Uncertainties in the predicted isotopic concentrations in spent nuclear fuel represent one of the largest
sources of overall uncertainty in criticality calculations that use burnup credit. The methods used to
propagate the uncertainties in the calculated nuclide concentrations to the uncertainty in the predicted
neutron multiplication factor (keff) of the system can have a significant effect on the uncertainty in the
safety margin in criticality calculations and ultimately affect the potential capacity of spent fuel transport

Isotopic characterization of spent fuel via depletion and decay calculations is necessary for
determination of source terms for subsequent system analyses involving heat transfer, radiation
shielding, isotopic migration, etc. Unlike fresh fuel assumptions typically employed in the criticality
safety analysis of spent fuel configurations, burnup credit applications also rely on depletion and
decay calculations to predict the isotopic composition of spent fuel. These isotopics are used in

This publication records the proceedings of a technical meeting organized by the IAEA and
held in London 29 August–2 September 2005 with sixty participants from 18 countries. As
indicated in the title, the objective of this meeting was to provide a forum for exchange of
technical information on spent fuel burnup credit applications and thereby compile state-ofthe-
art information on technical advances related to spent fuel transportation, storage,
reprocessing and disposition.

Target accuracy on LWR neutronics parameters is 2 to 5 times lower than the a priori uncertainty (1σ)
due to nuclear data. This paper summarizes the experimental facilities and the integral measurements that are required
for code qualification. The rigorous use of integral information through trend analysis method is described. Trends
on JEF2 data from Keff measurements and P.I.Es are presented. These trends were accounted for in the new JEFF3
evaluations. The role of fundamental experiments, such as worth measurement of separated isotopes, is emphasized.

As part of a larger program to study mixed-oxide fuel subject to high burnup, some UO2 samples were exposed and analyzed. This report discusses results from the analysis of a UO sample that was burned in a boiling-water reactor (BWR) to approximately 57 GWd/t. The sample

The purpose of this calculation report, Range of Applicability and Bias Determination for Postclosure
Criticality of Commercial Spent Nuclear Fuel, is to validate the computational method used to perform
postclosure criticality calculations. The validation process applies the criticality analysis methodology
approach documented in Section 3.5 of the Disposal Criticality Analysis Methodology Topical Report.1
The application systems for this validation consist of waste packages containing transport, aging, and

Spent fuel transportation and storage cask designs based on a burnup credit approach must
consider issues that are not relevant in casks designed under a fresh-fuel loading assumption. For
example, the spent fuel composition must be adequately characterized and the criticality analysis
model can be complicated by the need to consider axial burnup variations. Parametric analyses are
needed to characterize the importance of fuel assembly and fuel cycle parameters on spent fuel

This report attempts to summarize and consolidate the existing knowledge on axial
burnup distribution issues that are important to burnup credit criticality safety calculations.
Recently released Nuclear Regulatory Commission (NRC) staff guidance permits limited burnup
credit, and thus, has prompted resolution of the axial burnup distribution issue. The reactivity
difference between the neutron multiplication factor (keff) calculated with explicit representation

This report documents the work performed by ORNL for the Yucca Mountain Project (YMP)
M&O contractor, Framatome Cogema Fuels. The goal of this work was to obtain k values for inf
infinite arrays of flooded boiling-water-reactor (BWR) fuel assemblies as a function of various
burnup/enrichment and cooling-time combinations. These scenarios simulate expected limiting
criticality loading conditions (for a given assembly type) for drift emplacements in a repository. Upon

The Interim Staff Guidance on burnup credit (ISG-8) issued by the United States Nuclear Regulatory
Commission’s (U.S. NRC) Spent Fuel Project Office recommends restricting the use of burnup credit to
assemblies that have not used burnable absorbers. This recommended restriction eliminates a large portion
of the currently discharged spent fuel assemblies from cask loading, and thus severely limits the practical
usefulness of burnup credit. In the absence of readily available information on burnable poison rod (BPR)