NLS2023033, 10 CFR 50.55a Relief Request RC3-02
| ML23178A273 | |
| Person / Time | |
|---|---|
| Site: | Cooper  |
| Issue date: | 06/27/2023 |
| From: | Chapin B Nebraska Public Power District (NPPD) |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| NLS2023033 | |
| Download: ML23178A273 (1) | |
Text
H Nebraska Public Power District "Always there when you need us" 10 CFR 50.55a(g)(5)(iii)
NLS2023033 June 27, 2023 U.S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, D.C. 20555-0001
Subject:
10 CFR 50.55a Relief Request RC3-02 Cooper Nuclear Station, Docket No. 50-298, License No. DPR-46
Dear Sir or Madam:
The purpose of this letter is for the Nebraska Public Power District (NPPD) to request that the Nuclear Regulatory Commission grant relief from, and authorize alternative to, Containment Inservice Inspection (CISI) code requirements for Cooper Nuclear Station pursuant to 10 CFR 50.55a(g)(5)(iii). The reliefrequest pertains to the visual examination requirements of American Society of Mechanical Engineers (ASME) Code Rules for Inservice Inspection of Nuclear Power Plant Components. The relief request is needed for the third Ten-Year CISI Interval (April 1, 2016 through February 28, 2026). The applicable code for the third ten-year interval is the ASME Section XI, 2007 Edition through the 2008 Addenda.
Attachment 1 contains Relief Request RC3-02. Attachment 2 contains RC3-02 Figure 1.
Relief Request RC3-02 is applicable to the Third Ten-Year CISI Interval. NPPD requests approval of this relief request by June 22, 2024.
This letter contains no regulatory commitments.
Should you have any questions concerning this matter, please contact Linda Dewhirst, Regulatory Affairs and Compliance Manager, at (402) 825-5416.
' of Plant Operations
/dv Attachments: 1. 10 CFR 50.55a Relief Request RC3-02
- 2. RC3-02 Figure 1 COOPER NUCLEAR STATION 72676 648A Ave/ P.O. Box 98 / Brownville, NE 68321 http://www.nppd.com
NLS2023 033 Page 2 of2 cc: Regional Administ rator w/ attachments USNRC - Region IV Cooper Project Manager w/ attachments USNRC - NRR Plant Licensing Branch IV Senior Resident Inspector w/ attachme nts USNRC -CNS NPG Distribut ion w/ attachments CNS Records w/ attachme nts
NLS2023033 Attachment 1 Page 1 of 5 10 CFR 50.55a Relief Request RC3-02 Containment Drywell Head Bolting Proposed Alternative in Accordance with 10 CFR 50.55a(g)(5)(iii)
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ASME Code Component(s) Affected Code Class: MC Examination Categories: E-G
Reference:
IWE-2313(b) VT-1 Visual Examinations Item Numbers: E8.10
==
Description:==
Bolted Connections Component Numbers: DW-FLG-BLT
Applicable Code Edition and Addenda
The ASME Code of Record for the Containment Inservice Inspection (CISI) Program Third Ten-y ear Interval at Cooper Nuclear Station is ASME Section XI, 2007 Edition, 2008 Addenda, "Rules for Inservice Inspection of Nuclear Power Plant Components" as modified by 10 CFR 50.55a.
Applicable Code Requirement
The following Code requirements for inspection of containment bolting is as follows:
Paragraph IWA-2200, Examination Methods: When performing VT-1, surface, radiographic, or ultrasonic examination on a component with defined surface or volume, essentially 100% of the required surface or volume shall be examined. Essentially 100% coverage is achieved when the applicable examination coverage is greater than 90%; however, in no case shall the examination be terminated when greater than 90% coverage is achieved, if additional coverage of the required examination surface or volume is practical. Nonmandatory Appendix S provides guidance that may be used for evaluating examination coverage.
Nonmandatory Appendix S, Evaluating Coverage for Section XI Nondestructive Examination, Paragraph S-3200:
(a) Determine the area of the required component examination surface using manufacturer's drawings or actual dimensions.
(b) Determine the area of the component examination surface affected by surface limitations. The actual dimensions of inaccessible component surfaces should be documented. Note that bolting may be VT-1 visual examined in place. In such instances, only those surfaces that are accessible for examination are required to be examined.
NLS2023033 Attachment 1 Page 2 of 5 10 CFR 50.55a Relief Request RC3-02 Containment Drywell Head Bolting Proposed Alternative in Accordance with 10 CFR 50.55a(g)(5)(iii)
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(c) Calculate the examination coverage.
Paragraph IWA-2210, Visual Examination - Visual examination shall be conducted in accordance with the written procedure requirements of Section V, Article 9, T-921 and T-941, and the examination report requirements of T-990.
Paragraph IWA-2211, VT-1 Examination
- (a) VT-1 examination is conducted to detect discontinuities and imperfections on the surface of components, including such conditions as cracks, wear, corrosion, or erosion.
- (c) Direct visual examination distance requirements shall be as specified in Table IWA-2211-1.
- Table IWA-2211-1 states the maximum direct examination distance is 2 feet.
Paragraph IWE-2313 (b), VT-1 Visual Examinations - in accordance with IWE-2500 and Table IWE-2500- 1, Examination Category E-G, to assess the condition of containment pressure retaining bolting.
Table IWE-2500-1, Examination Category E-G, Pressure Retaining Bolting - Requires 100% of each bolted connection to be examined. Notes 1 and 2 state the following:
- 1. Examination shall include bolts, studs, nuts, bushings, washers, and threads in base material and flange ligaments between fastener holes.
- 2. Examination may be performed with the connection assembled and bolting in place under tension, provided the connection is not disassembled during the interval. If the bolted connection is disassembled for any reason during the interval, the examination shall be performed with the connection disassembled.
Impracticality of Compliance Pursuant to 10 CFR 50.55a, "Codes and Standards," paragraph (g)(5)(iii), relief is requested from the 100 percent visual examination coverage requirement of the subject bolting due to configuration interferences which limit the VT-1 coverage that can be obtained.
There are seventy-six (76) primary containment drywell head flange bolt assemblies that connect the drywell head flange to the containment drywell shell flange. The bolting assemblies that were examined in the disassembled condition consist of the following:
NLS2023033 Attachment 1 Page 3 of 5 10 CFR 50.55a Relief Request RC3-02 Containment Drywell Head Bolting Proposed Alternative in Accordance with 10 CFR 50.55a(g)(5)(iii)
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Bolting Components Total no. of No. of bolting Percentage of bolting components components examined components at examined by by VT-1 joint to examine VT-1 Bolts 76 76 100 Upper Spherical Washers 76 76 100 Lower Spherical Washers 76 6 8 Nuts 76 33 43 Combined coverage (t) 304 191 191/304 X 100 = 63%
(1) Note surface area of the bolting component was not used to determine coverage but rather coverage was conservatively determined by counting the number of components that received a qualified direct VT-1 examination vs. number of components used to assemble the 76 bolting joints.
As part of the original construction of the drywell shell flange, the lower spherical washers and nuts were tack welded to the lower side of the drywell shell flange for ease of disassembly and reassembly. Over the life of CNS, tack welds failed on 6 of the lower spherical washers and 33 nuts making those components accessible for direct VT-1 visual examination along with the bolts and upper spherical washers that are accessible. Gusset plates on the lower drywell flange between each nut/washer assembly interfere and preclude achieving the required 100% VT-1 examination of the remaining nuts and/or washers that remain welded to the drywell head flange.
See Attachment 2 (RC3-02 Figure 1) that illustrates the limitations encountered.
During the previous 2nd ten-year CISI interval, VT-3 examinations of the bolting were conducted on the accessible portions after disassembly as required per the 2001 Edition/2003 Addenda applicable during the 2nd interval as modified by 10CFR50.55a. VT-1 examinations were not required during the 2nd interval. VT-3 examinations were conducted to determine the general mechanical and structural condition of the bolting with no issues noted.
Burden Caused by Compliance Compliance with the Code coverage requirements would require removal of the nuts and washers by cutting and/or grinding the tack welds of the bottom side of the drywell shell flange.
Attempting to conduct the VT-1 examinations of the nuts/washers in place would only achieve a limited amount of additional examination coverage due to interference from the adjacent gusset plates located between each nut/washer location. Additional cleaning such as hydrolazing to improve the accessible surfaces would result in an estimated dose of 3 .5 Rem in a contaminated
NLS2023033 Attachment 1 Page 4 of 5 10 CFR 50.55a Relief Request RC3-02 Containment Drywell Head Bolting Proposed Alternative in Accordance with 10 CFR 50.55a(g)(5)(iii)
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area to personnel for little additional gain of examination coverage. NPPD considers performance of these activities in order to meet the 100% code examination requirement to be impractical due to the cost, increased radiation exposure, impact to plant equipment, and personnel resources required.
Proposed Alternative and Basis for Use The subject bolting that was disassembled and accessible received direct VT-1 examinations using ASME Section XI qualified Level II examiners and procedure to the maximum extent practical utilizing the best available techniques, and all results were acceptable. Approximately 63% of the drywell head bolting was examined and credited in accordance with Table IWE-2500-1, Examination Category E-G, Pressure Retaining Bolting.
Remote VT-1 visual examinations were attempted on the remaining nuts and washers that are tack welded in place to the lower side of the drywell shell flange. The nuts and washers are partially inaccessible limiting the ability of the VT-1 qualified examiners from achieving a full code qualified examination. The in-place nuts and washers were examined remotely using ASME Section XI Code qualified Level II examiners and procedure with assistance from the invessel visual inspection (IVVI) team and cameras. Due to the physical limitations experienced, a fully qualified code exam could not be credited and therefore was considered best effort. In accordance with the principles of As Low as Reasonably Achievable (ALARA), the best effort visual examinations exams were conducted while the refueling cavity and flange area was flooded for refueling thus minimizing dose to the examiners compared to performing the examinations directly located in the refueling cavity. No service induced degradation was observed with the best effort remote visual examinations.
Based on acceptable results of the direct VT-1 examinations along with the best effort remote visual examinations, it is reasonable to conclude that service-induced degradation would have been detected. Additionally, the drywell head to drywell shell flange joint is tested for leakage at the end of each refueling outage as required by 10 CFR 50, Appendix J. Therefore, this proposed alternative demonstrates an acceptable level of quality and safety by providing reasonable assurance of structural integrity of the drywell flange pressure retaining bolting.
Duration of Proposed Alternative Relief is requested for the 3rd 10-year CISI Interval for Cooper Nuclear Station, which began April 1, 2016, and will end on February 28, 2026. In conclusion, NPPD has determined that authorizing the proposed alternative as described herein provides an acceptable level of quality and safety and does not adversely impact the health and safety of the public.
NLS2023033 Page 5 of 5 10 CFR 50.55a Relief Request RC3-02 Containment Drywell Head Bolting Proposed Alternative in Accordance with 10 CFR 50.55a(g)(5)(iii)
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Precedent None
NLS2023033 Page 1 of2 10 CFR 50.55a Relief Request RC3-02 Containment Drywell Head Bolting RC3-02 Figure 1
10 CFR 50.55a Request Number RC3-02 Containment Drywell Head Bolting 1
Gussets Washer/nut assembly DW-FLG-Drywell head flange Drywell shell flange I
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IRC3-02 Figure 1