AEP-NRC-2021-35, Request for Relief Related to American Society of Mechanical Engineers (ASME) Code Case N-729-6 Supplemental Examination Requirements, ISIR-5-05

Request for Relief Related to American Society of Mechanical Engineers (ASME) Code Case N-729-6 Supplemental Examination Requirements, ISIR-5-05

ML21124A237
Person / Time
Site:	Cook
Issue date:	05/04/2021
From:	Lies Q Indiana Michigan Power Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
AEP-NRC-2021-35
Download: ML21124A237 (37)

Text

INOIANA Indiana Michigan Power MICHIGAN Cook Nuclear Plant POWER- One Cook Place Bridgman, Ml 49106 An ARP Company indianamichiganpower.com 8 0 UN DL ES S ENE RG y

• May 4, 2021 AEP-NRC-2021-35 10 CFR 50.55a Docket No.: 50-316 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D.C. 20555-0001 Request for Relief related to American Society of Mechanical Engineers (ASME)

Code Case N-729-6 Supplemental Examination Requirements, ISIR-5-05 Pursuant to 10 CFR 50.55a(z)(2), Indiana Michigan Power Company (l&M), the licensee for D.C.

Cook Nuclear Plant (CNP) Unit 2, requests Nuclear Regulatory Commission approval of the enclosed request for an alternative for CNP Unit 2, based upon the specified Code Case requirements representing a hardship or unusual difficulty without a compensating increase in the level of quality and safety. Enclosure 1 to this letter identifies the affected components, applicable ASME Boiler and Pressure Vessel Code (Code) Case requirements, reason for request, proposed alternative, and basis for use. The alternative is proposed to be applied during the next operating cycle and will conclude at the end of the next refueling outage, U2C27.

As part of the current CNP Unit 2 refueling outage, U2C26, the Unit 2 Reactor Vessel Closure Head (RVCH) visual examination was performed in accordance with the requirements in ASME Section XI Code Case N-729-6, Table-1. During this examination, it was discovered that relevant conditions of accumulated residues and discoloration exist on the Unit 2 RVCH.

Code Case N-729-6, Paragraph -3142.2, requires nozzles with relevant conditions to have supplemental examinations consisting of a volumetric examination of the nozzle tube and surface examination of the partial-penetration weld or surface examination of the nozzle tube inside surface, the partial-penetration weld, and nozzle tube outside surface below the weld, in accordance with Paragraph -3200(b). As described in the enclosure of this request, l&M is requesting an alternative to the specified requirements of Code Case N-729-6, Paragraph -3142.2, pursuant to 10 CFR 50.55a(z)(2), as the provisions that require supplemental examinations represent a hardship or unusual difficulty without a compensating increase in the level of quality and safety. l&M submitted a similar relief request for CNP Unit 1 on October 5, 2020 (ML20279A713). The safety evaluation was received on February 12, 2021 (ML21034A155).

NRC Verbal approval of the proposed relief is requested prior to entry into Mode 2, which is scheduled to occur on or about May 15, 2021.

U.S. Nuclear Regulatory Commission AEP-NRC-2021-35 Page 2 There is one new commitment in this letter, as specified in Enclosure 2. Should you have any questions, please contact Mr. Michael K. Scarpello, Director of Regulatory Affairs, at (269) 466-2649.

1-~ ,t Sincerely, Q. Shane Lies Site Vice President DLW/kmh

Enclosures:

1. Proposed Alternative in Accordance with 10 CFR 50.55a(z)(2) Request for an Alternative to American Society of Mechanical Engineers (ASME) Code Case N-729-6 for Replacement Reactor Vessel Closure Head Penetration Nozzles.

2. Regulatory Commitment for Reactor Vessel Closure Head (RVCH) Inspection.

U.S. Nuclear Regulatory Commission AEP-NRC-2021-35 Page 3 c:

R. J. Ancona - MPSC J. B. Giessner - NRC Region Ill EGLE - RMD/RPS NRC Resident Inspector S. P. Wall - NRC, Washington D.C.

A. J. Williamson - Ft. Wayne AEP, w/o enclosure

Enclosure 1 to AEP-NRC-2021-35 Indiana Michigan Power Company - Donald C. Cook Nuclear Plant - Unit 2 Proposed Alternative in Accordance with 10 CFR 50.55a(z)(2)

Request for an Alternative to the American Society of Mechanical Engineers (ASME) Code Case N-729-6 for Replacement Reactor Vessel Closure Head Penetration Nozzles

1. ASME Code Component Affected Head with nozzles and partial-penetration welds of Components I Primary Water Stress Corrosion Cracking Numbers:

(PWSCC) resistant materials American Society of Mechanical Engineers Code Class: (ASME) Boiler and Pressure Vessel Code (Code),

Class 1 ASME Section XI 2013 Edition and no addenda ASME Section XI, Division 1, Code Case N-729-6,

References:

Alternative Examination Requirements for PWR Reactor Vessel Upper Heads with Nozzles Having Pressure-retaining Partial-Penetration Welds,Section XI, Division 1 Examination Table IWB-2500, Category B-P Category:

Table 1 of ASME Code Case N-729-6 Item Number( s ): B4.30 Pressure retaining components Reactor Vessel Closure Head (RVCH) with nozzles and partial-penetration welds of primary water stress corrosion cracking PWSCC-resistant

Description:

materials Penetrations - 30, 35, 37, 38, 41, 43, 44, 52, 54, 55,61,66,67,69, 74 Unit / Inspection D.C. Cook Nuclear Plant, Unit 2 (CNP)/ 5th Ten-Interval Year In-service Inspection (ISi) Interval (March 1, Applicability: 2020 to February 28, 2030)

2. Applicable Code Edition and Addenda

The Fifth Ten-year ISi interval Code of Record for CNP is the 2013 Edition of ASME Code,Section XI, no addenda.

Examinations of the RVCH and penetration nozzles are performed in accordance with ASME Code Case N-729-6, Alternative Examination Requirements for Pressurized Water Reactor Vessel Upper to AEP-NRC-2021-35 Page 2 Heads with Nozzles having Pressure-Retaining Partial-Penetration Welds,Section XI, Division 1 (Reference 1), as conditioned by 10 CFR 50.55a(g)(6)(ii)(D).

10 CFR 50.55a(g)(6)(ii)(D) requires, in part, that licensees of pressurized water reactors shall augment the ISi program with ASME Code Case N-729-6 subject to the conditions specified in paragraphs (g)(6)(ii)(D)(2) through (8) of this section.

3. Applicable Code Requirement

10 CFR 50.55a(g)(6)(ii)(D)(1) requires:

(D) Augmented ISi requirements: Reactor vessel head inspections-(1) Implementation. Holders of operating licenses or combined licenses for pressurized-water reactors as of or after June 3, 2020 shall implement the requirements of ASME BPV Code Case N-729-6 instead of ASME BPV Code Case N-729-4, subject to the conditions specified in paragraphs (g)(6)(ii)(D)(2) through (8) of this section, by no later than one year after June 3, 2020.

Paragraph -3141 of Code Case N-729-6 states, regarding in-service visual examinations (VE):

(a) The VE required by -2500 and performed in accordance with IWA-2200 and the additional requirements of this Case shall be evaluated by comparing the examination results with the acceptance standards specified in -3142.1.

(b) Acceptance of components for continued service shall be in accordance with -3142.

(c) Relevant conditions for the purposes of the VE shall include evidence of reactor coolant leakage, such as corrosion, boric acid deposits, and discoloration.

Paragraph -3142.1 Acceptance by VE of Code Case N-729-6 states:

(a) A component whose VE confirms the absence of relevant conditions shall be acceptable for continued service.

(b) A component whose VE detects a relevant condition shall be unacceptable for continued service until the requirements of ( 1), (2), and (c) below are met.

(1) Components with relevant conditions require further evaluation. This evaluation shall include determination of the source of the leakage and correction of the source of leakage in accordance with -3142.3.

(2) All relevant conditions shall be evaluated to determine the extent, if any, of degradation. The boric acid crystals and residue shall be removed to the extent necessary to allow adequate examinations and evaluation of degradation, and a subsequent VE of the previously obscured surfaces shall be performed, prior to return to service, and again in the subsequent refueling outage. Any degradation detected shall be evaluated to determine if any corrosion has impacted the structural integrity of the component. Corrosion that has reduced component wall thickness below design limits shall be resolved through repair/replacement activity in accordance with IWA-4000.

to AEP-NRC-2021-35 Page 3 (c) A nozzle whose VE indicates relevant conditions indicative of possible nozzle leakage shall be unacceptable for continued service unless it meets the requirements of -3142.2 or

-3142.3.

Paragraph -3142.2 Acceptance of Supplemental Examination of Code Case N-729-6 states:

A nozzle with relevant conditions indicative of possible nozzle leakage shall be acceptable for continued service if the results of supplemental examinations [-3200(b )] meet the requirements of-3130.

Paragraph -3142.3 Acceptance by Corrective Measures or Repair/Replacement Activity of Code Case N-729-6 states:

(a) A component with relevant conditions not indicative of possible nozzle leakage is acceptable for continued service if the source of the relevant condition is corrected by a repair/replacement activity or by corrective measures necessary to preclude degradation.

(b) A component with relevant conditions indicative of possible nozzle leakage shall be acceptable for continued service if a repair/replacement activity corrects the defect in accordance with IWA-4000.

Paragraph 3200(b) Supplemental Examinations of Code Case N-729-6 states:

(b) The supplemental examination performed to satisfy -3142.2 shall include volumetric examination of the nozzle tube and surface examination of the partial-penetration weld, or surface examination of the nozzle tube inside surface, the partial penetration weld, and nozzle tube outside surface below the weld. In accordance with Fig. 2, or the alternative examination area or volume shall be analyzed to be acceptable in accordance with Mandatory Appendix I.

The supplemental examinations shall be used to determine the extent of the unacceptable conditions and the need for corrective measures, analytical evaluation, or repair/ replacement activity. *

4. Reason for Request

Indiana Michigan Power Company (l&M), the licensee for CNP Unit 2, is requesting approval of an alternative to the specified requirements of ASME Code Case N-729-6, Paragraph -3142.2 pursuant to 10 CFR 50.55a(z)(2), as the provisions that require a supplemental examination represent a hardship or unusual difficulty without a compensating increase in the level of quality and safety.

l&M performed the VE of the RVCH nozzle penetrations in the as-found condition during the current Unit 2 refueling outage (U2C26) in accordance with ASME Code Case N-729-6, Table 1. During the examination, compressed air was used to remove lightly adhered accumulated residues and discoloration. Residues and discoloration that remained were determined to be relevant conditions in the as-found state. Fifteen (15) penetrations were determined to have relevant conditions pursuant to Code Case N-729-6, Paragraph -3141(c). Representative photographs of the relevant conditions can be found in Attachment 2 to this enclosure. Specifically, Nozzles 30, 35, 37, 38, 41, 43, 44, 52, 54, 55, 61, 66, 67, 69, and 74 (Figure 1 at the end of this enclosure). For the purpose of this examination, the term accumulated residues is used by the l&M qualified inspector to denote any buildup of materials that reside within the annular region of the nozzle that may inhibit the final to AEP-NRC-2021-35 Page 4 determination for the absence of leakage. The material is not limited to boric acid and may be small pieces of insulation or any other type of material that will inhibit the clear view of the annular area surrounding the nozzle.

The l&M qualified examiner concluded that the relevant conditions did not have active leakage characteristics because the pattern of residue on the nozzles was not consistent with the traditional patterns seen in Control Rod Drive Mechanism (CROM) nozzle leaks based on Reference 7.

Samples from the relevant conditions were obtained in an attempt to better categorize the source.

The deposits on the Unit 2 RVCH were too small to provide enough material for chemical analysis to be performed.

A review of previous inspection results noted limited staining and debris but no evidence of degradation or active leakage. The previous inspection was performed prior to the issuance of Regulatory Issue Summary (RIS) 2018-06 (Reference 2), and the noted conditions were able to be dispositioned by engineering as acceptable. The as-found condition of the Unit 2 RVCH in U2C26 is similar to the condition identified during the previous inspection. The discoloration is understood to be caused by previous outage worker practices related to head vent piping removal and TECSA seal leakage. The associated cleanup of the previous leakage is identified as the cause of the relevant conditions categorized as discoloration in U2C26. The accumulated residue is believed to be from maintenance activities and the ventilation system.

The relevant conditions on the 15 specific nozzles in the scope of this relief request require consideration, per RIS 2018-06, that some or all of the relevant conditions possibly came from the nozzles. Code Case N-729-6, Paragraph -3142.2, requires that nozzles with relevant conditions undergo supplemental examinations consisting of a volumetric examination of the nozzle tube and surface examination of the partial-penetration weld or surface examination of the nozzle tube inside surface, the partial-penetration weld, and nozzle tube outside surface below the weld, in accordance with Paragraph -3200(b ).

CO2 cleaning and subsequent bare metal visual (BMV) examination were completed, and all relevant conditions were removed. No degradation was noted by the BMV examination. Photographs of the as left condition are contained in Attachment 3 to this enclosure. The CO2 cleaning returns the unit to service with a clean reactor head that will support implementation of an effective visual examination during the next outage which, as discussed below, is the alternative proposed in support of this relief request. Removing all accumulated residues and discoloration also precludes RVCH degradation during the next operating cycle.

While these actions are insufficient to absolutely determine that the nozzles are free from reactor coolant pressure boundary leakage, they support a conclusion that no significant degradation of the RVCH is currently occurring.

5. Proposed Alternative and Basis for Use

10 CFR 50.55a(z)(2) requires demonstrating that compliance with the specified requirements represent a hardship or unusual difficulty without a compensating increase in the level of quality and safety. This section discusses the identified hardship, proposed alternative, and supporting basis that shows the supplemental volumetric examination provides a hardship without a compensating increase in quality and safety.

to AEP-NRC-2021-35 Page 5 Identified Hardship per 10 CFR 50.55a(z)(2)

In order to perform the supplemental volumetric and surface examinations required in Code Case N-729-6, Paragraph -3200(b ), it would be necessary to mobilize equipment and approximately 18 qualified personnel to the site on an emergent basis. The supplemental volumetric examinations require access to the underside of the highly contaminated RVCH which would expose personnel to elevated dose rates not previously planned for this refueling outage. The additional dose for this work described above is estimated to be approximately 3.0 Rem.

The mobilization of personnel and the completion of the required supplemental examinations would increase the risk of COVID-19 infection. Performing the examinations requires relatively large number of individuals to be put into an undesirable situation due to the current COVID-19 Public Health Emergency. l&M continues to implement extensive measures in the current U2C26 outage to limit the number of individuals inside the protected area to prevent the spread of COVID-19. All non-essential work was deferred to reduce the number of required interactions between l&M and contract employees. l&M has mandated remote work locations and strict mask and social distancing policies, and has also minimized the number of contractors supporting the outage. Adding an additional 18 supplemental workers and the necessary l&M oversight would increase the risk of spreading COVID-19 due to increased time on site and close working conditions required for performing examinations.

Additionally, all remaining outage activities associated with reactor assembly and startup would be delayed. This would require retention of l&M and contract employees, thus extending the potential risk of COVID-19 infection.

For these reasons, the supplemental examinations represent a hardship or unusual difficulty, pursuant to 10 CFR 50.55a(z)(2).

Proposed Alternative As an alternative to performing supplemental examinations required by Paragraph -3142.2, l&M proposes performing the Code Case required BMV examination of the CNP Unit 2 RVCH in the next refueling outage (U2C27) in accordance with the latest revision of Code Case N-729 endorsed in 10 CFR 50.55a. The examination will be conducted in accordance with Paragraph-3140, and the results will be evaluated in accordance with Paragraph -3142. l&M considers this to be a regulatory commitment (See Enclosure 2 of this letter). As discussed above, l&M performed CO2 cleaning of the RVCH head and a post-cleaning BMV examination (see Attachment 3 to this enclosure). The examination did not reveal any RVCH degradation or further relevant conditions. These actions in conjunction with the corrective actions discussed below are intended to provide a high level of confidence that l&M will have the necessary baseline conditions to support performing effective visual examinations proposed in this alternative.

Basis for Use and Limited Increase in Quality and Safety The items listed below provide the information l&M used to conclude that the relevant conditions are likely not indicative of RVCH leakage. The volumetric examination would confirm l&M's conclusion that the identified conditions are not nozzle leakage. However, in the unlikely event that a nozzle leak exists or develops, the proposed alternative, the evaluation of the structural integrity of the replacement PWSCC resistant RVCH, and the CNP leakage detection program serve as a basis for concluding that nozzle leaks occurring during the next operating cycle would be detected prior to developing into a safety concern.

to AEP-NRC-2021-35 Page 6 In Reference 4, l&M identified Thermal Couple Sealing Assembly (TECSA) seal leakage and reactor head vent disassembly practices as the source of leakage onto the RVCH (Unit 1 Inspection - Fall 2020). Based on a review of the previous BMV and comparison of the previous staining and current discoloration, the reactor head vent disassembly practices are suspected to have contributed to the U2C26 relevant conditions. l&M has taken corrective action to prevent reoccurrence of any likely sources of leakage from contacting the RVCH in the future. Additionally, l&M identified accumulated residues in the annulus region which are obscuring the ability to fully examine the weld. This accumulated debris is not indicative of nozzle leakage. Based on this, the supplemental volumetric examination does not provide a compensating increase in quality or safety. Each item mentioned above is discussed in detail.

• Review of the previous examination shows absence of degradation on the RVCH The penetration nozzles on the Unit 2 RVCH were examined in refueling outage U2C23 (Fall 2016), consistent with Code Case N-729-1. The as-found condition of the Unit 2 RVCH in U2C26 is similar to the condition identified during the previous inspection. Although the current guidance requires identification of more relevant conditions, the previous examinations showed similar levels of debris and discoloration. There were no relevant conditions identified in the U2C23 inspection; however, staining and debris were noted and required engineering disposition. A review of the previous examinations also showed no evidence that would be indicative of a through wall leak or a degraded condition.

For the U2C26 inspection, Code Case N-729-6 and the supplemental guidance in RIS 2018-06 were used to determine if the identified discoloration and accumulated residues represent relevant conditions. RIS 2018-06, which has provided clarification as to expectations for classifying relevant conditions, was not yet issued to the industry at the time of the U2C23 inspection. Based on the guidance in RIS 2018-06, the noted relevant conditions that could not be removed by light cleaning can no longer be dispositioned regardless of the identified source.

l&M posits that the relevant conditions discovered in U2C26 do not represent a degraded condition of the RVCH. l&M assessed the identified relevant conditions and, for the reasons stated in this relief request, concluded that the relevant conditions are most likely the result of sources other than RVCH penetration leakage. However, using the direction provided in RIS-2018-06, the possibility of RVCH penetration leakage cannot be completely refute~.

• The pattern of accumulated residues is not consistent with RVCH nozzle leaks, and one source causing the relevant indications has been identified.

Each penetration-to-head interface (annulus) is closely scrutinized in accordance with guidance in Reference 7, and a determination is made as to whether there are any boric acid deposits, corrosion, or discoloration on or close to the annulus. Small and newly formed leak paths may result in a minimal amount of boron deposit buildup. An active leak will produce a localized buildup of light-colored boric acid crystals. If leakage has occurred over several outages the deposits can resemble popcorn, stalagmites, or spaghetti. In some cases, the "spaghetti" has even formed into a ball. In general, buildup tends to be seen most frequently on the downhill side of a penetration because the leak runs downhill and the boron is deposited as the water evaporates.

to AEP-NRC-2021-35 Page 7 The characteristics of the identified relevant conditions of discoloration are not consistent with industry examples of deposits from penetration leaks. l&M as-found examination identified several small locations of discoloration in the annulus area of five penetrations (30, 38, 43, 67, and 74). There were also swirling patterns visible on the RVCH surface around and also on the penetrations where discoloration was identified. The swirl patterns are indicative of mopping that was performed during cleanup of previous leakage on the head. In a previous cycle, staining from head vent removal was identified. The subsequent cleanup /

decontamination from the resulting staining is believed to be the cause of the discoloration around several penetrations. l&M has performed corrective actions to prevent further possible leakage onto the RVCH. Additionally, l&M will benchmark the industry to determine best practices for decontamination I cleanup to prevent further staining in the penetration annulus.

l Additionally, there was accumulated residue identified in the annulus region of eleven penetrations (35, 37, 41, 43, 44, 52, 54, 55, 61, 66, and 69). Note that penetration 43 had relevant conditions of both staining and accumulated residues. As previously mentioned, accumulated residue is considered to be any buildup of material on or in the annular region.

Residue of this type was found to cover portions of the head like a tightly-adhering coating or taking the form of loose, granular material mainly on the uphill side of the penetrations and has been observed in previous BMV examinations.

l&M obtained samples of the residue and attempted chemical composition analysis of the deposits. The samples must be approximately1/2 gram to be able to analyze. The residue on the head was so minimal that no penetration contained enough material to be able to perform the chemical analysis. Although a chemical composition was not able to be obtained, l&M does not believe that this accumulated residue is due to nozzle leakage. These 11 penetrations were listed as relevant conditions only because the guidance in RIS 2018-06 directs this action. Therefore, these 11 penetrations were determined to have relevant conditions.

l&M took corrective actions to resolve leakage from two identified sources in response to conditions identified during the last Unit 1 outage. The corrective actions taken for Unit 1 would also be applicable for Unit 2 starting with the current U2C26 outage. Additional corrective action to benchmark the industry decontamination practices to prevent further relevant conditions around the penetration annulus was taken for U2C26. A discussion of the corrective actions to prevent the reoccurrence of the leakage onto the RVCH head is below.

Unit 1 Actions Already Taken o Preclude future TECSA leakage

• In 2018, a new parts vendor was utilized to provide the TECSA components.

l&M identified issues with existing part quality and vendor instruction. These parts were used for U2C26 outage.

• Beginning in U1C29, the methodology for the TECSA inspection was changed to allow for performing the TECSA inspections when the RVCH is removed and on the stand. This allows greater access during the inspection and cleaning of the seating surfaces. Following implementation of this new inspection method leakage was not observed in the subsequent startup. These practices were used for the U2C26 outage.

to AEP-NRC-2021-35 Page 8 Following the U 1C30 outage, l&M also initiated a corrective action to determine why the continuing TECSA leakage was not corrected earlier. This action is also applicable to Unit 2.

o Preclude leakage due to outage worker practices Following the U1 C30 outage, l&M initiated a corrective action to provide training to eliminate worker practices that lead to vent water inadvertently contacting the head. These worker practices were used during the current U2C26 outage.

o If leakage is observed, the following additional actions will be taken l&M monitors the TECSA seal locations, as well as the RVCH, during start-up with specific targeted walk downs performed at 300#, 1000#, and Normal Operating Pressure and Normal Operating Temperature. During these walk downs personnel verify no leakage, record any observed leakage (including locations and quantity), obtain photos of the leakage, if possible, and report leakage to the Outage Command Center and Operations. These conditions will also be documented in the Corrective Action Program.

If environmental conditions permit, l&M personnel will clean accessible boric acid deposits identified during the specified walk downs utilizing wetted lint-free cloths.

Corrective Actions Initiated for U2C26 o l&M initiated a corrective action to benchmark the industry to determine best practices for cleanup / decontamination on the head. This is intended to eliminate the staining on the 5 identified penetrations.

o l&M believes that the accumulated debris on the head could not be easily removed with light cleaning due to extended time on the head combined with previous leakage and decontamination / cleaning practices. The debris found on the RVCH during inspection activities has been removed by CO2 cleaning .

• RVCH Structural Integrity l&M replaced the Unit 2 RVCH in 2007. The replacement RVCH is constructed with PWSCC resistant materials with an outer surface of SA-508 Grade 3 manganese molybdenum low alloy steel. The CROM and in-core instrumentation (ICI) nozzles are Alloy 690. Evaluations were performed and documented in MRP-375 (Reference 3) to demonstrate the acceptability of extending the inspection intervals for ASME Code Case N-729-1, item B4.40 components.

Based on plant service experience, factor of improvement (FOi) studies using laboratory data, deterministic study results, and probabilistic study results, MRP-375 supported extended inspection intervals. This information documents the structural suitability of the RVCH for extended periods of time.

Per MRP-375, much of the laboratory data indicated an FOi of 100 for Alloy 690/52/152 versus Alloy 600/182/82 (for equivalent temperature and stress conditions) in terms of crack growth to AEP-NRC-2021-35 Page 9 rates. In addition, laboratory and plant data demonstrate an FOi in excess of 20 in terms of the time to PWSCC initiation. This reduced susceptibility to PWSCC initiation and growth supports elimination of all volumetric examinations throughout the plant service period, and by extension, supports not performing volumetric examinations during U2C26.

Deterministic calculations demonstrate that the alternative volumetric re-examination schedule is sufficient to detect any PWSCC before it could develop into a safety significant circumferential flaw that approaches the large size (i.e., more than 300 degrees of circumferential extent) necessary to produce a nozzle ejection. The deterministic calculations also demonstrate that any base metal PWSCC would likely be detected prior to a through-wall flaw occurring. Probabilistic calculations based on a Monte Carlo simulation model of the PWSCC process, including PWSCC initiation, crack growth, and flaw detection via ultrasonic testing, show a substantially reduced effect on nuclear safety compared to a RVCH with Alloy 600 nozzles examined per current requirements.

As documented in MRP-375, the resistance of Alloy 690 and corresponding weld metals Alloy 52 and 152 is demonstrated by the lack of PWSCC indications reported in these materials, in up to 24 consecutive years of service for thousands of Alloy 690 steam generator tubes, and more than 22 consecutive years of service for thick-wall and thin-wall Alloy 690 applications.

This operating experience includes service at pressurizer and hot-leg temperatures higher than those on the RCS.

Based on the above information, the RVCH nozzles and attachment welds are less susceptible to the initiation and growth of PWSCC flaws. Due to reduced susceptibility of Alloy 690 and low growth rates of PWSCC, MRP-375 provides reasonable assurance of the low probability of current nozzle leaks and that the structural integrity of the RVCH nozzles will be maintained over the next operating cycle.

Additionally, following CO2 cleaning, l&M performed a BMV examination. The BMV showed that no significant degradation exists on the RVCH. The proposed alternative to perform a BMV examination of the RVCH in accordance with the current version of Code Case N-729 during the next refueling outage will enable either confirmation that no leakage from the reactor vessel pressure boundary is occurring or will identify any possible leakage before it could challenge the structural integrity of the RVCH. Corrective actions taken to control any future leakage from the seals and the vent pipe are expected to minimize potential degradation during the next cycle of operation.

• The CNP Technical Specifications (TS) require monitoring of operational leakage CNP leakage detection program serves two distinct purposes related to this relief request.

The first purpose is to support the conclusion that a RVCH nozzle leak does not currently exist. The operational leakage for CNP was reviewed for the previous 15 months. The unidentified leakage over this entire period was between O and 0.051 gpm. There was no increase in RCS leakage that would be indicative of a through wall leak of the RVCH nozzles.

Second, the CNP leakage detection program would detect increases in operational leakage consistent with the formation of nozzle leaks during the cycle. Increased operational leakage would be identified and addressed prior to challenging the structural integrity of the RVCH.

CNP has operational RCS leakage requirements established in TS 3.4.13. The Pressurized Water Reactor Owners Group developed WCAP-16465-NP (Reference 6) to provide to AEP-NRC-2021-35 Page 10 standardized action levels and response guidelines that address increasing unidentified RCS leakage less than TS limits. CNP has adopted these industry standard administrative requirements which create three tiered action levels. Each tier is described in detail below.

Tier 1 Action Level

1. One seven (7) day rolling average of daily Unidentified RCS leak rate greater than or equal to (0.1) gpm.

2. Nine (9) consecutive daily Unidentified RCS leak rates greater than baseline mean (µ).

Tier One Action Guidelines if any Tier One Action Level is exceeded,

• Confirm dates, times and data.

• Evaluate trend of affected parameter (Pzr Level, VCT Level, Tave, and Pzr Pressure).

• Evaluate trend of associated Tier One triggers.

• Run confirmatory leak rate calculation with different times (Confirmatory leak rate calculation cannot overlap the initial calculation).

• Check for abnormal trends for other leakage indicators (Containment Radiation Monitors, Dew Point, and Containment Sump Level).

If initial indication is confirmed, then perform the following:

• Increase frequency of leakage testing.

• Perform increased frequency sampling

• Initiate an Action.

Tier 2 Action Level

1. Two (2) consecutive daily Unidentified RCS leak rates greater than or equal to (0.15) gpm.

2. Two (2) of three (3) consecutive daily Unidentified RCS leak rates greater than or equal to

(µ+2o).

Tier Two Action Guidelines if any Tier Two Action Level is exceeded,

• Perform Tier One response.

• Commence a leak investigation:

o Review recent plant evolutions to determine any "suspect" source(s).

o Evaluate changes in other leakage detection indications.

o Initiate outside containment walk-downs of the chemical and volume control system (CVCS), safety injection (SI), and residual heat removal (RHR) systems.

• Identify the source of the increase in leakage:

o Check any components or flow paths recently changed or placed in service, shutdown, vented, drained, filled, etc.

o Check any maintenance activity that may have resulted in decreasing or increasing leakage.

o Check any filters recently alternated or changed. Inspect filter housing for gasket leakage. Check seal injection filters and reactor coolant filter for signs of leakage.

to AEP-NRC-2021-35 Page 11 Tier 3 Action Level

1. One (1) daily Unidentified RCS leak rate greater than or equal to (0.3) gpm.

2. One (1) daily Unidentified RCS leak rate greater than or equal to (µ+3cr).

Tier Three Action Guidelines if any Tier Three Action Level is exceeded,

• Perform Tier One and Tier Two responses.

• If the increased leak rate is indicated inside containment, then perform the following:

o Begin planning for a containment entry while carrying out other actions. Obtain proper approval for containment entry.

o Obtain samples from the Containment Sump, Reactor Cavity and Pipe Tunnel (annulus) sumps (during respective pump out) and analyze for activity, a larger than expected boric acid concentration and other unexpected chemicals.

o Evaluate other systems for indications of leakage (Component Cooling Water, Service Water, etc.).

o Obtain a containment atmosphere sample for indications of RCS leakage.

o Sample Containment Ventilation condensate for activity.

• Identify source of the leak.

• Quantify the leakage.

• Initiate plan to correct the leak.

• Monitor containment airborne radiation levels as well as area radiation monitors. Sample the containment atmosphere for indications of RCS leakage.

• Monitor other containment parameters (temperature, pressure, dew point, etc.).

• If the leak source is found and isolated or stopped, then re-perform RCS leak rate calculation.

Summary Based on RIS 2018-06, leakage from the RVCH penetrations cannot be excluded. Evaluation of the as-found condition of the RVCH supports the conclusion that it is unlikely that the identified relevant conditions are the result of RVCH penetration leakage. However, the assessments that have been performed, including evaluation of the form and location of the discoloration and accumulated residues, support the conclusion that the identified conditions are most likely the result of decontaminating I cleaning of the RVCH and accumulation of residues that obscure examination of portions of the penetration annular areas.

CO2 cleaning of the RVCH has been performed in order to remove existing relevant conditions.

Corrective actions have been taken to eliminate or mitigate any possible leakage from the seals and vent piping. Additional corrective action for Unit 2 is being taken to improve decontamination practices. These actions will provide a baseline for performing visual examinations in the next outage.

The substantial margins in structural integrity for the RVCH penetrations and shell provide a high level of confidence that CNP Unit 2 can be operated safely through the next cycle of operation. The above evaluations and proposed alternative visual examination, during the next outage, provide a high level of confidence in continued integrity of the RVCH. The additional personnel exposure and risks to staff from COVID-19 associated with performing additional volumetric and surface examinations represent a hardship without a compensating increase in the level of quality and safety.

to AEP-NRC-2021-35 Page 12

6. Duration of Proposed Alternative

The proposed alternative will be utilized until the end of refueling outage U2C27.

7. Precedent This request is comparable to that submitted for the CNP U1C30 outage (Reference 4), approved by the NRC via Reference 5.

Similar to U1C30, l&M is requesting relief from the specified requirements of Code Case N-729-6, Paragraph -3142.2, pursuant to 10 CFR 50.55a(z)(2) due to relevant conditions on the RVCH identified during inspections for U2C26. CNP evaluated the RVCH from both Unit 1 and Unit 2 and determined that the indications are most likely from sources other than a nozzle leak. Both CNP Units 1 and 2 have replacement heads constructed from PWSCC resistant Alloy 690 materials. l&M utilized the same process that was used on Unit 1 to determine that the suspected source of the leakage is not RVCH nozzle leakage. l&M is proposing the same Code Case alternative that was accepted for CNP U1 C30.

8. References

1. ASME Boiler and Pressure Vessel Code Case N-729-6, "Alternative Examination Requirements for PWR Reactor Vessel Upper Heads With Nozzles Having Pressure-Retaining Partial-Penetration WeldsSection XI, Division 1," March 2016.

2. NRC Regulatory Issue Summary (RIS) 2018-06, "Clarification of the Requirement for Reactor Pressure Vessel Upper Head Bare Metal Visual Examinations," December 10, 2018 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML18178A137).

3. MRP-375, "Material Reliability Program: Technical Basis for Reexamination Interval for Alloy 690 PWR Reactor Vessel Top Head Penetration Nozzles," February 2014.

4. Indiana Michigan Power Company letter, "Request for Relief related to American Society of Mechanical Engineers (ASME) Code Case N-729-6 Supplemental Examination Requirements, ISIR-5-04," October 5, 2020 (ADAMS Accession No. ML20279A713).

5. NRC Letter to Indiana Michigan Power, "Donald C. Cook Nuclear Plant , Unit 1 - Relief Request ISIR-5-04 Related to ASME Code Case N-729-6 Supplemental Examination Requirements of Reactor Vessel Closure Head Penetration Nozzles (EPID L-2020-LLR-0133

[COVID-19))," February 12, 2021 (ADAMS Accession No. ML21034A155).

6. WCAP-16465-NP, "Pressurized Water Reactor Owners Group Standard RCS Leakage Action Levels and Response Guidelines for Pressurized Water Reactors," Revision 0, September 2006.

7. Boric Acid Corrosion Guidebook, "Managing Boric Acid Corrosion Issues at PWR Power Stations," Revision 2, July 2012.

to AEP-NRC-2021-35 Page 13 Figure 1:

Reactor Vessel Closure Head Penetrations with Identified Conditions 210*

I I

oo*

U2 REACTOR VESSEL CLOSURE HEAD

Attachment 1 to Enclosure 1 to AEP-NRC-2021-35 Relevant Condition Discussion GENERAL (Reference I & M Drawing DC-13745 at the end of this attachment)

The 15 relevant conditions reported during the as-found Visual Examination of the RVCH were characterized as either accumulated residues and/or discoloration.

Eleven ( 11) penetrations had accumulated residues identified as a relevant condition. The penetrations with accumulated residues as a relevant condition are located around the RVCH perimeter near the periphery. For the purpose of this examination, the term accumulated residues, is used by the l&M qualified inspector to denote any buildup of materials that reside within the annular region of the nozzle that may inhibit the final determination for the absence of leakage. The material is not limited to Boric Acid, it may be small pieces of insulation or any other type of material that will inhibit the clear view of the annular area surrounding the nozzle.

These accumulated residues have been observed on the past two bare metal Visual Examinations as well, with the comment sections documenting that there were minor amounts of dust and debris on all surfaces of the RVCH. This debris has been noted to be accumulating on the RVCH for multiple years, as far back as the Visual Examination performed in 2012. The dust and debris blew onto the head via the ventilation system with no discernible pattern, as seen in the referenced drawing showing the location of the relevant conditions, and when the debris landed, it predominantly accumulated at the uphill (highest point) of the associated penetrations. All of the accumulated residues were removed via carbon dioxide cleaning with no relevant conditions identified after cleaning. These 11 penetrations were listed as relevant conditions because they were found in the annulus. Based on the guidance in RIS 2018-06, this accumulated residue could potentially mask nozzle leakage.

Five (5) penetrations had discoloration as a relevant condition. One (1) penetration had both accumulated residues and discoloration as relevant conditions. The five penetrations with discoloration as a relevant condition are grouped together in roughly one quadrant of the RVCH from 270 degree(°) to 0°. Four (4) of the five (5) are adjacent to each other, and the fifth is one penetration away from the four (4) others. Like the penetrations with accumulated residues, penetrations with discoloration are located around the RVCH perimeter near the periphery.

From previous Visual Examinations, staining originating from reactor head activities was identified at penetration 55. A faint streak dripped down the side of the CROM at penetration 55 causing the staining on the RVCH. Four (4) of the penetrations with discoloration are grouped around penetration 55 with the other penetration having discoloration located nearby. All of these spots of discoloration appear to be consistent with decontamination activities performed on the RVCH for the staining.

During RVCH decontamination, wet mop heads are utilized to clean the area, cleaning around the penetration, and in the process of reaching around penetration 55, it is likely that the boric acid that had stained the RVCH went into solution with the demineralized water used for decontamination and caused discoloration around the various penetrations. All of the discoloration was successfully removed via carbon dioxide cleaning with no relevant conditions identified after cleaning and no degradation noted around these penetrations.

to Enclosure 1 to AEP-NRC-2021-35 Page 2 PENETRATION 30 Relevant Condition - Discoloration RVCH Location - - Azimuth 280° The discoloration at this penetration is predominantly located at the go 0 azimuth of the penetration, oriented in the same general direction of penetration 55.

PENETRATION 35 Relevant Condition - Accumulated residues RVCH Location - - Azimuth 170° After light cleaning with air, some of the accumulated residue remained and masked portions of the nozzle annulus from further examination.

PENETRATION 37 Relevant Condition - Accumulated residues RVCH Location - - Azimuth 260° After light cleaning with air, some of the accumulated residue remained and masked portions of the nozzle annulus from further examination.

PENETRATION 38 Relevant Condition - Discoloration RVCH Location - -Azimuth 315° The discoloration at this penetration is predominantly located at the 45° azimuth of the penetration, oriented in the same general direction of penetration 55.

PENETRATION 41 Relevant Condition - Accumulated residues RVCH Location - -Azimuth 225° After light cleaning with air, some of the accumulated residue remained and masked portions of the nozzle annulus from further examination.

PENETRATION 43 Relevant Condition - Discoloration and Accumulated residues RVCH Location - - Azimuth 335° After light cleaning with air, some of the accumulated residue remained and masked portions of the nozzle annulus from further examination. The discoloration at this penetration is predominantly located at the 45° azimuth of the penetration, oriented in the same general direction of penetration 55.

PENETRATION 44 Relevant Condition - Accumulated residues RVCH Location - - Azimuth 35° After light cleaning with air, some of the accumulated residue remained and masked portions of the nozzle annulus from further examination.

PENETRATION 52 Relevant Condition - Accumulated residues RVCH Location - - Azimuth go 0 After light cleaning with air, some of the accumulated residue remained and masked portions of the nozzle annulus from further examination.

to Enclosure 1 to AEP-NRC-2021-35 Page 3 PENETRATION 54 Relevant Condition - Accumulated residues RVCH Location - - Azimuth 290° After light cleaning with air, some of the accumulated residue remained and masked portions of the nozzle annulus from further examination.

PENETRATION 55 Relevant Condition - Accumulated residues RVCH Location - - Azimuth 345° After light cleaning with air, some of the accumulated residue remained and masked portions of the nozzle annulus from further examination.

PENETRATION 61 Relevant Condition - Accumulated residues RVCH Location - - Azimuth 250° After light cleaning with air, some of the accumulated residue remained and masked portions of the nozzle annulus from further examination.

PENETRATION 66 Relevant Condition - Accumulated residues RVCH Location - - Azimuth 295° After light cleaning with air, some of the accumulated residue remained and masked portions of the nozzle annulus from further examination.

PENETRATION 67 Relevant Condition - Discoloration RVCH Location - -Azimuth 334° The discoloration at this penetration is predominantly located at the 45° azimuth of the penetration .

PENETRATION 69 Relevant Condition - Accumulated residues RVCH Location - - Azimuth 65° After light cleaning with air, some of the accumulated residue remained and masked portions of the nozzle annulus from further examination.

PENETRATION 74 Relevant Condition - Discoloration RVCH Location - - Azimuth 339° The discoloration at this penetration is predominantly located at the 45° azimuth of the penetration.

to Enclosure 1 to AEP-NRC-2021-35 Page4 Excer t from DC-137 45:

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Attachment 2 to Enclosure 1 to AEP-NRC-2021-35 Supporting Reactor Vessel Closure Head (RVCH) As Found Inspection Photographs The photos described as "as found" are taken after cleaning with compressed air.

to Enclosure 1 to AEP-NRC-2021-35 Page2 to Enclosure 1 to AEP-NRC-2021-35 Page 3 to Enclosure 1 to AEP-NRC-2021-35 Page4 to Enclosure 1 to AEP-NRC-2021-35 Page 5 to Enclosure 1 to AEP-NRC-2021-35 Page 6 to Enclosure 1 to AEP-NRC-2021-35 Page 7 to Enclosure 1 to AEP-NRC-2021-35 Page 8 Attachment 3 to Enclosure 1 to AEP-NRC-2021-35 Supporting Reactor Vessel Closure Head (RVCH) As Left Inspection Photographs to Enclosure 1 to AEP-NRC-2021-35 Page 2 to Enclosure 1 to AEP-NRC-2021-35 Page 3 to Enclosure 1 to AEP-NRC-2021-35 Page4 to Enclosure 1 to AEP-NRC-2021-35 Page 5 to Enclosure 1 to AEP-NRC-2021-35 Page 6 to Enclosure 1 to AEP-NRC-2021-35 Page 7 to Enclosure 1 to AEP-NRC-2021-35 Page 8 Enclosure 2 to AEP-NRC-2021-35 Regulatory Commitment for Reactor Vessel Closure Head (RVCH) Inspection REGULATORY COMMITMENT The following table identifies an action committed to by Indiana Michigan Power Company (l&M) in this document. Any other actions discussed in this submittal represent intended or planned actions by l&M. They are described to the U. S. Nuclear Regulatory Commission (NRC) for the NRC's information and are not regulatory commitments. All commitments discussed in this table are one-time commitments.

Commitment Scheduled Completion Date (if applicable):

l&M will perform a bare metal visual (BMV) inspection of the CNP Unit 2 Cycle 27 Refueling Unit 2 RVCH in the next refueling outage in accordance with the outage latest revision of Code Case N-729 endorsed in 10 CFR 50.55a.

This commitment is related to the D.C. Cook (CNP) Unit 2 relief request ISIR-5-05.