ML19338F054

Updated LER 80-017/01T-1:on 800326,reanalysis of Piping & Supports for Main Steam Sys Outside Containment Revealed Design Deficiencies If All Five Safety Relief Valves Opened on Any Manifold.Caused by Load Resulting from Open Valves

ML19338F054
Person / Time
Site:	Beaver Valley
Issue date:	09/30/1980
From:	Lacey W DUQUESNE LIGHT CO.
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I)
Shared Package
ML19338F050	List: ML19338F049 ML19338F054
References
LER-80-017-01T, LER-80-17-1T, NUDOCS 8010070464
Download: ML19338F054 (2)

Text

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J Attachment To LER 80-17/OlT-1 Beaver Valley Power Station Duquesne Light Company Docket No. 50-334 During the reanalysis of the piping and supports for the main steam system outside containment, it was determined that the existing design did not meet the B31.1 allowables. The interim criteria had been met for station start-up as the DBE seismic and deadweight loads were .in the acceptable range. For the long-term solution, the inclusion of occasional loads presented an unacceptable condition, as the magnitude of loads and stresses caused by the safety relief valves opening resulted in generation of stresses over allowable limits. The load combination of pressure, deadweight, and occasional loods, including all seismic effects, as defined in the FSAR, yielded stresses over the code allowables.

"he original analysis performed on this portion of the main steam system had been qualified using improper load combinations. Bending stresses and local stresses were calculated and compared against acceptable limits, but the two loadings had not been combined together as was required.

The reanalysis indicated that the main steam line was deficient in design if all five safety relief valves opened on any manifold. The overstressed condition existed in the connections at the manifold to each of the safety relief valves.

Also, both ends of the pipe between the main steam line and the manifold were overstressed at the junction point. The blowdown force caused by the valve opening resulted in the unsupported discharge elbow transmitting forces and moments into the manifold and run pipe. The analysis used to generate these results was an equivalent static method. Thrust force was calculated in the discharge piping and applied at the discharge elbow. These static results were combined with results from the seismic analysis to form the occasional loading case.

The solution to this problem was to revun the discharge piping such that the manifold and associated piping were unloaded during safety valve lift.

The modification included an anchor at the valve house roof to take the blowdown force. The piping between the safety relief valves and the roof was routed to take advantage of available space, to avoid interferences, and to minimize effects from thermal, seismic, and dynamic conditions which existed in the system.

The modified discharge piping was reanalyzed using NUPIPE, considering thermal, deadweight, seismic, and dynamic conditions. The dynamic condition was analyzed

• using forcing functions devel'oped by a steam hammer analysis. The forcing functions were the input for a time history analysis in NUPIPE. The load combinations utilized are in compliance with the code requirements and FSAR commitments, and all stresses were found to be acceptable.

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