ML23299A197
| ML23299A197 | |
| Person / Time | |
|---|---|
| Site: | Callaway  |
| Issue date: | 10/26/2023 |
| From: | Ameren Missouri, Union Electric Co |
| To: | Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML23299A195 | List: |
| References | |
| ULNRC-06831 | |
| Download: ML23299A197 (1) | |
Text
Enclosure 1 to 10 CFR 50.55a Request Number C3R-01 ULNRC-06831 Page 1 of 5 Proposed Alternative In Accordance with 10 CFR 50.55a(z)(1)
Alternative Provides Acceptable Level of Quality and Safety
- 1. ASME Code Component(s) Affected Callaway Energy Center (Callaway Plant), Unit 1 Containment Building
2. Applicable Code Edition and Addenda
The third interval of Callaway's Containment Exterior Concrete and Tendon Inspection Program is based on the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel (BPV) Code,Section XI, Subsection IWL, 2007 Edition through 2008 Addenda. The third interval began on September 9, 2016 and is scheduled to end on September 8, 2026.
3. Applicable Code Requirement
IWL-2420 states that:
(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.
(b) The 1, 3, and 5 year examinations shall commence not more than 6 months prior to the specified dates and shall be completed not more than 6 months after such dates. If plant operating conditions are such that examination of portions of the post-tensioning system cannot be completed within this stated time interval, examination of those portions may be deferred until the next regularly scheduled plant outage.
(c) The 10-year and subsequent examinations shall commence not more than 1 year prior to the specified dates and shall be completed not more than 1 year after such dates. If plant operating conditions are such that examination of portions of the post-tensioning system cannot be completed within this stated time interval, examination of those portions may be deferred until the next regularly scheduled plant outage.
Subarticle IWL-2500 requires examinations of the unbonded post-tensioning system be performed in accordance with the requirements of Table IWL-2500-1 (L-B), "Examination Category L-B, Unbonded Post-Tensioning System," which includes the following requirements:
Table IWL-2500-1 (L-B), Item Number L2.10 requires that selected tendon force and elongation be measured in accordance with IWL-2522.
Table IWL-2500-1 (L-B), Item Number L2.20 requires that tendon single wire samples be removed and examined for corrosion and mechanical damage as well as tested to obtain yield strength, ultimate tensile strength, and elongation on each removed wire in accordance with IWL-2523. The selected tendons are subsequently retensioned as required per IWL-2523.3 because wire removal requires de-tensioning in order to safely obtain wire samples.
to 10 CFR 50.55a Request Number C3R-01 ULNRC-06831 Page 2 of 5 Table IWL-2500-1 (L-B), Item Number L2.30 requires that a detailed visual examination be performed on selected tendon anchorage hardware and adjacent concrete extending 2 feet from the edge of the bearing plate in accordance with IWL-2524. The quantity of free water released from the anchorage end cap as well as any that drains from the tendon during examination shall be documented.
Table IWL-2500-1 (L-B), Item Numbers L2.40 and L2.50 require that samples of selected tendon corrosion protection medium (CPM) and free water be obtained and analyzed in accordance with IWL-2525 and IWL-2526.
4. Reason for Request
Pursuant to 10 CFR 50.55a, "Codes and standards," paragraph (z)(1), an alternative is proposed to the ASME Section XI, Subsection IWL requirements for the visual examination and physical testing of the unbonded post-tensioning system. The basis of the request is that the proposed alternative would provide an acceptable level of quality and safety.
In accordance with IWL-2420, Callaway Energy Center is required to examine and test the unbonded post-tensioning system every 5 years. Additionally, Table IWL-2500-1, Examination Category L-B, Items L2.10, L2.20, L2.30, L2.40, and L2.50 provide the examination requirements for the unbonded post-tensioning system. This relief request is proposing to extend the examination and testing interval for the unbonded post-tensioning system, including detailed visual examinations of concrete adjacent to tendon bearing plates from 5 years to 10 years. Specifically, a visual examination only will be performed of the concrete containment and the accessible steel hardware without tendon cover removal for the 40th year surveillance which is scheduled to be performed in the Fall of 2024 but is required to be completed no later than June 20, 2025. The 45th year surveillance is due to be performed at any time from June 20, 2028 to June 20, 2030 during the subsequent fourth interval.
The technical justification for the proposed alternative is described in the next section of this request and is based on the results obtained and documented during the post-tensioning system examinations performed at Callaway between 1985 and 2021.
Benefits from the proposed change include less exposure to industrial safety hazards for examination and test personnel and fewer undesired conditions for the unbonded post-tensioning system. Hazards and undesired conditions include:
- 1. Working with high levels of stored energy (i.e., tendons, pressurized containers/lines filled with grease, hydraulic equipment).
- 2. Working with solvents and hot petroleum products and their associated fumes.
- 3. Working at heights and working with heavy loads (test equipment).
- 4. Repetitive cycling and loading of the tendons (detensioning/tensioning).
- 5. Exposing tendon hardware to environmental conditions.
This request only applies to the post-tensioning system and the associated examinations that require close-in access of the tendon end anchorage areas. The visual examinations required by ASME Section XI Table IWL-2500-1, Examination Category L-A, which include examination of the exposed areas of the containment concrete surface and the tendon end caps, will continue to be performed at 5-year intervals.
to 10 CFR 50.55a Request Number C3R-01 ULNRC-06831 Page 3 of 5
5. Proposed Alternative and Basis for Use
As an alternative, the below is proposed in lieu of the ASME Section XI, Subsection IWL examination and testing frequency requirements for the unbonded post-tensioning system:
Extend the interval between post-tensioning system examinations and tests, including detailed visual examinations of concrete adjacent to tendon bearing plates from 5 years to 10 years. Specifically, a visual examination only will be performed of the concrete containment and the accessible steel hardware without tendon cover removal for the 40th year surveillance which is scheduled to be performed in the Fall of 2024 but is required to be completed no later than June 20, 2025. Additionally, physical testing would only be performed if visual examination results indicate a need for such testing as determined by the Responsible Engineer (IWL-2330). Example conditions that could require removal of the tendon end cap and further examination per Item Numbers L2.10, L2.20, L2.30, L2.40, and L2.50 are:
Evidence of possible damage to the enclosed post-tensioning hardware as indicated by conditions such as end cap deformation found during external visual examination. Conditions observed by removal of the end cap would determine the extent of additional examinations per L2.10, L2.20, L2.30, L2.40, or L2.50.
Active corrosion on a bearing plate or end cap that requires further investigation as determined by the Responsible Engineer in an engineering evaluation.
Evidence of gross leakage of corrosion protection medium will be evaluated and a plan developed for corrective actions as defined in an engineering evaluation documented by the Responsible Engineer.
Justification:
The results of the 9 post-tensioning system in-service examinations conducted at Callaway between 1985 and 2021 show that the system is continuing to perform its intended function and that it can be expected to do so until well past the June 20, 2030 completion deadline of the 45th year surveillance. Performance of the unbonded post-tensioning system is summarized below. Additionally, a detailed evaluation of previous visual examination findings / test results is contained in a technical report provided in Enclosure 2.
a) Tendon Force The mean force in each of the tendon groups is projected by log-linear regression, and 95% confidence limit computations have shown that it will (for each group) remain above the specified minimum until well after the proposed June 20, 2030 completion deadline of the 45th year surveillance.
b) Condition of End Anchorage Hardware and Extracted Wires End anchorage hardware and tendon wires extracted for tensile testing show no signs of damage or active corrosion. Corrosion that has been observed is concluded to have occurred prior to filling of the tensioned tendon duct with corrosion protection medium.
The small number of missing buttonheads documented in the surveillance reports represents an inconsequential (and acceptable) fraction of the total. Occasional to 10 CFR 50.55a Request Number C3R-01 ULNRC-06831 Page 4 of 5 buttonhead loss is normal for BBRV1 tendons (wires anchored by cold formed buttonheads) and generally occurs during or shortly after tensioning. Nothing in the surveillance reports indicates that the number of missing buttonheads is increasing over time. Additionally, no free water has been found at tendon anchorages.
c) Tendon Wire Strength and Ductility Most tensile tests on samples cut from extracted wires show that yield strength, ultimate tensile strength and elongation at failure are essentially the same as those found during material certification testing in the late 1970s. With the exception of the low tensile strengths reported for the wire extracted from tendon V39 during the 35th year surveillance, test results not meeting acceptance criteria are concluded to be due to deficiencies in testing techniques. The low tensile strength reported for the V39 wire is considered to be a unique condition. There is nothing in the test data to suggest that either yield strength, tensile strength or ductility degrade with time under load.
d) Corrosion Protection Medium Characteristics Results of corrosion protection medium (CPM) tests to determine absorbed water content, corrosive ion concentrations and neutralization number confirm that acceptance criteria (with one exception) have been met. In particular:
o All corrosive ion concentrations are below the 10-ppm upper limit, and most are below the indicated limit of resolution applicable to the ion. Maximum concentrations of chloride, nitrate and sulfide ions are 0.5022, 2.84 and 0.5020, respectively. Ion concentrations show no trend of increasing over time.
o Neutralization numbers are, with one exception, acceptable. The single exception is a 16.8 base number (vs. a 17.5 lower acceptance limit) reported for one 15th surveillance year sample. While trends of the mean and minimum base number values show a slow decrease with time, these are projected to remain above the 17.5 lower limit until well after the June 20, 2030 completion deadline of the 45th surveillance.
o All reported absorbed water content values are below the 10% (of dry weight) upper limit; the maximum reported value is 0.58%. Water content shows no trend of increasing with time.
6. Duration of Proposed Alternative
This relief request will remain in effect for the 40th year surveillance and through the remainder of the current third interval of Callaway's Containment Exterior Concrete and Tendon Inspection Program which is scheduled to end on September 8, 2026.
7. Precedents
Letter from M. Markley (U.S. Nuclear Regulatory Commission) to C. Gayheart (Southern Nuclear Operating Co., Inc.), "Vogtle Electric Generating Plant, Units 1 and 2 - Inservice Inspection Alternative VEGP-ISI-ALT-19-01 For Containment Tendon Inservice Inspection Extension (EPID No. L-2019-LLR-0017)," dated July 11, 2019 (ML19182A077) 1 The BBRV system, which uses cold formed buttonheads to anchor individual wires, was introduced by the Swiss engineering firm BBR in 1944.
to 10 CFR 50.55a Request Number C3R-01 ULNRC-06831 Page 5 of 5 Letter from J. Danna (U.S. Nuclear Regulatory Commission) to B. Hanson (Exelon Generation Company, LLC), "Three Mile Island Nuclear Station, Unit 1 - Relief From the Requirements of the American Society of Mechanical Engineers Code RE: Examination and Testing for Containment Unbonded Post-Tensioning System (EPID L-2018-LLR-0132)," dated September 19, 2019 (ML19226A023)
Letter from J. Danna (U.S. Nuclear Regulatory Commission) to D. Stoddard (Dominion Energy Nuclear Connecticut, Inc.), "Millstone Power Station, Unit No. 2 - Proposed Alternative RR 05 to the Requirements of the ASME Code Re: Containment Unbonded Post-Tensioning System Inservice Inspection Requirements (EPID L-2019-LLR-0120)," dated October 20, 2020 (ML20287A471)
Letter from N. Salgado (U.S. Nuclear Regulatory Commission) to D. Rhoades (Exelon Generation Company, LLC), "Braidwood Station, Units 1 and 2 and Byron Station, Unit Nos. 1 and 2 - Proposed Alternative to the Requirements of the American Society of Mechanical Engineers Boiler & Pressure Vessel Code (EPIDS L-2020-LLR-0099 and L-2020-LLR-0100)," dated August 3, 2021 (ML21134A006)
Letter from J. Danna (U.S. Nuclear Regulatory Commission) to D. Rhoades (Exelon Generation Company, LLC), "Calvert Cliffs Nuclear Power Plant, Units 1 and 2 -
Alternative to the Requirements of the ASME Section XI, Subsection IWL Concerning Unbound Post-Tensioning Systems (EPID L-2020-LLR-0135)," dated September 2, 2021 (ML21190A004)
Letter from J. Dixon-Herrity (U.S. Nuclear Regulatory Commission) to M. Lacal (Arizona Public Service Company), "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)," dated May 12, 2022 (ML22124A241)