ML23299A198

Enclosure 2: Callaway RR Tech Report Containment Post-Tensioning System Inservice Inspection Technical Report Basis for Proposed Extension of Examination Interval, Revision 0

ML23299A198
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Site:	Callaway
Issue date:	06/16/2023
From:	Hill H BCP Engineers and Consultants
To:	Office of Nuclear Reactor Regulation
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ULNRC-06831
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Enclosure 2 to Callaway RR Tech Report ULNRC-06831 Page 1 of 62 Rev. 0 20230616 CALLAWAY POWER STATION CONTAINMENT POST-TENSIONING SYSTEM IN-SERVICE INSPECTION TECHNICAL REPORT BASIS FOR PROPOSED EXTENSION OF EXAMINATION INTERVAL Revision 0 Report Prepared by:

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

BCP Engineers and Consultants 16 June 2023 to ULNRC-06831 Callaway RR Tech Report Page 2 of 62 Rev. 0 20230616 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 PROGRAM CHANGES AND CONCLUSIONS ........... 8 2.1 Proposed Program Changes ..................................................................... 8 2.2 Conclusions ............................................................................................... 9

3. BACKGROUND OF CURRENT ISI REQUIREMENTS AND BASIS FOR PROPOSED CHANGES ............................................................................................................... 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 Changes / Relief from 10CFR50.55a and IWL Requirements ..................................................................................................... 12

4. CALLAWAY EXAMINATION HISTORY AND RESULTS EVALUATION ................. 18 4.1 Tendon Force Trends and Forecasts ....................................................... 20 4.2 Wire Examination and Test Results Evaluation ....................................... 29 4.3 End Anchorage Hardware and Concrete Condition ................................. 34 4.4 Corrosion Protection Medium Testing ...................................................... 38

5. OVERALL

SUMMARY

, CONCLUSIONS AND RECOMMENDATIONS .................. 44 5.1 Summary of Surveillance Results ............................................................ 44

6. REFERENCES ........................................................................................................ 47

7. TABLES AND FIGURES .......................................................................................... 49 to ULNRC-06831 Callaway RR Tech Report Page 3 of 62 Rev. 0 20230616 LIST OF ABREVIATIONS AEL Arché Engineering Laboratories ANS American Nuclear Society ANSI American National Standards Institute APHA American Public Health Association ASME American Society of Mechanical Engineers ASTM American Society for Testing and Materials CPM Corrosion protection medium CR Condition report EF Elongation at failure kip Kilo-pound (1,000 pounds) ksi Kips per square inch LCL Lower confidence limit NCR Non-conformance report NRC Nuclear Regulatory Commission ORNL Oak Ridge National Laboratory pH Potential of hydrogen (a scale use to measure acidity and basicity) ppm Parts per million PTL Pittsburgh Testing Laboratories RE Responsible engineer SIT Structural integrity test USNRC United States Nuclear Regulatory Commission UTS Ultimate tensile strength to Callaway RR Tech Report ULNRC-06831 Page 4 of 62 Rev. 0 20230616

1. PURPOSE, CONTAINMENT / ISI PROGRAM DESCRIPTION AND ORGANIZATION This report provides the technical evaluation and justification supporting a request for relief to allow departure from 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 Callaway containment ISI program conforms to these regulatory and code requirements.

1.1 Containment Description The Callaway containment is a reinforced and post-tensioned concrete pressure vessel that serves as the final barrier (after fuel cladding and the reactor coolant system pressure boundary) against release of radioactive material from the reactor core to the outside environment.

The major structural elements of the containment are a cylinder wall, a hemispherical dome roof and a flat foundation mat. The cylinder and dome are pre-stressed; the foundation mat is conventionally reinforced (not pre-stressed). The cylinder and lower 45° of the dome incorporate three equally spaced buttresses that provide anchorage for the circumferential (hoop) pre-stressing tendons.

A carbon steel liner covers the inside surface of the containment and ensures a high degree of leak tightness during operating and accident conditions.

Principal containment dimensions, as given in Callaway FSAR (Reference 6.3) Section 3.8.1.1, are as follows:

• Cylinder and dome inside radius: 70 ft

• Cylinder height from top of base mat to dome spring line: 135 ft

• Cylinder wall thickness: 4 ft

• Dome thickness: 3 ft

• Foundation mat thickness: 10 ft

• Liner thickness: 1/4 in The containment wall and dome are pre-stressed with 170 wire BBRV (wires anchored by cold formed buttonheads) tendons. The ASTM A421 (Reference 6.4) wires have a diameter of 0.250 inches.

The pre-stressing system consists of circumferential (also horizontal or hoop) and meridional (inverted U) tendon groups. Circumferential tendons anchor at buttresses that extend out from the face of the cylinder wall and dome. Inverted U tendons anchor at the to Callaway RR Tech Report ULNRC-06831 Page 5 of 62 Rev. 0 20230616 bottom of the base mat; a tunnel (the tendon gallery) below the mat provides access to the inverted U tendon anchorages.

The circumferential group is comprised of 165 overlapping hoop tendons, each spanning a nominal 240 degrees. Of these, 135 are located below the dome spring line. The remaining 30 circumferential tendons are located between the spring line and the dome 45° azimuth.

Two sub-groups of inverted U tendons pre-stress the cylinder wall and dome in the meridional direction1. The sub-groups, each consisting of 43 tendons, intersect over the dome at 90 degrees in plan.

Containment tendons were initially tensioned to the mean end anchorage seating forces shown in the table below (Reference 6.5).

Inverted U Tendons All (Cylinder& Dome) Circumferential Tendons 1,502.2 kip 1,474.6 kip After tendons were tensioned, the ducts and end anchorage caps were filled with a micro-crystalline wax (Visconorust 2090-P4 supplied by the Viscosity Oil Company) for corrosion protection.

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 forces are, as specified in Reference 6.5:

• Circumferential2 tendon minimum required mean force - 1,227 kip

• Inverted U tendon minimum required mean force - 1,160 kip 1 Only the central inverted U tendons are purely meridional. Those away from the center provide a circumferential force component.

2 The original design specified a lower value, 1,119 kips, for the circumferential tendons in the dome. To maintain consistency with the license renewal application Time Limited Aging Analysis of Callaway Containment Pre-stressed Tendons (Reference 6.5), this technical report does not apply the lower minimum to dome circumferential tendons. It treats all circumferential tendons as a single sub-group with a minimum required mean force of 1,227 kip.

to Callaway RR Tech Report ULNRC-06831 Page 6 of 62 Rev. 0 20230616 1.2 Containment ISI Program Summary Description Continuing containment structural3 integrity is verified through regular examinations and tests performed at intervals of 5 years 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). The ISI program requires visual examination of the accessible containment concrete surface and examination and testing of small samples of circumferential and meridional tendons. Each sample includes tendons selected at random from the population of tendons not previously examined as well as one tendon common to consecutive examinations. Tendon examinations and tests are performed in accordance with the requirements of Subsection IWL. Concrete surface visual examinations follow the applicable guidelines given in the American Concrete Institute reports referenced in IWL.

Tendon examinations and tests consist of the following:

• Visual examination to detect corrosion and damage at tendon end anchorages (including concrete adjacent to bearing plates) and along the length of wire extracted for strength and ductility testing.

• Collection and quantification of free water found at anchorages.

• Measurement of tendon force applied at the end anchorage.

• Measurement of the strength and ductility of sample wires extracted from designated tendons.

• Laboratory analysis of corrosion protection medium samples to determine absorbed water content, concentration of corrosive ions and reserve alkalinity.

• Laboratory analysis to determine the pH of free water found in tendon end caps and ductwork.

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

to Callaway RR Tech Report ULNRC-06831 Page 7 of 62 Rev. 0 20230616 1.3 Report Organization The remainder of this report consists of the following 6 parts:

Part 2 - Summary of Proposed Program Changes and Conclusions Part 3 -- Background of Current ISI Requirements and Basis for Proposed Changes Part 4 - Callaway Examination History and Results Analysis / Evaluation Part 5 - Overall Summary, Conclusions and Recommendations Part 6 - References Part 7 - Tables and Figures to Callaway RR Tech Report ULNRC-06831 Page 8 of 62 Rev. 0 20230616

2.

SUMMARY

OF PROPOSED PROGRAM CHANGES AND CONCLUSIONS

[Note: This report and the Relief Request that it supports address only proposed departures from the in-service inspection requirements covered by ASME Section XI, Subsection IWL Table IWL-2500-1 Examination Category L-B. Category L-A concrete examinations will continue to be performed as required by Subsection IWL. Also, containment liner and penetration assembly in-service inspection requirements specified in Subsection IWE will continue to be implemented in accordance with the current ISI plan.]

Proposed containment pre-stressing system examination program changes and associated conclusions are summarized in 2.1 and 2.2 below.

2.1 Proposed Program Changes The following changes to current ISI requirements are proposed and evaluated in this report.

• (ASME Section XI Table IWL-2500-1, Examination Category LB) Extend the interval of post-tensioning system examinations and tests and detailed visual examination of concrete adjacent to tendon bearing plates from 5 years to 10 years with future examinations to be performed in accordance with the following schedule:

Post-Tensioning System - Proposed Surveillance Schedule Surveillance Year Earliest Start Latest Finish (Years after January 1984 SIT) 45th January 2028 January 2030 55th January 2038 January 2040 65th January 2048 January 2050 th 75 January 2058 January 2060

• (ASME Section XI Table IWL-2500-1, Examination Category LB, Item L2.40)

Reduce the number of corrosion protection medium (CPM) chemical tests, eliminating routine testing for corrosive ion concentration and absorbed water content.

The above proposed changes relate only to the post-tensioning system and the associated examinations that require close-in access to tendon end anchorage areas.

to Callaway RR Tech Report ULNRC-06831 Page 9 of 62 Rev. 0 20230616 ASME Section XI Table IWL-2500-1, Examination Category LA 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.

2.2 Conclusions The evaluations addressed in Parts 3 and 4 of this technical report support the conclusion that the proposed changes to the current requirements specified in Subsection IWL, as described in Section 2.1 above, can be implemented with no adverse impact on the safe operation of the plant.

In addition, it is concluded the proposed examination interval will enhance personnel safety, limit potential degradation of containment structural integrity and reduce the risk of damage to plant equipment.

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3. BACKGROUND OF CURRENT ISI REQUIREMENTS AND BASIS FOR PROPOSED CHANGES 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 requirements development is summarized in 3.1, 3.2 and 3.3 below. The basis for the proposed changes to the current requirements 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, In-service Surveillance of Ungrouted Tendons in Pre-stressed Concrete Containment Structures. This document, drafted at about the time that the first pre-stressed concrete containment structures were being placed into service and well before the accumulation of prototype containment pre-stressing system performance data, described the following as an acceptable basis for system examinations:

• Examination schedule - 1, 3 and 5 years after the preoperational structural integrity test and every 5 years thereafter.

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

• Wire extraction - one wire from a tendon in each group (dome, vertical, hoop);

extraction requires de-tensioning.

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

• Physical tests - tendon liftoff force and extracted wire 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 probably represent consensus opinions reached at the time among the individuals involved in guide development). Also, it does not address the possible need for changes as future operating experience accumulated.

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 to Callaway RR Tech Report ULNRC-06831 Page 11 of 62 Rev. 0 20230616 the examination interval and wire-testing program as described in the original 1973 issue.

The final revision, Revision 3, was issued in July 1990.

Neither the initial issue of the regulatory guide nor later revisions addressed the use of past performance as a basis for increasing examination intervals or reducing specific examination and testing requirements.

Regulatory Guide 1.35 was withdrawn in August 2015 following the incorporation, by reference, of ASME Section XI, Subsection IWL into USNRC 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 IWL4, 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 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 and corrosion protection medium samples.

3.3 USNRC Regulation 10CFR50.55a In 1996, the NRC amended 10CFR50.55a to include the containment ISI requirements5 given in the 1992 edition (with the 1992 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 and corrosion protection medium samples.

4 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.

5 The 10CFR50.55a amendment includes additional examination requirements and also takes certain exceptions to IWL.

to Callaway RR Tech Report ULNRC-06831 Page 12 of 62 Rev. 0 20230616 3.4 Basis for Proposed Changes / Relief from 10CFR50.55a and IWL Requirements This section of the technical report includes a generalized summary of post-tensioning system performance observed during more than 4 decades of periodic examinations conducted at 24 domestic nuclear plant sites with 41 pre-stressed concrete containments.

It is intended to show that containment post-tensioning systems are continuing to perform well and that, in general, system examination intervals could be significantly increased without compromising safe operation of the plant.

This qualitative summary is based on the authors experience as described below.

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

• 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.

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

• Review of USNRC informational bulletins and generic letters.

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

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

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

• 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.

As the summary is intended to be qualitative, specific references are not cited as the bases for generalized statements regarding post-tensioning system performance.

As noted in 3.1, 3.2 and 3.3 above, the examination intervals and wire 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.

to Callaway RR Tech Report ULNRC-06831 Page 13 of 62 Rev. 0 20230616 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.

The results of unbonded post-tensioning system examinations performed over more than 4 decades at the 41 nuclear units with pre-stressed containments provide ample evidence, as discussed below, that prescriptive requirements currently in IWL are in many cases overly conservative and that an acceptable level of quality and safety can be maintained by performing Table IWL-2500-1 Examination Category L-B examinations at intervals greater than 5 years and by relaxing certain specific testing requirements.

Therefore, it is reasonable to base containment ISI programs on individual plant performance and to reduce the level of examination effort when it is shown that this can be done with no reduction in the margin of safety provided by the containment structure.

The lessening of certain containment ISI requirements, as addressed in this report and the associated Relief Request that it supports, provides the following benefits:

• 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 petroleum products under pressure and working in proximity to high energy plant systems.

• 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 changes is based on industry-wide operating experience accumulated over more than 4 decades during examination of 41 containments having unbonded post-tensioning systems and, in particular, the operating experience documented during the post-tensioning system examinations performed at Callaway between 1985 and 2021. The general conclusions regarding post-tensioning system performance are listed below. Conclusions specific to Callaway are addressed in detail in Parts 4 and 5 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 to Callaway RR Tech Report ULNRC-06831 Page 14 of 62 Rev. 0 20230616 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 <br />0.278 hours <br />0.00165 weeks <br />3.805e-4 months <br /> (~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 time trend becomes essentially flat6. Given this general trend, it can be stated with a high degree of confidence that the examination interval may be increased beyond 5 years with no compromise of safety function if the following conditions are satisfied:

• The current group (circumferential, vertical or dome or, for hemispherical dome containments, circumferential or inverted U) mean pre-stressing force, computed using both the trend of individual tendon force data acquired to date and the mean of the most recently acquired data, exceeds 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 examinations may be omitted from the trend computation7.

• The forecast group mean pre-stressing force, determined using the data acquired to date and computed for conservatism at the 95% lower confidence limit, remains above the minimum required levels until well past the deadline for completion of the subsequent examination.

6 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.

7 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.

to Callaway RR Tech Report ULNRC-06831 Page 15 of 62 Rev. 0 20230616

• Common tendon force trend lines, adjusted up or down, as applicable, to current group mean force levels, indicate that group means will remain above required minima with acceptable margins through the deadline for completion of the subsequent examination.

3.4.2 System Hardware Condition History There have been relatively few significant issues associated with post-tensioning system hardware (tendon wire / strand8, anchor heads, wedges, shims and bearing plates).

Active corrosion is typically found only on the parts of bearing plates exposed to outside atmospheric conditions.

Instances of deformation, damage and degradation are rare and almost always associated with singular construction events. Missing buttonheads are occasionally reported but affect only an inconsequential fraction of the total number of wires comprising the containment tendons.

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

• 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 and snow melt entered the caps through these holes and submerged the short lengths of wire, located just below the anchor heads, that were not coated with CPM. A number of wires were severely corroded and found to be no longer effective as pre-stressing elements.

End cap redesign and new maintenance procedures to prevent future flooding above the ring girder were implemented. The condition has not recurred.

• A unique combination of steel chemistry and high hardness led to the failure of anchor heads in both units of a two-unit plant. Several failures have occurred at random times over the past 4 decades. Industry-wide evaluations established that anchor heads of this type are not in use elsewhere.

8 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, only the Vogtle units are currently operating.

to Callaway RR Tech Report ULNRC-06831 Page 16 of 62 Rev. 0 20230616 The problem has been addressed by implementing an enhanced examination program. Corrective action consists of replacing failed or cracked anchor heads as these are found.

3.4.3 Wire 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 to 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:

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

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

• Personnel assigned to the testing work did not always have the requisite experience.

In general, tests that conform to ASTM specifications and that are performed by experienced technicians show that both strength and elongation are not reasonably close to, but exceed, the minima (240 ksi and 4%, 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, in general9, no benefit to ongoing tests to measure these parameters. 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.

Deleting the requirement for wire tests, when justified by evaluation of specific plant operating experience, eliminates the unnecessary and 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.

9 Testing has identified random instances of low breaking strength and low ductility. If a significant number of randomly selected wires have failed to meet acceptance criteria, the wire tests should be continued.

to Callaway RR Tech Report ULNRC-06831 Page 17 of 62 Rev. 0 20230616 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:

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

• A bulk fill to limit water intrusion into tendon ductwork.

• 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. However, there is evidence that the reserve alkalinity (as measured by a test for base number) of CPM may degrade over time.

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 base number.

Industry experience would suggest that CPM samples collected during end anchorage examinations should be tested only under the following conditions:

• Level 3 or greater corrosion is found on pre-stressing system load bearing elements that are in contact with CPM.

• Free water is found during tendon end anchorage examinations.

• Corrosive ion concentrations show an increasing trend over time.

• Absorbed water content shows an increasing trend over time.

• Base number shows a decreasing trend over time.

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).

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4. CALLAWAY EXAMINATION HISTORY AND RESULTS EVALUATION The Callaway containment post-tensioning system examination program generally conforms to the guidance in USNRC Regulatory Guide 1.35 (through the 15th year, or 5th consecutive, examination) or the requirements of 10CFR50.55a and, as cited therein, ASME Section XI, Subsection IWL (starting with the 20th year, or 6th consecutive, examination). The program consists of the following examination activities:

• Visual examination of the concrete exterior surface (as previously discussed, this activity will continue to be performed in accordance with past practice and is not addressed further in this report).

• Measurement of force applied by the sample tendons at the end anchorage.

• Testing of wires, extracted from designated tendons, to determine ongoing tensile strength and ductility.

• Visual examination of sample tendon end anchorage hardware and concrete surrounding the bearing plates to detect cracking, deformation, corrosion, missing buttonheads or broken wires, water intrusion into tendon ductwork and other indications of degradation.

• Testing of corrosion protection medium (CPM) samples for the presence of corrosive ions (specifically, chloride, nitrate and sulfide) and absorbed water and, to verify continuing reserve alkalinity10.

For each surveillance, a specified number of sample tendons is selected at random from the overall population and, with the exception of one tendon in each group (circumferential, meridional) that is common to consecutive surveillances, excludes tendons previously examined11.

Callaway has completed 9 pre-stressing system examinations. These examinations were based on Regulatory Guide 1.35 or 10CFR50.55a / ASME Section XI Subsection IWL as shown below.

Elapsed Time, Years, from Examination Year January 1984 SIT to Governing Document No. Performed Surveillance Mid-Pointa 1 1985 1.4 Reg Guide 1.35 10 The CPM is formulated to neutralize strong acids that would otherwise have the potential to attack post-tensioning system hardware.

11 As subsequently noted, one tendon (other than the common tendons) has been included in more than one surveillance sample (V1 examined in surveillance years 3 and 5).

to Callaway RR Tech Report ULNRC-06831 Page 19 of 62 Rev. 0 20230616 Elapsed Time, Years, from Examination Year January 1984 SIT to Governing Document No. Performed Surveillance Mid-Pointa 2 1987 3.5 Reg Guide 1.35 3 1989 5.5 Reg Guide 1.35 4 1994 10.5 Reg Guide 1.35 5 1999 15.4 Reg Guide 1.35 6 2004 20.6 10CFR50.55a / IWL 7 2010 26.2 10CFR50.55a / IWL 8 2015 31.4 10CFR50.55a / IWL 9 2021 37.2b 10CFR50.55a / IWL Note a: Most surveillance reports indicate only the months during which the surveillance begins and ends. However, a few note the beginning and ending dates. For consistency, and to simplify time computations, all surveillances are treated as beginning and ending at mid-month. For timing purposes, each surveillance is treated as being performed at a single point in time midway between the beginning and end. The SIT date is treated as mid-January 1984.

Note b: Surveillance delayed, per an approved relief request, due to limitations imposed by the COVID-19 pandemic.

Subsections 4.1 through 4.4 of this report provide a comprehensive evaluation of Callaway post-tensioning system examination results as documented in the 1, 3, 5, 10, 15, 20, 25, 30 and 35-year tendon surveillance reports (References 6.7 through 6.15).

These address the following aspects of examination results:

Subsection 4.1 - Tendon Force Trends and Forecasts Par. 4.1.1 -- Circumferential Tendon Force Trends and Forecasts Par. 4.1.2 -- Meridional Tendon Force Trends and Forecasts Par. 4.1.3 -- Tendon Mean Force Trend Summary and Conclusions Subsection 4.2 - Wire Examination and Test Results Evaluation Par. 4.2.1 -- Wire Visual Examination and Condition Par. 4.2.2 -- Wire Yield Strength Par. 4.2.3 -- Wire Ultimate Tensile Strength (UTS)

Par. 4.2.4 -- Wire Elongation at Failure Par. 4.2.5 -- Wire Visual Examination and Test Summary Subsection 4.3 - End Anchorage Hardware / Concrete Condition Par. 4.3.1 -- Corrosion Par. 4.3.2 - Free Water Par. 4.3.3 - Missing Button Heads and/ Discontinuous Wires Par. 4.3.4 - Load-Bearing Component Damage and Distortion to Callaway RR Tech Report ULNRC-06831 Page 20 of 62 Rev. 0 20230616 Par. 4.3.5 -- Concrete Cracking Adjacent to Bearing Plates Par. 4.3.6 -- End Anchorage Condition Summary and Conclusions Subsection 4.4 - Corrosion Protection Medium Testing Par. 4.4.1 -- Corrosive Ion Tests Par. 4.4.2 - Reserve Alkalinity / Base Number Par. 4.4.3 -- Water Content Par. 4.4.4 -- CPM Test Summary and Conclusion The proposed extension of the tendon surveillance interval to 10 years is justified if it can be shown with a high degree of confidence that the post-tensioning system with its several components will continue to perform its intended function and meet examination acceptance criteria until well beyond the end of the extended interval. Justification of the proposed extension is demonstrated by the evaluations and analyses presented in 4.1 through 4.4 below.

4.1 Tendon Force Trends and Forecasts Force (lift-off force or the force required to separate the anchor head from the shim stack) in designated sample tendons (and additional tendons if 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 above the lower limits specified in Reference 6.5 until well after the January 2030 deadline for completion of the next surveillance if the interval is extended to 10 years. Circumferential and meridional tendon force trends and forecasts are developed and evaluated in 4.1.1 and 4.1.2 below.

The purpose of a lift-off force measurement is to determine how the initial seating force in a tendon (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 force computed for 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.,

circumferential or meridional).

Tendons, with the exception of the few that have been de-tensioned and re-tensioned during surveillances, are effectively undisturbed; forces measured at the anchorage to Callaway RR Tech Report ULNRC-06831 Page 21 of 62 Rev. 0 20230616 reflect the losses due to elastic shortening12, concrete creep, concrete shrinkage and tendon wire stress relaxation.

Circumferential and meridional force trends are addressed separately in subsections 4.1.1 and 4.1.2 below. The following characteristics of the trends are evaluated in each of these sub-sections.

• Log-Linear Trends and LCLs Concrete creep strain, concrete shrinkage strain and pre-stressing steel stress relaxation are shown by relatively short-term tests13 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 and 95% lower confidence limit (LCL) on trend line values are computed using all applicable lift-off force data acquired during the 1-year through 35-year surveillances.

The log-linear trend slope and intercept as well as LCL values are computed using the methods developed in Probability and Statistics for Engineers by Irwin Miller and John E. Freund (Reference 6.16).

Trends and LCLs are plotted and evaluated. LCLs, (and, by default, trends) are shown to remain above minimum required group mean force levels for more than 50 years after the deadline for completion of the next surveillance if the interval is extended to 10 years. This demonstrates that extension of the examination interval will not compromise the safety of the plant.

• Common Tendon Trend-Based Forecast As can be seen on Figures 1 and 3, and as discussed below, surveillance data exhibits a significant degree of scatter. Reasons for the scatter, which is typical regardless of the containment, are not well understood. A lower confidence limit is constructed and used to account for, in a statistical sense, this scatter. The use of a 95% confidence limit is based on a precedent set in the standard (ANSI / ANS 56.8, Reference 6.17) that governs the conduct of another safety related activity, the containment integrated leakage rate test.

12 Elastic shortening loss is the loss in tendon force resulting from the strain induced in the concrete by subsequent tendon tensioning. It is generally greatest for the first tendon tensioned and is zero for the last tendon tensioned.

13 Creep and shrinkage tests are typically conducted for 6 months and relaxation tests for 1,000 hours0 days <br />0 hours <br />0 weeks <br />0 months <br /> (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 second license extension is granted).

to Callaway RR Tech Report ULNRC-06831 Page 22 of 62 Rev. 0 20230616 Figures 2 and 4 are plots of common tendon lift-off forces. These plots exhibit much less scatter than those shown in Figures 1 and 3. Since the scatter of the common tendon force data is relatively small, it is reasonable to postulate that the true trend of group mean force is relatively close to the common tendon force trend (it is assumed, without accounting for tendon geometry, that all tendons in a group tend to lose force at about the same rate). This postulate leads to the following alternative approach to determining the trend of group mean force:

o A weighted logarithmic centroid of surveillance times, To, is computed as:

To = Exp {[Fi

• Log10 (Ti)] / Fi}

where all summations are from 1 to n, the number of lift-off data sets Fi is the lift-off force measured at Ti o It is postulated that there is sufficient data such that the true mean force, FmTrue, at To is equal to:

FmTrue = (Fi) / n o An alternative log-linear mean force, FmAlt, is computed as:

FmAlt = FmTrue + bc * [Log10 (T) - Log10 (To)]

where bc is the slope (kip per unit logarithmic interval) of the common tendon trend line 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.

4.1.1 Circumferential Tendon Trends and Forecasts Circumferential tendon forces measured during each of the 9 surveillances are listed in Table 2 and plotted on Figure 1.

4.1.1.1 Circumferential Tendon Mean Force Trend / All Data

[Note: Par. 4.5.5 of Specification C-1003(Q), Specification for In-service Inspection of the Containment Building Post-Tensioning System & Exterior Concrete Shell, Reference 6.18, identifies a minimum required mean force of 1,118 kips for the 30 circumferential tendons above the dome spring line (tendon rings 46 through 55) and a minimum mean of 1,227 kips for tendons in the cylinder wall. The license renewal application pre-stressing tendon time limited aging analysis, or TLAA, (AMNROLI00015-CALC-007, to Callaway RR Tech Report ULNRC-06831 Page 23 of 62 Rev. 0 20230616 Reference 6.5) sets a more conservative criterion by treating the dome and cylinder circumferential tendons as a single group with the 1,227-kip-minimum required mean force. The present calculation follows the TLAA approach and treats all circumferential tendons as a single group with the 1,227-kip minimum required mean force.]

The measured force data listed in Table 2 are plotted on Figure 1 which also includes the extrapolated log-linear trend of the mean, the LCL curve and a line indicating the 1,227-kip minimum acceptable mean circumferential tendon force. The measured force points on the plot exhibit a relatively large scatter which is typical of lift-off data. Scatter is the result of variations in initial seating force and elastic shortening loss as well as factors such as anchorage temperature (affects the thickness of the shim stack which has a direct bearing on the force in the short length of tendon between the anchor head and inflection point) that are generally not quantified.

The trend line, computed based on the postulate that the true mean is a log-linear function of time and using the method of least squares, as developed in Reference 6.16, suggests that mean circumferential tendon force is defined by the equation:

FCm = 1,335.3 - 18.06

• Log10 (T) where T is, as earlier noted, years since the January 1984 SIT.

The trend line, which is based on the previously stated postulate, remains well above the minimum line at T = 10014, which is 54 years after the latest date for completion of the next surveillance if the interval is extended to 10 years. If the examination interval is extended from 5 years to 10 years, the latest time for completion of the next examination is T = 46 (January 2030), the SIT anniversary date plus the one-year tolerance allowed by IWL-2420(c). The forecast trend line ordinates at T = 46 and T = 100 years are 1,305 kip and 1,299 kip, respectively. The LCLs at T = 46 and T = 100 years are 1,291 and 1,280 kip, respectively.

The forecast trend line and LCL ordinates at T = 46 and T= 100 years are summarized below along with margins between ordinates and the 1,227-kip lower limit on mean circumferential tendon force.

14 T = 100, represented by a major grid line on the logarithmic abscissa scale, is a convenient reference point and is not otherwise intended to have particular significance.

to Callaway RR Tech Report ULNRC-06831 Page 24 of 62 Rev. 0 20230616 T = 46 T = 100 Trend or LCL Ordinate, kip Margin, kip Ordinate, kip Margin, kip Trend Line 1,305 78 1,299 72 95% LCL 1,291 64 1,280 53 The extrapolated trend and LCL values at T = 46 and T = 100 years, computed using all surveillance data, support the proposed extension of the examination interval.

4.1.1.2 Circumferential Common Tendon Force Trend and Alternative Trend Figure 2 is a plot of circumferential common tendon 45BA measured forces and includes the log-linear trend line. The 1,227-kip minimum required mean force is not shown on the plot as it is not applicable to individual tendons, half of which are per design expected to fall below the minimum, and half above, at the end of the initially specified plant operating lifetime of 40 years. Scatter is seen to be small relative to that illustrated in Figure 1. The trend line equation is:

FCc = 1,330.4 - 23.60

• Log10 (T)

If circumferential tendon mean force is postulated to follow a log-linear trend, the mean value at any time, FCm(T), is defined by the following relationship:

FCm (T) = FCmTrue (To) + b * [Log10 (T) - Log10 (To)]

where FCmTrue (To) is the true mean at To and b is the slope of the trend The mean, Fm, of the circumferential tendon lift-off forces is 1,318.8 kips. The corresponding weighted mean time, To, of lift-off force measurement is 8.13 years.

If the true mean value of lift-off force at To = 8.13 years is postulated to be equal to the 1,318.8-kip computed mean and the slope, b, of the trend is postulated to be that of the common tendon trend (-23.60 kip per unit logarithmic interval), then the alternative circumferential tendon mean force trend can be expressed as:

FCmAlt = 1,318.8 - 23.60 * [Log10 (T) - Log10 (8.13)]

Forecast mean circumferential tendon forces at T = 46 years and T = 100 years are, from the above equation:

FCmAlt (46) = 1,318.8 - 23.60 * [Log10 (46) - Log10 (8.13)] = 1,301 kip FCmAlt (100) = 1,318.8 - 23.60 * [Log10 (100) - Log10 (8.13)] = 1,293 kip to Callaway RR Tech Report ULNRC-06831 Page 25 of 62 Rev. 0 20230616 The forecast T = 46 mean of 1,301 kip is 74 kip above the 1,227-kip minimum required value. The forecast T = 100 mean of 1,293 kip is 66 kip above the minimum.

The above analysis shows, subject to the assumptions used in its development, that circumferential tendon mean force will remain above the minimum required value for more than 54 years beyond the deadline for completion of the next surveillance. Therefore, this alternative trend analysis also supports the extension of examination interval to 10 years.

4.1.1.3 Circumferential Tendon Force Evaluation Summary and Conclusions It is concluded, based on the statistical analyses and other evaluations discussed above, that mean circumferential tendon force will, with a high degree of probability, remain above the 1,227-kip minimum required value for at least 54 years beyond the 2030 (T =

46 years) deadline for completion of the next surveillance if the interval is extended to 10 years.

This conclusion is supported by the following:

a) The circumferential tendon mean force trend, computed using all measured force data acquired during the 9 examinations conducted to date, remains above the 1,227-kip minimum through T = 100 (years since the January 1984 structural integrity test).

b) The 95% lower confidence limit on circumferential tendon mean force, computed using measured force data acquired during the 9 surveillances completed to date, remains above the 1,227-kip minimum through T = 100 years.

c) Circumferential tendon mean force, computed using the slope of the common tendon (45BA) measured force trend, remains above the 1,227-kip minimum through T = 100 years.

Numerical values of trended forces, UCLs and margins (above the 1,227-kip minimum) at T = 46 years and T = 100 years are summarized below.

T = 46 T = 100 Trend or LCL Ordinate, kip Margin, kip Ordinate, kip Margin, kip Trend Line, all lift-off data 1,305 78 1,299 72 95% LCL, all lift-off data 1,291 64 1,280 53 Common tendon alternative 1,301 74 1,293 66 analysis trend to Callaway RR Tech Report ULNRC-06831 Page 26 of 62 Rev. 0 20230616 The foregoing analyses and evaluations, and the conclusions derived therefrom, support the proposed extension of the interval between containment post-tensioning system examinations to 10 years from the current 5 years.

4.1.2 Meridional Tendon Trends and Forecasts Meridional tendon measured force data are listed in Table 4 and plotted on Figure 3, which also includes the extrapolated log-linear trend of the mean, the LCL curve and a line indicating the 1,160-kip minimum acceptable mean meridional tendon force. Scatter is noticeably less than that shown for the circumferential tendon lift-off forces on Figure

1. The lesser scatter may result from the long vertical runs of the meridional (inverted U) tendons which limit friction-induced force variations to a fraction of overall tendon length.

The trend line, computed based on the postulate that the true mean is a log-linear function of time and using the method of least squares, as developed in Reference 6.16, suggests that mean meridional tendon force is defined by the equation:

FMm = 1,433.1 - 27.06

• Log10 (T) where T is, as earlier noted, years since the January 1984 SIT The trend line, which is based on the previously stated postulate, remains well above the minimum line at T = 100, which is 54 years after the latest date for completion of the next surveillance if the interval is extended to 10 years. If the examination interval is extended from 5 years to 10 years, the latest time for completion of the next examination is T = 46 (January 2030), the SIT anniversary date plus the one-year tolerance allowed by IWL-2420(c). The forecast trend line ordinates at T = 46 and T = 100 years are 1,388 kip and 1,379 kip, respectively. The LCLs at T = 46 and T = 100 years are 1,374 and 1,360 kip, respectively.

The forecast trend line and LCL ordinates at T = 46 and T= 100 years are summarized below along with margins between ordinates and the 1,160-kip lower limit on mean meridional tendon force.

T = 46 T = 100 Trend or LCL Ordinate, kip Margin, kip Ordinate, kip Margin, kip Trend Line 1,388 228 1,379 219 95% LCL 1,374 214 1,360 200 The extrapolated trend and LCL values at T = 46 and T = 100 years, computed using all surveillance data, support the proposed extension of the examination interval.

to Callaway RR Tech Report ULNRC-06831 Page 27 of 62 Rev. 0 20230616 4.1.2.1 Meridional Common Tendon Force Trend and Alternative Trend Figure 4 is a plot of circumferential common tendon V65 measured forces and includes the log-linear trend line. The 1,160-kip minimum required mean force is not shown on the plot as it is not applicable to individual tendons as previously addressed. Scatter is seen to be smaller than that illustrated in Figure 3. The trend line equation is:

FMc = 1,451.6 - 35.25

• Log10 (T)

If meridional tendon mean force is postulated to follow a log-linear trend, the mean value at any time, FMm(T), is defined by the following relationship.

FMm (T) = FMmTrue (To) + b * [Log10 (T) - Log10 (To)]

where FMmTrue (To) is the true mean at To and b is the slope of the trend The mean, Fm, of the meridional tendon lift-off forces is 1,406.5 kips. The corresponding weighted mean time, To, of lift-off force measurement is 9.53 years.

If the true mean value of lift-off force at To = 9.53 years is postulated to be equal to the 1,406.5-kip computed mean and the slope, b, of the trend is postulated to be that of the common tendon trend (-35.25 kip per unit logarithmic interval), then the alternative meridional tendon mean force trend can be expressed as:

FMmAlt = 1,406.5 - 35.25 * [Log10 (T) - Log10 (9.53)]

Forecast mean meridional tendon forces at T = 46 years and T = 100 years are, from the above equation:

FMmAlt (46) = 1,406.5 - 35.25 * [Log10 (46) - Log10 (9.53)] = 1,382 kip FMmAlt (100) = 1,406.5 - 35.25 * [Log10 (100) - Log10 (9.53)] = 1,371 kip The forecast T = 46 mean of 1,382 kip is 222 kip above the 1,160-kip minimum required value. The forecast T = 100 mean of 1,371 kip is 211 kip above the minimum.

The above analysis shows, subject to the assumptions used in its development, that meridional tendon mean force will remain above the minimum required value for more than 54 years beyond the deadline for completion of the next surveillance. Therefore, this alternative trend analysis also supports the extension of the examination interval to 10 years.

to Callaway RR Tech Report ULNRC-06831 Page 28 of 62 Rev. 0 20230616 4.1.2.2 Meridional Tendon Force Evaluation Summary and Conclusions It is concluded, based on the statistical analyses and other evaluations discussed above, that mean meridional tendon force will with a high degree of probability remain above the 1,160-kip minimum required value for at least 54 years beyond the 2030 (T = 46 years) deadline for completion of the next surveillance if the interval is extended to 10 years.

This conclusion is supported by the following:

a) The meridional tendon mean force trend, computed using all measured force data acquired during the 9 examinations conducted to date, remains above the 1,160-kip minimum through T = 100 (years since the January 1984 structural integrity test).

b) The 95% lower confidence limit on meridional tendon mean force, computed using measured force data acquired during the 9 surveillances completed to date, remains above the 1,160-kip minimum through T = 100 years.

c) Meridional tendon mean force, computed using the slope of the common tendon (V65) measured force trend, remains above the 1,160-kip minimum through T =

100 years.

Numerical values of trended forces, UCLs and margins (above the 1,160-kip minimum) at T = 46 years and T = 100 years are summarized below.

T = 46 T = 100 Trend or LCL Ordinate, kip Margin, kip Ordinate, kip Margin, kip Trend Line, all lift-off data 1,388 228 1,379 219 95% LCL, all lift-off data 1,374 214 1,360 200 Common tendon alternative 1,382 222 1,371 211 analysis trend The foregoing analyses and evaluations, and the conclusions derived therefrom, support the proposed extension of the interval between containment post-tensioning system examinations to 10 years from the current 5 years.

Callaway RR Tech Report to Page 29 of 62 ULNRC-06831 Rev. 0 20230616 4.1.3 Tendon Mean Force Trend Summary and Conclusions The trend of the mean force is analyzed separately for the circumferential and meridional tendon groups. Each analysis includes the following 3 computations that are based on the postulate that mean force varies linearly with the logarithm of time.

• Log-linear trend based on measured forces recorded during the 9 surveillances completed to date.

• 95% lower confidence limit (LCL) on the trend of measured forces.

• Log-linear trend based on the common tendon trend.

The margins between minimum required group mean force (MRV) and forecast group mean force / LCL at T = 46 years (deadline for completion of the next surveillance if the interval is extended to 10 years) and T = 100 years are summarized in the table below.

Summary of Margins between Forecast and Minimum Required Mean Forces Tendon Margin, kip Forecast Basis Group / MRV T = 46 Years T = 100 Years Log-linear trend, all lift-off forces 78 72 Circumferential /

95% LCL, all lift-off forces 64 53 1,227 kip Common tendon slope trend 74 66 Log-linear trend, all lift-off forces 228 219 Meridional / 1,160 95% LCL, all lift-off forces 214 200 kip Common tendon slope trend 222 211 The 6 trends / LCLs evaluated all show the trend line and LCL curve remaining above the group minimum required mean force through T = 100 (years after the SIT), which is 54 years after the deadline for completion of the next surveillance if the interval is extended to 10 years.

Therefore, based on the above summary, it is concluded that the proposed extension of the interval to 10 years is fully supported by the analysis of tendon mean force trends.

4.2 Wire Examination and Test Results Evaluation Wire used to fabricate the tendons used in the Callaway containment was subject to numerous mechanical property tests (Reference 6.19). Ultimate tensile strength was to Callaway RR Tech Report ULNRC-06831 Page 30 of 62 Rev. 0 20230616 determined for 10 gage length specimens cut from each end of each wire coil (each heat of steel yielded a number of coils of varying weights). In addition, yield strength and elongation at failure were determined for 1 specimen from every 10 th coil. These tests verified that the wire used in tendon fabrication met the ASTM A421 specifications for yield strength, tensile strength and elongation. There is no industry wide data to suggest that these properties change with time under load.

During each surveillance, sample wires were extracted from at least one tendon in each group, visually examined for damage / corrosion and tested to determine yield strength, ultimate tensile strength and elongation at failure. Tests were performed on three or more specimens cut from each of the wires. Two of these specimens were located close to the sample wire ends and one was near the center.

In addition, one wire found to be broken was extracted. Also, an additional wire was extracted from a tendon after the first wire extracted was found to have areas with an unacceptable level of corrosion. Specimens were cut from all extracted wires and tested.

Additional tests were performed to confirm results that did not meet acceptance criteria.

Tables 6 through 8 summarize the results of the tests on extracted wires.

4.2.1 Wire Visual Examination and Condition Each extracted wire was examined for corrosion over its entire length. All extracted wires except those from 10th year surveillance sample tendon 12CB were found to be in Level 1 (or A) condition; i.e., bright metal with no evidence of corrosion. Two wires were extracted from 12CB. The first had areas of Level 2 and Level 3 corrosion (see table below). A second wire was extracted after the Level 3 corrosion was found on the first wire. Corrosion on the second wire was Level 1 and Level 2. None of the corrosion found was active. The Level 3 corrosion, concluded to have occurred prior to the time that CPM was installed in the 12CB ducting, is addressed in NCR No. FN513-001 (Reference 6.20).

It is considered to be a unique condition and not the result of time-dependent degradation.

Corrosion levels are defined in the following table.

Level Characteristic 1 (or A) No visible corrosion (bright metal in the case of extracted wires) 2 (or B) Light rusting with no pitting 3 Rust with pitting up to 0.003 in depth 4 Rust with pitting 0.003 to 0.006 in depth 5 Rust with pitting greater than 0.006 in depth to Callaway RR Tech Report ULNRC-06831 Page 31 of 62 Rev. 0 20230616 4.2.2 Wire Yield Strength Tables 6 lists the yield strengths of test wires extracted from tendons during the 9 surveillances conducted to date.

Yield strength is defined in ASTM A421 (Reference 6.4) as the stress at 1% elongation.

The lower acceptance limit is, per the ASTM, 85% of the specified minimum tensile strength or, 0.85

• 240 = 204 ksi. As can be seen in Table 6, all yield stress values except those shown for the 3rd year surveillance exceed the 204-ksi minimum.

The yield stress values listed for the 3rd year surveillance are the test results provided by Arché Engineering Laboratories (AEL). Additional tests on specimens cut from the tendon V1 test wire were performed by Pittsburgh Testing Laboratories (PTL). The V1 test wire results provided by the two laboratories (included in Appendix C to the surveillance report, Reference 6.8) do not agree, as shown in the table below.

Tendon V1 Extracted Wire Yield Strength Test Results Testing Wire Gage Test Specimen / Yield Strength, ksi Lab Diameter Length 1(a) 1(b) 2(a) 2(b) 3(a) 3(b) N/A Mean AEL 0.250 100 185 182 192 N/A 152 159 N/A 174 1 2 3 2A 2B 2C 2D Mean 213 211 189 218 206 190 195 PTL 0.249 20 1A 1B 1C 1D N/A N/A N/A 204 213 217 197 192 N/A N/A N/A Yield strengths reported by AEL varied from 152 to 192 ksi with a mean of 174 ksi. Those reported by PTL varied from 189 to 218 ksi with a mean of 204 ksi. As noted in the table, the gage lengths used by the 2 laboratories differed by a factor of 5. This, by itself, should not impact measured yield values but does indicate that testing procedures 15 may have been significantly different. Also, the wire diameters reported by the labs differed by 0.001 which probably resulted in a 0.8% difference in the wire areas used to compute the yield.

The substantial difference in yield strengths reported by the two laboratories shows that one, and possibly both, sets of data are not representative of the true yield. For this reason, the 3rd year surveillance yield strength values listed in Table 6 for both extracted 15 Since yield is defined at a specified strain, its determination can be procedure sensitive.

Callaway RR Tech Report to Page 32 of 62 ULNRC-06831 Rev. 0 20230616 wires (from tendons 35AB and V1) cannot be treated as valid. Consequently, it can be concluded that there is no credible evidence of unacceptable tendon wire yield strengths.

The exam mean yield strength values listed in the right hand column of Table 6 fluctuate from surveillance to surveillance but do not show a consistent trend with time. Therefore, it can be concluded that wire yield strength is not impacted by time under load. This conclusion is reinforced by the results of tests on similar ASTM A421 wire extracted from containment tendons during surveillances at other nuclear power facilities.

4.2.3 Wire Ultimate Tensile Strength (UTS)

Tables 7 lists the UTS of test wires extracted from tendons during the 9 surveillances conducted to date.

Two of the three specimens from the tendon V1 wire extracted during the 3rd year surveillance are, at 232 and 234 ksi, below the 240 ksi acceptance limit. The UTS reported for the 3rd specimen is 241 ksi. These 3 specimens were tested by Arché Engineering Laboratories. An additional 11 specimens cut from the same wire were tested by Pittsburgh Testing Laboratories. UTS values for the 11 specimens ranged from 239 to 246 ksi with all but one at or above 242 ksi.

The difference in UTS values reported by the two laboratories shows that one, and possibly both, sets of data are not representative of the true tensile strength. Therefore, as in the case of yield strength values, the 3rd year surveillance UTS values listed in Table 7 for both extracted wires (from tendons 35AB and V1) cannot be treated as valid.

Otherwise, all test specimens except five of the six cut from the V39 wire extracted during the 35th year surveillance met the 240 ksi acceptance criterion for UTS. There is nothing to suggest that failure of the five V39 specimens below 240 ksi is the result of wire damage or corrosion, or a problem with test equipment or performance. Therefore, it is concluded that the low strength values, which range from 231 to 239 ksi, are valid. Reason for the low UTS values is not determined (and cannot be traced to a low strength coil or coils).

However, strength is close to the acceptance limit with the lowest specimen break occurring at 231 ksi and, as shown later, elongation at failure was acceptable (4%) for all 6 specimens. The low UTS results were accepted at the time of the surveillance as documented in Ameren Condition Report CR 202103224-001 (Reference 6.21).

The mean of the tensile strengths found for specimens tested during each surveillance is shown in the last column of Table 7. The mean values appear to vary in a random manner and exhibit no trend. If the V39 test wire results are omitted from the 35th year surveillance exam mean, the 25CB test wire mean result of 249 ksi is within 5 ksi of the exam means shown for the 1st, 10th and 15th year surveillances This supports the conclusion, based to Callaway RR Tech Report ULNRC-06831 Page 33 of 62 Rev. 0 20230616 on the evaluation of test results reported for many other plants, that wire tensile strength does not degrade with time under load.

4.2.4 Wire Elongation at Failure Table 8 lists the elongations at failure of test wires extracted from tendons during the 9 surveillances conducted to date.

As shown on the table, four of the six 1st year surveillance specimens, all nine of the 3rd year specimens16, three of the 10th year specimens and five of the 25th year specimens had EF values below the 4% acceptance limit. Wire testing performed through the 25th year surveillance used surveillance vendor procedures and 100-inch gage length specimens rather than the procedures and 10-inch specimens specified by ASTM A421.

Since much of the overall elongation at failure occurs in the necked down region adjacent to the failure location, elongation computed as a percentage of gage length is lower for the longer test specimens.

The 25th year elongation results were evaluated in Condition Report CR 2010-04223 (Reference 6.22). The evaluation concluded that containment integrity was not adversely affected by the low elongations documented in the surveillance report. The CR did not, however, address possible errors caused by departures from the ASTM procedures for measuring elongation at failure.

Tests on wires extracted during the 30th and 35th year surveillances were performed by a testing laboratory using ASTM procedures and 10-inch gage lengths as specified by ASTM A421. As shown in Table 8, elongations listed for the two most recent surveillances are generally greater than those listed for the 25 th year and earlier surveillances. This is consistent with use of the shorter gage length. Also, the 30th and 35th year surveillance (exam) means are greater than those shown for the earlier surveillances.

Since the elongations reported for the 30th and 35th year surveillances are generally in line with those found for new material during the material certification tests performed in the late 1970s (Reference 6.19), it is concluded that wire ductility is not degrading with time under load.

16 The 3rd year surveillance results shown in Table 8 are those reported by Arché Engineering Laboratories. Pittsburgh Testing Laboratories (PTL) subsequently tested 8 additional specimens, cut from the V1 extracted wire, for elongation at failure. PTL reported 7 elongations ranging from of 5.0% to 6.0% and 1 at 4.2%.

to Callaway RR Tech Report ULNRC-06831 Page 34 of 62 Rev. 0 20230616 4.2.5 Wire Visual Examination and Test Summary The above evaluations show that tendon wire strength and ductility are essentially invariant with time. In addition, visual examination of the 21 wires (including 1 broken wire) extracted from Callaway tendons between 1985 and 2021 has, with one exception uncovered no evidence of an unacceptable level of corrosion or in-service damage.

Since examinations and tests conducted over a period of 36 years have shown that there are no trends indicating that wire condition, strength and ductility are degrading over time, it is concluded that extending the examination interval from 5 years to 10 years will not compromise plant safety.

4.3 End Anchorage Hardware and Concrete Condition During each of the surveillances, end anchorage areas were visually examined for evidence of corrosion, presence of free water, missing buttonheads, discontinuous wires and damage to / distortion of load-bearing components including the bearing area concrete adjacent to bearing plates. Results of these examinations are summarized in 4.3.1 through 4.3.5. Conclusions based on documented end anchorage conditions are given in 4.3.6.

4.3.1 Corrosion Corrosion levels are defined in 4.2.1 above. Levels 1 (A) and 2 (B) are acceptable and Level 3 is generally acceptable. Levels 4 and 5 require evaluation prior to acceptance.

Depth of pitting is usually a judgment call based on visual examination of a corroded area.

No active corrosion was observed on bearing plates, anchor heads, shims, buttonheads or wires. Results of examinations for corrosion are summarized in the following table.

to Callaway RR Tech Report ULNRC-06831 Page 35 of 62 Rev. 0 20230616 Callaway End Anchorage Item Corrosion Summary Surveillance Corrosion Levels Year Level A on buttonheads; Level 1 on anchor heads, bushings and bearing 1st plates; Level 1 & 2 on shims Level 1 on buttonheads; Level 1 & 2 on anchor heads, shims and bearing 3rd plates (bushing corrosion not reported separately)

Level 1 on buttonheads and bearing plates; Level 1 & 2 on anchor heads, 5th bushings (except as noted following) and shims; Level 3 (a 3/16 diameter spot) on the 52AC bushing (accepted per NCR 89N353-004, Reference 6.23)

Level 1 on buttonheads, bushings and bearing plates. Level 1 & 2 on anchor 10th heads and shims.

Level 1 on buttonheads; Level 2 on anchor heads, bushings, shims and 15th bearing plates Level A & B on buttonheads; Level 1 & 2 on anchor heads and bushings; 20th Level 2 on shims and bearing plates Level 1 on buttonheads, bushings and shims; Level 1 & 2 on anchor heads 25th and bearing plates 30th Level 1 on all items 35th Level 1 (or A) on all items As shown in the above table, corrosion was limited to Levels 1 (A) and 2 (B) on all items examined, with the exception of a small area of Level 3 (accepted by evaluation) as noted on the 5th year surveillance line. There is no evidence that either the incidence or level of corrosion is increasing with time.

4.3.2 Free Water No free water was found during any of the 9 surveillances completed to date.

4.3.3 Missing Buttonheads and Discontinuous Wires The following table identifies the number of missing buttonheads and discontinuous wires that were not documented prior to the surveillance year noted.

to Callaway RR Tech Report ULNRC-06831 Page 36 of 62 Rev. 0 20230616 Callaway End Anchorage Examinations - Missing Buttonheads and Discontinuous Wires Surveillance Protruding / Missing Buttonheads and Discontinuous Wires Not Previously Year Documented One buttonhead protruding 1.8 at the V35 shop end 1st One buttonhead missing at the shop end of V74 One buttonhead missing at the field end of V74 3rd One buttonhead missing at the A end of tendon 45BA One buttonhead missing at the 52AC field end (NCR 89N353-009, 5th Reference 6.24) One broken wire found during de-tensioning of 20AC (NCR 89N353-008, Reference 6.25) 10th No missing buttonheads or broken wires not previously documented 15th No missing buttonheads or broken wires not previously documented 20th No missing buttonheads or broken wires not previously documented 25th No missing buttonheads or broken wires not previously documented No missing buttonheads or broken wires not previously documented; two 30th buttonheads protruding following re-tensioning 35th No missing buttonheads or broken wires not previously documented As noted in the above table, only 5 protruding / missing buttonheads and 1 broken wire, none of which were previously documented, were found during the 9 surveillances performed to date. If the 2 missing V74 (1st year surveillance) buttonheads are postulated to be from different wires, then a total of 6 previously undocumented ineffective wires were found during the course of these surveillances.

Fifty-nine17 sample tendons, 35 circumferential and 24 meridional, with ~10,030 wires, were examined over the course of these surveillances. The 6 ineffective wires represent 0.06% of the those in the 59 tendons. This is a structurally insignificant percentage.

4.3.4 Load Bearing Components Damage and Distortion No damaged, cracked or distorted load bearing components (bearing plates, anchor heads, shims) were found during any of the 9 surveillances completed to date.

17 Meridional tendon V80 was added to the 35th year sample following observation of a possible CPM stain on the containment wall. Only visual examinations and CPM tests were performed; tendon force was not measured.

to Callaway RR Tech Report ULNRC-06831 Page 37 of 62 Rev. 0 20230616 4.3.5 Concrete Cracking Adjacent to Bearing Plates Bearing area concrete (concrete adjacent to bearing plates) cracks wider than 0.010 found during the 9 surveillances completed to date are tabulated below.

Bearing Area Concrete Cracks >0.010 in Width Surveillance Crack Parameters Location1 Year Number Maximum Length Maximum Width V35 Shop Numerous 14 0.025 V35 Field 2 12 0.025 1st V65 Shop 4 24 0.030 V74 Field 4 6-1/2 0.015 3rd No cracks wider than 0.010 found 5th V65 Shop 3 24 0.050 V15 Field 1 8 0.012 10th V65 Shop 3 46 0.050 15th V65 Shop 1 30 0.015 20th V65 Shop 1 30 0.015 25th No cracks wider than 0.010 found 30th No cracks wider than 0.010 found 35th No cracks wider than 0.010 found Note 1: The shop end of a tendon is fitted with a small diameter anchor head and buttonheaded in the fabrication facility. The small diameter head allows the shop end to be pulled into the trumpet assembly, extending the tendon wires beyond the field end bearing plate to facilitate installation of the field end anchor head. A bushing is threaded onto the shop end anchor head after field end buttonheading is completed and the head is pulled out of the trumpet. The bushing provides the additional bearing area required by the anchor head.

Common meridional tendon V65 was examined during each of the 9 surveillances. The maximum width of the 4 shop end cracks wider than 0.010, as measured during the 1 st year surveillance, is 0.030. The 3rd year report notes that no cracks were observed at the V65 shop end. The 5th year and 10th year reports identify 3 cracks wider than 0.010, with maximum measured widths of 0.050. The 15 and 20th year reports identify 1 crack with a maximum width of 0.015, while the 25th through 35th year reports state that no cracks at this location are wider than 0.010.

It is unlikely that the widths of cracks at the V65 shop end increased and decreased over time as noted. Rather, it is probable that improved methods of identifying true width, by measuring below-surface enhanced widening (a consequence of concrete fines sloughing off at the surface edges), as well as examiner judgment, are responsible for the reported changes. Treating the more recent measurements as valid representations of to Callaway RR Tech Report ULNRC-06831 Page 38 of 62 Rev. 0 20230616 the V65 shop end crack widths (all <0.010) supports a conclusion that no cracks wider than 0.010 have been found at tendon end anchorages.

4.3.6 End Anchorage Condition Summary and Conclusions Tendon end anchorage hardware and adjacent concrete have performed well throughout the life of the plant (through the most recent surveillance in 2021) and show no trends of deteriorating condition.

There have been no findings of active corrosion on load-bearing elements of the pre-stressing system. With the exception of one small spot of Level 3 corrosion on a bushing, all corrosion found during system examinations was Level 1 (or A) or Level 2 (or B).

No free water was found at anchorages during any of the 9 surveillances completed to date.

Only 6 discontinuous wires (broken wires or wires with missing buttonheads) not previously reported were found. These represent only a miniscule fraction (0.06%) of the

~10,030 wires comprising the 59 tendons examined.

No damage, cracking or distortion was found during visual examinations of bearing plates, anchor heads and shims.

Cracks observed in bearing are concrete are concluded to be under 0.010 in width and are considered acceptable without evaluation. Such cracks as were observed are considered to be the result of concrete shrinkage constrained by the rigid bearing plates.

There is no evidence of structural cracks (those caused by applied loads) in the vicinity of surveillance sample tendon end anchorages.

Considering the above, it can be concluded that end anchorage conditions are stable and unlikely to change significantly before the January 2030 proposed deadline for completion of the next surveillance. And, it can consequently be concluded that the end anchorage examination interval can be extended to 10 years without compromising the safety of the plant.

4.4 Corrosion Protection Medium Testing Corrosion protection medium (CPM) test samples were collected at the ends of each examined tendon during each of the 9 surveillances. CPM samples were tested for the presence of three corrosive ions (chlorides, nitrates and sulfides), absorbed water content and neutralization (base) number.

to Callaway RR Tech Report ULNRC-06831 Page 39 of 62 Rev. 0 20230616 The testing procedures for water content and neutralization number use bulk samples and appear to be straightforward as well as consistent over time.

Tests for corrosive ions do not determine the concentration in bulk samples but, rather, the concentration in a quantity of distilled water kept in contact with a prepared CPM surface area for a specified time and at a specified temperature. In addition, the tests for ion concentration in the water sample have changed over time to reflect advances in analytical chemistry techniques as well as other changes to the standardized ASTM and APHA procedures used in testing the water extractions. Also, the corrosive ion test procedures (as well as sample preparation techniques) may have varied among the different laboratories used for this work. This must be accounted for in the evaluation of test results.

During the 9 surveillances completed to date, 155 samples were tested as shown in the following table.

Number of CPM Samples Tested Surveillance Year 1st 3rd 5th 10th 15th 20th 25th 30th 35th Number Tested I 22 I 25 I 28 I 12 I 12 I 12 I 14 I 14 I 16 I Corrosion protection medium test results are summarized below and addressed in detail in subsections 4.4.1 through 4.4.3. Conclusions and recommendations for future testing are included in 4.4.7.

• All tested samples met the Table IWL-2525-1 10 ppm upper limit on chloride, nitrate and sulfide ion concentration.

• All tested samples met the Table IWL-2525-1 10% upper limit on water content.

• With one exception, samples met the Table IWL-2525-1 criterion (base number not less than 17.518) for reserve alkalinity. The sole exception is the 16.8 base number reported for the 6AC shop end sample collected during the 15 th year surveillance.

18 The Subsection IWL Table IWL-2525-1 lower limit on base number is 50% of the specified minimum as-installed number. All CPM used at Callaway is Visconorust 2090P-4 which is specified to have a minimum base number of 35 when installed.

to Callaway RR Tech Report ULNRC-06831 Page 40 of 62 Rev. 0 20230616 4.4.1 Corrosive Ion Tests Results of the corrosive ion tests are summarized in the following table which shows the range of concentrations reported for samples tested during each surveillance year.

Summary of CPM Corrosive Ion Test Results Surveillance Year / Range of Sample Ion Concentrations, ppm19 Calendar Year Chlorides Nitrates Sulfides 1st / 1985 0.05 - 0.20 0.10 - 0.47 0.005 - 0.070 rd 3 / 1987 < 0.1 - 0.4 < 0.1 - 0.9 All < 0.1 5th / 1989 < 0.044 - 0.132 < 0.050 - 1.275 < 0.0127 - 0.026 10th / 1994 All < 0.50 All < 0.50 All < 0.50 th 15 / 1999 All < 0.50 0.97 - 2.84 All < 0.50 20th / 2004 All < 0.50 All < 0.50 All < 0.50 th 25 / 2010 All < 0.50 All < 0.50 All < 0.50 30th / 2015 All < 0.50 All < 0.50 All < 0.50 35th / 2021 All < 0.50 All < 1.0 All < 0.50 The less than symbol (<) indicates either a minimum level of detectability or a concentration below which a reliable test result cannot be assured. The 0.5 ppm minima (1.0 ppm for nitrates beginning about 2017) are typical of those reported for tests performed across the industry since the late 1990s.

All chloride and sulfide concentrations shown in the table are below the 0.50 ppm minimum level of reportability. Nitrate concentrations shown for tests performed in 2004 and later are below the minimum reportable level of 0.50 ppm (1.0 ppm for the 35th year surveillance samples tested in 2021)20.

Nitrate concentrations reported for tests performed across the industry in the late 1990s and earlier tend to vary erratically from surveillance to surveillance. This has been attributed to the difficulty of obtaining consistent results with the procedures used at the time. More recent tests almost always show nitrate concentrations that are below the 19 Concentrations reported for water extractions prepared as specified in Subsection IWL Table IWL-2525-1.

20 Reports documenting the surveillances performed at Callaway and other plants do not address the reason for the increase in minimum reportable nitrate concentration from 0.50 ppm to 1.0 ppm.

to Callaway RR Tech Report ULNRC-06831 Page 41 of 62 Rev. 0 20230616 0.50 (or 1.0) ppm minimum reportable value. For this reason, as well as for the reason that there is no conceivable source for nitrate contamination in tendon ductwork, it is concluded that the nitrate levels shown above for the 15th year and earlier surveillances are not representative of true conditions. All sample nitrate concentrations are concluded to be below the minimum reportable level.

Given the results shown for samples collected during the four most recent surveillances and the fact that there is no credible source for either chloride, nitrate or sulfide contamination in tendon ductwork, it is concluded that routine testing for these corrosive ions should be discontinued. Such tests should only be performed if Level 3 or greater corrosion is found on load-bearing elements of the pre-stressing system that are in contact with CPM or free water is found during end anchorage examinations.

4.4.2 Reserve Alkalinity / Base Number CPM reserve alkalinity, and the corresponding degree of protection that it provides against corrosion is defined by a base number (also referred to as a neutralization number) determined using the procedure specified in Subsection IWL Table IWL-2525-1.

Results of base number tests are summarized in the following table and illustrated graphically by the Figure 5 plot.

Summary of CPM Base Number Test Results Surveillance Year / Sample Base Number Minimum, Mean and Maximum Calendar Year Minimum Mean Maximum 1st / 1985 50.2 57.0 63.8 3rd / 1987 29.0 53.2 66.0 th 5 / 1989 43.7 54.0 64.0 10th / 1994 36.9 51.2 63.6 15th / 1999 16.8 39.9 56.7 th 20 / 2004 35.6 47.8 62.4 25th / 2010 32.0 49.8 63.2 th 30 / 2015 21.3 36.0 55.9 35th / 2021 18.2 28.7 38.9 As can be seen in the above table and on Figure 5, base number test results exhibit a relatively high degree of scatter which is typical of tests performed on samples collected at other plants. For this reason, major significance should not be attached to individual base number values. However, the (log-linear) regression lines fitted to the surveillance to Callaway RR Tech Report ULNRC-06831 Page 42 of 62 Rev. 0 20230616 minimum, mean and maximum base number values shown on Figure 5 all decrease with time. This supports the generally accepted conclusion that the reserve alkalinity of the CPM tends to slowly break down.

As individual sample test results are not necessarily meaningful, future focus should be on the trend of the surveillance means. While this trend currently shows the mean base number remaining above the 17.5 lower acceptance limit until well beyond T = 100 years, means computed for the 30th and 35th year surveillances suggest that the rate of decrease could be accelerating. Therefore, base number testing should be continued to ensure the ongoing protective function of the CPM.

4.4.3 Water Content The range of sample water contents reported for the 9 surveillances completed to date is shown in the table below.

CPM Sample Water Content, %1, Range Surveillance Year 1st 3rd 5th 10th 15th 20th 25th 30th 35th Water Content Min 0.05 <0.12 <0.10 <0.10 <0.10 <0.10 <0.10 <0.10 <0.10 Water Content Max 0.29 0.42 0.302 0.35 0.22 0.11 0.20 0.583 0.11 Note 1: Water content computed as a % of sample dry weight; Note 2: The 3rd year report shows water contents to with a single significant figure following the decimal.

The 5th year max value, shown in the surveillance report as 0.303%, is rounded to 0.30% in the table.

Note 3: The 0.58% shown is for a single sample; all remaining 30th year samples have water contents of 0.31% or less.

There is no discernable trend to maxima listed in the above table. And, as no free water was found during the examinations performed during any of the 9 surveillances completed to date, there is no reason to expect the absorbed water content of the CPM to increase over time. The largest of the maxima listed above, 0.58%, is only a small fraction of the 10% acceptance limit.

Given that sample water contents are small relative to the acceptance limit, that there is no trend for the maximum values to increase over time and that free water has not been found during any surveillance, it is concluded that there is no need to continue routine testing for sample water content. Such tests should only be performed if Level 3 or greater corrosion is found on load bearing elements in contact with CPM or if free water is found during tendon end anchorage examinations.

to Callaway RR Tech Report ULNRC-06831 Page 43 of 62 Rev. 0 20230616 4.4.4 CPM Test Summary and Conclusion Post-tensioning system end anchorage hardware and extracted wires have been examined for damage and corrosion during 9 surveillances spanning a period of 36 years from 1985 to 2021. Corrosion protection medium samples collected during these surveillances have been tested for the presence of corrosive ions, reserve alkalinity and absorbed water. The results of these examinations and tests are summarized below.

• There has been no evidence of active corrosion; all observed corrosion is concluded to have occurred during handling, shipping, storage or installation of tendon hardware or otherwise prior to filling of the tendon ductwork with CPM.

• Corrosive ion (chlorides, nitrates, sulfides) concentrations in sample extractions are well below the 10-ppm limit and show no trend of increasing over time.

• Absorbed water contents are well below the 10% (of dry weight) limit and show no trend of increasing over time.

• Base (neutralization) numbers vary over a wide range. While all samples but one met the acceptance criteria, test data trends suggest that there is a slow-degradation CPM reserve alkalinity over time. However, the current trend of the mean shows that this should remain well above the 17.5 acceptance limit through T = 100 years.

An evaluation of the CPM test results, as summarized above, leads to the conclusion that the interval between such tests can be extended to 10 years with no adverse consequences.

In addition, unless evidence of active corrosion is found during visual examinations of end anchorage hardware and extracted wires or there is evidence of free water infiltration into tendon ducting, there should be no need to continue routine testing for corrosive ion concentration and absorbed water content. It is concluded that these tests need to be done only if free water, active corrosion or Level 3 or greater corrosion LVfound.

Tests to determine base number should continue to be performed on CPM samples collected during future surveillances.

Free water, if found, will be collected and analyzed to determine pH as required by Subsection IWL.

to Callaway RR Tech Report ULNRC-06831 Page 44 of 62 Rev. 0 20230616

5. OVERALL

SUMMARY

, CONCLUSIONS AND RECOMMENDATIONS A summary of post-tensioning system surveillance results, conclusions based thereon and recommendations for surveillance program changes follow.

5.1 Summary of Surveillance Results The results of the 9 post-tensioning system in-service examinations conducted at Callaway between 1985 and 2021 show that the system is continuing to perform its intended function and that it can be expected to do so until well past the proposed January 2030 deadline for completion of the next surveillance. Performance of the system, determined by evaluations of the visual examination findings / test results as detailed in Part 4 of this technical report, is summarized below.

a) Tendon Force The mean force in each of the tendon groups is projected by log-linear regression and 95% confidence limit computations to remain above the specified minimum until well after the proposed January 2030 deadline for completion of the next surveillance.

b) Condition of End Anchorage Hardware and Extracted Wires End anchorage hardware and tendon wires extracted for tensile testing show no signs of damage or active corrosion. Corrosion that has been observed is concluded to have occurred prior to filling of the tensioned tendon duct with corrosion protection medium.

The small number of missing buttonheads documented in the surveillance reports represents an inconsequential (and acceptable) fraction of the total. Occasional buttonhead loss is normal for BBRV21 tendons (wires anchored by cold formed buttonheads) and generally occurs during or shortly after tensioning. Nothing in the surveillance reports indicates that the number of missing buttonheads is increasing over time.

No free water has been found at tendon anchorages.

c) Tendon Wire Strength and Ductility Most tensile tests on samples cut from extracted wires show that yield strength, ultimate tensile strength and elongation at failure are essentially the same as those found during material certification testing in the late 1970s. With the exception of the low tensile strengths reported for the wire extracted from tendon V39 during the 35th year surveillance, test results not meeting acceptance criteria are 21 The BBRV system, which uses cold formed buttonheads to anchor individual wires, was introduced by the Swiss engineering firm BBR in 1944.

to Callaway RR Tech Report ULNRC-06831 Page 45 of 62 Rev. 0 20230616 concluded to be due to deficiencies in testing techniques. The low tensile strength reported for the V39 wire is considered to be a unique condition. There is nothing in the test data to suggest that either yield strength, tensile strength or ductility degrade with time under load.

d) Corrosion Protection Medium Characteristics Results of corrosion protection medium (CPM) tests to determine absorbed water content, corrosive ion concentrations and neutralization number confirm that acceptance criteria (with one exception) have been met. In particular:

o All corrosive ion concentrations are below the 10-ppm upper limit and most are below the indicated limit of resolution applicable to the ion. Maximum concentrations of chloride, nitrate and sulfide ions are 0.5022, 2.84 and 0.5020, respectively. Ion concentrations show no trend of increasing over time.

o Neutralization numbers are, with one exception, acceptable. The single exception is a 16.8 base number (vs a 17.5 lower acceptance limit) reported for one 15th surveillance year sample. While trends of the mean and minimum base number values show a slow decrease with time, these remain above the 17.5 lower limit until well after the proposed January 2030 deadline for completion of the next surveillance.

o All reported absorbed water content values are below the 10% (of dry weight) upper limit; the maximum reported value is 0.58%. Water content shows no trend of increasing with time.

5.2 Conclusions Based on the evaluations detailed in Part 4 of this technical report and summarized above, it is concluded that the Callaway containment post-tensioning system will continue to perform its design function until well after the January 2030 deadline for completion of the next surveillance and, in particular that:

• Tendon group mean force will remain above the specified minimum.

• End anchorage hardware and tendon wire will remain free of active corrosion.

• Tendon wire yield strength, tensile strength and ductility will not change over time.

• Corrosion protection medium will retain its protective properties.

• Free water will not be a concern.

22 Lower limit of resolution.

to Callaway RR Tech Report ULNRC-06831 Page 46 of 62 Rev. 0 20230616 5.3 Recommendations On the basis of the above conclusions, it is recommended that the post-tensioning system examination and testing interval be extended to 10 years. This interval extension will maintain an acceptable level of quality and safety and will reduce personnel exposure to a number of industrial safety hazards associated with system examination / testing.

These include:

• Working at heights.

• Working in a de facto confined space (the tendon gallery).

• Working with high pressure hydraulic systems.

• Working near high energy plant systems.

• Working around solvent and hot petroleum product fumes.

• Working around containers and pressurized lines filled with hot petroleum products.

• Close-in exposure to high levels of stored elastic energy in tendons (sudden rotation during force measurement has resulted in high-speed shim ejection).

• Handling heavy loads, often in the vicinity of critical plant components.

Also, it is recommended that routine CPM testing be limited to determination of neutralization (base) number and that additional tests for corrosive ion concentration and absorbed water content be performed only if:

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

• Free water is found at anchorages.

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

to Callaway RR Tech Report ULNRC-06831 Page 47 of 62 Rev. 0 20230616

6. REFERENCES 6.1 USNRC Regulation 10CFR50.55a, Codes and Standards.

6.2 ASME Boiler and Pressure Vessel Code,Section XI, Subsection IWL, 2007 Edition with the 2008 Addenda.

6.3 Callaway Energy Center Final Safety Analysis Report, Section 3.8, Design of Category I Structures, Revision OL-22, November 2016.

6.4 ASTM A421 Specification for Uncoated Stress Relieved Wire for Pre-stressed Concrete, published by the American Society for Testing and Materials.

6.5 Calculation No. AMNROL100015-CALC-007, Time Limited Aging Analysis of Callaway Containment Pre-stressed Tendons for License Renewal (LR), Revision 0, 18 November 2021.

6.6 USNRC Regulatory Guide 1.35, In-service Inspection of Ungrouted Tendons in Pre-stressed Concrete Containments, Revisions 1, 2 and 3.

6.7 First Year Physical Surveillance of the Callaway Unit 1 Containment Building /

Surveillance Report, Prepared by Inryco, Revision 0, 16 August 1985.

6.8 Containment Structure Post-Tensioning System Surveillance / Test Report /

Preliminary / (Third Year Surveillance) / SNUPPS / Callaway Unit 1, report prepared by VSL Corporation, September 1987.

6.9 Fifth Year Physical Surveillance of the Callaway Unit I Containment Building / Post-Tensioning Surveillance Report, prepared by Precision Surveillance Corporation, Revision 0, 06 October 1989.

6.10 Tenth Year Physical Surveillance of the Callaway Unit I Containment Building /

Post-Tensioning Surveillance Report, prepared by Precision Surveillance Corporation, Revision 0, 23 October 1994.

6.11 Fifteenth Year Physical Surveillance of the Callaway Unit I Containment Building /

Post-Tensioning Surveillance Report, prepared by Precision Surveillance Corporation, Revision 0, 12 August 1999.

6.12 Twentieth Year Physical Surveillance of the Post-Tensioning System at the Callaway Nuclear Plant / Post-Tensioning Surveillance Report, prepared by Precision Surveillance Corporation, Revision 0, 28 April 2005.

6.13 Final Report for the Callaway Nuclear Plant 25th Year Containment Building Tendon Surveillance, report prepared by Precision Surveillance Corporation, Revision A, 26 July 2010.

6.14 Final Report for the 30th Year Tendon Surveillance at Callaway Nuclear Power Plant, report prepared by Precision Surveillance Corporation, Revision C, 07 October 2015.

6.15 Final Report for the 35th Year Tendon Surveillance at Callaway Energy Center, report prepared by Precision Surveillance Corporation, Revision 2, 02 July 2021.

to Callaway RR Tech Report ULNRC-06831 Page 48 of 62 Rev. 0 20230616 6.16 Miller, Irwin and John E. Freund, Probability and Statistics for Engineers, Prentice-Hall, Englewood Cliffs, NJ, 1965.

6.17 ANSI / ANS 56.8, Containment System Leakage Testing Requirements, published by the American Nuclear Society.

6.18 Specification C-1003(Q), Specification for In-service Inspection of the Containment Building Post-Tensioning System & Exterior Concrete Shell, Revision 16.

6.19 Document 10466-C-155-208-03, Inryco, Inc., Certification of Tendon Wire.

6.20 Ameren Non-Conformance Report NCR FN513-001.

6.21 Ameren Condition Report CR 202103224-001, Containment Tendon Wire Does Not Meet Ultimate Strength Acceptance Criteria.

6.22 Ameren Condition Report CR 2010-04223-001, Ctmt Post Tension Wire Does Not Meet Elongation Acceptance Criteria.

6.23 Ameren Non-Conformance Report NCR 89N353-004.

6.24 Ameren Non-Conformance Report NCR 89N353-009.

6.25 Ameren Non-Conformance Report NCR 89N353-008.

to Callaway RR Tech Report ULNRC-06831 Page 49 of 62 Rev. 0 20230616

7. TABLES AND FIGURES Tables and figures cited in the preceding text follow.

to Callaway RR Tech Report ULNRC-06831 Page 50 of 62 Rev. 0 20230616 Table 1 - List of US Containments1 with Ungrouted Pre-stressing Systems Plant / Unit Containment Type2 / Notation3 Millstone 2 Shallow dome w / hoop, vertical & dome tendon groups; B Ginna Vertical tendons only; anchored in rock; B TMI 1 Shallow dome w / hoop, vertical & dome tendon groups; B, N Calvert Cliffs 1 & 2 Shallow dome w / hoop, vertical & dome tendon groups; B V. C Summer Shallow dome w / hoop, vertical & dome tendon groups; B Oconee 1, 2 & 3 Shallow dome w / hoop, vertical & dome tendon groups; B Vogtle 1 & 2 Hemispherical dome w / hoop & inverted U tendon groups; S Crystal River 3 Shallow dome w / hoop, vertical & dome tendon groups; B, N Turkey Point 3 & 4 Shallow dome w / hoop, vertical & dome tendon groups; B Farley 1 & 2 Shallow dome w / hoop, vertical & dome tendon groups; B Palisades Shallow dome w / hoop, vertical & dome tendon groups; B, N Zion 1 & 2 Shallow dome w / hoop, vertical & dome tendon groups; B, N Braidwood 1 & 2 Shallow dome w / hoop, vertical & dome tendon groups; B Byron 1 & 2 Shallow dome w / hoop, vertical & dome tendon groups; B BWR Mark II (cylinder - cone) containment w / hoop & vertical tendon LaSalle 1 & 2 groups; B Point Beach 1 & 2 Shallow dome w / hoop, vertical & dome tendon groups; B Callaway Hemispherical dome w / hoop & inverted U tendon groups; B ANO 1 & 2 Shallow dome w / hoop, vertical & dome tendon groups; B South Texas 1 & 2 Hemispherical dome w / hoop & inverted U tendon groups; B Wolf Creek Hemispherical dome w / hoop & inverted U tendon groups; B Ft. Calhoun Shallow dome with spiral and dome tendon groups; B, N Palo Verde 1, 2 & 3 Hemispherical dome w / hoop & inverted U tendon groups; B San Onofre 1 & 2 Hemispherical dome w / hoop & inverted U tendon groups; S, N Rancho Seco Shallow dome w / hoop, vertical & dome tendon groups; S, N Trojan Hemispherical dome w / hoop & inverted U tendon groups; B, N Note 1: Bellefonte 1 & 2, which are still incomplete, Midland 1 & 2, which were terminated prior to fuel load and Robinson & TMI 2, which have grouted tendon systems, are not listed.

Note 2: All units are PWRs except LaSalle (BWR).

Note 3: B - BBRV system with buttonheaded wires; S - strand system with wedge anchors; N - unit(s) are no longer in operation.

to Callaway RR Tech Report ULNRC-06831 Page 51 of 62 Rev. 0 20230616 Table 2 - Summary of Circumferential Tendon Forces, Sheet 1 of 2 T, Time FM, Surveillance 1 Since SIT, Tendon Measured Year Years Force, kip 9AC 1,340 26AC2 1,339 5BA 1,357 1 1.4 45BA 1,312 51BA 1,284 1CB 1,372 9CB 1,324 5AC 1,320 14BA 1,389 18BA 1,380 3 3.5 35BA2 1,355 45BA 1,346 47BA 1,286 11CB 1,322 12AC 1,312 20AC2 1,280 42AC 1,282 52AC 1,270 5 5.5 20BA 1,320 44BA 1,325 45BA 1,281 20CB 1,290 45AC 1,357 10 10.5 45BA 1,314 12CB2 1,310 6AC 1,340 15 15.4 45BA 1,340 40CB2 1,327 48AC2 1,314 20 20.6 45BA 1,298 44CB 1,366 49AC 1,285 45BA 1,303 25 26.2 27CB 1,336 33CB2 1,366 Note 1: Common tendon cells shaded.

Note 2: Tendon de-tensioned for test wire removal.

to Callaway RR Tech Report ULNRC-06831 Page 52 of 62 Rev. 0 20230616 Table 2 - Summary of Circumferential Tendon Forces, Sheet 2 of 2 T, Time FM, Surveillance Since SIT, Tendon1 Measured Year Years Force, kip 16AC2 1,305 45BA 1,288 30 31.4 2CB 1,319 46CB 1,281 31AC 1,337 45BA 1,269 35 37.2 25CB2 1,278 49CB 1,291 Note 1: Common tendon cells shaded.

Note 2: Tendon de-tensioned for test wire removal.

Table 3 - Summary of Circumferential Common Tendon 45BA Forces Surveillance T, Time Since FM, Measured Force, Year SIT, Years kip 1 1.4 1,312 3 3.5 1,346 5 5.5 1,281 10 10.5 1,314 15 15.4 1,340 20 20.6 1,298 25 26.2 1,303 30 31.4 1,288 35 37.2 1,269

Callaway RR Tech Report to Page 53 of 62 ULNRC-06831 Rev. 0 20230616 Table 4 - Summary of Meridional Tendon Forces T, Time FM, Surveillance Since SIT, Tendon1 Measured Year Years Force, kip V20 1,411 V35 1,418 1 1.4 V65 1,450 V742 1,451 V12 1,411 V18 1,451 3 3.5 V47 1,397 V65 1,446 V27 1,386 V41 1,402 53 5.5 V65 1,382 V66 1,387 V842 1,361 V15 1,432 10 10.5 V65 1,438 V682 1,428 V92 1,426 15 15.4 V65 1,415 V76 1,422 V13 1,397 20 20.6 V302 1,365 V65 1,407 V7 1,433 25 26.2 V532 1,409 V65 1,419 V262 1,369 30 31.4 V45 1,383 V65 1,397 V392 1,391 35 37.2 V65 1,378 V81 1,340 Note 1: Common tendon cells shaded.

Note 2: Tendon de-tensioned for test wire removal.

Note 3: V1, de-tensioned during year 3, omitted from table & trend.

to Callaway RR Tech Report ULNRC-06831 Page 54 of 62 Rev. 0 20230616 Table 5 - Summary of Meridional Common Tendon V65 Forces Surveillance T, Time Since FM, Measured Force, Year SIT, Years kip 1 1.4 1,450 3 3.5 1,446 5 5.5 1,382 10 10.5 1,438 15 15.4 1,415 20 20.6 1,407 25 26.2 1,419 30 31.4 1,397 35 37.2 1,378 to Callaway RR Tech Report ULNRC-06831 Page 55 of 62 Rev. 0 20230616 Table 6 - Wire Test Results1 / Yield Strength Exam Yield Strength, ksi Wire Exam Tendon Year Specimen 1 Specimen 2 Specimen 3 Mean, ksi Mean, ksi 26AC 238 238 238 238 1 233 V74 227 228 229 228 35AB 152 174 176 171 3 35AB2 155 188 180 179 V1 192 185 182 186 20AC 232 229 227 229 20AC3 238 235 235 236 5 226 V1 223 220 220 221 V84 217 221 217 218 V68 215 215 218 216 10 V684 226 229 226 227 220 12CB 213 217 217 216 40CB 224 222 222 223 15 225 V9 227 228 229 228 48AC 235 232 232 233 20 229 V30 226 225 226 226 33CB 255 250 251 252 25 33CB2 250 256 N/A 240 V53 228 231 225 228 16AC 233 235 234 234 30 234 V26 230 234 239 234 25CB 232 233 227 231 35 V39 221 215 213 224 218 V395 218 224 216 Note 1 - Values in shaded cells do not meet the 204 ksi minimum yield acceptance criterion Note 2 - Confirmatory tests to verify low elongation at failure Note 3 - Test specimens from broken wire Note 4 - Additional wire removed for corrosion examination Note 5 - Confirmatory tests to verify low breaking strength to Callaway RR Tech Report ULNRC-06831 Page 56 of 62 Rev. 0 20230616 Table 7 - Wire Test Results1 / Ultimate Tensile Strength (UTS)

Exam Ultimate Tensile Strength, ksi Wire Exam Tendon Year Specimen 1 Specimen 2 Specimen 3 Mean, ksi Mean, ksi 26AC 265 259 254 259 1 254 V74 246 246 252 248 35AB 241 241 242 242 3 35AB2 242 245 241 239 V1 241 232 234 236 20AC 267 263 267 266 20AC3 271 267 271 270 5 257 V1 249 252 248 250 V84 245 244 240 243 V68 243 243 240 242 10 V684 245 245 244 245 244 12CB 243 245 244 244 40CB 248 246 250 248 15 250 V9 250 253 252 252 48AC 261 256 258 258 20 257 V30 257 254 256 256 33CB 260 264 265 2

264 25 33CB 261 272 N/A 267 V53 269 271 267 269 16AC 259 262 259 260 30 259 V26 258 256 259 258 25CB 249 251 246 249 35 V39 239 232 231 242 5

235 V39 235 241 234 Note 1: Values in shaded cells do not meet the 240 ksi minimum UTS acceptance criterion.

Note 2: Confirmatory tests to verify low elongation at failure.

Note 3: Test specimens from broken wire.

Note 4: Additional wire removed for corrosion examination.

Note 5: Confirmatory tests to verify low breaking strength.

to Callaway RR Tech Report ULNRC-06831 Page 57 of 62 Rev. 0 20230616 Table 8 - Wire Test Results1 / Elongation at Failure Exam Elongation at Failure, % Wire Exam Tendon Year Specimen 1 Specimen 2 Specimen 3 Mean, % Mean, %

26AC 4.5 3.7 3.3 3.8 1 3.6 V74 2.7 3.0 4.1 3.3 35AB 1.2 1.5 1.5 1.7 3 35AB2 2.2 2.0 2.0 1.8 V1 2.8 1.2 1.8 1.9 20AC 4.9 4.6 5.2 4.9 20AC3 4.1 4.1 4.7 4.3 5 4.4 V1 4.0 4.1 4.1 4.1 V84 4.1 4.2 4.1 4.1 V68 4.6 4.0 4.2 4.3 10 V684 3.9 3.5 4.0 3.8 4.0 12CB 4.0 4.0 4.0 4.0 40CB 4.0 4.2 4.0 4.1 15 4.2 V9 4.2 4.4 4.4 4.3 48AC 5.2 4.2 4.0 4.5 20 4.3 V30 4.0 4.0 4.1 4.0 33CB 1.3 1.6 2.2 1.9 25 33CB2 2.0 2.4 N/A 3.1 V53 4.3 4.5 4.0 4.3 16AC 4.5 5.2 4.8 4.8 30 4.7 V26 4.8 4.8 4.2 4.6 25CB 4.0 5.0 4.5 4.5 35 V39 4.5 4.0 4.0 4.5 4.4 V395 4.2 4.8 5.0 Note 1: Values in shaded cells do not meet the 4% minimum elongation acceptance criterion.

Note 2: Confirmatory tests to verify low elongation at failure.

Note 3: Test specimens from broken wire.

Note 4: Additional wire removed for corrosion examination.

Note 5: Confirmatory tests to verify low breaking strength.

to Callaway RR Tech Report ULNRC-06831 Page 58 of 62 Rev. 0 20230616 Figure 1 - Circumferential Tendon Force Trend & LCL 1,500 Lift-Off Force Data Point (Typ) 1,450 Circumferential Tendon Mean Force Trend Line F (kip) = 1,335.3 - 18.06

• Log10 (T) 1,400 F, Tendon Force, kip 1,350 1,300 1,250 95% LCL on Mean Force 1,200 Minimum Required Mean Circumferential Tendon Force FMin (kip) 1,227 1,150 1,100 1 10 100 T, Time Since SIT, Years (Logarithmic Scale)

Callaway RR Tech Report to Page 59 of 62 ULNRC-06831 Rev. 0 20230616 Figure 2 - Circumferential Common Tendon 45BA Force Trend 1,500

/

Lift-Off Force

/ Data Point (Typ) 1,450 /

V v

/ Circumferential Common Tendon 45BA Mean Force Trend Line

/

c- F (kip) = 1,330.4 - 23.60

• Log10 (T) 1,400

~v /

1-- 1--

F, Tendon Force, kip 1,350 1--~ I*

1,300 ~

~

1,250 1,200 1,150 1,100 1 10 100 T, Time Since SIT, Years (Logarithmic Scale) to Callaway RR Tech Report ULNRC-06831 Page 60 of 62 Rev. 0 20230616 Figure 3 - Meridional Tendon Force Trend & LCL 1,500 I Lift-Off Force

\ Meridional Tendon Mean Force Trend Line

\ Data Point (Typ)

~

l I F (kip) = 1,433.1 - 27.06

• Log10 (T) 1,450 ~ ~ "t--...

1,400 I

I

~-

I I

I I I I I I I

i.

I I

' II I

I

~ I I

~*

htl, I'--...

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la. ~ I I

I

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III

.~ II I I

• I'--. I*

• II I I

I r-,....1'-...

F, Tendon Force, kip 1,350 I'--.

""' I 95% LCL on Mean Force 1,300 1,250 Minimum Required Mean Meridional Tendon Force 1,200 FMin (kip) 1,160

--- --- ---f-A 1,150 1,100 1 10 100 T, Time Since SIT, Years (Logarithmic Scale) to Callaway RR Tech Report ULNRC-06831 Page 61 of 62 Rev. 0 20230616 Figure 4 - Meridional Common Tendon V65 Force Trend 1,500 Meridional Common Tendon V65 Mean Force Trend Line I F (kip) = 1,451.6 - 35.25

• Log10 (T) 1,450

~

11,,.

1,400 F, Tendon Force, kip 1,350 --- r---..

---

Lift-Off Force Data Point (Typ) 1,300 1,250 1,200 1,150 1,100 1 10 100 T, Time Since SIT, Years (Logarithmic Scale)

Callaway RR Tech Report Page 62 of 62 Rev. 0 20230616 Figure 5 - Corrosion Protection Medium Base Number Trends 100 90 80

1. I Trend of the maxima Min 70 I I II

~ J ..............

60 I

I I -~ ~I *

<Ii i. Mean Base Number

~ I ~ I' Jr,-. r---r--- r---~

I

,. ol I

50 J I

• I J I

I Max I/ I I I ~

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I

• I minimum 40 I

I I required base 1,

I J

~ I number = 17.5 J,__ I J ~ I J Log. (Min) r--- ,......

I I I I

I 30 ~ I I J

I I Log. (Mean)

Trend of the minima I 20 I I

• Log. (Max) 10 Minimum required base number = 17.5 0

1 10 100 T, Time Since SIT, Years (Logarithmic Scale)