Information Notice No.79-37 - Cracking in Low Pressure Turbine Discs
UNITED STATES ISINS No.: 6870
NUCLEAR REGULATORY COMMISSION Accession No:
OFFICE OF INSPECTION AND ENFORCEMENT 7910250525
WASHINGTON, D.C. 20555
December 28, 1979
Information Notice No. 79-37
CRACKING IN LOW PRESSURE TURBINE DISCS
Description of Circumstances:
An anonymous 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 Regulations 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 Westinghouse's Turbine
Division on November 20, 1979 established that cracking, 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 ultrasonic examination) for crack detection have been
developed and are being implemented 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 greater depth than the
keyway cracks found to date. According to Westinghouse, these bore cracks
have been metallurgically examined and preliminary findings 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 meeting was held on December 17, 1979 between the NRC staff, Westinghouse
and utility representatives to discuss the disc cracking problem, repair
alternatives, 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 program that included a list of nuclear power
plants already inspected, recommended 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 during
28 additional months of turbine operation. The NRC staff is evaluating the
turbine inspection results and analysis by Westinghouse.
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Information Notice No. 79-37 December 28, 1979
Page 2 of 2
Westinghouse also notified the staff that extrapolation of information
obtained from Indian Point Unit 3 staff that extrapolation of information
obtained Westinghouse also notified the inspection and analysis indicates
that disc cracking could be significant at Indian Point Unit 2 and the
turbines should be sooner than the inspected spring outage 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 category 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 completed 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 Category A plants be inspected as their service
periods approach five years or in the event significant corrosion problems
become evident during this timer. The NRC staff is currently reviewing the
need for inspection of those PWR plants having other interfacing turbine
designs 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
cracking 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 Westinghouse thus far were essentially limited
to the keyways (disc outlet) of selected discs whereas the Zion Unit 1
inspection results indicated 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 findings, although subject to change, no indicated possible
higher missile exit energies in some cases than previously expected.
This Information Notice is provided as an early notification of a possibly
significant matter, the allegations and the generic safety implications of
which are currently undergoing review by the NRC staff. It is expected that
recipients so indicate, further licensee actions may be requested or
required. Embedded cracking 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 regarding this matter, please contact the Director of the
appropriate NRC Regional Office.
Enclosures: As stated
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Enclosure 1
CATEGORY AA
UTILITY STATION UNIT
Florida, P&L Turkey Point 3
Consolidated ED. Indian Point 2
PASNY Indian Point 3
Arkansas P&L Russellville 1
VEPCO Surry 1
Carolina P&L Robinson 2
So. Calif. Ed. San Onofre 1
Yankee A. P. Rowe 1
Wisc. Mich. Pwr. Point Beach 1
Consumers Pwr. Palisades 1
Commonwealth Ed. Zion 1 1
Commonwealth Ed. Zion 2 2
Florida P&L Turkey Point 4
Nebraska PPD Cooper 1
Wisc. Mich. Pwr. Point Beach 2
Maine Yankee Bailey Point 1
Rochester G&E Ginna 1
Northern States Prairie Island 1
Wisc. P.S. Kewaunee 1
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Enclosure 1 (Continued) Page 2 of 3
CATEGORY A
UTILITY STATION UNIT
Alabama Power Farley 1
Alabama Power Farley 2
Baltimore G&L Calvert Cliffs 2
Carolina P&L Harris 1
Carolina P&L Harris 2
Carolina P&L Harris 3
Carolina P&L Harris 4
Cincinnati G&E Zimmer 1
Commonwealth Ed. Byron 1
Commonwealth Ed. Byron 2
Commonwealth Ed. Braidwood 1
Commonwealth Ed. Braidwood 2
Connecticut Yankee Haddam Neck 1
Duke Power McGuire 1
Duke Power McGuire 2
Duquesne Lt. Shippingport 1
Duquesne Lt. Beaver Valley 1
Duquesne Lt. Beaver Valley 2
Flordia Power Corp. Crystal River 3
Flordia Power & Lt. St. Lucie 1
Flordia Power & Lt. St. Lucie 2
Houston L&P So. Texas 1
Houston L&P So. Texas 2
Louisiana P&L Waterford 3
Metropolitan Ed. Three Mile Island 2
Northern States Pwr. Prairie Island 2
Pub. Service E&G Salem 1
Pub. Service E&G Salem 2
Pacific G&E Diablo Canyon 1
Pacific G&E Diablo Canyon 2
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Enclosure 1 (Continued) Page 3 of 3
CATEGORY A
UTILITY STATION UNIT
P.S. Indiana Marble Hill 1
P.S. Indiana Marble Hill 2
Puget Sound P&L Skagit 1
SMUD. Rancho Seco 1
TVA Sequoyah 1
TVA Sequoyah 2
TVA Watts Bar 1
TVA Watts Bar 2
VEPCO North Anna 1
VEPCO North Anna 2
VEPCO North Anna 3
VEPCO North Anna 4
VEPCO North Anna 2
WPPSS Hanford 2
WPPSS WNPS 1
WPPSS WNPS 3
WPPSS WNPS 4
WPPSS WNPS 5
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Enclosure 2
UTILITY STATION UNIT
Duke Power Co. Oconee 1
Duke Power Co. Oconee 2
Duke Power Co. Oconee 3
OPPD Ft. Calhoun 1
Baltimore Electric
& Gas Calvert Cliffs 1
Metropolitan Edison Three Mile Island 1
Indiana & Michigan
Electric D.C. Cook 1
Indiana & Michigan
Electric D.C. Cook 2
Northeast Utilities Millstone 2
Portland General
Electric Trojan 1
Toledo Edison Davis Besse 1
Arkansas Power &
Light Arkansas Nuclear One 2
WPPSS Hanford 1
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