ML23353A077
| ML23353A077 | |
| Person / Time | |
|---|---|
| Site: | Wolf Creek  |
| Issue date: | 01/16/2024 |
| From: | Jennivine Rankin Plant Licensing Branch IV |
| To: | Reasoner C Wolf Creek |
| Lee S, 301-415-3168 | |
| References | |
| EPID L-2023-LLR-0026 | |
| Download: ML23353A077 (1) | |
Text
January 16, 2024 WOLF CREEK GENERATING STATION, UNIT 1 - AUTHORIZATION AND SAFETY EVALUATION FOR ALTERNATIVE CONTAINMENT INSERVICE INSPECTION FREQUENCY (EPID L-2023-LLR-0026)
LICENSEE INFORMATION Recipients Name and Address:
Mr. Cleveland Reasoner Chief Executive Officer and Chief Nuclear Officer Wolf Creek Nuclear Operating Corporation P.O. Box 411 Burlington, KS 66839 Licensee:
Wolf Creek Nuclear Operating Corporation Plant Name and Unit:
Wolf Creek Generating Station, Unit 1 (Wolf Creek)
Docket No.:
50-482 APPLICATION INFORMATION Submittal Date: May 17, 2023 Submittal Agencywide Documents Access and Management System (ADAMS) Accession No.: ML23137A328.
Applicable Containment Inservice Inspection (CISI) Interval and Interval Start/End Dates:
The Wolf Creek third 10-year CISI interval, began on September 10, 2018 and is scheduled to end on September 9, 2028.
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.
CISI 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 (L-B), 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) (Item Nos. L2.10, L2.20, L2.30, L2.40 and L2.50) for the 35th year surveillance and every 10 years thereafter at Wolf Creek. The proposed alternative eliminates the IWL-2520 examinations for the 40th year (currently scheduled during the third 10-year CISI Interval) and every 10 years thereafter at Wolf Creek. The examination and physical testing requirements of subsubarticle IWL-2520 will only be performed at 40 years (+/- 12 months) following the completion of the containment Structural Integrity Test if the Responsible Engineer (RE) determines that conditions detected during the general visual examinations and detailed visual examination performed on containment accessible concrete surfaces and tendon end caps in accordance with table IWL-2500-1 (L-A),
Examination Category L-A, Concrete, indicate possible degradation of tendon hardware.
STAFF EVALUATION The U.S. Nuclear Regulatory Commission (NRC) staff reviewed the information provided in the proposed alternative request 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 by table IWL-2500-1 (L-A). Any indications identified during these examinations may lead to additional examinations in accordance with table IWL-2500-1 (L-B), as determined by the RE. 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 surveillance reports for Wolf Creek 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. The NRC staff conducted an online regulatory audit to examine the licensees non-docketed information with the intent to gain a better understanding of the alternative request, to verify information, and to identify information that may require docketing to support the basis of the NRC staffs licensing decision (ML23277A277).
A summary of the NRC staffs evaluation of each item number is provided below.
Item No. L2.10, Tendon Force Trends and Forecasts Section 5.2.1 of the enclosure to the application, the licensee states, in part, that: (1) that tendon force measurements have remained above the minimum required value (MRV), and that the predicted mean tendon forces for each type of tendon will remain above the required minimum design prestress force well beyond the end of the current operating license, and (2) Measured tendon elongations have met the applicable acceptance standards during all surveillances.
During a regulatory audit, the NRC staff reviewed the lift-off force data presented in figures 1, 2, and 3 of the enclosure to the licensees submittal and tendon surveillance reports, and verified that the projected lift-off forces remain above the MRV (i.e., 1,227 kip (kilo pound), 1,159 kip, and 1,119 kip for the cylinder hoop, vertical, and dome hoop tendons, respectively) through the next proposed inspection and through the end of the current 60-year operating license.
Based on the statistical analyses of past surveillance results, and the significant margin between the measured force trend (forecast) values and the MRV, the NRC staff finds it acceptable to extend the interval of the tendon force and elongation measurements (ASME Code,Section XI, table IWL 2500-1 (L-B), Item No. L2.10) for a one-time deferral for Wolf Creek to perform the next tendon testing from 5 to 10 years for the third 10-year CISI interval.
The NRC staffs evaluation of the tendon force and elongation measurements (ASME Code,Section XI, table IWL 2500-1 (L-B), Item No. L2.10) at 40 years if required by the RE is discussed below in the summary section of this safety evaluation (SE). The NRC staffs evaluation of the fourth and fifth intervals is also discussed below in the Summary section of this SE.
Item No. L2.20, Wire Examination and Test Results Section 5.2.2 of the enclosure to the licensees submittal states: (1) Visual examination of all wires removed from tendons since initial tendon installation have shown no signs of corrosion or physical damage, and (2) Results of tension tests on all wires removed from tendons have met applicable acceptance standards, including material specification requirements for ultimate tensile strength ( 240 ksi (kilo pound per square inch)) and elongation at failure ( 4%).
During a regulatory audit, the NRC staff reviewed the test results of tendon wire specimens and observed that all test results of tendon wire specimens met the American Standard Test Materials A421, Standard Specification for Stress Relieved Steel Wire for Prestressed Concrete, acceptance criteria for ultimate strength and elongation.
Since the examination and testing of extracted sample wires have shown no signs of degradation of condition, strength, or elongation over a time period of approximately 35 years, and the licensee has not identified any corrosion, the NRC staff finds it acceptable to extend the interval of the 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 Wolf Creek to perform the next tendon wire examination and testing from 5 to 10 years for the third 10-year CISI interval.
The NRC staffs evaluation of the tendon wire examinations and tests (ASME Code,Section XI, table IWL 2500-1 (L-B), Item No. L2.20) at 40 years if required by the RE is discussed below in the Summary section of this SE. The NRC staffs evaluation of the fourth and fifth intervals is also discussed below in the Summary section of this SE.
Item No. L2.30, Anchorage Hardware and Surrounding Concrete Inspection Section 5.2.3 of the enclosure to the licensees submittal discusses the examination results of tendon anchorage areas performed periodically at Wolf Creek through the 35th year surveillance. During each of the surveillances, end anchorage areas were visually examined for evidence of corrosion, broken wires or missing buttonheads, damage or distortion of load bearing components, and cracks in concrete adjacent to bearing plates.
Based on the results of surveillances conducted to date, the licensee concluded, in part, that:
- 1) Cracking of concrete adjacent to bearing plates at several tendon end anchorages areas has been documented and evaluated as acceptable. These cracking conditions are considered typical in structures of this age, and do not represent evidence of abnormal degradation of the containment or post-tensioning system.
- 2) Visual examinations of tendon anchorage hardware (anchorheads, shims, buttonheads, and bearing plates) have met the applicable acceptance standards, with exceptions as noted. Cracks have not been detected in any tendon anchorage component.
During a regulatory audit, the NRC staff observed several instances of broken wires and protruding buttonheads. The worst example discovered occurred during the 25-year surveillance where tendon V7 had two broken wires and five protruding buttonheads. The NRC staff reviewed the licensees nonconformance/corrective action report (NCR) Nos. FN1054-001, FN1054-002, and Engineering Disposition - Change Package No. 013427, Revision 0, which documented that the loss of these seven wires will have insignificant impact on the overall performance of the containment post-tensioning system. The NRC staff also reviewed the 20th year surveillance report and noted Level 3 corrosion on the tendon ends and six instances of concrete cracking greater than 0.01 inch. The NRC staff further reviewed the licensees Work Order #05-274942-001 and found that the licensee cleaned the corrosion and re-inspected the tendon ends. In addition, the NRC staff noted that the maximum concrete crack size is 0.022 inch, which is less than the 0.04-inch maximum width based on the second-tier criteria of section 5.2.1 of American Concrete Institute 349.35-02, Evaluation of Existing Nuclear Safety-Related Concrete Structures. The NRC staff verified the cracking to be minor and not active degradation.
The NRC staff concludes that there is no impact on the structural integrity of the post-tensioning system. 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 NRC staff finds it acceptable to extend the interval of the examination of tendon anchorage areas (ASME Code,Section XI, table IWL 2500-1 (L-B), Item No. L2.30) for a one-time deferral for Wolf Creek to perform the next examination of tendon anchorage areas from 5 to 10 years for the third 10-year CISI interval.
The NRC staffs evaluation of the examination of tendon anchorage areas (ASME Code,Section XI, table IWL 2500-1 (L-B), Item No. L2.30) at 40 years, if required by the RE, is discussed below in the summary section of this SE. The NRC staffs evaluation of the fourth and fifth intervals is also discussed below in the summary section of this SE.
Item No. L2.40 and L2.50, CPM and Free Water Testing Section 5.2.4 of the enclosure to the licensees submittal indicates that results of tendon CPM tests have met acceptance standards during all examinations, and free water (less than 1 ounce) was only detected during the 20th year surveillance at Tendon V30. Section 5.2.5 of the enclosure to the licensees submittal also indicates that the difference in CPM installed and that removed from a tendon exceeded 10 percent of the net duct volume during the 3rd, 10th, and 20th year surveillances.
During a regulatory audit, the NRC staff reviewed the results of recent tendon CPM tests at Wolf Creek for chlorides, nitrates, sulfides, absorbed water content, and reserve alkalinity (expressed as neutralization or base number) for surveillance years 30, 35, and the surveillance summary reports for years 1 through 35, and observed that the CPM analysis results have met all the acceptance limits required by the ASME table IWL-2525-1. The NRC staff noted that the PH analysis on free water has not been performed at Wolf Creek since only a trace amount of free water has been detected one time at Tendon V30, and the quantity is insufficient for lab analysis. In addition, the NRC staff noted the measured CPM voids up to 17 percent of the tendon duct net volume in the 3rd, 10th, and 20th year surveillances that exceed 10 percent of the net tendon duct volume limit set by ASME Code Section XI subparagraph IWL-3221.4. The licensees engineering evaluation noted that more CPM was installed than removed and determined the as-left state of the subject tendons is acceptable. The NRC staff reviewed the licensees engineering evaluation and verified that the presence of voids, as noted above, has not revealed degradation in past and present inspections, and that the leak-tight integrity and the structural integrity of the containment are maintained, and no deterioration is found in the tendon system.
Based on the adequate test results, the NRC staff finds it acceptable to extend the interval of the examination of CPM and free water (ASME Section XI, table IWL2500-1(L-B), Item Nos L2.40 and L2.50) for a one-time deferral for Wolf Creek to perform the next testing 5 to 10 years for the third 10-year CISI interval.
The NRC staffs evaluation of the examination of CPM and free water (ASME Code,Section XI, table IWL 2500-1 (L-B), Item Nos. L2.40 and No. L2.50) at 40 years, if required by the RE, is discussed below in the Summary section of this SE. The NRC staffs evaluation of the fourth and fifth intervals is also discussed below in the Summary section of this SE.
Summary Based on the above evaluation, the NRC staff determines 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. The NRC staffs regulatory audit also verified information in the licensees application. Therefore, the NRC staff finds that the use of Proposed Alternative C13R-01 for Wolf Creek for the third 10-year CISI interval provides an acceptable level of quality and safety.
The NRC staff authorizes the proposed alternatives to extend the interval of the concrete containment unbonded post-tensioning system examinations (ASME Code,Section XI, table IWL 2500-1 (L-B), Item Nos. L2.10, L2.20, L2.30, L2.40 and L2.50) for a one-time deferral for Wolf Creek to perform the next examination and testing from 5 to 10 years for the third 10-year CISI interval (September 10, 2018 through September 9, 2028).
Section 5.1 of the enclosure to the application, the licensee states that the examination and physical testing requirements of IWL-2520 will only be performed at 40 years (+/- 12 months) following the completion of the containment Structural Integrity Test if the RE determines that conditions detected during the general visual examinations and detailed visual examination performed on containment accessible concrete surfaces and tendon end caps in accordance with table IWL-2500-1 (L-A) indicate possible degradation of tendon hardware. The NRC staff finds this proposed alternative acceptable because the examination and physical testing requirements of subsubarticle IWL-2520 need to be performed at 40 years if the RE detects possible degradation of tendon hardware.
The NRC staff finds it reasonable to approve a one-time interval extension based on its review of the plant-specific testing results and operating experience provided in the request. However, the NRC staff does not find it reasonable to extend the inspection intervals for the fourth and fifth CISI intervals without reviewing the third CISI inspection results of the general visual examinations, and the results of the detailed visual examination of suspect areas conducted prior to the initiation of the fourth CISI interval. Therefore, the NRC staff does not authorize the licensees request for the proposed alternatives to be applicable to the fourth and fifth CISI intervals.
CONCLUSION As set forth above, the NRC staff determines that the proposed alternative, as described in the licensees letter dated May 17, 2023, and modified by the staffs evaluation Summary section above, 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 CI3R-01 at Wolf Creek for the third 10-year CISI interval (September 10, 2018, to September 9, 2028) 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: January 16, 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: 2024.01.16 12:12:55 -05'00'
ML23353A077 OFFICE NRR/DORL/LPL4/PM NRR/DORL/LPL4/LA NRR/DEX/ESEB/BC NRR/DORL/LPL4/BC NAME SLee PBlechman ITseng JRankin DATE 12/19/2023 1/4/2024 10/23/2023 01/16/2024