An Empirical Approach to Bounding the Axial Reactivity Effects of PWR Spent Nuclear Fuel

One of the significant issues yet to be resolved for using
burnup credit ~BUC! for spent nuclear fuel ~SNF! is establishing
a set of depletion parameters that produce an adequately conservative
representation of the fuel’s isotopic inventory. Depletion
parameters ~such as local power, fuel temperature, moderator temperature,
burnable poison rod history, and soluble boron concentration!
affect the isotopic inventory of fuel that is depleted in a
pressurized water reactor ~PWR!. However, obtaining the detailed
operating histories needed to model all PWR fuel assemblies
to which BUC would be applied is an onerous and costly
task. Simplifications therefore have been suggested that could
lead to using “bounding” depletion parameters that could be
broadly applied to different fuel assemblies. This paper presents
a method for determining a set of bounding depletion parameters
for use in criticality analyses for SNF.