The ANS/ANS-8.1 standard requires that calculational methods used in determining criticality
safety limits for applications outside reactors be validated by comparison with appropriate critical
experiments. This report provides a detailed description of 34 fresh fuel critical experiments and
their analyses using the SCALE-4.2 code system and the 27-group ENDF/B-IV cross-section library.
The 34 critical experiments were selected based on geometry, material, and neutron interaction

The requirements of ANSI/ANS-8.1 specify that calculational methods for away-from-reactor
criticality safety analyses be validated against experimental measurements. If credit is to be taken for
the reduced reactivity of burned or spent fuel relative to its original "fresh" composition, it is
necessary to benchmark computational methods used in determining such reactivity worth against
spent fuel reactivity measurements. This report summarizes a portion of the ongoing effort to

The objective of this calculation is to document the Grand Gulf Unit 1 (GGl) reactivity calculations for sixteen critical statepoints in· cycles 4 through 8. The GG1 reactor is a boiling water reactor (BWR) owned and operated by Entergy Operations Inc. The Commercial Reactor Criticality (CRC) evaluations support the development and validation of the neutronic models used for criticality analyses involving commercial spent nuclear fuel to be placed in a geologic repository. This calculation is performed as part of the evaluation in the CRC program.

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

The benefits of burnup credit and the technical issues associated with utilizing burnup credit in spent
nuclear fuel (SNF) casks have been studied in the United States for almost two decades. The issuance of the
U.S. Nuclear Regulatory Commission (NRC) staff guidance for actinide-only burnup credit in 2002 was a
significant step toward providing a regulatory framework for using burnup credit in transport casks. However,
adherence to the current regulatory guidance (e.g., limit credit to actinides) enables only about 30% of the existing

The validity of the computation of pressurized-water-reactor (PWR) spent fuel isotopic
composition by the SCALE system depletion analysis was assessed using data presented in the report.
Radiochemical measurements and SCALE/SAS2H computations of depleted fuel isotopics were
compared with 19 benchmark-problem samples from Calvert Cliffs Unit 1, H. B. Robinson Unit 2,
and Obrigheim PWRs. Even though not exhaustive in scope, the validation included comparison of
predicted and measured concentrations for 14 actinides and 37 fission and activation products.

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 summarizes the results of an initial investigation into the uncertainties associated with the burnup records maintained by nuclear power plants. The results indicate that there is an overall uncertainty of about 2 percent in the burnup records, which must be accounted for in spent fuel applications.

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

Burnup credit is an ongoing technical concern for many countries that operate commercial
nuclear power reactors. In a multinational cooperative effort to resolve burnup credit issues, a
Burnup Credit Working Group has been formed under the auspices of the Nuclear Energy Agency
of the Organization for Economic Cooperation and Development. This working group has
established a set of well-defined calculational benchmarks designed to study significant aspects of
burnup credit computational methods. These benchmarks are intended to provide a means for the