ML15223A436

PWROG-15066-NP, Revision 0, Responses to Follow-Up NRC RAI 2 on the DC Cook Units 1 and 2 Reactor Internals Aging Management Program.

ML15223A436
Person / Time
Site:	Cook
Issue date:	07/28/2015
From:	Mckinley J, Mary Walsh PWR Owners Group, Westinghouse
To:	Office of Nuclear Reactor Regulation
References
AEP-NRC-2015-69, PA-MSC-0983, Rev. 1 PWROG-15066-NP, Rev 0
Download: ML15223A436 (17)

Text

ENCLOSURE 2 to AEP-NRC-201 5-69 Pressurized Water Reactor Owners Group (PWROG)-1 5066-NP, Revision 0 Responses to Follow-Up NRC RAI 2 on the DC Cook Units 1 and 2 Reactor Internals Aging Management Program

PRESSURIZED WATER REACTOR OWNERS GROUP PWROG PWROG-1 5066-NP Revision 0 WESTINGHOUSE NON-PROPRIETARY CLASS 3 Responses to Follow-Up NRC RAI 2 on the DC Cook Units 1 and 2 Reactor Internals Aging Management Program Materials Committee PA-MSC-0983, Revision 1, Task 8 July 28, 2015

• Westinghouse

WESTINGHOUSE NON-PROPRIETARY CLASS 3 PWROG-1 5066-NP Revision 0 Responses to Follow-Up NRC RAI 2 on the DC Cook Units 1 and 2 Reactor Internals Aging Management Program PA-MSC-0983, Revision 1, Task 8 Joshua K. McKinley*

Reactor Internals Aging Management Mary Ann T. Walsh*

Reactor Internals Aging Management July 28, 2015 Verifier: Karli N. Szweda*

Reactor Internals Aging Management Reviewer: Michael A. Burke*

Materials Center of Excellence Approved: Patricia C. Paesano*, Manager Reactor Internals Aging Management Approved: James P. Molkenthin*, Program Director PWR Owners Group PMO

• Electronically approved records are authenticated in the electronic document management system.

Westinghouse Electric Company LLC 1000 Westinghouse Drive Cranberry Township, PA 16066, USA

© 2015 Westinghouse Electric Company LLC All Rights Reserved

WESTINGHOUSE NON-PROPRIETARY CLASS 3 ii LEGAL NOTICE This report was prepared as an account of work performed by Westinghouse Electric Company LLC. Neither Westinghouse Electric Company LLC, nor any person acting on its behalf:

1. Makes any warranty or representation, express or implied including the warranties of fitness for a particular purpose or merchantability, with respect to the accuracy, completeness, or usefulness of the information contained in this report, or that the use of any information, apparatus, method, or process disclosed in this report may not infringe privately owned rights; or

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DISTRIBUTION NOTICE This report was prepared for the PWR Owners Group. This Distribution Notice is intended to establish guidance for access to this information. This report (including proprietary and non-proprietary versions) is not to be provided to any individual or organization outside of the PWR Owners Group program participants without prior written approval of the PWR Owners Group Program Management Office. However, prior written approval is not required for program participants to provide copies of Class 3 Non-Proprietary reports to third parties that are supporting implementation at their plant, and for submittals to the NRC.

July28, 2015 PWROG-1 5066-NP PWROG-15066-NP Revision 0

WESTINGHOUSE NON-PROPRIETARY CLASS 3 1 From Nuclear Regulatory Commission Letter, "Donald C. Cook Nuclear Plant, Units 1 and 2 - Follow-Up Request for Additional Information Concerning the Reactor Vessel Internals Aging Management Program Submittal (TAC Nos. MF0050 and MFO051)," May 5, 2015.

Follow-Up RAI Response to Al 7 and RAI-6 Regarding CASS Components Backqiround In accordance with Al 7 of the MRP-22 7-A SE, the licensee provided its evaluation of the cast austenitic stainless steel (CASS) RVI components for DC Cook 1 and 2 in Attachments 3 and 4, respectively, of Westinghouse L TR-RIAM-14-24, Revision (Rev.) 1, "Reports for D.C. Cook, Units 1 and 2 for PWROG PA-MSC-0983 Cafeteria Tasks 3, 4, and 5 Deliverables (Non-Proprietary)"- heretofore referred to as the Al 7 reports. These reports were included as Enclosure 6 of the licensee's final RAI response, dated October 22, 2014 (ADAMS Accession No. ML14316A449).

Additional information is requiredin order to demonstrate that the MRP-22 7-A guidelines are adequate for aging management of the CASS components identified in Table 1 below. Table 1 summarizes the licensee's determination of the components' susceptibility to thermal embrittlement (TE) and irradiationembrittlement (IE) in the Al 7 reports, the generic material and FMECA classificationfrom MRP-191, and the additionalinformation requiredfor each CASS component. The licensee determined susceptibility to TE based on the screening criteria established for non-irradiatedCASS in the U.S. NRC letter from C. Grimes, Office of Nuclear Reactor Regulation, dated May 19, 2000, "License Renewal Issue No. 98-0030, ThermalAging Embrittlement of Cast Austenitic Stainless Steel Components" (ADAMS Accession No. ML003717179, the C.

Grimes Letter). The licensee determined susceptibility to IE based on the MRP-191 generic IE threshold for CASS components. Screening of CASS components for the synergistic effects of IE and TE using more recent IE and TE thresholds for irradiated CASS promulgated by staff in a June 2014 white paper (ADAMS Accession No. ML14163A112) has not yet been addressed for DC Cook 1 and 2.

Table 1 - DC Cook CASS RVI Components Requiring FurtherEvaluation CASS Component Plant-Specific Generic IE Generic Additional TE Susceptibility MRP-1 91 Information Susceptibility Based on Material and Needed Based on May MRP-191 FMECA( 3 )

2000 C. Group

________________ Grimes Letter _______ _______

DC Cook 1 CRGT' 1 ) Assembly - YES(2 ) NO 304 SS Plant-Specific Guide Plates/Cards Evaluation and Group 3 Inspection Criteria for Cracking CRGT( 1 ) Assembly - YES(2 ) NO 304 SS Justification for Housing Plates AlI 1Resolution( 4 )

_________ ____ ___ _ _ ___ ___ ___ Group 0 _ _ _ _ _ _ _ _

PWROG-1 5066-NP July 28, 2015 Revision 0

WESTINGHOUSE NON-PROPRIETARY CLASS 3 2 CASS Component Plant-Specific Generic IE Generic Additional TE Susceptibility MRP-191 Information Susceptibility Based on Material and Needed Based on May MRP-191 FMECA' 3 )

2000 C. Group Grimes Letter _____________

DC Cook 1 Upper Instrumentation YES( 2 ) NO 304 SS Justification for Conduit and Supports AlI 1Resolution( 4 )

- Brackets, Clamps, Group 0 Terminal Blocks, Conduit Straps Lower Support YES( 2 ) YES CF8 CASS Plant-Specific Column Assemblies - Functionality Lower Support Group 1 Analysis or Column Bodies Inspection Plan DC Cook 2 Upper Instrumentation YES( 2 ) NO 304 SS Justification for Conduit and Supports AlI 1Resolution( 4 )

- Brackets, Clamps, Group 0 Terminal Blocks, Conduit Straps Upper Support Plate NO NO 304 SS Justification for Assembly - Plate, Group 2 - Al 1 Resolution( 4 )

Flange, and Upper Ring or Skirt Support Ring or Skirt Group 0 -

Plate and Flange Lower Support NO YES CF8 CASS Plant-Specific Column Assemblies - Functionality Lower Support Group 1 Analysis or Column Bodies Inspection Plan( 4 )

Notes:

(1) Control rod guide tube (CRGT) components are assumed to be CASS by the licensee since documentation of constructionalmaterials was not located.

(2) Susceptibility to TE is due to lack of CMTR data and assumed delta ferrite greater than 20 percent, as indicated in Tables 3.1-1 and 4.1-1 of the licensee's Al 7 reports in Attachments 3 and 4 of L TR-RIA M- 14-24.

(3) FMECA - Failure Modes, Effects, and CriticalityAnalysis. Generic FMECA results for Westinghouse RVl are provided in MRP-191, Table 6-5.

(4) The staff's recent IE and TE screening criteria for irradiatedCASS were provided in a June 2014 white paper. Synergistic effects of lE and TE based on these 2014 screening criteria should be considered for these components, as part of the justification, evaluation, or functionality analysis.

PWROG-15066-NP Revision 0

WESTINGHOUSE NON-PROPRIETARY CLASS 33 3 For those components identified in Table 1 as needing "Justification for AlI 1Resolution",

the licensee's reports for AlI 1(Attachments 1 and 2 of LTR-RIAM-14-24) state that "[a]

FMECA expert panel review applying the same methodology as used in the development of MRP- 191 was conducted for these components ... [and] concluded that the aging management strategies of MRP-22 7-A were still applicable based on a consideration of the likelihood of failure and the likelihood of damage and the resulting classification of components." No additionaldetails were provided regardingthis determination.

Re quest Part (a) for Follow-Up RAI-2 For those confirmed CASS components designated in Table 1 as needing "Justification for AlI 1Resolution, "provide justification for the determination that the MRP-22 7-A guidelines are still applicable to the above components based on the MRP-191 methodology, in accordance with All1. This justification should include the plant-specific screening results for all aging mechanisms, explanation of the likelihood of component failure, the likelihood of core damage, the resulting FMECA group for the components, the categorizationand ranking of the components, and a discussion of how the final aging management strategy was determined. The justification must account for the additionalembrittlement mechanisms (IE and/or TE) for CASS that were not generically considered for these components due to their treatment as non-CASS in MRP-191. This justification must take into considerationthe potential synergistic effects of IE and TE for the CASS components. Screening criteria for IE and TE of irradiatedCASS that are acceptable are detailed in a June 2014 white paper (ADAMS Accession No. ML 141 63Al112).

Re quest Part (b) for Follow-Un RAI-2 The CRG T assembly guide plates/cards are generically analyzed as 304 stainless steel in MRP-191 and assigned to FMECA Group 3 in that report. MRP-22 7-A specifies that the Guide Plates/Cardsare to be inspected as primary components for loss of material (wear) using the VT-3 visual examination method on the 10-year inservice inspection (ISI) interval. At DC Cook 1, the CRG T guide plates/cards are assumed to be CASS and susceptible to TE. Additionally, MRP-191 indicates that the guide cards screened in for cracking due to SCC (welds) and fatigue, for the generic guide card material. Given that the susceptibility of the CASS guide plates/cardsto TE would make these components more likely to fail if cracks were present, provide an evaluation of the susceptibility of the guide cards to cracking. If the guide cards are susceptible to cracking, propose plant-specific inspection criteria for these components that would be sufficient for detecting cracking, orprovide an evaluation of the components justifying that no additional inspections, other than the MRP-22 7-A inspection criteria, are necessary for these CASS components considering their susceptibility to cracking.

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WESTINGHOUSE NON-PROPRIETARY CLASS 34 4 Request Part(c) for Follow-UID RAI-2 The DC Cook 1 lower support column (LSC) bodies are susceptible to TE and IE and therefore require an analysis to demonstrate their functionality during the period of extended operation, considering aging degradation of the LSC bodies due to TE and IE.

The DC Cook 2 LSC bodies screened as not susceptible [to] TE based on the criteria of the May 2000 C. Grimes Letter for non-irradiatedCASS, but are susceptible to IE based on MRP-191. Howe ver, if the DC Cook 2 LSC bodies have delta ferrite greaterthan 15 percent, synergistic effects of both TE and IE are applicable, based on the more recent IE and TE thresholds for irradiatedCASS established in the June 2014 white paper.

The licensee indicated in response to RAI-6(b) that the methodology for demonstrating the functionality of the LSC bodies is currently under development by the PWROG. An alternative to the functionality analysis could involve a plant-specific change to the inspection criteria for these expansion components. Any plant-specific inspection criteria should take into account the following: The LSC bodies are categorized as "Expansion" components in MRP-22 7-A for cracking due to IASCC and IE. Howe ver, the "Primary" linked component in MRP-22 7-A for the LSC bodies, the CRGT lower flange welds, is not a good predictorfor either IASCC or IE because of the low neutron fluence exposure for the CRG T lower flange welds.

Submit the analysis to demonstrate the functionality of the DC Cook 1 and 2 LSC bodies during the period of extended operation, considering aging degradationdue to the synergistic effects of IE and TE, or propose a plant-specific change to the inspection criteria for these components.

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WESTINGHOUSE NON-PROPRIETARY CLASS 3 5 RespDonses:

Response to Request Part (a):

The components in Table 1 of follow-up RAI 2 that are designated as needing "Justification for AlI 1Resolution" are repeated in the following list:

• Unit 1 o Control rod guide tube (CRGT) Assembly - Housing plates o Upper instrumentation conduit and supports - brackets, clamps, terminal blocks, conduit straps

• Unit 2 o Upper instrumentation conduit and supports - brackets, clamps, terminal blocks, conduit straps o Upper support plate assembly - Plate, flange, and upper support ring or skirt Table 1 summarizes the plant-specific results of the DC Cook Units 1 and 2 expert panel elicitation [1]. This elicitation was conducted under the guidance of the process described in MRP-1 91, Section 6 [2]. Table 1 includes the plant-specific screening results, likelihood of failure, likelihood of core damage, and resulting FMECA group determined by the expert panel elicitation for these five components. In each case, the likelihood of component failure and likelihood of core damage were determined by the expert panel evaluating the component in light of the different material of construction and revised aging degradation mechanism screening by applying the expert panel ranking system provided in MRP-1 91, Tables 6-2 and 6-

3. Note that the resulting FMECA group was then determined based on the chart in Table 6-4 of MRP-1 91.

After the determination of the FMECA group, the expert panel considered each component for any impacts on the aging management strategies provided in MRP-227-A [4]. This was done by considering the FMECA ranking, the existing operating experience for the component, and how the potential degradation of that component would rank relative to other components with the same degradation mechanism(s) and a relevant situation (such as geometry or stress). The ranking consideration followed the "waterfall" concept used in the original MRP-227-A development. The upper support ring or skirt is already included in the MRP-227-A aging management strategy as an Existing Component. The expert panel determined that the addition of TE as a degradation mechanism did not increase the FMECA grouping and that the current Existing Component inspection requirement was still adequate for the component [1].

For the other four components or component groups in Table 1, the expert panel determined that even with the addition of TE as a degradation mechanism, the Primary, Expansion, and Existing Components strategies in MRP-227-A are adequate and appropriate for managing potential aging in these components with fabrication material different from the original MRP-191 assumption.

To address the potential for synergistic effects of TE and IE, Indiana Michigan Power (I&M) is currently working with the Electric'Power Research Institute (EPRI) Industry Working Group and PWROG-1 5066-NP July 28, 2015 Revision 0

WESTINGHOUSE NON-PROPRIETARY CLASS 36 6 the Pressurized Water Reactor Owners Group (PWROG) to resolve the impact of the revised NRC staff TE threshold limits guidance [3] on the previous evaluations of RVI CASS component embrittlement. The revised threshold limits that have been proposed by the NRC are still under active discussion as recently as a meeting on June 2-4, 2015 [6]. It is noted that previous evaluations, including this current evaluation for DC Cook Units 1 and 2, have been performed using the screening process identified in MRP-191 [2], which formed the basis for the component rankings and recommended inspections identified in MRP-227-A [4]. The DC Cook Units 1 and 2 responses to A/LAI 7 were based on TE threshold criteria identified in Reference 5, as recommended in the NRC safety evaluation of MRP-227-A.

The process in Reference 5 is less complex than that outlined in the revised NRC guidelines, but has slightly different and, in some cases, more conservative thresholds. The PWROG program is expected to deliver a resolution of this issue by the fourth quarter of the present calendar year. Note that in the case of the components listed in Table 1, the potential synergistic effects of TE and IE are not expected to occur because all of these components are sufficiently removed from the active core to have irradiation exposure levels below both the limits of MRP-191 [2] and Reference 3 screening [1].

References

1. Westinghouse Letter, LTR-RIAM-14-87, Revision 1, "Summary of DC Cook Units 1 and 2 Expert Elicitation Panel Meeting Minutes for Reactor Internals Components, and Materials,' September 26, 2014.

2. Materials Reliability Program:Screening, Categorization, and Ranking of Reactor Internals Components for Westinghouse and Combustion EngineeringPWR Design (MRP-19 1). EPRI, Palo Alto, CA: 2006. 1013234.

3. U.S. Nuclear Regulatory Commission Document, "NRC position on Aging Management of CASS Reactor Vessel Internal Components" (ADAMS Accession Number ML14163A112).

4. Materials Reliability Program:Pressurized Water Reactor Intemnals Inspection and Evaluation Guidelines (MRP-227-A). EPRI, Palo Alto, CA: 2011. 1022863.

5. U.S. Nuclear Regulatory Commission Letter, "License Renewal Issue No. 98-0030, Thermal Aging Embrittlement of Cast Austenitic Stainless Steel Components," May 19, 2000 (NRC ADAMS Accession No. ML003717179).

6. U.S. Nuclear Regulatory Commission Document, "Summary of June 2-4, 2015, Annual Materials Programs Technical Information Exchange Public Meeting," July 14, 2015 (NRC ADAMS Accession No. ML15162A925).

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WESTINGHOUSE NON-PROPRIETARY CLASS 37 7 Table 1: Expert Panel FMECA Results (Revised based on Expert Panel Elicitation)

Screened-in Likelihood Lklho Assembly Subassembly Component Material Degradation of Failure o MC Damage Group Mechanisms L, M, H LMH Control Rod Guide Tube Hosn CF Assemblies Platen 5F L M1 and Flow Downcomers ______ ____

Brackets, Upper Clamps, Instrumentation Terminal Upper Conduit and Blocks, and CF8 5LLI Itras Supports Conduit Assembly Straps ______ ____

Flangle CF8 5 L M 1 Upper Support CF8 5 L M 1 Upper Support Pae ____ ________________

Plate Assembly Upe Support CF8 1A, 4, 5 M M2 Ring or Skirt _____ _____________ _ _____

scc 1 SCC of Welds 1A

_________ FMECA Groups Failure Consequence (Damage Likelihood) IASCC 2 Likelihood Low Medium High Wear 3 High 2 3 3 Fatigue 4 Thermal Embrittlement 5 Irradiation Embrittlement 6 None 0 0 0_____ Void Swelling 7 Irradiation ISR/IC; Thermal SR 8 None (Values for mechanisms did not exceed Nn screening threshold values.)

PWROG-1 5066-NP July 28, 2015 Revision 0

WESTINGHOUSE NON-PROPRIETARY CLASS 3 8 Response to Request Part (b):

The susceptibility of the potentially CASS guide cards at DC Cook Unit 1 was evaluated as part of the expert panel elicitation performed in support of responding to A/LAI 1 and 2 [1]. This was conducted as part of the effort to revise the RVI aging management program for DC Cook Unit 1 to conform to MRP-227-A. The expert panel was conducted under the guidance of the process described in MRP-1 91, Section 6 [2]. Table 2 includes the plant-specific screening results, likelihood of failure, likelihood of damage, and resulting FMECA group determined by the expert panel elicitation for CASS guide cards. In each case, the likelihood of component failure and likelihood of core damage were determined by the expert panel evaluating the component in light of the potential different material of construction and revised aging degradation mechanism screening by applying the expert panel ranking system provided in MRP-191, Tables 6-2 and 6-

3. Note that the resulting FMECA group was then determined based on the chart in Table 6-4 of MRP-191.

The conclusion of the expert panel review was that the CASS guide cards did not have enough increased susceptibility due to the addition of TE as an aging degradation mechanism to require changes to the current aging management strategy at DC Cook Unit 1 under MRP-227-A [1, 3].

The expert panel assigned the same categorization and ranking for the CASS guide cards as for the Type 304 SS guide cards in MRP-1 91 in order to manage the potential for wear degradation of the cards.

Aging degradation mechanism screening was conducted using the criteria provided in MRP-175

[4] and used in MRP-191 [1]. TE was the only additional aging degradation mechanism that screened in for the CASS guide cards. Irradiation effects, including irradiation embrittlement, were considered for screening but were eliminated due to the distance of the guide cards from the active core region (this would be true for either the original screening criteria or the proposed revised criteria [5]). SCC of the welds and fatigue were maintained as degradation mechanisms because there are still welds present on the CASS guide cards and the switch to CASS did not significantly affect the screening criteria from MRP-175 for these two mechanisms. SCC of the guide card away from the welds was considered, but this was determined to not be an issue based on comparison of the CASS and Type 304 SS screening criteria and the fact that a change in the material between the two would not be accompanied by a change in the stresses in the guide card.

The conclusion that cracking effects would not become more of a concern for the CASS guide cards than they were for assumed guide cards fabricated from Type 304 SS was based primarily on three observations [1]:

• Changing between CASS CF8 and Type 304 SS for a component where both are provided as alternate materials would not result in a difference in the stress, function, or geometry of the part. This factored into both the assignment of the likelihood of failure and the likelihood of damage.

• Welds on a component fabricated from CASS material would be similar to those on the chemically equivalent wrought material (such as for CF8 and Type 304 SS). A weld PWROG-1 5066-NPJuy2,01 Revision 0

WESTINGHOUSE NON-PROPRIETARY CLASS 3 9 locally melts material and then it re-solidifies. The same process occurs for welds on castings or on forgings.

• Thermal embrittlement of CASS does not result in a complete loss of fracture toughness.

Even with complete thermal embrittlement, a significant amount of fracture toughness would remain in the card.

The final conclusion that the potential presence of CASS guide cards at DC Cook Unit 1 does not require a change to the aging management strategy of MRP-227-A was based on several considerations [1].

• The determinations of screened-in degradation mechanisms, likelihood of failure, likelihood of damage, and FMECA group and ranking provided by the expert panel when assuming CASS material.

• The scope of the current VT-3 Primary Component inspection for wear required under MRP.-227-A [3], which would detect gross failures.

• The redundancy of the component - failures at multiple cards would be required for the control rods to slip out of place and the failure of the control rods in one CRGT assembly to insert would not preclude safe shutdown.

• The periodic monitoring of control rod functionality under current plant procedures.

Thus, the potential presence of CASS guide cards at DC Cook Unit 1 does not require changes to the aging management strategies provided in MRP-227-A.

Table 2: Expert Panel FMECA Results for CRGT Guide PlateslCards (Revised based

_________ ~ on Expert Panel Elicitation) _________

Screened-in Likelihood Lklho Assembly Subassembly Component Material Degradation of Failure o MC Damage Group Mechanisms L, M,H L ,H ____

Control Rod Upper Guide Tube Gud Internals Assemblies PltsCrs CF8 lA, 3, 4, 5 H M3 Assembly and Flow

_________ Downcomers _______ __ __________

SCC 1 SCC of Welds 1A

__________ FMECA Groups Failure Consequence (Damage Likelihood) IASCC 2 Likelihood Low Medium High Wear 3 High 2 3 3 Fatigue 4 Medium 1 2 3 Thermal Em brittlem ent 5 Low 1 1 2 Irradiation Embrittlement 6 None 0 0 0 Void Swelling 7 Irradiation ISR/IC; Thermal SR 8 None (Values for mechanisms did not exceed Nn screening thresholdvalues.) ____

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WESTINGHOUSE NON-PROPRIETARY CLASS 3 10 References

1. Westinghouse Letter, LTR-RIAM-14-87, Revision 1, "Summary of DC Cook Units 1 and 2 Expert Elicitation Panel Meeting Minutes for Reactor Internals Components, and Materials," September 26, 2014.

2. Materials Reliability Program:Screening, Categorization, and Ranking of Reactor Internals Components for Westinghouse and Combustion Engineering PWR Design (MRP-191). EPRI, Palo Alto, CA: 2006. 1013234.

3. Materials Reliability Program:PressurizedWater Reactor Internals Inspection and Evaluation Guidelines (MRP-227-A). EPRI, Palo Alto, CA: 2011. 1022863.

4. Materials Reliability Program:PWR Internals MaterialAging DegradationMechanism Screening and Threshold Values (MRP-1 75). EPRI, Palo Alto, CA: 2005. 1012081.

5. U.S. Nuclear Regulatory Commission Document, "NRC position on Aging Management of CASS Reactor Vessel Internal Components" (ADAMS Accession Number ML14163A112).

July28, 2015 PWROG-1 5066-NP PWROG-15066-NP Revision 0

WESTINGHOUSE NON-PROPRIETARY CLASS 3 11 Response to Request Part (c)

The strategy for managing the aging degradation of the DC Cook Units 1 and 2 CASS lower support column bodies was developed in compliance with the Inspection and Evaluation Guidelines, MRP-227-A [1]. The aging degradation screening of the CASS lower support column bodies is recorded in MRP-1 91, Table 5-1 [2], which is a basis document for MRP-227-A. In MRP-191, the CASS lower support column bodies were screened in as susceptible to irradiation assisted stress corrosion cracking (IASCC), void swelling (VS), and the embrittlement mechanisms, thermal embrittlement (TE) and irradiation embrittlement (IE:). The expert panel conclusions documented in MRP-191 [2] served as the basis for the aging management program guidelines provided in MRP-227-A [1]. The NRC is concerned that there may be a combined effect of TE: and IE:, which is discussed in new guidelines issued by the NRC [3].

The EPRI Industry Working Group and the PWROG are working to resolve the impact of the revised NRC staff thermal embrittlement threshold limits guidance [3]. There are slight differences between the industry's position and the revised NRC guidance. The industry's position with regard to the susceptibility of low molybdenum content CASS (CF3 and CF8) material to IE is more conservative than the NRC guidance (1 dpa vs. 1.5 dpa). The new NRC guidance for the potential for susceptibility to combined TE and IE is more restrictive than the industry criterion for lE alone, (i.e. ferrite content 15 percent vs. 20 percent and fluence 0.45 dpa vs 1.0 dpa). The NRC has recently discussed the guidance for IE and TE for CASS [6] and more information on the NRC guidance and a resolution of the NRC and industry positions are expected to be forthcoming. The PWROG program is expected to deliver a resolution of this issue by the fourth quarter of the present calendar year.

The DC Cook lower support column bodies are static cast, A296, Grade CF8. For the DC Cook Unit 1 lower support column bodies, the certified material test reports (CMTRs) were not located. Thus, their ferrite content values are conservatively assumed to have potentially exceeded 20 percent, screening the DC Cook Unit 1 lower support column bodies as potentially susceptible to TE.

For DC Cook Unit 2 lower support column bodies, the ferrite contents were calculated using the appropriate equations for the Hull's equivalent factors and using the chemical compositions provided by the CMTRs. However, not all of the elemental chemical compositions required for the Hull's equivalent factors are provided in the located CMTRs. Specifically, the molybdenum (Mo) and nitrogen (N) contents, which affect the chromium equivalent and nickel equivalent factors, respectively, are not reported in plant vintage CMTRs. Thus, the calculations of the ferrite content of the DC Cook Unit 2 lower core support column bodies assume a maximum Mo content (0.5%) and a representative nitrogen content from typical melt processing (0.04%). The 96 lower support column bodies in DC Cook Unit 2 have calculated ferrite contents ranging from a minimum of 9.8 percent to a maximum of 14.3 percent. Thus, all 96 DC Cook Unit 2 lower support column bodies have ferrite content less than or equal to 20 percent and therefore, are not susceptible to TE, based on the guidelines of [4].

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WESTINGHOUSE NON-PROPRIETARY CLASS 3 12 It is recognized that the DC Cook Unit 1 and Unit 2 lower support column bodies screen as susceptible to IE. Thus, the DC Cook Unit 1 lower support column bodies screen-in as susceptible to IASCC, VS, and both embrittlement mechanisms, TE and IE, while the DC Cook Unit 2 lower support column bodies screen-in for the same aging mechanisms, with the exception of TE.

In addition, it is noted that the PWROG has advised the NRC staff that a project, PA-MSC-1103, to provide a generic functionality evaluation of the lower support structure has been undertaken by the industry. An update on this project was provided during meetings between the industry and the NRC staff as recently as June 2015 [6]. The summary report for the first phase of PA-MSC-1103 was requested by the NRC and submitted by the PWROG for the NRC's information under Reference [7]. The project will develop a methodology which will form the basis for generic or plant-specific functionality analyses and complete the first steps in substantiating the qualitative safety argument. The project has an expected completion date of 2017.

References

1. Materials Reliability Program:Pressurized Water Reactor Internals Inspection and Evaluation Guidelines (MRP-22 7-A). EPRI, Palo Alto, CA: 2011. 1022863.

2. Materials Reliability Program:Screening, Categorization,and Ranking of Reactor Internals Components for Westinghouse and Combustion Engineering PWR Design (MRP-191). EPRI, Palo Alto, CA: 2006. 1013234.

3. U.S. Nuclear Regulatory Commission Document, "NRC position on Aging Management of CASS Reactor Vessel Internal Components" (ADAMS Accession Number ML14163A112).

4. U.S. Nuclear Regulatory Commission Document, "License Renewal Issue No. 98-0030, Thermal Aging Embrittlement of Cast Austenitic Stainless Steel Components," (ADAMS Accession No. ML003717179).

5. Indiana Michigan Power Company Letter, AEP-NRC-2014-60, "Donald C. Cook Nuclear Plant Units 1 and 2 Final Response to Request for Additional Information Concerning the Reactor Vessel Internals Aging Management Program," October 22, 2104, (ADAMS Accession Number ML14316A449).

6. U.S. Nuclear Regulatory Commission Document, "Summary of June 2-4, 2015, Annual Materials Programs Technical Information Exchange Public Meeting," July 14, 2015 (NRC ADAMS Accession No. ML15162A925).

7. PWR Owners Group Letter OG-15-83, "Submittal of PWROG-14048-P, Revision 0, "Functionality Analysis: Lower Support Columns" to the NRC for Information Only (PA-MSC-1103), March 13, 2015 (ADAMS Accession Number ML15077A113).

5066-NP July 28, 2015 PWROG-1 PWROG-15066-NP Revision 0

Enclosure 3 to AEP-NRC-2015-69 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 I&M. They are described to the U. S. Nuclear Regulatory Commission (NRC) for the NRC's information and are not regulatory commitments.

Commitment Date l&M will continue to participate in the Pressurized Water Reactor August 31, 2017 Owners Group (PWROG) project for lower support columns.

I&M will provide a supplemental response to the NRC on this request for additional information when an acceptable methodology is developed by the PWROG project.