ML19347B732
| ML19347B732 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 09/18/1980 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML19347B726 | List: |
| References | |
| IEB-79-13, NUDOCS 8010150593 | |
| Download: ML19347B732 (2) | |
Text
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. SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION ACTIONS TAKEN IN RESPONSE TO BULLETIN 79-13 " CRACKING IN FEEDWATER SYSTEM PIPING" FOR THREE MILE ISLAND NUCLEAR STATION, UNIT I (TMI-1)
METROPOLITAN EDISON COMPANY OF GENERAL PUBLIC UTILITIES SYSTEM DOCKET NO. 50-289 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 in' side contain-ment. Leaking circumferential cracks were identified in the 16-inch feedwater elbows adjacent to two steam generator nozzle to elbow welds. Subsequent radio-graphic 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 Reactor Regulation which informed licensees of the D. C. Cook failures and requested specific information on feedwater system design, fabrication, inspection and operating histories. To further explore the generic nature of the cracking problems, the Office of Inspection and Enforcement requested licensees of PWR plants in current outages to immediately conduct volumetric examination of certain teedwater piping welds. As a result ~of these actions several other licensees reported cracking in the steam generator nozzle to feedwater piping weid vicinity. On June 25, 1979, IE Bulletin 79-13 was issued. The Bulletin required inspection of the steam generator nozzle-to-pipe welds and adjacent areas within 90 days and reinspection of these welds, the feedwater piping welds to the first support, the feedwater piping to containment penetration and the auxiliary feed-water to main feedwater piping connection at the next refueling outage.
Instrumentation was installed at several plants which had experienced feedwater pipe cracking. As a result of this instrumentation and other modeling and analysis by a Westinghouse Owner's Group, significant cyclic stresses were discovered to occur in the feedwater piping in the vicinity of the steam generator nozzle. The cyclic stresses were caused by mixing and stratification of cold auxiliary feedwater with hot water from the steam generator in the feedwater piping during low flow conditions. Metallurgical analysis of the cracked feedwater piping has identified the mode of failure as fatigue assisted by corrosion which supports the findings of the Westinghouse Owner's Group.
In an August 24, 1979 meeting with the B&W Owner's Group at Bethesda Maryland, the group identified steam generator design differences between those fabricated 1
by B&W and tf.ose fabricated by Westinghouse and Combustion Engineering and described operating conditions which would preclude the occurrences of strati-fication of cold auxiliary feedwater with hot water from the steam generator 1
during normal operation.
In addition the B&W Owner's Group reported that 95 welds in the main and auxiliary feedwater piping at Crystal River Unit 3 and at Davis Besse had been radiographically examined and no cracks had been detected.
Based upon the identified mode of cracking of the feedwater to nozzle weld, the operating and design characteristics o*f the B&W steam generator, and the satis-factory inspection results on welds in the main and auxiliary feedwater piping on Crystal River Unit 3 and on Davis Besse, IE Bulletin 79-13 was revised.
8910150 @ 3 I
d,
If there were no stratification of cold auxiliary feedwater with hot steam generator water during start-up, hot standby and cold shutdown, the revised IE Bulletin 79-13 relieved B&W fabricated facilities of the requirement of inspection of main and auxiliary feedwater nozzle and pipe welds.
It has been reported that stratification of cold auxiliary feedwater with hot steam generator water will not occur, during start-up, hot standby or cold shutdown operations of the Three Mile Island Unit 1 steam generators. There-fore Three Mile Island facility would not be required to inspect the nozzle to pipe and pipe to pipe welds in the main and auxiliary feedwater lines at this time.
Feedwater nozzle to pipe weld cracking is still under generic review by the staff. Should the staff determine that actions beyond those stated in IE Bulletin 79-13 are necessary to ensure adequate feedwater line integrity, the licensee will be notified at that time.
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