ML16208A462

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Safety Evaluation for Request for Alternative Associated with Reactor Pressure Vessel Internals and Components Inspection for the Fifth 10-Year Interval
ML16208A462
Person / Time
Site: Monticello Xcel Energy icon.png
Issue date: 08/03/2016
From: David Wrona
Plant Licensing Branch III
To: Gardner P
Northern States Power Company, Minnesota
Kuntz R
References
CAC MF7111
Download: ML16208A462 (11)
v • d • e


Text

UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 August 3, 2016 Mr. Peter A. Gardner Site Vice President Monticello Nuclear Generating Plant Northern States Power Company - Minnesota (NSPM) 2807 West County Road 75 Monticello, MN 55362-9637

SUBJECT:

MONTICELLO NUCLEAR GENERATING PLANT- REQUEST FOR ALTERNATIVE ASSOCIATED WITH REACTOR PRESSURE VESSEL INTERNALS AND COMPONENTS INSPECTION FOR THE FIFTH 10-YEAR INTERVAL (CAC NO. MF7111)

Dear Mr. Gardner:

By letter dated November 20, 2015 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML15324A305), as supplemented by letter dated June 2, 2016 (ADAMS Accession No. ML16155A023}, the Northern States Power Company - Minnesota (NSPM or the licensee) submitted request for alternative relief request (RR)-01 O for its fifth 10-year interval inservice inspection (ISi) program plan for reactor vessel (RV) interior surfaces, attachments, and core support structures at Monticello Nuclear Generating Plant (MNGP).

Specifically, pursuant to Title 10 of the Code of Federal Regulations (10 CFR), Section 50.55a (z)(1 ), the licensee submitted the request to use Boiling Water Reactor Vessel and Internals Project (BWRVIP) guidelines as an alternative to certain requirements of Section XI, "Rules for ISi of Nuclear Power Plant Components," of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code) for an ISi of RV interior surfaces, attachments, and core support structures on the basis that the alternative provides an acceptable level of quality and safety.

The U.S. Nuclear Regulatory Commission (NRC) staff reviewed the proposed alternative and determined, as set forth in the enclosed safety evaluation, that NSPM adequately addressed all of the regulatory requirements set forth in 10 CFR 50.55a(z)(1 ), and that the proposed alternative to use the requirements of ASME Code, provides an acceptable level of quality and safety. The NRG staff authorizes the use of the proposed alternative for the remainder of the fifth 10-year inspection interval of the ISi program which ends May 31, 2022.

All other requirements of the ASME Code,Section XI, for which an alternative has not been specifically requested remain applicable, including third-party review by the Authorized Nuclear lnservice Inspector. Any ASME Code,Section XI, RVI components that are not included in this request for an alternative will continue to be inspected in accordance with the ASME Code,Section XI, requirements.

The NRG staff notes that if NSPM intends to take exceptions to, or deviations from, the NRG staff-approved BWRVIP inspection guidelines, this will require NSPM to revise and re-submit

P. Gardner this request for an alternative. NSPM shall obtain NRC staff approval for such exceptions prior to implementing the revised inspection guidelines for the MNGP unit's RV interior surfaces, attachments, and core support structures.

If you have any questions, please contact Robert Kuntz at 301-415-3733, or via e-mail at Robert. Kuntz@nrc.gov.

Sincerely, oL-~ 9 v__ _

David J. Wrona, Chief Plant Licensing Branch 111-1 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-263

Enclosure:

Safety Evaluation cc w/enclosure: Distribution via Listserv

UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION REQUEST FOR ALTERNATIVE RELIEF REQUEST (RR)-010 REGARDING INSPECTION OF REACTOR PRESSURE VESSEL INTERNALS AND COMPONENTS NORTHERN STATES POWER COMPANY - MINNESOTA MONTICELLO NUCLEAR GENERATING PLANT DOCKET NO. 50-263 (CAC NO. MF7111)

1.0 INTRODUCTION

By letter dated November 20, 2015 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML15324A305), as supplemented by letter dated June 2, 2016 (ADAMS Accession No. ML16155A023), the Northern States Power Company- Minnesota (NSPM or the licensee) submitted request for alternative RR-010 for its fifth 10-year interval inservice inspection (ISi) program plan for reactor vessel internals (RVI) components at Monticello Nuclear Generating Plant (MNGP). In this safety evaluation (SE), the term "RVI components" includes reactor vessel (RV) interior surfaces, attachments, and core support structures. In the request for an alternative, the licensee proposed to use Boiling Water Reactor Vessel and Internals Project (BWRVIP) guidelines as an alternative to certain requirements of Section XI, "Rules for ISi of Nuclear Power Plant Components," of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code) for ISi of RV interior surfaces, attachments, and core support structures.

2.0 REGULATORY EVALUATION

ISi of ASME Code Class 1, 2, and 3 components is performed in accordance with Section XI of the ASME Code and applicable addenda as a way to detect anomaly and degradation indications so that structural integrity of these components can be maintained. This is required by 10 CFR 50.55a(g), except where specific relief has been granted by the U.S. Nuclear Regulatory Commission (NRC or Commission) pursuant to 10 CFR 50.55a(g)(6)(i). 10 CFR 50.55a(z) states that alternatives to the requirements of paragraphs (b) through (h) of 10 CFR 50.55a or portions thereof may be used, when authorized by the Director, Office of Nuclear Reactor Regulation. A proposed alternative must be submitted and authorized prior to Enclosure

implementation. The applicant or licensee must demonstrate that: (1) the proposed alternative would provide an acceptable level of quality and safety; or (2) compliance with the specified requirements of this section 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), components (including supports) that are classified as ASME Code Class 1, 2, and 3 must meet the requirements, except design and access provisions and preservice examination requirements, set forth in Section XI of editions and addenda of the ASME Code that become effective subsequent to editions specified in paragraphs (g)(2) and (3) of this section, 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 successive 120-month inspection intervals (following the initial 120-month inspection interval) must comply with the requirements in the latest edition and addenda of the ASME Code, which was incorporated by reference in 10 CFR 50.55a(a) 12 months before the start of the 120-month interval (or the optional ASME Code Cases listed in NRC Regulatory Guide (RG) 1.147, Revision 17), subject to the conditions listed in 10 CFR 50.55a(b). The applicable ASME Code of record for the fifth 10-year ISi interval for MNGP is ASME Code,Section XI, 2007 Edition through the 2008 Addenda.

3.0 LICENSEE'S EVALUATION Components for Which an Alternative is Requested ASME Code,Section XI, Class 1, Examination Categories B-N-1 and B-N-2, Code Item Nos.

813.10, Vessel Interior; 813.20, Interior Attachments within Beltline Region; 813.30, Interior Attachments Beyond Beltline Region; and 813.40, Core Support Structure.

Examination Requirements from Which an Alternative is Requested ASME Code,Section XI requires a visual examination (VT) of certain RVI components. These examinations are included in Table IWB-2500-1, Categories B-N-1 and B-N-2, and identified with the following item numbers:

  • B 13.1 O - Examine accessible areas of the RV interior during each period using a VT-3 examination, as defined in paragraph IWA-2213 of Section XI of the ASME Code.
  • 813.20 - Examine interior attachment welds within the RV beltline region during each interval using a VT-1 examination, as defined in paragraph IWA-2211 of Section XI of the ASME Code.
  • 813.30 - Examine interior attachment welds outside of the beltline region during each interval using a VT-3 examination, as defined in paragraph IWA-2213 of Section XI of the ASME Code.
  • 813.40 - Examine accessible surfaces of the welded core support structures during each interval using a VT-3 examination, as defined in paragraph IWA-2213 of Section XI of the ASME Code.

These examinations are performed to periodically assess the structural integrity of the RV interior surfaces, attachments, and core support structures.

Licensee's Basis for Requesting an Alternative and Justification for Granting Request In its letter dated November 20, 2015, the licensee submitted, in lieu of ASME Code,Section XI, requirements, an alternative inspection program per the BWRVIP guidelines for Category B-N-1 and B-N-2 RV interior surfaces, attachments, and core support structures at MNGP. The licensee stated that implementation of the alternative inspection program will maintain an adequate level of quality and safety of the affected welds and components and will not adversely impact the health and safety of the public. As part of its justification for the relief, the licensee stated that boiling-water reactors (BWRs) now examine the RV interior surfaces, attachments, and core support structures in accordance with BWRVIP inspection and evaluation (l&E) guidelines in lieu of ASME Code,Section XI, criteria. The proposed alternative includes examination methods, examination volume, frequency, training, successive and additional examinations, flaw evaluations, and reporting. The BWRVIP guidelines were written to address the safety significant RVI components and to examine and evaluate the examination results using appropriate methods and reexamination frequencies. Furthermore, the licensee stated that this alternative to ASME Code,Section XI, requirements is requested pursuant to 10 CFR 50.55a(z)(1 ).

Alternative Examination In lieu of the requirements specified in Section XI of the ASME Code, the licensee proposed to examine the MNGP RVI components in accordance with BWRVIP l&E guideline requirements in the following BWRVIP reports for RVI surfaces, attachments, and core support structures.

  • BWRVIP-38, "BWRVIP Shroud Support Inspection and Flaw Evaluation Guidelines"
  • BWRVIP-41, Revision 3, "BWR Jet Pump Assembly Inspection and Flaw Evaluation Guidelines"
  • BWRVIP-47-A, "BWR Lower Plenum Inspection and Flaw Evaluation Guidelines"
  • BWRVIP-48-A, "Vessel ID [Inside Diameter] Attachment Weld Inspection and Flaw Evaluation Guidelines"
  • BWRVIP-76, Revision 1-A, "BWR Core Shroud Inspection and Flaw Evaluation Guidelines"
  • BWRVIP-138, Revision 1-A, "Updated Jet Pump Beam Inspection and Flaw Evaluation Guidelines"
  • BWRVIP-180, "Access Hole Cover Inspection and Flaw Evaluation Guidelines"
  • BWRVIP-183, "Top Guide Grid Beam Inspection and Flaw Evaluation Guidelines"
  • BWRVIP-94, Revision 2, "BWRVIP Program Implementation Guide" The licensee stated that, consistent with the current implementation of the BWRVIP guidelines, NSPM proposes to implement the BWRVIP program and applicable guidelines for the requested alternative without use of an authorized inspection agency. The licensee further indicated that results of examinations and deviations for the BWR fleet are reported under an established protocol between the BWRVIP and the NRC. Also, since the BWRVIP guidelines are revised periodically, the licensee clarified that if new guidance includes changes that are less conservative than those approved by the NRC, this less conservative guidance shall be implemented only after NRC approval.

In Table 1 of Attachment 1 of its submittal dated November 20, 2015, the licensee provided a comparison of the ASME Code,Section XI, examination requirements for Category B-N-1 and B-N-2 categories for RVI surfaces, attachments, and core support structures with the current BWRVIP guideline requirements, as applicable to the MNGP. In Attachment 2 of the submittal, the licensee provided additional justification regarding comparison of the inspection requirements of ASME Code Section XI Table IWB-2500-1, Item Nos. B13.10, B13.20, B13.30, and B13.40 to the inspection requirements in the BWRVIP guidance documents. As an example, the following excerpt from the Attachment 2 of the licensee's submittal indicates the applicable ASME Code,Section XI, category/item numbers that are applicable to some of the MNGP RVI components:

  • Jet Pump - Item No. B13.20
  • Core Shroud Support - Item No. 813.40 Based on the examination method, scope, frequency, and flaw evaluation criteria, the licensee stated that the above examples demonstrate that the inspection techniques recommended by the BWRVIP l&E guidelines are equivalent to or superior to the inspection techniques mandated by the ASME Code,Section XI ISi program. For instance, the BWRVIP's inspection of jet pump riser braces per BWRVIP-41 (Example 2), uses enhanced VT-1 (EVT-1), whereas, the ASME Code uses VT-1. The BWRVIP's inspection of core spray piping bracket welds per BWRVIP-48-A (Example 3), uses EVT-1 every 8 years for plants with a 2-year fuel cycle, whereas, the ASME Code uses VT-3 every 10 years. Therefore, the licensee concluded that implementation of the BWRVIP l&E guidelines for the MNGP RVI surfaces, attachments, and core support structures would provide an acceptable level of quality and safety.

4.0 STAFF EVALUATION The NRG staff reviewed the information provided by the licensee in its submittal of November 20, 2015, as supplemented by the June 2, 2016, response to the NRG staff's request for additional information (RAI), regarding its proposed alternative to the ASME Code,Section XI, ISi requirements and the technical bases for the alternatives. The NRG staff reviewed the status of the referenced BWRVIP reports and found application of the referenced BWRVIP reports to be acceptable, provided that the NRG conditions associated with the latest SE for each BWRVIP report are implemented. This finding is supported by the NRG staff's observations and the subsequent evaluations:

  • Although furnace-sensitized stainless steel vessel attachment welds tend to be more susceptible to intergranular stress corrosion cracking (IGSCC), the NRG staff's approval of the BWRVIP-48-A l&E guidelines is an indication that the alternative monitoring of IGSCC in this type of welds is acceptable.
  • The licensee did not include BWRVIP-139, "BWR Vessel Internals Project, Steam Dryer Inspection and Flaw Evaluation Guidelines" to monitor active aging degradation in the steam dryer. This is acceptable because the MNGP has installed a replacement Westinghouse steam dryer in 2011. The NRG staff noted that this type of steam dryer has adequate operating history for MNGP since 2011 and for BWRs in Europe.

Subsection 3.0.3.1.8, "Thermal Aging & Neutron Irradiation Embrittlement of Cast Austenitic Stainless Steel (CASS) Program," states in the summary that this program is in accordance with ASME Code,Section XI, Subsection IWB, Category B-N-1 and B-N-2, requirements. Since the licensee clarified (see the discussion on licensee's response to RAl-4 below) that none of the CASS components are B-N-1 or B-N-2 components as

defined by Section XI of the ASME Code, the CASS components are outside the scope of this request for an alternative.

  • Some of the 8WRVIP reports that are included in this request for an alternative have not been approved by the NRC (i.e., without the"- A" designation). This is appropriate because use of the specific l&E guidelines in these 8WRVIP reports for the ASME Code,Section XI, Examination Categories 8-N-1 and 8-N-2, Code Item Nos. 813.1 O to 813.40 RV components have already been accepted by the NRC staff in prior applications, as indicated in the June 30, 2014, SE for Grand Gulf Nuclear Station, Unit 1 (ADAMS Accession No. ML14148A262), and the March 10, 2016, SE for Clinton Power Station, Unit 1 (ADAMS Accession No. ML16012A344).

The NRC staff has evaluated the licensee's response to the RAls and noted that Table 1 of RR-010 compares the current ASME Code,Section XI examination category requirements with the current 8WRVIP guideline requirements. However, the acceptance standards of the two were not compared in the table. Therefore, in RAl-1, the NRC staff requested the licensee to:

( 1) identify the major differences between the flaw acceptance standard between the ASME Code and the applicable 8WRVIP documents, and (2) use the 813.20 components as an example to discuss how RR-010 will change the disposition of detected flaws.

In its response to RAl-1 (1 ), the licensee stated that "[t]here are no major differences between flaw acceptance standards of Section XI of the ASME Code and the applicable 8WRVIP documents, although, there are some differences in evaluation reporting requirements and flaw re-inspection requirements." The NRC staff accepts this conclusion because the licensee has provided explanations and examples to support this conclusion. In the response to RAl-1 (2), the licensee stated that, the flaw evaluation process for the 813.20 components does not change since the 8WRVIP-48-A flaw evaluation requirements invoke the use of ASME Section XI flaw evaluation requirements." Hence, RAl-1 is resolved.

To assess the impact of using the alternative inspections and disposition of indications on MNGP RVI integrity, the NRC staff reviewed the 8WR Vessel and Internals Inspection Summaries for the Spring 2013 Refueling Outages (RFO) dated April 11, 2014 (ADAMS Accession No. ML14125A303), and found that, although Table 1 of RR-01 O showed that the 8WRVIP examination has alternative requirements for inspection of the ASME Code, Item 813.10, "Reactor Vessel Interior," the April 11, 2014, report showed no inspection record for this item.

Consequently, RAl-2(1) was issued to request the licensee to explain how RR-010 will change the recording of RVI inspection results. The response to RAl-2(1) indicated that 8-N-1 category examinations were performed in the 2015 RFO instead of the 2013 RFO, and, therefore, no examination results were available for inclusion in the 2013, inspection summary.

The 2013, inspection summary documented flaws that were detected in the core shroud, shroud support, core spray piping, and jet pump assembly. To assess the adequacy of applying 8WRVIP reports to these components, RAl-2(2) requested the licensee to: (a) discuss evaluation of the worst detected flaws in these components, (b) confirm whether any of the flawed components are ASME Code components but were inspected and evaluated in accordance with the 8WRVIP reports, and (c) confirm that a plant-specific leakage assessment was performed, as required by 8WRVIP-18 (core spray), 8WRVIP-41 Uet pump assembly), and 8WRVIP-76 (core

shroud), or the ASME Code,Section XI, for operability. The licensee's response to RAl-2(2) provided summaries of limiting flaw evaluation results for core shroud welds and shroud support welds, showing that all flaws have met allowable structural safety margins. Flaw indications in core spray piping and jet pumps were either repaired or dispositioned as having no structural impact. Thus, RAl-2(2)(a) is resolved. For RAl-2(2)(b), the licensee identified additional inspection items (Table 1a) to supplement Table 1 in the original submittal and clarified that all l&E of these components were performed in accordance with the ASME Code,Section XI, and BWRVIP requirements. RAl-2(2)(b) is resolved. For RAl-2(2)(c), the licensee confirmed that no leakage assessments were performed for jet pumps and the core shroud because the detected flaws did not trigger the requirement for a leakage assessment. For the detected crack in the core spray piping which required a leakage assessment, the assessment concluded that the reduced coolant flow can still support adequate core cooling to maintain peak clad temperature during postulated loss of coolant accidents. RAl-2(2)(c) is resolved.

RAl-3 requested the licensee to confirm the information in Footnote 4 of RR-010, which states that BWRVIP-25 is not applicable in this request for an alternative because the MNGP plant-specific analysis for the rim holddown bolts was approved in NUREG-1865. Approval of the MNGP plant-specific analysis is an indication that NSPM has satisfactorily addressed a major action item in the September 6, 2000, SE for BWRVIP-25 and, therefore, is allowed to apply BWRVIP-25 to MNGP. The licensee's response states that "NSPM requests to include BWRVIP-25 within the scope of this alternative request. Upon approval of this alternative, the core plate will be managed in accordance with BWRVIP-25 and will continue to credit the evaluation in lieu of the inspections as described in NUREG-1865." This statement has revised the information in Footnote 4 regarding applicability of BWRVIP-25 in this request for an alternative, and RAl-3 is thus resolved.

Consistent with the approach of not listing irrelevant BWRVIP reports in Section E.1 of the submittal, RAl-4 requested that the licensee explain the inclusion of BWRVIP-41, Revision 3, BWRVIP-47-A, and BWRVIP-183, or consider deletion from the list of Section E1 if they are outside the scope of the request for an alternative as indicated in Footnote 5 of RR-010 and Footnote 1 in Section 8 of BWRVIP-183. In response, the licensee added "CASS" in front of the "components" in the revised Footnote 5 to avoid misunderstanding: "However, none of the CASS components are B-N-1 or B-N-2 components as defined by ASME [Code],Section XI, and are outside of the scope of this 10 CFR 50.55a(z)(1) request for an alternative." This revision provides clarification that only CASS components of BWRVIP-41, Revision 3, and BWRVIP-47-A are outside of the scope of RR-010. Further, the licensee explained that, "the Top Guide is not a specified component in the MNGP ASME XI ISi Program, therefore, the footnote in Section 8 of BWRVIP-183 is not applicable for MNGP." As such, NSPM provided justifications to include BWRVI P-41, Revision 3, BWRVI P-47-A, and BWRVI P-183 guidelines as alternative in RR-010. RAl-4 is resolved.

Based on the above evaluation regarding previous inspection results of RVI components, the NRC staff concludes that most RVI component inspections did not reveal the presence of any indications at MNGP. For those RVI components where indications were found, the licensee's responses to RAl-1 and RAl-2 indicated that the licensee's disposition of detected flaw indications is equivalent to what the ASME Code,Section XI required for these or similar components, and is, therefore, acceptable. Further, since: (1) the MNGP RVI inspection

program has been developed and implemented to meet the requirements of the relevant BWRVIP reports, and (2) the BWRVIP l&E guidelines require the same or more frequent inspections than ASME Code,Section XI, criteria for RVI components that are susceptible to aging degradation mechanisms (Section 3.0 of this SE), subsequent inspections of the RVI components at MNGP per the relevant BWRVIP l&E guidelines will provide reasonable assurance that any emerging aging effects will be identified in a timely manner. In addition, frequent inspections in accordance with the BWRVIP l&E guidelines will enable the licensee to effectively monitor existing aging degradation in RVI surfaces, attachments, and core support structures during the fifth ISi interval.

The above determination, supplemented by the NRC staff's observations listed at the beginning of this section and resolution of all technical concerns raised in the RAls, supports the NRC staff's conclusion that the implementation of the inspection parameters specified in the licensee's proposed alternative will continue to ensure that the integrity of the RVI components is maintained with an acceptable level of quality and safety.

5.0 CONCLUSION

Based on the information provided in the licensee's submittals, the NRC staff concludes that the alternatives proposed by the licensee will ensure that the integrity of the RVI surfaces, attachments, and core support structures is maintained with an acceptable level of quality and safety. Therefore, pursuant to 10 CFR 50.55a(z)(1 ), the licensee's proposed alternative for MNGP is authorized for the fifth 10-year ISi interval, which ends on May 31, 2022.

All other requirements of the ASME Code,Section XI, for which an alternative has not been specifically requested remain applicable, including third-party review by the Authorized Nuclear lnservice Inspector. Any ASME Code,Section XI, RVI components that are not included in this request for an alternative will continue to be inspected in accordance with the ASME Code,Section XI, requirements.

The NRC staff notes that if the licensee intends to take exceptions to, or deviations from, the NRC staff-approved BWRVIP inspection guidelines, this will require the licensee to revise and re-submit this request for an alternative. The licensee shall obtain NRC staff approval for such exceptions prior to implementing the revised inspection guidelines for the MNGP unit's RV interior surfaces, attachments, and core support structures.

Principal Contributor: Simon Sheng, NRA Date of issuance: August 3 , 2o1 6

ML16208A462 *via email OFFICE DORL/LPL3-1 /PM DORL/LPL3-2/LA DE/EVI B/BC

  • DORL/LPL3-1 /PM NAME RKuntz SRohrer JMcHale DWrona DATE 7/27/2016 7/27/2016 7/26/2016 8/03/2016
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