ML053220019
| ML053220019 | |
| Person / Time | |
|---|---|
| Site: | Cook  |
| Issue date: | 12/01/2005 |
| From: | Raghavan L Plant Licensing Branch III-2 |
| To: | Nazar M Indiana Michigan Power Co |
| Tam P | |
| References | |
| TAC MC6704 | |
| Download: ML053220019 (11) | |
Text
December 1, 2005 Mr. Mano K. Nazar Senior Vice President and Chief Nuclear Officer Indiana Michigan Power Company Nuclear Generation Group One Cook Place Bridgman, MI 49106
SUBJECT:
DONALD C. COOK NUCLEAR PLANT, UNIT 1 (DCCNP-1) - ALTERNATIVES REGARDING REPAIR OF WELD 1-PZR-23 ON PRESSURIZER NOZZLE TO VALVE INLET LINE (TAC NO. MC6704)
Dear Mr. Nazar:
By letter dated April 12, 2005, as supplemented by letters dated April 15 and April 22, 2005, Indiana Michigan Power Company, proposed an alternative under Relief Request ISIR-15, for DCCNP-1 to the repair requirements of Code Case N-504-2, Alternative Rules for Repair of Classes 1, 2, and 3 Austenitic Stainless Steel Piping, to perform a full structural weld overlay over nozzle-to-safe-end weld 1-PRZ-23. The full structural overlay was necessary due to discovery of an axial flaw in weld 1-PRZ-23 that exceeded the through-wall acceptance criteria allowed by the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code). The Nuclear Regulatory Commission (NRC) staff reviewed the referenced submittals and documented its review results in the enclosed safety evaluation (SE).
As delineated in the SE, the NRC staff concludes that the alternatives proposed in Relief Request ISIR-15 for a full structural overlay of weld 1-PRZ-23 at DCCNP-1 will provide an acceptable level of quality and safety. Therefore, pursuant to 10 CFR 50.55a(a)(3)(i), the NRC staff authorizes the proposed alternative for the life of the component.
If you have any questions, please call the Project Manager, Mr. Peter Tam at 301-415-1451.
Sincerely,
\\RA\\
L. Raghavan, Chief Plant Licensing Branch III-1 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-315
Enclosure:
As stated cc w/encl: See next page
ML053220019 OFFICE NRR/LPL3-1/PM NRR/LPL3-1/LA EMCB/SC OGC NRR/LPL3-1/BC NAME PTam THarris TChan*
JZorn LRaghavan DATE 11/18 /05 11/18/05 8/9/05 11/30/05 12/1/05
SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION INSERVICE INSPECTION PROGRAM RELIEF REQUEST ISIR-15 DONALD C. COOK NUCLEAR PLANT, UNIT 1 (DCCNP-1)
INDIANA MICHIGAN POWER DOCKET NO. 50-315
1.0 INTRODUCTION
By letter dated April 12, 2005 (Agencywide Document Access and Management System (ADAMS) Accession No. ML051100417), as supplemented by letters dated April 15 (Accession No. ML051160173) and April 22, 2005 (Access No. ML051290122), Indiana Michigan Power Company (the licensee), proposed an alternative under Relief Request ISIR-15, for DCCNP-1 to the repair requirements of Code Case N-504-2, Alternative Rules for Repair of Classes 1, 2, and 3 Austenitic Stainless Steel Piping, to perform a full structural weld overlay over nozzle-to-safe-end weld 1-PRZ-23. The full structural overlay was necessary due to discovery of an axial flaw in weld 1-PRZ-23 that exceeded the through-wall acceptance criteria allowed by the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code). Safe-end-to-elbow weld 1-RC-9-01F, which is adjacent to weld 1-PRZ-23, ultimately became part of the full structural overlay and will be evaluated (tracked by TAC No.
MC8807) under a separate safety evaluation.
2.0 REGULATORY EVALUATION
Pursuant to Title 10 of the Code of Federal Regulations (10 CFR) Section 50.55a(g)(4), ASME Code Class 1, 2, and 3 components (including supports) must meet the requirements, except the design and access provisions and the preservice examination requirements, set forth in ASME Code,Section XI, to the extent practical within the limitations of design, geometry, and materials of construction of the components. The regulations require that inservice examination of components and system pressure tests conducted during the first 10-year interval and subsequent intervals comply with the requirements in the latest edition and addenda of Section XI of the ASME Code incorporated by reference in 10 CFR 50.55a(b), 12 months prior to the start of the 120-month interval, subject to the limitations and modifications listed therein. The inservice inspection (ISI) Code of record for DCCNP is the 1989 edition with no addenda of the ASME Code.
Alternatives to these requirements may be authorized or relief granted by the Nuclear Regulatory Commission (NRC) pursuant to 10 CFR 50.55a(a)(3)(i), 10 CFR 50.55a(a)(3)(ii), or 10 CFR 50.55a(g)(6)(i). In proposing alternatives or requesting relief, the licensee must demonstrate that: (1) the proposed alternatives provide an acceptable level of safety and quality; (2) compliance would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety; or (3) conformance is impractical for the facility.
ENCLOSURE Regulatory Guide 1.147, Inservice Inspection Code Case Acceptability, ASME Section XI, Division 1, lists Code Cases approved by the NRC that provide acceptable alternatives to the mandatory ASME Code provisions.
The licensee submitted the subject relief request pursuant to 10 CFR 50.55a(a)(3)(i), with three proposed alternatives to the implementation of N-504-2, for the remaining service life of weld 1-PRZ-23.
3.0 TECHNICAL EVALUATION
3.1 Code Requirements for which Relief is Requested IWA-4000 and IWB-4000 of ASME Section XI require repairs to be performed in accordance with the Owners Design Specification and the original Construction Code of the component or system.
3.2 Licensees Proposed Alternative to the ASME Code The licensee proposed using N-504-2 for repair of weld 1-PRZ-23 with the following exceptions:
(1)
Use of a nickel-based alloy weld material, Alloy 52, rather than the low carbon (0.035 percent maximum) austenitic stainless steel.
(2)
Relaxation from the requirement to perform delta ferrite measurements to meet the 7.5 Ferrite Number requirement of N-504-2.
(3)
Performance of a system pressure test and an ultrasonic examination of the weld overlay using Code Case N-416-1, Alternative Pressure Test Requirement for Welded Repairs or Installation of Replacement Items by Welding, Class 1, 2, and 3,Section XI, Division 1," (N-416-1), versus the hydrostatic test requirement under N-504-2.
3.3 Licensees Basis for Relief Pursuant to 10 CFR 50.55a(a)(3)(i), the licensee stated that the weld overlay has been designed consistent with the requirements of ASME N-504-2, "Alternative Rules for Repair of Classes 1, 2, and 3 Austenitic Stainless Steel Piping." The specific thickness and length have been computed according to the guidance provided in N-504-2.
The overlay will completely cover the indication with Alloy 52 material. Alloy 52 material is highly resistant to primary water stress corrosion cracking (PWSCC).
The licensee stated that in order to perform this repair, it is necessary to weld to the carbon steel nozzle material. The Code of Construction allows welding to the carbon steel nozzle without post-weld heat treatment. The Code of Construction exemption for post-weld heat treatment is based on the pressurizer safety nozzle material (SA-216 WCC, P-No. 1, Group 2 material) thickness being less than 1.25 inches and the carbon content being less than 0.30 percent. The nozzle thickness is 1.22 inches and the maximum specified carbon content is 0.25 percent. The Code of Construction does not require pre-heat or post-weld heat treatment for a component 1.25 inches thick or less with a maximum carbon content of 0.30 percent.
The licensee stated that N-504-2 was approved for generic use in Regulatory Guide 1.147, Revision 13, and was developed for austenitic stainless steel material.
An alternate application for nickel-based and carbon materials is proposed due to the specific configuration of the subject weld. Therefore, the methodology of N-504-2 shall be followed with the following exceptions:
C Paragraph (b) of N-504-2 requires that the reinforcement weld material shall be low carbon (0.035 percent maximum) austenitic stainless steel. In lieu of the stainless steel weld material, a consumable welding wire highly resistant to PWSCC has been selected for the overlay weld material. This material is a nickel-based alloy weld material, commonly referred to as Alloy 52, and will be applied using a machine gas tungsten arc welding process. Alloy 52 contains about 30 percent chromium that imparts excellent corrosion resistance to this material. This material is suitable for welding over the carbon steel nozzle, Alloy 82/182 weld material, stainless steel safe end, stainless steel weld material, and stainless steel piping as it is compatible with the existing weldment and base materials. The licensee stated that this alternative provides an acceptable level of safety and quality.
C Paragraph (e) of N-504-2 requires as-deposited delta ferrite measurements of at least 7.5 Ferrite Number for the weld reinforcement. The licensee proposed that Delta ferrite measurements will not be performed for this overlay because the deposited Alloy 52 is 100 percent austenitic and contains no delta ferrite due to the high nickel composition (approximately 60 percent nickel).
C Paragraph (h) of N-504-2 requires a system hydrostatic test of the completed repair if the flaw(s) penetrated the original pressure boundary or if there is any observed indication of the flaw penetrating the pressure boundary during repair.
In lieu of hydrostatic testing, a system pressure test and an ultrasonic examination of the weld overlay shall be performed in accordance with the Third Interval ISI Program and N-416-1. The licensee stated that this alternative requirement is sufficient to demonstrate that the overlay is of adequate quality to ensure the pressure boundary integrity. The repair, pre-service inspection, and ISI examination of the weld overlay repair shall be performed in accordance with the ISI Program, NUREG-0313, Revision 2, Generic Letter 88-01, and approved plant procedures as specified by the ISI Repair/Replacement Program. The weld overlay shall be examined in accordance with the industry-developed Performance Demonstration Initiative (PDI) procedure. As required by N-416-1 (Alternative Pressure Test Requirement for Welded Repairs or Installation of Replacement Items by Welding, Class 1, 2, and 3), nondestructive examination (NDE) shall be performed to ASME Section III, 1992 Edition, Subsection NB requirements to the extent practical. A description of the required examinations is provided in Tables 1, 2, and 3 of the subject relief request.
The licensee stated that the use of overlay filler material that provides excellent resistance to PWSCC develops an effective barrier to flaw extension by corrosion processes. The design of the overlay for the nozzle-to-safe end weldment uses methods that are standard in the industry. There are no new or different approaches in this overlay design that are considered first of a kind or inconsistent with previous approaches. The overlay has been designed as a full structural overlay in accordance with N-504-2. The licensee concluded that the alternative repair approach described above presents an acceptable level of quality and safety that meets the requirements of 10 CFR 50.55a(a)(3)(i).
3.4 NRC Evaluation Under the rules of IWA-4120 in editions and addenda up to and including the 1989 Edition with the 1990 Addenda, defects shall be removed or reduced in size in accordance with IWA-4300. Alternatively, the component may be evaluated and accepted in accordance with the design rules of either the Construction Code, or Section III, when the Construction Code was not Section III. N-504-2 was used by the licensee to increase the pipe wall thickness of weld 1-PRZ-23 in order to reduce the maximum allowable through-wall dimension of the defect to less than the 75 percent through-wall. This is the maximum radial extent allowed by the Code using the flaw evaluation procedures in Section XI Appendix C. N-504-2 was unconditionally approved by the NRC staff for use under Regulatory Guide 1.147, Revision 13; therefore, the use of N-504-2 as an alternative to the mandatory ASME Code repair provisions is acceptable to the NRC staff, provided that all provisions of the Code Case are complied with.
The first proposed exception to the N-504-2 provisions involved the use of a nickel-based alloy weld material, rather than low-carbon austenitic stainless steel. The licensee stated that Paragraph (b) of N-504-2 requires that the reinforcement weld material shall be low-carbon (0.035 percent maximum) austenitic stainless steel. In lieu of the stainless steel weld material, Alloy 52/152, a consumable welding wire highly resistant to PWSCC, was proposed for the overlay weld material. Operational experience and published data has shown that PWSCC in Alloy 82/182 welds will blunt at the interface with the stainless steel base metal, carbon steel base metal, or Alloy 52/152 weld metal. The licensee is applying a 360-degree, full structural weld overlay to control growth of the axial crack and ultimately maintain structural integrity of weld 1-PRZ-23. The weld overlay will put compressive stress around the weldment, thus impeding growth of the existing crack and therefore, will fulfill all structural requirements, independent of the existing flawed weld.
The NRC staff notes that the use of 52/152 material is consistent with weld filler material used to perform several similar weld overlays to operating boiling-water reactor (BWR) facilities with similar geometry and overlay dimensions. Studies have been performed by the Electric Power Research Institute in qualifying weld overlays for application in BWRs, and in these applications, the studies have not identified any issues with shrinkage stress or weld contraction stresses. The similarities of design between BWR nozzles and the weld overlay dimensions of weld 1-PRZ-23 provide reasonable assurance that there is a correlation in the performance of weld shrinkage and weld contraction stresses in the subject weld. The NRC staff concludes, therefore, that the proposed use of Alloy 52/152 weld material for the structural overlay provides an acceptable level of quality and safety and is acceptable.
The second proposed exception to the N-504-2 provisions involved Paragraph (e) of N-504-2, which requires as-deposited delta ferrite measurements of at least 7.5 Ferrite Number for the weld reinforcement. The licensee proposed not to perform delta ferrite measurements for this overlay because the deposited Alloy 52 material is 100 percent austenitic and contains no delta ferrite due to the high nickel composition (approximately 60 percent nickel). In its letter dated April 22, 2005, the licensee revised the subject relief request to manually weld a portion of Alloy 152 over the newly deposited semi-automatic wire production weld (Alloy 52). During a telecon with the licensee, the licensee indicated that it was necessary to perform this welding over a portion of weld 1-PRZ-23 in order to achieve an as-welded contour that allowed for completing the post-weld ultrasonic examination required by N-504-2 without losing ultrasonic contact. The licensee indicated in its April 22, 2005, letter that heat input requirements were controlled and maintained at 22,000 joules/inch whereas the average heat input for the production weld was 27,174 joules/inch. Maintaining the heat input within certain parameters is a function of the Weld Procedure Specification (WPS), and is necessary to maintain as-welded properties and minimize high residual stresses in the deposited weld. The licensee also indicated that its vendor had completed impact requirements (Charpy V-Notch) for the manual welding version of the Alloy 52/152 WPS. The licensee indicated that the vendor completed the required tests and documented them in a Procedure Qualification Record (PQR). The licensee indicated that the revised PQR and WPS satisfactorily bound the parameters for the production weld.
The NRC staff concludes that, based on the control of heat input properties, successful completion of the Charpy V-Notch tests, and on the NRC staffs earlier conclusion, the use of Alloy 52/152 filler material provides an acceptable level of quality and safety.
Accordingly, the NRC staff finds the licensees proposed elimination of the performance of the delta ferrite testing acceptable.
The third exception proposed by the licensee is to perform a system pressure test and an ultrasonic examination of the weld overlay in accordance with the licensees third interval ISI Program and N-416-1. The licensee stated that the examination of the repair weld shall be performed in accordance with the ISI Program, NUREG-0313, Revision 2, Generic Letter 88-01, and PDI procedure. Acceptance criteria shall be ASME Section XI, IWB-3514, Standards for examination Category B-F, Pressure Retaining Dissimilar Metal Welds, and Category B-J, Pressure Retaining Welds In Piping.
N-416-1 was approved for use by the NRC staff in Regulatory Guide 1.147 Revision 12.
The NRC staff asked the licensee why it chose to use the N-416-1 version rather than the most current version, N-416-2, which is approved under Regulatory Guide 1.147 Revision 13. The licensee indicated that N-416-1 was used because it was the version currently listed in its Third Interval ISI Program. The NRC staff reviewed the differences between Revisions 12 and 13 and noted no significant changes in the requirements between the two code cases, and that only the scope of applicability was changed in Revision 13.
N-416-1 requires that NDE shall be performed in accordance with the methods and acceptance criteria of the applicable subsection of the 1992 Edition of Section III. The acceptance criteria in Section III do not allow the presence of cracks, regardless of length, and are geared more towards construction type welds. The licensees use of the post-repair NDE requirements of N-504-2 utilizing the appropriate PDI procedure as mentioned above is acceptable. The post-repair examination volume includes the full thickness of the weld overlay plus 25 percent of the underlying base metal thickness.
The specimen sets for PDI qualification for weld overlay examinations include construction type flaws. Therefore, use of PDI-qualified personnel and procedures for the examination of the weld overlay will result in the reliable detection of construction type flaws and meets the intent of compliance with the applicable subsection of the 1992 Edition of Section III, and therefore, provides an acceptable level of quality and safety.
The licensees submittal indicated that the Code of Construction does not require pre-heat or post-weld heat treatment (PWHT) for a component 1.25 inches thick or less with a maximum carbon content of 0.30 percent. The licensee stated in its April 22, 2005, letter, that the exemption for PWHT is based on the pressurizer safety nozzle material (SA-216 WCC, P-No.1 Group 2 material) thickness being less than 1.25 inches, and the carbon content being less than 0.30 percent. The nozzle thickness was stated to be 1.22 inches, and maximum specified carbon content is 0.25 percent.
The NRC staff asked NRC regional inspectors to verify that the final overlay weld did not exceed the thickness limits allowed by the defined Code exemption. At this point, the licensee reported by telephone that the as-welded overlay extended to an area of the nozzle that exceeded 1.25 inches in thickness. The licensee indicated in its supplemental letter of April 15, 2005, that the post-weld heat treatment exemption still applied by using ASME Section III, 1992 Edition, NB-4622.3, Definition of Nominal thickness governing PWHT. NB-4622.3 states that the nominal thickness in Table NB4622.7(b)-1 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. The NRC staff does not agree with the licensees assertion that NB-4622.3 supports the licensee's position of an exemption from PWHT because the subject table applies only to materials being joined by welding and does not address structural overlays. Secondly, the material being welded on is the dominating factor for PWHT requirements. The NRC staff concludes that the PWHT exemption conclusion made by the licensee in this instance is inconsistent with current industry practice and past NRC staff determinations.
The NRC staff informed the licensee that NRC did not agree with the licensees conclusion, but chose to grant relief from the PWHT requirement for the following reasons:
1.
The high toughness of the Alloy 52/152 material being used to perform the overlay. This material does not require Charpy v-notch testing because of its high impact properties.
2.
Industry experience has shown that if any cracking were to occur, the crack would blunt at the Alloy 52/152 to carbon steel interface.
3.
The post-weld ultrasonic examination prior to returning the component to service as required by N-504-2, would identify any short-term cracking such as hot tears or hydrogen cracking.
4.
The 1.25-inch thickness criterion was exceeded by a very small margin.
5.
The licensees April 22, 2005, letter, states (Table 3, ISI Requirements) that the licensee will be performing volumetric and surface examination of the overlay for the next two outages.
Based on the above discussion, the NRC staff concludes that there is not an overriding nuclear safety issue sufficient to require the plant to shut down and perform the PWHT of the weld overlay area on weld 1-PRZ-23. This conclusion should not be construed to be NRC approval of the licensees interpretation of the Code thickness exemption for PWHT of similar configurations.
During the conduct of the welding of the overlay, the NRC staff learned that the structural overlay intended for weld 1-PRZ-23 extended beyond to include nozzle-to-safe-end weld 1-RC-9-01F. During a series of telephone conversations, the licensee indicated that it did not include weld 1-RC-9-01F as part of the relief request since it felt that weld 1-RC-9-01F was part of the scope covered by the relief request. The NRC staff disagrees with the licensees conclusion that the scope of the licensee's April 12, 2005, submittal and subsequent supplements, include both welds 1-PRZ-23 and 1-RC-9-01F. A separate relief request is appropriate for the application of the weld overlay for weld 1-RC-9-01F since the same filler material was used to perform a structural overlay for both welds. This is tracked under TAC No. MC8807.
4.0 CONCLUSION
Based on the discussion above, the NRC staff concludes that the alternatives proposed in Relief Request ISIR-15 for a full structural overlay of weld 1-PRZ-23 at DCCNP-1, will provide an acceptable level of quality and safety. Therefore, pursuant to 10 CFR 50.55a(a)(3)(i), the NRC staff authorizes the proposed alternative for the life of the component.
All other ASME Code,Section XI requirements for which relief was not specifically requested and approved in this relief request remain applicable, including third-party review by the Authorized Nuclear Inservice Inspector.
Principal Contributor: T. Steingass Date: December 1, 2005
Donald C. Cook Nuclear Plant, Units 1 and 2 cc:
Regional Administrator, Region III U.S. Nuclear Regulatory Commission 2443 Warrenville Road, Suite 210 Lisle, IL 60532-4352 Attorney General Department of Attorney General 525 West Ottawa Street Lansing, MI 48913 Township Supervisor Lake Township Hall P.O. Box 818 Bridgman, MI 49106 U.S. Nuclear Regulatory Commission Resident Inspector's Office 7700 Red Arrow Highway Stevensville, MI 49127 James M. Petro, Jr., Esquire Indiana Michigan Power Company One Cook Place Bridgman, MI 49106 Mayor, City of Bridgman P.O. Box 366 Bridgman, MI 49106 Special Assistant to the Governor Room 1 - State Capitol Lansing, MI 48909 Mr. John A. Zwolinski Safety Assurance Director Indiana Michigan Power Company Nuclear Generation Group One Cook Place Bridgman, MI 49106 Michigan Department of Environmental Quality Waste and Hazardous Materials Div.
Hazardous Waste & Radiological Protection Section Nuclear Facilities Unit Constitution Hall, Lower-Level North 525 West Allegan Street P. O. Box 30241 Lansing, MI 48909-7741 Lawrence J. Weber, Plant Manager Indiana Michigan Power Company Nuclear Generation Group One Cook Place Bridgman, MI 49106 Mr. Joseph N. Jensen, Site Vice President Indiana Michigan Power Company Nuclear Generation Group One Cook Place Bridgman, MI 49106