ML20092D721

Safety Evaluation for Operation of Peach Bottom Atomic Power Station,Unit 3

ML20092D721
Person / Time
Site:	Peach Bottom
Issue date:	06/20/1984
From:	PECO ENERGY CO., (FORMERLY PHILADELPHIA ELECTRIC
To:
Shared Package
ML20092D702	List: ML20092D697 ML20092D707 ML20092D712 ML20092D718 ML20092D721
References
NUDOCS 8406220121
Download: ML20092D721 (5)

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' ATTACHMENT C PHILADELPHIA ELECTRIC COMPANY PEACH BOTTOM ATOMIC POWER STATION UNIT 3 DOCKET No. 50-278 ,

. SAFETY EVALUATION FOR THE dFsRAff0R 5f FBKCH 5dffDA Af6sIU F5R2R~EfKfi6R'ORif 3 i.

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l Attachment C i Docket No. 50-278 O

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SUBJECT:

Safety Evaluation for the Operation of Peach Bottom Atomic Power Station Unit 3 r.

IN{gggUgg{gg Philadelphia Electric Company performed inspections of the Peach Bottom Unit 3 jet pump instruuentation penetrations in response to I.E. Information Notice 84-41 and NRC Generic Letter 84-11. As part of this program, ultrasonic examinations were performed on the five welds associated with each jet pump instrumentation penetration. Circumferential crack-like indications were found on weld No. 2 on each of the two jet pump instrumentation penetrations (see Figure No.1) . In addition to the crack-like indications, the "B" loop No. 2 weld also showed three pin-hole leaks.

Philadelphia Electric Company contracted General Electric company to analyze these indications and to provide their recommendations. All circumferential indications would' require a weld overlay in order to provide the structural reinforcement i O necessary for 18 months of full power operation. The weld overlays were designed and sized as full structural overlays; thus meeting the requirements of NRC Generic Letter 84-11, and providing all ASME Code safety margins.

Overlay weld procedures were prepared to perform these temporary repairs with the concurrence of the on-site representative of the Hartford Steam Boiler Inspection und Insurance Company.- Both. welds received the weld overlays as recommended by General Electric Company. These overlays were

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made to provide additional structural reinforcement and prevent potential leakage.

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m EA9E9E9EEE The "A" loop circumferential indication was in the 12 o' clock position on the safe-end side of the No. 2 weld. The "B" loop circumferential indication with three pin-hole leaks was in the 12 o' clock position on the reducer side of the No. 2 weld. The pipe material at both of these locations is 4" nominal, Schedule 80 TP-304 Stainless Steel. The minimal wall thickness of these ,

i wolds is 0.337".

General Electric Company performed a fracture mechanics analysis on the crack indications identified in both welds. The analyses showed that these indications would not violate the code required safety factor of three for at least 9,000 hours0 days <br />0 hours <br />0 weeks <br />0 months <br /> of full power service'. Although a through-wall leak was present on the "B" loop, the weld was still within the allowable requirements since the ASME Code safety factor of three can be maintained with a through-wall crack of over 40% of the circumference in length.

General Electric Company recommended applying a 0.125" thick by 1.5" long overlay on each weld to assure leak-free operation for a minimum of 18 months of fu11' power operation.

() EY^hEATI96 The ultrasonic exmaination techniques used in the detection of the crack-like indications has been demonstrated to be capable of finding IGSCC cracking at Battelle Columbus Laboratories and the EPRI NDT Center in Charlotte, North Carolina. The ~

technicians participating in.the examination have been certified as being able to detect _ service induced IGSCC by an actual demonstration using cracked specimens in accordance with NUREG IE Dulletin 83-02 and NRC Generic Letter 84-11.

The overlay design applied to these welds is conservative since it was designed to accommodate-a hypothetical.through-wall crack, 360 degrees in circumference. The overlay weld as applied-is a full structural overlay and meets all the requirements of NRC Generic Letter 84-11.

The welding procedures-and welders used to perform the weld 4

overlays were qualified to procedures which meet the requirements.

of the ASME Code Section IX 1980-Edition including the Winter 1981 Addenda. .The welding procedure-required an adequate cooling water flow inside the? pipe which produced desired compressive stresses on-the inside diameter.of=the pipe similar to those O

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O produced by IHSI. Crack propagation into the weld metal is not likely to occur by IGSCC since the high ferrite weld material is not susceptible to IGSCC. The fracture mechanics analysis was done in accordance with Section XI, Appendix X to the ASME Code.

9969bSE198 We have concluded, based on the considerations discussed ,

above, that:

1. The Unit 3 ultrasonic examination was conducted by personnel trained in the detection of IGSCC cracking and certified by ultrasonic technique demonstration at Battelle Laboratories in Columbus, Ohio and at the EPRI NDT Center in Charlotte, North Carolina, in accordance with I.E. Bulletin 83-02 and NRC Generic Letter 84-11.

The procedure and instrumentation used in this exmaination has been proven capable of detecting and characterizing intergranular stress corrosion cracking.

. 2. The Fracture Mechanics Analysis performed on the crack indications and the applied overlay temporary repairs possess an inherent safety factor of three and provide O full structural margins in accordance with NRC Generic Letter 84-11.

3. The overwhelming laboratory and industry experience to date has shown that 1GSCC will fail in a leak before break manner.

It can be concluded that Unit 3 of the Peach Bottom Atomic Power Station can operate at full-load power for at least 18 months with reasonable assurance that the health and safety of the public will not be endangered by oepration in the proposed manner.

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