ML12355A429
| ML12355A429 | |
| Person / Time | |
|---|---|
| Site: | Ginna  |
| Issue date: | 01/08/2013 |
| From: | Thadani M Plant Licensing Branch 1 |
| To: | Joseph Pacher Ginna |
| Thadani M NRR/DORL/LPL1-1 301-415-1476 | |
| References | |
| TAC ME8247 | |
| Download: ML12355A429 (7) | |
Text
UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 January 8, 2013 Mr. Joseph E. Pacher Vice President RE. Ginna Nuclear Power Plant RE. Ginna Nuclear Power Plant, LLC 1503 Lake Road Ontario, NY 14519
SUBJECT:
RE. GINNA NUCLEAR POWER PLANT - ASME CODE EVALUATION OF REACTOR VESSEL BOTTOM MOUNTED INSTRUMENT NOZZLE A86 PENETRATION FLAW INDICATIONS (TAC NO. ME8247)
Dear Mr. Pacher:
By letter dated March 16,2012 (Agencywide Document Access and Management System (ADAMS) Accession No. ML12080A141) and supplement dated October 23,2012, (ADAMS Accession No. NIL12299A471) Constellation Energy Group, Inc., (the licensee) submitted a report to the U.S. Nuclear Regulatory Commission (NRC), addressing discovery of two indications of flaws in the bottom mounted instrumentation (BMI) penetration nozzle A86, located in the RE. Ginna Nuclear Power Plant's (Ginna) reactor pressure vessel.
The licensee stated that two indications of flaws were found in the nozzle A86 during ultrasonic testing of the BMI nozzles at Ginna conducted as part of the Spring 2011 outage. The flaw indication number 1 is an outside diameter circumferential indication, likely a result of fabrication process. Flaw indication number 2 is a small fusion indication, also, likely resulting from the fabrication process. It was detected at nozzle A86 penetration, near flaw indication number 1.
The licensee has requested neither a relief from requirements nor approval of an alternative to the requirements. Instead, the licensee provided its evaluation to demonstrate that flaw indications discovered are within the acceptable limits of the requirements of American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code)Section XI analytical evaluation rules. Indication number 1 is embedded and significantly away from the wetted surface and is not a result of primary water stress-corrosion cracking (PWSCC). In addition, the licensee provided a Westinghouse evaluation to demonstrate that the indication number 1 meets the basis for acceptability of continued service in accordance with the ASME Code Section XI analytical evaluation rules. The licensee classified indication number 2 as a laminar flaw, most likely a result of lack of fUSion, at the nozzle A86-to-weld interface. This indication also is not exposed to wetted surface and is not a result of PWSCC.
The NRC staff has completed the review of the licensee's submittals, and concludes that the projected growth of the two flaws is predicted to remain well within the acceptable range for continuing service for a 40-year life of the Ginna plant operation. Our conclusion is based on the enclosed safety evaluation.
J. Pacher
-2 Please contact me at 301-415-1476 or email Mohan.Thadani@nrc.gov, if you have any questions.
Sincerely, Mohan C. Thadani, Senior Project Manager Plant licensing Branch 1-1 Division of Operating Reactor licensing Office of Nuclear Reactor Regulation Docket No. 50-244
Enclosure:
Safety Evaluation cc w/encl: Distribution via listserv
UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555*0001 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION FLAWS IN BOTTOM MOUNTED INSTRUMENTS PENETRATION NOZZLE A86 CONSTALLATION ENERGY GROUP, INC.
RE. GINNA NUCLEAR POWER PLANT, LLG R E. GINNA NUCLEAR POWER PLANT DOCKET NO. 50-244
1.0 INTRODUCTION
By letter dated March 16, 2012 (Agencywide Document Access and Management System (ADAMS) Accession No. ML12080A141) and supplement dated October 23,2012, (ADAMS Accession No. ML12299A471) Constellation Energy Group, Inc., (the licensee) submitted a report addressing discovery of two indications of flaws in the bottom mounted instrumentation (BMI) penetration nozzle A86, located in the RE. Ginna Nuclear Power Plant (Ginna) reactor pressure vessel for the U.S. Nuclear Regulatory Commission's (NRC's) evaluation.
The licensee stated that two indications were found in nozzle A86 during ultrasonic testing of the 8MI nozzles at Ginna conducted as part of the Spring 2011 outage. Flaw indication number 1 is a circumferentially oriented planar flaw, extending from the nozzle wall from the weld-to nozzle interface, likely a result of the fabrication process. Flaw indication number 2 is a laminar flaw, also, likely resulting from the fabrication process. It was detected at nozzle A86 penetration, near flaw indication number 1.
The licensee has requested neither a relief from requirements nor approval of an alternative to the requirements. Instead, the licensee provided its evaluation to demonstrate that flaw indications discovered are acceptable via the requirements of ASME Code Section XI analytical evaluation rules. Indication number 1 is embedded and significantly away from the wetted surface and is not a result of primary water stress-corrosion cracking (PWSCC). In addition, the licensee provided a Westinghouse evaluation to demonstrate that indication number 1 meets the basis for acceptability of continued service in accordance with the ASME Code Section XI analytical evaluation rules. The licensee stated that indication number 2 is classified as a laminar flaw. most likely a result of lack of fUSion. at the nozzle A86-to-weld interface. This indication also is not exposed to wetted surface and is not a result of PWSCC.
2.0 REGULATORY EVALUATION
The American SOCiety of l\\IIechanical Engineers Boiler and Pressure Vessel Code (ASME Code) requires that inservice inspection (lSI) of Class 1, Class 2, and Class 3 components shall be performed in accordance with Section XI, "Rules for Inservice Inspection of Nuclear Power Plant
- 2 Components," of the ASME Code and applicable editions and addenda as required by Title 10 of the Code of Federal Regulations (10 CFR) Part 50.55a (g), except where specific written relief has been granted by the Commission pursuant to 10 CFR 50.55a(g)(6)(i).
Pursuant to 10 CFR 50.55a(g)(4), ASME Code Class 1, 2, and 3 components (including supports) shall meet the requirements, except the design and access provisions and the preservice examination requirements, set forth in Section XI of the ASME Code to the extent practical within the limitations of design, geometry, and materials of construction of the components. As required by ASME Code, "bare-metal" visual examinations were to have been conducted on the Ginna BMI nozzles. Due to configurational issues posed by the plant design at Ginna, the licensee conducted ultrasonic examinations on the Ginna BMI nozzles.
When flaws are detected by volumetric examinations, acceptance of them by supplemental examination, repairs, replacement, or analytical evaluation shall be in accordance with ASME Code,Section XI, IWB-3130, "Inservice Volumetric and Surface Examinations." In this application, Table IWB-3663-1, "Reactor Vessel Head Penetration Nozzle Acceptance Criteria,"
as required in IWB-3660, "Acceptance by Analytical Evaluation," was applied. These IWB subarticles are from the 2004 Edition with no Addenda of the ASME Code,Section XI, the applicable ASME Code edition for the current fifth lSI interval at Ginna.
3.0 TECHNICAL EVALUATION
Two indications were found during the Spring 2011 examinations of the 36 BMI nozzles installed at Ginna. Both indications were located in the A86 nozzle. The first indication was identified as a circumferentially oriented planar flaw, extending from the nozzle wall to the weld-to-nozzle interface. The licensee identified the dimensions of this flaw as,
... 1.35 inch circumferentially by 0.161 inch in through wall depth. The nozzle wall thickness is approximately 0.59 inches making the indication approximately 27 percent of the nozzle wall in depth.
The licensee performed a case-by-case evaluation of the first indication in accordance with Table IWB-3661-1 of the ASME Code. The evaluation was based on the following assumptions, inputs, and criteria:
- The indication size was taken directly from the ultrasonic examination;
- Stress input was derived using recent plant conditions with the original BMI nozzle fatigue evaluation methodology (including effects from Steam Generator replacement, and an Extended Power Uprate);
- The growth mechanism was identified to be solely fatigue due to the indication being non-surface breaking and hence not subject to a water environment stress corrosion cracking;
- The fatigue growth rate was determined using air-environment data from NUREG/CR-6721 for Alloy 600;
- Weld residual stress was accounted for by setting the R ratiO from NUREG/CR 6721 equal to 1, a conservative approach that models the residual stress as dominating the cyclical fatigue loading;
- 3
- Through-wall stress distribution profile was represented using a fourth-order approximation; and
- The crack tip stress intensity factor was taken from API 579-1/ASME FFS-1 (Reference 7 of Attachment 1 to the licensee's submittal).
The NRC staff reviewed the above assumptions, inputs, and criteria, and found the approach acceptable.
In response to the NRC staff's request for additional information (RAI), the licensee provided additional information dated October 23, 2012. The additional information, showed that: (1) the licensee confirmed that the external mechanical loads used in the evaluation had been calculated in a site-specific manner, and that these loads were bounded by the BMI nozzle design allowable loads; (2) the licensee provided details concerning the calculation of the axial membrane and bending stress reported in Attachment 1, allowing the NRC staff to review how this value was generated; and (3) the licensee confirmed that the methodologies used to calculate new loads on the BMI would capture changes in loading due to plant modifications having occurred after the methodologies were developed -- the methodology addressed the updated conditions of the plant In response to the NRC staff's RAI, the licensee provided a complete calculation supporting the licensee's submittal for the NRC staff's review. In reviewing the complete calculation, the NRC staff confirmed its validity and determined that the procedure is in accordance with ASME Code,Section XI. The only notable deviation was the use of a stress intensity factor for which the analyst made extra allowances to extend the area of applicability of the factor in the presented calculation. To confirm that the factor was used properly, the licensee used extreme case of a solid bar in place of a hollow cylinder, assuring that the stress intensity factor should be roughly 10 percent higher than would be indicated through a direct application of the factor without modification. To conservatively bound this, the licensee applied a factor of 2 to the growth rate calculation, effectively increasing the stress intensity factor by 18 percent The NRC staff concludes that this bounded the inaccuracy of using the factor in an unmodified fashion.
Based on the above, the NRC staff accepted the licensee's evaluation, and concluded that the evaluation conservatively predicted an end-of-life size of the indication, using credible loading and degradation mechanisms. In order for an indication to be considered acceptable by the ASME Code,Section XI, the indication must be calculated to remain smaller than 75 percent of the through-wall thickness for axial flaws. The licensee justified applying this criterion to the circumferential flaw by citing the fact that the hoop stress acting on an axial flaw is higher than the axial stress acting on a circumferential flaw. In addition the licensee stated that the loads acting on the BMI nozzle are "very low and primarily due to internal pressure and external mechanical loading." The NRC staff accepts this argument in light of the final results of the evaluation indicating that the indication would grow to only 32 percent through-wall over a period of 40 years of operation, leaving ample material. Specifically, the indication, which is now 0.167 inch deep, is projected to grow to 0.188 inches deep, while the BMI nozzle is 0.595 inches thick. This would ensure adequate structural integrity for a period of 40-years of plant operation.
The second indication was reported as a laminar flaw. This flaw was sized at 0.16 inch axial by 0.25 inch circumferential by 0.0 inch through-wall depth. The licensee determined that this flaw was acceptable in accordance with the ASME Code criteria. The NRC staff agrees.
-4 8ased on the review detailed above, the NRC staff accepts that the subject flaw will meet the ASME Code,Section XI, IW8-3660 requirements for an additional 40 years.
4.0 CONCLUSION
S The NRC staff concludes that the projected growth of the two flaws is predicted to be well within the acceptable range specified in the licensee's requirements for Ginna in Subparagraph IW8 3144 of 2004 Edition, with no Addenda, of Section XI of the ASME Code. Therefore, the NRC staff concludes that the projected growth poses no significant challenge to the integrity of the component, and the 8MI nozzle A86 is acceptable for continued service for 40 years of operation at the Ginna plant.
Principal Contributor: D. Widrevitz Date: January 8, 2013
J. Pacher
- 2 Please contact me at 301-415-1476 or email Mohan.Thadani@nrc.gov. if you have any questions.
Sincerely.
IRA!
Mohan C. Thadani. Senior Project Manager Plant Licensing Branch 1-1 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-244
Enclosure:
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