ET 22-0002, Operating Corp 10 CFR 50.55a Request Number I4R-08 for the Fourth Inservice Inspection Program Interval, Relief for Extension of Follow Up Examination and Visual Examination Requirements for Reactor Pressure Vessel Head .
| ML22095A252 | |
| Person / Time | |
|---|---|
| Site: | Wolf Creek  |
| Issue date: | 04/04/2022 |
| From: | Boyce M Wolf Creek |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| ET 22-0002 | |
| Download: ML22095A252 (6) | |
Text
P.O. Box 411 l Burlington, KS 66839 l 620-364-8831 Michael T. Boyce Vice President Engineering April 4, 2022 ET 22-0002 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555 - 0001
Subject:
Docket No. 50-482: 10 CFR 50.55a Request Number I4R-08 for the Fourth Inservice Inspection Program Interval, Relief for Extension of Follow up Examination and Visual Examination Requirements for Reactor Pressure Vessel Head Penetration Nozzles with Mitigated Alloy 600/82/182 Peened Surface Commissioners and Staff:
Pursuant to 10 CFR 50.55a(z)(1), Wolf Creek Nuclear Operating Corporation (WCNOC) hereby requests Nuclear Regulatory Commission (NRC) approval of 10 CFR 50.55a Request Number I4R-08 for the fourth ten-year interval of WCNOCs Inservice Inspection (ISI) Program.
During Refueling Outage 24 (RF24), which occurred during Spring 2021, WCNOC implemented the Ultra High-Pressure Cavitation Peening (UHPCP) process on Reactor Pressure Vessel Head Penetration Nozzles (RPVHPNs) with Alloy 600/82/182 surfaces. In the Attachment to this submittal, WCNOC is requesting a change to the examination interval of the follow-up inspections for peened RPVHPNs and associated welds, as well as allowing relief for visual examinations on RPVHPNs during the outages when volumetric examination is performed.
WCNOC requests approval by March 1, 2023, to allow for planning RF26 (Spring 2024) and RF27 (Fall 2025).
This letter contains no commitments. If you have any questions concerning this matter, please contact me at (620) 364-8831 X8687, or Ron Benham at (620) 364-4204.
Sincerely, Michael T. Boyce MTB/rlt
ET 22-0002 Page 2 of 2
Attachment:
10 CFR 50.55a Request I4R-08 cc:
S. S. Lee (NRC), w/a S. A. Morris, (NRC), w/a G. E. Werner (NRC), w/a Senior Resident Inspector (NRC), w/a
Attachment to ET 22-0002 Page 1 of 4 Wolf Creek Nuclear Operating Corporation 10 CFR 50.55a Request I4R-08 Request for Relief for Extension of Follow up Examination and Visual Examination Requirements for Reactor Pressure Vessel Head Penetration Nozzles with Mitigated Alloy 600/82/182 Peened Surface in Accordance with 10 CFR 50.55a(z)(1)
Attachment to ET 22-0002 Page 2 of 4 10 CFR 50.55a Request Number I4R-08 Request for Relief for Extension of Follow up Examination and Visual Examination Requirements for Reactor Pressure Vessel Head Penetration Nozzles with Mitigated Alloy 600/82/182 Peened Surface in Accordance with 10 CFR 50.55a(z)(1)
Alternative Provides Acceptable Level of Quality and Safety
- 1. ASME Code Components Affected Component:
Reactor Vessel Closure Head (RVCH) Nozzles Code Class:
Class 1 Examination Category:
B-P Code Item Number:
B4.50 B4.60
==
Description:==
Control Rod Drive Mechanism (CRDM) Nozzles Core Exit Thermocouple Nozzle Assy (CETNA) Nozzles Head Vent Pipe Size:
4.00 Inch (Nominal Outside Diameter)
NPS 1 inch schedule 160 pipe Material:
RVCH SA533 Grade B, Class 1 Nozzle SB 167 N06600 (Alloy 600)
Alloy 82/182 weld material
2. Applicable Code Edition and Addenda
American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code)
Section XI, 2007 Edition through 2008 Addenda ASME Code Case N-729-6 as conditioned by 10 CFR 50.55a(g)(6)(ii)(D)
3. Applicable Code Requirement
10 CFR 50.55a(g)(6)(ii)(D)(1) requires that examinations of the reactor vessel head be performed in accordance with ASME Code Case N-729-6 subject to the conditions specified in paragraphs 10 CFR 50.55a(g)(6)(ii)(D)(2) through (8).
10 CFR 50.55a(g)(6)(ii)(D)(5) states the following:
Peening. In lieu of the inspection requirements of Table 1, Items B4.50 and B4.60, and all other requirements in ASME BPV Code Case N-729-6 pertaining to peening, in order for a RPV upper head with nozzles and associated with J-groove welds mitigated by peening to obtain examination relief from the requirements of Table 1 for unmitigated heads, peening must meet the performance criteria, qualification, and examination requirements stated in MRP-335, Revision 3-A, with the exception that a plant specific alternative request is not required and the NRC condition 5.4 of MRP-335, Revision 3-A does not apply.
Attachment to ET 22-0002 Page 3 of 4 MRP-335, Revision 3-A requires a follow-up examination to be performed in the second refueling outage subsequent to peening for plants with heads that the reactor pressure vessel head penetration nozzles (RPVHPNs) and associated J-groove welds have experienced effective degradation years (EDY) < 8, and are free of pre-peening flaws. MRP-335, Revision 3-A also requires a bare metal visual examination (VE) to be performed every refueling outage.
4. Reason for Request
Wolf Creek Nuclear Operating Corporation (WCNOC) performed peening on the RPVHPNs and associated J-groove welds in Refueling Outage 24 which occurred in Spring, 2021.
The warranty from the vendor that provided the peening service specifies that the follow-up inspection be conducted in the third refueling outage subsequent to the peening being performed, whereas MRP-335, Rev 3-A, Section 4.3 specifies the follow-up inspection two outages following peening. To perform inspections in both the second and third outage subsequent to the peening adds unnecessary dose and expense to the refueling outage.
Performance of the follow-up examinations in two separate outages results in hardships that are not compensated by a corresponding increase in safety or quality. Additionally, combining the two inspections to one inspection as proposed would reduce entries into a Locked High Radiation Area decreasing the potential for industrial safety issues and contamination exposure, A VE is performed each outage to detect leakage through the RPVHPNs. During outages when volumetric/surface exams are being conducted, a leak path assessment is performed which would make any leakage though the RPVHPNs evident. Performing a VE during outages when volumetric/surface examinations are being performed also adds unnecessary dose and expense to the refueling outage.
5. Proposed Alternative and Basis for Use
The peening process performed at Wolf Creek Generating Station (WCGS) on RPVHPNs met all requirements including performance criteria, mitigation process criteria, examination criteria, adverse effects criteria and inspectability criteria as required by Appendix II of Code Case N-729-6. The subject RPVHPNs and associated J-groove welds have experienced EDY
< 8 and were free of pre-peening flaws. MRP-335, Revision 3-A, Section 4.3 requires a follow-up inspection in the second refueling outage subsequent to peening for these components.
On the contrary, item B4.20 of Table 1 of Code Case N-729-6, the volumetric or surface exam frequency is 8 calendar years or before reinspection years (RIY) = 2.25, whichever is less.
WCNOC proposes to perform the MRP-335, Revision 3-A follow-up inspection in the third refueling outage subsequent to peening to align with the post-peening warranty follow-up inspection requirements.
The pre-peening baseline inspection was conducted prior to the peening being performed in the same outage. As allowed by MRP-335, Revision 3-A, the pre-peening baseline inspection was performed by an ultrasonic examination of the nozzle tube and a demonstrated ultrasonic leak path assessment. It is possible that a flaw (crack) existed in the J-groove weld that was outside of the examination boundary.
Attachment to ET 22-0002 Page 4 of 4 The purpose of the follow-up inspection is to detect flaws in the J-groove weld (that were outside the detectable range during the pre-peening baseline inspection) that have grown through wall or into the nozzle tube. Performing the follow-up inspection in the third refueling outage subsequent to peening will allow one extra cycle for any undetected flaws (that may have been present at the time of peening) to grow into the region where they would be detected. Performing the follow-up inspection in the third outage subsequent to peening will still fall within the schedule of Code Case N-729-6, since it is within 8 years and RIY < 2.25 for unmitigated Alloy 600 components on RPV upper heads, which ensures adequate safety margin is maintained.
Furthermore, WCGS Technical Specification (TS) 3.4.13 requires operational leakage monitoring, which includes containment sump monitoring and containment atmosphere radioactivity monitoring (TS 3.4.15). Moreover, the plant will continue to perform bare metal VEs as required by MRP-335 Rev 3A, except in outages where volumetric/surface examinations are being performed, as proposed below. These tools would provide reasonable assurance of structural integrity over the inspection extension period. In addition, if any leakage is identified, the nozzle would be required to be repaired by the plant and would not impact the basis of this technical analysis.
Lastly, WCNOC proposes to perform a VE of each RPVHPN for evidence of pressure boundary leakage every refueling outage unless volumetric/surface examinations are being performed. The leak path assessment performed during the volumetric/surface examinations will make any leakage through the RPVHPNs evident.
6. Duration of Proposed Alternative
The proposed alternative will be utilized to perform the follow-up inspection in WCNOC Refueling Outage 27 (Fall 2025) instead of Refueling Outage 26 (Spring 2024). WCNOC will assume the inspection schedule required by MRP-335, Revision 3-A with the conditions of 10 CFR 50.55a following Refueling Outage 27.
- 7. References
- 1. ASME Boiler and Pressure Vessel Code Case N-729-6 Alternative Examination Requirements for PWR Reactor Vessel Upper Heads With Nozzles Having Pressure-Retaining Partial-Penetration WeldsSection XI, Division 1
- 2. Electric Power Research Institute Topical Report MRP-335, Revision 3-A, dated November 2016