ML25352A142
| ML25352A142 | |
| Person / Time | |
|---|---|
| Site: | Davis Besse  |
| Issue date: | 12/18/2025 |
| From: | Robert Kuntz NRC/NRR/DORL/LPL3 |
| To: | Vistra Corp, Vistra Operations Company |
| References | |
| EPID L-2025-LLA-0159 | |
| Download: ML25352A142 (0) | |
Text
1 REQUEST FOR ADDITIONAL INFORMATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION
((FUR))DAVIS BESSE CHANGE TO TS 3.8.1 ACTION A.3 COMPLETION TIME ENERGY HARBOR NUCLEAR GENERATION LLC DAVIS-BESSE, UNIT 1 DOCKET NO. 05000346 Regulatory Basis Title 10 of the Code of Federal Regulations (10 CFR) Part 50, Appendix A, General Design Criterion (GDC) 17 requires, in part, that an onsite and offsite electric power system shall be provided to permit functioning of structures, systems, and components important to safety and shall provide sufficient capacity and capability. Regulatory Guide 1.93, Availability of Electric Power Sources, (Agencywide Documents Access and Management System (ADAMS)
Accession No. ML090550661) and BTP 8-8, Onsite (Emergency Diesel Generators) and Offsite Power Sources Allowed Outage Time Extensions, (ML113640138) provide guidance that support compliance with GDC 17. Regulatory Guide 1.93describes guidelines when the number of available electric power sources are less than the number of sources required by the limiting conditions for operation (LCOs) for a facility. Branch Technical Position (BTP) 8-8provides guidance from a deterministic perspective, including defense-in-depth aspects, for one-time or permanent allowed outage time (AOT) extensions for the emergency diesel generators (EDGs) and offsite power sources from the current AOT up to 14 days.
10 CFR 50.36(c)(2) requires that technical specifications (TSs) include Limiting Condition for Operation (LCOs). Per 10 CFR 50.36(c)(2)(i), LCOs are the lowest functional capability or performance levels of equipment required for safe operation of the facility. The regulation also requires that when an LCO of a nuclear reactor is not met, the licensee shall shut down the reactor or follow any remedial action permitted by the TS until the condition can be met.
Question 1 BTP 8-8 provides guidance from a deterministic perspective, including defense-in-depth aspects, for one-time or permanent AOT extensions for the EDGs and offsite power sources from the current AOT up to 14 days.
BTP 8-8, in section B, states, in part, that:
A supplemental power source should be available as a backup to the inoperable EDG or offsite power source, to maintain the defense-in-depth design philosophy of the electrical system to meet its intended safety function. The supplemental source must have capacity to bring a unit to safe shutdown (cold shutdown) in case of a loss of offsite power (LOOP) concurrent with a single failure during plant operation (Mode 1)..
The permanent or temporary power source can be either a diesel generator, gas or combustion turbine, or power from nearby hydro units.
Confirm that the SBODG will be employed as a supplemental power source and discuss conformance to BTP 8-8. If the SBODG does not conform to BTP8-8, please provide justification as to why conformance to BTP 8-8 is not needed..
2 Question 2 BTP 8-8 further states that the availability of the alternate AC (AAC) source should be verified within the last 30 days before entering extended AOT by operating or bringing the power source to its rated voltage and frequency for 5 minutes and ensuring all its auxiliary support systems are available or operational. LAR section 3.2 states that the SBODG will be demonstrated functional by verifying its periodic test is current prior to the start of the extended 15-day CT.
Will verification of the periodic testing of the SBODG meet the guidance in BTP for testing the availability of the AAC? If not, describe how reliance on the periodic testing will adequately demonstrate the availability of the SBODG as the AAC. If additional testing is needed to ensure availability of the SBODG as the AAC will this additional testing be included as compensatory measures?
Question 3 BTP 8-8 states that the plant should have formal engineering calculations for equipment sizing and protection and have approved procedures for connecting the AAC or supplemental power sources to safety buses.
- 1) Discuss or provide a summary of the calculations for equipment sizing and protection and 2) describe the approved procedures for connecting the SBODG.
Question 4 BTP 8-8 states that the AOT should be limited to 14 days and the licensee must provide justification for the duration of the requested AOT (actual hours plus margin based on plant-specific past operating experience). LAR section 2.3 states that the 13 days provides the duration necessary to restore the X02 transformer tap changer, including two days for replacement of the transformer bushings, for a total of 15 days.
Discuss the specific tasks and duration of the tasks for an extended CT duration of 15 days.
Provide the justification of the duration of the extended CT (i.e., based on operating experience, etc.).
Question 5 BTP 8-8 provides guidance that 1) the availability of the AAC shall be checked every 8-12 hours (once per shift), 2) if the AAC becomes unavailable any time during the extended AOT, the unit shall enter the LCO and start shutting down within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />, 3) preplanned maintenance will not be scheduled if severe weather conditions are anticipated, and 4) no discretionary switchyard maintenance will be performed.
Provide justification for why the above items are not needed or add them to the compensatory measures. Confirm that the remaining operable offsite circuit through transformer X01 is protected.
3 Question 6 10 CFR 50.36(c)(2) requires that TSs include Limiting Condition for Operation (LCOs). Per 10 CFR 50.36(c)(2)(i), LCOs are the lowest functional capability or performance levels of equipment required for safe operation of the facility. The regulation also requires that when an LCO of a nuclear reactor is not met, the licensee shall shut down the reactor or follow any remedial action permitted by the TS until the condition can be met.
The NRC staff noted that the Davis-Besse markup TS page (Attachment 2 to the LAR) is missing some information and requirements. The current proposed changes appear to have potential for misinterpretation by licensee operators.
Justify how the proposed TS provides assurance that the specification would not be misinterpreted or revise the proposed Davis-Besse TS 3.8.1 Required Action A.3 marked-up pages, as needed, to have an appropriate amount of detail and include the following elements:
- 1. An expiration date for using the extended CT;
- 2. Limit one-time use of the 15-day CT to specific equipment, regardless of whether maintenance is completed during the attempt;
- 3. Specify applicable equipment by designation (e.g., transformer X02) - one option is to add the requirement into the compensatory measures list;
- 4. Conditions for when the offsite circuit CT extension is applicable, (e.g., startup transformer repairs);
- 5. Remedial actions for compensatory measure equipment if discovered unavailable during the maintenance evolution (e.g., restore to available status within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />); and
- 6. In TS 3.8.1 Required Action A.3, reference the document that contains the list of all risk management actions and compensatory measures; (i.e., Vistra OpCo letter).
An effective option is to place an asterisk at the existing CT and create a footnote with the details at the bottom of the TS page.