ML20205G173

Ro:On 870222,steam Line Break on Scavenging Steam Vent Line from Moisture Separator Reheater Experienced.Caused by Classic Fatigue Failure in Heat Affected Zone of Weld Joining Alloy 800 Matl.Temporary Restraints Added

ML20205G173
Person / Time
Site:	Waterford
Issue date:	03/18/1987
From:	Carns N LOUISIANA POWER & LIGHT CO.
To:	Martin R NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV)
References
W3E87-139, NUDOCS 8703310389
Download: ML20205G173 (3)

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_d l) i March 18, 1987 i MAR 2 31987 j d W3E87-139 A4.05 QA Mr. R. D. Martin Regional Administrator, Region IV U. S. Nuclear Regulatory Commission 611 Ryan Plaza Drive Suite 1000 Arlington, TX 76011

SUBJECT:

Waterford SES Unit 3 MSR Scavenging Steam Vent Line Break

Dear Mr. Martin:

The attached report on Waterford-3's MSR scavenging steam vent line break may be of interest to you and is hereby forwarded.

Yours very truly,

'?]/ J' e N. S. Carns Plant Manager - Nuclear NSC/dm Attachments cc: B. W. Churchill, W. M. Stevenson, J.11. Wilson, NRC Resident Inspectors' Office (W3), Administrator Nuclear Energy Division (State of Louisiana),

American Nuclear Insurers, Project Files, Administrative Support K

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Moisture Separator Reheater (MSR) Scavenging Steam Vent Line Break On the morning of February 22, 1987, while operating at full power, Waterford-3 experienced a steam line break on the scavenging steam vent line coming from the Moisture Separator Reheater (MSR). Power was reduced and the plant was stabilized at about 70% power with the break isolated. There were no personnel injuries and with exception of the broken line, material damage was limited to insulation in the immediate area. During the course of the event, a large quantity of steam condensed in the turbine building. Chemistry samples were  ;

taken and confirmed that no activity was being released to the drain system from the condensed steam. Temporary repairs isolating the broken line were effected during the day and the plant commenced a return to full power during the evening.

The attached sketch is a simplified drawing of the system. The four scavenging steam vent lines (two per MSR) are relatively long runs of piping to the extrac-tion steam header and the condenser. The movement of the line to the extraction I

steam header where the failure occurred apparently was such that fatigue failure was induced.

An evaluation of the broken section revealed that the failure occurred in the Heat Affected Zone of the weld joining the Alloy 800 material to the Carbon Steel outlet flange. An analysis of the failure determined it to be an example of a " classic" fatigue failure caused by the movement of the scavenging steam vent lines. As a precautionary measure, all four control sections to the No. 1 Extraction Steam Line were replaced on March 7, 1987.

A " Control Section" is a short length of pipe utilized at Waterford-3 to insure correct flow through the innermost reheater U-Tubes, thereby providing the same tube wall temperature in both the upper and lower Icg of each U-Tube. Like an orifice, the flow is maintained at a constant rate so long as upstream and down-stream pressures remain constant. Unlike an orifice, the pressure reduction is gradual rather than abrupt, and the erosive effects of flashing are reduced.

The four (4) Control Sections to No. I heater extraction line and the four (4) alternate control sections at the condenser are 2.5 ins. O.D. x 1.0937 ins. I.D.

x 19.00 ins. overall length. They are fabricated of SB 408 Alloy 800 bar stock welded at the ends to Carbon Steel flanges to facilitate installation.

Temporary restraints have been added to the scavenging steam vent lines. A permanent station modification is in progress to ensure proper restraint and support of these lines to reduce the potential for any further fatigue failure.

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