Taking credit for the reduced reactivity of spent nuclear fuel in criticality analyses is referred to
as burnup credit. Criticality safety evaluations employing burnup credit require validation of the
depletion and criticality calculation methods and computer codes with available measurement
data. To address the issues of burnup credit criticality validation, the U.S. Nuclear Regulatory
Commission initiated a project with Oak Ridge National Laboratory to (1) develop and establish

This report presents results from a parametric study of equilibrium fuel cycle costs for a closed fuel cycle with multi-recycling of plutonium in fast reactors (FRs) compared to an open, once-through fuel cycle using PWRs. The study examines the impact on fuel cycle costs from changes in the unit costs of uranium, advanced PUREX reprocessing of discharged uranium dioxide (UO2) fuel and fast-reactor mixed-oxide (FR-MOX) fuel, and FR-MOX fuel fabrication.

Expanding interest in nuclear power and advanced fuel cycles indicate that use of mixed-oxide (MOX) fuel in the current and new U.S. reactor fleet could become an option for utilities in the coming decades. In light of this renewed interest, EPRI has reviewed the substantial knowledge base on MOX fuel irradiation in light water reactors (LWRs). The goal was to evaluate the technical feasibility of MOX fuel use in the U.S. reactor fleet for both existing and advanced LWR designs (Generation III/III+).

Within the context of long-term waste management and sustainable nuclear fuel supply, there continue to be discussions regarding whether the United States should consider recycling of light-water reactor (LWR) spent nuclear fuel (SNF) for the current fleet of U.S. LWRs. This report presents a parametric study of equilibrium fuel cycle costs for an open fuel cycle without plutonium recycling (once-through) and with plutonium recycling (single-recycling using mixed-oxide, or MOX, fuel), assuming an all-pressurized water reactor (PWR) fleet.

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-

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

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)

Ever since the 1950s, plutonium, used in fas reactors, has been seen as the key to unlocking the vast energy resource contained in the the world's uranium reserves. However, the reductions in expected nuclear reactor installation rates, combined with discovery of additional uranium, have led to a lengthening in the perceived time interval before fast reactors, the most effective users of plutonium, will make large demands on plutonium supplies. THere are several options concerning its use or storage in the meantime.

This report presents the analyses and results for the potential occurrence of external criticality events which could result from plutonium waste forms emplaced in a geologic repository similar to the one being developed at Yucca Mountain. The analyses evaluate both the MOX spent fuel and the immobilized plutonium waste forms in a repository if the waste package has degraded and if the fissile material has migrated to the invert and out into the far-field.

As part of the plutonium waste form development and down-select process, repository analyses have been conducted to evaluate the long-term performance of these forms for repository acceptance. Intact and degraded mode criticality analysis of mixed oxide (MOX) spent fuel is presented in Volume I, while Volume II presents the evaluations of the waste form containing plutonium immobilized in a ceramic matrix.