05000368/LER-1979-033-01, Unisolatable Leak Discovered at Seal Cavity Pressure Sensing Line to 2PT-6006 for Reactor Coolant Pump 2P32A.Caused by Mechanical Fatigue Resulting from Low Stress Cyclic Loading.Mods Complete

Unisolatable Leak Discovered at Seal Cavity Pressure Sensing Line to 2PT-6006 for Reactor Coolant Pump 2P32A.Caused by Mechanical Fatigue Resulting from Low Stress Cyclic Loading.Mods Complete

ML19345B439
Person / Time
Site:	Arkansas Nuclear
Issue date:	11/20/1980
From:	Shively C ARKANSAS POWER & LIGHT CO.
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV)
Shared Package
ML19345B434	List: 05000368/LER-1979-033, Forwards Updated LER 79-033/01X-1 05000368/LER-1979-033-01, Unisolatable Leak Discovered at Seal Cavity Pressure Sensing Line to 2PT-6006 for Reactor Coolant Pump 2P32A.Caused by Mechanical Fatigue Resulting from Low Stress Cyclic Loading.Mods Complete
References
LER-79-033-01X, LER-79-33-1X, NUDOCS 8012010324
Download: ML19345B439 (4)

LER-1979-033, Unisolatable Leak Discovered at Seal Cavity Pressure Sensing Line to 2PT-6006 for Reactor Coolant Pump 2P32A.Caused by Mechanical Fatigue Resulting from Low Stress Cyclic Loading.Mods Complete

Event date:
Report date:
3681979033R01 - NRC Website

text

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Od REVISED REPORT - PREVIOUS REPORT DATE 5/25/79 U.S. NUCLE AR REGULATORY COMMISSION NRC f 0RM 364 LICENSEE EVENT REPORT EXHIBIT A CONTROL BLOCK: l l l l l l IPLEASE PRINT OR TYPE ALL REOUIRED INFORMATIONI l AlR l Al' N] 0 l 2 lgl 010 l -l0 l 0 l 0l Oj 0 l-l 0 l0 lg l1 l 1 l1 l 1 lgl clar lg 1,

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j EVENT DESCRIPTION AND PRO 8ABLE CONSEQUENCES O'o 4

rETrl i During Mode 3 operation, an unisolatable leak was discovered at the seal i I

EIT) I cavity pressure sensino line to 2PT-6006. for the Reactor Coolant Pumo. I I 2P32A.

The leak was verified to be from a crack in the weld and heat I

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i affected zone of the weld that attaches the line to the cavity.

The leakt o s to 1:; I rate was estimated to be less than GPM.

No similar occurrences.

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CAUSE DESCRsPTION AND CORREC flVE ACTIONS 27 l Based on macroscopic and microscopic observations, the crack is character +

i o m I istic of high cycle fatique.

No signs of corrosion cracking.

Concluded i m i that the break is a result of a mechanical fatigue resulting from low i

m i stress cyclic loading. Vibration analysis completed. Modifications to i i angers and installation of vibration dampening material reduced vibratiop h

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Reportable Occurrence Report No.

50-368/79-033/01X Rev. 1 2.

Report Date:

11/20/80 3.

Occurrence Date:

5/14/80 4

Facility: Arkansas Nuclear One - Unit Two Russellville, Arkansas 5.

Identification of Occurrence:

Abnormal degradation discovered in the reactor coolant pressure boundary, identified as unisolatable leak.

Reportable per T.S. 6.9.1.8.c.

6.

Conditions Prior to Occurrence:

Steady-State Power Reactor Power 0

Mwth Hot Standby Net Output 0

Hwe Cold Shutdown Percent of Full Power 0 Refueling Shutdown Load Changes During Routine Power Operation Routine Startup X

opera tion MODE 3

Routine Shutdown Operation Other (specify) 7.

Description of Occurrence:

An unisolatable leak was discovered at the seal cavity pressure sensing line to 2PT-6006, for the Reactor Coolant Pump, 2P32A.

The leak was verified.to be from a crack in the weld and heat affected zone of the weld that attaches the line to the pump seal cavity.

Leak rate was estimated to be < GPM.

Cooldown and depressurization was initiated immediately per requirements of Action Statement T.S. 3.4.6.2.a.

b Rt ortabic Occurrence Report No. 50-368/79-033/01X Rev. 1

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8.

Designation oc Apparent Cause of Occurrence:

Design Procedure Fhnufacture Unusual Service Condition Including Environmental Installation /

Construction Component Failure X

(See Failure Data)

Operator Other (specify)

The leaking pipe was removed from the pump seal by cutting through the weld behind the crack so the entire crack was preserved intact.

The type 316 stainless steel schedule 80 3/4 inch pipe was sent to Southwest Researcn Institute for failure analysis.

A fractographic examination was conducted on a section of the weld that included one crack tip. The macroscopic virface appearance indicated fatigue with multiple initiation sites.

Scanning electron microscope fractographs from the fracture surface revealed evidence of periodic markings indicative of high cycle fatigue.

Energy dispersive x-ray spectroscopy of the fracture surface revealed no contaminate species. Metallographic sections of the primary crack showed unbranched, predominately transgranular, propagation.

The pipe base metal was verified to be within tolerance of composition and hardness, as set in ASTM Standard A-312. There were no signs of external corrosion or chloride stress corrosion cracking.

Failure analysis concluded that the crack is purely the result of mechanical fe'.igue resulting from relatively low stress cyclic loading.

9. Analysis of Occurrence:

. Analysis of the fault indicated that the fatigue in the weld adjoining the rotating equipment was a result of (1) vibration (possible in resonance) of the pump, (2) Inadequately supported flange and/or associated piping hangs from the end of a horizontal pipe section.

4

- r Reportable Occurrence Report No. 50-368/79-033/01X Rev. 1 i

10

Corrective Action

The pipe section was upgraded to a schedule 160. A design change

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4 modified associated hangers and added rubber material on several

- hanger to pipe attachments to dampen pipe vibrations.

The reactor

- coolant pump seal removal procedures were revised for added insurance thai. the rubber vibration dampening material is reinstalled following maintenance on each of the affected pipe hangers and tr.at the pipe-hangers are tightened properly.

l Vibration measurements were taken on.the 2P32A and 2P32C pumps following modification. The data was evaluated and it was verified t

i that the vibration was reduced to an acceptable level.

Dye penetrant

- inspections were made at several weld connections on the seal piping j

and no additional evidence of cracks were discovered.

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Failure Da'ta:

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No similar occurrences.

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