ML24225A101
| ML24225A101 | |
| Person / Time | |
|---|---|
| Site: | Callaway  |
| Issue date: | 08/13/2024 |
| From: | Mahesh Chawla Plant Licensing Branch IV |
| To: | Diya F Union Electric Co |
| Chawla M | |
| References | |
| EPID L-2023-LLR-0061 | |
| Download: ML24225A101 (7) | |
Text
August 13, 2024 CALLAWAY PLANT, UNIT NO. 1 - AUTHORIZATION AND SAFETY EVALUATION FOR ALTERNATIVE REQUEST C3R-01 (EPID L-2023-LLR-0061)
LICENSEE INFORMATION Recipients Name and Address:
Fadi Diya Senior Vice President and Chief Nuclear Officer Ameren Missouri Callaway Energy Center 8315 County Road 459 Steedman, MO 65077 Licensee:
Union Electric Company, doing business as Ameren Missouri Plant Name and Unit:
Callaway Plant, Unit No. 1 (Callaway)
Docket No:
50-483 APPLICATION INFORMATION Submittal Date: October 26, 2023 Submittal Agencywide Documents Access and Management System (ADAMS) Package Accession No.: ML23299A195.
Supplement Date: December 21, 2023.
Supplement ADAMS Accession No.: ML23355A180.
Applicable Containment Inservice Inspection (CISI) and Interval Start/End Dates: The Callaway third 10-year CISI interval, began on September 9, 2016, and is scheduled to end on September 8, 2026.
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.
Inservice Inspection (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, 2007 Edition with the 2008 Addenda.
Brief Description of the Proposed Alternative: The licensees proposed alternative, as modified by the supplement, corresponding to the above code requirements, is to extend the interval for 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) from 5 to 10 years during the third 10-year CISI interval. Accordingly, the proposed alternative eliminates the IWL-2520 examinations for the 40th year as specified by IWL-2420 currently scheduled during the third 10-year CISI Interval. Section 5 of enclosure 1 to the proposed alternative request also states in part, physical testing would only be performed if visual examination results indicate a need for such testing as determined by the Responsible Engineer Example conditions which require removal of the tendon end cap and further examination per Item Nos. L2.10, L2.20, L2.30, L2.40, and L2.50 are noted in section 5 of enclosure 1 to the proposed alternative.
STAFF EVALUATION The licensee proposed the request, as modified by the supplement, for alternative frequency to the containment unbonded post-tensioning system ISI (C3R-01) at Callaway. Specifically, the request concerns the following examination requirements in table IWL-2500-1 (L-B) of ASME Code,Section XI, subsection IWL.
Item No. L2.10 requires that selected tendon force and elongation be measured every 5 years in accordance with paragraph IWL2522, Tendon Force and Elongation Measurements.
Item No. 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. This inspection must be performed every 5 years in accordance with paragraph IWL2523, Tendon Wire and Strand Examination and Testing.
Item No. L2.30 requires that a detailed visual examination on selected tendon anchorage hardware and adjacent concrete extending 2 feet from the edge of the bearing plate be performed every 5 years in accordance with paragraph IWL2524, Examination of Tendon Anchorage Areas. In addition, the quantity of free water released from the anchorage end cap, as well as any free water that drains from the tendon during examination, must be documented.
Item No. L2.40 requires that samples of selected tendon corrosion protection medium (CPM) be obtained and analyzed every 5 years in accordance with paragraph IWL2525 and IWL-2526, Examination of Corrosion Protection Medium and Free Water, and Removal and Replacement of Corrosion Protection Medium, respectively.
Item No. L2.50 requires that samples of free water be obtained and analyzed every 5 years in accordance with paragraph IWL2525.
The U.S. Nuclear Regulatory Commission (NRC) staff reviewed the information provided in the proposed alternative request, as modified by the supplement, 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 ASME Code,Section XI, table IWL-2500-1 (L-A)
Examination Category L-A, Concrete. 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 ASME Code,Section XI, 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 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 Callaway examination history and results evaluation 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 4, Callaway Examination History and Results Evaluation, of enclosure 2 to the licensees proposed alternative request. Section 4 summarizes the results of the nine previous surveillance examinations conducted between 1985 and 2021 for (1) tendon force trends, (2) wire test results, (3) anchorage hardware and concrete condition, and (4) CPM testing. The NRC staff also performed a regulatory audit (ML24212A282) of non-docketed surveillance reports to verify the information in section 4. A summary of the NRC staffs evaluation of each item number is provided below.
Item No. L2.10, Tendon Force Trends and Forecasts In section 4.1, Tendon Force Trends and Forecasts of enclosure 2 to the proposed alternative request, the licensee provided tendon mean force trends by log-linear regression and 95 percent low confidence limit (LCL) computations for the circumferential and meridional tendons.
The NRC staff reviewed the lift-off force data presented in tables 2 and 4 of enclosure 2 to the proposed alternative request and noted that the tendon lift-off forces for all nine previous examinations have measured higher than the minimum required value (MRV) (i.e., 1227 kilo pounds (kip) and 1160 kip, for the circumferential and meridional tendons, respectively). The NRC staff reviewed figures 1 and 3 of enclosure 2 to the proposed alternative request and noted that the projected mean tendon force trend lines by log-linear regression and 95 percent LCL computations for the circumferential and meridional tendons remain above the MRV beyond the deferred next inspection and through T = 100 years. Based on the statistical analyses of past surveillance results, 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 the licensee to perform the next tendon testing from 5 to 10 years for the third 10-year CISI interval at Callaway.
Item No. L2.20, Wire Examination and Test Results In section 4.2.1, Wire Visual Examination and Condition of enclosure 2 to the proposed alternative request, the licensee summarizes the wire visual examination condition as Level 1 (or A) (i.e., no visible corrosion), during all surveillances, except for the 10th year. During the 10th year surveillance, two wires from tendon 12CB exhibited corrosion up to Level 3 (i.e., rust with pitting up to 0.003 in depth).
Wire tests shall meet the American Society for Testing and Materials (ASTM) A421, Specification for Uncoated Stress Relieved Wire for Prestressed Concrete, specifications for minimum tensile strength of 204 ksi (kips per square inch) for yield strength, 240 ksi for ultimate strength, and a minimum of 4 percent elongation at failure. The NRC staff reviewed the tendon wire test results provided in tables 6, 7, and 8 in enclosure 2 to the proposed alternative request. Table 6, Wire Test Results / Yield Strength, which demonstrates that the wire tests from the previous nine examinations have met the minimum yield strength except for the 3rd year surveillance. The licensee noted in section 4.2.2, Wire Yield Strength, of enclosure 2 to the proposed alternative request, that the lower tested yield strength in the samples during the 3rd year may be attributed to the procedure and equipment used at the laboratories performing the tests. Based on table 6, the yield strength capacities of all other wires tested during other examinations reached an average stress of 220 ksi or greater. Similarly, the results of the ultimate tensile strength test on table 7, Wire Test Results / Ultimate Tensile Strength (UTS), indicate an anomaly for the 3rd year surveillance. The applicants engineer also evaluated the tested UTS of the tendon V39 wires at 235 ksi for the 35th year surveillance and attributed it to testing equipment variation and determined it as acceptable. The results of table 8, Wire Test Results / Elongation at Failure, for wire elongation tests at failure reveals tests not meeting the minimum 4 percent requirement per ASTM A421 at years 1, 3, 10, and 25 surveillances. The licensee noted the wire testing performed through the 25th year surveillance used 100-inch specimens instead of 10-inch specified by ASTM A421, and the longer specimens resulted in an overall low percentage in elongation. The wires that failed the elongation test passed the yield and ultimate strength tests, with exception of the anomaly observed at the 3rd year, which was attributed to the testing equipment. Considering that the actual wire stress for the containment during a postulated severe accident is significantly less than the yield limit, which corresponds to 1 percent elongation, the tendon remains effective in retaining the containment pressure boundary despite the elongation tests not reaching 4 percent.
The NRC staff finds the Level 3 corrosion in tendon 12CB acceptable because the corrosion is inactive and occurred prior to installation of CPM. Because there are no indications of degradation in the wires examined during the 3rd and 35th year surveillances, the NRC staff considers these test results anomalies and do not indicate a trend in declining wire tensile strength and ductility. Since the examination and testing of extracted sample wires has shown no degradation of condition, strength, or elongation over a time period of approximately 35 years, and has not identified any signs of active 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 the licensee to perform the next tendon testing from 5 to 10 years for the third 10-year CISI interval at Callaway.
Item No. L2.30, Anchorage Hardware and Surrounding Concrete Inspection In section 4.3, End Anchorage Hardware and Concrete Condition, of enclosure 2 to the proposed alternative request, the licensee summarizes the results of examinations for corrosion, free water, missing buttonheads and discontinuous wires, load bearing components damage and distortion, and concrete cracking adjacent to bearing plates. The NRC staff reviewed the results of these examinations summarized in subsections 4.3.1 through 4.3.5 of enclosure 2 to the proposed alternative request and noted the following:
Based on the results of the nine surveillances performed to date, all of the reported corrosion findings on the end anchorage were limited to Level 1 and 2, with exception to the 5th year surveillance, which discovered Level 3 corrosion (a 3/16 diameter spot) on a tendon 52AC bushing.
No free water was found during any of the nine surveillances completed to date.
Only up to two missing buttonheads or ineffective wires per tendon were discovered.
This represents a very small percentage of the total wires in each tendon and is structurally insignificant if omitted.
Although there are several instances of concrete cracking greater than 0.01 inch in the tendon anchorage bearing area, the licensee stated in the summary that those cracks were result of concrete shrinkage constrained by the bearing plates, and there is no evidence of structural cracking due to applied loads from the tendon anchorage.
Furthermore, the widest cracks, which was 0.05-inch wide at common tendon V65 during the 5th and 10th surveillance have reduced to less than 0.01 inch during the 25th, 30th, and 35th year surveillances, supporting the conclusion that the cracks are non-structural-related.
During the regulatory audit, the NRC staff reviewed the Callaway Plant Safety Evaluation Report (NCR 89N353) and verified the Level 3 corrosion at tendon 52AC is limited to a small spot and concludes it does not pose a performance risk to the tendon anchorage system. Surveillance findings to-date do not appear to indicate the presence of active corrosion or degradation mechanisms on the bearing plates, anchor heads, shims, buttonheads or wires 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 the licensee to perform the next examination of tendon anchorage areas from 5 to 10 years for the third 10-year CISI Interval at Callaway.
Item Nos. L2.40 and L2.50, Corrosion Protection Medium and Free Water Testing In section 4.4, Corrosion Protection Medium Testing of enclosure 2 to the proposed alternative request, the licensee summarizes the results of the CPM tests for chlorides, nitrates, sulfides, and absorbed water content. The NRC staff reviewed the summary of surveillance findings on the tendon CPM tests at Callaway for corrosive ions (chlorides, nitrates, and sulfides) and observed all three ion concentrations were well below the 10 parts per million (ppm) acceptance limit set by table IWL-2525-1 during all nine surveillances. Additionally, all nine surveillances performed to date reported absorbed water content less than the 10 percent limit. In section 4.4, the licensee also noted, with exception to the 15th year surveillance, the reserve alkalinity (base number) tests have met the table IWL-2525-1 criterion (base number not less than 17.5) during all surveillances. The exception occurred at tendon 6AC with a measured base number of 16.8.
The testing of free water for the pH value is not applicable as there has not been any water collected during the last nine surveillances.
During the regulatory audit, the NRC staff reviewed the surveillance reports for the 15th year through the 35th year surveillances for conformance to ASME Code,Section XI, IWL-3221.4, which requires the difference between CPM removed and installed not to exceed 10 percent of the tendon net duct volume (NDV). The NRC staff only observed one tendon with a CPM voids volume difference exceeding the 10 percent NDV, which happened during the 20th year surveillance. Considering the voids have been filled, the leak-tight integrity and the structural integrity of the containment are maintained, and no deterioration is found in the tendon system, the NRC staff considers this exceedance of CPM voids acceptable.
The NRC staff finds the reserve alkalinity test at tendon 6AC not meeting the table IWL-2525-1 criterion acceptable because all other CPM test for corrosive ions and absorbed water were well below the acceptance limits, and there are no other indications of corrosion at this tendon.
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 the licensee to perform the next CPM and free water testing from 5 to 10 years for the third 10-year CISI Interval at Callaway.
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 C3R-01 for Callaway for the third 10-year CISI interval provides an acceptable level of quality and safety.
The NRC staff authorizes the proposed alternative at Callaway, to extend the interval for concrete containment unbonded post-tensioning system examinations per ASME Code,Section XI, table IWL-2500-1 (L-B), Examination Category L-B (Item Nos. L2.10, L2.20, L2.30, L2.40 and L2.50) from 5 to 10 years during the third 10-year CISI interval. The licensee will continue to perform general visual examinations per table IWL-2500-1(L-A), and any indications identified during these examinations may lead to additional examinations in accordance with table IWL-2500-1 (L-B), Examination Category L-B (Item Nos. L2.10, L2.20, L2.30, L2.40 as determined by the Responsible Engineer during the third 10-year CISI interval.
If deferred inspections from the third interval are conducted in the fourth CISI interval, the Code edition used for the inspection shall be in accordance with 10 CFR 50.55a(g)(4)(ii), Applicable ISI Code: Successive 120-month intervals.
CONCLUSION As set forth above, the NRC staff has determined that the proposed alternative, as described in the licensees letter dated October 26, 2023, as supplemented by "ULNRC-06847, Supplement to Relief Request from Requirements of ASME BPV Code, Section XI, Subsection Iwl Regarding Examination and Testing of the Unbonded Post-Tensioning System (Relief Request [[SSC" contains a listed "[" character as part of the property label and has therefore been classified as invalid.)|letter dated December 21, 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 C3R-01 at Callaway Plant, Unit No. 1 for the third 10-year CISI interval 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: August 13, 2024 Jennivine K. Rankin, Chief Plant Licensing Branch IV Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation cc: Listserv SAMSON LEE Digitally signed by SAMSON LEE Date: 2024.08.13 15:29:50 -04'00'
- concurrence via email OFFICE NRR/DORL/LPL4/PM NRR/DORL/LPL4/LA*
NRR/DEX/ESEB/BC*
NAME MChawla PBlechman ITseng DATE 8/8/2024 8/12/2024 07/29/2024 OFFICE NRR/DORL/LPL4/BC*
NAME JRankin (SLee for)
DATE 8/13/2024