Spent Fuel Project Office Interim Staff Guidance - 8

Spent Fuel Project Office, Interim Staff Guidance - 8, Revision 1

In the past, criticality analysis of pressurized water reactor (PWR) fuel stored in racks and casks has assumed that the fuel is fresh with the maximum allowable initial enrichment. If credit is allowed for fuel burnup in the design of casks that are used in the transport of spent light water reactor fuel to a repository, the increase in payload can lead to a significant reduction in the cost of transport and a potential reduction in the risk to the public. A portion of the work has been performed at Oak Ridge National Laboratory (ORNL) in support of the U.S.

This research examines the practice of equating the reactivity of spent fuel to that of fresh fuel for the purpose of performing burnup credit criticality safety analyses for PWR spent fuel pool (SFP) storage conditions. The investigation consists of comparing kf estimates based on reactivity "equivalent" fresh fuel enrichment (REFFE) to kl estimates using the actual spent fuel isotopics.

STARBUCS is a new prototypic analysis sequence for performing automated criticality safety analyses of spent fuel systems employing burnup credit. A depletion analysis calculation for each of the burnup-dependent regions of a spent fuel assembly, or other system containing spent fuel, is performed using the ORIGEN-ARP sequence of SCALE. The spent fuel compositions are then used to generate resonance self-shielded cross sections for each region of the problem, which are applied in a three-dimensional criticality safety calculation using the KENO V.a code.

Spent Fuel Project Office, Interim Staff Guidance - 8, Revision 2 - Burnup Credit in the Criticality Safety Analyses of PWR Spent Fuel in Transport
and Storage Casks

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.

In 1999, the United States Nuclear Regulatory Commission (U.S. NRC) initiated a research program
to support the development of technical bases and guidance that would facilitate the implementation of burnup
credit into licensing activities for transport and dry cask storage. This paper reviews the following major areas of
investigation: (1) specification of axial burnup profiles, (2) assumption on cooling time, (3) allowance for
assemblies with fixed and removable neutron absorbers, (4) the need for a burnup margin for fuel with initial