ML19312E789
| ML19312E789 | |
| Person / Time | |
|---|---|
| Site: | Davis Besse  |
| Issue date: | 05/13/1980 |
| From: | Reid R Office of Nuclear Reactor Regulation |
| To: | Roe L TOLEDO EDISON CO. |
| References | |
| TAC-42050, NUDOCS 8006090532 | |
| Download: ML19312E789 (3) | |
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May 13,1980 Docket No. 50-346 Mr. Lowell E. Roe Vice President, Facilities Development Toledo Edison Cormany Edison Plaza 300 Madison Avenue Toledo, Ohio 43652
Dear Mr. Roe:
On December 28, 1979 the NRC Office of Inspection and Enforcement (IE) issued Information Notice No. 79-37 that discussed the discovery of cracks in the keyway and bore sections of discs in Westinghouse low-pressure turbines. A copy of this Information Notice with an errata sheet is enclosed.
Subsequently, all licensee /
users of low-pressure turbines manufactured by General Electric were invited to meet with the NRC staff and representatives of the vendor on January 9,1980 to discuss the probability of disc cracking in these turbines. A summary of this meeting and the General Electric Conpany's presentation are also enclosed with this letter.
At the time of the January 9 meeting General Electric did not have any recent results of ultrasoni: inspections of its low-pressure turbines. Since that date full UT inspections have been performed on six rotors at five nuclear power plants.
Some indications in the keyway region have been reported in discs at three of these plants. General Electric personnel believe that these indications were caused by water erosion rather than by stress corrosion.
The staff desires to learn more about the underlying reasons for the indications found and the probable rate of growth of these, indications and their effects on turbine disc integrity.
For this purpose we request that you provide the information sought in Enclosure 3 to this letter and address its safety significance. 'Jnder the provisions of 10 CFR 50.54(f) your response is requested within 30 days of the receipt of this letter.
A copy of this letter is being telecopied to you, along with Enclosure 3.
8006090539-a
i Mr. Lowell E. Roe It is ny understanding that additional UT inspections are to be performed by General Electric in the near future. We encourage this action as being the only certain means of determining the integrity of turbine discs. We also reconnend that if you have not already done so, that you develop a schedule for performing a full UT inspection of at least one of your low-pressure turbines forduring the next major outage of your plant.
This request for generic information was approved by GA0 under clearance number B-180225 (S79014); this clearance expires June 30, 1980.
Sincerely, l/
q g Robert W. Reid, Chief Operating Reactors Branch #4 Division of Licensing
Enclosures:
1.
Information Bulletin 79-37 2.
Meeting Summary 3.
Information Requests cc w/ enclosures:
See next page
l Toledo Edison Company cc w/ enclosure (s):
. S.
uclear Regulatory rJuanission Mr. Donald H. Hauser Esq.
The Cleveland Electric esident Inspector s Office.
5503 P. State Route 2 111uminating Company Oak Harbor, Ohio 43449 P. O. Box 5000 Cleveland, Ohio 44101 Director Technical Assessment fRadiationPrograms Of c a, P ttma Po t U.
v ronmental Protection Agency 18 MS ee
.W.
ai Washington, D.C.
20036 gto irginia 20460 U s. 5. Environmental Protection Agency Fu en y, e ry and Hodge 300 Madison Avenue Federal Activities Branch Toledo, Ohio 43604 Region V Office ATTN:
EIS COORDINATOR Mr. Robert B. Borsum 230 South Dearborn Street Babcock & Wilcox Chicago, Illinois 60604 Nuclear Power Generation Division Suite 420, 7735 Old Georgetown Road Bethesda, Maryland 20014 Ohio Department of Health Ida Rupp Public Library ATTN: Director of Health 310 Madison Street 450 East Town Street Port Clinton,0hio 43452 Colunbus, Ohio 43216 President, Board of County Comissioners of Ottawa County Port Clinton, Ohio 43452 l
Attorney General Department of Attorney General 30 East Broad Street Columbus, Ohio 43215 Harold Kahn, Staff Scientist Power Siting Commission 361 East Broad Street Columbus, Ohio 43216 Mr. Rick Jagger Industrial Comission State of Ohio 2323 West 5th Avenue Columbus, Ohio 43216 Mr. Ted Myers Licensing Engineer Toledo Edison Company Edison Plaza 300 Madison Avenue Toledo, Ohio ~ 43652
7-
,.s, UNITED STATES ISINS NO.:
6870 i
NUCLEAR REGULATORY COMMISSION Accession No.:
0FFICE 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 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 execuuves 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 ultra-sonic examint, tion) for crack detection have been developed and are being 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 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 De'cember 17, 1979 between tht NRC staff, Westinghouse and utility representatives to discuss the disc cracking problem, repair alter-natives, turbine oissile 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 itst 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 'I, Palisades, Indian Point Unit 3 e*~
and Zion Unit 1.
A?1 units except Point Beach Unit 2 will maka the plants return to power.
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with a small crack in the No. 2
.ons Westinghouse indicated that the during 28 additional months of t DUPLICATE DOCUMENT f;J the turbine inspection results a 9
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Page 2 of 2 i
Westinghouse also notified the staff that extrapolation of information obtained from Indian Point Unit 3 inspection and analysis indicates that disc cracking i
could be significant at Indian Point Unit 2 and the turbines should be inspected l
sooner than the spring outage ol' 1980.
The NRC staff is currently reviewing j
Consolidated Edison's plans for prompt evaluation of this potential problem at this unit.
j l lists the PWR plants having Westinghouse 1500/1800 rpm turbines.
l 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 l
the Spring 1980 outage period.
The Rowe unit is uninspectable by the present ultrasonic cechniques due to its design.
Westinghouse has recommended the j
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 time.
The NRC staff is currently reviewing the need for inspection of those PWR plants having other interfacing turbine designs shown i
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 i
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 i
Also, Westinghouse is currently re-evaluating their previously estimated 2
account.
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, now indicate possible higher missile exit energies in some l
cases than previously expected.
This Information Notice is provided as an early notification of a possibly i
l significant 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 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 questi_ons regarding this matter, please contact the Director of the appropriate l
NRC Regional Office.
Enclospres:
As stated 8
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4 FE3RUA2Y 2 1 BE MEMORANDUM FOR:
A. Schwencer, Chief Operating Reactors Branch #1, 00R FROM:
W. J. Ross, Project Manager Operating Reactors Branch #1, 00R MEETING WITH GENERAL ELECTRIC RELATED TO TURBINE DISC
SUBJECT:
CRACKS At the staff's request, representatives of General Electric met with the staff and licensee / user of G.E. turbines on January 9,1980 to discuss A
the design of and operational experience of low pressure turbines.
list of attendees at the non-pmprietary and proprietary sessions is attached.
In the non-proprietary session General Electric's personnel discussed the following topics:
(a) turbine wheel (disc) integrity; (b) minimizing wheel (discs) bursts. Copies of the slides used in this presentation are attached in Enclosure 3.
Turbine Wheel Integrity There has been no indication of cracks in the bore regions of G.E. low pressure turbine wheels. This experience includes the operation of 35 turbines at nuclear generating plans (22 BWRs-of which only three have actually b,een inspected) and 4000 wheels at 235 fossil units (percent of wheels inspected was not established at the meeting). A G.E. turbine has the following design characteristics:
(1) 14 wheels or discs per rotor with 38" or 43" active length buckets or blades.
(2) Rectangular axial keyway and circumferential locking ring minimize rotation of wheels on the turbine shaft (i.e.
minimize stress).
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i (3) Feedwater systems on pqthe e ' * -
flow domineralizar, good even with poor q
General Electric referenced a 1 bilities of turbine missiles as Entire document previously 4) entered into system under:
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4.1x10"8 (11fetime total)
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P General Electric continues to recommend that its users perform UT inspections of wheel bores at 6-year intervals. A satisfactory UT test has ben developed for this purpose. To date the three UT tests that have been performed were on nuclear turbines that had averaged about 3 years of operating experience.
Minimizing Wheel Bursts A brief ntview of actions taken by G.E. to eliminate the formation of cracks in turbine wheels was presented and included the following:
- 1) Forging process designed to eliminate internal cracks.
- 2) New wheels are inspected te visual. UT and magnetic particle techniques.
- 3) New wheels are tested at 1205 operating speed.
- 4) Tolerance of defects caused by stress and corrosion maximized through choice of material.
- 5) Provision for UT testing of wheels after installation and use.
General Electric's personnel provided the following responses to questions frem the audience.
1.
Retention of a 6-year interval for inspection of turbines was
. justified by operating experience and crack growth rate studies.
2.
Three G.E. turbines at nuclear plants (1 BWR and 2 PWR) have been inspected by UT and no indications observed. These turbines had seen about 3 years of service.
3.
All wheels of turbines at nuclear sites are inspectable in sites (without removal from the turbine). Approximately 5 days are required to inspect one la-wheel rotor.
Four additional days would be needed to comolete the inspection of a second rotor at the same site.
4.
The length of a crack is postulated by G.E. to be 4 to 5 times the depth detemired by UT.
5.
Overspeed devices on G.E. turbines are testable under load and retain their protective capability during the test.
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"$ gw INSTRUCTIONS asx.22281 s' k h l. ~ QIl 4
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(New Information, August 1979)
STEAM PURITY - STRESS CORROSION CRACKING l
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OEK 72281, STEAM PURITY -STRESS CORROSION CRACKING CONTENTS e
PAGE I.
G ENE R AL D ESCRIPTION.....................................................
3 II. OPE R ATION AL RECOMM ENDATIONS...........................................3 A. Once.Through Steam Supply Systems...........................................3 B. Drum Type Steam Supply Systems.........
...................................3 C. S team Purity M o nitoring.........................................
...4 III. M AINTENANCE RECOMMENDATIONS........................................
.5 A. Turb ine Deposi ts............................................................. 5 l
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