ML051160173
| ML051160173 | |
| Person / Time | |
|---|---|
| Site: | Cook  |
| Issue date: | 04/15/2005 |
| From: | Fadel D Indiana Michigan Power Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| AEP:NRC:5055-02 | |
| Download: ML051160173 (6) | |
Text
Indiana Michigan Power INDIANA Cook Nuclear Plant MICHIGAN One Cook Place Bridgman, Ml 49106 POWERS AERcom A unit of American Electric Powver April 15,2005 AEP:NRC:5055-02 10 CFR 50.55a Docket No. 50-315 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Mail Stop O-PI-17 Washington, DC 20555-0001 Donald C. Cook Nuclear Plant Unit 1 PROPOSED ALTERNATIVE TO THE AMERICAN SOCIETY OF MECHANICAL ENGINEERS CODE, SECTION XI REPAIR REQUIREMENTS - RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION
References:
- 1. Letter from D. P. Fadel, Indiana Michigan Power Company, to Nuclear Regulatory Commission, "Donald C. Cook Nuclear Plant Unit 1, Proposed Alternative to the American Society of Mechanical Engineers Code,Section XI Repair Requirements," AEP:NRC:5055-01, dated April 12, 2005.
In Reference 1, Indiana Michigan Power Company (I&M) proposed an alternative to the American Society of Mechanical Engineers (ASME) Code,Section XI repair requirements. The proposed alternative would allow I&M to repair a flaw discovered in a Unit 1 pressurizer safety valve line weld by using a weld overlay rather than removing the flaw as required by the ASME Code,Section XI.
The Nuclear Regulatory Commission (NRC) has requested additional information regarding the proposed alternative. The attachment to this letter provides the response to the NRC requests for additional information.
U. S. Nuclear Regulatory Commission AEP:NRC:5055-02 Page 2 This letter contains no new commitments. Should you have any questions, please contact Mr. John A. Zwolinski, Director of Safety Assurance at (269) 466-2428.
Sincerely, Engineering Vice President JRW/jen
Attachment:
Proposed Alternative to American Society of Mechanical Engineers (ASME) Code,Section XI Requirements - Response to Request for Additional Information c: R. Aben - Department of Labor and Economic Growth J. L. Caldwell - NRC Region III K. D. Curry - AEP Ft. Wayne, w/o attachment J. T. King - MPSC, w/o attachment C. F. Lyon - NRC Washington DC MDEQ - WHMD/HWRPS, Nv/o attachment NRC Resident Inspector
o1r' Attachment to AEP:NRC:5055-02 Proposed Alternative to American Society of Mechanical Engineers (ASME)
Code,Section XI Requirements Response to Request for Additional Information In Reference 1, Indiana Michigan Power Company (I&M) proposed an alternative to the ASME Code,Section XI repair requirements. The ,proposed alternative would allow the use of a weld overlay to repair a flaw discovered in a Donald C. Cook Nuclear Plant (CNP) Unit 1 pressurizer safety valve line weld (1-PRZ-23), rather than removing the flaw as required by the ASME Code.
The Nuclear Regulatory Commission (NRC) requested additional information regarding the proposed alternative. The response to the NRC's request for additional information is provided below.
- 1. Pleaseprovide the axial length and dimensions of the crack in relation to the originalnozzle to safe end weld 1-PZR-23. This information is necessary to detenrine if the application of Code Case N-504-2 is appropriate.
Response
The flaw is a multifaceted, axially oriented flaw located at approximately 8.0 inches counter clockwise from the top (12 o'clock) position when looking into the nozzle (toward the pressurizer). The estimated remaining ligament from the deepest portion of the flaw to the outside surface was measured to be approximately 0.17 inches, which equates to a flaw height of approximately 1.23 inches (i.e., 88 percent of thickness) based on a measured thickness of 1.4 inches (includes thickness of internal stainless steel cladding). The manual Performance Demonstration Initiative (PDI) ultrasonic test procedure used to obtain these dimensions is not qualified for depth sizing. Therefore, these dimensions are estimates based on the use of supplemental transducers (60 and 70 degree refracted longitudinal) focused in the outer 25 percent of the outside diameter. The transducers were supplied by Electric Power Research Institute (EPRI) personnel. A bare metal visual inspection and penetrant test (PT) of the weld verified that the flaw is not through-wall.
ASME Code Case N-504-2 paragraph (i) requires a preservice examination that includes a liquid penetrant and ultrasonic examination of the weld reinforcement to verify its integrity and to identify the original flaws in the outer 25 percent of the underlying pipe to benchmark its location for subsequent examinations of the overlay. The overlay design for weld 1-PRZ-23 is specifically designed to allow these examinations to be accomplished.
- 2. Please explain the controlsprovided to assure lte repair veld does not extend into tie area of the carbon steel nozzle which is greaterthan 1.25" thickness.
Attachment to AEP:NRC:5055-02 Page 2
Response
The repair weld does extend into an area of carbon steel nozzle that is greater than 1.25 inches thick. The response to Question 3 describes why this is acceptable.
- 3. If the repair weld extends into the carbon steel in an area where sectional thickness is greater than 1.25" thick, please explain why the application of the pre and post wveld heat treatmnent is unnecessary and what impact this welding may have on the material.
Response
Regarding preheat:
ASME Section III of the Code of Construction, Paragraph N-531, does not provide specific requirements for preheating, but does provide non-mandatory practices. These practices are contained in Appendix III. For P-I materials which have both a specified maximum carbon content in excess of 0.30 percent and a thickness in excess of 1 inch, there is a recommended preheat of 175 degrees Fahrenheit (oF1). For all other P-1 materials, the preheat is 50'F.
Since the maximum specified carbon content of the pressurizer nozzle (SA216, Grade WCC) is 0.25 percent, only a 50'F preheat is required Regarding post-weld heat treatment (PWHT):
The PWHT requirements of the Code are based on the nominal thickness of the weld as defined in ASME Section III, 1992 Edition, Paragraph NB-4622.3. This paragraph states that the nominal thickness is the thickness of the weld, the pressure retaining material for structural attachment welds, or the thinner of the pressure retaining materials being joined, whichever is least. This definition of nominal thickness for PWHT has been consistent for many years, including the latest edition of the Code. Per Table NB-4622.7(b)-l, a nominal thickness, as defined by Paragraph NB-4622.3, shall be less than or equal to 11/4 inches with a reported carbon content of 0.30 percent or less. The weld overlay is a nominal 1/2-inch deposit thickness, using ERNiCrFe-7 (Alloy 52). This alloy has a maximum carbon content of 0.04 percent. Therefore, where the overlay is only over the base material, the nominal thickness can be taken as the overlay thickness. Where the overlay is over the weld, the thickness is the sum of the overlay and existing weld. However, at this location, the base material is less than 1 1/4 inches. Per the Code, the nominal thickness is whichever is least; therefore, no PWHT is required. This position has been independently verified by knowledgeable industry Code personnel.
- 4. Please explain why Code Case N-416-1 is specified ratherthan Code Case N-416-2 which is currently approved uinder NUREG 1.147, Rev. 13. The discussion should include a comparison of limitationsbetween the two Code Cases and why the alternativepressure test requirementsprovide a suitable alternative to that specified under Code Case N-504-2.
Attachment to AEP:NRC:5055-02 Page 3
Response
Code Case N416-2 was approved for ASME Class 1, 2, and 3 components. Code Case N416-1 was approved for ASME Class 3 components. However, Code Case N416-1 was approved for use on ASME Class 1, 2, and 3 components for the CNP Inservice Inspection (ISI) program for the duration of the Second and Third ISI Intervals (Reference 2).
- 5. Tie Relief Request states that "The flaw was most likely caused by Primary Water Stress Corrosion Cracking (PWSCC). Pleaseprovide a supporting discussion to indicate why you came to this conclusion. The discussion should also address what actions were taken to assure other welds of similar design and construction and operationalconditionsdo not have this defect
Response
CNP, Areva and EPRI personnel conclude PWSCC based on the following:
- Multifaceted, axially oriented flaw as described in response to RAI Question 1
- Confinement of the flaw to the Alloy 82/182 weld material
- Lack of fatigue initiators for the weld that the flaw was detected in All other pressurizer welds of similar design, construction, and operational conditions were inspected using similar techniques as those used to inspect 1-PRZ-23. No recordable indications were observed in these other pressurizer welds. Details of these inspections and the results obtained will be submitted to the NRC within 60 days following completion of the Unit 1 Cycle 20 Refueling Outage, as required by NRC Bulletin 2004-01.
- 6. The Relief Request states that the specification was 0.25%. Please identify the specific carbon content of this nozzle fromn the certified material test reports in case a higher carbon content nozzle was installedand accepted during originalconstruction.
Response
The material specification for the pressurizer identifies the material of construction for the pressurizer nozzle as SA216, Grade WCC. The Westinghouse Quality Release did not identify a deviation from the material specification for this component. The Certified Material Test Report has a reported carbon content of 0.25 percent.
- 7. Please identify the Construction Code or Addenda applicable to the original nozzle iveld or that which will govern the overall repair,ratherthan having to assumefrom the list provided in the Relief Request which listed reference applies.
I , *.
- 1. I ,
Attachment to AEP:NRC:5055-02 Page 4
Response
ASME Section XI, 1989 (Inservice Inspection Code)
ASME Section XI, Case N-504-2 (Weld overlay)
ASME Section III, 1965 Edition, Winter 1966 Addenda (Code of Construction)
ASME Section III, 1992 Edition (Repair Inspection and Post Weld Heat Treatment)
- 8. The wveld overlay should be designed to allow for fill volume examination of tile effective area of the wield overlay plus 25% of the base metal thickness under the overlay. Please discuss your ability to achieve the requiredpreservice inspection examination volutmle (25%
of base metal uinder overlay). The discussion should address what action will be taken if the examination volume does not get 100% coverage.
Response
The design of the overlay for inspection was developed in collaboration with PCI, Wesdyne Level III, Areva NDE, and EPRI's PDI representatives to ensure adequate coverage of the overlay. The weld overlay was designed to provide the ability to examine the full volume of the effective area of the overlay plus 25 percent of the base metal thickness under the overlay. If full coverage cannot be attained, then the requirements of ASME Code Case N-460 will be followed for coverage less than 100 percent.
- 9. Please discuss if you are performing an Appendix VIII, Supplement 11 examination of the overlay for the examination required by N-504-2. Since there have been problems meeting the Code version of Supplement 11, if you intend to use the PDI version of Supplement 11 as an alternative, has a relief request been submitted to address this prior to obtain authorizationpriorto startup?
Response
Yes. This relief request will be submitted separately.
References:
- 1. Letter from Daniel P. Fadel, Indiana Michigan Power Company, to Nuclear Regulatory Commission, "Donald C. Cook Nuclear Plant Unit 1, Proposed Alternative to the American Society of Mechanical Engineers Code,Section XI Repair Requirements," AEP:NRC:5055-01, dated April 12, 2005.
- 2. Letter from John N. Hannon, NRC, to E. E. Fitzpatrick, I&M, "D. C. Cook, Units 1 and 2, Requesting Approval of Code Case N-416-1 as an Alternative to the Required Hydrostatic Pressure Test (TAC Nos. M92344 and M92345),"
dated July 24, 1995.