ML23229A499
| ML23229A499 | |
| Person / Time | |
|---|---|
| Site: | South Texas  |
| Issue date: | 08/17/2023 |
| From: | Georgeson C South Texas |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| NOC-AE-23003981, 35500333, EPID L-2023-LLR-0004 | |
| Download: ML23229A499 (1) | |
Text
August 17, 2023 NOC-AE-23003981 10 CFR 50.55a STI: 35500333 Attention: Document Control Desk U.S. Nuclear Regulatory Commission Washington, DC 20555-0001 South Texas Project Units 1 and 2 Docket Nos. STN 50-498 and STN 50-499 Supplement to Proposed Alternate Frequency to Containment Unbonded Post-Tensioning System Inservice Inspection (Relief Request RR-ENG-4-06) (EPID: L-2023-LLR-0004)
References:
- 1. Letter; C. Georgeson (STP) to Document Control Desk (NRC); Proposed Alternate Frequency to Containment Unbonded Post-Tensioning System Inservice Inspection (Relief Request RR-ENG-4-06); February 1, 2023; (NOC-AE-23003940) (ML23032A484).
- 2. Letter; D. Galvin (NRC) to T. Powell (STP); South Texas Project, Units 1 and 2 - Supplemental Information Needed for Acceptance of Requested Licensing Action Re: Proposed Alternative to the Requirements of the ASME Code (EPID L-2023-LLR-0004); March 6, 2023; (AE-NOC-23003363) (ML23061A175).
- 3. Letter; C. Georgeson (STP) to Document Control Desk (NRC); Supplement to Proposed Alternate Frequency to Containment Unbonded Post-Tensioning System Inservice Inspection (Relief Request RR-ENG-4-06) (EPID: L-2023-LLR-0004); March 9, 2023; (NOC-AE-23003947) (ML23068A364).
By Reference 1, STP Nuclear Operating Company (STPNOC) submitted a relief request to propose alternative frequency to the containment unbonded post-tensioning system inservice inspection. Based on discussion with NRC staff and feedback provided in Reference 2, STPNOC provided the revised relief request in Reference 3. An audit plan was proposed by the NRC to gather more information and the following revised relief request was developed. Please replace the Enclosure to Reference 3 in entirety with the Enclosure provided in this submittal.
The revised relief request provided in the Enclosure now only requests relief for one 10-year Containment Inservice Inspection (CISI) interval for Units 1 and 2 and includes surveillance result details requested by the NRC.
There are no new commitments in this letter.
NOC-AE-23003981 Page 2 of 2 If there are any questions regarding this letter, please contact Zachary Dibbern at (361) 972-4336 or me at (361) 972-7806.
C. H. Georgeson Digitally signed by C. H. Georgeson Date: 2023.08.17 14:24:20 -05'00' Christopher Georgeson General Manager, Engineering
Enclosure:
Revised Relief Request RR-ENG-4-06, Alternative Frequency to Containment Unbonded Post-Tensioning System Inservice Inspection cc:
Regional Administrator, Region IV U.S. Nuclear Regulatory Commission 1600 E. Lamar Boulevard Arlington, TX 76011-4511
NOC-AE-23003981 Enclosure Enclosure Revised Relief Request RR-ENG-4-06, Alternative Frequency to Containment Unbonded Post-Tensioning System Inservice Inspection
NOC-AE-23003981 Enclosure Page 1 of 27 Revised Relief Request RR-ENG-4-06, Alternative Frequency to Containment Unbonded Post-Tensioning System Inservice Inspection
- 1. ASME Code Components Affected
Description:
Inservice Examination of Concrete Containment Unbonded Post-Tensioning System Component: Concrete Containments, Units 1 and 2 Code Class: CC Examination Categories and Code Item Numbers:
Category L-B, Unbonded Post-Tensioning System Code Item Numbers: L2.10, L2.20, L2.30, L2.40, and L2.50
- 2. Applicable Code Edition American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel (BPV) Code, Section XI, Subsection IWL, 2013 edition (Reference 9.1). The 2013 edition is applicable for the fourth 10-year Containment Inservice Inspection Interval (CISI) that began September 9, 2019. (Reference 9.2)
The 2013 code edition is applicable for the current (4th) CISI interval, but it has not yet been used for a surveillance at STP. It will be used for the next surveillances to be performed in 2024. As described in section 6.2, past surveillances were governed by different codes and acceptance criteria. The following table summarizes the codes used for past surveillances.
Unit Nominal Year Applicable Code Remarks Plant Performed Year 1 1 1988 RG 1.35, April 79 2 1 1989 RG 1.35, April 79 1 3 1990 RG 1.35, April 79 2 3 1992 RG 1.35, April 79 1 5 1992 RG 1.35, April 79 2 5 1993 RG 1.35, April 79 1, 2 10 1998 RG 1.35, April 79 Expedited examination, per 10 10 CFR50.55a(b) CFR50.55a, as modified by 61 FR 41303 (Aug. 8, 1996) 1, 2 15 2004 ASME, IWL-1992 1, 2 20 2009 ASME, IWL-1992 1, 2 25 2014 ASME, IWL-2004 1, 2 30 2018 ASME, IWL-2004 Some acceptance criteria, wire and grease, are tied to the design specifications, which implemented the design code of record. The STP design code of record for the containment building is listed in Updated Final Safety Analysis Report (UFSAR) 3.8.1.2.1. It is ACI-ASME 359, 1973 proposed edition.
NOC-AE-23003981 Enclosure Page 2 of 27
3. Applicable Code Requirements
3.1 IWL-2420 UNBONDED POST-TENSIONING SYSTEMS (a) Unbonded post-tensioning systems shall be examined in accordance with IWL-2520 at 1, 3, and 5 years following the completion of the containment Structural Integrity Test and every 5 years thereafter.
3.2 IWL-2421 Sites With Multiple Plants (a) For sites with multiple plants, the requirements of IWL-2420 may be modified if the containments utilize the same prestressing system and are essentially identical in design, if post-tensioning operations for each subsequent containment constructed at the site were completed not more than 2 years apart, and if the containments are similarly exposed to or protected from the outside environment.
(b) When the conditions of (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-2520 shall be performed at 1, 3, and 10 years, and every 10 years thereafter.
In addition, the examinations required by IWL-2524 and IWL-2525 shall 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-2520 shall be performed at 1, 5, and 15 years, and every 10 years thereafter.
In addition, the examinations required by IWL-2524 and IWL-2525 shall be performed at 3 and 10 years and every 10 years thereafter.
STP completed the 30th year surveillance in 2018. The next scheduled surveillance is the 35th year surveillance. IWL-2421(b)(1) is applicable to Unit 1. IWL-2421(b)(2) is applicable to Unit
- 2. The next surveillance was due July 29, 2023 in Unit 1 and September 30, 2023 in Unit 2.
These nominal dates will be extended up to 1 year per IWL-2420(c), which makes the latest acceptable due dates July 29, 2024 in Unit 1 and September 30, 2024 in Unit 2.
The applicable requirements of IWL-2520 are paraphrased and summarized below.
IWL-2520 Examination of Unbonded Post-Tensioning Systems
- IWL-2521 requires random selection of tendons for surveillance.
- IWL-2522 requires tendon force measurements in selected tendons.
- IWL-2523 requires detensioning of one tendon per group, followed by removal and destructive examination of a single wire prior to retensioning. The removed wire is not replaced.
- IWL-2524 requires examination of anchorages of selected tendons. This requires removal of the end cap.
- IWL-2525 requires laboratory analysis of samples of the corrosion protection medium (grease) taken from each end of each examined tendon.
- IWL-2526 requires replacement of corrosion protection medium and measurement of difference in quantity between removal and replacement to identify potential voids in the duct.
NOC-AE-23003981 Enclosure Page 3 of 27 Use of IWL-2421(b) means that the requirements of IWL-2522 (tendon force measurement) and IWL-2523 (detension, wire removal and examination) are applied in alternating units at 5-year intervals (i.e. 10-year intervals between force measurements in a single unit) and all other surveillance requirements are performed in both units at each 5-year surveillance. In subsequent discussion, the unit in which all surveillance requirements are applied is described as full surveillance and the unit in which all except IWL-2522 and IWL-2523 are applied is described as partial surveillance.
4. Reason for Request
The currently required surveillance presents potential risk of injury to plant personnel and exposes the plant to potential physical damage without sufficient benefit in safety or quality to offset the costs and risks. Potential risks and hazards associated with surveillance are discussed further in Section 6.7. Past surveillance results in years 1, 3, 5, 10, 15, 20, 25, and 30 confirm that the STP post-tensioning system is in excellent condition in both units. The system is performing as designed and trending toward acceptable level of prestress force through 100 years, well beyond the Period of Extended Operation. Therefore, it is appropriate to implement an alternative surveillance schedule that reduces the number of tendon surveillances while maintaining an acceptable level of quality and safety, as allowed by 10 CFR 50.55a(z)(1).
- 5. Proposed Alternative Surveillance 5.1. The following is proposed as an alternative to IWL-2421(b), with the underlined portions marking the revised Code text:
(1) For Unit 1, all examinations required by IWL-2520 shall be performed at 1, 3, and 10 years, and every 10 years thereafter. In addition, the examinations required by IWL-2524 and IWL-2525 shall be performed at 5, 15, 25, and 40 years and every 10 years thereafter.
(2) For Unit 2, all examinations required by IWL-2520 shall be performed at 1, 5, 15, 25, and 40 years, and every 10 years thereafter. In addition, the examinations required by IWL-2524 and IWL-2525 shall be performed at 3 and 10 years and every 10 years thereafter.
The current surveillance schedule requires surveillance every 5 years, with the two units staggered such that full surveillance is performed in one unit and partial surveillance (exempting IWL-2522 and 2523) is performed in the other unit. The proposed alternative will have the effect of eliminating the IWL-2520 35th year surveillances in both units, and thereafter performing full surveillance in both units every 10 years, beginning at the 40th year.
The eliminated 35th year surveillances would be a partial surveillance in Unit 1 and a full surveillance in Unit 2. This relief request will only cover through year 40. Implementation of this plan in years 45 and beyond will require additional relief requests after the 40th year.
NOC-AE-23003981 Enclosure Page 4 of 27 In summary, if the NRC approves this proposed alternative for one interval, the future surveillance schedule for the duration of the 4th CISI interval will change from the current schedule to the alternative schedule shown below.
Current Schedule Alternative Schedule Year Unit 1 Unit 2 Unit 1 Unit 2 35 P F C C 40 F P F F F = Full surveillance, P = Partial Surveillance, C = Concrete only (visual)
- 6. Basis for Conclusion that Proposed Alternative has Acceptable Level of Quality and Safety 6.1 STP Design STP has 2 PWR units, each having a prestressed concrete containment. The 2 containments are essentially identical and located 600 feet apart. Each containment has the following design parameters:
- Inside radius = 75 feet
- Cylinder walls are 4 feet thick
- Hemispherical dome thickness is 3 feet
- Basemat thickness is 18 feet
- Inside surface (cylinder, dome and basemat) is lined with 3/8-inch carbon steel plate
- Inside height (top of basemat to top of dome) = 241 feet
- There are 3 buttresses, 120 degrees apart
- Each tendon is offset 120 degrees from the adjacent one below, such that every 3rd hoop tendon is anchored in the same buttress.
- Hoop tendons cover the full circumference, starting and ending in the same buttress
- There are 133 hoop tendons (108 in the cylinder wall and 25 in the dome)
- There are 96 Inverted-U tendons that are anchored in a tendon gallery underneath the basemat.
- Each tendon has 186 wires, each 1/4-inch diameter
- Steel wires are ASTM A421-77, type BA
- Wires have Guaranteed Ultimate Tensile Strength (GUTS) = 240 ksi
- Minimum installation prestress force was specified as 70% of GUTS, or 168 ksi The applicable design requirements include the following:
- Rated pressure capacity, P = 56.5 psig
- One-time Structural Integrity Test performed at 1.15 x P = 65 psig
- Minimum prestress force = 20% greater than required to offset internal pressure
- Design provides 1% additional steel wires to compensate for potential wire breakage
NOC-AE-23003981 Enclosure Page 5 of 27 6.2 Regulatory History Initially, Regulatory Guide (RG) 1.35 Proposed Revision 3, was applicable to STP. The surveillances conducted in years 1, 3, 5, and 10 implemented the requirements of RG 1.35.
Per the requirements of the Regulatory Guide, the surveillance schedule was based on years following the Structural Integrity Test. The Unit 1 Structural Integrity Test was completed in March 1987 and the Unit 2 Structural Integrity Test was completed in September 1988. In 1996, the NRC mandated a transition to ASME BPV Code, Section XI, Subsection IWL. (See 61 FR 41303, August 8, 1996.)
The transition mandate included a requirement to perform an expedited surveillance, which would be used thereafter (instead of Structural Integrity Test dates) to establish surveillance dates. STP performed the expedited surveillance coincident with the scheduled 10th year surveillances in 1998. The completion dates of the expedited surveillances, which thereafter define the due dates for subsequent surveillances, are July 29, 1998 in Unit 1 and September 30, 1998 in Unit 2.
Information Notice (IN) 99-10, Degradation of Prestressing Tendon Systems in Prestressed Concrete Containments discussed and highlighted several problems seen throughout the industry. Multiple plants observed liftoff forces that were significantly below predicted values.
Also, the variety of methods used by plants to calculate force trends did not meet NRC expectations. The IN clarified the NRCs position regarding the proper method to be used to calculate tendon force trends.
RG 1.35 was withdrawn in 2015 (80 FR 52067, August 27, 2015).
STP performed the 15th and 20th year surveillances using the 1992 edition of subsection IWL. During review of the License Renewal Application, STP committed to change to the 2004 edition. (See License Renewal Commitment 22, UFSAR Table 19A.4-1.) The Commitment was implemented, and the 2004 edition was used during the 25th and 30th year surveillances.
6.3 Prior STPNOC Relief Request STPNOC submitted a Relief Request in 2001, seeking an extension (doubling) of surveillance intervals specified in IWL-2421(b). The submittal (Reference 9.3) was revised and resubmitted in 2002 (Reference 9.4). The submittals made use of surveillance data through the 10th-year surveillances completed in 1998. STP made a presentation to the NRC in April 2003 to discuss the revised submittal (Reference 9.14).
During and following the presentation, the NRC provided the following feedback to STP.
- STP had only 10 years of surveillance data, but 10 years of data was not sufficient to establish a trend of excellent performance. The NRC pointed out that Calvert Cliffs (mentioned prominently in IN 99-10) discovered major problems during their 20th year surveillance after having acceptable surveillance results through 10 years.
- The NRC had recently seen a trend of poor performance throughout the industry, as summarized in IN 99-10.
Based on this feedback, STP withdrew the Relief Request (Reference 9.5).
NOC-AE-23003981 Enclosure Page 6 of 27 6.4 Significant Developments Since 2003 This Relief Request is substantially similar to the one STP submitted in 2001 and withdrew in 2003. Therefore, it is appropriate to review and consider new information that wasnt available in 2003:
- STP has surveillance data from surveillances conducted at years 15, 20, 25, and 30. The surveillance results confirm the ongoing excellent performance of the post-tensioning system in both units. These results should address the NRCs previous feedback that 10 years of data was insufficient.
- Industry performance has improved in this area and the NRC has approved similar relief requests at multiple other plants, e.g. Three Mile Island (2019), Vogtle (2019), Millstone (2020), Byron and Braidwood (2021), and Palo Verde (2022).
- STP submitted a license renewal application (LRA) in 2010 (Reference 9.6). During the extensive review, the NRC specifically reviewed the post-tensioning system, which is described in Section 4.5 of the LRA, Revision C. The LRA submittal was based on 20th year surveillance data. STP received seven Requests for Additional Information (RAI) focused specifically on the post-tensioning system. As documented in Sections 3.0.3.1.8, 3.0.3.2.23, and 4.5 of the Safety Evaluation Report (SER) that accompanied approval of the license extension, the NRC concurred with STPs conclusion that the prestress force trends were projected to be acceptable for the duration of the Period of Extended Operation. Additionally, STP has data that shows a favorable trend that goes beyond 60 years.
6.5 Surveillance Results (Years 1 - 30)
Anchorage Inspections Indications such as minor cracking and level 2 corrosion of shims that met the Code acceptance criteria have been documented (Reference 9.16 - 9.28). The only findings in either Unit that required further evaluation were occasional missing, malformed, or protruding buttonheads. The acceptance criteria for broken wires is stated in UFSAR 3.8.1.4.2.3. The design includes 1% surplus steel to account for breakage. The acceptance limit is 1%
breakage in any three adjacent tendons. Since there are 186 wires per tendon, this means a maximum of five broken wires in any three adjacent tendons.
A few ineffective wires have been identified during surveillances, but no evidence of any ongoing degradation mechanism has been identified other than degradation due to the performance of the surveillances. During each surveillance, two wires (one in a hoop tendon and one in an inverted-U tendon) are removed, visually examined, cut into pieces, and tested. Those wires are not replaced.
Unit 1 has 23 ineffective wires, 14 of which were identified during construction. Among the nine that have been identified as ineffective after construction, eight were deliberately destroyed during the surveillances. The 9th wire was damaged by unknown means during the 1st year surveillance. This wire was found intact at the start of the surveillance, but it was observed to be ineffective following detensioning, wire removal and retensioning.
NOC-AE-23003981 Enclosure Page 7 of 27 Unit 2 has 38 ineffective wires, 23 of which were identified during construction. Among the 15 that have been identified as ineffective after construction, eight were deliberately destroyed during surveillance and another four were inadvertently damaged during surveillances (years 15 and 25). There are only three unexplained wire failures that were found during surveillances, one each at years 10, 15, and 20.
In summary, 24 wires have become ineffective after the construction era. Most of them (21 of the total 24; 9 of 9 in Unit 1 and 12 of 15 in Unit 2) were damaged during surveillance, either deliberately or inadvertently. Therefore, performance of surveillance is the primary degradation mechanism that has been observed for wires.
Concrete Visual Examinations IWL 2310(a) requires a general concrete visual examination of concrete surfaces to identify areas of deterioration that require further examination or evaluation. IWL 2310(b) requires detailed visual examinations of any areas of deterioration identified in the general visual examination. At each surveillance in STP history, the general examination supported the conclusion that no detailed examinations were required. Therefore, the detailed examinations specified in IWL-2310(b) have never been performed at STP.
Corrosion Protection Medium (CPM)
The chemical requirements are stated in the design code of record (ACI-ASME 359), Section CC-2442.3.2. Paragraph (c) says, Each batch of coating material shall be analyzed for the presence of water-soluble chlorides, nitrates, and sulfides. The analysis shall conform to the limits shown in Table CC-2440-1. Those limits are 10 parts per million (ppm) for each of the three chemical types listed. The surveillance acceptance limits given in Table IWL-2525-1 are the same (10 ppm). Table IWL-2525-1 gives two additional limits that are not in the design code, namely water content less than 10% and reserve alkalinity (base number) at least 50%
of as-installed value. Those acceptance limits have been met during every surveillance in both Units.
Grease volume discrepancies were identified multiple times during the first 10 years, when the acceptance limit was 5% Net Duct Volume (NDV). See References 9.7 through 9.12.
Since switching to IWL at the 15th year and using an acceptance limit of 10% NDV, the limit has been met every time except once (see Reference 9.13). Each time the limit wasn't met, the condition was evaluated and accepted, as documented in References 9.7 - 9.13.
Liftoff Force Testing The License Renewal Application (LRA), Section 4.5, includes surveillance results through the 20th year. Liftoff testing was performed in Unit 1 during the 20th year surveillance. The most recent liftoff data used in Unit 2 was from the 15th year. Since then, the 25th year surveillance included liftoff testing in Unit 2 and the 30th year surveillance included liftoff testing in Unit 1. The methodology used to perform regression analysis is described in detail in Reference 9.29, pages 4-8, under the section heading Calculations Method.
The following pages show the trend line figures included in the LRA next to the corresponding updated figure using the most recent data. For each group of tendons, a comparison of the LRA figure to the updated figure shows very little change in trend.
For the inverted-U tendons, the trend line forecast value at year 60 declined by about 1%
compared to the trends shown in the LRA figures, while the 60-year forecast for hoop
NOC-AE-23003981 Enclosure Page 8 of 27 tendons increased by about the same amount. All trend lines shown used the same calculation method. On each page the bottom plot uses the most recent data (30th year surveillance in Unit 1, 25th year surveillance in Unit 2) and the top plot shows the trends computed during the prior liftoff testing (20th year data in Unit 1, 15th year data in Unit 2).
There are two noteworthy differences in the plots: 1) The older (top) ones are plotted on a semi-log scale and the newer (bottom) plots are plotted on linear scales; and 2) the older (top) plots for hoop tendons include both dome and cylinder tendons together, but the newer plots (bottom) are based on cylinder hoop tendons only. Overall, the figures show stable trends. In all cases, the trend line is substantially above the Minimum Required Value (MRV) for the entire Period of Extended Operation (through 60 years) and beyond.
NOC-AE-23003981 Enclosure Page 9 of 27 Liftoff Force Regression Analysis for Unit 1 Hoop Tendons Figure 6.5.1 is Fig. 4.5-2 in LRA, Revision C. It used data through year 20. Figure 6.5.2 is an updated version that includes 30th year surveillance data. The figures are not directly comparable because the top figure uses a semi-log plot. In Figure 6.5.1, the forecast value at year 60 is 1275 kips. In Figure 6.5.2, the forecast at year 60 has increased slightly to 1283 k, which remains above the minimum required value (1169 k). The trend is essentially stable.
Figure 6.5.1 Figure 6.5.2
NOC-AE-23003981 Enclosure Page 10 of 27 Liftoff Force Regression Analysis for Unit 2 Hoop Tendons Figure 6.5.3 is Fig. 4.5-4 in LRA, Revision C. It used data through year 15. Figure 6.5.4 is an updated version that includes 25th year surveillance data. The figures are not directly comparable because the top figure uses a semi-log plot. In Figure 6.5.3, the forecast value at year 60 is 1273 kips. In Figure 6.5.4, the forecast at year 60 has increased slightly to 1283 k (MRV = 1169 k). The trend is essentially stable.
Figure 6.5.3 Figure 6.5.4
NOC-AE-23003981 Enclosure Page 11 of 27 Liftoff Force Regression Analysis for Unit 1 Inverted-U Tendons Figure 6.5.5 is Fig. 4.5-2 in LRA, Revision C. It used data through year 20. Figure 6.5.6 is an updated version that includes 30th year surveillance data. The figures are not directly comparable because the top figure uses a semi-log plot. In Figure 6.5.5, the forecast value at year 60 is 1349 kips. In Figure 6.5.6, the forecast at year 60 has declined roughly 1% to 1334 k, but still far above the minimum required value (1150 k). The trend is essentially stable.
Figure 6.5.5 Figure 6.5.6
NOC-AE-23003981 Enclosure Page 12 of 27 Liftoff Force Regression Analysis for Unit 2 Inverted-U Tendons Figure 6.5.7 is Fig. 4.5-4 in LRA, Revision C. It used data through year 15. Figure 6.5.8 is an updated version that includes 25th year surveillance data. The figures are not directly comparable because the top figure uses a semi-log plot. In Figure 6.5.7, the forecast value at year 60 is 1366 kips. In Figure 6.5.8, the forecast at year 60 has declined very slightly to 1362 k, but it is still far above the minimum required value (1150 k). The trend is essentially stable.
Figure 6.5.7 Figure 6.5.8
NOC-AE-23003981 Enclosure Page 13 of 27 Liftoff Force History The following tables summarizes all liftoff testing at STP.
Unit 1 Vertical (Inverted U) Tendons Tendon Forces (Kips)
Nominal Tendon End Installed Predicted 95% of Measured Year Predicted 1 V126 Shop 1598 1376 1307 1402 Field 1621 1391 1321 1439 1 V144 Shop 1642 1401 1331 1400 Field 1567 1352 1284 1343 1 V227 Shop 1553 1345 1278 1336 Field 1556 1346 1279 1325 1 V245 Shop 1591 1366 1298 1363 Field 1565 1349 1282 1326 5 V126 Shop 1598 1350 1283 1385 Field 1621 1370 1302 1406 5 V214 Shop 1598 1358 1290 1380 Field 1631 1378 1309 1392 5 V242 Shop 1603 1363 1295 1381 Field 1608 1367 1299 1397 5 V248 Shop 1603 1354 1286 1359 Field 1608 1359 1291 1382 10 V126 Shop 1598 1348 1281 1340 Field 1621 1362 1294 1380 10 V129 Shop 1533 1286 1221 1290 Field 1609 1333 1267 1320 10 V230 Shop 1638 1379 1310 1380 Field 1596 1354 1287 1430 20 V126 Shop 1598 1338 1271 1363 Field 1621 1351 1283 1389 20 V111 Shop 1557 1295 1230 1334 Field 1577 1307 1242 1313 20 V133 Shop 1631 1341 1274 1356 Field 1579 1309 1244 1322 30 V126 Shop 1598 1332 1265 1347 Field 1621 1345 1278 1361 30 V137 Shop 1558 1291 1226 1286 Field 1567 1296 1231 1278 30 V222 Shop 1622 1354 1286 1342 Field 1582 1331 1264 1352
NOC-AE-23003981 Enclosure Page 14 of 27 Unit 2 Vertical (Inverted U) Tendons Tendon Forces (Kips)
Nominal Tendon End Installed Predicted 95% of Measured Year Predicted 1 V110 Shop 1605 1380 1311 1421 Field 1605 1380 1311 1377 1 V120 Shop 1580 1359 1291 1403 Field 1630 1402 1332 1400 1 V202 Shop 1630 1402 1332 1432 Field 1640 1410 1340 1422 1 V236 Shop 1605 1396 1326 1382 Field 1520 1338 1271 1370 5 V110 Shop 1605 1348 1281 1412 Field 1605 1348 1281 1362 5 V203 Shop 1610 1360 1292 1415 Field 1620 1361 1293 1407 5 V221 Shop 1580 1351 1283 1479 Field 1630 1394 1324 1452 5 V233 Shop 1580 1343 1276 1348 Field 1540 1309 1244 1338 15 V110 Shop 1605 1338 1271 1387 Field 1605 1338 1271 1354 15 V148 Shop 1640 1359 1291 1374 Field 1640 1359 1291 1375 15 V240 Shop 1605 1348 1280 1375 Field 1605 1348 1280 1380 25 V110 Shop 1605 1331 1264 1373 Field 1605 1331 1264 1361 25 V118 Shop 1590 1325 1259 1359 Field 1620 1343 1276 1368 25 V144 Shop 1585 1318 1252 1359 Field 1640 1350 1283 1402
NOC-AE-23003981 Enclosure Page 15 of 27 Unit 1 Hoop Tendons Tendon Forces (Kips)
Nominal Tendon End Installed Predicted 95% of Measured Year Predicted 1 1H091 Shop 1550 1326 1260 1380 Field 1612 1367 1299 1378 1 1H106 Shop 1579 1302 1237 1345 Field 1607 1321 1255 1354 1 1H130 Shop 1638 1368 1300 1383 Field 1582 1331 1264 1360 1 2H051 Shop 1539 1259 1196 1297 Field 1643 1329 1263 1321 1 2H054 Shop 1582 1335 1268 1376 Field 1589 1340 1273 1363 1 2H078 Shop 1643 1376 1307 1423 Field 1632 1369 1301 1373 1 2H111 Shop 1607 1338 1271 1386 Field 1577 1318 1252 1336 1 3H005 Shop 1579 1315 1249 1402 Field 1562 1304 1239 1356 1 3H032 Shop 1545 1285 1221 1345 Field 1632 1343 1276 1365 5 1H091 Shop 1550 1310 1245 1312 Field 1612 1386 1317 1329 5 1H112 Shop 1579 1318 1252 1281 Field 1542 1280 1216 1270 5 2H036 Shop 1637 1359 1291 1384 Field 1644 1364 1296 1381 5 2H048 Shop 1643 1364 1296 1380 Field 1620 1345 1278 1338 5 2H093 Shop 1607 1294 1229 1276 Field 1589 1302 1237 1270 5 2H129 Shop 1558 1293 1228 1345 Field 1553 1289 1225 1213 10 1H091 Shop 1550 1303 1238 1310 Field 1612 1341 1274 1280 10 1H043 Shop 1634 1356 1288 1330 Field 1553 1306 1241 1320 10 1H049 Shop 1610 1325 1259 1270 Field 1567 1298 1233 1330 10 1H127 Shop 1610 1356 1288 1340 Field 1542 1314 1248 1310 10 1H130 Shop 1638 1345 1277 1330 Field 1582 1310 1245 1290 10 2H129 Shop 1558 1287 1223 1320 Field 1553 1284 1220 1265 20 1H091 Shop 1550 1293 1228 1301 Field 1612 1330 1263 1300 20 1H031 Shop 1634 1345 1277 1356 Field 1642 1349 1282 1381 20 2H063 Shop 1631 1290 1225 1299 Field 1624 1286 1221 1280 30 1H091 Shop 1550 1287 1223 1269 Field 1612 1323 1257 1277 30 2H114 Shop 1643 1354 1286 1346 Field 1560 1306 1241 1293 30 3H023 Shop 1579 1287 1223 1350 Field 1550 1270 1207 1262
NOC-AE-23003981 Enclosure Page 16 of 27 Unit 2 Hoop Tendons Tendon Forces (Kips)
Nominal Tendon End Installed Predicted 95% of Measured Year Predicted 1 2H075 Shop 1600 1344 1277 1394 Field 1600 1344 1277 1398 1 1H094 Shop 1535 1289 1225 1283 Field 1620 1345 1278 1335 1 1H112 Shop 1535 1305 1240 1274 Field 1580 1343 1276 1303 1 1H124 Shop 1580 1343 1276 1312 Field 1580 1343 1276 1337 1 2H033 Shop 1520 1292 1227 1216 Field 1550 1302 1237 1354 1 2H105 Shop 1540 1309 1244 1418 Field 1580 1327 1261 1400 1 3H005 Shop 1580 1296 1231 1355 Field 1550 1271 1207 1375 1 3H029 Shop 1585 1300 1235 1392 Field 1550 1271 1207 1319 1 3H056 Shop 1570 1319 1253 1361 Field 1580 1311 1245 1346 5 2H075 Shop 1600 1320 1254 1324 Field 1600 1320 1254 1338 5 1H055 Shop 1550 1310 1244 1325 Field 1540 1301 1236 1298 5 1H106 Shop 1580 1304 1239 1308 Field 1570 1295 1230 1251 5 2H018 Shop 1540 1301 1236 1421 Field 1620 1353 1285 1352 5 2H045 Shop 1540 1278 1214 1356 Field 1570 1295 1230 1300 5 3H050 Shop 1610 1312 1246 1336 Field 1630 1337 1270 1323 10 2H030 Shop 1550 1299 1234 1280 Field 1570 1312 1246 1320 10 2H033 Shop 1520 1258 1195 1196 Field 1550 1277 1213 1280 10 2H036 Shop 1600 1330 1263 1290 Field 1570 1311 1245 1310 15 2H075 Shop 1600 1305 1240 1312 Field 1600 1305 1240 1343 15 3H008 Shop 1610 1303 1238 1304 Field 1630 1315 1250 1330 15 2H078 Shop 1620 1332 1265 1295 Field 1600 1320 1254 1308 25 2H075 Shop 1600 1298 1233 1283 Field 1600 1298 1233 1297 25 1H121 Shop 1540 1292 1227 1313 Field 1570 1310 1245 1297 25 2H126 Shop 1580 1317 1251 1319 Field 1540 1293 1228 1285
NOC-AE-23003981 Enclosure Page 17 of 27 All but two liftoff tests met the acceptance criteria (measured force at least 95% of predicted force). Those two were hoop tendons 2H033 (1st year, Unit 2) and 2H129 (5th year, Unit 1).
They were reported and explained to the NRC in Reference 9.30, and then discussed again in Reference 9.31 (RAI B3.3-2, item 3).
Wire Test Results At each "full surveillance", two tendons are detensioned (one hoop tendon and one vertical, "inverted U" tendon). One wire is removed from each (2 wires total each surveillance),
examined full length, and then cut into pieces for laboratory testing. Ultimate strength and strain (percent elongation) are recorded.
The acceptance criteria is stated in IWL-3221.2(b) as "not less than minimum specified values". The specified values are in the design specification, not the Code. For STP, wires are ASTM A421, type BA. The acceptance limits are 240 ksi minimum tensile strength and 4% minimum elongation. The following table summarizes results from surveillances performed under IWL (plant years 15, 20, 25 and 30).
Summary of Wire Test Results Year Unit 1 Unit 2 Source Min. Min. Min. Min.
Strength Elongation Strength Elongation 249 ksi 5.6%* Ref. 9.16, Table 6 1
243.4 ksi 4.3% Ref. 9.17, Table 6 251.5 ksi 7.8% Ref. 9.20, Table 6 5
246.4 ksi 8.1% Ref. 9.21, Table 6 10 243.3 ksi 5.5% Ref. 9.22, Table 6 15 260.0 ksi 4.5% Ref. 9.24, Table IX 20 269.3 ksi 4.6% Ref. 9.25, Table 8-1 25 250.1 ksi 5.9% Ref. 9.27, Table 8-1 30 248.1 ksi 5.6% Ref. 9.28, section 8.5
- As described in Step 5.5.2 of Reference 9.16, two anomalous results (3.1% and 3.9% elongation at failure) were invalidated and the tests were repeated using backup specimens. Reported result (5.6% minimum elongation) was obtained from the backup specimens.
All strength measurements exceeded the specified minimum (240 ksi). Except as noted above, all elongation measurements exceeded the specified minimum (4%). There is no detectable declining trend for either strength or elongation.
Summary of Results The following tables summarize all anomalous results identified in summary sections of surveillance reports. Many of these met acceptance limits and did not require further evaluation or inspection.
NOC-AE-23003981 Enclosure Page 18 of 27 Summary of Unit 1 Surveillance Findings Year Findings Evaluation/Resolution 1
- Vertical tendon V245 had 2
- This condition was identified prior to tablespoons of free water.[Ref. the surveillance. Corrective actions 9.16, section 5.3.2] included three separate examinations of this tendon. The examination during the surveillance continued and confirmed a declining trend with less water found during each observation. The conclusion was that the water was trapped during construction and NOT an
- Level 2 corrosion observed on ongoing leak.
shims associated with tendon 1H091. [Ref. 9.16, section
- Level 2 means discoloration with no 5.2.2] pitting. Observed on shim stack only.
No further evaluation or corrective action.
- One wire not seated when tendon 2H078 was retensioned.
- Acceptable because it met 1%
[Ref. 9.16, section 5.5.3] breakage allowance.
3
- All 10 surveillance tendons had
- This condition was reported to the grease voids > 5% NDV.[Ref. NRC and evaluated as acceptable.
9.7.]
- Damaged gasket observed on
- Since only minimal leakage was grease can associated with observed, the only corrective action tendon V248.[Ref. 9.18, was to re-examine this tendon at the Section 5.5.3] next scheduled surveillance (5th year).
5
- Damaged threads observed on
- All judged to be damaged during seven tendons in buttress 3, installation, not degradation. Tendons including two selected for were evaluated as unfit for liftoff random liftoff testing. [Ref. testing, but fully functional. Substitute 9.20, section 5.2.2] tendons were selected for liftoff testing.
- Six tendons have grease voids
- This condition was reported to the
> 5% NDV. [Ref. 9.20, section NRC and evaluated as acceptable.
4.7] See Ref. 9.8.
- Evaluated as effective and most
- One tendon was observed to likely damaged during initial have a deformed anchor head installation.
(tendon 2H129).[Ref. 9.20, section 5.2.2]
- No evidence of corrosion. Linear
- Surface damage (0.006 max) indications aligned with wire axis seen at three locations on the judged to be fabrication (drawing) wire removed from tendon damage.
2V242.[Ref. 9.20, Section 6.1]
NOC-AE-23003981 Enclosure Page 19 of 27 Summary of Unit 1 Surveillance Findings (contd)
Year Findings Evaluation/Resolution 5
- Tendon 2H129field end liftoff
- This condition was not identified until force was 94.1% of predicted, the 10th year surveillance. This which was below acceptance tendon and 2 adjacent tendons were limit of 95% of predicted. [LER all tested during 10th year 98-001, Ref. 9.30] surveillance and all met the acceptance limit. The evaluation and corrective actions were described to the NRC in LER 98-001.
10
- Four horiz. tendons had grease
- This condition was reported to the voids > 5% NDV. [Ref. 9.22, NRC and evaluated as acceptable.
Section 4.7] See Reference 9.9.
- Wire not broken. Tendon considered
- Following retensioning of effective because it was successfully tendon 1H049, one wire retensioned.
observed protruding about 1/8" (not reseated). [Ref. 9.22, Section 5.6.2]
- Repaired by chasing thread.
- Damaged thread observed on tendon V230 anchor head.
[Ref. 9.22, Section 7.2]
15 No issues identified in U1 (level 2
- Level 2 is discoloration without anchorage corrosion documented, pitting.
but met acceptance limit) [Ref.
9.24]
20 No new issues identified. [Ref.
9.25]
25 No new issues identified. [Ref.
9.27]
30 No new issues identified [Ref. 9.28]
NOC-AE-23003981 Enclosure Page 20 of 27 Summary of Unit 2 Surveillance Findings Year Findings Evaluation/Resolution 1
- Tendon 2H033 shop end liftoff
- This condition was not identified until force was 94.1% of predicted, the 10th year surveillance. This which was below acceptance tendon and 2 adjacent tendons were limit of 95% of predicted.[LER all tested during 10th year 98-001, Ref. 9.30] surveillance and all met the acceptance limit. The evaluation and corrective actions were described to the NRC in LER 98-001.
- The detensioned/retensioned vertical tendon V202 had
- This nonconformance was evaluated elongation 8.6% greater than and determined to be acceptable original installation. Acceptance following additional inspection of both limit was 5% at the time.[Ref. ends following retensioning.(Note 9.17, section 5.6.2] that current acceptance limit is 10%
in 2013 IWL-3221.1(d). This would not be an NCR today.)
- All 13 surveillance tendons had replacement grease volume
- This condition was not reported to exceed 5% volume limit (5.6% the NRC because the plant was in to 15.6% with an average of Mode 5 at time of discovery. The 11.6%).[Ref 9.17, section 4.7] condition was evaluated as acceptable for the same reasons as similar conditions reported to the NRC in References 9.7 - 9.13.
3
- No open cracks. One closed
- Evaluated as acceptable because it crack 0.02 to 0.05 width at was at surface only with no surface in buttress at tendon penetration into concrete.
3H110.[Ref. 9.19, section 4.2]
- Three improperly formed
- Judged acceptable; buttonhead area buttonheads identified. [Ref. was as large as properly formed 9.19, section 4.6.] buttonhead.
- Eight of 10 tendons had grease
- This condition was reported to the voids > 5% NDV. Ref. 9.19, NRC and evaluated as acceptable.
App. G] See Ref. 9.10.
5
- Eight of 10 tendons had grease
- This condition was reported to the voids > 5% NDV. [Ref. 9.21, NRC and evaluated as acceptable.
section 4.8.5] See Ref. 9.11.
NOC-AE-23003981 Enclosure Page 21 of 27 Summary of Unit 2 Surveillance Findings (contd)
Year Findings Evaluation/Resolution 5
- Level 2 corrosion (discoloration
- Level 2 is acceptable (no loss of without pitting) observed on material).
shim plates for two tendons and on bearing plate for one tendon
[Ref. 9.21, section 4.3.5]
- Level 2 corrosion seen on one
- Level 2 is acceptable (no loss of small area of wire removed material; discoloration without from detensioned vertical pitting).
tendon. [Ref. 9.21, section 4.6.2]
- Darkened areas of concrete
- Observation was potentially observed on containment walls consistent with grease seepage, but visible from inside buildings. no clear evidence of actual leakage.
[Ref. 9.21, section 4.9.3] Therefore, condition was judged acceptable. It was documented for comparison at next surveillance.
- 30 of 192 cans for vertical
- Judged acceptable; documented for tendons showed very slight follow-up inspection at next seepage (drops forming but not surveillance.
yet dripping).
10
- Two horizontal tendons had
- This condition was reported to the grease voids > 5% NDV . [Ref. NRC and evaluated as acceptable.
9.23, Section 4.7] See Reference 9.12.
- One missing wire on tendon
- Installation report noted one 1H085. . [Ref. 9.23, Section deformed buttonhead; assumed 4.6] deformed buttonhead failed. Meets acceptance criteria, which is 1%
breakage (five wires in any three adjacent tendons).
15
- Two vertical tendons had
- This condition was reported to the grease voids > 10% NDV [Ref. NRC and evaluated as acceptable.
9.24, page 5, item 10] See Reference 9.13.
- One missing buttonhead on
- No missing wires in adjacent tendon 1H070 and One tendons. Therefore missing protruding wire (after buttonhead meets acceptance retensioning) on 3H008. [Ref. criteria, which is 1% breakage, i.e.
9.24, page 4, item 4] five wires in any three adjacent tendons).
NOC-AE-23003981 Enclosure Page 22 of 27 Summary of Unit 2 Surveillance Findings (contd)
Year Findings Evaluation/Resolution 20
- Buttonhead missing on tendon
- Including this wire, there are three 2H021. [Ref. 9.25, Section nonconforming wires in three 4.4.2] adjacent tendons. This is within acceptance limit for wire breakage (
1%, i.e. five wires in any three adjacent tendons).
22 * (Concrete visual only;
- All indications were identified as inadvertently omitted* from 20th "information only" and were noted in year inspection) No findings. previous inspections (unchanged).
[Ref. 9.26, section 2.2]
25
- Following retensioning of
- Wires apparently damaged during tendon 2H126, 3 wires surveillance and not indicative of observed protruding (not degradation. (App. H of Ref. 9.27 reseated). [Ref. 9.27, Section says the three were part of an 6.2.4] "attempt to perform" wire removal.)
These three plus one removed for testing make four ineffective wires in this tendon. All wires were found effective in adjacent tendons.
Therefore, this meets the acceptance criteria of five broken wires within three adjacent tendons.
30 No issues identified [Ref. 9.28]
- The concrete exterior surveillance was omitted twice; Unit 1 during the 15th year surveillance and Unit 2 during the 20th year surveillance. Those omissions occurred due to misinterpretation of IWL surveillance interval requirements for multi-unit plants. STP became aware of the problem when Information Notice 2010-14 called attention to it. Corrective action included a concrete exterior inspection of Unit 2 during the 22nd year. There was no similar corrective action inspection in Unit 1 because Unit 1 had been inspected at the 20th year, shortly before the problem was discovered.
6.6 Applicability of IWL-2521(a)
RG 1.35, used during the first 10 years of surveillances, established a schedule for multi-unit plants that allowed liftoff force measurements in alternating units if the Structural Integrity Tests were separated by no more than 2 years. STP complied with that since the SIT tests are separated by 18 months (March 1987 in Unit 1 and September 1988 in Unit 2).
When the NRC mandated a transition to IWL, STP noted that IWL-2521(a) was slightly different from RG 1.35 in its definition of the 2-year limit. Whereas RG 1.35 said the Structural Integrity Tests must be separated by no more than 2 years, IWL-2521(a) applies the 2-year limit to completion of post-tensioning operations. The term is not defined within IWL. At STP, physical work (tensioning of last tendon) was completed 26 months apart (January 1986 in Unit 1 and March 1988 in Unit 2), which exceeds the 2-year limit. However, the Installation Final Reports were signed 23 months apart (July 1986 in Unit 1 and June 1988 in Unit 2), which is within the 2-year limit. In the nuclear industry, it is customary to regard work as incomplete until it is signed. Therefore, STP concluded in 2003 that STPs two units met the intent of IWL-2421(a). STP has followed that schedule in subsequent
NOC-AE-23003981 Enclosure Page 23 of 27 surveillances (15th, 20th, 25th, and 30th years). The first paragraph of the License Renewal SER, page 3-35 documents NRC scrutiny of the multi-unit surveillance schedule and the transition from RG 1.35 to IWL. The NRC did not express disagreement with STPs use of IWL-2521(a).
6.7 Risks Associated with Surveillances Performance of these surveillances, particularly liftoff testing, requires use of a crane to lift a work platform to access the tendon ends. Given the locations of the containment buttresses, this cannot be accomplished without lifting Heavy Loads, as defined by Generic Letter 81-07 and NUREG 0612, over buildings housing safety-related equipment. The specific buildings effected are the Fuel Handling Building, the Electrical Auxiliary Building, and the Mechanical Auxiliary Building. Potential load drops and crane collapses onto the roofs of these buildings have been evaluated and shown to be acceptable in the sense that the safety-related functions would be maintained. Nevertheless, surveillance of the post-tensioning system introduces some risk of damage to safety-related buildings from load drops. To comply with the guidance in Generic Letter 81-07 and NUREG 0612, lifts of heavy loads over safety-related structures should be minimized.
In addition, surveillance of the post-tensioning system introduces some risk of injury to personnel performing the surveillance and to personnel working below them. The personnel risks include:
- High locations (risk is to personnel performing work and also personnel under them).
- Each tendon is tensioned to roughly 1.5 million pounds, which represents a dangerous amount of stored elastic energy. Liftoff testing and detensioning introduces slight risk of sudden release of energy due to tendon failure or equipment mishandling or malfunction.
- Liftoff testing is performed using a hydraulic ram with hydraulic fluid contained in hoses under high pressure.
- The Corrosion Protection Medium (grease) is heated to facilitate placement in tendon ducts. Mishandling could result in burns.
6.8 Acceptability of Proposed Alternative Surveillance Schedule As shown in section 6.5, the performance has been excellent, with tendon force trends remaining above the Minimum Required Value (MRV) for the 40-year life for which the plant was designed, but also through the entire Period of Extended Operation and also beyond that through the 100th year of plant life. In addition, the MRV was established very conservatively, meaning that the trend lines shown in section 6.5 understate the actual available margin.
The conservatism of the design includes the following elements:
- The maximum calculated accident pressure is 41.2 psig, but the containment was designed for 56.5 psig rated pressure. This represents a margin of 37%.
- The post-tensioning system was designed to provide a minimum of 20% larger prestress force than required to offset internal pressure. This represents an additional
NOC-AE-23003981 Enclosure Page 24 of 27 20% margin. The internal pressure that would balance the prestress force would be 56.5 x 1.2 = 67.8 psig, which exceeds the maximum accident pressure by 64.6%.
- The design took no credit for concrete strength in tension, assuming it to be zero.
While concrete is weak in tension, its strength is greater than zero.
- The post-tensioning system was designed to provide the strength necessary to resist internal pressure without any credit taken for the liner plate or the reinforcing bars.
The liner plate by itself could resist approximately 15 psi, as shown below.
Hoop stress = PR/T = (15 psi)(75 ft x 12 in/ft)/(0.375 in) = 36,000 psi = 36 ksi (yield stress)
- The ultimate pressure capacity of the containment was estimated to be 141 psig.
The large design margin means that minor degradation would not threaten the containment's ability to perform its design function. The containment surveillance is intended to identify degradation early before it becomes major degradation. If a containment had very small design margin, it would be important to perform the surveillance relatively frequently to ensure degradation is identified before margin is lost. Given the large design margin, it is unlikely all margin will be eroded prior to the next surveillance interval.
The most recent surveillance of the post-tensioning system was performed at STP in 2018, which was the 30th year surveillance. The Proposed Alternative Surveillance, if approved, would skip the 35th year surveillance elements associated with IWL-2520 and perform full surveillances in both units during the 40th. The surveillance elements are considered individually below.
Tendon Forces As stated in IWL-2421(b), liftoff testing occurs at 10-year intervals in each individual unit, with the two units staggered on 5-year alternating schedules. The 30th year surveillance included liftoff testing in Unit 1, but not in Unit 2. Liftoff testing is scheduled to occur again in Unit 1 in year 40. Therefore, the proposed alternative would make no change to the Unit 1 surveillance schedule for liftoff testing. Liftoff testing is scheduled to occur in Unit 2 in years 35, 45 and 55. The proposed alternative would change that to years 40 and 50*, aligned with Unit 1 liftoff testing. That would introduce a one-time surveillance interval of 15 years between liftoff tests in Unit 2 (between years 25 and 40), with 10-year intervals thereafter*.
The one-time 15-year interval is acceptable because the trend lines established by regression of liftoff data through the 25th year remain significantly above the Minimum Required Value between years 25 and 40 and beyond. Liftoff testing performed in Unit 1 at year 30 showed no appreciable change in trend in that unit between the 20th year and 30th year data (see Section 6.5). Since the units are essentially identical and subject to the same conditions, it is reasonable to assume Unit 2 likewise did not degrade significantly between the 25th year and 30th year.
Therefore, the proposed alternative surveillance schedule provides an acceptable level of quality and safety with respect to liftoff forces.
NOC-AE-23003981 Enclosure Page 25 of 27 Concrete Exterior Examination The examinations required by IWL-2410 and IWL-2510 will continue unchanged, at 5-year intervals.
Wires Wire damage or breakage since construction has been very low. Nearly all wires determined to be ineffective after construction were damaged either deliberately or inadvertently during surveillances. No degradation mechanism other than the surveillance itself has been observed during the life of the plant. Total wire breakage is less than one-tenth the 1%
allowance (426 wires per unit) included in the design. The proposed alternative surveillance, which reduces the number of surveillances, will have the beneficial effect of reducing the opportunities to damage wires. Therefore, the proposed alternative surveillance provides an acceptable level of quality and safety, with respect to tendon wires.
Corrosion Protection Medium The purpose of the corrosion protection medium is to protect the tendons. Tendon liftoff force testing and wire removal and examination confirm that the tendons are behaving as designed. Chemistry samples of the corrosion protection medium have met acceptance limits during all surveillances. Volume discrepancies of the medium have been evaluated as being non-consequential and have not occurred during the three most recent surveillances. The proposed alternative surveillance skips the 35th-year surveillance and examines both Units in the 40th year. This proposed alternative schedule provides an acceptable level of quality and safety, with respect to the corrosion protection medium.
Anchorage Components The proposed alternative surveillance extends the interval for visual anchorage inspections from 5 years to 10 years*, but the 5-year interval for general visual exterior inspection IWL-2511 will remain unchanged at 5 years. Those 5-year inspections will include the anchorage area outside the end caps; the entire concrete surface area defined by IWL 2524.1 is visible with the end caps in place. Other than ineffective wires, anchorage inspections throughout the life of the plant have not identified any noteworthy issues. Therefore, the proposed alternative surveillance provides an acceptable level of quality and safety.
- Assuming acceptance of future relief requests for each 10-year interval; otherwise, surveillances will be continued as required.
7. Duration of Proposed Alternative
STPNOC requests approval to use the proposed alternative surveillance schedule during the fourth 10-year Containment Inservice Inspection Interval. The fourth interval ends September 8, 2029.
8. Precedents
8.1 Vogtle Electric Generating Plant, Units 1 and 2 - Inservice Inspection Alternative VEGP-ISI-ALT-19-01 for Containment Tendon Inservice Inspection Extension (EPID L-2019-LLR-0017);
July 11, 2019; ML19182A077.
NOC-AE-23003981 Enclosure Page 26 of 27 8.2 Three Mile Island Nuclear Station, Unit 1 - Relief from The Requirements Of The ASME Code Re: Examination And Testing For Containment Unbonded Post-Tensioning System (EPID-L-2018-LLR-0132); September 19, 2019; ML19226A023.
8.3 Millstone Power Station, Unit 2 - Proposed Alternative RR-05-05 to the Requirements of the ASME Code Re: Containment Unbonded Post-Tensioning System Inservice Inspection Requirements (EPID L-2019-LLR-0120); October 20, 2020; ML20287A471.
8.4 Braidwood Station, Units 1 And 2, And Byron Station, Units 1 and 2 - Proposed Alternatives to The Requirements of The American Society of Mechanical Engineers Boiler & Pressure Vessel Code (EPIDS L-2020-LLR-0099 and L-2020-LLR-0100); August 3, 2021; ML21134A006.
8.5 Palo Verde Nuclear Generating Station, Units 1, 2, And 3 - Relief Request 67 For an Alternate Frequency to Containment Unbonded Post-Tensioning System Inservice Inspection (EPID L-2021-LLR-0050); May 12, 2022; ML22124A241.
Code, Section XI, Subsection IWL, 2013 edition.
9.2 Inservice Inspection Program Plan and Inservice Testing Program Snubber Inservice Test Plan for the Fourth Ten-Year Interval; May 20, 2021; ML21144A109; NOC-AE-21003806.
9.3 Request for Approval of an Alternative Approach for Containment Tendon Surveillances (RR-ENG-37); September 26, 2001; ML012750097; NOC-AE-00000981.
9.4 Revised Request for Approval of an Alternative Approach for Containment Concrete and Tendon Surveillances (RR-ENG-37); August 20, 2002; ML022380251; NOC-AE-02001364.
9.5 Withdrawal of Relief Request, "Request for Approval of an Alternative Approach for Containment Tendon Surveillances (RR-ENG-37)"; August 26, 2003; ML032450235; NOC-AE-03001544.
9.6 License Renewal Application; October 25, 2010; ML103010257; NOC-AE-10002607 9.7 Special Report Regarding an Evaluation of The Unit 1 Third Year Containment Tendon Surveillance; May 5, 1990; ML20042F117; ST-HL-AE-003451.
9.8 Special Report Regarding an Evaluation of The Unit 1 Fifth Year Containment Tendon Surveillance; April 22, 1992; ML20095G411; ST-HL-AE-004064.
9.9 Special Report Regarding a Evaluation of the Unit 1 Tenth Year Containment Tendon Surveillance; August 12, 1998; ML20237B536; NOC-AE-00000250.
9.10 Special Report Regarding an Evaluation of The Unit 2 Third Year Containment Tendon Surveillance; March 30, 1992; ML20091C260; ST-HL-AE-004037.
9.11 Special Report Regarding an Evaluation of The Unit 2 Fifth Year Containment Tendon Surveillance; September 29, 1993; ML20057D861; ST-HL-AE-004587.
9.12 Special Report Regarding an Evaluation of Unit 1 and Unit 2 Containment Tendon Conditions; September 24, 1998; ML20153G254; NOC-AE-00000304.
9.13 Summary Report Regarding Results of the Unit 2, Year 15 Containment Tendon Surveillance; June 16, 2004; ML041730259; NOC-AE-04001735.
NOC-AE-23003981 Enclosure Page 27 of 27 9.14 04/15/2003 Summary of Meeting between NRC and South Texas Project Nuclear Operating Company RE: Risk-Based Proposal for Alternative Selection Criteria for Containment Tendon Testing.; April 25, 2023; ML031150748 9.15 CC-5206_Rev5_Tendon Design; Post Tensioning System Analysis; July 7, 1988; STI:
169 9.16 Final Report - First Year Inservice Tendon Surveillance, VSL Corp.; June 1988 (Unit 1);
STI: 532651.
9.17 Unit 2 Post-Tensioning System First Year Tendon Surveillance Final Report, VSL Corp.;
Jan. 1990; STI: 540148.
9.18 Unit 1 Post-Tensioning System 3rd Year Inservice Tendon Surveillance Final Report, VSL Corp.; April 1990; STI: 540149.
9.19 Third Year Inservice Tendon Surveillance Test Report Unit 2, VSL Corp.; May 1992; STI:
545624.
9.20 Fifth Year Tendon Surveillance Unit 1, VSL Corp.; Nov. 1992; STI: 545622.
9.21 Fifth Year Inservice Tendon Surveillance Test Report Unit 2, VSL Corp.; Nov. 1993; STI:
30129616.
9.22 10th Year Inservice Tendon Surveillance for Unit 1 Containment Post Tensioning System; November 5, 1998; STI: 30761614.
9.23 10th Year Inservice Tendon Surveillance for Unit 2 Containment Post Tensioning System; November 5, 1998; STI: 30722915.
9.24 Final Report for the 15th Year Post-Tensioning Surveillance; June 10, 2004; STI:
31757332.
9.25 Final Report for the 20th Year Post-Tensioning Surveillance; April 27, 2009; STI:
32463769.
9.26 Unit 2 Containment External Concrete Inspection (22nd Year); January 5, 2011; STI:
32823805.
9.27 Final Report for the 25th Year Tendon Surveillance at STP Nuclear Generating Station; July 29, 2014; STI: 33920413.
9.28 Final Report for the Containment Structure Tendon Surveillance - 30th Year; April 19, 2018; STI: 34665565.
9.29 Unit 1 30th Year Regression Analysis; April 19, 2018; STI: 34665567 9.30 LER 98-001 - Failure to Perform An adequate Technical Specification Surveillance Regarding Containment Structural Integrity; February 23, 1998; ML20203K135; NOC-AE-00000083.
9.31 Response to Requests for Additional Information for the South Texas Project License Renewal Application (TAC Nos. ME4936 and ME4937); October 10, 2011; ML11291A152; NOC-AE-11002732.