Text

Proposed Inservice Inspection Alternative FNP-ISI-ALT-2025-10 for Containment Unbonded Post-Tensioning System Inservice Inspection Requirements in Accordance with 10 CFR 50.55a(z)(1) (NL-25-0045)
	ML25058A186
Person / Time
Site:	Farley
Issue date:	02/27/2025
From:	Coleman J; Southern Nuclear Operating Co
To:	; Office of Nuclear Reactor Regulation, Document Control Desk
References
	NL-25-0045, FNP-ISI-ALT-2025-10
	Download: ML25058A186 (1)
	v • d • e

Regulatory Affairs 3535 Colonnade Parkway Birmingham AL 35243 205 992 5000 February 2, 2025 Docket Nos.: 50-348 NL-25-0045 50-364 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D. C. 20555-0001 Joseph M. Farley Nuclear Plant, Units 1 and 2 Proposed Inservice Inspection Alternative FNP-ISI-ALT-2025-10 for Containment Unbonded Post-Tensioning System Inservice Inspection Requirements in Accordance with 10 CFR 50.55a(z)(1)

Ladies and Gentlemen:

In accordance with 10 CFR 50.55a(z)(1), Southern Nuclear Operating Company (SNC) hereby requests Nuclear Regulatory Commission (NRC) approval of proposed inservice inspection (ISI) alternative FNP-ISI-ALT-2025-10 for Farley Nuclear Plant (FNP) Units 1 and 2. This proposed alternative, described in the Enclosure, would extend the inspection exam frequency of ASME Section XI Table IWL-2500-1 Examination Category L-B for item numbers L2.10, L2.20, L2.30, L2.40 and L2.50.

The Enclosure provides the justification for the requested alternative. Attachment 1 contains FNP Units 1 and 2 specific information to support the applicability of the methods in the Enclosure.

NRC approval is requested within twelve months of acceptance to support application of the revised schedule to the affected examination.

U. S. Nuclear Regulatory Commission NL-25-0045 Page 2 This letter contains no NRC commitments. If you have any questions, please contact Ryan Joyce at 205.992.6468.

Respectfully submitted, Jamie M. Coleman Regulatory Affairs Director JMC/was/cbg

Enclosure:

Proposed Alternative FNP-ISI-ALT-2025-10 in Accordance with 10 CFR 50.55a(z)(1)

Attachment:

Plant-Specific Tendon Report FNP Units 1 and 2 cc:

Regional Administrator, Region ll NRR Project Manager - Farley Nuclear Plant Senior Resident Inspector - Farley Nuclear Plant RType: CFA04.054

ENCLOSURE Proposed Alternative FNP-ISI-ALT-2025-10 in Accordance with 10 CFR 50.55a(z)(1)

Enclosure to NL-25-0045 Proposed Alternative FNP-ISI-ALT-2025-10 in Accordance with 10 CFR 50.55a(z)(1)

E-1 Request for Alternative FNP-ISI-ALT-2025-10 for Containment Unbonded Post-Tensioning System Inservice Inspection Requirements in Accordance with 10 CFR 50.55a(z)(1) 1.0 ASME CODE COMPONENTS AFFECTED:

Code Class:

CC

==

Description:==

Concrete Components of Light-Water Cooled Plants, IWL-2421, IWL-2520, Table IWL-2500-1 Examination Category: Table IWL-2500-1, Category L-B Item Numbers:

L2.10 - Tendon L2.20 - Wire or strand L2.30 - Anchorage hardware and surrounding concrete L2.40 - Corrosion protection medium L2.50 - Free water Component Number:

Farley Unit 1 Containment Building Farley Unit 2 Containment Building 2.0 APPLICABLE CODE EDITION AND ADDENDA:

The Fifth 10-year Inservice Inspection (ISI) interval Code of Record for Farley Nuclear Plant Unit 1 and Unit 2 is the 2007 Edition through the 2008 Addenda of American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code,Section XI, Rules for Inservice Inspection of Nuclear Power Plant Components. The current fifth 10-year interval start date was December 1, 2017, and the current scheduled interval end date is November 30, 2027.

Note: Present-day Subsection IWL requirements for concrete containment in-service inspection were originally intended to be a part of ASME Section III Division 2, specifically, Article CC-9000. As Division 2 does not address ISI intervals, scheduling of containment ISI examinations was keyed to the date of the pre-operational structural integrity test (SIT).

Well into the development of CC-9000, ASME Codes & Standards transferred responsibility for its development to Section XI as Subsection IWL. This necessitated various changes to format and references. However, no change was made to the examination scheduling requirements; these are still tied to the SIT date rather than the Section XI ISI interval. As a result, scheduled examination activities often cross interval boundaries. This should be considered during the evaluation of the relief request.

Enclosure to NL-25-0045 Proposed Alternative FNP-ISI-ALT-2025-10 in Accordance with 10 CFR 50.55a(z)(1)

E-2 3.0 APPLICABLE CODE REQUIREMENT:

Subsection IWL-2421(b) states that when the conditions of IWL-2421(a) are met, the inspection dates and examination requirements may be as follows:

(1) For the containment with the first Structural Integrity Test, all examinations required by IWL-2500 shall be performed at 1, 3, and 10 years and every 10 years thereafter. Only the examinations required by IWL-2524 and IWL-2525 need be performed at 5 and 15 years and every 10 years thereafter.

(2) For each subsequent containment constructed at the site, all examinations required by IWL-2500 shall be performed at 1, 5, and 15 years and every 10 years thereafter. Only the examinations required by IWL-2524 and IWL-2525 need be performed at 3 and 10 years and every 10 years thereafter.

Farley Nuclear Plant (FNP), Unit 1 and Unit 2 is currently required to examine the post-tensioning system every 10 years.

x Note: Farley received approval to use ASME IWL-2421(b) schedule for sites with two units during the 1st Containment Inspection Interval and subsequent intervals, reference NRC letter to Mr. L.M. Stinson, Southern Nuclear, Joseph M. Farley Nuclear Plant, Units 1 and 2 - Request for Relief No. RR-57 and RR-58 Regarding Containment Tendon Inspections (TAC Nos. MC7209 and MC7210), ADAMS Accession No. ML060830221.

Subsection IWL-2500 requires examinations be performed in accordance with the requirements of Table IWL-2500-1.

Table IWL-2500-1, Item Number L2.10 requires that selected tendon force and elongation be measured.

Table IWL-2500-1, Item Number L2.20 requires that tendon single wire samples be removed and examined for corrosion and mechanical damage as well as tested to obtain yield strength, ultimate tensile strength, and elongation on each removed wire. The selected tendons are subsequently re-tensioned as required per IWL-2523.3 because wire removal requires de-tensioning to safely obtain wire samples.

Table IWL-2500-1, Item Number L2.30 requires that a detailed visual examination be performed on selected tendon anchorage hardware and adjacent concrete extending 2 feet from the edge of the bearing plate. The quantity of free water released from the anchorage end cap as well as any which drains from the tendon during examination shall be documented.

Table IWL-2500-1, Item numbers L2.40 and L2.50 require that samples of selected tendon corrosion protection medium (CPM) and free water be obtained and analyzed.

4.0 REASON FOR REQUEST:

ASME Section XI Subsection IWL requires periodic visual examination of Containment Building concrete as well as physical testing of post-tensioning systems. The examination and testing to date have indicated the post-tensioning system is expected to maintain its safety-related function through the period of extended operation for Unit 1 (June 2037) and

Enclosure to NL-25-0045 Proposed Alternative FNP-ISI-ALT-2025-10 in Accordance with 10 CFR 50.55a(z)(1)

E-3 Unit 2 (March 2041). This alternative request proposes the examination frequency in Table IWL-2500-1, Examination Category L-B, Items L2.30 through L2.50, be increased from the present five years to 10 years in accordance with the schedule presented in Section 5.0.

Also, it is proposed that the interval between tendon force measurements (L2.10) be adjusted from the present 10 years in accordance with an alternating program shown in Section 5.0.

Based on maintaining an acceptable level of quality and safety, there are additional benefits to extending physical testing. Physical testing of tendons exposes personnel to various industrial safety hazards, including working at heights, handling high-pressure hydraulics, and operating near high energy systems and stored elastic energy. The work is often performed in difficult-to-reach areas, sometimes in adverse weather conditions, and involves exposure to hazardous materials such as solvents, hot petroleum products, and occasionally radiation fields. Removing tendon end caps and load testing or de-tensioning/tensioning the tendons unnecessarily cycles the tendons and exposes the system to an unsealed environment.

Reducing the frequency of tendon testing and eliminating tendon end cap removal can mitigate these risks, minimize environmental waste, and enhance safety for personnel.

5.0 PROPOSED ALTERNATIVE AND BASIS FOR USE:

In accordance with 10 CFR 50.55a(z)(1), FNP, Unit 1 & Unit 2 are proposing alternative examination requirements on the basis that these alternative actions will provide an acceptable level of quality and safety.

FNP, Unit 1 & Unit 2 will continue to perform a General Visual Examination and Detailed Visual Examination (when required) of accessible concrete and exposed steel hardware as required by Section XI Table IWL-2500-1, Item Numbers L1.11 and L1.12, as modified by 10 CFR 50.55a. If an end anchorage area general visual examination uncovers a condition indicative of possible damage to the enclosed post-tensioning system hardware or an anchor head failure, the end cap will be removed for further examination and evaluation by the Responsible Engineer (RE). Additional actions will be taken as specified by the RE following the evaluation.

The examination and physical testing of post-tensioning systems per the requirements of Section XI Table IWL-2500-1 Item Numbers L2.10, L2.30, L2.40, and L2.50 will be increased in accordance with the schedule presented below.

It is also requested that removal and testing of tendon wires item number L2.20 be done only when specified by the Responsible Engineer. This will eliminate the routine need to de-tension and re-tension tendons and the consequent possible damage to the remaining wires.

In addition, it is requested that routine CPM testing item number L2.40 be limited to determination of absorbed water content and that additional tests for corrosive ion concentration and neutralization number be performed only if:

Active corrosion is found on anchorage components and / or tendon wires.

Free water is found at anchorages.

CPM absorbed water content exceeds the Table IWL-2525-1 acceptance limit.

And, otherwise if specified by the RE.

Eliminating routine ion concentration and neutralization number testing has the benefit of reducing the quantity of hazardous reagents to be disposed of by the testing laboratory.

Enclosure to NL-25-0045 Proposed Alternative FNP-ISI-ALT-2025-10 in Accordance with 10 CFR 50.55a(z)(1)

E-4 Table 1 Current Examination Schedule Current Tendon Surveillance Schedule (includes the four most recent Unit 1 and Unit 2 surveillances for reference)

Year Units 1 & 2 Visual Examination, CPM Sampling &

Free Water Collection / Testing Tendon Force Measurement 2006 Performed Performed 2012 Performed N/A 2017 Performed Performed 2021 Performed N/A 2026 Perform Perform 2031a Perform N/A 2036 Perform Perform 2041a Perform N/A 2046 Perform Perform 2051b Perform N/A Table 2 Proposed Examination Schedule Proposed Tendon Surveillance Schedule (includes the four most recent Unit 1 and Unit 2 surveillances for reference)

Year Units 1 & 2 Visual Examination, CPM Sampling &

Free Water Collection / Testing Tendon Force Measurement 2006 Performed Performed 2012 Performed N/A 2017 Performed Performed 2021 Performed N/A 2031a Perform Perform 2041a Perform N/A 2051b Perform Perform Note a: For scheduling purposes, each future surveillance is due at mid-year and must be performed between 30 June of the year prior to the year shown and 30 June of the year following the year shown. 2041 exams will only apply to Unit 2 unless Unit 1 is granted subsequent license extension.

Note b: Schedule continues as above if subsequent license extension is granted.

x Include Unit 1 Groups 1 and 2 augmented examinations (examinations of tendons subject to repair / replacement activity during 2012 and 2019) with the Population 1 (see footnote

Enclosure to NL-25-0045 Proposed Alternative FNP-ISI-ALT-2025-10 in Accordance with 10 CFR 50.55a(z)(1)

E-5 in Section 1.2 of Technical Report in Attachment) examinations to be performed per the above schedule.

x Eliminate the requirement for de-tensioning / re-tensioning of tendons, wire removal and wire sample testing (Subsection IWL Table IWL-2500-1 Item L2.20) unless specified by the RE.

x Limit initial corrosion protection medium laboratory tests (Subsection IWL Table IWL-2500-1 Item L2.40) to that which determines absorbed water content; perform the corrosive ion and reserve alkalinity tests only on those samples that have a water content above the acceptance limit, are collected at an anchorage where free water and / or corrosion is found or if specified by the IWL Responsible Engineer (RE).

The Attachment to this Enclosure provides a detailed discussion of the historical basis for examination and testing of containment post-tensioning systems. The Attachment to this Enclosure also includes the FNP, Unit 1 & Unit 2 specific observations that provide a basis for deviation from the Section XI examination and testing requirements included in Table IWL-2500-1, Examination Category L-B.

Additional Supporting Actions ASME Section XI Subsection IWL program at FNP, Unit 1 & Unit 2 is credited for managing Containment Building degradation. The Examination Category L-A visual examinations (every 5 years) being performed are expected to be capable of identifying conditions that would allow water intrusion into the tendons and gross leakage of CPM which would be precursors for providing an environment that could allow corrosion of the tendon wires or inaccessible tendon hardware covered by the tendon end cap. Such conditions would be evaluated by the RE to identify required additional actions to assure no corrosive environmental conditions exist. FNP, Unit 1 & 2 mean prestressing forces are predicted to be acceptable well beyond the 2037 and 2041 expiration dates of the extended Unit 1 and Unit 2 licenses 45th year (Unit

1) / 40th year (Unit 2) surveillance based on acceptable performance over 45 years; therefore, extending the surveillance in accordance with the schedule shown above will continue to provide an acceptable level of quality and safety.

Summary and Conclusions The results of the post-tensioning system inservice examinations conducted at FNP from 1977 to 2021 (Unit 1) and 1980 to 2021 (Unit 2) show that the system is continuing to perform its intended function and that it can be expected to do so until well past the June 2037 (Unit

1) and March 2041 (Unit 2) expiration of the extended operating period license. Visual Examination, CPM Sampling & Free Water Collection / Testing, Tendon Force Measurements will be scheduled June 30, 2031, plus or minus one year. General Visual examination (L1.11) of all accessible concrete surface areas will remain scheduled for the 45th year (Unit

1) / 40th year (Unit 2) surveillance which will occur in 2026 and will continue to be performed in accordance with IWL requirements.

6.0 DURATION OF PROPOSED ALTERNATIVE:

The proposed alternative is requesting to follow the proposed schedule shown in section 5.0 Table 2. As noted in the preceding Proposed Tendon Surveillance Schedule the 60-year license for Unit 1 expires before the 2041 inspection date and Unit 2 expires the year of the 2041 inspection date. If the license for Farley Units 1 and 2 is not renewed, then this 2041 inspection would not occur. If the license for Farley Units 1 and 2 is extended beyond the existing end dates, the Proposed

Enclosure to NL-25-0045 Proposed Alternative FNP-ISI-ALT-2025-10 in Accordance with 10 CFR 50.55a(z)(1)

E-6 Tendon Surveillance Schedule would continue with the same alternating schedule until the end of the new license date.

7.0 PRECEDENTS

This submittal is similar to NRC Approved requests listed below.

x Letter from Michael Markley (USNRC) to Cheryl A. Gayheart (Southern Nuclear Operating Co., Inc.), Vogtle Electric Generating Plant, Units 1 and 2 - Inservice Inspection Alternative VEGP-ISI-ALT-19-01 for Containment Tendon Inservice Inspection Extension (EPID No. L-2019-LLR-0017), dated July 11, 2019, ADAMS Accession No. ML19182A077.

x Letter from Michael Markley (USNRC) to Steven Snider (Duke Energy),

OCONEE NUCLEAR STATION, UNITS 1, 2, AND 3 - PROPOSED ALTERNATIVE TO ASME CODE RE: CONTAINMENT UNBONDED POST-TENSIONING SYSTEM INSERVICE INSPECTION REQUIREMENTS (EPID L-2021-LLR-0034), dated December 7, 2021, ADAMS Accession No. ML21335A106 x

Letter from James G. Danna (USNRC) to Daniel Stoddard (Dominion Energy),

MILLSTONE POWER STATION, UNITS 2 - PROPOSED ALTERNATIVE RR-05-05 TO THE REQUIREMENTS OF THE ASME CODE RE: CONTAINMENT UNBONDED POST-TENSIONING SYSTEM INSERVICE INSPECTION REQUIREMENTS (EPID L-2019-LLR-0120), dated October 20, 2020, ADAMS Accession No. ML20287A471

8.0 ACRONYMS

ASME American Society of Mechanical Engineers CFR Code of Federal Regulations CPM Corrosion Protection Medium FNP Farley Nuclear Plant ISI Inservice Inspection NRC Nuclear Regulatory Commission PSI Preservice inspection PWR Pressurized Water Reactor RE Responsible Engineer SIT Structural Integrity Test

9.0 REFERENCES

1) American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel (B&PV)

Code,Section XI, 2007 Edition, 2008 Addenda.

2) Farley Nuclear Plant 5th Ten Year interval Inspection Plan and Schedule

ATTACHMENT Plant-Specific Tendon Report FNP Units 1 and 2

FNP RR Technical Report Page 1 of 73 Revision 1 / 20230620 JOSEPH M. FARLEY NUCLEAR PLANT UNITS 1 & 2 CONTAINMENT POST-TENSIONING SYSTEM INSERVICE INSPECTION BASIS FOR PROPOSED EXTENSION OF EXAMINATION INTERVAL TECHNICAL REPORT Report Prepared by:

Howard T. Hill, PhD, P.E. (California Civil Certificate C 22265)

BCP Technical Services, Inc.

Revision 1 / 20 June 2023

FNP RR Technical Report Page 2 of 73 Revision 1 / 20230620 Table of Contents

1. PURPOSE, CONTAINMENT / ISI PROGRAM DESCRIPTION AND ORGANIZATION............................................................................................................................... 4 1.1 Containment Description............................................................................................. 4 1.2 Containment ISI Program Summary Description................................................. 6 1.3 Report Organization..................................................................................................... 7

2.

SUMMARY

OF PROPOSED ALTERNATIVES....................................................................... 8

3. BACKGROUND OF CURRENT ISI REQUIREMENTS AND BASIS FOR PROPOSED ALTERNATIVES................................................................................................... 10 3.1 Regulatory Guide 1.35............................................................................................... 10 3.2 ASME Section XI / Subsection IWL....................................................................... 11 3.3 USNRC Regulation 10CFR50.55a......................................................................... 11 3.4 Basis for Proposed Deviations / Relief from 10CFR50.55a and IWL Requirements............................................................................................................................ 11

4. FNP EXAMINATION HISTORY AND RESULTS ANALYSIS / EVALUATION............ 17 4.1 Tendon Force Trends and Forecasts.................................................................... 19 4.2 End Anchorage Condition......................................................................................... 26 4.3 Wire Examination and Test Results Evaluation................................................. 40 4.4 Corrosion Protection Medium Testing................................................................... 42

5. OVERALL

SUMMARY

, CONCLUSIONS AND RECOMMENDATIONS....................... 46 5.1 Surveillance Results Overall Summary................................................................ 46 5.2 Conclusions................................................................................................................... 47 5.3 Recommendations...................................................................................................... 48

6. REFERENCES................................................................................................................................ 50

7. TABLES AND FIGURES.............................................................................................................. 53

FNP RR Technical Report Page 3 of 73 Revision 1 / 20230620 ACI ANS ANSI ASME ASTM BH CPM EF FNP FSAR ILRT kip ksi LCL MRV MT NCR NRC ORNL pH ppm Rc RE SIT LIST OF ABBREVIATIONS American Concrete Institute American Nuclear Society American National Standards Institute American Society of Mechanical Engineers American Society for Testing and Materials Buttonhead Corrosion protection medium Elongation at failure Farley Nuclear Plant Final Safety Analysis Report Integrated leakage rate test Kilo-pound (1,000 pounds)

Kips per square inch Lower confidence limit Minimum Required Value Magnetic particle testing NoQ-conformance report Nuclear Regulatory Commission Oak Ridge National Laboratory Potential of hydrogen (a measure of acidity or basicity)

Parts per million Rockwell C (a measure of hardness)

Responsible Engineer Structural Integrity Test USNRC United States Nuclear Regulatory Commission UTS Ultimate tensile strength

FNP RR Technical Report Page 4 of 73 Revision 1 / 20230620

1. PURPOSE, CONTAINMENT / ISI PROGRAM DESCRIPTION AND ORGANIZATION This report provides the technical evaluation / justification supporting a request for relief to allow alternatives to certain containment in-service inspection (ISI) requirements specified in USNRC Regulation 10CFR50.55a (Reference 6.1) and, by reference therein, ASME Section XI, Subsection IWL (Reference 6.2). The current Farley Nuclear Plant (FNP) containment ISI program conforms to these regulatory and code requirements with modifications as allowed by approved relief requests.

1.1 Containment Description The FNP containments are essentially identical reinforced and post-tensioned concrete pressure vessels that serve as the final barriers (after fuel cladding and the reactor coolant system pressure boundary) against the release of radioactive material from the reactor core to the outside environment. The design basis internal pressure for both containments is 54 psig (Final Safety Analysis Report, Reference 6.3).

Each containment consists of a conventionally reinforced concrete flat base mat with a central reactor cavity connected to and supporting a pre-stressed concrete cylinder and a pre-stressed concrete shallow dome.

The cylinder is thickened at three equally-spaced locations with vertical buttresses that provide anchorage for the hoop pre-stressing tendons (see below).

The dome consists of a central spherical cap and outer toroidal section that transitions into a massive ring girder which serves as a connection between the dome and cylinder.

The ring girder also provides anchorage for the dome pre-stressing tendons and the upper ends of the vertical tendons. The interior surface of the containment is lined with a 1/4 inch (thicker at penetration regions) steel plate for leak tightness. Principal containment dimensions are, as shown in Reference 6.3:

x Cylinder inside radius - 65 ft.

x Inside height - 183 ft.

x Cylinder wall concrete thickness (increases at the wall to mat haunch) - 3 ft. 9 in.

x Dome thickness (increases at the transition to the ring girder) - 3 ft. 3 in.

x Base mat thickness - 9 ft.

FNP RR Technical Report Page 5 of 73 Revision 1 / 20230620 The cylinder wall and dome are post-tensioned with 1701 wire BBRV (wires anchored by cold-formed buttonheads) tendons. The ASTM A421 (Reference 6.4) wires have a diameter of 0.250 inches and a specified minimum ultimate tensile strength of 240 ksi.

The cylindrical wall is pre-stressed with both circumferential (hoop) and vertical tendons.

Wall circumferential pre-stressing consists of 1352 tendons arranged in 3 overlapping 45-tendon sub-groups, each spanning 240 degrees plus the width of a buttress. Vertically adjacent sub-groups are offset by 120 degrees to provide continuous overlap of pre-stressing force. Circumferential (hoop) tendons anchor at the buttress faces.

Circumferential tendon designations include two letters identifying the buttresses at which the tendons are anchored. The order of the letters, which may differ depending on the source document, is not significant; i.e., H20AB and H20BA identify the same tendon.

Wall vertical pre-stressing consists of 130 tendons anchored at the top of the ring girder and the bottom of the base mat. A tunnel (the tendon access gallery) below the base mat provides access to the lower anchorages.

Dome pre-stressing consists 93 tendons arranged in 3 layered sub-groups, each having 31 equally spaced and parallel (in plan-view) tendons. The layers intersect at 60 degrees.

Dome tendons anchor at the vertical face of the ring girder.

Tendon forces decrease with time as a result of elastic shortening (the effect of sequential tensioning operations), concrete shrinkage, concrete creep and pre-stressing wire relaxation losses. Mean tendon forces must remain above specified minima to ensure that concrete remains in a state of membrane compression under postulated accident pressure and temperature conditions. Minimum required mean tendon forces as specified in FSAR (Reference 6.3) Paragraph 18.4.3 are shown below. FSAR minima are shown as kips / wire. The kips per tendon minima are computed for 170 wire tendons.

x Hoop Tendon Group:

6.01 kips / wire 1,021.7 kips / tendon x Vertical Tendon Group:

6.81 kips / wire 1,157.7 kips / tendon x Dome Tendon Group 6.35 kips / wire 1,079.5 kips / tendon 1 Due to a duct constriction, Unit 1 tendon H16AC could not be installed with 170 wires; it was installed with 90 wires.

2 Both containments were designed for 135 tendons. Due to a blocked duct, Unit 2 tendon H5EF could not be installed. Following the failure of the H11AB anchor head in 2017, tendon H11BC was de-tensioned and abandoned in place as discussed in Part 4 paragraph 4.2.4.3.

FNP RR Technical Report Page 6 of 73 Revision 1 / 20230620 1.2 Containment ISI Program Summary Description Continuing structural3 integrity of the FNP containments is verified through regular examinations and tests (also referred to as surveillances) performed in accordance with the requirements of USNRC Regulation 10CFR50.55a (Reference 6.1) and, by reference therein, ASME Section XI, Subsection IWL (Reference 6.2) as modified by approved relief requests. The ISI program, as detailed in the Fifth-Ten-Year ISI Interval Containment Inspection Plan (Reference 6.5), requires visual examination of the entire accessible concrete surface and examination and testing of random samples selected from the tendon population. Surface visual examinations follow the applicable guidelines given in the ACI reports referenced in Subsection IWL and are not considered further in this report which addresses only the pre-stressing system.

Examination and testing of the post-tensioning system currently follows ASME B & PV Code (2007 Edition with 2008 Addenda)Section XI, Subsection IWL requirements as modified by approved relief requests. Examinations and tests, performed on a random sampling of tendons4, are described below:

x Visual Examination Anchorage area concrete and post-tensioning system hardware are visually examined for the following indications of damage or degradation:

o Cracking or spalling at the surface of concrete adjacent to bearing plates.

o Accumulation of water in endcaps.

o Lack of corrosion protection medium (CPM) coverage on anchor heads, shims and buttonheads.

o Corrosion on bearing plates, anchor heads, shims and buttonheads.

o Protruding or missing buttonheads.

o End anchorage component cracking or distortion.

3 Containment liner ISI, performed to assess leak tight integrity, is covered by Subsection IWE and is not addressed in this technical report.

4 Random samples are drawn from the following populations:

Population 1 - All tendons not previously included in a surveillance sample or included in Populations 2 and 3, with the exception of one tendon in each group (hoop, vertical or dome) designated as a common tendon and examined during each consecutive surveillance.

Population 2 - Unit 1 augmented examination Group 1 comprised of tendons subject to repair

/ replacement activity in 2012.

Population 3 - Unit 1 augmented examination Group 2 comprised of tendons subject to repair

/ replacement activity in 2019.

FNP RR Technical Report Page 7 of 73 Revision 1 / 20230620 x Tendon Force Measurement and Wire Testing5 The force at each end of the sample tendon is measured by applying jacking force just sufficient to loosen the shim stack (thus ensuring that all tendon load is carried by the calibrated jacks).

Also, a single wire (in addition to any found to be broken in service) is removed from one tendon in each group, examined for damage and corrosion and tested to determine yield strength, ultimate strength and elongation at failure.

x CPM Sampling and Testing Samples of CPM are collected at each end of each tendon and analyzed for water content, concentration of corrosive ions and reserve alkalinity.

x Free Water Collection and Testing Free water, if found in sufficient quantity for sampling, is collected and tested to determine pH.

1.3 Report Organization The remainder of this report consists of the following 6 parts:

Part 2 Summary of Proposed Alternatives Part 3 Background of Current ISI Requirements and Basis for Proposed Alternatives Part 4 FNP Examination History and Results Analysis / Evaluation Part 5 Overall Summary, Conclusions and Recommendations Part 6 References Part 7 Tables and Figures 5 In accordance with the provisions of ASME Section XI Paragraph IWL-2421, tendon force measurements and wire extraction / testing follow an alternating schedule as detailed in the Fifth-Ten-Year ISI Interval Containment Inspection Plan (Reference 6.5).

FNP RR Technical Report Page 8 of 73 Revision 1 / 20230620

2.

SUMMARY

OF PROPOSED ALTERNATIVES The following alternatives to the currently approved ISI program are proposed and evaluated in this report:

x Extend the interval for visual examination (Subsection IWL Table IWL-2500-1 Items 2.30, L2.40 and L2.50) of Unit 1 and Unit 2 end anchorage areas from 5 years to 10 years as shown the schedule below.

x Extend the interval for complete Unit 1 and Unit 2 post-tensioning system examinations that include tendon force measurements (Subsection IWL Table IWL-2500-1 Items 2.10, 2.30, L2.40 and L2.50) in accordance with the following schedule.

Proposed Tendon Surveillance Schedule (includes the four most recent Unit 1 and Unit 2 surveillances for reference)

Year Units 1 & 2 Visual Examination, CPM Sampling &

Free Water Collection / Testing Tendon Force Measurement 2006 Performed Performed 2012 Performed N/A 2017 Performed Performed 2021 Performed N/A 2031a Perform Perform 2041a Perform N/A 2051b Perform Perform Note a: For scheduling purposes, each future surveillance is considered to be due at mid-year and must be performed between 30 June of the year prior to the year shown and 30 June of the year following the year shown.

Note b: If applicable.

x Include Unit 1 Groups 1 and 2 augmented examinations (examinations of tendons subject to repair / replacement activity during 2012 and 2019) with the Population 1 (see footnote in Section 1.2) examinations to be performed per the above schedule.

x Eliminate the requirement for de-tensioning / re-tensioning of tendons, wire removal and wire sample testing (Subsection IWL Table IWL-2500-1 Item 2.20).

x Limit initial corrosion protection medium laboratory tests (Subsection IWL Table IWL-2500-1 Item 2.40) to that which determines absorbed water content; perform the corrosive ion and reserve alkalinity tests only on those samples that have a

FNP RR Technical Report Page 9 of 73 Revision 1 / 20230620 water content above the acceptance limit, are collected at an anchorage where free water and / or corrosion is found or if specified by the IWL Responsible Engineer6 (RE).

The above proposed alternatives relate only to pre-stressing tendon tests and the associated examinations that require close-in access to tendon end anchorage areas.

Visual examination of the exposed areas of the containment concrete surface and tendon end caps will continue to be performed at 5-year intervals in accordance with past practice.

This report and the Relief Request that it supports address only proposed alternatives to the in-service inspection requirements covered by ASME Section XI, Subsection IWL Table IWL-2500-1 Examination Category L-B. The Category L-A concrete surface examinations will continue to be performed in accordance with Subsection IWL as modified by approved relief requests. Containment liner and penetration assembly examinations and tests will continue to be implemented in accordance with Subsection IWE as modified by approved relief requests.

Based on the evaluation of past examination results as discussed in subsequent sections of this report, it is concluded that implementation of the alternative containment in-service inspection program recommended herein will provide an equivalent level of assurance that the structural integrity of the Unit 1 and Unit 2 containments is maintained at the highest level.

6 A registered professional engineer having qualifications and responsibilities as identified in ASME Section XI Paragraph IWL-2330.

FNP RR Technical Report Page 10 of 73 Revision 1 / 20230620

3. BACKGROUND OF CURRENT ISI REQUIREMENTS AND BASIS FOR PROPOSED ALTERNATIVES Containment in-service inspection (also referred to herein as surveillance and in-service examination) requirements originated with the issuance of Regulatory Guide 1.35 (Reference 6.6) in the early 1970s and are currently mandated by ASME Section XI, Subsection IWL, which is incorporated by reference into USNRC regulation 10CFR50.55a. A brief history of current requirement development is summarized in 3.1, 3.2 and 3.3 below. The basis for the proposed alternative program is discussed in 3.4.

3.1 Regulatory Guide 1.35 In February 1973, the U. S. Atomic Energy Commission issued the initial version of Regulatory Guide 1.35, Inservice Surveillance of Ungrouted Tendons in Pre-stressed Concrete Containment Structures. This document, drafted prior to the completion of the first pre-stressed concrete containment structures and well before the accumulation of prototype containment pre-stressing system performance data, described the following as an acceptable basis for system examinations:

x Examination schedule - 1, 3 and 5 years after the pre-operational structural integrity test and every 5 years thereafter.

x Examination sample size - 6 dome, 5 vertical and 10 hoop tendons.

x Wire / strand extraction - one wire / strand from a tendon in each group (dome, vertical, hoop); extraction requires de-tensioning.

x Visual examinations for damage, deterioration and corrosion - corrosion protection medium, end anchorage hardware, anchorage area concrete and extracted wires

/ strands.

x Physical tests - tendon lift-off force and extracted wire / strand strength and elongation at failure.

The regulatory guide does not discuss the basis for the examination interval, the sample size or the various tests and examinations to be included in an acceptable program (these represent consensus opinions reached among the individuals involved in guide development). Also, it does not address the possible need for changes as future operating experience accumulates.

Subsequent revisions to Regulatory Guide 1.35 added procedures for corrosion protection medium chemical analyses (added in Revision 3), substantially changed the sampling process and included numerous other additions and clarifications but retained the examination interval and wire / strand testing program as described in the original 1973 issue. The final revision, Revision 3, was issued in July 1990.

FNP RR Technical Report Page 11 of 73 Revision 1 / 20230620 Regulatory Guide 1.35 was withdrawn in August 2015 following the incorporation, by reference, of ASME Section XI, Subsection IWL into NRC regulation 10CFR50.55a.

3.2 ASME Section XI / Subsection IWL The 1989 edition of the ASME Boiler and Pressure Vessel Code Section XI included Subsection IWL for the first time, which provided comprehensive and detailed requirements for a concrete containment in-service inspection program. During the development of IWL7, which commenced in the 1970s, it was concluded that NRC acceptance and endorsement (by reference in 10CFR50.55a) of the document would be expedited if departures from the program described in Regulatory Guide 1.35 were minimized. For this reason, the examination interval, strength / elongation testing of wire

/ strand samples and relatively extensive chemical testing of corrosion protection medium samples mandated in IWL are unchanged from those identified in Regulatory Guide 1.35, Rev. 3.

Subsection IWL has been revised numerous times since its initial incorporation into Section XI in 1989. None of these revisions have altered the examination interval or the basic requirement to test wire / strand and corrosion protection medium samples.

3.3 USNRC Regulation 10CFR50.55a The 1996 amendment to 10CFR50.55a incorporated, by reference and with specified exceptions and additions, the ISI requirements given in the 1992 edition with addenda of ASME Section XI, Subsection IWL. Subsequent amendments have referenced later editions / addenda of IWL but none have addressed changes to either the examination interval or the requirements for testing wire / strand and corrosion protection medium samples.

3.4 Basis for Proposed Deviations / Relief from 10CFR50.55a and IWL Requirements

[Note: This section of the technical report includes a generalized summary of post-tensioning system performance observed during 4 decades of periodic examinations conducted at 24 U. S. nuclear plant sites with 41 pre-stressed concrete containments. It is intended to show that containment post-tensioning systems, with few exceptions, are continuing to perform well and that, in general, system examination intervals could be significantly increased without compromising safe operation of the plant.]

7 The author of this technical report has been a member of the IWL working group since the 1970s (when it was still being developed as an addition, CC-9000, to ASME Section III, Division 2) and served as chair of the working group during its later development and much of the period leading up to its incorporation into Section XI in 1989.

FNP RR Technical Report Page 12 of 73 Revision 1 / 20230620 The material covered in this section is based on the report authors experience as described below:

x Participation in containment post-tensioning system examinations at U. S. and foreign sites.

x USNRC funded research, performed under contract to ORNL, on age-related decrease in pre-stressing force and other age-related effects at ~20 U. S.

containments.

x Four decades of interacting with fellow members of the IWL working group.

x Review of USNRC informational bulletins and generic letters.

x Review of system performance history in connection with preparation of program basis documents for license renewal applications.

x Forecasting tendon forces in connection with the preparation of minimum required pre-stressing force calculations.

x Work on a USNRC-funded project to review and recommend updates to Regulatory Guides 1.35, 1.35.1 and 1.90, which all address in-service inspection of pre-stressed containments.

x A three-year association with the Crystal River 3 containment repair project; assignments included evaluating the condition of tendons not affected by the repair work.

The following summary is qualitative; specific references are not cited as the bases for the generalized statements regarding post-tensioning performance.

As noted in 3.1, 3.2 and 3.3 above, the examination intervals and wire / strand testing addressed in the 1973 original issue of Regulatory Guide 1.35 are now, 50 years later, still incorporated effectively unchanged into the current edition of ASME Section XI, Subsection IWL.

In addition, the current edition of ASME Section XI, Subsection IWL specifies corrosion protection medium chemical testing procedures that are effectively unchanged from those described in Regulatory Guide 1.35, Revision 3, issued in July 1990.

The results of unbonded post-tensioning system examinations performed over the last 4 decades at 24 domestic sites with a total of 41 pre-stressed containments (listed in Table

1) provide ample evidence, as discussed below, that prescriptive requirements currently in IWL are in many cases overly conservative. These industry results as well as FNP plant-specific operating experience as subsequently discussed support the implementation of alternative programs with fewer prescriptive requirements.

FNP RR Technical Report Page 13 of 73 Revision 1 / 20230620 Reducing prescriptive requirements, as addressed in this report and the associated Relief Request that it supports, has the following advantages:

x It reduces personnel and equipment safety hazards associated with working at heights, handling of heavy loads, working with high-pressure hydraulic equipment, working close to tendon end anchorages that can suddenly release stored mechanical energy, working with hot (>150 °F) corrosion protection medium that is under pressure, working in proximity to high-energy plant systems and working in radiation-controlled areas.

x It reduces the potentially deleterious cycling of tendon loads that occurs during de-tensioning / re-tensioning for wire removal and to a lesser extent during the measurement of lift-off forces.

The technical justification for the proposed deviations is based on operating experience accumulated over the past 4 decades at the 24 domestic plants with containments having unbonded post-tensioning systems and, in particular, the operating experience documented during the post-tensioning system examinations performed at FNP. The general conclusions regarding post-tensioning system performance are listed below.

Conclusions specific to FNP are addressed in detail in subsequent sections of this report.

3.4.1 Pre-Stressing Force Trend Containment design criteria typically require that the post-tensioning system provide sufficient pre-stressing force at the end of 40 years (period of initial licensure considered to be the plant operating lifetime when design work on existing plants commenced) to maintain membrane compression in the walls and dome under specified accident conditions.

Post-tensioning system design was based on a postulated linear decrease in pre-stressing force with the logarithm of time (log-linear decrease). The log-linear function was selected as this provided a reasonably good fit to the results of relatively short-term creep, shrinkage and relaxation tests and was consistent with expectations based on the calculated response of theoretical models that represent materials as an assemblage of linear springs and dashpots. Concrete creep and shrinkage tests were typically conducted for 180 days and pre-stressing steel relaxation tests for 1000 hours0.0116 days 0.278 hours 0.00165 weeks 3.805e-4 months (~40 days).

Designing for a 40-year plant operating lifetime required extrapolating concrete test durations by a factor of 80 and steel test durations by a factor of almost 400.

Post-tensioning system examination data have shown, with relative consistency, that the rate of change of pre-stressing force with the logarithm of time tends to decrease with time. Within 20 to 25 years after the completion of pre-stressing operations, the force

FNP RR Technical Report Page 14 of 73 Revision 1 / 20230620 time trend becomes essentially flat8. Given this general trend, it can be stated with a high degree of confidence that the examination interval may be increased beyond 10 years with no compromise of safety function if the following conditions are satisfied:

x The current mean pre-stressing force (hoop, vertical, dome, inverted U) computed using both the trend of individual tendon force data acquired to date and the mean of the most recently acquired data exceed the minimum required level by significant margins. The margin deemed significant is established through an evaluation by the Responsible Engineer. If the trend of the mean is considered to be a log-linear function, data acquired during the year 1, 3 and 5 surveillances may be omitted from the trend computation9.

x The forecasted mean pre-stressing forces (hoop, vertical, dome, inverted U),

determined using the data acquired to date and computed, for conservatism, at the 95% lower confidence limit, remain above the minimum required levels until well past the deadline for completion of the subsequent surveillance.

3.4.2 System Hardware Condition History Industry-wide, there have been relatively few significant issues associated with containment post-tensioning system hardware (tendon wire / strand10, anchor heads, wedges, shims and bearing plates).

Active corrosion is typically found only on the exposed parts of bearing plates. Free water at end anchorage areas, when found in quantities that are sufficient to allow collection and testing, has almost never been observed to cause corrosion.

Instances of deformation / damage / degradation are rare and almost always associated with singular construction events.

Most exceptions to the above are the result of unique situations that are plant-specific and not indicative of an industry-wide problem.

8 As discussed in Section 4 of this report, scatter of measured tendon forces tends to obscure the true trend of the mean. The conclusion regarding flattening of the trend is based on statistical analysis rather than an observed characteristic of the plotted data.

9 Industry-wide data tend to show that mean force (vs. log time) decreases significantly more rapidly during the first 10 years following completion of pre-stressing operations than it does during subsequent years. In addition, measurements made during the early years of plant life are often known to be less accurate than those made later using improved technology.

10 The only U. S. containments with strand tendons, anchored with hardened wedges rather than cold formed buttonheads are Rancho Seco, San Onofre (2 & 3) and Vogtle (1 & 2). Of these plants, only the Vogtle units are currently operating.

FNP RR Technical Report Page 15 of 73 Revision 1 / 20230620 Two widely reported exceptions, one involving wire corrosion and the other anchor head material are described below. Occurrences have been limited to the plants where these were first observed.

x Debris blocked the drains at the perimeter of a shallow dome resulting in flooding that submerged the caps at the upper end of the vertical tendons. The hold-down bolt holes in the tops of the caps were not well sealed. Storm water entered the caps through these holes and submerged the short lengths of uncoated wire just below the anchor heads. A number of wires were severely corroded and found to be no longer effective as pre-stressing elements.

New maintenance procedures to prevent future flooding above the ring girder were implemented. The condition has not recurred.

x A unique combination of steel chemistry and high hardness led to the failure of anchor heads in both Farley Nuclear Plant units. This matter is covered extensively in subsequent parts of this report.

This problem, which is unique to Farley, has been addressed by implementing an enhanced examination and corrective action program.

3.4.3 Wire / Strand Test Results Wire sample tests, performed by certified laboratories using appropriate equipment and procedures as specified in the applicable ASTM standards, show that strength and elongation at failure do not degrade with time. While past industry data often show reported strength and elongation vary significantly from examination to examination, close evaluation of the data suggests that such fluctuations can generally be attributed to variations in the testing, specifically:

x Many of the earlier tests were performed using vendor procedures that differ from those specified by the applicable ASTM standards.

x Testing equipment was often vendor-fabricated and did not meet ASTM specifications.

x Personnel assigned to the testing work did not always have the necessary experience.

In general, tests that conform to ASTM specifications and that are performed by experienced technicians show that both strength and elongation are not only close to, but exceed, the minima (240 ksi and 4.0%, respectively) specified for ASTM A421 (Reference 6.4) wire.

As there is no evidence that either strength or elongation (at failure) decrease with time under load, it is concluded that there is no benefit to ongoing tests for these parameters.

FNP RR Technical Report Page 16 of 73 Revision 1 / 20230620 And, it is to be noted that there is no precedent across the broader (beyond nuclear power plants) industry to periodically evaluate the continuing mechanical properties of pre-stressing system hardware and other steel structural members.

Relaxing the requirement for wire / strand tests, when justified by evaluation of specific plant operating experience, reduces the deleterious cycling of tendon force resulting from the de-tensioning and re-tensioning needed to allow wire removal. It also reduces the industrial hazard associated with the de-tensioning and re-tensioning operation.

3.4.4 Corrosion Protection Medium Test Results Effectively all U. S. containments that have ungrouted tendons use a corrosion protection medium (CPM) product supplied by the Viscosity Oil Company. CPM formulations have changed over time, but the basic product remains the same, i.e., a microcrystalline wax that provides the following protective functions:

x An essentially waterproof coating on tendon wires and end anchorage hardware.

x A bulk-fill to limit water intrusion into tendon ductwork.

x A chemically built-in alkalinity to neutralize acid conditions that could lead to corrosion.

There is no industry operating experience to indicate that the CPM used in U. S.

containments has degraded over time in such a manner as to result in tendon or end anchorage hardware corrosion. Such hardware problems as have been found are attributable to either gross loss of medium from the ductwork, end anchorage design features that prevent full coverage of metallic components at the time of CPM injection, or metallurgical characteristics of certain anchor head production batches.

Current CPM testing requirements mandate relatively complex procedures, as described or referenced in ASME Section XI (Reference 6.2) Table IWL-2525-1, to determine absorbed water content, corrosive ion concentration and residual reserve alkalinity. As corrosive ions cannot enter the ductwork in the absence of water intrusion, and reserve alkalinity cannot be brought into play in the absence of acid ion presence in the bulk CPM, there is little or no benefit gained by testing CPM samples for ion concentrations and reserve alkalinity unless there is evidence of free or absorbed water.

Consequently, industry experience would suggest that CPM samples collected during end anchorage examinations should be initially tested only to determine absorbed water content and that additional tests should be conducted only if there is evidence of sufficient water to establish potentially corrosive conditions, or if specific unit / plant test data indicate a history of problems with the CPM. Modifying testing programs accordingly would reduce the environmental problems associated with disposal of the reagents used in these processes (the procedure for determining water content does not require use of reagents).

FNP RR Technical Report Page 17 of 73 Revision 1 / 20230620

4. FNP EXAMINATION HISTORY AND RESULTS ANALYSIS / EVALUATION The visual examination results and test data used in the development of Sections 4.1 through 4.4 are those documented in FNP in-service inspection reports, References 6.7 through 6.23.

FNP has completed, to date, 11 surveillances of the Unit 1 post-tensioning system and 10 surveillances of the Unit 2 system. These were performed in the years as shown in the following table. The SIT year (References 6.24 and 6.25) is also shown for reference.

The examinations were conducted in accordance with Regulatory Guide 1.35, Revision 2, or 10CFR50.55a / ASME Section XI Subsection IWL as noted.

SIT and Surveillance Number /

Year Year Performed Unit 1 Year Performed Unit 2 Governing Document(s)

SIT 1977 1980 ASME III / Div. 2 / CC-6000 1 / 1 1978 1981 Reg Guide 1.35, Revision 2 2 / 3 1980 1983 Reg Guide 1.35, Revision 2 3 / 5 1981-1982 1985 Reg Guide 1.35, Revision 2 4 / 10 1987 1990 Reg Guide 1.35, Revision 2 5 / 15 1992 1995 Reg Guide 1.35, Revision 2 6 / 20 1997 2000 (Unit 1) Reg Guide 1.35, Revision 2 (Unit 2) 10CFR50.55a / IWL 7 / 25 2002 2006 10CFR50.55a / IWL 8 / 30 2006 2012 10CFR50.55a / IWL 9 / 35 2012 2017 10CFR50.55a / IWL 10 / 40 2017a 2021 10CFR50.55a / IWL 11 / 45 2021a N/A 10CFR50.55a / IWL Note a: The Unit 1 40th year surveillance (2017) included a random sample from Augmented Examination Group 1, tendons subject to repair / replacement activity following the failure of the H7AB anchor head in 2012. The Unit 1 45th year surveillance (2021) included a random sample from Augmented Examination Group 1 and a random sample from Augmented Examination Group 2, tendons subject to repair / replacement activity following the discovery of the H11AB cracked anchor head in 2017.

As noted above, surveillances conformed to the guidance in Regulatory Guide 1.35, Revision 2 (Reference 6.6), through the Unit 1 surveillance in 1997. Per regulatory guide position 1.3, Unit 2 is exempt from the requirements to measure lift-off forces, de-tension tendons and extract wires for testing. In addition, ASME Section XI, paragraph IWL-2421 allows the measurement of lift-off forces (and tendon de-tensioning / test wire extraction) to alternate between the two units, with Unit 2 lift-off forces measured in surveillance year 15 and every 10 years thereafter. Unit 2 surveillances were performed under Regulatory

FNP RR Technical Report Page 18 of 73 Revision 1 / 20230620 Guide 1.35 through the year 15 surveillance in 1995. Therefore, Unit 2 tendon forces and wire strengths / elongations were measured only during the 25 and 35-year surveillances.

As a consequence of the Regulatory Guide 1.35 and Subsection IWL scheduling, Unit 1 and Unit 2 tendon lift-off force measurements (and associated wire extraction / testing) were performed as shown below:

Unit 1: Surveillance years 1, 3, 5, 10, 15, 20, 30 and 40 Unit 2: Surveillance years 25 and 35 Sections 4.1 through 4.4 of this report provide a comprehensive evaluation of FNP post-tensioning system examination results as documented in the applicable surveillance reports.

Section 4.1 - Tendon force trends and forecasts x Unit 1 and Unit 2 hoop tendon force trends and forecasts x Unit 1 and Unit 2 vertical tendon force trends and forecasts x Unit 1 and Unit 2 dome tendon force trends and forecasts x Unit 1 and Unit 2 common tendon trends Section 4.2 - End anchorage condition Section 4.3 - Extracted wire condition and mechanical properties Section 4.4 - Corrosion protection medium chemical properties and free water analysis The proposed extension of the tendon examination interval to 10 years is justified if the extension can be separately justified for each of the 4 post-tensioning system performance categories listed above.

In this report, surveillances are generally referred to by calendar year and / or time, T, since the SIT date. Plots of time-dependent parameters use T for the time axis. Tables listing time-dependent parameters show both the calendar year of the surveillance and the applicable value of T.

T is calculated as the difference between the surveillance mid-point date and the SIT mid-point date, each expressed as decimal years. Mid-points are determined as decimal years midway between the event (SIT or surveillance) starting and ending dates as shown in the applicable reports (or, in Reference 6.5 as noted). To simplify computations, starting and ending dates are treated as the middle of the month during which the surveillance (or SIT) begins and ends. Values of T computed for Units 1 and 2 are shown in the following tables.

FNP RR Technical Report Page 19 of 73 Revision 1 / 20230620 FNP Unit 1 SIT & Surveillance Dates and Time, T, Since SIT Event Start End T', Mid-Point T,

Year Month Year Month Year & Fraction Years Since SIT SIT 1977 2

1977 2

1977.13 0.0 1a 1978 6

1978 6

1978.46 1.3 3

1980 3

1980 6

1980.33 3.2 5

1981 9

1982 4

1982.00 4.9 10 1987 6

1987 8

1987.54 10.4 15 1992 6

1992 7

1992.50 15.4 20 1997 5

1997 6

1997.42 20.3 25 2002 8

2002 8

2002.63 25.5 30 2006 1

2006 3

2006.13 29.0 35 2012 4

2012 6

2012.38 35.3 40 2017 4

2017 9

2017.50 40.4 45 2021 11 2021 12 2021.92 44.8 Note a: Surveillance dates not noted in report; date shown is from Reference 6.5.

FNP Unit 2 SIT & Surveillance Dates and Time, T, Since SIT Event Start End T', Mid-Point T,

Year Month Year Month Year & Fraction Years Since SIT SIT 1980 5

1980 5

1980.38 0.0 1

1981 4

1981 5

1981.33 1.0 3

1983 5

1983 6

1983.42 3.0 5a 1985 9

1985 9

1985.71 5.3 10 1990 4

1990 5

1990.33 10.0 15 1995 5

1995 5

1995.38 15.0 20 2000 5

2000 6

2000.42 20.0 25 2006 1

2006 3

2006.13 25.8 30 2012 4

2012 6

2012.38 32.0 35 2017 4

2017 9

2017.50 37.1 40 2021 11 2021 12 2021.92 41.5 Note a: Surveillance dates not noted in report; date shown is from Reference 6.5.

4.1 Tendon Force Trends and Forecasts In the following discussions and evaluations, all computed mean forces and LCLs are rounded to a whole kip value. Computed values ending in (.5) are rounded to the nearest even number.

FNP RR Technical Report Page 20 of 73 Revision 1 / 20230620 Units 1 and 2 tendon forces were measured during the surveillances noted in the table below.

Unit Surveillance Year - Tendon Force Measurement Yes / No 1

3 5

10 15 20 25 30 35 40 45 1

Yes Yes Yes Yes Yes Yes No Yes No Yes No 2

No No No No No No Yes No Yes No N/A Force (lift-off force or the force required to separate the anchor head from the shim stack) in designated sample tendons, and additional tendons as mandated by procedure or specified by the Responsible Engineer, is measured during each examination. Measured force trends and forecasts provide ample evidence that mean pre-stressing in the containment wall and dome will remain at or above the lower limits shown in report Section 1.1 above until at least T = 100 years and well beyond the currently expected 80-year maximum operating lifetime of the units.

The purpose of a lift-off force measurement is to determine how the initial seating force in a tendon (seating force is used as a measure of the pre-stressing force contributed by the tendon) has been reduced by elastic shortening and time-dependent losses.

Reported tendon force is the average of the lift-off forces measured at the two anchorages. The mean of a number of tendon forces then serves as a reasonable estimate of the overall mean pre-stressing force provided by the applicable tendon group (i.e., hoop, vertical or dome).

Forces measured at tendon anchorages reflect the losses due to elastic shortening11, concrete creep, concrete shrinkage and tendon wire stress relaxation.

Concrete creep strain, concrete shrinkage strain and pre-stressing steel stress relaxation are shown by relatively short-term tests12 to vary more or less linearly with the logarithm of time. The log-linear characteristics established by these tests are used in containment design. For this reason, mean pre-stressing force trends are treated in this report as log-linear functions.

A log-linear mean force trend is computed for each of the Unit 1 tendon groups using all applicable lift-off force data acquired during the 1-year through 40-year surveillances. An additional trend is computed using only the 10-year through 40-year data (tendon forces 11 Elastic shortening loss is the loss in tendon force resulting from the compressive strain induced in the concrete by subsequent tendon tensioning. It is generally greatest for the first tendon tensioned and zero for the last tendon tensioned.

12 Creep and shrinkage tests are typically conducted for 6 months and relaxation tests for 1,000 hours0 days 0 hours 0 weeks 0 months (just under 42 days). These time frames are short relative to the expected service life of a containment (40, 60 or possibly even 80 years if a subsequent license extension is granted).

FNP RR Technical Report Page 21 of 73 Revision 1 / 20230620 were not measured during surveillance year 45) to address the generally observed tendency for the downward slope of the force-vs-log-time-trend to flatten over time.

Unit 2 tendon force measurements are limited to those obtained during surveillance years 25 and 35. Therefore, only a single trend is computed for each of the Unit 2 tendon groups.

Lift-off forces (and log-linear trend lines) are plotted on Figures 1 through 9. Each of these plots exhibits a significant degree of scatter, a phenomenon typical of lift-off force plots generated for other containments. As the number of tendons included in surveillance samples is a small fraction of the total, the mean force represented by a trend line fitted to scattered data is only an estimate of the true mean pre-stressing force provided by the tendon group. A meaningful lower limit on the true mean at any point in time is computed as the 95% lower confidence limit (95% LCL)13 on the trend line ordinate.

The 95% LCLs on-trend line ordinates are shown on the Unit 1 plots. The corresponding 95% LCL curves for the Unit 2 tendon groups, which would be based on only two data sets (those for the 25 and 35-year surveillances) would be effectively meaningless and are not computed.

Both the trend lines and LCL curves are extrapolated to T = 100 years, a major grid line on the plot abscissa.

The log-linear trend slope and intercept as well as LCL values, as applicable, are computed using the methods developed in Probability and Statistics for Engineers by Irwin Miller and John E. Freund (Reference 6.26).

Units 1 and 2 hoop, vertical and dome force trends are addressed separately in sub-sections 4.1.1 through 4.1.3 below.

4.1.1 Hoop Tendon Mean Force Trends, LCLs and Margins Unit 1 and Unit 2 hoop tendon mean force trends, LCLs (Unit 1 only) and margins above the 1,022-kip (rounded up from FSAR value of 1,021.7) minimum required value are addressed separately in 4.1.1.1 and 4.1.1.2 below.

13 The use of a 95% confidence limit is based on a precedent set in the standard (ANSI / ANS 56.8, Reference 6.27) that governs the conduct of another safety related activity--the containment integrated leakage rate test.

FNP RR Technical Report Page 22 of 73 Revision 1 / 20230620 4.1.1.1 Unit 1 Augmented Examination Groups 1 and 2 tendon force data is limited to 2 lift-off values for Group 1 and a single value for Group 2. As this amount of data is insufficient for generating trends, Groups 1 and 2 tendon forces are not addressed separately; Groups 1 and 2 sample tendon forces measured during the 2017 and 2021 surveillances are included with the Population 1 forces for trending purposes.

Unit 1 hoop tendon mean force trends and LCLs are illustrated by the plots in Figures 1 and 2. The first of these uses all data from surveillance year 1 onward to develop the trend and LCL. The second uses only data from surveillance year 10 onward.

Both figures show the trend line and LCL remaining above the 1,022-kip minimum required mean hoop tendon force beyond T = 100. The visual appearance of the plotted points suggest that the trend does not flatten over time. While contrary to expectations (as discussed above, the trend is expected to flatten over time) Figure 2 shows lower mean force and LCL values at T = 100 years than does Figure 1, both figures do provide conclusive evidence that the Unit 1 hoop tendon forces will remain above the minimum required value (MRV) throughout the presumed 80-year maximum operating lifetime of the unit.

Unit 1 hoop tendon mean force trend and LCL values at T = 100 years are listed with margins above the MRV in the following table. Trend values are based on the following log-linear regression line equations (surveillance year data range used to calculate trend shown in parentheses) included on the figures.

(1 through 40-year):

Force trend value, kip = 1,302.0 - 95.08

Log10(T)

(10 through 40-year):

Force trend value, kip = 1,375.1 - 140.69

Log10(T)

Unit 1 Hoop Tendon Mean Force Trend, LCL and Margin at T = 100 Years Lift-off Data Range Used to Compute Trend and LCL Values Trend, kip LCL, kip Value Margin Value Margin 1 through 40-year surveillance data 1,112 90 1,086 64 10 through 40-year surveillance data 1,094 72 1,035 13 4.1.1.2 Unit 2 The Unit 2 hoop tendon mean force trend (LCL not calculated for the reason previously discussed) is shown on Figure 3. The trend is relatively flat and crosses the T = 100-year ordinate at 1,183 kips, or 161 kips above the minimum required value. Value at T = 100 years is based on the trend line equation, F (kip) = 1,288.9 - 52.82

Log10(T), shown on the figure.

FNP RR Technical Report Page 23 of 73 Revision 1 / 20230620 4.1.2 Vertical Tendon Mean Force Trends, LCLs and Margins Unit 1 and Unit 2 vertical tendon mean force trends, LCLs (Unit 1 only) and margins above the 1,158-kip (rounded up from the FSAR value of 1,157.7) minimum required value are addressed separately in 4.1.2.1 and 4.1.2.2 below.

4.1.2.1 Unit 1 Unit 1 vertical tendon mean force trends and LCLs are illustrated by the plots in Figures 4 and 5. The first of these uses all data from surveillance year 1 onward to develop the trend and LCL. The second uses only data from surveillance year 10 onward.

Both figures show the trend line and LCL remaining above the 1,158-kip minimum required mean vertical tendon force beyond T = 100. As is the case for the hoop tendon data, the visual appearance of the plotted points suggest that the trend does flatten over time. This is expected and is confirmed by the trend and LCL values plotted on the figures. The trend line shown for the 10 through 40- year surveillance results case has a flatter slope (-28.64 kip per unit logarithmic interval) and greater T = 100 intercept (1,236-kip) than that shown for the 1 through 40-year surveillance results case (slope and T =

100 intercept of -36.80 and 1,221-kip, respectively).

Both figures provide conclusive evidence that the Unit 1 vertical tendon forces will remain above the minimum required value (MRV) throughout the presumed 80-year maximum operating lifetime of the unit.

Unit 1 vertical tendon mean force trend and LCL values at T = 100 years are listed with margins above the MRV in the following table. Trend values are based on the following log-linear regression line equations (surveillance year data range used to calculate trend shown in parentheses) included on the figures.

(1 through 40-year):

Force trend value, kip = 1,295.0 - 36.08

Log10(T)

(10 through 40-year):

Force trend value, kip = 1,293.4 - 28.64

Log10(T)

Unit 1 Vertical Tendon Mean Force Trend, LCL and Margin at T = 100 Years Lift-off Data Range Used to Compute Trend and LCL Values Trend, kip LCL, kip Value Margin Value Margin 1 through 40-year surveillance data 1,221 63 1,195 37 10 through 40-year surveillance data 1,236 78 1,216 58

FNP RR Technical Report Page 24 of 73 Revision 1 / 20230620 4.1.2.2 Unit 2 The Unit 2 vertical tendon mean force trend (LCL not calculated for the reason previously discussed) is shown on Figure 6. The trend slope is steeper than those computed for the Unit 1 surveillance results but still crosses the T = 100-year ordinate above the MRV. The mean force trend value at T = 100 years, based on the Figure 6 trend line equation, F (kip) = 1,364.0 - 80.29

Log10(T), is 1,203-kip, which is 45 kip above the MRV.

4.1.3 Dome Tendon Mean Force Trends, LCLs and Margins Unit 1 and Unit 2 dome tendon mean force trends, LCLs (Unit 1 only) and margins above the 1,080-kip (rounded up from the FSAR value of 1,079.5) minimum required value are addressed separately in 4.1.3.1 and 4.1.3.2 below.

4.1.3.1 Unit 1 Unit 1 dome tendon mean force trends and LCLs are illustrated by the plots in Figures 7 and 8. The first of these uses all data from surveillance year 1 onward to develop the trend and LCL. The second uses only data from surveillance year 10 onward.

Both figures show the trend line remaining above the 1,080-kip minimum required mean dome tendon force beyond T = 100. Also, Figure 8 shows the LCL computed using the 10 through 40-year surveillance data remaining above the MRV at T = 100. However, the Figure 7 LCL, which is computed using all surveillance data, crosses the MRV at T =

60.5 years. As is the case for the vertical tendon data, the visual appearance of the plotted points suggest that the trend does flatten over time. This is expected and is confirmed by the trend and LCL values plotted on the figures. The trend line shown for the 10 through 40-year surveillance results case has a flatter slope (-19.35 kip per unit logarithmic interval) and greater T = 100 intercept (1,156-kip) than that shown for the 1 through 40-year surveillance results case (slope and T = 100 intercept of -99.69 and 1,090-kip, respectively).

Both figures provide reasonable evidence that the Unit 1 dome tendon forces will remain above the minimum required value (MRV) throughout the postulated 80-year maximum operating lifetime of the unit.

Unit 1 dome tendon mean force trend and LCL values at T = 100 years are listed with margins above (or below) the MRV in the following table. Trend values are based on the following log-linear regression line equations (surveillance year data range used to calculate trend shown in parentheses) included on the figures.

(1 through 40-year):

Force trend value, kip = 1,288.9 - 99.69

Log10(T)

(10 through 40-year):

Force trend value, kip = 1,294.2 - 19.35

Log10(T)

FNP RR Technical Report Page 25 of 73 Revision 1 / 20230620 Unit 1 Dome Tendon Mean Force Trend, LCL and Margin at T = 100 Years Lift-off Data Range Used to Compute Trend and LCL Values Trend, kip LCL, kip Value Margin Value Margin 1 through 40-year surveillance data 1,090 10 1,052

(-28) 10 through 40-year surveillance data 1,156 76 1,091 11 4.1.3.2 Unit 2 The Unit 2 dome tendon mean force trend (LCL not calculated for the reason previously discussed) is shown on Figure 9. The trend slope, between those computed for the Unit 1 surveillance results, crosses the T = 100-year ordinate above the MRV. The mean force trend value at T = 100 years, based on the Figure 9 trend line equation, F (kip) =

1,285.5 - 62.97

Log10(T), is 1,160-kip, which is 80 kip above the MRV.

4.1.4 Pre-Stressing Force Summary and Conclusion The tendon force trends and LCLs presented in 4.1.1 through 4.1.3 above are summarized in the following table.

Lift-Off Data Trend and LCL Summary Group /

MRV Unit Lift-Off Data Time, T, Range, Years Value, kip, & Margin, kip, Over / Under MRV At T = 100 Years Trend Margin LCL Margin Hoop 1,022 kip 1

1 - 40 1,112 90 1,086 64 1

10 - 40 1,094 72 1,035 13 2

25 & 35 1,183 161 N/A Vertical 1,158 kip 1

1 - 40 1,221 63 1,195 37 1

10 - 40 1,236 78 1,216 58 2

25 & 35 1,203 45 N/A Dome 1,080 kip 1

1 - 40 1,090 10 1,052

(-28)a 1

10 - 40 1,156 76 1,091 11 2

25 & 35 1,160 80 N/A Note a: The LCL curve crosses the 1,080-kip MRV line at T = 60.5 years.

The above table shows the hoop, vertical and dome tendon mean force trends remaining above the respective MRVs though T = 100 years, which is beyond the postulated 80-year maximum operating lifetime of the units.

FNP RR Technical Report Page 26 of 73 Revision 1 / 20230620 In addition, the Unit 1 hoop and vertical group LCL values (Unit 2 LCLs are not computed as previously discussed) as well as the dome LCL values computed using the 10-through-40-year surveillance lift-off data remain above the respective MRVs at T = 100. Only the dome LCL values computed using all lift-off data fall below the associated MRV before T

= 100.

In all, 10 of the 10 hoop and vertical group trend and LCL values listed above and 4 of the 5 dome group trend & LCL values are over the associated MRVs at T = 100.

Only the dome group LCL values computed using all (surveillance years 1 - 40) data fall below the 1,080-kip MRV before T = 100 years. However, the dome group all-data LCL remains above the MRV until T = 60.5 years after the 1980 SIT or until the year 2040.

This is 7 years after the 2033 deadline for completing the Unit 2 50th year surveillance (the next surveillance scheduled if the interval is extended as proposed in this technical report; see table in Part 2 above), which includes lift-off force measurements.

On the basis of the tendon group force trends and confidence limits on the trended forces as presented above, it is concluded that the interval between pre-stressing system surveillance activities may be extended as proposed in Part 2 of this technical report with no adverse impact on safe operation of the plant.

4.2 End Anchorage Condition During each of the surveillances, end anchorage areas were visually examined for evidence of corrosion, presence of free water, broken wires or missing buttonheads, damage to / distortion of load-bearing components and cracks in concrete adjacent to bearing plates. Results of these examinations are summarized in 4.2.1 through 4.2.5.

4.2.1 Corrosion Severity of corrosion, as documented in surveillance reports, is defined by alphabetic and numeric levels. The definitions went through several changes over time as noted below.

x Unit 1 1st year surveillance, 1978: Corrosion not addressed in the report.

x Unit 1 3rd year surveillance, 1980 through Unit 2 5th year surveillance, 1985:

Level Definition (Levels A and B Acceptable)

A Bright metal with no visible oxidation B

Reddish-brown metal with no pitting C

Metal having patches of red oxide with no pitting D

Metal having patches of red oxide with pitting E

Heavy rusting with substantial pitting F

Conditions more severe than E

FNP RR Technical Report Page 27 of 73 Revision 1 / 20230620 x Unit 1 10th year surveillance, 1987 through Unit 1 40th year / Unit 2 35th year surveillances, 2017:

Level Definition (Levels A and B Acceptable)

A No visible rust B

Rust that appears to have formed at installation; no evidence of progressing C

New or progressive rust x Unit 1 45th year surveillance / Unit 2 40th year surveillance, 2021:

Anchor Heads, Bushings, Shims and Bearing Plates Level Definition (Levels A and B Acceptable)

A No visible rust B

Rust that appears to have formed at installation; no evidence of progressing C

New or progressive rust Wires and Buttonheads Level Definition (Levels 1 and 2 Acceptable) 1 No visible corrosion 2

Reddish-brown color; no pitting 3

0.000 < pitting < 0.003 4

0.003 < pitting < 0.006 5

> 0.006 pitting Corrosion documented during surveillances conducted through the Unit 1 45th year / Unit 2 40th year is summarized below. Corrosion levels reported are A or B (1 or 2) except as noted.

End Anchorage Corrosion Surveillance Year Unit 1 Unit 2 1

Corrosion not addressed in surveillance report.

Conditions similar to Unit 1 3rd year; however, observed bearing plate corrosion found to have transferred from the uncoated gasket retainer plate to the surface of the bearing plate coating. Coatings intact.

FNP RR Technical Report Page 28 of 73 Revision 1 / 20230620 End Anchorage Corrosion Surveillance Year Unit 1 Unit 2 3

Level D & E corrosion reported on bearing plates (locations not noted) inside and outside the end cap gasket.

Inside corrosion not progressing; condition accepted as is.

Corrosion on H25CA shop end buttonheads. Degree of corrosion and number of corroded buttonheads not noted. Report notes water intrusion past damaged O ring and lack of full CPM coverage at anchor head.

Level C corrosion below coating on H34FD, H25EF and D227 shop end bearing plates; concluded to have no adverse impact on containment integrity.

5 Bearing plate corrosion found to have transferred from retainer plates (see Unit 2 1st year); also, small areas of Level C corrosion on the edges of 25 bearing plates (locations not noted) where concrete trimming resulted in damage to coating at bearing plate edge. Condition deemed not detrimental.

Level C corrosion at edges of hoop tendon bearing plates. Conclusions state that there is no sign of abnormal degradation; therefore, observed corrosion was accepted as is.

3 Year re-examination (see Note a)

Four shims on tendon H29AB (end not noted) and one each on the shop ends of H26AB and H39AB had small areas of non-progressing Level E corrosion; concluded to have been present prior to filling of tendon ducts and end caps with CPM.

N/A 10 (See discussion below)

Small area of Level C corrosion with no apparent penetration found on one shim (location not noted); accepted as is.

10 (of 22 examined) bearing plates had areas of Level C corrosion; most accepted as is. Shop end bearing plates of V14, V31, V72 and V120 buffed to bright metal and recoated.