NOC-AE-07002168, Summary Assessment of Pressurizer Nozzle Safe End Weld Overlays: Shrinkage and Fatigue Crack Growth (RR-ENG-2-43)

Summary Assessment of Pressurizer Nozzle Safe End Weld Overlays: Shrinkage and Fatigue Crack Growth (RR-ENG-2-43)

ML071560122
Person / Time
Site:	South Texas
Issue date:	05/29/2007
From:	Jenewein B South Texas
To:	Document Control Desk, NRC/NRR/ADRO
References
NOC-AE-07002168, TAC MD1414, TAC MD1415, TAC MD1416, TAC MD1417, TAC MD1418, TAC MD1419, TAC MD1420, TAC MD1421, TAC MD1422, TAC MD1423
Download: ML071560122 (4)

Text

MET" O Xam ff AV`t 1a 783A May 29, 2007 NOC-AE-07002168 File No.: G25 10 CFR 50.55a U.S. Nuclear Regulatory Commission Attention: Document Control Desk One White Flint North 11555 Rockville Pike Rockville, MD 20852-2738 South Texas Project Unit 2 Docket No. STN 50-499 Summary Assessment of Pressurizer Nozzle Safe End Weld Overlays:

Shrinkagqe and Fatigue Crack Growth (RR-ENG-2-43) (TAC Nos. MD1414-1423)

Reference:

Letter dated September 28, 2006, from David W. Rencurrel, STPNOC, to NRC Document Control Desk, "Response to Request for Additional Information on Proposed Alternative to ASME Section XI Requirements for Application of a Weld Overlay (RR-ENG-2-43) (TAC Nos. MD1414-1423)," (NOC-AE-06002068)

Pursuant to 10 CFR 50.55a(a)(3)(i), the STP Nuclear Operating Company (STPNOC) requested approval to use an alternative to the requirements of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code),Section XI for the structural weld overlays on the South Texas Project Unit 1 and Unit 2 pressurizer spray, relief, safety and surge nozzle safe-ends. NRC approval to perform the structural weld overlays in Unit 2 was given April 2, 2007. The overlays performed in the April 2007 Unit 2 refueling outage (2RE12) were the pressurizer spray, relief, safety, and surge nozzle safe-ends. This supplement to the request fulfills commitments made in the correspondence referenced above.

STPNOC completed a stress analysis of the pressurizer spray, relief, safety, and surge nozzle safe-ends pre-emptive weld overlay prior to restart of Unit 2. Summaries of the results are provided in the attachment. The stress analysis results support the conclusion that structural weld overlays are a suitable pre-emptive measure for anticipated flaw development.

There are no commitments in this submittal.

If there are any questions, please contact either Mr. Philip L. Wal er at (361) 972-8392 or me at (361) 972-7431.

SB. L Jenewein Ma ager, ting/Programs PLW

Attachment:

Summary Assessment of Pressurizer Spray, Relief, Safety, and Surge Nozzle Safe-End Weld Overlays: Shrinkage and Fatigue Crack Growth STI NO: 32165714 c-1"7

NOC-AE-07002168 Page 2 of 2 cc:

(paper copy) (electronic copy)

Regional Administrator, Region IV A. H. Gutterman, Esquire U. S. Nuclear Regulatory Commission Morgan, Lewis & Bockius LLP 611 Ryan Plaza Drive, Suite 400 Arlington, Texas 76011-8064 Mohan C. Thadani U. S. Nuclear Regulatory Commission Richard A. Ratliff Thad Hill Bureau of Radiation Control Steve Winn Texas Department of State Health Services Harry Holloway 1100 West 49th Street Eddy Daniels Austin, TX 78756-3189 Marty Ryan NRG South Texas LP Senior Resident Inspector J. J. Nesrsta U. S. Nuclear Regulatory Commission R. K. Temple P. 0. Box 289, Mail Code: MN1 16 E. Alarcon Wadsworth, TX 77483 Kevin Polio City Public Service C. M. Canady Jon C. Wood City of Austin Cox Smith Matthews Electric Utility Department 721 Barton Springs Road C. Kirksey Austin, TX 78704 City of Austin

Attachment NOC-AE-07002168 Page 1 of 2 South Texas Project Unit 2 Summary Assessment of Pressurizer Spray, Relief, Safety, and Surge Nozzle Safe-End Weld Overlays:

Shrinkage and Fatigue Crack Growth Shrinkage Assessment:

Stress for Assumed Shrinkage Limits on design stress due to shrinkage were determined prior to completing the weld overlay.

The calculation was performed using WESTDYN 7.1, a program acceptable for use in piping analysis, with an assumed pipe temperature of 70"F. A displacement of 0.25-inch was applied to the pressurizer safe end as cold spring loading for the surge and spray nozzles. This displacement is assumed as the main loading input to represent shrinkage due to the nozzle weld overlay. The bendinkstress due to shrinkage by 0.25-inch as determined by computer calculations is 13,089 psi fiitle spray nozzle. The bending stress for the surge nozzle was determined to be 1620 p K The code allowable stress for piping at 70'F is 32,000 psi.

Consequently, piping will qualify under code stress requirements where shrinkage does not exceed 0.25-inch.

Stress for Actual Shrinkage Actual shrinkage on the nozzles following the overlay was measured at 90" intervals around the circumference of the overlay. For points where maximum measured shrinkage occurred:

Pressurizer Safe Maximum Stress Code End Shrinkage Allowable Surge Nozzle N1 0.225 inch 1458 psi* 40,000 psi Spray Nozzle N2 0.156 inch 8168 psi* 32,000 psi Safety Nozzle N3 0.202 inch 21,190 psi 40,000 psi Relief Nozzle N4A 0.176 inch 16,653 psi 40,000 psi Safety Nozzle N4B 0.370 inch 30,589 psi 40,000 psi Safety Nozzle N4C 0.188 inch 21,559 psi 40,000 psi

• These stress values were determined as a ratio of the actual shrinkage to the assumed shrinkage (0.25-inch).

In addition, stress in an un-reinforced fabricated tee connection in the relief piping calculated using a stress intensification factor was found to be 23,057 psi. The code allowable stress for this piping at 70"F is 28,200 psi. Therefore, the code stress limitations are not exceeded.

Because the piping is designed for significantly greater shrinkage and still satisfies code design requirements, the actual shrinkage experienced results in even greater design margin.

Consequently, there is no need to update the shrinkage calculation to reflect the actual values.

Attachment NOC-AE-07002168 Page 2 of 2 The design pressure and normal operating pressure are 2,485 psig and 2,235 psig, respectively. With the additional stress provided by the structural weld overlay, the total stresses remain significantly below the code allowable stresses.

Fatigue crack growth assessment:

WCAP-16611 -P, "South Texas Units 1 and 2 Pressurizer Safety/Relief, Spray, and Surge Nozzles Structural Weld Overlay Qualification," August 2006, addresses the issue of fatigue crack growth. If a flaw in the piping is assumed to extend through 75% of the pipe thickness, the following table shows the expected service life before the flaw grows through the base metal.

Pressurizer Safe End Expected Service Life Surge Nozzle N1 23 years Spray Nozzle N2 19 years Safety Nozzle N3 40 years Relief Nozzle N4A 40 years Safety Nozzle N4B 40 years Safety Nozzle N4C 40 years Consequently, such a flaw would not grow through-wall before the next inservice inspection.

There is additional assurance in that post-weld overlay inspection did not identify any significant flaws in the inspectable volume of the base metal for the pressurizer spray, relief, safety, or surge nozzle safe-end weld overlays.