ML050750428
| ML050750428 | |
| Person / Time | |
|---|---|
| Site: | Prairie Island  |
| Issue date: | 04/07/2005 |
| From: | Raghavan L NRC/NRR/DLPM/LPD3 |
| To: | Solymossy J Nuclear Management Co |
| Chawla M, 415-8371, NRR/DLPM | |
| References | |
| TAC MC3883, TAC MC3884 | |
| Download: ML050750428 (9) | |
Text
April 7, 2005 Mr. Joseph M. Solymossy Site Vice President Prairie Island Nuclear Generating Plant Nuclear Management Company, LLC 1717 Wakonade Drive East Welch, MN 55089
SUBJECT:
PRAIRIE ISLAND NUCLEAR GENERATING PLANT, UNITS 1 AND 2 -
EVALUATION OF RELIEF REQUEST TO USE CODE CASE N-661 (TAC NOS. MC3883 AND MC3884)
Dear Mr. Solymossy:
By letter to the U.S Nuclear Regulatory Commission (NRC) dated July 28, 2004, Nuclear Management Company, LLC (NMC, the licensee), requested that the NRC approve an alternative to the requirements of IWA-4221(a) and IWA-4221(b) of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code)Section XI, 1998 Edition with the 2000 Addenda. Specifically, the licensee requested that the NRC approve the use of ASME Code Case N-661, Alternative Requirements for Wall Thickness Restoration of Class 2 and 3 Carbon Steel Piping for Raw Water Service for use at Prairie Island Nuclear Generating Plant, Units 1 and 2 (PINGP). The request was made pursuant to Title 10 of the Code of Federal Regulations (10 CFR) 50.55a(a)(3)(i) to address replacement or internal weld repair of wall thinning conditions resulting from various wall thinning degradation mechanisms such as erosion, corrosion, cavitation, and pitting in Class 2 and 3 carbon steel raw water piping systems.
Based on the information provided in the licensees submittal, the NRC staff concludes that the licensee has provided an acceptable alternative to the requirements of IWA-4221(a) and IWA-4221(b) of the ASME Code,Section XI, 1998 Edition with the 2000 Addenda, subject to the following three conditions which must be met when using Code Case N-661. These conditions are: (a) if the root cause of the degradation has not been determined, the repair is only acceptable for one cycle, (b) weld overlay repair of an area can only be performed once in the same location, and (c) when through-wall repairs are made by welding on surfaces that are wet or exposed to water, the weld overlay repair is only acceptable until the next refueling outage.
The NRC staff concludes that the proposed alternative, as supplemented by the three conditions listed above provides reasonable assurance of structural integrity and an acceptable level of quality and safety. Therefore, the proposed alternative is authorized pursuant to 10 CFR 50.55a(a)(3)(i) for the PINGP, for the current 10-year inservice inspection (ISI) interval, or until Code Case N-661 is approved for general use by reference in Regulatory Guide (RG) 1.147, Inservice Inspection Code Case Acceptability, ASME Section XI, Division 1." At that time, if the licensee intends to continue implementing ASME Code Case N-661, it must
J. Solymossy follow all provisions of Code Case N-661 with limitations or conditions, specified in the RG 1.147, if any. All other ASME Code,Section XI, requirements for which relief was not specifically requested and authorized herein by the NRC staff remain applicable, including third party review by the Authorized Nuclear Inservice Inspector.
A copy of the Safety Evaluation is enclosed.
Sincerely,
/RA/
L. Raghavan, Chief, Section 1 Project Directorate III Division of Licensing Project Management Office of Nuclear Reactor Regulation Docket Nos. 50-282 and 50-306
Enclosure:
As stated cc w/encl: See next page
J. Solymossy follow all provisions of Code Case N-661 with limitations or conditions, specified in the RG 1.147, if any. All other ASME Code,Section XI, requirements for which relief was not specifically requested and authorized herein by the NRC staff remain applicable, including third party review by the Authorized Nuclear Inservice Inspector.
A copy of the Safety Evaluation is enclosed.
Sincerely,
/RA/
L. Raghavan, Chief, Section 1 Project Directorate III Division of Licensing Project Management Office of Nuclear Reactor Regulation Docket Nos. 50-282 and 50-306
Enclosure:
As stated cc w/encl: See next page DISTRIBUTION PUBLIC PDIII-1 Reading ACRS OGC NRay DLPMDPR LRaghavan AMohseni GHill(4) EDO Contact THarris MChawla KOBrien, RGN-III WRuland ADAMS No: ML050750428 *No major changes to SE dated 12/7/04 (ML043500369)
OFFICE PM:PD3-1 PM:PD3-1 LA:PD3-1 EMCB:B:SC* OGC SC:PD3-1 NAME NRay MChawla DClarke for TChan LRaghavan THarris DATE 3/17/05 3/23/05 3/16/05 12 /07/04 4/6/05 4/7/05 OFFICIAL RECORD COPY
Prairie Island Nuclear Generating Plant, Units 1 and 2 cc:
Jonathan Rogoff, Esquire Tribal Council Vice President, Counsel & Secretary Prairie Island Indian Community Nuclear Management Company, LLC ATTN: Environmental Department 700 First Street 5636 Sturgeon Lake Road Hudson, WI 54016 Welch, MN 55089 Manager, Regulatory Affairs Nuclear Asset Manager Prairie Island Nuclear Generating Plant Xcel Energy, Inc.
Nuclear Management Company, LLC 414 Nicollet Mall, R.S. 8 1717 Wakonade Drive East Minneapolis, MN 55401 Welch, MN 55089 John Paul Cowan Manager - Environmental Protection Division Executive Vice President & Chief Nuclear Minnesota Attorney Generals Office Officer 445 Minnesota St., Suite 900 Nuclear Management Company, LLC St. Paul, MN 55101-2127 700 First Street Hudson, WI 54016 U.S. Nuclear Regulatory Commission Resident Inspector's Office Craig G. Anderson 1719 Wakonade Drive East Senior Vice President, Group Operations Welch, MN 55089-9642 Nuclear Management Company, LLC 700 First Street Regional Administrator, Region III Hudson, WI 54016 U.S. Nuclear Regulatory Commission 801 Warrenville Road Lisle, IL 60532-4351 Administrator Goodhue County Courthouse Box 408 Red Wing, MN 55066-0408 Commissioner Minnesota Department of Commerce 85 7th Place East, Suite 500 St. Paul, MN 55101-2198
SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELIEF REQUEST TO USE ASME CODE CASE N-661 NUCLEAR MANAGEMENT COMPANY, LLC PRAIRIE ISLAND NUCLEAR GENERATING PLANT, UNITS 1 AND 2 DOCKET NOS. 50-282 AND 50-306
1.0 INTRODUCTION
By letter to the U.S Nuclear Regulatory Commission (NRC, Commission) dated July 28, 2004 (ADAMS No. ML042100484), Nuclear Management Company, LLC (NMC, the licensee),
requested that the NRC approve an alternative to the requirements of IWA-4221(a) and IWA-4221(b) of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code)Section XI, 1998 Edition with the 2000 Addenda. Specifically, the licensee requested that the NRC approve the use of ASME Code Case N-661, Alternative Requirements for Wall Thickness Restoration of Class 2 and 3 Carbon Steel Piping for Raw Water Service for use at the Prairie Island Nuclear Generating Plant, Units 1 and 2 (PINGP). The request was made pursuant to Title 10 of the Code of Federal Regulation (10 CFR) 50.55a(a)(3)(i) to address replacement or internal weld repair of wall thinning conditions resulting from various wall thinning degradation mechanisms such as erosion, corrosion, cavitation, and pitting in Class 2 and 3 carbon steel raw water piping systems. The licensee stated the primary reason for the request was to provide adequate time for additional examination of adjacent piping so that pipe replacement can be planned to reduce impact on system availability including Maintenance Rule applicability of replacement materials.
2.0 REGULATORY EVALUATION
The regulation at 10 CFR 50.55a(g) specifies that inservice inspection (ISI) of nuclear power plant components shall be performed in accordance with the requirements of the ASME Code,Section XI, except where specific written relief has been granted by the Commission pursuant to 10 CFR 50.55a(g)(6)(i). As stated in 10 CFR 50.55a(a)(3), alternatives to the requirements of paragraph (g) may be used, when authorized by the NRC, if (i) the proposed alternatives would provide an acceptable level of quality and safety or (ii) compliance with the specified requirements would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.
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 the ASME Code,Section XI, Rules for Inservice Inspection (ISI) of Nuclear Power Plant Components, 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.
3.0 LICENSEES PROPOSED ALTERNATIVE
3.1 ASME Code Components Affected
All ASME Code Section XI, Class 2 and 3 carbon steel piping for raw water services.
3.2 Applicable ASME Code Requirement ASME Code,Section XI, 1998 Edition with the 2000 Addenda:
IWA-4221(a) requires that items used for repair/replacement activities shall meet the applicable Owners Requirements.
IWA-4221(b) requires that an item to be used for repair/replacement activities shall meet the Construction Code specified in accordance with (1), (2), or (3) below.
(1) When replacing an existing item, the new item shall meet the Construction Code to which the original item was constructed.
(2) When adding a new item to an existing system, the Owner shall specify a Construction Code that is no earlier than the earliest Construction Code used for construction of any originally installed item in that system.
(3) When adding a new system, the Owner shall specify a Construction Code that is no earlier than the earliest Construction Code used for other systems that perform a similar function.
IWA-4422.1(a) states that a defect is considered removed when it has been reduced to an acceptable size.
3.3 Reason for Request
Relief is requested from replacement or weld repair of wall thinning conditions in ASME Code,Section XI, Class 2 and 3 carbon steel raw water piping systems to the design specification and the original construction code. The wall thinning conditions may be the result of various degradation mechanisms such as erosion, corrosion, cavitation, and pitting. The licensee stated the primary reason for this relief request is to provide adequate time so that pipe replacement can be planned to reduce impact on system availability including Maintenance Rule applicability of replacement materials.
3.4 Proposed Alternative and Basis for Use The licensee will implement the requirements of ASME Code Case N-661 as an alternative under 10 CFR 50.55a(a)(3)(i) for Class 2 and 3 raw water piping system repairs resulting from degradation mechanisms such as erosion, corrosion, cavitation, or pitting as an alternative to
the requirements of the ASME Section XI code as referenced above. The licensee stated that these types of defects are typically identified by small leaks in the piping system or by pre-emptive non-code required examinations performed to monitor the degradation mechanisms. The alternative repair technique described in Code Case N-661 involves the application of additional weld metal on the exterior of the piping system that restores the wall thickness requirement. The licensee stated that the repair technique will be utilized whenever the engineering evaluation determines that such a repair is suitable for the particular defect or degradation being resolved. The licensee stated that provisions for use of this Code Case will be addressed in the Repair/Replacement Program for PINGP.
The licensee stated that the provisions will require that adjacent areas be examined to verify that the repair will encompass the entire flawed area and that no other unacceptable degraded locations exist within a representative area dependent on the degradation mechanism present.
The licensee will perform an evaluation of the degradation mechanism to determine the re-examination schedule to be performed over the life of the repair. The repair will be considered to have a maximum service life of two fuel cycles unless the re-examinations conducted during each of the two fuel cycles establish the expected life of the repair.
Additionally, the licensee stated the following restrictions will be placed on the use of Code Case N-661, to ensure that the use of the Code Case will provide an acceptable alternative pursuant to 10 CFR 50.55a(a)(3)(i):
(a) If the root cause of the degradation has not been determined, the repair is only acceptable for one cycle.
(b) Weld overlay repair of an area can only be performed once in the same location.
(c) When through-wall repairs are made by welding on surfaces that are wet or exposed to water, the weld overlay repair is only acceptable until the next refueling outage.
The basis for use of the repair technique described in Code Case N-661 is that the ASME Code subcommittee for Section XI determined that this repair technique provides an acceptable alternative to the requirements of IWA-4000 and provides an acceptable level of quality and safety. Therefore, the proposed alternative is justified per 10 CFR 50.55a(a)(3)(i).
Code Case N-661 was approved by the ASME Section XI Code Committee on July 23, 2002, however, it has not been incorporated into NRC Regulatory Guide (RG) 1.147, Inservice Inspection Code Case Acceptability, ASME Section XI Division 1, and thus is not available for application at nuclear power plants without specific NRC approval. Therefore, NMC is requesting use of the alternative repair technique described via this relief request.
3.5 Duration of Proposed Alternative The licensee requested authorization of Code Case N-661 to be used for the PINGP, 10-year ISI interval or until the NRC publishes Code Case N-661 in a future revision of RG 1.147. Upon incorporation into the Regulatory Guide, the licensee stated they will review and follow the conditions specified. The licensee also stated that all other ASME Code,Section XI requirements for which relief was not specifically requested and authorized by the NRC staff will
remain applicable including third party review by the Authorized Nuclear Inservice Inspector.
4.0 STAFF EVALUATION By letter dated July 28, 2004, NMC requested that the NRC approve an alternative to the requirements of IWA-4221(a) and IWA-4221(b) of the ASME Section XI, 1998 Edition with the 2000 Addenda. Specifically, the licensee requested that the NRC approve ASME Code Case N-661 for use at PINGP. The request was made pursuant to 10 CFR 50.55a(a)(3)(i) to address replacement or internal weld repair of wall thinning conditions resulting from various wall thinning degradation mechanisms such as erosion, corrosion, cavitation, and pitting in Class 2 and 3 carbon steel raw water piping systems. The licensee stated the reason for the relief request was to provide adequate time for additional examination of adjacent piping so that pipe replacements can be planned to reduce impact on system availability and availability of replacement materials.
The licensee is proposing to use the provisions of Code Case N-661 to perform an alternative repair of degraded components which involves the application of weld metal overlay on the exterior of the piping system to restore the wall thickness of the component. The licensee stated that this repair technique will be utilized whenever engineering evaluations determine that such a repair is suitable for the particular defect or degradation being resolved. Provisions for use of this Code Case will be addressed in the licensees Repair and Replacement Program. The licensee stated that those provisions will require that adjacent areas be examined to verify that the entire flawed area will be encompassed by the repair and that there are no other unacceptable degraded locations within a representative area dependent on the degradation mechanism present. An evaluation of the degradation mechanism will be performed by the licensee to determine the re-examination schedule to be performed over the life of the repair. The licensee stated the repair will be considered to have a maximum service life of two fuel cycles unless re-examinations during each of the two fuel cycles are performed to establish the expected life of the repair.
The NRC staff finds the licensees reasoning in support of its request for relief acceptable. This finding is based on the fact that the NRC staff has reviewed Code Case N-661 for inclusion in RG 1.147. The NRC staffs review of Code Case N-661 established three conditions that the licensee agreed to place on the use of Code Case N-661 to assure that the Code Case will provide an acceptable alternative pursuant to 10 CFR 50.55a(a)(3)(i). These conditions are:
(a) If the root cause of the degradation has not been determined, the repair is only acceptable for one cycle.
(b) Weld overlay repair of an area can only be performed once in the same location.
(c) When through-wall repairs are made by welding on surfaces that are wet or exposed to water, the weld overlay is only acceptable until the next refueling outage.
The NRC staff established these three conditions based on the following considerations:
(a) If the root cause of the degradation has not been determined, a suitable reinspection frequency cannot be established.
(b) Weld overlay repair of an area can only be performed once to ensure that ineffective repairs are not being repeatedly implemented in the same location.
(c) Performing through-wall weld repairs on surfaces that are wet or exposed to water would produce welds that include weld defects such as porosity, lack of fusion, and cracks. It is highly unlikely that a weld can be made on an open root joint with water present on the backside of the weld without having several weld defects. These types of weld defects can, and many times do, lead to premature failure of a weld joint.
5.0 CONCLUSION
Based on the information provided in the licensees submittal, the NRC staff concludes that the licensee has provided an acceptable alternative to the requirements of IWA-4221(a) and IWA-4221(b) of the ASME Code,Section XI, 1998 Edition with the 2000 Addenda, subject to the following three conditions which must be met when using Code Case N-661. These conditions are: (a) if the root cause of the degradation has not been determined, the repair is only acceptable for one cycle, (b) weld overlay repair of an area can only be performed once in the same location, and (c) when through-wall repairs are made by welding on surfaces that are wet or exposed to water, the weld overlay repair is only acceptable until the next refueling outage. The NRC staff concludes that the proposed alternative, as supplemented by the three conditions listed above provides reasonable assurance of structural integrity and an acceptable level of quality and safety. Therefore, the proposed alternative is authorized pursuant to 10 CFR 50.55a(a)(3)(i) for the PINGP, for the current 10-year ISI interval, or until Code Case N-661 is approved for general use by reference in RG 1.147. At that time, if the licensee intends to continue implementing Code Case N-661, it must follow all provisions of Code Case N-661 with limitations or conditions, specified in RG 1.147, if any. All other ASME Code,Section XI, requirements for which relief was not specifically requested and authorized herein by the NRC staff remain applicable, including third party review by the Authorized Nuclear Inservice Inspector.
Principal Contributor: E. Reichelt, NRR Date: April 7, 2005