ML19256G354

Responds to IE Bulletin 79-13, Cracking in Feedwater Sys Piping. Outlines Unit 1 Insp & Repair

ML19256G354
Person / Time
Site:	Point Beach
Issue date:	11/19/1979
From:	Fay C WISCONSIN ELECTRIC POWER CO.
To:	James Keppler NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
References
IEB-79-13, NUDOCS 7912310139
Download: ML19256G354 (3)

Text

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3C Wisconsin Electnc posta coupsur 231 W. MICHIGAN, P.O. BOX 2046, MILWAUKEE, WI 53201 November 19, 1979 ,

Mr. J. G. Keppler, Regional Director ~

Office of Inspection and Enforcement i Region III U. S. NUCLEAR REGULATORY COMMISSION 799 Roosevelt Road Glen Ellyn, Illinois 60137

Dear Mr. Keppler:

DOCKET NOS. 50-266 AND 50-301 REPORT ON UNIT 1 INSPECTION AND REPAIR IN RESPONSE TO IE BULLETIN 79-13 POINT BEACH NUCLEAR PLANT, UNITS 1 AND 2 IE Bulletin 79-13 was issued by the NRC Office of Inspection and Enforcement on June 25, 1979. This Bulletin requires PWR licensees to inspect portions of the steam generator feedwater piping, to repair or justify continued operation if any Code discontinuities were found during the inspections, and to report the results to the NRC. The inspection and repair of Unit 2 was detailed in our letter of July 12, 1979, which responded to the Bulletin for Unit 1.

requirements for Unit 2 and presented our initial plan One of the feedline reducers removed from Unit 2 was destructively examined at our request by Southwest Research Institute. The final metallurgical evaluation report on this Unit 1979.

2 reducer was transmitted to you by our letter of August 28, The deepest crack found in that reducer was less than 0.047 inches deep. The August 28, 1979 letter also detailed our plans for replacement of portions of the Unit 1 feedwater piping during that Unit's normal refueling outage.

Two pieces from the Unit 2 reducer were also sent to Brookhaven Laboratory in accordance with a NRC request.

During the refueling outage of Unit 1 which commenced on October 5, 1979, the reducer, a length of sixteen inch diameter pipe, a three inch diameter branch connection, and a sixteen inch diameter elbow were removed and replaced with a prefabricated piping section in each of the two steam generator feedlines.

No ultrasonic or radiographic examinations of the welds were performed prior to removal. This course of action was followed in order to avoid conflicting interpretation of results and lengthy

analysis, pqy031979 7912310 I%

a Mr. J. G. Keppler November 19, 1979 t

After removal of the piping sections, the inside of the steam generator nozzles were inspected. The visual examinations revealed minor pitting of about the same or lesser magnitude than that found in Unit 2. Dye penetrant examination revealed a few minor surface cracks in one of the nozzles located away from the weld and counterbore region. The indications were ground out and, in '

some cases, were repair welded. The repair welding was not necessary per Code requirements because all the indications were ground out without going below minimum wall thickness but was performed to provide a better finished job. Inspection of the interior surface of the sixteen inch diameter valve adjacent to the elbow revealed no cracking, pitting, or other discrepancies.

Inspection of the three inch branch connection weld revealed no discrepancies other than that it had been originally welded without the use of a weldolet. This fact was previously known and reported to the NRC in Licensee Event Report 79-006.

After completion of the reducer to nozzle and valve to elbow welds, the welds were stress relieved. After heat treatment, the welds were inspected radiographically and ultrasonically. The radiographs indicated that the welds were acceptable per the construction code and Bulletin requirements. Both the radiographic and ultrasonic examinations will provide baseline references for future examinations.

The three inch auxiliary feedwater piping was replaced with new pipe from the check valve to its connection with the main feedwater piping. The three inch branch connection welds were made using weldolets in accordance with the construction code.

These welds were radiographically and ultrasonically inspected to provide baseline data.

Visual inspection of the eighteen inch ends of the removed reducers indicated the presence in each of an intermittent circum-ferential crack following a machining grove where the counterbore met the transition machining to bring the wall to the normal inner diameter. In this respect, the results were the same as those for Unit 2. .

Ultrasonic inspection of the eighteen inch ends of the removed reducers was performed using the instruments, calibration standards, and techniques that would normally be used for a Section XI examination of piping of this size and type. The results of this examination very clearly revealed the counterbore transition area indications that were visually observed, The amplitude of the ultrasonic signals returned from the crack in some areas exceeded 100% DAC. This is an amplitude that under Section XI rules would have required further testing to determine actual depth and a stress analysis and/or fracture mechanics evaluation if operation were to continue without repair.

1661 302 Mr. J. G. Keppler November 19, 1979 k

On October 22, 1979, after our inspection and repair efforts on both Unit 2 and Unit 1 were essentially complete, we received Revision 2 to IE Bulletin 79-13 dated October 16, 1979.

We have no record of receiving Revision 1. This revision reduced the inspection requirements contained in the original Bulletin, but retained the requirement that the feedwater line to containment penetration weld inside containment be inspected. In the Point '

Beach Nuclear Plant,;this weld is subjected to relatively low stresses compared to Code allowable stress levels. Also, this weld does not carry auxiliary feedwater and is isolated from the auxiliary feed-water connection by a check valve, We continue to believe, as explained in our August 28, 1979 letter, that the existence of small cracks in this weld should they exist is of no safety significance and accordingly, as stated in our August 28, 1979 letter, these welds will not be inspected.

It is our intention to reinspect the reducer to nozzle welds radiographically and ultrasonically in both Unit 1 and Unit 2 during their next respective refueling outages.

The piping sections removed from Unit 1 are presently being retained at the Point Beach Nuclear Plant. No destructive examinations have been performed to date. Metallurgical samples are readily available to the NRC if desired. ,

should you have any questions regarding our program or inspection results, do not hesitate to call.

Very truly yours,

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C. W. Fay, Director Nuclear Power Department Copy to: Office of Inspection and Enforcement Pashington, D. C. 20555 Mr. A. Schwencer, Chief Office of Nuclear Reactor Regulation 1661 303

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