ML20125B935

Recommends Notifying Aslab of Westinghouse Turbine Disk Cracking,Based on Info in 791105 Anonymous ltr,791120 Telcon W/Westinghouse & PNO-III-79-43 Re Low Pressure Disk Cracks at Zion Unit 1

ML20125B935
Person / Time
Site:	Saint Lucie, North Anna
Issue date:	12/12/1979
From:	Boyle M Office of Nuclear Reactor Regulation
To:	Pawlicki S Office of Nuclear Reactor Regulation
Shared Package
ML20125B934	List: ML20125B935 ML20125B939
References
REF-GTECI-A-37, REF-GTECI-IT, TASK-A-37, TASK-OR NUDOCS 7912310377
Download: ML20125B935 (3)

Text

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l' N(o, UNITED STATES NUCLEAR REGULATORY COMMISSION n

WASHINGTON, D. C. 20555

$" 4***** /

DEC 12 Docket Nos. 50-338/339 l

f1EMORANDUM FOR:

S. S. Pealicki, Chief Materiais Engineering Branch l

THRU:

R. M, Gamble, Section Leader Materials Integrity Section FRCM:

M. L. Boyle, Man.ger Generic Task A-37

SUBJECT:

NOTIFICATION OF ASLAB 0F WESTINGHOUSE TURBINE DISK CRACKING On June 20, 1979, members of the staff presented testimony before the Atomic Safety and Licensing Appeal Board in the matter of Virginia Electric and Power Company (North Anna Power Station, Units 1 and 2, Docket Nos. 50-338/339) concerning pump house settlement and turbine missiles. Since the time of this hearing, additional inforination concerning the integrity of Westinghouse turbine disk material has been received by the staff. The nature of this information is such that the Atomic Safety arj Licensing Appeal Board should be notified.

An anonymous letter (Attachment 1) dated November 5,1979 was sent to the Director of the Office of Inspection and Enforcement (with a copy sent to Commissioner Peter A. Bradford) regarding allegations of stress corrosion cracks in Westinghouse turbine disks. On November 20, 1979, Mr. V. S. Anderson of Westinghouse's Turbine Division confirmed, in a telecon with the staff, that cracks have been found in several turbine disks. Also, on Ncvember 20, 1979, the Office of Inspection and Enforcemtnt issued a preliminary notification of evr.nt or unusual occurrence, PNO-III-79-43, concerning cracks in the low pres-i sure turbine disks of Commonwealth Edison Company's Zion Station Unit 1 (see ).

The staff has informally received copies of a proprietary Westinghouse report that contains descriptive information abouc turbine disk cracks and turbine missile exit energies. This report indicates that the cracking may be more widespread than previously reported.

From this report, it appears that Westinghouse's calculated value of Pi and possibly P2 and P3 may have been too low and may be revised upward.

From the information available to the staff at this time, it does not appear that the values of P, P2 and P3 calculated by the staff and presented in the i

written testimony before the Atomic Safety and Licensing Appeal Board are affected by the report of the recent Wertinghouse turbine cracks.

In their calculations of the factor of improvement of the P t probability the staff assumed an increase in crack growth rate due to stress corrosion cracking and assumed the existence of cracks initially present in the turbine disk of the 90000016 7912 a y e M%

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a S. S. Pawlicki DEC 1 0 M order of those found at Zion' Station Unit 1.

The crack size reported in the' proprietary Westinghouse report was.less severe 'than that at Zion Station

Unit'l.

~

The staff also has reason to believe that West 4ghouse is in the process 'of.

elevating some of their previously estimated turbine missile exit. energies.

'This, apparently, is in response to some recent missile test results which indicate that non-symmetric missile impacts with turbine internals may result in higher missile energies-than those previously estimated.

Missil'e energies affect the estimation of P, the probability of barrier

)

3 penetration and equipment damage. P3 was assumed to be unity in the staff i

evaluation of North Anna turbine. missile risks reported in the SER. This_is a conservative assumption implying that plant structures and other barriers offer no resistance to turbine missiles.

Hence the Westinghouse reassessment of missile energies does not change the conclusions reported in the SER.

j In the staff's testimony on North Anna turbine missile risks, missile energies are discussed in reference to measuring the amount of conservatism associated with'the assumption that P3 is unity. The discussion is based on staff's analyses which include non-sym1eric impact effects. Thus it appears to the staff that the Westinghouse reassessment is a recognition of the same effect that the staff has used in its analyses and which typically resulted in higher missile energy estimates than those previously reported by Westinghouse.

Thus, we have found from a preliminary evaluation of the data known about the cracks reported in the Westinghouse turbine disks and the potentially higher missile energies, that the conclusions reached _ in the staff testimony are still valid.

However, we cannot preclude the possibility that some technical information submitted in response to our investigation into these events would change our conclusions.

The Division-of Operating Reactors is coordinating an effort with the Office of Inspection and Enforcement, the Division of Systems Safety and the Division of Site Safety and Environmental Analysis to evaluate any safety implications of this recent experience. As the staff receives more technical details on the turbine disk cracking, we will forward them to the Office of the Executive Legal Director for distribution to the Atomic Safety and Licensing Appeal Board. The Westinghouse report is not attached because of its proprietary j

nature. However, the staff will request that the report be released by i

Westinghouse and if Westinghouse ag,srees, it will be forwarded to the Board,

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M. L. Boyle Materials Integrity Section Materials Engineering Branch For enclosure & cc's, see attached sheet gg7 s

1

F S. S. Pawlicki n:;

Enclosure:

As stated cc:

H. R. Denton E. G. Case V. Stello R. J. Mattson D. R. Vassallo D. F. Ross F. Schroeder D. G. Eisenhut R. C. DeYoung H. D. Thornburo T. F. Engelhardt N. C. Moseley B. K. Grimes J. P. Knight S. A. Varga W. E. Kreger S. S. Pawlicki 90000(;,18 R. M. Gamble H. F. Conrad V. S. Noonan W. S. Hazelton K. G. Hoge G. W. Knighton K. M. Campe W. J. Collins S. A. Treby D. T. Swanson

0. D. Parr A. W. Dromerick MTEB Members M. L. Boyle

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