ML24040A196
| ML24040A196 | |
| Person / Time | |
|---|---|
| Site: | South Texas  (NPF-076, NPF-080) |
| Issue date: | 02/13/2024 |
| From: | Jennivine Rankin NRC/NRR/DORL/LPL4 |
| To: | Gerry Powell South Texas |
| Galvin D, NRR/DORL/LPL4 | |
| References | |
| EPID L-2023-LLR-0004 | |
| Download: ML24040A196 (1) | |
Text
February 13, 2024 SOUTH TEXAS PROJECT, UNITS 1 AND 2 - AUTHORIZATION AND SAFETY EVALUATION FOR ALTERNATIVE REQUEST NO. RR-ENG-4-06 (EPID L-2023-LLR-0004)
LICENSEE INFORMATION Recipients Name and Address:
Mr. G. T. Powell President and Chief Executive Officer STP Nuclear Operating Company P.O. Box 289 Wadsworth, TX 77483 Licensee:
STP Nuclear Operating Company Plant Name and Units:
South Texas Project (STP), Units 1 and 2 Docket Nos.:
50-498 and 50-499 APPLICATION INFORMATION Submittal Date: February 1, 2023 Submittal Agencywide Documents Access and Management System (ADAMS) Accession No.: ML23032A484.
Supplement Dates: March 9, 2023; August 17, 2023; and December 14, 2023.
Supplement ADAMS Accession Nos.: ML23068A364, ML23229A499, and ML23348A375.
Applicable Inservice Inspection (ISI) and Interval Start/End Dates: STP, Units 1 and 2, fourth 10-year containment ISI (CISI) interval; September 9, 2019, to September 8, 2029.
Alternative Provision: The licensee requested an alternative under Title 10 of the Code of Federal Regulations (10 CFR), 50.55a(z)(1), Acceptable level of quality and safety.
ISI Requirement: American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code),Section XI, Rules for Inservice Inspection of Nuclear Power Plant Components, subsection IWL, table IWL-2500-1, Examination Category L-B, Unbonded Post-Tensioning System, Item Nos. L2.10, L2.20, L2.30, L2.40 and L2.50.
Applicable Code Edition and Addenda: ASME Code,Section XI, 2013 Edition.
Brief Description of the Proposed Alternative: The licensees proposed alternative, corresponding to the above code requirements, is to perform the concrete containment unbonded post-tensioning system examinations per table IWL-2500-1 (L-B), Examination Category L-B (Item Nos. L2.10, L2.20, L2.30, L2.40 and L2.50) according to the schedule specified by subparagraph IWL-2421(b) except at the 35th year. The proposed alternative eliminates the subsubarticle IWL-2520, Examination of Unbonded Post-Tensioning Systems, examinations for the 35th year currently scheduled during the fourth 10-year CISI interval.
STAFF EVALUATION The licensees February 1, 2023, proposed alternative was subsequently replaced by the March 9, 2023, August 17, 2023; and December 14, 2023, supplements, respectively. The March 9, 2023, supplement addressed a U.S. Nuclear Regulatory Commission (NRC) supplemental information request dated March 6, 2023 (ML23061A175). The August 17, 2023, supplement addressed concerns arising from the NRC regulatory audit, as documented in the audit summary dated February 7, 2024 (ML24033A300). The December 14, 2023, supplement was in response to a request for additional information (RAI) issued on November 29, 2023 (ML23334A006). The RAI requested the licensee to clarify whether the proposed alternative extends beyond the proposed alternative for the 35th year examinations. Therefore, the NRC staffs evaluation is based on the revised proposed alternative provided in the supplement dated December 14, 2023.
The NRC staff reviewed the information provided in the proposed alternative request, as supplemented, and noted that the licensee will continue to conduct the general visual examinations and detailed visual examination of suspect areas, on a 5-year frequency as required in table IWL-2500-1 (L-A) Examination Category L-A, Concrete. The NRC staff noted the licensees conclusion that no detailed visual examinations were required based on the results of previous general visual examinations at each surveillance in STP history. Any indications identified during these examinations may lead to additional examinations in accordance with table IWL-2500-1 (L-B), as determined by the responsible engineer. As required by paragraph IWL-2511, Accessible Areas, this would include examination of the concrete surfaces and tendon end anchorage areas on a 5-year frequency to identify evidence of damage, degradation, deformation of the end cap, water intrusion, corrosion, concrete cracking, or corrosion protection medium (CPM) leakage. Tendon end caps are required to be removed for this examination if there is evidence of tendon end cap deformation or damage.
The NRC staff also reviewed the plant-specific information, and summary results of examinations conducted for each of the requirements of ASME Code,Section XI, subsection IWL, table IWL-2500-1 (L-B), Item Nos. L2.10, L2.20, L2.30, L2.40, and L2.50. This information is specifically described in section 6.5 of the enclosure of the proposed alternative. Section 6.5 also includes tables summarizing (1) the lift-off testing of vertical (inverted-U) tendons and hoop tendons, (2) wire test results, and (3) surveillance findings and evaluation and resolution. The regulatory audit of non-docketed surveillance reports confirmed the information in section 6.5.
A summary of the NRC staffs evaluation of each item number is provided below.
Item No. L2.10, Tendon Force Trends and Forecasts Section 6.5, subsection Liftoff Force Testing of the enclosure of the proposed alternative states that the measured tendon forces and trend forecasts trend line of the prestressing forces in the containment will remain substantially above the specified minimum required value (MRV) limits for the entire period of extended operation (through 60 years) and beyond. In section 6.5, the licensee also provided a summary of past tendon lift-off results and plotted the data with forecast values and 95 percent lower confidence limit for hoop tendons and inverted-U tendons at each unit.
The NRC staff reviewed the lift-off force data presented in figures 6.5.2, 6.5.4, 6.5.6, and 6.5.8 of the enclosure of the proposed alternative and verified that the projected lift-off forces remain above the MRV (i.e., 1169 kilo pounds (kip) and 1150 kip, for the hoop and inverted-U tendons, respectively) beyond the deferred next inspection and through the end of the period of extended operation for both units. Based on the statistical analyses of past surveillance results, and the ample margin between the measured force trend (forecast) values and the MRV, the NRC staff finds it acceptable to extend the interval of the post-tensioning system examinations and tests (ASME Code,Section XI, table IWL 2500-1 (L-B), Item No. L2.10) for a one-time deferral for STP to perform the next tendon testing from 10 to 20 years for the fourth 10-year CISI interval at STP, Unit 2.
Item No. L2.20, Wire Examination and Test Results Section 6.5, subsection Wire Test Results of the enclosure of the proposed alternative describes the following wire test results: (1) sample test wires (one hoop tendon and one vertical, inverted-U tendon) were extracted, examined full length, and tested for ultimate tensile strength and strain during each full surveillance, and (2) all specimens exceeded the minimum 240 kilo pound per square inch (ksi) ultimate stress, and all elongation measurements met the minimum 4 percent criteria.
The NRC staff reviewed the test tendon wire test results described in the table, Summary of Wire Test Results, in the enclosure of the proposed alternative and observed that all test results of tendon wire specimens met the American Society of Testing and Materials (ASTM)
A421, Specification for Uncoated Stress Relieved Wire for Prestressed Concrete, acceptance criteria for ultimate strength and elongation except for two elongation tests (3.1 and 3.9 percent) at Unit 1 during the 1st year test. As described in the note to the table, these two anomalous results were retested using backup specimens and a minimum 5.6 percent elongation was achieved. A finding in the table, Summary of Unit 2 Surveillance Findings, in the enclosure of the proposed alternative, noted level 2 corrosion (discoloration without pitting) on a small area of a wire removed from a vertical tendon during the 5th year surveillance at STP, Unit 2. The staff finds the level 2 corrosion acceptable because it does not include material loss and its only occurring one time does not warrant further evaluation. Since the examination and testing of extracted sample wires has shown no degradation of condition, strength, or elongation over a time period of approximately 30 years, and has not identified any signs of advanced corrosion, the NRC staff finds it acceptable to extend the interval of tendon wire examinations and tests (ASME Code,Section XI, table IWL 2500-1 (L-B), Item No. L2.20) for a one-time deferral for STP to perform the next tendon wire examination and testing from 10 years to 20 years for the fourth 10-year CISI interval at STP, Unit 2.
Item No. L2.30, Anchorage Hardware and Surrounding Concrete Inspection Section 6.5, subsection Anchorage Inspections of the enclosure of the proposed alternative summarizes the results of end anchorage examinations performed periodically through the 30th year surveillance for STP, Unit 1 and the 25th year surveillance for Unit 2.
The NRC staff reviewed the tables, Summary of Unit 1 Surveillance Findings, and Summary of Unit 2 Surveillance Findings, in section 6.5 of the enclosure of the proposed alternative for findings related to paragraph IWL-2524, Examination of Tendon Anchorage Areas (Item No. L2.30) examinations and noted the following:
Level 2 corrosion (discoloration with no pitting) was observed on tendon shims during the 1st year surveillance at STP, Unit 1 and during the 5th year surveillance at STP, Unit 2. The licensee evaluated the corrosion and determined the level 2 corrosion, with no material loss, met the code acceptance criteria.
A surface crack ranging from 0.02 to 0.05 inches width at the buttress for Tendon 3H110 discovered during the year 3 surveillance for STP, Unit 2 was evaluated and accepted because it was at the surface only with no penetration into the concrete.
There were 24 new wires that have become ineffective after the construction era.
Sixteen of the 24 wires were damaged deliberately for testing. The licensee evaluated each case of discovered unseated wires, broken strands, or ineffective buttonheads during each ISI, and determined all cases met the acceptance criteria stated in Updated Final Safety Analysis Report section 3.8.1.4.2.3 (1 percent breakage in any three adjacent tendons).
Besides two tablespoons of free water collected during year 1 surveillance of the vertical Tendon V245 on STP, Unit 1, no free water has been discovered during other surveillances. The free water discovered at Tendon V245 was determined to be trapped water during construction and not an ongoing leak.
Beyond the list of inspection findings mentioned above, the NRC staff notes that the licensee did not identify cracking in the anchorage assembly, active corrosion, or concrete cracking greater than 0.01 inch adjacent to the bearing plates. Surveillance findings to-date do not appear to indicate the presence of active degradation mechanisms that will cause significant degradation if the inspection interval is extended. Therefore, the staff finds it acceptable to extend the interval of anchorage hardware examinations and surrounding concrete inspection (ASME Code,Section XI, table IWL2500-1(L-B), Item No. L2.30) for a one-time deferral for STP to perform the next examination of tendon anchorage areas from 5 years to 10 years for the fourth 10-year CISI interval for STP, Units 1 and 2.
Item Nos. L2.40 and L2.50, CPM and Free Water Testing Section 6.5, subsection Corrosion Protection Medium (CPM) of the enclosure of the proposed alternative states that CPM tests for chlorides, nitrates, sulfides, absorbed water content, and reserve alkalinity (base number) have met the acceptance limits set in table IWL-2525-1 during every surveillance. Additionally, the licensee stated that since switching to IWL at the 15th year, the acceptance limit of 10 pecent net duct volume (NDV) in for CPM voids have been met during all surveillances except once. During the regulatory audit, the NRC staff reviewed the summary of surveillance findings for tendon CPM tests at STP for chlorides, nitrates, sulfides, absorbed water content, and reserve alkalinity (expressed as neutralization or base number) for both units, and confirmed the statements in the proposed alternative that the CPM analysis results have met the acceptance limits required by ASME Code, table IWL-2525-1. The testing of free water for the pH value is not applicable as there has not been any water collected since year 1 as described under Item No. L2.30.
The licensee reported CPM voids greater than 5 pecent NDV to the NRC in special reports per the original Technical Specifications section 4.6.1.6.1.d.(2) requirement, which limits the maximum duct voids to 5 percent NDV. The NRC staff reviewed the special reports between the 3rd year to 15th year surveillance periods against the requirements of ASME Code,Section XI, subparagraph IWL-3221.4 and noted that despite several tendons with CPM volume differences exceeding 10 percent NDV, those voids have been filled and there is no evidence of grease leakage. The presence of voids has not revealed degradation in past and present inspections, the leaktight integrity and the structural integrity of the containment are maintained, and no deterioration is found in the tendon system. Therefore, the NRC staff considers this exceedance of CPM voids acceptable.
Based on the adequate test results, and no indication that the conditions will degrade over time, the NRC staff finds it acceptable to extend the interval of the examination of CPM and free water (ASME Code,Section XI, table IWL2500-1(L-B), Item Nos. L2.40 and L2.50) for a one-time deferral for STP to perform the next CPM and free water testing from 5 years to 10 years for the fourth 10-year CISI Interval for STP, Units 1 and 2.
Summary Based on the above evaluation, the NRC staff determined that the licensee has demonstrated adequate performance of the unbonded post-tensioning system by presenting adequate plant-specific post-tensioning system inspection results, operating experience and corrective actions, and technical evaluations demonstrating applied tendon prestress level will remain acceptable beyond the deferred next inspection. Therefore, the NRC staff finds that the use of proposed alternative RR-ENG-4-06 for STP, Units 1 and 2 for the fourth 10-year CISI interval (September 9, 2019, through September 8, 2029) provides an acceptable level of quality and safety.
CONCLUSION As set forth above, the NRC staff has determined that the proposed alternative, as described in the licensees letter dated December 14, 2023, is acceptable as a one-time deferral on the basis that the proposed alternative provides an acceptable level of quality and safety.
The NRC staff concludes that the licensee has adequately addressed the regulatory requirements set forth in 10 CFR 50.55a(z)(1).
Accordingly, the NRC staff authorizes the use of proposed alternative RR-ENG-4-06 at STP, Units 1 and 2 for the fourth 10-year CISI interval (September 9, 2019, through September 8, 2029) as a one-time deferral, as stipulated in the staff evaluation summary section above.
All other ASME Code,Section XI, requirements for which an alternative was not specifically requested and authorized remain applicable, including third -party review by the Authorized Nuclear Inservice Inspector.
Principal Contributors: S. Lai, NRR G. Wang, NRR Date: February 13, 2024 Jennivine K. Rankin, Chief Plant Licensing Branch IV Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation cc: Listserv Jennivine K.
Rankin Digitally signed by Jennivine K. Rankin Date: 2024.02.13 15:48:20 -05'00'
- concurrence via email NRR-028 OFFICE NRR/DORL/LPL4/PM NRR/DORL/LPL4/LA*
NRR/DEX/ESEB/BC*
NAME DGalvin PBlechman ITseng DATE 2/12/2024 2/12/2024 1/31/2024 OFFICE NRR/DORL/LPL4/BC*
NAME JRankin DATE 2/13/2024