ML20235N253

Forwards Stress Analysis of Thin Pipe Region in Steam Generator Main Steam Line 12. Results of Analysis Indicate That Max Primary Hoop Stress Is Below Code Allowable Stress Level of 17,500 Psi.Relief from Flaw No Longer Requested

ML20235N253
Person / Time
Site:	Calvert Cliffs
Issue date:	09/30/1987
From:	Tiernan J BALTIMORE GAS & ELECTRIC CO.
To:	NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM)
Shared Package
ML20235N256	List: ML20235N253 ML20235N316 ML20235N369 ML20235N433
References
NUDOCS 8710060448
Download: ML20235N253 (3)

Text

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B ALTIMORE GAS AND ELECTRIC CHARLES CENTER P. O. BOX 1475 BALTIMORE, MARYLAND 21203 JosepN A.TIERNAN VicE PnEsIDENT NUCLEAR ENERGY September 30, 1987 U. S. Nuclear Regulatory Commission Washington, DC 20555 ATTENTION: Document Control Desk

SUBJECT:

Calvert Cliffs Nuclear Power Plant Unit No.1; Docket No. 50-317 Main Steam Pioinn Flaw at Calvert Cliffs Unit 1

REFERENCES:

(a) Letter from Mr. A. R. Thornton (BG&E) to Mr. A. C. Thadani (NRC),

dated December 16, 1986, Request for Approval of Main Steam Piping Evaluation per ASME Section XI, IWB-3600 and Relief from IWB-3610(b)

(b) Letter from Mr. A. R. Thornton (BG&E) to Mr. A. C. Thadani (NRC), l dated December 19, 1986, Request for Approval to Update to Later i Edition of ASME Code Section XI for Acceptance Standards  ;

(c) Letter from Mr. A. C. Thadani (NRC) to Mr. J. A. Tiernan (BG&E),

dated March 26, 1987, Final Approva of and Safety Evaluation Concerning ASME Code Update and Relief for Main Steam Piping Flaw at Calvert Cliffs Unit 1 Gentlemen:

This letter requests the NRC to review additional information regarding the pipe flaw on Unit I and to modify the March 26, 1987, Safety Evaluation. References (a) and (b) requested ASME Code relief and update to a later Code because of an existing flaw in the base metal of the No.12 steam generator main steam line adjacent to and downstream of weld No. EB-01-1005-05. Reference (c) updated the ASME Code Section XI requirements for this flaw to the 1983 Edition with Addenda through Summer 1983 in accordance with 10 CFR 50.55a(g)(4)(iv). In addition, Reference (c) granted relief from the require-ments of IWB-3610(b) until the next Unit I refueling outage. This was necessary at the time because we had not yet shown that we met the primary hoop stress limits of the original construction code (B31.1-67) required by Article IWB-3610(b) using simplified techniques. The basis for the approval of the relief was that 1) the affected pipe retains adequate fracture toughness, 2) a limit load analysis shows sufficient wall thickness remaining to prevent yielding, 3) the affected pipe will be replaced or repaired at the next Unit I refueling outage, and 4) the affected pipe is an isolated case.

8710060448 870930 PDR P

ADOCK 05000317 PDR 30 [

Document Control Desk September 30, 1987 Page 2 A flaw evaluation analysis was provided to the NRC in Reference (a) to satisfy the requirements of Article IWB-3610. Part of this analysis was a draft fracture mechanics evaluation prepared by Southwest Research Institute (SwRI). The evaluation showed that the rupture load is two times greater than the maximum anticipated load. In addition, the evaluation demonstrated no significant crack growth or propagation for the remainder of plant life. Attachment 1 is a report of the final fracture mechanics evaluation performed by SwRI.

The analysis provided in Reference (a) demonstrated that primary longitudinal stress limits were met but primary hoop stress limits were not. The flaw evaluation was simplistic. A more detailed finite element analysis was needed. Therefore, BG&E contracted SwRI to perform a finite element analysis of the thin pipe region in No.12 steam generator main steam line. Attachment 2 is a report of the final stress analysis.

The results of the finite element analysis indicate that the maximum primary hoop stress is below the Code allowable stress level of 17,500 psi. In addition, the predicted maximum membrane plus bending stress level is below the ASME Boiler and Pressure Vessel Code allowable membrane plus bending stress level of 26,250 psi. This analysis meets the intent of the B31.1 Code in that a "more rigorous analysis" may be substituted for the simple hoop stress equation in Paragraph 104 of B31.1-67.

A third-party review of the SwRI evaluations was performed by Combustion Engineering.

This review concluded that the evaluations demonstrate that the pipe in its present configuration meets the requirements of the original Construction Code, USAS B31.1 (1967), and that full compliance with IWB-3610 (b) is accomplished. Attachment 3 is a report of this third-party review.

Based on the above information, it is our position that we no longer require relief for this flaw from Article IWB-3610(b) of the 1983 Edition with Addenda through Summer 1983 Section XI of the ASME Code. Because of this, the requirement in Reference (c) to repair or replace the affected pipe at the next refueling outage should not apply.

Therefore, we request you accept the evaluation of the existing flaw without requiring any repairs or modifications. If you concur with our evaluation, the Safety Evaluation enclosed in Reference (c) needs to be modified to reflect the new conclusion.

Should you have any questions regarding this subject, we would be pleased to discuss them with you.

Very truly yours, d

&&W JAT/SRC/dtm Attachments l

Document Control Dcsk September 30, 1987 Page 3 cc: D. A. Brune, Esquire J. E. Silberg, Esquire R. A.Capra,NRC S. A.McNeil,NRC .

W. T. Russell, NRC l T. Foley/D. C. Trimble, NRC l

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