donald c. cook nuclear plant, unit 1 form oar-1, owner's

,An/Ul'Cotrµny

BOUNDLESS ENERGY-

January 14, 2021

Docket No.: 50-315

U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D.C. 20555-0001

Donald C. Cook Nuclear Plant Unit 1 Form OAR-1, Owner's Activity Report

lndlana Michigan Power Cook Nuclear Plant

One Cook Place Bndgman, Ml 49106

1nd1Br1am!Ch1Qfillpower com

AEP-NRC-2021-01 10 CFR 50.55a

Enclosure 1 to this letter provides, from Indiana Michigan Power, the licensee for Donald C. Cook Nuclear Plant (CNP) Unit 1, a copy of Form OAR-1, Owner's Activity Report, for lnservice Inspection activities performed at CNP Unit 1 through the completion of the Unit 1 Cycle 30 Refueling Outage. This report meets the requirements of the American Society of Mechanical Engineers (ASME) Code Case N-532-5, "Repair/Replacement Activity Documentation Requirements and lnservice Inspection Summary Report Preparation and Submission Section XI, Division 1." This code case is used as an alternative to the requirements of the ASME Boiler and Pressure Vessel Code, Section XI, Article IWA-6000, as specified in Regulatory Guide 1.147, "lnservice Inspection Code Case Acceptability, ASME Section XI, Division 1," Revision 19, for the current inspection interval.

The Authorized Code Inspection Company is OneCIS Insurance Co., of Lynn, Massachusetts. The Authorized Nuclear lnservice Inspector is Howard M. Burkhart, Jr.

This letter also provides, as Enclosure 2, a copy of the analytical evaluation of relevant conditions identified during the Unit 1 Cycle 30 Refueling Outage as required by ASME Boiler and Pressure Vessel Code, Section XI, Subparagraph IWB-3144(b).

There are no new or revised commitments in this letter. Should you have any questions, please contact Mr. Michael K. Scarpello, Regulatory Affairs Director, at (269) 466-2649.

rnff-Michael K. Scarpello Director of Regulatory Affairs

MBE/mll

U. S. Nuclear Regulatory Commission

Enclosures:

AEP-NRC-2021-01

1. Form OAR-1, Owner's Activity Report for Donald C. Cook Nuclear Plant Unit 1 Cycle 30 Refueling Outage

2. Evaluation of Relevant Conditions found during Bottom-Mounted Instrument Examination

c: R. J. Ancona - MPSC EGLE - RMD/RPS J. B. Giessner - NRC Region Ill D. L. Hille - AEP Ft. Wayne NRC Resident Inspector R. M. Sistevaris - AEP Ft. Wayne S. P. Wall - NRC, Washington D.C. A. J. Williamson - AEP Ft. Wayne

Enclosure 1 to AEP-NRC-2021-01

Fonn OAR-1, Owner's Activity Report for Donald C. Cook Nuclear Plant Unit 1 Cycle 30 Refueling Outage

D. C. Cook Nuclear Unit 1 FORM OAR-1 OWNER'S ACTIVITY REPORT

Report Number

Plant

UnrtNo

1-2020-5-1-01

Donald C Cook Nuclear Plant, One Cook Place, Bndgman, M1ch1gan 49106

Commeroal service date 8/23/1975 Refueling outage no

(~ appltcablo)

Current Inspecilon interval 5th for Components and Supports (C&s) and 3rd for Containment ISi (GISI} Program (1st, 2nd, 3rd, 4th, other)

Current inspection period 1st for C&s and 1st for GISI (1st, 2nd, 3rd)

Edition and Addenda of Section Xl applicable to the inspection plans 2013 Ed1tJon/No Addenda

Date and revision of inspection plans 10/512020 Rev 1 for C&s, 3/1/2020 Revision O for GISI

Edition and Addenda of Section Xl applicable to repair/replacement activities, rf different than the inspection plans

EdrtJon and Addenda are the same as the Inspection Pf ans

Code Cases used for Inspection and evaluation N-722-1 and N-729-6 for C&S

(f •ppltcable, nc!udllg cases mod<fled by Case N-532 and later rovm,o~)

CERTIFICATE OF CONFORMANCE

I certJfy that (a) the statements made In this report are correct, (b) the examinations and tests meet the Inspection Plan as required by the

ASME Code, Section XI, and (c) the repair/replacement actlVltJes and evaluations supporting the completion of U1C30

U1C30

conform to the requirements of Section Xl (refuelrlg outage number)

Signed _l_J____:~:;____::~~-=---~---'.c....,_--_,_6,..;._~_'--__ .:....:•IS=l...:....P:...:.rog=ra=m"--Own::...;.;.:.;=er-- Date __ (;_2-....1./_2-_1..:.....i....{_2...._o ____ _

°""1efs or Ov.ool'• Dea,gnee, Title

CERTIFICATE OF INSERVICE INSPECTION

I, the undersigned, holding a valid commIssIon issued by the National Board of Boiler and Pressure Vessel Inspectors and

employed by OneCIS Insurance Co of Lynn, MA have inspected the rtems descnbed in this

Owner's Activity Report, and state that, to the best of my knowledge and belief, the 0,t.,ner has performed all actJvrtJes represented by this report in a=rdance with the reqU1rements of Section Xl.

By signing this certmcate neither the Inspector nor his employer makes any warranty, expressed or implied, concerning the repair/replacement actJvTtles and evaluation descnbed In this report Furthermore, netther the Inspector nor his employer shall be liable In any manner for any personal Injury or property damage or loss of any kmd ansIng from or connected with this inspection.

Commissions 9o33 8:t :rs :r N R Naboo•I Board Number and Endorsement

Page 1 of3

D. C. Cook Nuclear Unit 1 Table 1

Items with Flaws or Relevant Conditions That Required Evaluation for Continued Service

Examination Category and Item Number Item Description Evaluation Description

Relevant conditions discovered on the RPV bottom head surfaces and 17 penetrations include 1) staining from cavity seal leakage, 2) boric acid residue, and 3) streaking. Sampling of the boric acid determined the source to be

I refueling water cavity seal leakage, which occurs only when

N-722-1 B15.80 RPV bottom-mounted Instrument penetrations the refueling cavity is filled. The RPV bottom head was detemiined to be acceptable for continued service through analytical evaluation per IWB-3142.4 Acceptance by Analytical Evaluation. Due to legacy issues with respect to cavity seal leakage, visual examination per N-722-1 of the RPV bottom head Is conducted each refueling outage, which meets the requirements outlined in IWB-2420.

Relevant conditions Including corrosion, boric acid deposrts and discoloration were identified at 29 penetrations and on the Reactor Vessel Closure Head (RVCH) surfaces during Visual Examination (VE). After light cleaning, relevant conditions remained at 17 penetrations and on RVCH surfaces. After additional cleaning, no relevant conditions

Nozzles and partial-penetration welds of PWSCC-and no degradation of the RVCH was Identified during the

N-729-6 B4.40 resistant materials In head

as-left VE. The relevant conditions were attributed to spills from refueling operations and leakage from In-core lnstument (ICI) seals and were not Indicative of possible nozzle leakage. Relief was granted from performing the supplemental UT and surface examinations required under ASME Code Case N-72~ (ADAMS Accession Number ML20290A425). A subsequent VE wlll be performed in the next refueling outage per the Code Case.

Page 2 of 3

Code Class

1

3

1

D. C. Cook Nuclear Unit 1 Table 2

Abstract of Repair/Replacement Activities Required for Continued Service

Item Description Descnption of Work Date Completed Repair/Replacement Plan Number

1-Sl-22-00F Category 8-K Item Buff rounded Indications to acceptable s12e 10/6/2020 55537835-17

810 20 Piping Welded Attachment

ESW piping elbow downstream of 1-Replace pipe elbow, fittings, pipe stanchion and dram pipe 9/29/2020 56548573-02

WM0-715 RHR piping elbow on 1-S1-26 Blend pipe Indentations on RHR elbow 10/5/2020 65552243-01

Page 3 of 3

Enclosure 2 to AEP-NRC-2021-01

Evaluation of Relevant Conditions found during Bottom-Mounted Instrument Examination

AR 2020-7659-2, Evaluation of Relevant Conditions Identified during BMI Exam

This condition evaluation was performed in accordance with PMP-7030-CAP-003 Rev. 18 (Conduct of Condition Evaluations). See attached, "CE Form." Peer review completed by Glenn Chatterton, 1/13/2021.

Detailed Description:

Pursuant to procedure EHl-5054-RHI Step 4.2, this condition report Is generated to document that the inspection results from the visual examination (VE) of the Bottom Mounted Instrumentation (BMI)

penetrations did not meet the acceptance criteria of ASME Code Case N-722-1. Per Step 4.3, when the acceptance criteria are not met, then an evaluation is performed in accordance with 10 CFR 50.55a, the applicable ASME Code and the applicable Code Case.

Description of Condition:

The visual examination report documents the visual examination of the Bottom Head Surfaces and BMI penetrations that was completed by qualified examiners per 12-QHP-5050-NDE-027 Rev. 5 under WO 55529757-01 on 9/23/2020. In this visual examination report, the following relevant conditions were identified:

Staining from Cavity Seal leakage o Surfaces o Penetrations (3, 7, 9, 13, 17, 18, 20, 24, 33, 39, 40, 42, 43, 45, 53, 56, 57)

White Boric Acid Residue o Penetrations (13, 53)

White Streaks o Penetration (17)

Assessment/ Analysis:

No screening comments were required to be addressed. The description of condition accurately reflects the condition and, therefore, no additional scope is required.

Visual examination ofthe BMI penetrations is performed per the requirements of Code Case N-722-1 (Additional Examinations for PWR Pressure Retaining Welds in Class 1 Components Fabricated with Alloy 600/82/182 Materials). Table 1 (Item B15.80) of N-722-1 states that the acceptance standard for BMI penetrations is contained In IWB-3522 of ASME B&PV Section XI (2013 Edition).

IWB-3522 states the followlnq:

A component whose visual examination (IWA-5240) detects any of the following relevant conditions shall meet IWB-3142 and IWA-5250 prior to continued service: (a) any through-wall or through-weld, pressure-retaining material leakage from insulated and nonInsulated components; (b) leakage In excess of limits establlshed by the Owner from mechanical connections (such as pipe caps, bolted connections, or compression fittings) or from components provided with leakage limiting devices (such as valve-packing glands or pump seals);


(c) areas of general corrosion of a component resulting from leakage; {d} discoloration or accumulated residues on surfaces of components, insulation, or floor areas that may be evidence of borated water leakage; or (e) leakages or flow test results from buried components in excess of limits established by the Owner.

Based on the visual examination report provided to Engineering, the identified relevant conditions meet the descriptions of items (c) and (d). Therefore, the requirements within IWB-3142 and IWA-5250 shall be met prior to continued service.

IWA-5250, item {b) states:

(b) If boric acid residues are detected on components, the leakage source and the areas of general corrosion shall be located. Components with local areas of general corrosion that reduce the wall thickness by more than 1096 shall be evaluated to determine whether the component may be acceptable for continued service, or whether repair/ replacement activities will be performed.

Based on the visual inspection report, the leakage source (cavity) and areas of general corrosion have been located. Leakage from the refueling cavity is a recurring event for Unit 1, with leakage most recently docun:iented In AR 2019-4591. Because this leakage occurs every outage, photos of the as-left and as-found condition of the bottom of the vessel are taken and compared, verifying the leakage Is from cavity leakage and not masking any leakage during the operating cycle. This cavity leakage Is the cause of the areas of minor surface corrosion and staining. Refer to the evaluation performed per IWB-3142.4 below for info~mation regarding the local areas of general corrosion.

IWB-3142 states:

IWB-3142.1, Acceptance by Visual Examination

(a) A component whose visual examination confirms the absence of the relevant conditions described In the standards of Table IWB-3410-1 shall be acceptable for continued service.

This subparagraph is not applicable because the visual examination report confirms the presence of relevant conditions.

(b) A component whose visual examination detects the relevant conditions described in the standards of Table IWB-3410-1 shall be unacceptable for continued service, unless such components meet the requirements of IWB-3142.2, IWB-3142.3, or IWB-3142.4.

This subparagraph is applicable based on the relevant conditions as documented In the visual examination report. The requirements of IWB-3142.2, IWB-3142.3, or IWB-3142.4 shall be met prior to continued service.

IWB-3142.2, Acceptance by Supplemental Examination

A component containing relevant conditions shall be acceptable for continued service if the results of supplemental examinations (IWB-3200) meet the requirements of /WB-3130.


This subparagraph is not applicable, because Supplemental Examination is not being performed. Supplemental Examination would require the mobilization of specialized equipment and qualified personnel on an emergent basis. This would involve exposing personnel to elevated dose rates while circumventing the extensive measures taken by CNP during U1C30 to limit the number of individuals on site to prevent the spread of COVID-19.

IWB-3142.3, Acceptance by Corrective Measures or Repair/Replacement Activity

A component containing relevant conditions is acceptable for continued service if the relevant conditions are corrected by a repair/ replacement activity or by corrective measures to the extent necessary to meet the acceptance standards of Table IWB-3410-1.

This subparagraph is not applicable because corrective measures and repair/replacement activities are not being performed.

IWB-3142.4, Acceptance by Analytical Evaluation

A component containing relevant conditions is acceptable for continued service if an analytical

evaluation demonstrates the components acceptability. The evaluation analysis and evaluation

acceptance criteria shall be specified by the Owner. A component accepted for continued service based on analytical evaluation shall be subsequently examined in accordance with IWB-2420{b) and IWB-2420{c). If the subsequent IWB-2420{b) and IWB-2420{c) examinations reveal that the relevant conditions remain essentially unchanged, or the changes In the relevant conditions are within the limits predicted by the analytical evaluation, and the design Inputs for the analytical evaluation have not been affected by activities such as power uprates, the existing analytical evaluation may continue to be used, provided it covers the time period until the next examination.

Acceptance Criteria:

The owner specified acceptance criteria for the evaluation of sources of boric acid leakage is any areas of general corrosion that reduce the wall thickness by more than 10%, as specified in IWA-5250, item {b).

Evaluation Method:

To establish the acceptability of the visual examination results, the following items are considered:

1) Source and age of the boric acid residue 2) Worst-case corrosion rate 3) Corrective Actions

1) As previously discussed, the source of the boric acid residue was determined to be from the refueling cavity leakage. This condition has been well-documented in the corrective action program and is a recurring issue for CNP Unit 1.


To determine the age ofthe boric acid residue, a small sample of boric acid was retrieved from Penetration 53. This analysis is documented in AR 2020-7521-3. Due to the small sample size available, it does not meet the requirements to be considered a quantitative analysis (A larger sample was not possible, as the total boric acid residue was not enough to meet the full geometric sample requirements). However, the analysis was sufficient to qualitatively conclude that the boric acid residue is older than one operating cycle (analysis performed on 9/22/2020). This supports that active leakage ls not occurring. This also indicates that the boric acid residue remained from the previous refueling outage and was not sufficiently cleaned when engineering inspected the vessel. This condition has been entered into the corrective action program.

2) According to the EPRI Boric Acid Corrosion Guidebook, Rev. 2, page A-2, "corrosion rates in aerated water at temperatures less than 140°F are acceptably low to not pose a serious problem with leakage of borated water." On page A-3, the corrosion rate reported for aerated borated water at 140°F is 0.015 In/yr.

"Tavg Since Flood Up" displays a graph of the average temperature of the refueling cavrty water. This average temperature is well below 140°F and, thus, is conservatively bounded. Using the corrosion rate of 0.015 in/yr for 16 days of flood-up during U1C30, the maximum amount of corrosion that could be expected is 0.000658 Inches, assuming that corrosion occurred on the vessel.

Additionally, graph "U1C29 RCS Cavity Temp (F)" shows during the entire time the refueling cavity was filled during U1C29 (~54 days). This graph shows that the RCS temperature has remained below 115°F during the time the refueling cavity was filled, with all but the first day at temperatures below 100°F. The temperature will not begin to significantly increase until after the refueling cavity is drained, as shown on 5/3/2019 on the attached graph. Therefore, any water that leaked from the refueling cavity would not be more than 115°F. Conservatively assuming the corrosion rate for 140F water, this corresponds to a maximum amount of corrosion of 0.00222 inches.

From original design drawings, the RPV wall thickness at the bottom head is 5.3125 inches. An evaluation has been performed to determine the total corrosion that could have occurred on the bottom head based on conservative assumptions as to the duration of boric acid deposits related to cavity leakage over the life of the condition. It has been conservatively determined that a maximum of 0.02 inches of corrosion could have occurred. Given this amount of corrosion, this is within the 10% identified/allowed by IWA-5250(b).

Since the leakage is only present when the refueling cavity is filled, there is no potential for any corrosion or degradation to occur during the operating cycle.

3) To reduce the risk of further corrosion or degradation, the bottom head and BM l's were cleaned by Radiation Protection and inspected by Engineering in the tasks below. Completion comments state that cleaning was satisfactory and that there was no apparent boric acid on the lower surface of the vessel or BMI penetrations, only staining from past leakage. The cleaning during U1C30 reduces the risk of masking pressure boundary leakage and discovering boric acid residue when performing the visual inspection in the future. The following WO's tracked these actions:

55529757-03, Engineering Inspection of lower vessel head, pre-cleaning 55529757-16, RP clean bottom of reactor vessel/insulation/floor 55529757-17, Engineering final approval for reactor pit cleaning


55529757-22 Contingency, Engineering and RP walkdown to prepare for pressure washing

55529757-24 Contingency, Engineering and RP post-cleaning walkdown

Per IWB-3142.4, "A component accepted for continued service based on analytical evaluation shall be

subsequently examined in accordance with IWB-2420(b) and IWB-2420(c)."

IWB-2420 states:

(b) If a component is accepted for continued service in accordance with IWB-3132.3 or IWB-3142.4, the areas containing flaws or relevant conditions shall be reexamined during the next three inspection periods listed in the schedule of the Inspection Program of IWB-2400. Alternatively, acoustic emission

may be used to monitor growth of existing flaws in accordance with IWA-2234. For vessel welds, the three successive inspections are not required if the following conditions are met: {1} The flaw is characterized as subsurface in accordance with Figure IWA-3320-2. {2} The weld containing the flaw is acceptable for continued service in accordance with /WB-3600, and

the flaw is demonstrated acceptable for the intended service life of the component.

(c) If the reexaminations required by (b) reveal that the flaws or relevant conditions remain essentially unchanged, or that the flaw growth is within the growth predicted by the analytical evaluatlon, for three successive inspection periods, then the component examination schedule may revert to the original schedule of successive inspections or the inspection interval defined by the analyttcal evaluation, whichever is limiting.

CNP continues to implement actions to identify leak locations and resolve cavity leakage. CNP intends to

continue to perform visual exams each outage until the cavity leakage can be successfully mitigated.

Condition Evaluation Template, Rev. 18

Ila Jm[mn ,,.._, .. --~!lli!llJ AR Number: 2020-7659-2 I Subject: Evaluate Relevant Conditions identified

during BMI exam & .. --- - -

~:,.· ... ,.. I~ ....... ., •• ~- 1••l·••~ - .......... ,

2a. Do the screening comments found in the parent Action identify any specific or additional scope beyond the description of condition? D Yes (document scope impacts in the field below) ~ No (continue to 2b without documenting scope impacts)

No screening comments were required to be addressed. The description of condition accurately reflects the condition and, therefore, no additional scope is required. 2b. Does the description of condition accurately reflect the condition? ~ Yes ( continue to 2c without documenting) D No (document any inaccuracies in the field below)

NIA 2c. Document a basic evaluation of the condition to determine if any corrective actions are needed beyond those already taken. Consider discussing the direct cause of the problem. Detailed Description:

Pursuant to procedure EHl-5054-RHI Step 4.2, this condition report is generated to document that the inspection results from the visual examination (VE) of the Bottom Mounted Instrumentation (BMI) penetrations did not meet the acceptance criteria of ASME Code Case N-722-1. Per Step 4.3, when the acceptance criteria are not met, then an evaluation is performed in accordance with 10 CFR 50.55a, the applicable ASME Code and the applicable Code Case.

Description of Condition:

The visual examination report documents the visual examination of the Bottom Head Surfaces and BMI penetrations that was completed by qualified examiners per 12-QHP-5050-NDE-027 Rev. 5 under WO 55529757-01 on 9/23/2020. In this visual examination report, the following relevant conditions were identified:

- Staining from Cavity Seal Leakage 0 Surfaces

0 Penetrations (3, 7, 9, 13, 17, 18, 20, 24, 33, 39, 40, 42, 43, 45, 53, 56, 57)

- White Boric Acid Residue 0 Penetrations (13, 53)

- White Streaks 0 Penetration (17)

Assessment/ Analysis:

No screening comments were required to be addressed. The description of condition accurately reflects the condition and, therefore, no additional scope is required .


Visual examination of the BMI penetrations is performed per the requirements of Code Case N-722-1 (Additional Examinations for PWR Pressure Retaining Welds In Class 1 Components Fabricated with

Alloy 600/82/182 Materials}. Table 1 (Item BlS.80} of N-722-1 states that the acceptance standard for BMI penetrations is contained in IWB-3522 of ASME B&PV Section XI (2013 Edition}.

IWB-3522 states the following:

A component whose visual examination {IWA-5240} detects any of the following relevant conditions shall meet IWB-3142 and IWA-5250 prior to continued service: (a) any through-wall or through-weld, pressure-retaining material leakage from insulated and noninsulated components; (b) leakage in excess of limits established by the Owner from mechanical connections (such as pipe caps, bolted connections, or compression fittings) or from components provided with leakage limiting devices (such as valve-packing glands or pump seals}; (c) areas of general corrosion of a component resulting from leakage; {d) discolor(Jtion or accumulated residues on surfaces of components, insulation, or floor areas that may be evidence of borated water leakage; or (e) leakages or flow test results from buried components in excess of limits established by the Owner.

Based on the visual examination report provided to Engineering, the identified relevant conditions meet

the descriptions of items (c} and (d}. Therefore, the requirements within IWB-3142 and IWA-5250 shall

be met prior to continued service.

IWA-5250, item (b) states:

{b) If boric acid residues are detected on components, the leakage source and the areas of general corrosion shall be located. Components with local areas of general corrosion that reduce the wall thickness by more than 10% shall be evaluated to determine whether the component may be acceptable for continued service, or whether repair/ replacement activities will be performed.

Based on the visual inspection report, the leakage source (cavity) i:lnd areas of general corrosion have

been located. Leakage from the refueling cavity is a recurring event for Unit 1, with leakage most

recently documented in AR 2019-4591. Because this leakage· occurs every outage, photos of the as-left

and as-found condition of the bottom of the vessel are taken and compared, verifying the leakage is

from cavity leakage and not masking any leakage during the operating cycle. This cavity leakage is the

cause of the areas of minor surface corrosion and staining. Refer to the evaluation performed per IWB-

3142.4 below for information regarding the local areas of general corrosion.

IWB-3142 states:

IWB-3142.1, Acceptance by Visual Examination

(a) A component whose visual examination confirms the absence of the relevant conditions described In the standards of Table IWB-3410-1 shall be acceptable for continued service.

This subparagraph is not applicable because the visual examination report confirms the presence of relevant conditions.


(b) A component whose visual examination detects the relevant conditions described in the standards of Table IWB-3410-1 shall be unacceptable for continued service, unless such components meet the requirements of IWB-3142.2, IWB-3142.3, or IWB-3142.4.

This subparagraph is applicable based on the relevant conditions as documented in the visual examination report. The requirements of IWB-3142.2, IWB-3142.3, or IWB-3142.4 shall be met prior to continued service.

IWB-3142.2, Acceptance by Supplemental Examination

A component containing relevant conditions shall be acceptable for continued service if the results of supplemental examinations {IWB-3200} meet the requirements of IWB-3130.

This subparagraph is not applicable, because Supplemental Examination is not being performed. Supplemental Examination would require the mobilization of specialized equipment and qualified personnel on an emergent basis. This would involve exposing personnel to elevated dose rates while circumventing the extensive measures taken by CNP during U1C30 to limit the number of individuals on site to prevent the spread of COVID-19.

IWB-3142.3, Acceptance by Corrective Measures or Repair/Replacement Activity

A component containing relevant conditions is acceptable for continued service if the relevant conditions are corrected by a repair/ replacement activity or by corrective measures to the extent necessary to meet the acceptance standards of Table IWB-3410-1.

This subparagraph is not applicable because corrective measures and repair/replacement activities are not being performed.

IWB-3142.4, Acceptance by Analytical Evaluation

A component containing relevant conditions is acceptable for continued service if an analytical

evaluation demonstrates the components acceptability. The evaluation analysis and evaluation

acceptance criteria shall be specified by the Owner. A component accepted for continued service based on analytical evaluation shall be subsequently examined in accordance with IWB-2420{b) and IWB-2420{c). If the subsequent IWB-2420{b) and IWB-2420{c) examinations reveal that the relevant conditions remain essentially unchanged, or the changes in the relevant conditions are within the limits predicted by the analytical evaluation, and the design Inputs for the analytical evaluation have not been affected by activities such as power uprates, the existing analytical evaluation may continue to be used, provided it covers the time period until the next examination.

Acceptance Criteria:

The owner specified acceptance criteria for the evaluation of sources of boric acid leakage is any areas of general corrosion that reduce the wall thickness by more than 10%, as specified in IWA-5250, item (b).


Evaluation Method:

To establish the acceptability of the visual examination results, the following items·are considered:

1) Source and age of the boric acid residue 2) Worst-case corrosion rate 3) Corrective Actions

1) As previously discussed, the source of the boric acid residue was determined to be from the refueling c.ivity leakage. This condition has been well-documented in the corrective action program and is a recurring issue for CNP Unit 1.

To determine the age of the boric acid residue, a small sample of boric acid was retrieved from Penetration 53 and was analyzed by chemistry department personnel. Due to the small sample size available, it does not meet the requirements to be considered a quantitative analysis. However, the analysis was sufficient to qualitatively conclude that the boric acid residue is older than one operating cycle (analysis performed on 9/22/2020). This supports that active leakage is not occurring. This also indicates that the boric acid residue remained from the previous refueling outage and was not sufficiently cleaned when engineering inspected the vessel. This condition has been entered into the corrective action program.

2) According to the EPRI Boric Acid Corrosion Guidebook, Rev. 2, page A-2, "corrosion rates in aerated water at temperatures less than 140°F are acceptably low to not pose a serious problem with leakage of borated water." On page A-3, the corrosion rate reported for aerated borated water at 140°F is 0.015 in/yr.

The attached graph "Tavg Since Flood Up" displays the average temperature of the refueling cavity water during outage U1C30. This average temperature is well below 140°F and, thus, is conservatively bounded. Using the cor~osion rate of 0.015 in/yr for 16 days of flood-up during U1C30, the maximum amount of corrosion that could be expected is 0.000658 inches, assuming that corrosion occurred oh the vessel.

Additionally, graph "U1C29 RCS Cavity Temp (F)" displays the average temperature of the refueling cavity water during the entire time the refueling cavity was filled in U1C29 (~54 days). This graph shows that the RCS temperature has remained below 115°F during the time the refueling cavity was filled, with all but the first day at temperatures below 100°F. The temperature will not begin to significantly increase until after the refueling cavity is drained, as shown on 5/3/2019 on the attached graph. Therefore, any water that leaked from the refueling cavity would not be more than 115°F. Conservatively assuming the corrosion rate for 140°F water, this corresponds to a maximum amount of corrosion of 0.00222 inches.

From original design drawings, the RPV wall thickness at the bottom head is 5.3125 inches. An evaluation h~s been performed to determine the total corrosion that could have occurred on the bottom head based on conservative assumptions as to the duration of boric acid deposits related to cavity leakage over the life of the condition. It has been conservatively determined that a maximum of 0.02 inches of corrosion could have occurred. This conservatively calculated amount of corrosion is within the 10% allowed by IWA~S250(b) and is therefore acceptable for continued service until the next visual examination.


Since the leakage is only present when the refueling cavity is filled, there is no potential for any corrosion or degradation to occur during the operating cycle.

3) To reduce the risk of further corrosion or degradation, the bottom head and BM l's were cleaned by Radiation Protection and inspected by Engineering in the tasks below. Completion comments state that cleaning was satisfactory and that there was no apparent boric acid on the lower surface of the vessel or BMI penetrations, only staining from past leakage. The cleaning during U1C30 reduces the risk of masking pressure boundary leakage and discovering boric acid residue when performing the visual inspection in the future. The following WO's tracked these actions:

55529757-03, Engineering inspection of lower vessel head, pre-cleaning 55529757-16, RP clean bottom of reactor vessel/insulation/floor 55529757-17, Engineering final approval for reactor pit cleaning 55529757-22 Contingency, Engineering and RP walkdown to prepare for pressure washing 55529757-24 Contingency, Engineering and RP post-cleaning walkdown

Per IWB-3142.4, "A component accepted for continued service based on analytical evaluation shall be subsequently examined in accordance with IWB-2420(b) and IWB-2420(c)."

IWB-2420 states:

(b) If a component is accepted for continued service in accordance with IWB-3132.3 or IWB-3142.4, the areas containing flaws or relevant conditions shall be reexamined during the next three inspection periods listed in the schedule of the Inspection Program of IWB-2400. Alternatively, acoustic emission may be used to monitor growth of existing flaws In accordance with IWA-2234. For vessel welds, the three successive inspections are not required if the following conditions are met: {1} The flaw is characterized as subsurface in accordance with Figure IWA-3320-2. {2} The weld containing the flaw is acceptable for continued service in accordance with IWB-3600, and the flaw is demonstrated acceptable for the intended service life of the component.

(c) If the reexaminations required by (b} reveal that the flaws or relevant conditions remain essentially unchanged, or that the flaw growth is within the growth predicted by the analytical evaluation, for three successive inspection periods, then the component examination schedule may revert to the original schedule of successive inspections or the Inspection interval defined by the analytical evaluation, whichever is limiting.

CNP continues to implement actions to identify cavity leak locations and resolve cavity leakage. CNP intends to continue to perform visual exams each outage until the cavity leakage can be successfully mitigated. 2d. Is the condition evaluation scope to evaluate the potential failure of a critical component?

(Review the Engineering Review Screening tab.) D Yes, a Critical Component failure has occurred (Complete and attach Error!

Reference source not found., Error! Reference source not found.) D Yes, however no Critical Component failure occurred (Include basis below) [><]No


NIA ~ .. -l•Yi:liYiTil

Does the parent Action description of condition and/or screening comments describe how and whether the condition has been or will be corrected/fixed or document how the condition was corrected?

0Yes !ZI No (document new, SMART corrective actions in the fields below)

SMART - Specific , Measurable , Actionable , Reasonable , Timely

No new corrective action assignments are required to be generated as a result of this condition evaluation. As discussed in the attached "AR 2020-7659-2 _CE, " the corrective actions include determining the source/age of the boric acid residue (AR 2020-7521-3), worst-case corrosion

rates, and planned cleaninf? of the bottom head per WO 55529757. Assign.# Resp Group Due Date Action Required

~ ] ia.'••~ IE,C!111-IJlllll ■ lllll

Do the screening comments in the parent action require an extent of condition to be performed OR was the issue a critical component failure?

D Yes (document the extent of condition review and applicable SMART corrective actions below)

!ZI No NIA

Assign.# I Resp Group Due Date Action Required

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donald c. cook nuclear plant, unit 1 form oar-1, owner's

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