Validation of SCALE (SAS2H) Isotopic Predictions for BWR Spent Fuel

Thirty spent fuel samples obtained from boiling-water-reactor (BWR) fuel pins have been
modeled at Oak Ridge National Laboratory using the SAS2H sequence of the SCALE code system.
The SAS2H sequence uses transport methods combined with the depletion and decay capabilities
of the ORIGEN-S code to estimate the isotopic composition of fuel as a function of its burnup
history. Results of these calculations are compared with chemical assay measurements of spent fuel
inventories for each sample. Results show reasonable agreement between measured and predicted
isotopic concentrations for important actinides; however, little data are available for most fission
products considered to be important for spent fuel concerns (e.g., burnup credit, shielding,
source-term calculations, etc.).
This work is a follow-up to earlier works that studied the ability to predict spent fuel
compositions in pressurized-water-reactor (PWR) fuel pins. Biases and uncertainties associated
with BWR isotopic predictions are found to be larger than those of PWR calculations. Such
behavior is expected, as the operation of a BWR is significantly more complex than that of a PWR
plant, and in general the design of a BWR has a more heterogeneous configuration than that of a
PWR. Nevertheless, this work shows that the simple models employed using SAS2H to represent
such complexities result in agreement to within 5% (and often less than 1%) or less for most nuclides
important for spent fuel applications. On the other hand, however, the set of fuel samples analyzed
represent a small subset of the BWR fuel population, and results reported herein may not be
representative of the full population of BWR spent fuel.