05000260/LER-1980-053-03, Discovered Leak on Heat Exchanger During Steady State Operation.Caused by Leaking Inner Head Gasket on RHR Heat Exchanger Due to Loose Flange Nuts.Gasket Replaced & New Nuts W/Locking Tabs Installed

Discovered Leak on Heat Exchanger During Steady State Operation.Caused by Leaking Inner Head Gasket on RHR Heat Exchanger Due to Loose Flange Nuts.Gasket Replaced & New Nuts W/Locking Tabs Installed

ML19350D669
Person / Time
Site:	Browns Ferry
Issue date:	05/11/1981
From:	TENNESSEE VALLEY AUTHORITY
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
Shared Package
ML19350D619	List: 05000260/LER-1980-053, Forwards Updated LER 80-053/03X-1 05000260/LER-1980-053-03, Discovered Leak on Heat Exchanger During Steady State Operation.Caused by Leaking Inner Head Gasket on RHR Heat Exchanger Due to Loose Flange Nuts.Gasket Replaced & New Nuts W/Locking Tabs Installed
References
LER-80-053-03X, LER-80-53-3X, NUDOCS 8105180318
Download: ML19350D669 (3)

LER-1980-053, Discovered Leak on Heat Exchanger During Steady State Operation.Caused by Leaking Inner Head Gasket on RHR Heat Exchanger Due to Loose Flange Nuts.Gasket Replaced & New Nuts W/Locking Tabs Installed

Event date:
Report date:
2601980053R03 - NRC Website

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8 60 el QQCK ET NUM8 ER 64 69 EvtNT OATE 74 79 REPGRT DAT E 40 EVENT CESCRIPTION AND PROBABLE CONSEGUENCES h Iot2i lWith unit in steady state operation it was found durine TI-36A that there was leak on I go,3, lthe 2C heat exchanger. Redundant systems were available. There waP no public health l in14; l hazard.

See technical specification 3.5.B.S.

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BFRO-50-259/7823.I io,3, l8043; 260/8033, 8034, 8035.

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Tir.n.ssro *.'t.11ey Authority Form DF-17 Browns Ferry Nuclear Plant BF 15.2 3/24/81 LER SUPPLEMENTAL INFORMATION BFRO-50 260 /_80053R1 Technical Specification Involved 3.5.B.5 Reported Under Technical Specification

6. 7. 2. b (2)

Date of Occurrence 12/5/80 Time of Occurrence 1240 Unit 2

Identification and Description of Occurrence:

During routine test TI-36A, it was found that RHR heat exchanger 2C was leaking.

Cenditions Prior to Occurrence:

Unit 1 at 99% steady state power.

i Unit 2 at 97% steady state power Unit 3 refuel outage Action specified in the Technical Specification Surveillance Requirements met due to inoperable ecuipment. Describe.

Perforned testing required by Tech. Spec. 4.5.B.5 Apparent Cause of Occurrence:

Leaking inner head gasket due to loose flange nuts caused by thermal cpeling and vibration.

Analysis of Occurrence:

There was no danger to the health or safety of the public, no damage to plant or equipment and no resulting significant chain of events.

Ccerective Action:

The gasket was replaced and new nuts with locking tabr ere used to hold the gasket in place. The heat exchanger was then tested par F0!I-49.

Failure Dat:1:

259/8043, 259/7823, 260/8033, 260/8034, 260/8035.

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ATTACHMENT 2 BFRO-50-260/8053 R1 Recurrent problems have been evident concerning leaking floating head gaskets on the RHR heat exchangers. Apparently thermal cycling and vibration caused loosening of the lock nuts.

Corrective action has consisted of increasing the torque applied to the nuts, installing half size lock nuts, monitoring the RHR system for radiation present, and installing locking tabs.

A report dated February 5, 1981' entitled, " Browns Ferry Nuclear Plant RHR Heat Exchanger Floating Head Stud Tensioning Investigation Report and Recommendations," proposes the following conclusions and recommendations.

Conclusions:

1.

The 750 ft-lb torque applied to the nuts does not exert consistent.

uniform seating stress to the existing gaskets.

2.

There is a possibility of exceeding stud yield tension if the torque is incraased above 750 ft-lbs unless stud elongacion is monitored.

3.

RHR heat exchanger floating heads should be reassembled using stud elongation as the acceptance criteria rather than torque vf_ *e.

Accuracy of the elongation measuring device must be t.001 in.

or less to assure proper stress levels and to detect any relaxation of stress over operating periods.

Recommendations:

1.

Develop an elongation measuring tool and stud end design capable of measuring elongation with a repeatable accuracy of

.001 inch.

2.

Perform 100% baseline measurement on the next coavenient heat exchanger to verify stressed and unstressed stud elongation measure-ment of 0.025 t.002 inches.

3.

Remeasure elongation af ter a minimum of one shutdown cooling cycle comparing measurements to the original stressed condition.

4.

Reassemble RHR heat exchangers 2D and 3C using lock tabs and 0.25 1 002 inches stud elongation.

3.

Revise MM7-49 to reflect these procedures.