ML20045G412
| ML20045G412 | |
| Person / Time | |
|---|---|
| Site: | Perry  |
| Issue date: | 07/06/1993 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20045G408 | List: |
| References | |
| NUDOCS 9307130319 | |
| Download: ML20045G412 (4) | |
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WASHINGTON, D C. 20555-0001 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO SNUBBER OPTIMIZATION OF FEEDWATER SYSTEM THE CLEVELAND ELECTRIC ILLUMINATING COMPANY. ET AL.
PERRY NUCLEAR POWER PLANT. UNIT 1 DOCKET NO. 50-440 I
l.0 INTRODUCTION The Cleveland Electric Illuminating Company (CEI) implemented a snubber optimization program for the Perry Nuclear Plant (PNPP), Unit 1, during refueling outage 3 (RF03).
Included in this RF03 snubber optimization effort is the feedwater piping system within the drywell.
The feedwater piping consists of two loops designated Loop A and Loop B.
These two loops are symmetric. The four snubbers removed from Loop A have identifications as IN27H0002, IN27H0008, IN27H0009, and IN27H0025, and those from Loop B as IN27H0014, IN27H0020, IN27H0021, and IN27H0026. All of these snubbers are hydraulic snubbers with sizes ranging from 30 to 70 KIPS.
2.0 EVALUATION One of the analytical techniques used for the piping system with snubber optimization was the application of ASME Code N-411, " Alternative Damping Values for Response Spectra Analysis of Class 1, 2, 3 Piping,Section III, Division 1."
Code Case N-411 is endorsed by Regulatory Guide (RG) 1.84.
" Design and Fabrication Code Case Acceptability, ASME Section III, Division 1," Revision 28, dated April 1992. RG 1.84 contains five conditions which must be met for Code Case N-411 to be applicable.
Condition (5) specifies the 1
requirement for a case-specific evaluation for piping in which intergranular stress corrosior cracking (IGSCC) has occurred.
For PNPP, indications had been detected in the N4C and N4E feedwater nozzle-to-safe end weldments, during RF02 Inservice Inspection (ISI).
The indications could not be definitely confirmed to be-IGSCC related based on the results of the examinations.
However, the licensee proceeded to perform a case-specific evaluation for the impact of the cracking on the piping system (Reference 1).
This evaluation was submitted for staff review on May 8, 1992, j
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a The staff also reviewed GE Design Report 23A6987, Revision 1 (Reference 2) which provides the analysis and results of Loop A.
Due to symmetry, they are also directly applicable to Loop B.
Some concerns were at first identified on the methodologies used for the Perry feedwater piping analysis. Additional concerns were later identified regarding the lack of an auditable form of the analysis results being provided for staff review.
Following a conference call on May 15, 1992, the staff met with CEI and General Electric (GE) personnel on May 18, 1992, in Rockville, Maryland, to discuss the concerns.
During the meeting, additional comments were raised by the staff.
Specifically, a demonstration of the adequacy of the modal analysis result for the modified support configuration was absent.
The licensee responded to the above concerns and comments, and subsequently incorporated them into their submittal of May 20, 1992 (Reference 3).
The latter included an overview discussion of the Perry feedwater snubber optimization project and a project summary white paper provided by GE.
Based on a preliminary review of the above information, the staff did not identify any obvious safety concerns regarding the snubber optimization for the feedwater lines, and determined that the licensee's analysis appeared to be consistent with applicable design basis requirements. The staff concluded that while a more in-depth review was necessary, the plant restart from RF03 implementing snubber optimization was acceptable (Reference 4).
The staff has since performed a more in-depth evaluation for the above issue, and finds that the preliminary conclusion remains valid.
This evaluation is summarized in the following.
Reference 1 provides the results of the fracture analysis performed by CEI prior to RF03 with the interface loadings of snubber optimization fully considered.
This case-specific evaluation projected flaw growth on an assumed 12,000 hours0 days <br />0 hours <br />0 weeks <br />0 months <br /> of operation until RF04. The acceptance criteria for the flaw analysis was based on ASME Section XI, Appendix C, 1986, Edition.
It found that the flaw sizes are well within the ASME Code acceptable limit.
It also found that, as an additional conservative measure, the licensee applied " mechanical stress improvement" to mitigate future flaw growth.
i Reference 3 provides a summary of the methodologies and criteria utilized for the snubber optimization program of the feedwater system.
The staff finds them to be consistent with the staff requirements required for plants which would be subjected to current licensing review, and therefore, are acceptable.
In addition, Reference 3 also provides the updated results of the piping analysis performed. Maximum calculated stresses are found to compare favorably to the allowable stresses for normal and upset, emergency, and faulted conditions.
The natural frequencies and the corresponding maximum modal displacements of the modified system configuration conform to what would be expected without the deleted snubbers. Although some support loads calculated after the snubber optimization are found to exceed the original calculated loads, they are still 1
well within the corresponding design loads for each of the service load levels.
Spot checking of GE's computerized outputs also confirms the adequacy of the
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nozzle and penetration designs.
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3.0 CONCLUSION
Based on the information provided, the staff concludes that:
1.
The feedwater system snubber optimization analysis, as performed by GE and CEI, conforms to all Perry UFSAR allowable limits and all the pertinent design basis loading conditions, 2.
The application of Code Case N-411 conforms to the requirements of RG 1.84, including the case-specific evaluation which demonstrates ample safety margin in the feedwater system considering the presence of the potentially IGSCC-induced flaws, 3.
Mechanical Stress improvements has been applied during RF03 to the subject feedwater nozzle-to-safe end weldments to mitigate future flaw propagation, and 4.
Implementation of snubber optimization is believed to enhance overall plant safety and reliability, as well as plant maintenance.
Therefore, the staff concludes that the snubber optimization for the feedwater system is consistent with ASME Code requirements, does not compromise the structural integrity of the feedwater system piping, and is therefore acceptable.
Principal Contributor:
A. Lee Date: July 6, 1993 I
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REFERENCES 1.
Letter from M. D. Lyster (CEI) to Document Control Desk (USNRC) dated May 8, 1992 (PY-CEI/NRR-1491 L).
2.
GE Design Report 23A6987, Revision 1 "Feedwater System Loop'A' Piping and Equipment loads," January 21, 1992.
3.
Letter from M. D. Lyster (CEI) to Document Control Desk (USNRC) dated May 20, 1992 (PY-CEI/NRR-1499 L).
l 4.
Letter from J. R. Hall (NRC) to M. D. Lyster (CEI) dated May 22, 1992 (TAC No. M81879).
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