ML20148P887

Updates Developments in Turbine Missile Issue at Facility. Based on Conservatisms for Calculation of Critical Crack Ratio,Continued Operation Until 801229 Is Justified.Licensee Will Meet W/Nrc on 801229 to Present Addl Justification

ML20148P887
Person / Time
Site:	North Anna
Issue date:	12/23/1980
From:	Novak T Office of Nuclear Reactor Regulation
To:	Buck J, Quarles L, Rosenthal A NRC ATOMIC SAFETY & LICENSING APPEAL PANEL (ASLAP)
References
NUDOCS 8101150892
Download: ML20148P887 (3)

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.. UNITED STATES f 3e g NUCLEAR REGULATORY COMMISSION

E W ASHINGTON, D, C. 20555

$p December 23, 1980 ,

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Alan S. Rosenthal, Esq. , Chairman h6- @O H Dr. John H. Buck, Member Dr. Lawrence R. Quaries, Member ;c ,,

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Jy, Atomic Safety and Licensing Appeal Board - :;

Washington, D. C. 20555 s u 33 y p' "S

In the Matter of l Virginia Electric and Power Company (Licensee) i (North Anna Power Station, Units 1 and 2) ,

Docket Nos. 50-338/339 _(Turbine Mis.ile s Issue)

' Gentlemen:

In an affidavit filed with the Appeal Board on February 19, 1980, relating to the I j

potential for cracking in the North Anna, Unit 1, turbines, the Staff had indicated that, based on the model developed and being used by the Staff at that time, the I I

worst crack expected to be found in the North Anna, Unit 1, turbine would not exceed a value of 0.5 critical crack size at 120 percent design overspeed prior to it's regularly scheduled refueling outage in December,1980, which was subsequently post-poned to January 1,1981.

The Chairman of the Appeal Board has been notified by telephone by the Licensee on December 19, 1980 and the NRC Staff on December 22 and 23,1980 of new information regarding the potential for cracking in the North Anna, Unit 1, turbines. By this  !

letter, the Staff is confirming such prior oral notification of the existence of new information and an analysis of the infonnation currently available to the Staff.

On December 4,1980 the NRC Staff Tirst learned of information derived from the Farley Unit 1 turbine inspection. This infonnation began to be quantified on l December 12, 1980. The Staff used that preliminary information in order to assess the effect the data may have on the staff's turbine cracking model. By December 19, 1980, the Staff determined that the value for the ratio of the postulated crack '

size to critical crack size could be potentially as high as about 1.0 for North i Anna, Unit 1. This value was calculated for the potential cracks that might exist in the North Anna, Unit 1 turbine, utilizing the Staff's conservative model, including an aspect ratio (depth versus length of crack) of 1 to 4.

Because of this high value, and the potential impact it may have on the basis for continued safe operation of North Anna, Unit 1, the Staff has reexamined its evalu-ati6n of the potential for crack progation in the turbine at North Anna, Unit 1, over the last couple of days. The Staff requested the licensee to provide its written justification supporting continued operation until January 1,1981. A copy of the Licensee's response is attached for the information of the Appeal Board.

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The Staff has determined that, based on overall conservatisms for the calculation of the critical crack ratio, continued operation until December 29, 1980 while the licensee gathers additional information is justified. On that date, the licensee will meet with the Staff to present its additional justification for continued THIS DOCUMENT CONTAINS 3

y P0OR QUAUTY PAGES B1013 5 0

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. t 2-operation with respect to:-(a) presenting new. facts regarding the Farley turbine  !'

inspection, and (b) providing technical justification and basis for its position, presented orally to the. Staff on December 23, 1980, that even if disc one of the i' turbine were.to fail it would not penetrate the turbine casing and thus would. not adversely affect the health and safety of the public. j

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North- Anna, Unf t 1, is presently in a coast down mode of. operation. (57 percent . power l as of September 23, 1980) and is reducing power by about i percent per day. North l Anna, Unit 1, is presently scheduled to shut down on January 1,1981 for the second i refueling outage. The Staff.. understands that North Anna, Unit 1, may not resume .

operations until the . Appeal . Board has had an opportunity to evaluate the licensee's ,

inspection report regarding the results of the North Anna, Unit 1, turbine inspection to be conducted during the forthcoming refueling outage.  :

Sincerely, c M M ,

Thomas M. Novak, Assistant Director for Operating Reactors  !

~

Division of Licensing ,

Enclosure:

Licensee Letter Dated December 23, 1980 4

cc: E. Case D. Eisenhut R. Vollmer ,

V. Noonan  :

T. Novak R. Clark ,

R. Tedesco ,

L. Engle cc w/ enclosure:

See next page s

. 1 Virginia Electric tad Power Company ,

cc: Richard M. Foster, Esq. Mrs. June Allen ' '

Musick, Williamson, Schwartz, North Anna Environmental Coalition Leavenworth & Cope, P.C. 1105-C Olive Street P. O. Box 4579 Greensboro, North Carolina 27401 Boulher, Colorado 80306 Michael W. Maupin, Esquire Mr. Jaraes Torson Hunton, Williams, Gay and Gibson 501 Leroy Socorro, New Mexico 87801 P. O. Box 1535 -

Richmond, Virginia 23212 Alderrran Library Route 2, Box 568 Manuscripts Department Gordonsville, Virginia 22042 l

University of Virginia 1 Charlottesville, Virginia 22901 Mr. James C. Dunstance '

' State Corporation Comission Cormonwealth of Virginia Mr. Edward Xube Blandon Building Board of Supervisors Louisa County Courthouse Richmond, Virginia 23209 P. O. Box 27 U. S. Environmental Protection Agency Louisa Virginia 23093 R'egion 111 Office Ellyn R. Weiss, Esquire ATTH: EIS COORDINATOR Sheldon, Harmon, Roisrtan and Weiss Curtis Building 1725 I Street, N.W., Suite 506 6th and Walnut Streets Washington, D. C. 20006 Philadelphia, Pennsylvania 19106 l Mr. W. R. Cartwright, Station Manager Director, Criteria and Standards Ihision 4 P. O. Box 402 Cffice of Radiation Frograms (A!G-460)

Mineral, Virginia 23117 U.S. Fr. viro:= ental Protection Agency Washington, D.C. 20460 Mr. Anthony Gambardella Office of the Attorney General 11 South 12th Street - Room 308 Mr. Paul W. Purdom Richmond, Virginia 23219 Environmental Studies Institute Drexel University 32nd and Chestnut Streets Mr. Allan Tattersall Philadelphia, Pennsylvania 19104 Resident Inspector / North Anna c/o U.S. NRC Atomic Safety and Licensing P. O. Box 128 Appeal Board Panel Spotsylvania, Virginia 22553 U. S. Nuclear Regulatory Comission 4

Washington, D. C. 20555 Comonwealth of Virginia Council on the Environment 903 Ninth Street Office Building Richmond, Virginia 23129 O

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VIDG5MTA EsJECrWIC AND POWEH COMW $ OF 2 j R A C1pcOw p.VIROTN ja S DB 61 TO- D . G . G. G E N H UT I ~

i FROM d . T. R HOD E.6 l

December 23, 1980 Mrf Earc Id R. Denton, Director ' Serial No.1015 l

' Office of Nuclear Reactor Regulation N0/SGE;emy l Attention: Mr. Robert A. Clark, chief Docket No. W 338 Operating Heactors Branch No. 3 License No. NFF-4 >

Division of Licensing U. S. Fuelearpa:gulatory Connission

'Ashington. D. c. 20555 Dedr Mr. Dentou: ,

TUREIhT HIS$1LE CONCERN

! EORrH ANNA UNIT NO.1 -

ConfirminE our dicussions with Mr . V . $ . No enan on,,t)ececber 22, 1980, ve believe tbst there is sufficient conservatisa in the ',eAleclations to permit the, continued operation of the North Anu 1 turbines until January 1,1981 vithout undus risk of failure. Specifically, the major areas of-tonnervativa s re,:

l. The fracture mechanics analysis used to determine the critical crack size as sumes a sha rp neraight crack, wherean, stress corroeien cracks are branch ed . Limited analytical and experimental evidence indicates that the critical size of strees corrosion cracks is at least 1.7 to 2 tines greater than that which the fracture wachanics model predicts.

j 2. De fracture wechanica model utilized a hypo thetical elliptical

crack with an a:2e ratio of 1:4 This model adequately decribes the i early stages when several cracks way grow tosether to form long, shallow cracks. F.ovever, the deeper cracks dich have been observed i' tu the Cooper. Zion, and Yankee Enve torbines all exhibited a:2c ratios appenaching 1:2. The ultrasonic inspection at Parley gave.

resulta vbich indicate that the ratio is not larger than 1:3.5.

nese changes in the a:2c ratio vill result in increases in the critical crack size by a factor of 1.1 to 1.8,

3. The stress used in the analynia contains contributions fron, rotation,

,- the shrink fit, stca be nding, and themsl gradients. The wodel used to calculate the thernal gradient straes conservatively assceed ,

a eevere startyp condition, Dnder steady state conditions for 1 l

gradually decreasing loads, 'With will be representative of the North Anna operation until January 1. 1981, the disk stresees are p expect ed to be at least 10% lover. Thie vill reeult in an increase i

in the critical crack eize by s factor of approxirately 1,2, l

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I Mr. Harold R. Denton, Directer ymp Euenoc an rown Commdte u

Conaldering the above - three f actors, it -is reasonables to expect that the ,

critical crack sizes used in ~ the analysis are conservative by at least ~2.25 l (1.7 x 1.1 x 1.2). De ratio a/acR can aimilarly be reduced.

l In addition, several other factors need be considered. In evaluating the risk of failure, it wast- be ressenbered that not all disk.s are observed to crack, and not all cracks propogate at the naxi::um observed rate. It should also be noted that the crack growth rate observed in the FarIey turbine acd used ~

H for these analyses greatly exceeds the rates previously observed in many other tu rbines. herefore, it is likely. that the cracking that occurs at North. Anna, if any, vill be considerably less than that which occurred at Farley. s To further assure the safe operation of the enit until Jacuary 1.1981, the I unit will not be subjected to cyclic operation. We further intend that if the unit is tripped, for any reason, it will remain shutdown until af ter the turbines are inspected.

l Very truly yours, ,

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/ B. R. Sylvta ff' Manager s Nucicar Operations and Maintenance cc: Mr. James P. O'Reilly, Director Of fice of Inspection and Enf orce::ent  :

Region II l Atlanta, Georgia 30303 Mr. B. Joe ioungblood, Chief Licensing Branch No. 1 Division of Licensing i

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