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 
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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 

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