel storage field, the assumption of freshness has been used to achieve the conservative aspect of criticality safety procedures. Nevertheless, after being irradiated in a reactor core, the fuel elements have obviously lost part of their original reactivity. The concept of taking into account this reactivity loss in criticality safety analysis is known as burnup credit.