05000324/LER-1981-049-01, /01T-0:on 810506,insp of RHR Heat Exchangers Revealed Partial Displacement of 2B Heat Exchanger Divider Plate.Caused by Blockage of Heat Exchanger Water Box Tubes. Damaged Divider Plate Is Undergoing Repairs

/01T-0:on 810506,insp of RHR Heat Exchangers Revealed Partial Displacement of 2B Heat Exchanger Divider Plate.Caused by Blockage of Heat Exchanger Water Box Tubes. Damaged Divider Plate Is Undergoing Repairs

ML20004B227
Person / Time
Site:	Brunswick
Issue date:	05/19/1981
From:	Poulk R CAROLINA POWER & LIGHT CO.
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
Shared Package
ML20004B221	List: 05000324/LER-1981-049, Forwards LER 81-049/01T-0 05000324/LER-1981-049-01, /01T-0:on 810506,insp of RHR Heat Exchangers Revealed Partial Displacement of 2B Heat Exchanger Divider Plate.Caused by Blockage of Heat Exchanger Water Box Tubes. Damaged Divider Plate Is Undergoing Repairs
References
LER-81-049-01T, LER-81-49-1T, NUDOCS 8105270415
Download: ML20004B227 (3)

LER-1981-049, /01T-0:on 810506,insp of RHR Heat Exchangers Revealed Partial Displacement of 2B Heat Exchanger Divider Plate.Caused by Blockage of Heat Exchanger Water Box Tubes. Damaged Divider Plate Is Undergoing Repairs

Event date:
Report date:
3241981049R01 - NRC Website

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REPORT DATE 80 EVENT OESCRIPTION AND pao 8ABLE CONSEQUENCES h (TT7] [ As a result of problems discovered with the Unit No.1 RHR heat exchangers, reported ini loIaI lLER 1-81-32, a special inspection of the Unit No. 2 RHR heat exchangers, type CEU, l

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lgo,ajl size $2-8-144,wasperformedtodetermineifsimilarproblemsexisted.

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,oj.,,prevealed a partial displacement of the 2B heat exchanger divider place.

g ; testing and analysis of the 2A heat exchanger determined that a higher than design dif-l l l O ; 2 l lferential pressure across its divider place would exist at the design flow rate. This j io,,j ldid not affect public health or safety. Technical Specifications 3.7.1.lb, 6.9.1.81 1

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43 44 47 CAUSE DESCRIPTION AND CORRECTIVE ACTIONS h l i l 0 l l A blockage of the heat exchanger water box tubes caused by an accumulation of shells fel J

both heat exchangers resulted in the 2B divider plate displacement and the calculated I i

The shells were removed from each heat exchanger which en-l g greduced capability in 2A.

l g labled the return of 2A to normal. The damaged divider plate in 2B is presentiv under-1 l

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d With the unit at power, an evaluation, based on indications of heat exchanger tube obstructions found during inspections of the Unit No. 1 RHR heat exchangers, was performed on the Unit No. 2 RHR heat exchangers to ascertain their operability.

Information concerning the condition of the RHR 2B heat exchanger was obtained using two techniques, ultrasonic and differential pressure testing. Both methods gave indications of divider plate damage. The lower head was th,en removed te obtain verification of the damage.

The divider plate separates the service water effluent from effluent in the RHR heat exchanger below the tube sheet. The top of the divider plate is weldod to the tube sheet, both sides are welded to the water box walls, and the bottem fits into a groove in the water box cover. The divider plate is 1" thick x 44 3/4" s

high x 54" wide and is made of SB-4n2, Alloy 715 (70-30 Cu-Ni) material.

The divider plate was found buckled in the center at the bottom whare it fits in the groove in the water box cover, and was displaced approximately 3 tr.ches at the bottom center of the divider plate. The deflection started approximately 3 inches from one side and 9 inches from the other. The welds along the top and sides of the plate remained intact (the plate was replaced in April of 1980, reference IIR 2-80-30).

Shells of various sizes were found on the inlet side and formed a layer averaging 2 inches in thickness with areas as much as 5 inches thick.

Additional shell blockage was also found inside approximately 50*. of the tubes.

Examination of RHR heat exchanger 2A using the ultrasonic test technique determined that the divider plate was intact with no displacement. Differential

. pressure tests, however, detected excessive dp's at design flow rates, and so RHR service water subsystem 2A was also declared inoperable.' 'The bottom head of the 2A heat exchanger was removed and the baffle plate was found to be intact as indicated by the ultrasonic test.

Shells of various sizes were found on tt.1 inlet side of the heat exchanger, and formed a layer approximately 1/4" to 1/2" thick. Additional shell blockage was also found inside affecting approximately 60*. of the tubes.

An evaluation of design and operating data determined that shells found in the 2B heat exchanger had blocked and obstructed tubes, producing excessive differential pressures across the divider plate during the operation of an RHR service water pump. These differential pressures produced stresses greater than the divider plate could withstand, causing it to bow to the as found condition.

The presence of shells in the heat exchanger resulted from a buildup of oyster shells on the walls of the main service water piping. As the oysters died, their shells fell off and slowly collected in the heat exchanger. The oyster buildup resulted from the chlorination system being out of service for an extended period due to operating difficulties.

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The high dp on the 2A RER heat exchanger was the result of shells found in the heat exchanger that had blocked and obstructed tubes (as in the 2B heat exchanger). The shell buildup was not as extensive as in the 2B heat exchanger due to its more infrequent use. With fewer shells, the differential pressures during pump operation were not sufficient to cause divider plate deformation.

The shells were removed from the water box and the tubes were cleaned to remove all obstructions in both heat exchangers. The divider plate of 2B is currently being repaired.

A review was made of the service water venting procedure, vent location, and piping arrangement to determine if problem areas txisted, the result of which could lead to a water hammer. None were fegn6. The piping itself was also inspected for evidence of water hammer damage or movement, and none was found.

An evaluation and inspection was performed on all other safety related loads cocied by service water to verify that the necessary cooling capability existed.

All the D/G heat exchangers were inspected as they see frequent service. While a limited amount of shells were found, the volume had no impact on the cooling capabilitys Random inspections or reviews of recent inspections were performed on the other safety related heat exchangers. All of these see infrequent service, and so there would not have been the opportunity for a gradual buildup of shells. No shell buildup problems were identified.

ACTIONS TO PREVENT RECURRENCE:

1.

PT 8.1.4 will be revised to include as a prerequisite that the RHR service water headers have been verified full by venting.

2.

The tubes in all the heat exchangers will be cleaned to remove ob-structions.

3.

A design review of the divider plate adequacy will be made.

4.

Service water piping will be cleaned as necessary to ensure that shell blockage from existing growth on the piping will not endanger the per-formance of safety related heat exchangers.

i.

The chlorinction of service water will be reinitiated to prevent future shell growth.

6.

The RHR heat exchangers will be monitored for shell buildup to ensure that divider plate stresses are maintained acceptably low.

7.

Existing periedic inspection procedures for' safety related service water cooled exchangers will be reviewed to assure that they are adequate.