ML19305D130
| ML19305D130 | |
| Person / Time | |
|---|---|
| Site: | Point Beach  |
| Issue date: | 02/25/1980 |
| From: | Schwencer A Office of Nuclear Reactor Regulation |
| To: | Burstein S WISCONSIN ELECTRIC POWER CO. |
| References | |
| NUDOCS 8004140087 | |
| Download: ML19305D130 (6) | |
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UNITED STATES
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NUCLEAR REGULATORY COMMISSION E
WASHINGTON,0. C. 20555 L\\
'Q%l.cl FEBRUARY,,6 y Docket Nos. 50-266 l
and 50-301 Mr. Sol Burstein Executive Vice President Wisconsin Electric Power Conpany i
231 West Michigan Street Milwaukee, Wisconsin 53201
Dear Mr. Burstein:
The cracking that was found in the feedwater system piping at your plants, 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 recomendations 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, HUW$ v A. 'Schwencer, Chief Operating Reactors Branch #1 Division of Operating Reactors
Enclosure:
Safety Analysis of Interim Actions Taken to Eliminate Feedwater Piping Cracks cc: w/ enclosure See next page
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8004140 o n
- lr.SolBurstein FEBRUARY 3 5 580 aisconsin Electric Power Company cc
- Mr. Bruce Churchill, Esquire Shaw, Pittman, Potts and Trowbridge 1800 M Street, N.W.
Washington, D. C.
20036
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Document Department University of Wisconsin l
Stevens Point Library Stevens Point, Wisconsin 54481 Mr. Glenn A. Reed, Manager Nuclear Operations l
Wisconsin Electric Power Company Point Beach Nuclear Plant 6610 fluclear Road l
Two Rivers, Wisconsin 54241 l
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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 examinations 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 i
Reactor Regulation which infomed licensees of the D. C. Cook failures and requested specific inforamtion on feedwater system design, fabrication, inspection and oper-ating histories. To further explore the generic nature of the cracking problem, the Office of Inspection and Enforcement requested licensees of PWR plants in current outages to imediately conduct volumetric examination of certain feedwater 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, IE Bulletin 79-13 was issued. The Bulletin required inspection of the steam cener-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 to containment penetration and the auxiliary feedwater to main feedwater piping connection were required to "
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 oioing 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 f acilities:
1.
Nature and extent of the cracking.
2.
Metallurgical evaluation of the cracking including identification of the r. ode 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 cefects in its feeawater piping.
No anomolies were found in the Code require: stress aralyses at the facilities.
Prer. the results of instrumentation installed at several plants which have ex erienced feedwater piping cracks and other modeling and analyses by a utility sponsore: Ganers e
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 recommendations 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 hammer loads. However, design changes such as "J" tubes have been made and operational changes have occurred to minimize the possibility of water haar.er.
In the unlikely event of a feedwater pipe break from a severe water hammer, 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-I ing problems in PWR's.
It is anticipated that the Pipe Crack Study Group will complete its work by June 1980 and provide recommendations for review and implemen-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 the piping integrity will be maintained until the recommendations of the Owners Group and the Pipe Crack Study Group have been evaluated.
Should the staff determine that further actions are required after evaluation of the Owners Group and Pipe Crack Study Group recommendations, the licensees will be notified at that time.
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Table 1 - Sununary of PWR Feedwater PI' ping' Cracks Pl.AllT EXTDIT OF CRACKINC (N0ZZI.E VICINITY)
PIPING CollPONENT PR0llABLE CAUSE, COMMENTS Ita x.
I.orntion max.
No. of I. town liep t h liepth Crack Crncked Mcstinghouse D. C. Cook 1/2 Thru wall TOP 8 of 8 elbow corrosion Assisted 2 cracks thru wall Fatir,ue Ilcaver Valley 0.400" 9 0' clock 3 of 3 cibow corrosion Assisted 13 additionni fab. rel Fatigue Indicat tusin.repal red Kawaunce 0.050" 7 O' clock 2 of 2 pipe corrosion Assistd 3" dia. aux. feed near Fatigue SG inlet 4
Pt. Beach 1/2 0.047" 3 O' clock 2 of 2 reducer Corrosion Assisted 3" dia.' aux, feed near Fatigue SG l'nlet II.It. Robinson 2 0.750" 9 0' clock 3 of 3 reducer Corrosion Assisted Shallow cracking in no Fatigue under thermal sleeve Snicht 1 0.235" 4 of 4 cibow corrosion Assisted reducer Fatigue i
l San Onofre 1 0.100" lower half 3 of 3 reducer Stress Assisted
'Hultiple branched crac of reducer Corroulun evidence of nome fatig l
Surry 1/2 0.080" 2 and 5 6 of 6 reduc'er Corrosion Assisted j
O' clock Fatigue j
Cinna 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 Fatigue henkeeRowe
, Gross fabrication
' defects in riiping
2 Tab l e Sur.anary of PWR Feedwnter Piping Cracks i.
Pl. ANT EXTENT OF CRACKING (N0ZZLE VICINITY)
PIPING COMPONENT PROBABLE CAUSE COMMENTS Hax.
Location max.
No. of Lines Depth Depth Crack Cracked O
Comhuntinn Eng_incering HI1latone 2 0.250" 12 0' clock 2 of 2 pipe Not analyzed I'n l i sailes 0.170" 3 and 9 0' clock 2' of 7 pipe corrosion Assisted Cracks found also at w Fatigue vicinity of horizontal Piping 4
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