ML19309A991
| ML19309A991 | |
| Person / Time | |
|---|---|
| Site: | Zion File:ZionSolutions icon.png |
| Issue date: | 02/25/1980 |
| From: | Schwencer A Office of Nuclear Reactor Regulation |
| To: | Peoples D COMMONWEALTH EDISON CO. |
| References | |
| NUDOCS 8004020463 | |
| Download: ML19309A991 (6) | |
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UNITED STATES y
g NUCLEAR F..iULATORY COMMISSION 3
8 l' 5 ilNGTON, D. C. 20$55
%,,,,,s HERGkttt y Docket Nos. 50-295 and 50-304 Mr. D. Louis Peoples Director of Nuclear Licensing Comonwealth Edison Company Post Office Box 767 Chicago, Illinois 60690
Dear Mr. Peoples:
The cracking that was found in the feedwater system pipirig 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 nondestnictive 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 reconmendations 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, f W#
A. Schwencer, Chief Operating Reactors Branch #1 l
Division of Operating Reactors j
Enclosure:
Safety Analysis of Interim Actions Taken to Eliminate Feedwater Piping Cracks cc: w/encle'sure See next page 8 004 020 hQ
Mr. D. Louis Peoples Commonwealth Edison Company FISRL';RY 2 5 3ec cc: Robert J. Vollen, Esquire 109 North Dearborn Street Chicago, Illinois 60602 Dr. Cecil Lue-Hing Director of Research and Development Metropolitan Sanitary District of Greater Chicago 100 East Erie Street Chicago, Illinois 60611 Zion-Benton Public Library District 2600 Emmaus Avenue
. Zion, Illinois 60099 Mr. Phillip P. Steptoe Isham, Lincoln and Beale Counselors at Law One First National Plaza 42nd Floor Chicago, Illinois 60603 Susan N. Sekuler, Esquire Assistant Attorney General Environmental Control Division 188 West Randolph Street, Suite 2315 Chicago, Illinois 60601 G
s SAFETY ANALYSIS OF, INTERIM ACTIONS TAKEN TO ELIMINATE FEEDWATER PIPING CRACKS l
On May 20, 1979, Indiana and Nichigan 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 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 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-to-piping weld vicinity.
On June 25, 1979,-
IE Bulletin 79-13 was issued. The Bulletin req 0 ired 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 be inspected.
In conformance with the Bulletin, the licensees of the plants listed in the attached Table 1 com,nleted the radiogranhic examinations end found craccinC i' the feedwater oiping systems.
Meetings and/or telephone conference calls were held with the respective licersess to discuss the following items regarding the feedwater piping cracks at their facilities:
1.
Nature anc' extent of the cracking.
2.
Matallurgi:a1 evaluation of the cracking including identification of tne. 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 submittet and reviewed by the staff prior to the units returning to power.
The extent cf ne cracking at the facilities is summarized in Table 1.
The mode of failure at all the f acilities discussed in this analysis, witn the excection of Yankee Rowe, was i:enti-fied as fatigue assisted by corrosion. Tne Yankee Rowe facility had grcss ft:rication defects in its feedwater piping.
No anomolies were found in the Code recuire: stress analyses at the facilities.
From the results of instrumentation installed at several plants which have ex:erienced feecwater piping cracks and other mooelirg and analyses by a utility secnscri: Gwners
2 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 los flow conditions. The Owners Group is expected to complete their investigations and make recommendations for changes in design and operating procedures in February 1930.
The licensees have repaired and/or replaced the affected piping in most c &ses 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 f aulted loads including seist.1ic and limited water loads without loss of pipin.:
integrity. Pipe breaks have occurred in the. past in feedwater piping as the result of water hanrer loads.
However, design changes such as "0" tubes have been made and operational changes have occurred to minimize the possibility of water ht2ner.
In the unlikely event of a feedwater pipe break from a severe water hanner, 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 C ack 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 recommendations for review and implemen-tation by licensees.as new criteria for operating plants.
We conclude that repairs to the feedwater piping, the nondestructive inspecti:ns' performed and scheduled, and the analyses performed for flawed piping ensure nat the piping integrity will be maintainec until the recommendatioss of the Owne s Group and the Pipe Crack Study Group have been evaluated. Should the staff citerrine that further actions are required after evaluation of the Owners Group and Pi:e Crack Study Group recommendations, the licensees will be notified at that time.
8
Table 1 - Sunanary of PWR Fcc<Iwnter Piping'Crccks EXTEt4T OF CHACKING (N0ZZI.E VICIN1'IT)
PIPING CoffPONENT PRORABLE CAUSE C0FelENTS Pl. ANT X
Hax.
Locntion smax.
No. of 1.Inwn Depth Depth Crack Crncked Westinghouse D. C. Cook 1/2 Thru wall TOP 8 of 8 elbow corrosion Assisted 2 cracks thru well Fatigue Denver Valley 0.400" 9 0' clock 3 of 3 elbow corrosion Assisted 13 uddittoisal fab. rela Fatigue 1udIcattunn repuireal Kawaunce 0.050" 7 0' clock 2 of 2 pipe Corrosion Assistd 3" dia. aux. feed near Fatigue SC inlet l' t. Ilench 1/2 0.047" 3 0' clock 2 of 2 reducer Corrosion Assisted 3" dia. 'sux. feed r.en.
Fatigue SG lulet ll.p. Robinson 2 0.750" 9 0' clock 3 of 3 reducer Corrosion Assisted Shallow cracking in no Fatigue under theriesi siceve Snical 1 0.235" 4 of 4 c1how Corresion Assisted reducer Fatigue San onofre 1 0.100" lower half 3 of 3 reducer Stress Assisted Hultiple branched crac of reducer Corrouton evidence of nomic fatig Surry 1/2 0.080" 2 and 5 6 of 6 reduc'er Corrosion Assisted O' clock Fatigue Cinnn 0.107" 8:30 O' clock 2 of 2 elbow Stress Assisted Cracks also at deep Corrosion / Corrosion machining maarks Fatigue 7lon I/7 0. 0 1111 "
4 0' clock 11 of 18 olinew litro Coi onfon Auntutod Fatigue innkeeRowe Gross fabrication
' defects in piping
2 4
Table 1 - Summiary of PWR Feedwater Piping Cracks Pl. ANT EXTENT OF CRACKING (N0ZZLE VICINITY)
PIPING COMPONENT PROBABI.E CAUSE cot 9ENTS Hax.
Location max.
No. of Lines Depth Depth Crack Cracked Coahustion Englucering HI11 stone 2 0.250" 12 0' clock 2 of 2 pipe Not analyzed Pallnnilen 0.170" 3 and 9 0' clock 2 of 2 pipe Corrosion Assisted Cracks found also at w Fatigue vicinity of horizontal piping e
l e
e e
.