United States Nuclear Regulatory Commission - Protecting People and the Environment

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. 
.

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 
.

                                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
.

                         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
.

                         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
.

                               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

Page Last Reviewed/Updated Thursday, November 13, 2014