Item A-7: Mark I Long-Term Program (former USI)

DESCRIPTION

During testing for an advanced BWR containment system design (MARK III), suppression pool hydrodynamic loads were identified which had not been considered in the original design of the MARK I containment system. To address this issue, a MARK I Owners Group was formed and the assessment was divided into a short- term and a long-term program. The results of the NRC staff's review of the MARK I Containment Short-Term

Program were documented in NUREG-0408.[1] The long-term program was conducted to provide a generic basis to define suppression pool hydrodynamic loads and the related structural acceptance criteria, such that a comprehensive reassessment of each MARK I containment system could be performed.

A series of experimental and analytical programs were conducted by the MARK I Owners Group to provide the necessary bases for the generic load definition and structural assessment techniques. The generic methods proposed by the MARK I Owners Group, as modified by the NRC staff's requirements, were to be used to perform plant-unique analyses which would identify the plant modifications, if any, needed to restore the originally intended margin of safety in the MARK I containment designs. This item was originally identified in

NUREG-0371[2] and was later declared a USI in NUREG-0510.[3]

CONCLUSION

This USI was RESOLVED with the issuance of Supplement 1 to NUREG-0661[4] and SRP[5] Section 6.2.1.1C. For operating BWRs, MPA D-01 was established by DL/NRR for implementation purposes.