ML20084L541

AO 50-237/1974-41:on 740823,during Shutdown Insp,Pin Hole Leak Discovered on 2B Reactor Feed Pump Min Flow Line to Condenser.Caused by Erosion in Min Flow Line.Line Weld Ground Out & Mod Initiated to Replace Line Section

ML20084L541
Person / Time
Site:	Dresden
Issue date:	08/30/1974
From:	Stephenson B COMMONWEALTH EDISON CO.
To:	James Keppler NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
Shared Package
ML20084L534	List: ML20084L529 ML20084L541
References
623-74, NUDOCS 8305230358
Download: ML20084L541 (3)

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• e' salth Ediso'n g One Firs vil P'a 1 C Ne g e, l'in d s y- Address r iy to. Post 0:hce Box /67 Chicago Illinois 60690 BBS Ltr.#623-74 Dresden Nuclear Power Station

'R. R. #1 Morris, Illinois 60450 August 30, 1974 k lJ g V s Mr. Jamea 0. Keppler, Regional Director Directorate of Regulatory Operations-Region III 50-237 c4 d@ff)E

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U. S. Atomic Energy Coaxassion * ** ' -c 1,au f-799 Roosevelt Road ' :~ 7" ,d Glen Ellyn, Illinois 60137 i c5  % "S. N/

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SUBJECT:

REPORT OF ABNORMAL OCCURRENCE PER SECTION 6.6.B 0F THE TECFRICAL' .

SPECIFICATIONS. 6 RFP MIlm4UM FIIT4 LINE LEAK.

References:

1) R m latory Guide 1.16 Rev.1 Appendix A

2) Notification of Region III of AEC Regulatory Operations Telephone: Mr. F. Maura, 1000, hours on August 23, 1974 Telegram: Mr. J. Keppler, 1312 hours0.0152 days <br />0.364 hours <br />0.00217 weeks <br />4.99216e-4 months <br /> on August 23, 1974

3) Drawing Number: M-14 Report Number 50-237/1974-41 .

Report Date: August 30, 1974 Occurrence Date August 23, 1974 Facility: Dresden Nuclear Powcr Station, Morris, Illinois IDENTIFICATION OF OCCURRENCE At about 0300 on August 23, 1974, operating personnel were searching for condenser vacuum leaks during unit shutdown. A pin-hole leak was dio-covered en 2B reactor feed pump minimum flow line to the condenser.

CONDITIONS PRIOR TO OCCURRENCE Prior to the occurrence, the reactor was in the refuel mode with all control rods inserted at position "00". r' DESCRIPPION 0? OCCURRENCF so .$ pr s At about 0300 on August 23, 1974, operating personnel were cearching for condenser vacuum leaks during unit shutdown. A pin-hole leak was discovered on 2B reactor feed punp mini:::um flow line to the condensor. The pinhole was located in a fillet weld around a patch that was tr.ade over a pt evious leak in the line.

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Mr. James G. Keppler 9 - 2-9 August 30, 1974 DESIGNATION OF APPARD7P CAUSE OF CCCURRENCE (Other)

Apparent cause of the occurrence was erosion of the minimum flow line resulting from leakage past normally closed reactor feed pump minimum flow valve PCV 2-3201B. Data taken late in July, 1974 revealed little reduction in pipe wall thickness, at the time of repair to PCV 2-3201B. ,

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It was assumed, prior to grinding out the weld, that the leak f developed between the original pipe and welded patch.

In the process of grinding out the complete weld, it was noted that the weld contained slag pockets and that the pin hole was located in one of these pockets. This fact coupled with the valve leakage problem con-tributed directly te the line failurc.

f ANALYSIS OF OCCURRHK:E The health and safety of the plant personnel nor the public were jeopardized as a result of this pin hole leak. With three (3) reactor feed pumps on Unit 2, normal full load operation requires two operable pumps with one in standby. The 10,C00 GET capacity pumps are constant creed pumps, uith a minicum flow setting of 900 GPM. Vnenever the feedwater requirements fall below this minimum flow, the minimum flow control valve slowly opens up allowing feedwater recirculation back into the condenser hot well. Therefore, the minimum flow line is in service during minimum feedwater flow conditions and pump startup only.

During norinal operation, this line is under vacuum conditions which

indicates that leakage would be into the lino rather than out. Thus, the only water leakage would be curing pump minimum flow conditions.

i In reviewing the area where the leak occurred, only a very minimal i

amount (wetting the surface of the pipo) of water was discharged through the pin-hole.  ;

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. CORRFCTIVE ACTIONS The correctivo action taken was to grind out the weld and reweld the patch using a certified welder and rod. The usage of a certified welder 1

was not required for this non-safety related component but this was thought to be the ,est method available.

1 In addition to the above action, a modification has been initiated ,

l .to replace the section of line on all three minimum flow lines for Unit 2

! and 3 The sections of pipe have been problem areas in the past due to.the l erosion created by the piping configuration. These carbon steel sections s will be replaccd with chrcme-moly material which will be more resistive to corrosion / erosion.

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Mr. James G. Kepp er August 30, 1974 i

l Erosion of piping is accelerated by leakage past minimum flow valves and station has completed repairs to 23 and 2C valves. Repairs to 2A minimum flow valve will be scheduled as soon as possible, and should be completed during refueling outage scheduled to begin in November, 1974.

FAILURE DATA A previous failure occurred on June 12, 1973 where the section of piping was found to be eroded on 2B reactor feed pump minimum flow line creating a leak. At that time, the corrective action was to weld a patch over the eroded area to prevent further leakage.

Sincerely, p k j

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L .eB; ,Stephenson gf4IO Superintendent BBS:RLWido 9

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