ML20140B011

Ack Commitments Made in Re Recent Findings of Eggcrate Degradation in Plant Sgs.Eggcrate Evaluation Areas Encl

ML20140B011
Person / Time
Site:	San Onofre
Issue date:	05/30/1997
From:	Fields M NRC (Affiliation Not Assigned)
To:	Nunn D SOUTHERN CALIFORNIA EDISON CO.
References
NUDOCS 9706050257
Download: ML20140B011 (5)

Text

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May 30, 1997 l Mr. Dwight E. Nunn  !

Vice President Southern California Edison Company i San Onofre Nuclear Generating Station  ;

P. O. Box 128 '

San Clemente, California 92674-0128

SUBJECT:

SAN ONOFRE NUCLEAR GENERATING STATION UNIT 3 STEAM GENERATOR -

EGGCRATE DEGRADATION ISSUE

Dear Mr. Nunn:

The purpose of this letter is to acknowledge the commitments made in your 7 letter dated May 16, 1997, regarding the recent findings of eggcrate degradation in the San Onofre Unit 3 steam generators. Specifically, Southern  !

California Edison (SCE) committed to submit a comprehensive evaluation of the condition of the San Onofre Unit 3 steam generators at least 7 days prior to entry into Mode 4. Following submittal of this report, SCE will meet with the NRC staff to discuss this evaluation prior to Mode 4 entry. SCE further >

committed to submit a final report within 90 days after restart from the current refueling outage.  !

Enclosed is a list of areas that, as a minimum, should be thoroughly addressed l in the forthcoming report. If you have any questions, please call me at (301) i 414-3062.

l Sincerely, Original Signed By )

l Mel B. Fields, Project Manager Project Directorate IV-2 l Division of Reactor Projects III/IV

! Office of Nuclear Reactor Regulation

> Docket No. 50-362 DISTRIBUTIOJ:

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\ . . . . . ,o Mr. Dwight E. Nunn Vice President Southern California Edison Company  ;

San Onofre Nuclear Generating Station P. O. Box 128 San Clemente, California 92674-0128

SUBJECT:

SAN ON0FRE NUCLEAR GENERATING STATION UNIT 3 STEAM GENERATOR EGGCRATE DEGRADATION ISSUE

Dear Mr. Nunn:

The purpose of this letter is to acknowledge the commitments made in your letter dated May 16, 1997, regarding the recent findings of eggerate degradation in the San Onofre Unit 3 steam generators. Specifically, Southern ,

California Edison (SCE) committed to submit a comprehensive evaluation of the l condition of the San Onofre Unit 3 steam generators at least 7 days prior to entry into Mode 4. Following submittal of this report, SCE will meet with the NRC staff to discuss this evaluation prior to Mode 4 entry. SCE further committed to submit a final report within 90 days after restart from the current refueling outage. , l l

Enclosed is a list of areas that, as a minimum, should be thoroughly addressed i in the forthcoming report. If you have any questions, please call me at (301) {

415-3062. 1 Sincerely, ,

f. .2 , W7%

Mel B. Fields, Project Manager Project Directorate IV-2 Division of Reactor Projects III/IV .

Office of Nuclear Reactor Regulation l Docket No. 50-362

Enclosure:

Eggerate Evaluation Areas l cc w/ encl: See next page i

• i

. Mr. Dwight E. Nunn  :

cc w/ encl: ,

i Mr. R. W. Krieger, Vice President Resident Inspector / San Onofre NPS  !

Southern California Edison Company c/o U.S. Nuclear Regulatory Commission. - !

San Onofre Nuclear Generating Station Post Office Box 4329  ;

P. O. Box 128 San Clemente, California 92674  :

San Clemente, California 92674-0128 ,

Mayor Chairman, Board of Supervisors City of San Clemente County of San Diego 100 Avenida Presidio ,

1600 Pacific Highway, Room 335 San Clemente, California 92672  ;

San Diego, California 92101 Mr. Harold B. Ray Alan R. Watts, Esq. Executive Vice President ,

Woodruff, Spradlin & Smart Southern California Edison Company 701 S. Parker St. No. 7000 San Onofre Nuclear Generating Station Orange, California 92668-4702 P.O. Box 128 San Clemente, California 92674-0128 i Mr. Sherwin Harris Resource Project Manager Public Utilities Department City of Riverside 3900 Main Street Riverside, California 92522 Dr. Harvey Collins, Chief Division of Drinking Water and Environmental Management L California Department of Health Services P. O. Box 942732 Sacramento, California 94234-7320

. Regional Administrator, Region IV

! U.S. Nuclear Regulatory Connission '

Harris Tower & Pavilion 611 Ryan Plaza Drive, Suite 400 Arlington, Texas 76011-8064 ,

Mr. Terry Winter Manager, Power Operations San Diego Gas & Electric Company P.O. Box 1831 San Diego, California 92112-4150 '

1 l Mr. Steve Hsu

Radiologic Health Branch i

State Department of Health Services Post Office Box 942732 i Sacramento, California 94234 i

, _ _ _ _ _ _ . . _. _ _ __. _ __~ _

l l

l SAN ON0FRE NUCLEAR GENERATING STATION UNIT 3 STEaN GENERATOR EGGCRATE ISSUE.

l EVALUATION AREAS

]

1. The ATH0S code was used to assist in the prediction of flow accelerated corrosion (FAC) regions areas for the San Onofre Unit 3 cteam generators i (SGs). Discuss the ability of ATH0S to predict the lack of FAC regions ,

observed in the SONGS Unit 2 SGs. '

2. Discuss your approach for determining the eggerate degradation i mechanism. Discuss the cause of the degradation mechanism, how it will  !

be minimized or eliminated and how this will be verified. Discuss '

implications for the Unit 2 SGs and relevant actions that will be taken.

3. Discuss the objectives and results from secondary side visual (and eddy current, if applicable) inspections. Discuss how the baseline condition  !

(current condition) of the eggcrates is being determined, how and which structural elements are being measured, and in what form the baseline conditions are being recorded.

4. Discuss the extent of the eggerate degradation and how this affects SG tube integrity for the' full range of test, normal operating, and accident conditions. Discuss the design bases for the eggerate structures in the SONGS SGs and how the design bases are affected by the degradation. Discuss the criteria and the basis for criteria that will be applied for dispositioning tubes potentially affected by loss of eggerate support. I 1

5. Discuss future inspection plans related to the eggerates for both SONGS units. Discuss the' techniques, the scope, and the disposition process (acceptance criteria).

]

6. Discuss the approach to be used to determine the potential growth rate l of degradation of the eggerate structures. 1

7. Discuss how the potential growth rate of degradation of the eggerate ,

structures is being incorporated into the assessment of the length of the next operating cycle. Discuss the proposed length of the next operating cycle for Unit 3 and provide the basis for the proposed length. Address the probability for tube rupture to occur during the  !

l current operating cycle for Unit 2 and during the next operating cycle for Unit 3 as a result of operating with potential or actual degradation l of the eggcrate structures and whether or not the probability of tube rupture has increased. Discuss the possibility that the margins of safety in the eggerate structures and affected tubes have decreased as a result of the observed degradation.

f

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. 8. Explain in sufficient detail the analysis performed to verify the functionality of the Unit 3 SG tubes under design basis accident conditions, considering the identified degradation of the eggerates.

• State if the analysis is linear or non-linear and explain how the gaps i between the tubes and support plates are represented in the structural model. Also, explain how each loading is applied to the tubes, and how tube deformations / stresses are determined under combined loading conditions.

9. Identify the materials used for all the structural elements associated with the tube supports (e.g., eggerate supports, baffle, deflector, -

vertical support grids, diagonal spacer strips, wrapper bar). Also identify the design and acceptance criteria used for determining the. ,

adequacy of tube support structural elements. Specifically, state the Code, Section and Editions from which the acceptance criteria were established and provide the basis for your choice.

10. In assessing the fluid-elastic instability of the SG tubes due to critical flow-induced vibration, discuss the details of the formulas used for determining the critical flow velocity under degraded SG eggerate condition. Justify any empirical parameters used.

11. Confirm the calculated cross flow velocities by actual measurements of some critical local cross flow velocities in the secondary side flow of the SG under the degraded conditions.

12. . Confirm the calculated natural frequency of the most critical SG tubes with available test data which is representative of the degraded eggerate and inboard lattice bars conditions.

13. For the evaluation of SG tube stresses under accident conditions, confirm that the normal flow-induced vibration load under degraded conditions is combined with the accident loads.

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