CNL-18-102, Response to Request for Additional Information Regarding Application to Modify Watts Bar Nuclear Plant Unit 1 Technical Specifications to Extend Surveillance Requirement 3.3.1.5, 3.3.2.2, and 3.3.6.2 Specified .
| ML18206A416 | |
| Person / Time | |
|---|---|
| Site: | Watts Bar  |
| Issue date: | 07/24/2018 |
| From: | Henderson E Tennessee Valley Authority |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| CNL-18-102, EPID L-2018-LLA-0187 | |
| Download: ML18206A416 (5) | |
Text
Tennessee Valley Authority, 1101 Market Street, Chattanooga, Tennessee 37402 CNL-18-102 July 24, 2018 10 CFR 50.90 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D.C. 20555-0001 Watts Bar Nuclear Plant, Unit 1 Facility Operating License No. NPF-90 NRC Docket No. 50-390
Subject:
Response to Request for Additional Information Regarding Application to Modify Watts Bar Nuclear Plant Unit 1 Technical Specifications to Extend Surveillance Requirement 3.3.1.5, 3.3.2.2, and 3.3.6.2 Specified Intervals (390-WBN-TS-2018-14) (EPID L-2018-LLA-0187)
References:
- 1. TVA Letter to NRC, Application to Modify Watts Bar Nuclear Plant Unit 1 Technical Specifications to Extend Surveillance Requirement 3.3.1.5, 3.3.2.2, and 3.3.6.2 Specified Intervals (390-WBN-TS-2018-14), dated July 8, 2018 (ML18189A001)
- 2. NRC Electronic Mail to TVA, Request for Additional Information Regarding Watts Bar Unit 1 Extension of Surveillance Requirement Intervals (EPID L-2018-LLA-0187), dated July 18, 2018 (ML18199A182)
In Reference 1, Tennessee Valley Authority (TVA) submitted an expedited request for an amendment to Facility Operating License No. NPF-90 for Watts Bar Nuclear Plant (WBN)
Unit 1. This expedited license amendment request (LAR) requested Nuclear Regulatory Commission (NRC) approval of a modification to WBN Unit 1 Technical Specification (TS)
Surveillance Requirement (SR) 3.0.2 and Table SR 3.0.2-1 to permit the extension of certain functions associated with SRs 3.3.1.5, 3.3.2.2, and 3.3.6.2 to no later than October 1, 2018, in order that these SRs can be performed during the WBN U1R15 outage, scheduled to commence in September 2018. The SRs for which an extension is requested are currently due to be completed no later than August 17, 2018. The reason for this SR extension request was due to an anomaly in the solid state protection system (SSPS) Train B test circuitry.
U.S. Nuclear Regulatory Commission CNL-18-102 Page 2 July 24, 2018 In Reference 2, the NRC transmitted a request for additional information (RAI) and requested a response by July 24, 2018. The enclosure to this letter provides the TVA response to the RAI.
As noted in Reference 1, TVA requests approval of the expedited LAR by August 16, 2018, and that the implementation of the revised TS be effective immediately to avoid an unnecessary operational transient to initiate a plant shutdown.
Consistent with the standards set forth in 10 CFR 50.92(c), TVA has determined that the additional information, as provided in this letter, does not affect the no significant hazards determination associated with the request provided in Reference 2.
There are no new regulatory commitments associated with this submittal. Please address any questions regarding this request to Ed Schrull at 423-751-3850.
I declare under penalty of perjury that the foregoing is true and correct. Executed on this 24th day of July 2018.
Respectfully, Signed by: E. K. Henderson Erin K. Henderson Director, Nuclear Regulatory Affairs
Enclosure:
Response to Request for Additional Information Regarding Application to Modify Watts Bar Nuclear Plant Unit 1 Technical Specifications to Extend Surveillance Requirement 3.3.1.5, 3.3.2.2, and 3.3.6.2 Specified Intervals (390-WBN-TS-2018-14) (EPID L-2018-LLA-0187) cc (Enclosure):
NRC Regional Administrator - Region II NRC Senior Resident Inspector - Watts Bar Nuclear Plant NRC Project Manager - Watts Bar Nuclear Plant Director, Division of Radiological Health - Tennessee State Department of Environment and Conservation
Enclosure CNL-18-102 E1 of 3 Response to Request for Additional Information Regarding Application to Modify Watts Bar Nuclear Plant Unit 1 Technical Specifications to Extend Surveillance Requirement 3.3.1.5, 3.3.2.2, and 3.3.6.2 Specified Intervals (390-WBN-TS-2018-14)
Nuclear Regulatory Commission (NRC) Introduction The regulatory requirements and guidance which the U.S. Nuclear Regulatory Commission (NRC) staff is considering in its review of the application include the following:
Title 10 of the Code of Federal Regulations (10 CFR) Part 50 establishes the fundamental regulatory requirements with respect to the domestic licensing of nuclear production and utilization facilities. Specifically, Appendix A, General Design Criteria for Nuclear Power Plants, to 10 CFR Part 50 provides, in part, the necessary design, fabrication, construction, testing, and performance requirements for structures, systems, and components important to safety.
GDC 21, "Protection System Reliability and Testability," requires that the system be designed for high functional reliability and in service testability, with redundancy and independence sufficient to preclude loss of the protection function from a single failure and preservation of minimum redundancy despite removal from service of any component or channel.
GDC 22, "Protection System Independence," requires that the system be designed so that natural phenomena, operating, maintenance, testing and postulated accident conditions do not result in loss of the protection function.
In order to complete its evaluation for acceptability of extension of surveillance requirement interval for reactor trip system and engineered safety feature actuation system safety functions, the NRC staff will need to verify the basis for the licensees determination that the existing fault is limited to the SSPS Train B test circuitry and does not affect the functionality of the associated safety systems. Though past performance history data was provided by TVA, the NRC staff notes that this performance is based on a period of operation during which the current anomaly (fault) was not present. Once the NRC staff confirms the basis for system operability, an evaluation of the effects of continued operation during the extended surveillance period will be performed.
NRC RAI-1 The licensee stated in its LAR that troubleshooting, post maintenance testing, an independent Westinghouse review, and engineering judgement were used to determine that the cause of the unexpected opening of reactor trip breaker (RTB) B was an anomaly associated with the solid state protection system (SSPS) Train B test circuitry when aligned to the intermediate range trip circuits of the universal logic board. However, no documentation of the specific results of these troubleshooting activities was provided, nor was there any technical description regarding how it was concluded that the problem has been isolated to within the test portion of the circuitry. The NRC staff requests the licensee submit additional information on the specific results of the aforementioned activities. This information will be used as a basis for the staff being able to have reasonable assurance that the operability determination was properly made.
Enclosure CNL-18-102 E2 of 3 TVA Response to RAI-1 Following the performance of Surveillance Instruction (SI) 1-SI-99-10-B on June 13, 2018, TVA performed an operability determination in accordance with TVA procedure NEDP-22, Operability Determinations and Functional Evaluations. The operability determination took into account the work order that performed the SI and the post maintenance testing (PMT) that was performed to verify logic operability. A copy of the operability determination and the associated work order (including the troubleshooting and the PMT) have been provided to the NRC for their review. As noted in the operability determination, SSPS Train B can perform its required safety function. The testing circuitry of SSPS Train B specific to the intermediate range is degraded/non conforming and is the most probable cause of the spurious opening of RTB B when aligning the intermediate range channels to test.
As noted in the below response to NRC RAI-2, the entire SI was not able to be performed; therefore, the Surveillance Requirements (SRs), for which an extension is requested, were not completed in their entirety.
NRC RAI-2 Section 2.3 of the LAR states that conditions which result in a spurious RTB B opening are repeatable and are present only when test switches are aligned to perform testing of the intermediate range trip functions. The LAR also states; Testing was performed that verified all logic functions work as designed, indicating that SSPS Train B is capable of performing its safety function. If trip functions can be verified in this manner, then it is unclear why extension of surveillance test interval is needed for functions that are not impacted by the spurious failure (i.e. functions not related to intermediate range requirements). The NRC staff requests the licensee submit explain why tests of safety functions cannot be performed within the required surveillance interval.
TVA Response to RAI-2 Upon identification of the unexpected tripping of RTB B, surveillance testing was stopped and a troubleshooting plan was developed. During troubleshooting, two universal cards were replaced and an undervoltage driver board was reseated. Further troubleshooting concluded that the problem was not associated with either of the replaced boards or the reseated board. After the troubleshooting concluded, the PMT was performed to verify logic operability. The PMT included a portion of SI 1-SI-99-10-B, however the entire SI was not performed. Therefore, although the logic was verified to work as designed, the SRs, for which an extension is requested, were not completed in their entirety. As noted in the response to RAI-1, a copy of the work order that documented the performance of 1-SI-99-10-B and the PMT have been provided to the NRC for their review. See the response to RAI-3 regarding the risk associated with the unknown failure mechanism associated with the testing circuitry.
Enclosure CNL-18-102 E3 of 3 NRC RAI-3 The LAR states that the risk associated with performing the repairs of the test circuitry and completing the SI while at power or continuing troubleshooting and testing, is deemed unacceptable. To complete its evaluation of the requested surveillance extension, the NRC staff must review and evaluate the risks associated with test performance and compare them with the risks associated with extending the surveillance intervals. To support this evaluation, the NRC staff requests the licensee to submit additional information pertaining to qualitative and quantitative risk assessment related to performing surveillance testing.
TVA Response to RAI-3 As noted in Section 3.2.2 of the referenced License Amendment Request, TVA evaluated four alternatives for addressing the inability to perform the SSPS Train B automatic logic surveillances due a faulty test circuitry. This evaluation was based on a decision risk matrix performed in accordance with TVA procedure OPDP-11, Operational Decision-Making Issue Evaluation Process. The decision risk matrix was used to assist in evaluating the risk associated with various decision options. The risk matrix took into account the following considerations:
x Nuclear safety/risk x
Personnel industrial safety x
Radiological safety (dose) x Impact on safety culture x
Operations distraction x
Potential to cause more damage x
Reliability x
Generation availability x
Schedule impact The decision risk matrix that was performed for the SSPS test circuitry determined that extending the requested SRs until the next WBN Unit 1 refueling outage, unless WBN Unit 1 enters Mode 5 before then, and subsequently performing the troubleshooting and repairs to the SSPS Train B test circuitry, poses the least amount of risk to the unit when compared to the other options evaluated such as performing further troubleshooting and repairs while at power or immediately transitioning the unit to Mode 5 to perform the troubleshooting and repairs. A copy of the decision risk matrix has been provided to NRC for review. Due to the unknown failure mechanism associated with the testing circuitry, there is risk associated with aligning an unknown failure mechanism in the test circuity to fully functional logic trip functions, which would be required to complete the testing, thereby providing a risk to the site for a potential unplanned entry into a Technical Specification shutdown required action.
Reference TVA Letter to NRC, Application to Modify Watts Bar Nuclear Plant Unit 1 Technical Specifications to Extend Surveillance Requirement 3.3.1.5, 3.3.2.2, and 3.3.6.2 Specified Intervals (390-WBN-TS-2018-14), dated July 8, 2018 (ML18189A001)