Slides - WM2014 Symposia, March 2-6, 2014, Phoenix, AZ

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 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

Presented at the NEI Used Fuel Management Conference, St. Petersburg, FL, May 7-9, 2013

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.

Presented at the NEI Used Fuel Management Conference, St. Petersburg, FL, May 7-9, 2013

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

Presented at the NEI Used Fuel Management Conference, St. Petersburg, FL, May 7-9, 2013

Presented at the NEI Used Fuel Management Conference, St. Petersburg, FL, May 7-9, 2013

Presented at the NEI Used Fuel Management Conference, St. Petersburg, FL, May 7-9, 2013

The objective of this calculation is to evaluate commercial spent nuclear fuel (CSNF) bumup uncertainty based on pressurized water reactor (PWR) and boiling water reactor (BWR) records kept by each utility. The bumup uncertainties will be used to adjust either the waste package loading curves or the bumup values of assemblies shipped to the repository.
This engineering calculation supports the burnup credit methodology in Reference 1 and is performed in accordance with the AREVAIFANP procedures in References 2 and 3.

Presented at the NEI Used Fuel Management Conference, St. Petersburg, FL, May 7-9, 2013

The Interim Staff Guidance on burnup credit issued by the U.S. Nuclear Regulatory Commission's Spent Fuel Project Office recommends restricting the use of burnup credit to assemblies that have not used burnable absorbers. This 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.

Presented at the NEI Used Fuel Management Conference, St. Petersburg, FL, May 7-9, 2013

This report is part of a report series designed to document benchmark-quality radiochemical assay data
against which computer code predictions of isotopic composition for spent nuclear fuel can be validated
to establish the uncertainty and bias associated with the code predictions. The experimental data analyzed
in the present report were acquired from two international programs: (1) ARIANE and (2) REBUS, both
coordinated by Belgonucleaire. All measurements include extensive actinide and fission product data of

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)

The purpose of this calculation is to determine the required minimum burnup as a function of initial pressurized water reactor (PWR) assembly enrichment that would permit loading of fuel into the 21 PWR waste package (WP), as provided for in QAP-2-0 Activity Evaluation, Perform Criticality, Thermal, Structural, & Shielding Analyses (Reference 7.1).

This report has been prepared to qualitatively assess the amount of burnup credit (reactivity margin) provided by ISG-8 compared to that provided by the burnup credit methodology developed and currently applied in France. For the purposes of this study, the methods proposed in the DOE Topical Report have been applied to the ISG-8 framework since this methodology (or one similar to it) is likely to form the basis of initial cask licensing applications employing limited burnup credit in the United States.

The U.S. Nuclear Regulatory Commission's guidance on burnup credit for pressurized-water-reactor (PWR) spent nuclear fuel (SNF) recommends that analyses be based on a cooling time of five years. This recommendation eliminates assemblies with shorter cooling times from cask loading and limits the allowable credit for reactivity reduction associated with cooling time. This report examines reactivity behavior as a function of cooling time to assess the possibility of expanding the current cooling time recommendation for SNF storage and transportation.

Taking credit for the reduced reactivity of spent nuclear fuel (SNF) in criticality analyses is referred to as burnup credit (BUC). Criticality safety evaluations require validation of the computational methods with critical experiments that are as similar as possible to the safety analysis models, and for which the keff values are known. This poses a challenge for validation of BUC criticality analyses, as critical experiments with actinide and fission product (FP)

This analysis is prepared by the Mined Geologic Disposal System (MGDS) Waste Package Development Department (WPDD) to provide pressurized water reactor (PWR) isotopic composition data as a function of time for use in criticality analyses. The objectives of this evaluation are to generate burnup and decay dependant isotopic inventories and to provide these inventories in a form which can easily be utilized in subsequent criticality calculations.

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

Presented at the NEI Used Fuel Management Conference, St. Petersburg, FL, May 7-9, 2013

Burnup credit (BUC) is a concept applied in the criticality safety analysis of spent nuclear fuel
in which credit or partial credit is taken for the reduced reactivity worth of the fuel due to both fissile
depletion and the buildup of actinides and fission products that act as net neutron absorbers.
Typically, a two-step process is applied in BUC analysis: first, depletion calculations are performed
to estimate the isotopic content of spent fuel based on its burnup history; second, three-dimensional