Disposal Criticality Analysis Methodology Topical Report describes a methodology for performing postclosure criticality analyses within the repository at Yucca Mountain, Nevada. An important component of the postclosure criticality analysis is the calculation of conservative isotopic concentrations for spent nuclear fuel. This report documents the isotopic calculation methodology. The isotopic calculation methodology is shown to be conservative based upon current data for pressurized water reactor and boiling water reactor spent nuclear fuel.

The purpose of this study is to provide insights into the neutronic similarities that may exist between a
generic cask containing typical spent nuclear fuel assemblies and commercial reactor critical (CRC) state-
points. Forty CRC state-points from five pressurized-water reactors were selected for the study and the
type of CRC state-points that may be applicable for validation of burnup credit criticality safety
calculations for spent fuel transport/storage/disposal systems are identified. The study employed cross-

This report presents studies to assess reactivity margins and loading curves for pressurized water reactor
(PWR) burnup-credit criticality safety evaluations. The studies are based on a generic high-density 32-
assembly cask and systematically vary individual calculational (depletion and criticality) assumptions to
demonstrate the impact on the predicted effective neutron multiplication factor, keff, and burnup-credit
loading curves. The purpose of this report is to provide a greater understanding of the importance of

A conservative end effect keff bias curve for actinide-only burnup credit casks is presented
in this paper. Rather than performing axially burnup-dependent analysis, cask designers can, if
they choose to, analyze casks with a uniform axial burnup (at assembly average burnup value) and
add the keff bias values to conservatively bound the actinide-only end effect. Earlier studies
suggested 1-3% increase in keff to account for the end effect, but they included fission products
as well as actinides for their analyses.

Five commercial reactor criticals (CRCs) for the LaSalle Unit 1 boiling-water reactor
have been analyzed using KENO V.a, the Monte Carlo criticality code of the SCALE 4 code
system. The irradiated fuel assembly isotopics for the criticality analyses were provided by the
Waste Package Design team at the Yucca Mountain Project in the United States, who performed
the depletion calculations using the SAS2H sequence of SCALE 4. The reactor critical
measurements involved two beginning-of-cycle and three middle-of-cycle configurations. The

This report investigates trends in the radiological decay properties and changes in relative nuclide importance associated with increasing enrichments and burnup for spent LWR fuel as they affect the areas of criticality safety, thermal analysis (decay heat), and shielding analysis of spent fuel transport and storage casks. To facilitate identifying the changes in the spent fuel compositions that most directly impact these application areas, the dominant nuclides in each area have been identified and ranked by importance.

The objective of this calculation is to establish an isotopic database to represent commercial spent nuclear fuel (CSNF) from boiling water reactors (BWRs) in criticality analyses performed for the proposed Monitored Geologic Repository at Yucca Mountain, Nevada. Confirmation of the conservatism with respect to criticality in the isotopic concentration values represented by this isotopic database is performed as described in Section 3.5.3.1.2 of the Disposal Criticality Analysis Methodology Topical Report (Reference 7.1).

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.

The attached documents are an extensive list of references relevant to burnup credit criticality analysis. Some of the references may be available within the CURIE document collection.