Modification of Vacuum Breakers on Mark I Containments (Generic Letter 83-08)
UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20555 February 2, 1983 See Attached Listing Gentlemen: SUBJECT: MODIFICATION OF VACUUM BREAKERS ON MARK I CONTAINMENTS (GENERIC LETTER 83-08 ) In the latter stages of the generic resolution of the Mark I Containment Long-Term Program suppression pool dynamic load definition, a potential failure mode of the vacuum breakers (connecting the ring header inside the torus to the drywell) in the chugging and condensation oscillation phases of blowdown to the torus during a LOCA was identified. In the "Mark I Containment Program Full-Scale Test Program Final Report" (NEDE-24539-P) it was reported that during the first full-scale test (M1), which had the highest initial vacuum breaker opening pressure, damage to the vacuum breaker pallet hinge and latching magnet occurred. In subsequent tests run at a lower opening pressure, with the vacuum breaker strengthened, damage was limited to the pallet sealing gasket which did not affect operability. At the time this was discovered, the generic phase of the Mark I Containment Long-Term Program was nearing completion; however, the Mark I Owners Group did commit to resolve this issue. Two vacuum breaker owner groups were formed, one for those with Atwood Morrill vacuum breakers that is using MPR as consultants, and one for those with GPE vacuum breakers that is using NUTECH as consultants. It is our understanding, based on a September 10, 1982 meeting with General Electric and the Mark I Owners Group, this effort has been completed and the results have been applied to obtain plant specific resolutions. Although this issue was not included within the scope of the Mark I Containment Long-Term Program as identified in NUREG-0661, these vacuum breakers provide protection to maintain containment integrity and, as such, are subject to staff review. Therefore, we request that within 90 days of receipt of this letter you provide a commitment to submit the results of the plant unique calculations which either formed the bases for modifications to the vacuum breakers or provide the justification for their as-built acceptability. Schedules for completion of any modifications should also be included in your response. 8302030089 . 2 It is suggested, if possible, that the resolution of this issue be submitted with the Mark I Long-Term Program - Plant Unique Analysis Report for post- implementation review. This request for information was approved by the Office of Management and Budget under Clearance Number 3150-0091 which expires October 31, 1985. Sincerely, Darrell G. Eisenhut, Director Division of Licensing cc: Service List
Page Last Reviewed/Updated Tuesday, March 09, 2021
Page Last Reviewed/Updated Tuesday, March 09, 2021