ML17339A662
| ML17339A662 | |
| Person / Time | |
|---|---|
| Site: | Turkey Point  |
| Issue date: | 02/22/1980 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML17339A661 | List: |
| References | |
| IEB-79-13, NUDOCS 8003170059 | |
| Download: ML17339A662 (4) | |
Text
SAFETY ANALYSIS OF ACTIONS TAKEN IN RESPONSE TO BULLETIN 79-13 "CRACKING IN
.FEEDWATER SYSTEM PIPING" 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 con-tainment.
Leaking circumferential cracks were identified in the 16-inch feedwater elbows adjacent to two steam generator nozzle to elbow welds.
Sub-sequent raidographic 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 inspect i on and operating 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 nozzle to feedwater piping weld 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 feedwater to main feedwater piping conection at the next refueling outa ge.
In conformance with the Bulletin, the Florida power.
and Light Company evidenc completed the initial padiqgraphic and visual ex t'
h examvna ions and has not found evidence o
cracking of tlie feedwater piping of the T
k P
e ur ey oint Plant, Unit From the results of instrumentation installed at several plants which have experienced feedwater piping cracks and other modeling and analysis by a
utility sponsored Owners Group, it has been shown that significant cyclic stresses 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.
Metallurgical analysis of cracked feedwater piping has identified the mode of failure as fatigue assisted by corrosion.
The Owners Group is expected to complete its investigations and make recommenda-tions for changes in design and operating procedures in February 1980.
In addition, the HRC has instituted a Pipe Crack Study Group to review this and other pipe cracking problems in PWR's.
It is anticipated that the Pipe Crack Study Group will corqlete its work by June 1980 and provide recommendations to be implemented by licensees as new criteria for operating plants, if required.
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Altrough cracking has not been identified through the inspec ions performed to date, the Staff feels that the cyclic stress induced by the thermal transient present when cold auxiliary feedwater at low rates injected into the main feedwater may result in such cracking in the future.
The Staff and the S.ners Group both have performed independent analyses and have determined that flawed piping could withstand challenges from operating and faulted loads including seismic and limited water hammer loads without loss of piping integrity.
Pipe breaks have occurred in the past in feedwater piping as the result of water hammer loads.
- However, measures such as "J" tubes have been instituted and operational changes have have occurred to minimize the possibility of water hamner'.
In the unlikely event of a feedwater pipe break from a severe eater hammer, the consequences have been analyzed as a design base accident and acceptable measures have been established to deal with the event.
We conclude that the nondestructive inspections performed and scheduled and the aralyses performed for flawed piping ensure piping integrity for the Turkey Point Plant until the recommendations of the Owners Group and the Pipe Crack Study Group have been evaluated.
Should the Staff determine thai further actions are required after evaluation of the Owners Group arxi Pipe Crack Study recommendations, the licensees will be notified at that tiKe.
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