nureg/cr-6700 - Oak Ridge National Laboratory

ABSTRACT
This report investigates trends in the radiological decay properties and changes in relative nuclide importance
associated with increasing enrichments and burnup for spent LWR fuel as they affect the areas of criticality
safety, thermal analysis (decay heat), and shielding analysis of spent fuel transport and storage casks. To
facilitate identifying the changes in the spent fuel compositions that most directly impact these application
areas, the dominant nuclides in each area have been identified and ranked by importance. The importance is
investigated as a function of increasing burnup to assist in identifying the key changes in spent fuel
characteristics between conventional- and extended-burnup regimes. Studies involving both pressurizedwater-reactor
(PWR) fuel assemblies and boiling-water-reactor (BWR) assemblies are included. This study
is seen to be a necessary first step in identifying the high-burnup spent fuel characteristics that may adversely
affect the accuracy of current computational methods and data, assess the potential impact on previous
guidance on isotopic source terms and decay-heat values, and thus help identify areas for methods and data
improvement. Finally, several recommendations on the direction of possible future code validation efforts
for high-burnup spent fuel predictions are presented.
iii