ML19305D639
| ML19305D639 | |
| Person / Time | |
|---|---|
| Site: | Beaver Valley |
| Issue date: | 02/25/1980 |
| From: | Schwencer A Office of Nuclear Reactor Regulation |
| To: | Dunn C DUQUESNE LIGHT CO. |
| References | |
| TAC-11766, NUDOCS 8004150318 | |
| Download: ML19305D639 (6) | |
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UNITED STATES l
8 NUCLEAR REGULATORY COMMISSION o
WASHINGTON,0. C. 20555 7.g jE
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FEB 2 51980 Docket No. 50-334 Mr. C. N. Dunn, Vice President i
Operations Division Duquesne Light Comany 435 Sixth Avenue Pittsburgh, Pennsylvania 15219
Dear Mr. Dunn:
i The cracking that was found in the feedwater system piping at your plant, is summarized in Table 1 of the enclosed safety analysis.
The NRC Staff has reviewed the actions you have taken and finds that the repair program, the nondestructive inspections and leakage testing per-formed following the repairs are adequate to insure that the integrity of the feedwater piping will be maintained until the recommendations of the Owners' Group and the NRC's Pipe Crack Study Group have been evaluated.
Should we determine that further licensing actions are required after these evaluations, you will be notified.
Sincerely
$$W A. Schwencer, Chief Operating Reactors Branch #1 Division of Operating Reactors
Enclosure:
Safety Analysis of Interim Actions Taken to Eliminate Feedwater Piping C-acks cc: w/ enclosure See next page I
1 i
L 80041503(8
Mr. C. N. Dunn Duquesne Light Conpany Gerald Cha'rnoff, Esquire Mr. Janes A. Werling cc:
Jay E. Silberg, Esquire Plant Superintendent Shaw, Pittman, Potts and Trowbridge Beaver Valley Power Station 1800 M Street, N.W.
P. O. Box 4 Washington, D. C.
20036 Shippingport, Pennsylvania 15077 l
Karin Carter, Esquire Mr. John A. Levin Special Assistant Attorney General Public Utility Commission Bureau of Administrative Enforcement P. O. Box 3265 5th Floor, Executive House Harrisburg, Pennsylvania 17120 Harrisburg, Pennsylvania 17120 Mr. J. D. Sieger, Superintendent Mr. Roger Tapan of Licensing and Compliance Stone and Webster Engineering Duquesne Light Conpany Corporation Post Office Box 4 P. O. Box 2325 Shippingport, Pennsylvania 15077 Boston, Massachusetts 02107 Mr. J. D. Woodward R & D Center Westinghouse Electric Corporation Building 7-303 Pittsburgh, Pennsylvania 15230 B. F. Jones Memorial Library 663 Franklin Avenue Aliquippa, Pennsylvania 15001 Mr. Jack Carey Technical Assistant Duquesne Light Company i
P. O. Box 4 Shippingport, Pennsylvania 15077 Mr. R. E. Martin Duquesne Light Conpany 435 Sixth Avenue Pittsburgh, Pennsylvania 15219 j
Marvin Fein Utility' Counsel City of Pittsburgh 313 City-County Building Pittsburgh, Pennsylvania 15219
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SAFETY ANALYSIS OF. INTERIM ACTIONS TAKEN TO ELIMINATE FEEDWATER PIPING CRACKS On May 20, 1979, Indiana and Michigan Power Company notified the NRC of cracking in two feedwater lines at their D. C. Cook Unit 2 facility. The cracking was discovered following a shutdown on May 19 to investigate leakage inside contain-ment. Leaking circumferential cracks were identified in the 16-inch diameter feed-water elbows adjacent to two steam generator nozzle to elbow welds. Subsequent radiographic examinat' ions revealed cracks in all eight steam generator feedwater lines at this location on both units 1 and 2.
On May 25, 1979, a letter was sent to all PWR licensees by the Office of Nuclear Reactor Regulation which informed licensees of the D. C. Cook failures and requested
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specific inforamtion on feedwater system design, fabrication, inspection w oper-ating histories. To further explore the generic nature of the cracking probicm, the Office of Inspection and Enforcement requested licensees of PWR plants in current outages to immediately conduct volumetric examination of certain feedwate.-
piping welds. As a result of these actions several other licensees reported cracking in the steam generator feedwater nozzle-to-piping weld vicinity. On June 25, 1979, i
IE Bulletin 79-13 was issued. The Bulletin required inspection of the steam gener-ator nozzle-to-pipe welds and adjacent areas within 90 days.
If flaws were found in these welds, the feedwater piping welds to the first support, the feedwater piping i
to containment penetration and the auxiliary feedwater to main feedwater piping connection were required to be inspected.
In conformance with the Bulletin, the licensees of the plants listed in the-
. attached Table 1 completed the radiographic examinations and found cracking in the feedwater piping systems.
Meetings and/or telephone conference calls were held with the respective licensess to discuss the following items regarding the feedwater piping cracks at their i
f acilities :
l.
Nature and extent of the cracking.
2.
Metallurgical evaluation of the cracking including identification of the r. ode i
of failure.
3.
Stress analyses 4.
Operating history 5.
Feedwater chemistry 6.
Corrective actions 7.
Safety Implications The licensees' interim reports containing the information above were submitted and reviewed by the staff prior to the units returning to power. The extent of the cracking at the facilities is summarized in Table 1.
The mode of f ailure at all the f acilities discussed in this analysis, with the exception of Yankee Rowe, was icenti-fied as fatigue assisted by corrosion. The Yankee Rowe facility had gross fasrication defects in its feedwater piping.
No anomolies were found in the Code require: stress analyses at the facilities.
From the results of instrumentation installed at several plants which have ex:erienced feeowater piping cracks and other modeling and analyses by a utility sponsore: Gwners
[
Group, significant cyclic stresses have been identified that occur in the feedwater piping in the vicinity of the steam generator nozzle from mixing and stratification of cold auxiliary feedwater with hot water from the steam generator during low flow conditions. The Owners Group is expected to complete their investigations and make recomendations for changes in design and operating procedures in February 1980.
The licensees have repaired and/or replaced the affected piping in most cases with -
improved designs to minimize stress risers.
In addition, the licensees have com-mitted to reinspect the steam generator to feedwater piping weld vicinities at the subsequent refueling outage.
Although the piping has been repaired at the facilities listed in Table 1 the staff feels that cracking could re-occur in the future at these facilities.
The staff and Owners Group both have performed independent analyses and have deter-mined that flawed feedwater piping could withstand challenges from operating and faulted loads including seismic and limited water loads without loss of piping integrity. Pipe breaks have occurred in the past in feedwater piping as the result of water hamer loads. However, design etianges such as "J" tubes have been made and operational changes have occurred to minimize the possibility of water hamer.
In the unlikely event of a feedwater pipe break from a severe water hamer, the consequences have been analyzed as a design base accident and acceptable measures to deal with the event have been established.
The NRC has instituted a Pipe Crack Study Group to review this and other pipe crack-ing problems in PWR's.
It is anticipated that the Pipe Crack Study Group will complete its work by June 1980' and provide recomendations for review and impbmen-tation by licensees as new criteria for operating plants.
We conclude that repairs to the feedwater piping, the nondestructive inspections ~
performed and scheduled, and the analyses performed for flawed piping ensure that -
l the' piping integrity will be maintained until the recomendations of the Owners Group and the Pipe Crack Study Group have been evaluated. Should the staff determine r
that further actions are required after evaluation of the Owners Group and Pipe Crack Study Group recomendations, the licensees will be notified at that time.
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Tchle 1 - Summary of PWR Fecdwater PI' ping'Cracko Pl.AN r FK; RENT OF CRACKING (N0ZZI.E VICINITY)
PIPING COMPONENT PROBABLE CAUSE COHN10(TS lin a.
I.orntion max.
No. of I.lin.n Igt h Depth Crack Cracked Weatinghouse D. C. Cook 1/2 Thrn unit TOP 8 of 8 elbow corrosion Assisted 2 cracks thru wall FatiRue Benver Vnlicy 0.400" 9 0' clock 3 of 3 elbow Corrosion Assisted 13 uddillonal fab rela Futiguo indications.repnIred Kawaunce 0.050" 7 O' clock 2 of 2 pipe corrosion Assista 3" dia. aux. feed near Fatigue SG inlet Pt. Beach 1/2 0.047" 3 0' clock 2 of 2 reducer Corrosion Assisted 3" dia.~ aux, feed near Fatigue SG inlet II.n.Rohlnson 2 0.750" 9 0' clock 3 of 3 reducer Corrosion Assisted Shallow cracking in no Fatigue under thermal sleeve Salem 1 0.235" 4 of 4 ethow corrosion Assisted reducer Fatigue San onofre 1 0.100" lower half 3 of 3 reducer Stress Assisted
'Hultiple branched crac of reducer corrosion evidence of nome fatig Surry 1/2 0.080" 2 and 5 6 of 6 reduc'er corrosion Assisted O' clock FatiRue G1nna 0.107" 8:30 0' clock 2 of 2 elbow Stress Assisted Cracks also at deep Corrosion / Corrosion machining marks Fatigue
- Zion 1/2 0.088" 4 0' clock 8 of 8 elbow pipe Corrosion Assisted l
Fatigue f
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, Gross fabrication 5,nkeeRowe defects in piping
2 Table 1 - Summiary of PWR Fee.dwater Piping Cracks Pl. ANT EX,TFNT OF CRACKING (N0ZZIE VICINITY)
PIPING COHPONENT PROBABLE CAUSE CO69 TENTS Hax.
Location max.
No. of Lines Depth Depth Crack Cracked Combustion Engineering Hillstone 2 0.250" 12 0' clock 2 of 2 pipe Not analyzed Palisades 0.170" 3 and 9 0' clock 2 of 2 pipe Corrosion Assisted Cracks found also at we Fatigue vicinity of horizontal piping 4
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