NRC SFST ISG-5: Confinement Evaluation

Several changes have occurred since the issuance of NUREG-1536, “Standard Review Plan
(SRP) for Dry Cask Storage Systems,” that affect the staff’s approach to confinement
evaluation. The attachment to this ISG integrates the current staff approach into a revision of
ISG-5. The highlights of the changes include:
• Reflects October 1998 revisions to 10 CFR 72.104 and 10 CFR 72.106.
• Expands and clarifies acceptance criteria associated with confinement analysis and
acceptance of “leak tight” testing instead of detailed confinement analysis.
• Updates staff review guidance for design and requirements for the cask seal monitoring
system and adds guidance for accident analysis of “latent” failure concerns.
• Updates source term guidance to (1) include ISG-5 recommendations, (2) include
actinide activity that contributes greater than 0.01% of the design basis activity, and
(3) allow for a reduction of fines that can escape the cask (with justification by applicant).
• Deletes non-mechanistic (confinement boundary failure) accident analysis and revise
staff review guidance for evaluation of normal, off-normal, and accident cases. The
significant change is that the evaluated leaks are related to the as-tested leak rate.
• Updates confinement analysis section to reflect ISG-5 and describe what types of
analysis should be done. Dose to lens of the eye will be addressed if skin dose and
TEDE do not exceed 15 rem.

Revision 1