ML25104A263

SLR - Request for Additional Information - Set 2

ML25104A263
Person / Time
Site:	Indian Point, Dresden
Issue date:	04/14/2025
From:	Mark Yoo NRC/NRR/DNRL/NLRP
To:
Shared Package
ML25104A261	List: ML25104A262 ML25104A263
References
Download: ML25104A263 (1)

Text

REQUEST FOR ADDITIONAL INFORMATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION DRESDEN, UNITS 2 AND 3, SUBSEQUENT LICENSE RENEWAL REVIEW - SAFETY CONSTELLATION ENERGY GENERATION, LLC DRESDEN, UNITS 2, 3 DOCKET NO. 05000237, 05000249 ISSUE DATE: 4/14/2025 Set # 2 RAI 4.3.3-3 Regulatory Basis Pursuant to 10 CFR 54.21(c), the SLRA must include an evaluation of time-limited aging analyses (TLAAs). The applicant must demonstrate that (i) the analyses remain valid for the subsequent period of extended operation, (ii) the analyses have been projected to the end of the subsequent period of extended operation, or (iii) the effects of aging on the intended function(s) will be adequately managed for the subsequent period of extended operation.

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Background===

The following report indicates that in the detailed EAF analysis for the limiting locations, the Fen calculations use the average temperature approach considering the threshold temperature for a material type (

Reference:

Structural Integrity Associates (SIA) 2200483.305P, Environmentally Assisted Fatigue Calculations for Sentinel Locations at Dresden, Revision 1).

Issue SLRA Section 4.3.3 does not clearly discuss the following: (1) whether the average temperature approach is used only for simple, linear transients; and (2) if not, why the conservatism of the applicants approach is comparable to or greater than that of the modified rate approach described in NUREG/CR-6909, Rev. 1, Section 4.4 (i.e., plant-specific demonstration of the adequacy of the applicants approach).

Request Clarify the following: (1) whether the average temperature approach is used only for simple, linear transients; and (2) if not, why the conservatism of the applicants approach is comparable to or greater than that of the modified rate approach described in NUREG/CR-6909, Rev. 1, Section 4.4 (i.e., plant-specific demonstration of the adequacy of the applicants approach).

RAI 4.3.6-1 Regulatory Basis Pursuant to 10 CFR 54.21(c), the SLRA must include an evaluation of time-limited aging analyses (TLAAs). The applicant must demonstrate that (i) the analyses remain valid for the subsequent period of extended operation, (ii) the analyses have been projected to the end of the subsequent period of extended operation, or (iii) the effects of aging on the intended function(s) will be adequately managed for the subsequent period of extended operation.

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Background===

SLRA Section 4.3.6.2 addresses the thermal fatigue TLAA for the DNPS Unit 2 jet pump riser repair/mitigation clamps (also called jet pump riser brace (JPRB) clamps). SLRA Section 4.3.6.2 provides the following explanation regarding the JPRB clamps. During the fall 2001 refueling

outage for DNPS Unit 2, a crack was detected in the JPRB for jet pumps 9/10. The SLRA also explains that a mechanical clamping system designed to structurally replace these welds was installed on both jet pump risers in 2003.

Issue SLRA Section 4.3.6.2 does not clearly discuss which specific welds of the jet pump assembly are structurally replaced by the JPRB clamps. The staff also noted that typically two jet pumps share one riser pipe. However, the SLRA explains that the mechanical clamp system was installed on both jet pump risers of the jet pumps 9/10, indicating that the jet pumps 9/10 have two riser pipes rather one riser pipe.

In addition, SLRA Section 4.3.6.2 explains that the JPRB clamps were also installed on the other JPRBs of Unit 2 to preclude high cycle fatigue cracking concerns. However, the SLRA section does not clearly discuss the following items related to the JPRB clamps for vibration mitigation: (1) whether these vibration mitigation clamps are also subject to the fatigue TLAA in a similar manner as the repair clamp(s) are subject to the fatigue TLAA; (2) frequency and method of the periodic inspections for the repair and vibration mitigation clamps; and (3) whether the results of these inspections confirm the absence of cracking in the clamps due to fatigue or other degradation mechanisms (e.g., stress corrosion cracking).

Request

1. Discuss the following items: (1) which specific welds of the jet pump assembly (jet pumps 9/10) are structurally replaced by the JPRB repair clamps; (2) the degradation mechanism that led to the installation of the repair clamps; and (3) how many risers are associated with one pair of jet pumps.

2. Clarify whether the vibration mitigation clamps as well as the repair clamps are subject to the fatigue TLAA for jet pumps. In addition, describe the number of the repair clamps and the number of non-repair vibration mitigation clamps installed inside the Unit 2 reactor vessel, respectively.

3. Describe the following items: (1) frequency and method of the periodic inspections for the repair and vibration mitigation clamps; and (2) whether the results of these inspections confirm the absence of cracking in the clamps due to fatigue or other degradation mechanisms (e.g., stress corrosion cracking).

4. Revise SLRA Sections 4.3.6.2 and A.4.3.8 as needed based on the discussion above (e.g., (1) how many repair and vibration mitigation clamps are installed respectively and (2) whether the vibration mitigation clamps as well as the repair clamps are subject to the fatigue TLAA).

RAI 4.7.5-1 Regulatory Basis Pursuant to 10 CFR 54.21(c), the SLRA must include an evaluation of time-limited aging analyses (TLAAs). The applicant must demonstrate that (i) the analyses remain valid for the subsequent period of extended operation, (ii) the analyses have been projected to the end of the subsequent period of extended operation, or (iii) the effects of aging on the intended function(s) will be adequately managed for the subsequent period of extended operation.

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Background===

SLRA Section 4.7.5 addresses the fatigue TLAA for Dresden Unit 2 core spray replacement piping. The applicant explained that, in November 2009, all four lower sections of the core spray

system were replaced and thus removed all known piping flaws of the core spray piping inside the Unit 2 reactor pressure vessel.

The SLRA also indicates that, since the fatigue analysis for the replacement piping assumed the 40-year service life since the replacement (November 2009) until November 2049, the analysis was reevaluated to extend the evaluation period by additional 5 years (total 45 years) beyond the end of subsequent period of extended operation for Unit 2 (i.e., December 2049). The applicant dispositioned the fatigue TLAA in accordance with 10 CFR 54.21(c)(1)(i).

Issue SLRA Section 4.7.5 does not clearly describe the transients and transient cycles used in the existing 40-year fatigue analysis in comparison with the projected cycles for the service of the replacement core spray piping throughout the end of the subsequent period of extended operation to confirm that the transient cycles evaluated in the existing 40-year fatigue analysis are bounding for the projected cycles for the service of the replacement core spray piping.

Request Describe the transients and transient cycles used in the existing 40-year fatigue analysis in comparison with the projected cycles for the service of the replacement core spray piping throughout the end of the subsequent period of extended operation to confirm that the transient cycles evaluated in the existing 40-year fatigue analysis are bounding for the projected cycles for the service of the replacement core spray piping.

RAI B.2.1.33-1 Regulatory Basis Title 10 of the Code of Federal Regulations Section 54.21(a)(3) requires the applicant to demonstrate that the effects of aging for structures and components will be adequately managed so that the intended function will be maintained consistent with the current licensing basis (CLB) for the period of extended operation. As described in the SRP-SLR, an applicant may demonstrate compliance with 10 CFR 54.21(a)(3) by referencing the GALL-SLR Report when evaluation of the matter in the GALL-SLR Report applies to the plant.

Background :

Units 2 and 3 chimney is a tapered, cantilevered reinforced concrete structure with a height of 310 feet. SLRA Section 2.4.12 designates this chimney as a safety-related structure that provides a discharge path for treated gaseous waste.

During the NRC onsite audit from December 10-12, 2024, the staff observed significant surface efflorescence (white and black) and some minor spalling on the exterior of the Units 2 and 3 chimney from the ground up to about 25 feet elevation below the vent stack. The staff reviewed the work orders (WOs) from the past 10 years, including WO 01512813, WO 01601817, WO 01698314, WO 01793913, WO 01888740, WO-04867735, WO 04995283, WO 05112098, WO 05218686, WO 0532099, and WO 05429441, which indicate that chimney degradations in this area develop slowly over time and are likely to continue during the Subsequent Period of Extended Operation (SPEO). However, these WOs focus on recent degradation trends and do not consider long-term degradation patterns. Despite increasing the inspection frequency to annually for aviation safety purposes, no significant corrective actions have been taken to address the concrete conditions.

SLRA Section B.2.1.33, as modified by SLRA Supplement 2 (ML25072A153), enhances the acceptance criteria program element in the Structures Monitoring program by using quantitative second tier criteria from Chapter 5 in ACI 349.3R-02 for structural concrete. Due to the chimneys unique configuration and past operating experience, second tier criteria maybe insufficient to adequately manage effects of aging for the Units 2 and 3 chimney.

The staff also reviewed UFSAR Sections 3.3.1.1.2, 3.3.2.2.3, 3.7.2.4, and 3.8.4.3 along with UFSAR Figures 3.3-1, 3.3-2, 3.7-11, 3.7-12, 3.7-13, 3.8-44 to 3.8-46 and found that critical sections of the Units 2 and 3 chimney are located at 60 feet above grade for tornado loading and 208 feet above grade for safe shutdown earthquake (SSE) loading. However, UFSAR does not include calculation results for the chimneys lower sections, where observable degradations are occurring.

Issue SLRA does not make clear whether the observed degradations affect the Units 2 and 3 chimneys ability to perform its intended function. With the potential further degradations of the chimney, the Structures Monitoring program lacks specific degradation limits or acceptance criteria for the chimney that would trigger corrective actions, that require testing or engineering evaluations. Without these clear thresholds, it is uncertain how the Units 2 and 3 chimney will maintain its intended function during the SPEO.

Request

1. Update the SLRA to incorporate recent operating experience and degradation trends related to the Units 2 and 3 chimney.

2. Evaluate whether the observed degradations affect the Units 2 and 3 chimneys ability to perform its intended function.

3. Based on the chimneys unique configuration (height, critical loading sections, environmental exposure), aligning with the rate of degradation in the lower sections of the chimney and in accordance with Chapter 5 of ACI 349.3R-02, establish clear degradation limits or acceptance criteria (e.g., crack width, spalling depth and dimension, extent of efflorescence) with a technical basis for the Units 2 and 3 chimney, which will trigger corrective actions and ensure the chimneys structural integrity and intended function during the SPEO. Propose program enhancements if required.

RAI B.2.1.33-2 Regulatory Basis Title 10 of the Code of Federal Regulations Section 54.21(a)(3) requires the applicant to demonstrate that the effects of aging for structures and components will be adequately managed so that the intended function will be maintained consistent with the current licensing basis (CLB) for the period of extended operation. As described in the SRP-SLR, an applicant may demonstrate compliance with 10 CFR 54.21(a)(3) by referencing the GALL-SLR Report when evaluation of the matter in the GALL-SLR Report applies to the plant.

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Background===

SLRA Table 3.5.2-2, as modified by SLRA Supplement 2 (ML25072A153), added a Table 2 AMR item for the galvanized steel cable tray and its supports in the Units 2 and 3 Crib House exposed to water-flowing environment, which will be managed under the Structures Monitoring program.

During the NRC onsite audit from December 10-12, 2024, the staff observed significant and excessive corrosion of the south side lower cable tray and its supports running between 2A and 2B circulating water pumps in the Units 2 and 3 Crib House. This deterioration was due to periodic water intrusion from electrical penetrations (ductbanks) located above the tray. Interviews with the applicants staff revealed that this is a reoccurring issue. In 1996, a wider galvanized steel cable tray was installed underneath the original tray due to excessive deterioration of the original sheet metal cable tray from the same water in-leakage problem.

Over the years, the applicant had conducted engineering evaluations, testing and various mitigative actions to address the cable tray degradation and water in-leakage in the southeast portion of the Crib House.

SLRA Sections 3.5.2.2.2.1, item 4, and 3.5.2.2.2.3, item 3 indicate that inaccessible concrete elements of Group 6 structures (e.g., Crib House) are subject to an aggressive environment.

Test results from groundwater and raw water samples taken in 2023 confirm chloride levels exceeding 500 ppm, which defines an aggressive environment. This chloride exposure is detrimental to the south side cable tray and its supports due to recurring water intrusion from the electrical penetrations.

Issue The SLRA does not clearly demonstrate whether the observed degradation affects the ability of the south side lower cable tray and its supports in the Units 2 and 3 Crib House to perform their intended function. Given the significant and recurring degradation, the Structures Monitoring program lacks specific degradation limits or acceptance criteria for the cable tray and its supports exposed to water-flowing environment that would trigger corrective actions. Without clear thresholds, it is uncertain how these components will maintain their intended function during the SPEO.

Request

1. Update the SLRA to incorporate operating experience related to the south side lower cable tray and its supports in the Units 2 and 3 Crib House.

2. Evaluate whether the observed degradation affects the ability of the south side lower cable tray and its supports in the Units 2 and 3 Crib House to perform their intended function. Clarify whether these components will be replaced prior to entering the SPEO.

3. Based on past operating experience, establish clear degradation limits or acceptance criteria with a technical basis for the south side lower cable tray and its supports in the Units 2 and 3 Crib House. These criteria should trigger corrective actions for prompt repair or replacement to ensure their structural integrity and intended function during the SPEO. Propose program enhancements if required.

RAI 3.5.2.2.2.1-1 Regulatory Basis Title 10 of the Code of Federal Regulations Section 54.21(a)(3) requires the applicant to demonstrate that the effects of aging for structures and components will be adequately managed so that the intended function will be maintained consistent with the current licensing basis (CLB) for the period of extended operation. As described in the SRP-SLR, an applicant

may demonstrate compliance with 10 CFR 54.21(a)(3) by referencing the GALL-SLR Report when evaluation of the matter in the GALL-SLR Report applies to the plant.

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Background===

SRP-SLR states that cracking and distortion due to increased stress levels from settlement could occur in below-grade inaccessible concrete areas of structures for all Groups, and reduction in foundation strength, and cracking due to differential settlement and erosion of porous concrete subfoundations could occur in below-grade inaccessible concrete areas of Groups 1-3, 5-9 structures.

SLRA Table 3.5.1 claims that Table 1 AMR item 3.5.1-044, as modified by SLRA Supplement 2 (ML25072A153), aligns with NUREG-2191. Specifically, it indicates that the Structures Monitoring program will manage cracking and distortion of reinforced concrete in all inaccessible areas exposed to a groundwater/soil environment for yard and switchyards structures.

SLRA Section 3.5.2.2.2.1, Item 3, as modified by SLRA Supplement 2 (ML25072A153),

indicates that this aging effect and mechanism is insignificant for the Group 1, 2, 3, 6, and 9 concrete building structures founded on rock or natural compacted soil, and the DNPS Mark 1 containment and its associated support is established on the Reactor Building foundation slab, which rests on solid rock as specified in UFSAR Section 2.5.4. Consequently, cracking and distortion from increased stress levels due to settlement are not applicable to Group 4 internal containment structures.

Additionally, DNPS does not have concrete tanks or concrete missile barriers categorized as Group 7 structures, which would require aging management. Group 5 structure is evaluated as a Group 2 structure and concrete foundations for group 8 structures within the scope of subsequent license renewal are evaluated for aging management in SLRA Table 3.5.2-16 for yard structures.

Furthermore, SLRA Table 3.5.1 indicates that Table 1 AMR item 3.5.1-046, as modified by SLRA Supplement 2 (ML25072A153), is not used. The aging effects of reduction of foundation strength and cracking due to differential settlement and erosion of porous concrete subfoundation are managed under Table 1 AMR item 3.5.1-044.

UFSAR Section 2.5.4 states, Examination of cores from borings at the site and excavation for the construction of Units 1 and 2 show that all footings for major structures have a foundation of sound rock which eliminates the potential problems of soil consolidation and differential settlement. However, this statement does not explicitly identify which Units 1 and 2 concrete structures are supported on rock, nor does it clarify whether the Unit 3 in-scope concrete structures are similarly supported on rock.

Issue The SLRA does not explicitly identify which in-scope concrete structures are supported on rock, nor does it provide an adequate technical basis for identifying which concrete structures are rock-supported.

Request

1. Evaluate and provide a technical basis for whether all in-scope concrete structures (excluding yard and switchyard structures) are supported on rock, and identify those that are not.

2. For concrete structures that not supported on rock or cannot be identified to be supported on rock, provide the corresponding Table 2 items associated with Table 1 AMR item 3.5.1-044.