[en] The design approach for criticality of the disposal container and waste package will be dictated by existing regulatory requirements. This conclusion is based on the fact that preclosure operations and facilities have significant similarities to existing facilities and operations currently regulated by the NRC. The major difference would be the use of a risk-informed approach with burnup credit. This approach could reduce licensing delays and costs of the repository. The probability of success for this proposed seamless licensing strategy is increased, since there is precedence of regulation (10 CFR Part 63 and NUREG 1520) and commercial precedence for allowing burnup credit at sites similar to Yucca Mountain during preclosure. While NUREG 1520 is not directly applicable to a facility for handling spent nuclear fuel, the risk-informed approach to criticality analysis in NUREG 1520 is considered indicative of how the NRC will approach risk-informed criticality analysis at spent fuel facilities in the future. The types of design basis events which must be considered during the criticality safety analysis portion of the Integrated Safety Analysis (ISA) are those events which result in unanticipated moderation, loss of neutron absorber, geometric changes in the critical system, or administrative errors in waste form placement (loading) of the disposal container. The specific events to be considered must be based on the review of the system's design, as discussed in Section 3.2. A transition of licensing approach (e.g., deterministic versus risk-informed, performance-based) is not obvious and will require analysis. For commercial spent nuclear fuel, the probability of interspersed moderation may be low enough to allow nearly the same Critical Limit for both preclosure and postclosure, though an administrative margin will be applied to preclosure and possibly not to postclosure. Similarly the Design Basis Events for the waste package may be incredible and therefore not re quire an administrative margin, or at least one that is less than the one used currently (0.05) for all waste forms (e.g., CRWMS M and O 1999c, criteria 1.2.1.5, p. 10.) In this case, the margin-to-criticality for preclosure and postclosure in the subsurface facility would be closer to that used for postclosure (if any). This would facilitate a seamless transition, including the use of burnup credit