ML22293A408
| ML22293A408 | |
| Person / Time | |
|---|---|
| Site: | Watts Bar  |
| Issue date: | 11/14/2022 |
| From: | David Wrona Plant Licensing Branch II |
| To: | Jim Barstow Tennessee Valley Authority |
| Green K | |
| References | |
| EPID L-2022-LLL-0000 | |
| Download: ML22293A408 (6) | |
Text
November 14, 2022 Mr. James Barstow Vice President, Nuclear Regulatory Affairs and Support Services Tennessee Valley Authority 1101 Market Street, LP 4A-C Chattanooga, TN 37402-2801
SUBJECT:
WATTS BAR NUCLEAR PLANT, UNIT 2 - REVISION TO THE REACTOR VESSEL MATERIAL SURVEILLANCE CAPSULE WITHDRAWAL SCHEDULE (EPID L-2022-LLL-0000)
Dear Mr. Barstow:
By letter dated January 24, 2022, the Tennessee Valley Authority (TVA) submitted a request for U.S. Nuclear Regulatory Commission (NRC) staff review and approval for a revision to the reactor vessel material surveillance capsule withdrawal schedule for Watts Bar Nuclear Plant, Unit 2. The revised schedule was submitted in accordance with Title 10 of the Code of Federal Regulations (10 CFR) Part 50, Appendix H, Reactor Vessel Material Surveillance Program Requirements, III.B.3.
The NRC staff has reviewed TVAs request and concludes, as set forth in the enclosed safety evaluation, that the modified surveillance capsule withdrawal schedule for Watts Bar Nuclear Plant, Unit 2, is acceptable for implementation and satisfies the requirements of Appendix H to 10 CFR Part 50 and American Society for Testing and Materials (ASTM) E185-82, Standard Practice for Conducting Surveillance Tests for Light-Water Cooled Nuclear Power Reactor Vessels.
Sincerely, David J. Wrona, Chief Plant Licensing Branch II-2 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-391
Enclosure:
Safety Evaluation cc: Listserv David J.
Wrona Digitally signed by David J. Wrona Date: 2022.11.14 15:45:36 -05'00'
Enclosure SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO REVISION TO REACTOR VESSEL SURVEILLANCE CAPSULE REMOVAL SCHEDULE FOR TENNESSEE VALLEY AUTHORITY WATTS BAR NUCLEAR PLANT, UNIT 2 DOCKET NO. 50-391
1.0 INTRODUCTION
By letter dated January 24, 2022 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML22024A450), the Tennessee Valley Authority (TVA or the licensee) submitted a request to the U.S. Nuclear Regulatory Commission (NRC or Commission) for review and approval of a revision to the surveillance capsule withdrawal schedule for the reactor vessel material surveillance program for Watts Bar Nuclear Plant (Watts Bar), Unit 2. The revised schedule was submitted in accordance with Title 10 of the Code of Federal Regulations (10 CFR) Part 50, Appendix H, Reactor Vessel Material Surveillance Program Requirements, III.B.3.
Capsule W was scheduled to be removed during the Watts Bar, Unit 2, Cycle 5 refueling outage (U2R5) scheduled for fall 2023. However, recent adjustments in lead factors, estimated effective full power years (EFPY) to attain target fluence, and a reconciliation of actual accrued EFPY to date has shown that U2R5 is too early to satisfy the irradiation requirements of section 7 of the American Society for Testing and Materials (ASTM) E185-82, Standard Practice for Conducting Surveillance Tests for Light-Water Cooled Nuclear Power Reactor Vessels. The licensee requested NRC staff approval to reschedule the withdrawal of Capsule W. Under the proposed revised withdrawal schedule, Capsule W should be withdrawn at the outage nearest to but following 7.0 EFPY of operation and an expected capsule neutron fluence 1.94x1019 neutrons per square centimeter (n/cm2).
The licensee stated that the current capsule removal schedule is based on WCAP-18191-NP, Revision 0, Watts Bar Unit 2 Heatup and Cooldown Limit Curves for Normal Operation and Supplemental Reactor Vessel Integrity Evaluations (ML17289A327), and ASTM E185-82. The proposed revisions to the withdrawal schedule for Capsule W are based on the results of testing the specimens in Capsule U, documented in WCAP-18518-NP, Revision 0, Analysis of Capsule U from the Watts Bar Unit 2 Reactor Vessel Radiation Surveillance Program (ML20107F717).
2.0 REGULATORY EVALUATION
Title 10 of the Code of Federal Regulations (10 CFR) Part 50, Appendix H, Reactor Vessel Material Surveillance Program Requirements, requires licensees to implement reactor vessel material surveillance programs to monitor changes in the fracture toughness properties of ferritic materials in the reactor vessel beltline region of light water nuclear power reactors which result from exposure of these materials to neutron irradiation and the thermal environment.
Plant-specific surveillance programs must be consistent with the guidance in ASTM Standard Practice E185. In the design of a plant-specific surveillance program, a licensee may use the edition of ASTM Standard Practice E185 that was current on the issue date of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code to which the reactor vessel was purchased, or later editions through the 1982 edition.
NRC Administrative Letter 97-04, NRC Staff Approval for Changes to 10 CFR Part 50, Appendix H, Reactor Vessel Surveillance Specimen Withdrawal Schedules, summarizes the Commission decision that a license amendment is not required if the proposed withdrawal schedule changes satisfy the guidance in ASTM E185-82. Conformance with the ASTM standard is discussed in section 3.0 of this safety evaluation.
Appendix H of 10 CFR Part 50 describes reactor vessel material surveillance program requirements. Paragraph (lll)(B)(3) requires that, a proposed withdrawal schedule must be submitted with a technical justification as specified in Section 50.4. The schedule must be approved prior to implementation.
3.0 TECHNICAL EVALUATION
3.1 Evaluation Criteria of ASTM Standard Practice E185-82 For Watts Bar, Unit 2, TVA is applying the guidance in ASTM E185-82 as its basis for meeting the reactor vessel surveillance capsule withdrawal requirements of 10 CFR Part 50, Appendix H. Table 1 of ASTM E185-82 recommends that a minimum of three, four, or five surveillance capsules be removed from the vessels, based on the limiting amount of RTNDT shift (limiting RTNDT) that is projected to occur at the clad-vessel interface location of the reactor vessel at the end-of-licensed plant life (EOL). ASTM E185-82 establishes the criteria for determining the minimum number of capsules that are to be removed in accordance with a withdrawal schedule and the number of capsules that are to be tested. For plants with projected RTNDT shifts (i.e., RTNDT) less than 100 degrees Fahrenheit (56 degrees Celsius), three capsules are to be removed from the reactor vessel, and at least the first two capsules are expected to be tested (for dosimetry, tensile-ductility, Charpy-V impact toughness, and alloying chemistry).
Table 1 of ASTM Standard Practice E185-82 also provides specific criteria for removal of surveillance capsules. The removal times are based on criteria that the surveillance capsules be removed after a certain amount of power operation has elapsed or at various times when the reactor vessel shell is projected to achieve certain levels of neutron fluence. The intent of the standard is to obtain a set of test data over a range of neutron fluences for the reactor vessel that bounds the current life of the plant. Of key importance are the removal criteria for the second-to-last and final capsules planned to be withdrawn. For the second-to-last capsule in a withdrawal schedule, the ASTM standard directs that the capsules be pulled at either 15 effective full-power years (EFPYs) or at the time when the capsule is equivalent to the limiting fluence projected for the clad-based metal interface of the RV at EOL, whichever time comes first. For the final capsule that is planned for removal, ASTM E185-82 recommends that the capsule be removed at a time when the neutron fluence projected for the capsule is between the limiting fluence value projected for the RV at the EOL and two times that value.
With respect to the current operating term, the Watts Bar Unit 2 RV has a limiting RTNDT value less than 100 degrees Fahrenheit (56 degrees Celsius). As stated above, since the RTNDT value is less than 100 degrees Fahrenheit, ASTM E185-82 recommends that the licensee, at a minimum, remove three capsules from the reactor during the current operating period and test the first two capsules. The licensee has already removed one capsule (Capsule U), and an additional two capsules will be removed, as specified by its proposed new withdrawal schedule.
This proposed schedule meets the guidance in ASTM E185-82 for the reactor vessel surveillance program for Watts Bar Unit 2, and is, therefore, acceptable to the NRC staff.
3.2 Staff Evaluation of Proposed Changes to the Withdrawal Schedule The current surveillance capsule withdrawal schedule, as approved by the NRC staff in a letter dated November 20, 2017 (ML17312A260), is contained in Table 4.0-1 of the Watts Bar, Unit 2, Pressure-Temperature Limits Report (ML20351A248), dated December 2020. The withdrawal schedule identifies the available specimen capsules as Capsule U, Capsule W, and Capsule X.
Three capsules are identified as standby capsules: Capsule Z, Capsule V and Capsule Y.
In the case of a three-capsule withdrawal schedule, as is the case for Watts Bar Unit 2, Table 1 of ASTM E185-82 recommends that the first capsule be scheduled for withdrawal at 6 EFPY or at the time when the accumulated neutron fluence of the capsule exceeds 0.50x1019 n/cm2, whichever comes first. The first capsule (Capsule U) was withdrawn at approximately 2 EFPY, when the fluence had reached 0.5x1019 n/cm2, in accordance with ASTM E185-82. Additionally, Table 1 recommends that the second capsule be scheduled for withdrawal at 15 EFPY or at a time when the accumulated neutron fluence of the capsule corresponds to the approximate EOL fluence at the reactor vessel inner wall location, whichever comes first. For Watts Bar, Unit 2, the fluence corresponding to the approximate EOL fluence at the reactor vessel inner wall location, which the licensee has calculated to be 1.94x1019 n/cm2, is projected to occur at 7 EFPY (as shown in WCAP-18518-NP, Table 7-1).
The licensee stated that, following the analysis of the first capsule withdrawn and tested (Capsule U), the lead factors for all the capsules were revised, and the expected neutron fluence for Capsule U was updated to the actual value. The projected EFPY and expected neutron fluence for the second and third capsules (Capsules W and X) have been revised, as well. In order to comply with ASTM E185-82, the licensee proposed that the withdrawal of the second capsule occur during the outage nearest to but following 7.0 EFPY of operation. At that time, the projected fluence at for Capsule W is expected to be 1.94x1019 n/cm2, and this value aligns with the target fluence recommended in the Table 1 of ASTM E185-82. The licensee also proposed an editorial change to remove a reference to the end of cycle 5 (i.e., EOC 5) for Capsule W because the withdrawal timing will be dictated by the accumulated fluence, rather than a specific refueling outage.
ASTM E185-82 recommends that the third capsule be removed at a time when the neutron fluence projected for the capsule is between the limiting fluence value projected for the RV at EOL but not greater than two times that value. This criterion will be met by Capsule X for the current operating term for Watts Bar, Unit 2; therefore, the NRC staff finds that the licensee meets ASTM E185-82 for its remaining capsules in its program.
The NRC staff finds the withdrawal schedule change for Capsule W, from EOC 5 to a time following 7.0 EFPY and an expected capsule neutron fluence of 1.94x1019 n/cm2 to be consistent with Table 1 of ASTM E185-82 for the second capsule in a three-capsule surveillance program. Likewise, the staff finds the withdrawal schedule change for Capsule X to a time between 7.0 and 13.7 EFPY and a fluence between 1.94x1019 and 3.88x1019 n/cm2, to be consistent with the ASTM E185-82 for the third capsule in a three-capsule surveillance program.
The licensee also proposed to designate Capsule Z as a backup to Capsule W, in the event that the originally planned capsule is unable to be withdrawn, stating that Capsule Z is radiologically identical to Capsule W. The NRC staff confirmed in the Watts Bar Dual-Unit Updated Final Safety Analysis Report (ML22152A097) that each of the six capsules contains multiple mechanical test specimens of the limiting base material, which for Watts Bar, Unit 2, is the reactor vessel intermediate forging.
The licensees radiation analysis noted that both Capsule W and Capsule Z were located 34.0° from the core cardinal axes in the octagonally-symmetric core (ML20107F717). The NRC staff noted that the capsules have had the same thermal exposure in the reactor, and they are estimated to have the same lead factors. As a result, Capsules W and Z may be considered radiologically equivalent, and Capsule Z may be substituted for Capsule W if necessary.
Thus, the staff finds the withdrawal schedule change for Capsule Z in lieu of Capsule W (i.e.,
serving as a backup capsule) during the same outage (i.e., 7 EFPY and an expected neutron fluence of 1.94E19 n/cm2), to also be consistent with the ASTM E185-82 for the second capsule in a three-capsule surveillance program.
4.0 CONCLUSION
The NRC staff has reviewed the proposed revisions to the Watts Bar, Unit 2 reactor vessel material surveillance capsule withdrawal schedule and concludes that it is acceptable because it is consistent with the requirements of Appendix H to 10 CFR Part 50 and with the recommendations in the standard ASTM E185-82. The staff also approves the designation of Capsule Z as a backup to Capsule W because the composition, thermal exposure, and projected neutron fluence for the two capsules are equivalent.
Principal Contributors: C. Moyer, NRR O. Yee, NRR Date: November 14, 2022
ML22293A408 OFFICE NRR/DORL/LPL2-2/PM NRR/DORL/LPL2-2/LA NRR/DNRL/NVIB/BC NRR/DORL/LPL2-2/BC NAME KGreen RButler ABuford DWrona DATE 10/18/22 10/21/22 10/06/22 11/14/2022