05000336/LER-1980-011-03, /03L-0:on 800313,following Full Power Plant Trip, Two Broken Saddle Clamp Bolts Were Found on Hydraulic Snubber Hanger 490008 on Ms Lead to HP Turbine.Caused by Fatigue Cracking Due to High Vibration & Shear on Trips

/03L-0:on 800313,following Full Power Plant Trip, Two Broken Saddle Clamp Bolts Were Found on Hydraulic Snubber Hanger 490008 on Ms Lead to HP Turbine.Caused by Fatigue Cracking Due to High Vibration & Shear on Trips

ML19309E112
Person / Time
Site:	Millstone
Issue date:	04/11/1980
From:	NORTHEAST NUCLEAR ENERGY CO.
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I)
Shared Package
ML19309E107	List: 05000336/LER-1980-011, Forwards LER 80-011/03L-0 05000336/LER-1980-011-03, /03L-0:on 800313,following Full Power Plant Trip, Two Broken Saddle Clamp Bolts Were Found on Hydraulic Snubber Hanger 490008 on Ms Lead to HP Turbine.Caused by Fatigue Cracking Due to High Vibration & Shear on Trips
References
LER-80-011-03L, LER-80-11-3L, NUDOCS 8004180404
Download: ML19309E112 (2)

LER-1980-011, /03L-0:on 800313,following Full Power Plant Trip, Two Broken Saddle Clamp Bolts Were Found on Hydraulic Snubber Hanger 490008 on Ms Lead to HP Turbine.Caused by Fatigue Cracking Due to High Vibration & Shear on Trips

Event date:
Report date:
3361980011R03 - NRC Website

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60 61 DOCKET NUMUEH 68 69 E VEidT DATE 74 7b HEFOR T DATE 80 EVENT DESCnlPTioN AND PnoDADLE CONSEQUENCES h i Following a full power plant trip, 2 broken saddle clamp bolts were found on hydraulic l O 2 l snubber hanger 490008 on the f1S lead to the HP turbine.

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490002 bolt 3/4 inch UtlC I

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Bolts were replaced.

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LER 80-11/3L-0 Millstone Unit 2 Docket No. 50-336

EVENT DESCRIPTION

During power ascension on 3/13/80 following a full power plant trip, two broken pipe saddle clamp bolts were found on hydraulic snubber hanger 490008. This hanger is located on a main steam lead prior to the HP turbine.

The plant was at 30% power and the power ascension was halted until the broken bolts (1-1/2" UNF capscrews) were replaced.

All other hangers on the HP turbine steam leads were inspected satisfactorily.

Following another full power trip, with the plant at 99% power on 3/22/80, a broken saddle clamp bolt was found on hydraulic snubber hanger 490002.

The bolt (1-3/4" UNC machine bolt) was replaced and inspection revealed no other broken bolts on similar hangers.

Both bolts were carbon steel.

These events resulted in declaring hangers 490008 and 490002 inoperable and the plant was operated in accordance with Technical Specification Action Statement 3.7.8.1.

CAUSE DESCRIPTION The cause of the bolt failures was fatigue cracking due to high vibration levels and bolt shear on the plant trips. A UT inspection was conducted of all applicable bolting on HP turbine steam leads with no evidence of cracking found on the presently installed bol ting.

Review is ongoing to reduce main steam piping vibration levels and/or modify the hanger configuration to reduce fatigue loadings. Any further corrective actions will be implemented upon completion of the review.

There are no safety implications from these events in that these pipe supports are provided for a non-safety related purpose.

The

' original hydraulic snubber Technical Specification submittal included all snubbers in the plant. A change is pending to include only safety-related snubbers.

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