ML18138A070
| ML18138A070 | |
| Person / Time | |
|---|---|
| Site: | Surry  |
| Issue date: | 02/22/1980 |
| From: | Schwencer A Office of Nuclear Reactor Regulation |
| To: | Ferguson J VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.) |
| References | |
| NUDOCS 8003130699 | |
| Download: ML18138A070 (6) | |
Text
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Docket Nos~ 50-280 and 50-281 Mr. J. H. Ferguson Executive Vice President - Power Virginia Electric and Power Company Post Office Box 26666 Richmond, Virginia 23261
Dear Mr. Ferguson:
FEBRUARY 2 2.1980 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 recommendations of the Owners* Group and the NRC 1s Pipe Crack Study Group have been evaluated.
Should we determine that further licensing actions are required after these evaluations, you will be notified.
Sincerely,,;1
- 0. lltui/dd[/
Enclosure:
Safety Analysis of Interim Actions Taken to Eliminate Feedwater Piping Cracks cc:
w/enclosure See next page A. Sehwencer, Chief Operating Reactors Branch #1 Division of Operating Reactors I.
Mr. J. H. Ferguson Virginia Electric and Power Company cc:
Mr._ Michael w. Maupin Hunton and Williams Post Office Box 1535 Richmond, Virginia 23213 Mr. w. L. Stewart, Manager P. o. Box 315 Surry, Virginia 23883 Swem Li bra ry College of \\~illiam and Mary Williamsburg, Virginia 23185 Donald J. Burke
- u. s. Nuclear Regulatory Corrrnission Region I I Office of Inspection and Enforcement 101 Marietta Street, Suite 3100 Atlanta, Georgia 30303 FEBRUARY " 2 l980
SAFETY ANALYSIS 01: 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 elbqw welds. Subsequent radiographic examinations revealed cracks in all eight steam generator feedwater lines at this location on both units land 2.
On May 25,. 1979, a letter was sent to all PWR licensees by the Office of Nuclear Reactor Regulation which infornied 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 outa*ges to immediately 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-te-piping weld vicinity.
On June 25, 1979, IE Bulletin 79-13 was issued. The Bulletin required inspection of the steam aener-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 be inspected.
In conformance with the Bulletin, the licensees of the plants listed in the attacheci Table 1 col'l'!rleted the rad.io9r-arhic examiriations anri fom1".! crackin~ in the feedwater piping systems.
Meetings and/or telephone conference calls were held with the respective licer.se.es to discuss the following items regarding the feedwater pipirig cracks at their facilities:
- 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.
Operat, ng hi story
- 5; Feedwater chemistry
- 6. Corrective actions
- 7. Safety Implications The licensees' interim reports containing the infQrrnation above were submitte~ and reviewed-by the staff prior to the units returning to ;ewer. The extent of the crackina at the facilities is summarized in Table 1. The mode of failure at a11 the facilities discussed in this analysis*, vlith the exception of Yankee Rowe, was foenti-
- fied as fatiaue assisted by corrosion. The Yankee Rowe facility had gross fa=rica~ion defects in iis feedwater piping.* No anomalies were found in the Code require: stress analyses at the facilities.
From the results of instrumentation installed at several plants which have ex:erienced feedwater pi~in5 cracks and other modeling and analyses by a utility sponsore: Gwners
0 **
- Group, significant cyclic stresses have been identified that occur in the feedwater piping in tt,e vicinity of the steam generator nozzle from mixing and stratification of cold luxiliary feedwater with hot water from the steam generator during low flow cc-~ditions. The Owners Group is expected to complete their investigations and make reconmendations 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 l, 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 harrmer loads.
However, design changes such as 11 J 11 tubes have been made and operati ona 1 changes have occurred to minimize the possibility of water har.rner.
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 either 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 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,
I Table 1 - Sununary of PWR Feedwater 1'1:ping*cracks PLANT EXTENT OF CRACKING (NOZZLE VICJ.NITY)
Mnx.
~~_!-_!!_
West in_s!10use D. C. Cook 1/2 Thrn WRll Renver Vnlley 0.1100 11 Knwaunee 0.050" Pt. neach 1/2 0.0117" 11.ll.Rohinson 2
- o. 750" Snleh\\ 1 0.235" San Onofre 1 0.100" Surry 1/2 0.080" Ginna 0.107"
- Zion l/2 0.088"
,
- ri krP. Rowe Locntlon mnx.
Depth Crock TOP 9 O'clock 7 O'clock 3 O'clock 9 O'clock lower half of reducer 2 and 5 O'clock 8:30 O'clock 4 O'clock No. of J;ln<*fl Crocked 8 of 8 3 of )
2 of 2 2 of 2 3 of 3
'* of,,
3 of 3 6 of 6 2 of 2 8 of 8 PIPING COMPONENT elbow elbow pipe reducer reducer elhow reducer reducer red~cer elbow elbow pipe PROilAllLE CAUSE Corrosion Assisted Fatl ue Corrosion Assisted Fatigue Corrosion Assistd Fatigue Corrosion Assisted Fatigue Corrosion Assisted Fatigue Corrosion Assisted Fatigue Stress Assisted Corrmdun Corrosion Assisted Fatigue COMMENTS 2 cracks thru wall 13 udditionul fob. r.liiiiilt ind I cat Lu1rn.rcpa I re~
3" dia. aux. feed neur SG inlet 3" dia. aux. feed near SG inlet Shallow cracking in nozz under thermal sleeve Multiple branched cracks evlt!--nce of Home fa Stress Assisted Cracks also at deep Corrosion/Corrosion machining marks Fati ue Corrosion Assisted Fatigue Gross fabrication defects in piping
PLANT EXTimT OF CRACKING (NOZZLE VICINITY)
Max.
]?__CJ1_!._~
Comh1mt Lon E111* I nccrlng
_o_. _______.
Millstone 2 0.250" Pnllsacles 0.170" Location max.
_!)~.£ th Crack 12 O'clock No. of Lines Cracked 2 of 2 3 and 9 O'clock 2 of 2 2
.PIPING COMPONENT pipe pipe PROBABLE CAUSE Not analyzed Corrosion Assisted Fatigue
,l.
COMMENTS e*
Cracks found also at weld vicinity of horizontal i in
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