ML19261D620

Final Deficiency Rept:Overstressed Penetrations in Containment Shell.Design Drawings Are Being Revised to Move Snubbers & Secure Them Between Piping & Steel Containment. Mods Will Be Performed Prior to Respective Fuel Load Dates

ML19261D620
Person / Time
Site:	Sequoyah
Issue date:	06/15/1979
From:	TENNESSEE VALLEY AUTHORITY
To:
Shared Package
ML19261D619	List: ML19261D618 ML19261D620
References
NUDOCS 7906200383
Download: ML19261D620 (1)

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i ENCLOSURE '

SEQUOYAH NUCLEAR PLANT UNITS 1 AND 2 OVERSTRESSED PENETRATIONS IN THE CONTAINMENT SHELL ,

NCR CEB 79-14 10 CFR 50.55(e) FINAL REPORT Description of Condition The penetration insert plate for the containment spray (Penetrations X-48A and X-48B) and residual heat removal spray (Penetrations X-49A and X-49B) has been found to be overstressed in secondary bending as a result of the imposed nozzle loads. Under design loading conditions, this could result in buckling of the containment shell and insert plate through which these penetrations pass.

TVA originally supplied CBI with estimated penetration design loads which were used to design and fabricate the penetrations. IVA later revised these loads upward as a result of rigorous piping analysis of the systems.

CBI then rechecked the penetration stresses and found overstresses were present in several penetrations. CBI reported tnese overstressed condi-tions to TVA for support modification. However, the four subject penetraticas were omitted from the CBI list.

Specifically, the containment spray and the RHR spray have seismic snubbers secured between the piping and the shield building. This snubber configu-ration requires the piping system to absorb all of the relative dynamic movement between the steel containment and the shield building.

Safety Implications .

Had the deficiency gone uncorrected, the most likely result would be plastic deformation (without failure) of the containment shell and insert plate in the vicinity of these penetrations. Since this result cannot be.

verified by analytical or mechanical methods, it must be conservatively assumed that deformation would be sufficient to cause failure of the containment. Such failure would result in loss of containment integrity and could consequently advers,ely affect the safe operation of the plant.

Corrective Action To lower the loads for these "four nonconforming penetrations, TVA is revising the design drawings to move the snubbers and secure them between the piping and the steel containment. This modification eliminates the effect of the relative dynamic movement between the steel containment and shield buildings and reduces the loads on the penetrations to within the code allowable limits. Actual modifications to the penetrations will be performed on each unit before its respective fuel load date.

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