ML19182A077
| ML19182A077 | |
| Person / Time | |
|---|---|
| Site: | Vogtle  |
| Issue date: | 07/11/2019 |
| From: | Markley M Plant Licensing Branch II |
| To: | Gayheart C Southern Nuclear Operating Co |
| Lamb, 415-3100 | |
| References | |
| EPID L-2019-LLR-0017 | |
| Download: ML19182A077 (9) | |
Text
July 11, 2019 Ms. Cheryl A. Gayheart Regulatory Affairs Director Southern Nuclear Operating Co., Inc.
3535 Colonnade Parkway Birmingham, AL 35243
SUBJECT:
VOGTLE ELECTRIC GENERATING PLANT, UNITS 1 AND 2 - INSERVICE INSPECTION ALTERNATIVE VEGP-ISI-ALT-19-01 FOR CONTAINMENT TENDON INSERVICE INSPECTION EXTENSION (EPID NO. L-2019-LLR-0017)
Dear Ms. Gayheart:
By letter dated February 18, 2019, Southern Nuclear Operating Company, Inc. (SNC) requested an alternative to Subsection IWL of American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel (BPV) Code Section XI, 2007 Edition, 2008 Addenda for Vogtle Electric Generating Plant (Vogtle), Units 1 and 2, for the Fourth 10-year inservice inspection (ISI) interval that began on May 31, 2017, and ends on May 30, 2027. The ASME Code components associated with this alternative are the tendons that are part of the reactor containment building.
SNC requested to use an alternative tendon examination to the requirements in Subsection IWL.
The licensee submitted the alternative request pursuant to Sections 50.55a(z)(1) of Title 10 of the Code of Federal Regulations (10 CFR), which requires that the applicant demonstrate that the proposed alternative provides an acceptable level of quality and safety.
The U.S. Nuclear Regulatory Commission (NRC) staff has reviewed the subject request, and concludes that SNC has adequately addressed all of the regulatory requirements and that the proposed alternative provides an acceptable level of quality and safety. Therefore, the NRC staff authorizes the proposed alternative in accordance with 10 CFR 50.55a(z)(1) for the Fourth ISI interval Vogtle, Units 1 and 2. The NRC staffs safety evaluation is enclosed.
All other requirements of the ASME BPV Code,Section XI, for which relief has not been specifically requested and approved remain applicable, including a third-party review by the Authorized Nuclear Inservice Inspector.
If you have any questions, please contact the senior project manager at (301) 415-3100 or via email at John.Lamb@nrc.gov.
Sincerely,
/RA/
Michael Markley, Chief Plant Licensing Branch II-1 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket Nos. 50-424 and 50-425 cc: Listserv
Enclosure:
Safety Evaluation
SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION PROPOSED ALTERNATIVE TO ASME BPV CODE REQUIREMENTS VEGP-ISI-ALT-19-01 FOURTH TEN-YEAR INSERVICE INSPECTION PROGRAM INTERVAL SOUTHERN NUCLEAR OPERATING COMPANY VOGTLE ELECTRIC GENERATING PLANT, UNITS 1 AND 2 DOCKET NOS. 50-424 AND 50-425
1.0 INTRODUCTION
By letter dated February 18, 2019 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML19049A017), Southern Nuclear Operating Company, Inc. (SNC, licensee) requested alternative VEGP-ISI-ALT-19-01 to Subsection IWL of American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel (BPV) Code Section XI, 2007 Edition, 2008 Addenda for Vogtle Electric Generating Plant (Vogtle), Units 1 and 2. The ASME Code components associated with this alternative are the tendons that are part of the reactor containment building. SNC requested to use an alternative tendon examination to the requirements in Subsection IWL.
Specifically, pursuant to Title 10 of the Code of Federal Regulations (CFR) 10 CFR Part 50, Section 50.55a(z)(1), the licensee requested to use the proposed alternative on the basis that the alternative provides an acceptable level of quality and safety.
2.0 REGULATORY EVALUATION
Pursuant to 10 CFR 50.55a(g)(4), throughout the service life of a pressurized water-cooled nuclear power facility, components that are classified as ASME Code Class 1, 2, and 3 must meet the requirements, except the design and access provisions and preservice examination requirements, set forth in the ASME BPV Code,Section XI, to the extent practical, within the limitations of design, geometry, and materials of construction of the components.
Further, these regulations require that inservice examination of components and system pressure tests conducted during the First 10-year interval, and subsequent intervals, comply with the requirements in the latest edition and addenda of Section XI of the ASME BPV Code, incorporated by reference in paragraph (b) of 10 CFR 50.55a, on the date 12 months prior to the start of the 120 month interval, subject to the limitations and modifications listed therein.
Alternatives to requirements under 10 CFR 50.55a(g) may be authorized by the U.S. Nuclear Regulatory Commission (NRC) pursuant to 10 CFR 50.55a(z)(1) or 10 CFR 50.55a(z)(2). In proposing alternatives or requests for relief, the licensee must demonstrate that: (1) the proposed alternatives would provide an acceptable level of quality and safety; or (2) compliance with the specified requirements would result in hardship or unusual difficulty, without a compensating increase in the level of quality and safety.
ASME Code Section XI, 2007 Edition including Addenda through 2008, Subsection IWL-2500, Examination Requirements, states that examination shall be performed in accordance with the requirements of Table IWL-2500-1.
ASME Code Section XI, 2007 Edition including Addenda through 2008, Subsection IWL-2521.2 Tendons Affected by Repair/Replacement Activities, requires augmented examination of tendons affected by post-tensioning system repair/replacement activities. Table IWL-2521-2 requires an initial examination of tendons affected by post-tensioning system repair/replacement activities within one year (+/- 3 months) following the completion of repair/replacement activities.
Subsection IWL-2420 describes the inservice inspection schedule for unbonded post-tensioning systems and requires their examination at 1, 3, and 5 years following the completion of the Structural Integrity Test and every 5 years thereafter.
Based on the above, and subject to the following technical evaluation, the NRC staff finds that regulatory authority exists for the licensee to request, and the NRC to authorize, the proposed alternative requested by the licensee.
3.0 TECHNICAL EVALUATION
3.1 Background
By letter dated February 18, 2019, SNC requested, for Vogtle, Units 1 and 2, an alternative to Subsection IWL of ASME BPV Code,Section XI, 2007 Edition, 2008 Addenda, which requires an initial examination of containment tendons affected by post-tensioning system repair/replacement activities within one year (plus or minus 3 months) following the completion of repair/replacement activities. The alternative VEGP-ISI-ALT-19-01 proposes the use of an alternate tendon examination for tendons affected by repair/replacement activities at Vogtle, Units 1 and 2, during the fourth containment in-service inspection interval (ISI), which began May 31, 2017, and ends on May 30, 2027.
By letter dated February 18, 2019, the licensee stated that the results of the post-tensioning system inservice examinations conducted at Vogtle between 1987 to 2015 (Unit 1) and 1989 to 2015 (Unit 2), show that the system is continuing to perform its intended function and that it can be expected to do so until well past the January 2047 (Unit 1) and February 2049 (Unit 2) expiration of the extended operating period license.
The licensee stated that visual examination planned for the 35th year (Unit 1) / 30th year (Unit 2) surveillance, which will occur in 2020, will be adequate to determine when physical testing and examination per Examination Category L-B is required.
The licensee also stated that the ASME Section XI, Subsection IWL program at Vogtle, Units 1 and 2, is credited for managing containment building degradation. The Examination Category L-A visual examinations being performed every five years are expected to identify conditions that would allow water intrusion into the tendons and gross leakage of CPM, which would be precursors for providing an environment that could allow corrosion of the tendon wires or inaccessible tendon hardware covered by the tendon end cap. The licensee stated that such conditions would be evaluated by the Responsible Engineer (RE) to identify required additional actions to assure no corrosive environmental conditions exist. Vogtle, Units 1 and 2 mean prestresses are predicted to be acceptable well beyond the 40th year (Unit 1) / 35th year (Unit 2) surveillance based on acceptable performance over 30 years. Therefore, SNC submitted a proposed alternative to the Section XI required schedule, extending the surveillance an additional 5 years, which will continue to provide an acceptable level of quality and safety.
3.2 ASME Code Components Affected
Class CC Components, Post-Tensioning Horizontal Tendons This alternative applies to:
Code Class: CC
Reference:
IWL-2421, IWL-2520, Table IWL-2500-1 Examination Category: Table IWL-2500-1, Category L-B Item Number: L2.1 0, L2.20, L2.30, L2.40, and L2.50
==
Description:==
Examination of unbonded post-tensioning system Component Number: Unit 1 Vogtle Containment Building Unit 2 Vogtle Containment Building 3.3
Applicable Code Edition and Addenda
The licensee stated that Vogtle, Units 1 and 2, current code of record for the fourth containment ISI interval is the ASME Code,Section XI, 2007 Edition through the 2008 Addenda of the ASME Boiler and Pressure Vessel (B&PV) Code.
Subsection IWL of ASME Code Section XI, 2007 Edition, 2008 Addenda requires an initial examination of containment tendons affected by post-tensioning system repair/replacement activities within one year (plus or minus 3 months) following the completion of repair/replacement activities.
3.4 Applicable ASME Code Requirement Subsection IWL-2421(b) states that when the conditions of IWL-2421(a) are met, the inspection dates and examination requirements may be as follows:
(1) For the containment with the first Structural Integrity Test, all examinations required by IWL-2500 shall be performed at 1, 3, and 10 years and every 10 years thereafter. Only the examination of tendon anchorage areas (IWL-2524) and examination of corrosion
protection medium and free water (IWL-2525) need be performed at 5 and 15 years and every 10 years thereafter.
(2) For each subsequent containment constructed at the site, all examinations required by IWL-2500 shall be performed at 1, 5, and 15 years and every 10 years thereafter. Only the examination of tendon anchorage areas (IWL-2524) and examination of corrosion protection medium and free water (IWL-2525) need be performed at 3 and 10 years and every 10 years thereafter.
The licensee also stated that Vogtle, Units 1 and 2 are currently required to examine the post-tensioning system every 10 years.
Subsection IWL-2500 requires examinations be performed in accordance with the requirements of Table IWL-2500-1.
Table IWL-2500-1, Item Number L2.10 requires that selected tendon force and elongation be measured.
Table IWL -2500-1, Item Number L2.20 requires that tendon single wire samples be removed and examined for corrosion and mechanical damage as well as tested to obtain yield strength, ultimate tensile strength, and elongation on each removed wire. The selected tendons are subsequently retensioned as required per IWL-2523.3 because wire removal requires detensioning in order to safely obtain wire samples.
Table IWL-2500-1, Item Number L2.30 requires that a detailed visual examination be performed on selected tendon anchorage hardware and adjacent concrete extending 2 feet from the edge of the bearing plate. The quantity of free water released from the anchorage end cap as well as any which drains from the tendon during examination shall be documented.
Table IWL-2500-1, Item number L2.40 and L2.50 require that samples of selected tendon corrosion protection medium (CPM) and free water be obtained and analyzed.
3.5 Licensee Proposed Alternative and Basis for Use As an alternative to Subsection IWL of ASME Code,Section XI, the licensee requested to perform visual examination only of the concrete containment and accessible steel hardware visible without tendon cover removal during the 35th year (Vogtle, Unit 1) I 30th year (Vogtle, Unit 2) surveillance. The licensee stated that physical testing would be performed only if visual examination results indicate a need for such testing as determined by the RE (IWL-2330). The 35th year (Vogtle, Unit 1) I 30th year (Vogtle, Unit 2) surveillance is required to be completed no later than April 14, 2020, based on last performance. The 40th year (Vogtle, Unit 1) I 35th year (Vogtle, Unit 2) surveillance would be due at August 1, 2025, and would be completed during the subsequent 4th ISI interval. A common re-baselining date, August 1, 2010 (+/-1 year), is used to allow alignment of the schedule for all the Table IWL-2500-1 examinations (concrete and post-tensioning system) for Vogtle, Units 1 and 2 as stated in letter dated June 11, 2010 (ADAMS Accession No. ML100900129). The licensee proposed this one-time deferral of the physical testing of the post-tensioning system. This alternative is proposed for the fourth 10-year ISI interval, which began on May 31, 2017, and ends on May 30, 2027.
In its letter dated February 18, 2019, the licensee stated the proposed alternative:
In accordance with 10 CFR 50.55a(z)(1 ), [Vogtle Electric Generating Plant]
VEGP, Unit 1 & Unit 2 are proposing alternative examination requirements on the basis that these alternative actions will provide an acceptable level of quality and safety.
VEGP, Unit 1 & Unit 2 proposes to perform a General Visual Examination and Detailed Visual Examination (when required) of accessible concrete and exposed steel hardware as required by Section XI Table IWL-2500-1, Item Numbers L 1.11 and L 1.12, as modified by 10 CFR 50.55a. The examination and physical testing requirements of Section XI Table IWL-2500-1 Item Numbers L2.10, L2.20, L2.30, L2.40, and L2.50 will only be performed if the General Visual Examination and Detailed Visual Examination identify conditions where observations indicate there could be degradation of tendon hardware as documented by the Responsible Engineer in an engineering evaluation.
Example conditions that could require removal of the tendon end cap and further examination per Item Numbers L2.1 0, L2.20, L2.30, L2.40, and L2.50 are:
Evidence of possible damage to the enclosed post-tensioning hardware as evidenced by conditions such as end cap deformation found during external visual examination. Conditions observed by removal of the end cap would determine the extent of additional examinations per L2.1 0, L2.20, L2.30, L2.40, or L2.50.
Active corrosion on a bearing plate or end cap that requires further investigation as determined by the Responsible Engineer in an engineering evaluation.
Evidence of gross leakage of corrosion protection medium will be evaluated and a plan developed for corrective actions as defined in an engineering evaluation documented by the Responsible Engineer.
Physical testing of post-tensioning system examinations will be extended from 10 to 15 years and will be required in 2025 and 2040 for both units.
In Enclosure 2 to its letter dated February 18, 2019, the licensee stated the basis for the proposed alternative:
The results of unbonded post-tensioning system examinations performed over the last 4 decades at 24 domestic sites with a total of 41 pre-stressed containments (listed in Table 1) provide ample evidence, as discussed below, that prescriptive requirements currently in IWL are, in many cases, overly conservative. These industry results as well as VEGP plant-specific operating experience as subsequently discussed, support the implementation of alternative programs with fewer prescriptive requirements.
In Section 4.2.4, Tendon Mean Force Trend Summary and Conclusions, of Enclosure 2 to its letter dated February 18, 2019, the licensee provided the following table:
Unit Group / Mean Force Lower Limit Trend Projected Mean / Margin Above Lower Limit, Kip T = 40 T = 100 1
Cylinder Hoop /
1,336 kip Measured 1,512 / 176 1,487 /151 Normalized 1,510 / 174 1,491 / 155 Measured LCL*
1,484 / 148 1,450 / 114 Dome Hoop /
1,370 kip Measured 1,498 / 128 1,478 / 108 Normalized 1,486 / 116 1,461 / 91 Inverted U /
1,405 kip Measured 1,505 / 100 1,495 / 90 Normalized 1,507 / 102 1,493 / 88 Measured LCL*
1,470 / 65 1,447 / 42 2
Cylinder Hoop /
1,336 kip Measured 1,467 / 131 1,460 / 124 Normalized 1,467 / 131 1,458 / 122 Measured LCL*
1,438 / 102 1,415 / 79 Dome Hoop /
1,370 kip Measured 1,415 / 45 1,375 / 5 Normalized 1,470 / 100 1,456/ 86 Inverted U /
1,405 kip Measured 1,522 / 117 1,551** / 146 Normalized 1,522 / 117 1,541** / 136 Measured LCL*
1,477 / 72 1,477 / 72 Note:
- LCL: Lower Confidence Limit Licensee predicted tendon prestress curves depict a slight increase over time. The licensee acknowledged that is not an expected phenomenon and concluded that the computed trend lines are overly influenced by the effect of data scatter. The actual trend is essentially flat and there is no scenario where the actual prestressing force will decrease below the lower limit prior to T=100 years.
For further technical details, see the letter dated February 18, 2019.
3.6
NRC Staff Evaluation
The NRC staff reviewed the licensee request and noted from the table above that the trend of projected mean prestressing force remains above the applicable lower limit through T = 100 (year 2086) for Unit 1 and Unit 2, and will remain well above the applicable lower limit through T
= 40 (August 2026), the latest date for completion of the next surveillance under the proposed 15-year interval.
The NRC staff noted that the foregoing evaluations of tendon force trends, as well as the margins tabulated above, show that group mean prestressing forces will remain well above the minimum required levels through 2026 and will not fall below those levels at any time before 2086 (T = 100). The NRC staff also noted that the trends of group mean prestressing forces will be re-computed and evaluated when additional data is acquired during the next surveillance, to confirm that the mean values will remain above the applicable minimums. Damaged, cracked or distorted load bearing components (bearing plates, anchor heads, wedges, shims) have not been found during visual examinations. Several concrete cracks with maximum widths exceeding the threshold of 0.010 inch were found over the course of the surveillance program.
None of these are considered to have structural significance; they are not service induced or age-related degradation.
The NRC staff further noted that end anchorage visual examination trends show that the condition of both post-tensioning system hardware and concrete adjacent to tendon end anchorage bearing plates is stable and unlikely to experience significant change over the operating lifetime of the plant.
ASME Section XI, Subsection IWL program at Vogtle, Units 1 and 2, is credited for managing the containment building degradation. The Examination Category L-A visual examinations being performed every 5 years can identify conditions that would allow water intrusion into the tendons and gross leakage of CPM which would be precursors for providing an environment that could allow corrosion of the tendon wires or inaccessible tendon hardware covered by the tendon end cap. Such conditions would be evaluated by the RE to identify required additional actions to assure no corrosive environmental conditions exist. Therefore, extending the surveillance an additional 5 years will continue to provide an acceptable level of quality and safety. As such, the licensees alternative approach provides an acceptable level of quality and safety, consistent with the regulatory requirements in 10 CFR 50.55a(z)(1) and does not adversely impact the health and safety of the public.
4.0 CONCLUSION
Based on the information provided in the licensees submittal dated February 18, 2019, the NRC staff concludes that the proposed alternative VEGP-ISI-ALT-19-01 is acceptable, because it demonstrated that the proposed alternative provides an acceptable level of quality and safety.
Therefore, pursuant to 10 CFR 50.55a(z)(1) the implementation of the licensee-proposed alternative is authorized for the Vogtle, Units 1 and 2, 4th 10-year ISI interval, which began on May 31, 2017, and is scheduled to end on May 30, 2027.
All other ASME Code,Section XI requirements for which an alternative was not specifically requested and approved remain applicable, including a third-party review by an Authorized Nuclear In-service Inspector.
Principle Contributor: Dan Hoang, NRR/DE/ESEB Dated: July 11, 2019
- via e-mail