ML14056A525
| ML14056A525 | |
| Person / Time | |
|---|---|
| Site: | Watts Bar  |
| Issue date: | 02/26/2014 |
| From: | Andrew Hon Plant Licensing Branch II |
| To: | Schrull E, James Shea Tennessee Valley Authority |
| Andy Hon | |
| References | |
| TAC MF2549 | |
| Download: ML14056A525 (3) | |
Text
Chen, Qiao-Lynn From: Hon, Andrew Sent: Wednesday, February 26, 2014 3:52 PM To: 'Shea, Joseph W'; 'Schrull, Edward Dustin'; 'tahess@tva.gov' Cc: Regner, Lisa; Poole, Justin; Zimmerman, Jacob; Matharu, Gurcharan; Waig, Gerald
Subject:
Resend: Watts Bar Nuclear Plant, Unit 1 - Request for Additional Information Regarding Application To Modify Technical Specifications Related To AC Sources -Operating (TAC No. MF2549)-
ADAMSAccessionNumber: ML14056A525
Dear Mr. Shea:
By letter dated August 1, 2013 (Agencywide Documents Access and Management System (ADAMS)
Accession No. ML13220A103), Tennessee Valley Authority (the licensee) submitted a license amendment request (LAR) for revision to the Operating License for the Watts Bar Nuclear Plant, Unit 1. The proposed amendment would provide additional time to restore an inoperable offsite circuit and modify Surveillance Requirement (SR) 3.8.1.8, related to Technical Specification 3.8.1, "AC Sources- Operating."
The U.S. Nuclear Regulatory Commission (NRC) staff is reviewing your submittal and has determined that additional information is required to complete the review. The proposed questions below were discussed by telephone with your staff on February 25, 2014. Your staff confirmed that these questions did not include proprietary or security-related information that should be withheld from the public and agreed to provide a response in approximately 30 days from the date of this request for additional information (RAI).
BACKGROUND The current licensing basis of Watts Bar Unit 1 includes the capability to power each of the shutdown boards 1A-A and 18-B from common station service transformer (CSST) C and 0. For compliance with General Design Criterion (GOG) 17, each shutdown board has an immediately available normal source, CSST C for 1A-A and CSST D for 1B-B and an automatic transfer to the alternate source CSST 0 for 1A-A and CSST C for 1B-B. When Watts Bar Unit 2 is in commercial operation, the shutdown boards 2A-A and 2B-B will have similar configuration from CSST C and CSST D. The CSST C and D are each capable of powering shutdown loads during events such as:
a) Dual-unit trip as a result of an abnormal operational occurrence; b) Accident in one unit and concurrent shutdown of the second unit; c) Accident in one unit and spurious Engineered Safety Feature (ESF) actuation in the other unit.
The staff notes the following limitations for CSSTs A and B compared to CSSTs C and D:
a) CSSTs A and B are not automatically aligned to the shutdown busses.
b) CSSTs A and B do not have the capacity to supply loads on both units during limiting Design Basis Events.
c) CSSTs A and B cannot be aligned to more than one shutdown bus for dual unit shutdown.
RAI QUESTIONS
- 1. The LAR proposes to revise TS 3.8.1 and TS Bases 3.8.1 to add an allowance to use CSST A or 8 to meet the requirements of limiting conditions for operation (LCO) 3.8.1, with respect to qualified offsite 1
circuits that satisfy GDC 17 requirements and also change current licensing basis, as described in the UFSAR, to allow the use of CSST A and B as qualified sources of power. In addition to the differences in capabilities of transformers CSST A, B, C and D identified above, the LAR does not delineate the capability of offsite power through CSST A and B to be available in sufficient time following a loss of all onsite alternating current power supplies and the other offsite electric power circuit, to assure that specified acceptable fuel design limits and design conditions of the reactor coolant pressure boundary are not exceeded - a GDC 17 requirement. In view of these limitations, it appears that the proposed CSST A and B transformers may not satisfy the requirements for a 'qualified' power source as defined in GDC 17. If the intent of the LAR is to use transformers CSST A or Bas a temporary backup source of power for the shutdown busses and part of overall compensatory actions for the following conditions only, then the licensee is requested to provide the following supplemental information and TS markup for the staff's review:
- a. Transformer CSST C or D is removed from service for maintenance with one unit shutdown condition and the other unit in Mode 1,2,3 or 4, and
- b. Extend the Completion Time associated with TS LCO 3.8.1 Action A for CSST C or D to allow one qualified offsite circuit to be inoperable for up to 14 days for the operating unit.
- 2. The LAR proposes newTS SRs for transfers (automatic and manual to and from the maintenance feeds) associated with CSST A, 8 C and D. Please explain why the following manual transfers are not proposed as part of the SRs:
- a. The operation of breakers to complete the transfer of CSST A or B maintenance feed to the shutdown boards and energize the associated busses.
- b. The transfer of offsite power source from CSST A (or B) back to the corresponding GDC 17 qualified normal source through CSST C or D.
Please provide the appropriate TS Required Action(s), Note(s) or Completion Time(s) if the above actions were inadvertently omitted from the LAR.
- 3. Since the proposed offsite power sources through CSST A and B do not satisfy all the capabilities of the currently approved GDC 17 sources through CSST C and D, please identify all the compensatory measures that will be implemented as part of maintenance outages for CSST C and D. These actions should include as a minimum, verification of grid status, availability of all onsite AC and DC power sources, restriction of maintenance activities in switchyard and other onsite trip sensitive equipment, and no discretionary maintenance or testing allowed on the important to safety systems.
- 4. The staff is currently reviewing the degraded voltage relay (DVR) setpoint for the shutdown boards when supplied through the normal source using CSST C and D. Please verify that the DVR setpoint adequacy will be validated for shutdown boards when supplied through CSST A and 8 using the same methodology as approved for the normal source.
- 5. The LAR states that the CSST A orB will be used as an offsite power source during planned maintenance activities for CSST C or D. Please provide details on any equipment that may actuate, the procedures and time required to align the maintenance path to the shutdown boards for the operating unit(s) when CSST CorD is taken out of service. Include details on manual actions required in the event of a unit trip and transfer of plant busses from USST to CSST.
- 6. The LAR delineates conformance with requirements of GDC 17 and further states that the proposed amendment improves the ability of the plant to meet the design requirements for dual unit operation. The current TS allowed completion time (CT) is 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> when one offsite power source (through CSST C or D) is not available. The LAR proposes to extend the CT to 14 days if the CSST A (B) is available but not necessarily connected to the corresponding shutdown boards. Please provide the following additional information for the proposed extension period:
2
- a. Assuming both units operating in Mode 1, compare and contrast the consequences on dual unit operation, when supplied from normal sources CSST C and 0, or the proposed configuration during the 14 day extension period, when an accident signal in one unit requires dual unit shutdown. Provide details on the sequence of events that will assure that 'the preferred offsite power system is able to supply power within specified limits to components and systems required to ensure that fuel design limits and reactor coolant pressure boundary design conditions are not exceeded due to operational occurrences and the core is cooled and vital functions are maintained during postulated accidents in one unit while safely shutting down the other unit.'
- b. The LAR proposes full compliance with GOG 17 when either CSST A or B is aligned and connected to the associated shutdown boards. Assuming both units operating in Mode 1, CSST A or B is considered one of the GOG 17 sources and the auxiliary systems for both units are powered from the main generator, please provide details on all the proposed configurations of offsite power for the shutdown boards and the resultant sequence of events and final line up if an accident signal is generated at one unit requiring safe shutdown of both units.
- 7. The LAR proposes manual actions to align the maintenance feeders from CSST A or B to plant shutdown busses. Please confirm that the temporary configuration of securing breakers for CSST C or 0 and manually aligning breakers for CSST A or B will not preclude automatic actions associated with supplying power from onsite diesel generators during an emergency start.
The NRC staff considers that timely responses to RAis help ensure sufficient time is available for staff review and contribute toward the NRC's goal of efficient and effective use of staff resources. If circumstances result in the need to revise the requested response date, please contact me.
Accession No. ML14056A525 AndyHon, PE Project Manager (Watts Bar Nuclear Unit-1)
Plant Licensing Branch 11-2 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation 301-415-8480 OWFN08E5 Mail Stop 08G-9a andrew. hon@ nrc. gov 3