05000251/LER-1979-004-03, /03L-0 on 790315:vendor Reported Main Steam Line Mechanical Snubber,Returned for Routine Testing,Was in locked-up Condition.Caused by Damaged Thrust Bearing. X-stop Adjusted

/03L-0 on 790315:vendor Reported Main Steam Line Mechanical Snubber,Returned for Routine Testing,Was in locked-up Condition.Caused by Damaged Thrust Bearing. X-stop Adjusted

ML17338A655
Person / Time
Site:	Turkey Point
Issue date:	04/13/1979
From:	Schoppman M FLORIDA POWER & LIGHT CO.
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
Shared Package
ML17338A652	List: 05000251/LER-1979-004, Forwards LER 79-004/03L-0 05000251/LER-1979-004-03, /03L-0 on 790315:vendor Reported Main Steam Line Mechanical Snubber,Returned for Routine Testing,Was in locked-up Condition.Caused by Damaged Thrust Bearing. X-stop Adjusted
References
LER-79-004-03L-02, LER-79-4-3L-2, NUDOCS 7904230297
Download: ML17338A655 (4)

LER-1979-004, /03L-0 on 790315:vendor Reported Main Steam Line Mechanical Snubber,Returned for Routine Testing,Was in locked-up Condition.Caused by Damaged Thrust Bearing. X-stop Adjusted

Event date:
Report date:
2511979004R03 - NRC Website

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re or ed that a %fain Steam line mechanical snubber which had been returned for routine testing was in a "Locked-up" condition.

An examination during the upcoming refueling outage willverify the integrity of the Hain Steam. piping.

The mechanical snubbers that rely on an X-stop to minimize loadin durin operational transients have also been inspected and verified to be operationaL.

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REPORTABLE OCCURRENCE 251-79-4 LICENSEE EVERT REPORT PAGE T4'0 Additional Event Descri tion and Probable Conse uences:

While replacing hydraulic snubbers with mechanical snubbers in October of 1978, one mechanical snubber on a main steam line (Tag Number 84 in TS 3.13) was also replaced so that it could be returned to the vendor for routine testing On Harch 7, 1979, the vendor reported that the snubber was in a "locked-up" condition.

Subsequent disassembly showed that the thrust bearing had been damaged.

Nominal thermal growth of the piping at the snubber location is slight (calculated to be approximately 0.07 inch), therefore, a "locked-up" snubber at that. location would impose minimal thermal growth stress on the piping.

En addition, piping, stress at this location due to past dynamic transients, is judged to have been acceptable, based on an evaluation by the Architect-Engineer.

To further verify the integrity of the main steam piping at the location in question, the area will be visually examined during the upcoming refueling outage

. The intent of examin-ation will be to show that the piping is in satisfactory condition.

The mechanical snubbers that rely on the X-stop (described in the Cause Description) to minimize their loading during operational transients will also be inspected to verify operability.

Additional Cause Descri tion and Corrective Action:

The occurrence was caused by a damaged thrust bearing.

Tne thrust bearing was damaged because the snubber had been exposed to greater than. rated load.

During a transient (e.g., turbine trip),. the dynamic loading of the subject snubber should be low because the steam piping is restrained elsewhere along its length by an axial X-stop, which is intended to absorb dynamic transient loads.

However, due to excessive clearance between the piping attachment and the X-stop restraint, any transient. motion of the pipe would be greater than intended.

Xt has been determined that the amount of transient pipe motion allowed by the clearances in the X-stop probably caused the snubber to experi-ence greater than its 15,000 lb. rated load before the load could be absorbed by the X-stop.

The X-stop'as been adjusted so that it will properly absorb dynamic loads from operating transients.

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