Information Notice 1979-37, Cracking in Low Pressure Turbine Discs
| ML031180211 | |
| Person / Time | |
|---|---|
| Site: | 05000000 |
| Issue date: | 12/28/1979 |
| From: | NRC/OI |
| To: | |
| References | |
| IN-79-037, NUDOCS 7910250525 | |
| Download: ML031180211 (7) | |
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UNITED STATES
ISINS NO.:
6870
NUCLEAR REGULATORY COMMISSION
Accession No.:
OFFICE OF INSPECTION AND ENFORCEMENT
7910250525 WASHINGTON, D.C.
20555
December 28, 1979
IE Information Notice No. 79-37
CRACKING IN LOW PRESSURE TURBINE DISCS
Description of Circumstances
An anonvmous letter was received by the Director of the Office of Inspection and
Enforcement, on November 17, 1979 which alleged possible violation of Part 10 CFR
50.55e and/or 10 CFR 21 Requlations concerning reportability of recently discovered
stress corrosion cracking in Westinghouse 1800 rpm low pressure turbine discs.
Westinghouse had made a presentation on the turbine disc cracking to electric
utility executives on October 30, 1979.
Telephone discussions between the NRC staff and Westinohouse's Turbine Division
on November 20, 1979 established that crackinq, attributed to stress corrosion
phenomena, had been found in the keyway areas of several LP turbine discs at
operating plants and that inservice inspection techniques (i.e., in situ ultra- sonic examination) for crack detection have been developed and are beinq imple- mented in the field. The Office of Inspection and Enforcement was also notified
on November 20, 1979 that during the current overhaul of Commonwealth Edison's
Zion Unit 1 LP turbine, ultrasonic examination revealed embedded cracks located
on the inlet side on the disc bore area where no cracks had been previously
observed. Ultrasonic measurements indicate this disc bore cracking is of qreater
depth than the keyway cracks found to date.
According to Westinqhouse, these
bore cracks have been metallurgically examined and preliminary findinqs show them
not to be typical of classical stress corrosion cracking observed in the keyways.
The probable cracking mechanism and impact on disc integrity is being further
evaluated by Westinghouse.
A meetino was held on December 17, 1979 between the NRC staff, Westinghouse
and utility representatives to discuss the disc cracking problem, repair alter- natives, turbine missile evaluation, inspection techniques and plant inspection
priorities. In response to the staffs' request, Westinghouse provided the
staff an updated report on December 21, 1979 regarding the current field inspection
oroaram that included a list of nuclear power plants already inspected, recom- mended inspection schedules and pertinent information related to LP turbines
where cracks have been observed.
Inspections to date have identified turbine
disc cracks at Surry Unit 2, Point Beach Unit 2, Palisades, Indian Point Unit 3 and Zion Unit 1. All units except Point Beach Unit 2 will make repairs before
the plants return to power.
Point Beach returned to power on December 23, 1979
with a small crack in the No. 2 disc of LP Turbine No. 2. An analysis by
Westinghouse indicated that the observed crack will not attain critical dimensions
durinq 28 additional months of turbine operation. The NRC staff is evaluating
the turbine inspection results and analysis by Westinahouse.
IE Information Notice No. 79-37
December 28, 1979
Pace 2 of 2 Westinqhouse also notified the staff that extrapolation of information obtained
from Indian Point Unit 3 inspection and analysis indicates that disc crackina
could be significant at Indian Point Unit 2 and the turbines should be inspected
sooner than the spring outace of 1980. The NRC staff is currently reviewing
Consolidated Edison's plans for prompt evaluation of this potential problem
at this unit.
Enclosure 1 lists the PWR plants having Westinghouse 1500/1800 rpm turbines.
The AA cateaory represents those turbines which appear to have the earliest
need for inspection. With the exception of Yankee Rowe, Westinghouse has
recommended to utilities that Inspection of these machines be comDleted by
the Spring 1980 outage period. The Rowe unit is uninspectable by the present
ultrasonic techniques due to its design. Westinghouse has recommended the
remaining machines of the Cateqory A plants be inspected as their service
periods aooroach five years or in the event significant corrosion problems become
evident during this time. The NRC staff is currently reviewing the need for
inspection of those PWR plants having other interfacing turbine desions shown
in Enclosure 2. Changes to the forementioned inspection schedules proposed by
Westinghouse may be necessary as new technical information becomes available.
From the information available to the NRC staff at this time it appears that
crackinq may be more generically widespread in turbine discs (e.g., keyways and
bore areas) than previously observed. It is important to note that the UT
inspections performed by Westinahouse thus far were essentially limited to
the keyways (disc outlet) of selected discs whereas the Zion Unit 1 inspection
results indicate that examination of the disc bore section must be taken into
account.
Also, Westinghouse is currently re-evaluating their previously estimated
turbine missile energies based on recent missile test results from model symmetric
and non-symmetric missile impact tests. Their preliminary findinas, although
subject to chance, now indicate possible higher missile exit energies in some
cases than previously expected.
This Information Notice is provided as an early notification of a possibly
sianificant matter, the allegations and the generic safety implications of which
are currently undergoing review by the NRC staff.
It is expected that recipients
will review the information applicable to their facilities. If NRC evaluations
so indicate, further licensee actions may be requested or required.
Embedded
crackino in keyways and disc bore areas have been observed only in Westinghouse
LP turbines thus far.
However, the NRC staff. believes that turbines of other
manufacturers should be included in consideration of this problem.
No written response to this Information Notice is required. If you have any
questions recardinn this matter, please contact the Director of the appropriate
NRC Regional Office.
Enclosures:
As stated
Enclosure 1 CATEGORY AA
STATION
UTIL ITY
UNIT
Florida, P&L
Consolidated ED.
Arkansas P&L
Carolina PPbL
So. Calif. Ed.
Yankee A.P.
Wisc. Mich. Pwr.
Consumers Pwr.
Commonwealth Ed.
Commonwealth Ed.
Florida P&L
Nebraska PPD
Wisc. Mich. Pwr.
Maine Yankee
Rochester G&E
Northern States
Wisc. P.S.
Turkey Point
Indian Point
Indian Point
Russeliville
Surry
Robinson
San Onofre
Rowe
Point Beach
Palisades
Zion 1 Zion 2
Turkey Point
Cooper
Point Beach
Bailey Point
Ginna
Prairie Island
Kewaunee
3
2
3
1
1
2
1
1
1
1
1
2
4
1
2
1
1
1
1
Enclosure 1 (Continued) CATEGORY A
UTILITY
Alabama Power
Alabama Power
Baltimore G&L
Carolina P&L
Carolina P&L
Carolina P&L
Carolina P&L
Cincinnati G&E
Commonwealth Ed.
Commonwealth Ed.
Commonwealth Ed.
Commonwealth Ed.
Connecticut Yankee
Duke Power
Duke Power
Duquesne Lt.
Duquesne Lt.
Duquesne Lt.
Flordia Power Coro.
Flordia Power & Lt.
Flordia Power & Lt.
Houston L&P
Houston L&P
Louisiana P&L
Metropolitan Ed.
Northern States Pwr.
Pub. Service E&G
Pub. Service E&G
Pacific G&E
Pacific i&E
STATION
Fa rley
Farl ey
Calvert Cliffs
Harris
Harris
Harris
Harris
Zimmer
Byron
Byron
Braidwood
Braidwood
Haddam Neck
McGuire
McGui re
Shippinqport
Beaver Valley
Beaver Valley
Crystal River
St. Lucie
St. Lucie
So. Texas
So. Texas
Waterford
Three Mile Island
Prairie Island
Salem
Salem
Diablo Canyon
Diablo Canvon
UNIT
1
2
2
1
2
3
4
1
1
2
1
2
1
1
2
1
1
2
3
1
2
1
2
3
2
2
1
2
1
2
Enclosure 1 (Continued)
CATEGORY A
STATION UTILITY
UNIT
P.S. Indiana
P.S. Indiana
Puget Sound P&L
SMUD.
Marble Hill
Marble Hill
Skaqit
Rancho Seco
Sequoyah
Sequoyah
Watts Bar
Watts Bar
2
1
1
1
2
1
2
1
2
3
4
2 VEPCO
North
North
North
North
North
Anna
Anna
Anna
Anna
Anna
Hanford
WNPS
WNPS
WNPS
WNPS
2
1
3
4
5
Enclosure 2 UTILITY
Duke Power Co.
Duke Power Co.
Duke Power Co.
Baltimore Electric
& Gas
Metropolitan Edison
Electric
Indiana & Michican
Electric
Northeast Utilities
Portland General
Electric
Toledo Edison
Arkansas Power &
Light
STATION
Oconee
Oconee
Oconee
Ft. Calhoun
Calvert Cliffs
Three Mile Island
D.C. Cook
D.C. Cook
Millstone
Trojan
Davis Besse
Arkansas Nuclear One
Hanford
UNIT
1
2
3
1
11
1
22
11
2
1
IE Information Notice No. 79-37
December 28, 1979
Enclosure
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