CNL-14-015, Response to NRC Request for Additional Information Related to Application to Modify Technical Specifications Regarding AC Sources - Operating (TS-WBN-13-02)

Response to NRC Request for Additional Information Related to Application to Modify Technical Specifications Regarding AC Sources - Operating (TS-WBN-13-02)

ML14112A341
Person / Time
Site:	Watts Bar
Issue date:	04/21/2014
From:	James Shea Tennessee Valley Authority
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
CNL-14-015, L44 140421 004, TS-WBN-13-02
Download: ML14112A341 (13)

Text

L44 140421 004 Tennessee Valley Authority, 1101 Market Street, Chattanooga, Tennessee 37402 CNL-14-015 April 21, 2014 10 CFR 50.4 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission 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 NRC Request for Additional Information Related to Application to Modify Watts Bar Nuclear Plant, Unit 1 Technical Specifications Regarding AC Sources - Operating (TS-WBN-13-02)

References:

1. Letter from TVA to NRC, Application to Modify Watts Bar Nuclear Plant, Unit 1 Technical Specifications Regarding AC Sources - Operating (TS-WBN-13-02), dated August 1, 2013 (TAC No. MF2549)

[ML13220A103]

2. Electronic Mail from Andrew Hon (NRC) to Joseph W. Shea (TVA),

Watts Bar Nuclear Station, Unit 1 - Request For Additional Information -

Regarding Application to Modify Watts Bar Nuclear Plant, Unit 1 Technical Specifications Related To AC Sources - Operating (TS-WBN-13-02), dated February 26, 2014 (TAC No. MF2549)

[ML4056A525]

By letter dated August 1, 2013 (Reference 1), the Tennessee Valley Authority (TVA) submitted a license amendment request (LAR) for Watts Bar Nuclear Plant (WBN), Unit 1.

The purpose of the LAR was to modify limiting condition of operation (LCO) for Technical Specification 3.8.1 AC Sources Operating, provide additional time to restore an inoperable offsite circuit, modify Surveillance Requirement (SR) 3.8.1.8, and modify the current licensing basis, as described in the Updated Final Safety Analysis Report (UFSAR), for the available maintenance feeder for the Common Station Service Transformers (CSST A and B).

U.S. Nuclear Regulatory Comm ission Page 2 April 21 , 2014 On February 26, 2014, Mr. Andrew Hon, the Nuclear Regulatory Commission (NRC)

Project Manager for WBN Unit 1, transmitted a request for additional information (RAI) by electronic mail (email) (Reference 2) . The original due date for the RAI response was March 26, 2014. Following discussion with Mr. Hon , the new due date for these responses is April 21, 2014. to this letter provides TVA's response to the NRC RAI. Enclosure 2 provides a copy of revised LAR WBN-13-02, page E-1 17 of 48 resulting from the response to NRC question number 2.

There are no new regulatory commitments included in this submittal. Please address any questions regarding this submittal to Edward D. Schrull at (423) 751-3850.

I declare under penalty of perju ry that the foregoing is true and correct. Executed on the 21st day of April 2014.

ice President, Nuclear Licensing

Enclosure:

1. Response to Request for Additional Information, Offsite Power Availability Requirements

2. Revised License Amendment Request (LAR) page E-1 17 of 48 cc (Enclosure):

NRC Regional Administrator - Region II NRC Senior Resident Inspector - Watts Bar Nuclear Plant, Unit 1 NRC Project Manager - Watts Bar Nuclear Plant, Unit 1

ENCLOSURE 1 TENNESSEE VALLEY AUTHORITY WATTS BAR NUCLEAR PLANT, UNIT 1 RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION OFFSITE POWER AVAILABILITY REQUIREMENTS BACKGROUND The current licensing basis of Watts Bar Unit 1 includes the capability to power each of the shutdown boards 1A-A and 1B-B from common station service transformer (CSST) C and D. For compliance with General Design Criterion (GDC) 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 D 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.

NRC RAI No. 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 B to meet the requirements of limiting conditions for operation (LCO) 3.8.1, with respect to qualified offsite 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 B as a temporary backup source of power for the shutdown E1-1

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 staffs 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.

TVA Response TVA is not proposing to use transformers CSST A or B as a temporary back up power source. The proposed LAR credits upgrades made to CSST A and B to provide two new sources of preferred Class 1E power supply feeds in addition to the two normal Class 1E power supply feeds. The TS change is needed to support dual unit operations without requiring a dual unit shutdown during maintenance on either preferred power CSST C or D.

The amendment seeks to add an allowance to use CSST A or B to meet the requirements of LCO 3.8.1, with respect to qualified offsite circuits, provide additional time to operate with an offsite circuit inoperable when CSST C or D is inoperable, and add testing of the manual transfers of the shutdown boards to and from the maintenance feeds (i.e., CSSTs A and B).

TVA determined that testing of the manual transfers was required to show that these transfers are functional and could be used to supply power to the shutdown boards during conditions when either CSST C or D is out of service for maintenance or to restore power if CSST C or D fails. The requested change to TS 3.8.1 results from upgrades made to CSSTs A and B to provide two new sources of preferred Class 1E power supply feeds in addition to the two normal Class 1E power supply feeds. The upgrades to CSSTs A and B were completed as part of actions to address NUREG-0847, "Safety Evaluation Report Related to the Operation of Watts Bar Nuclear Plant, Unit 2," Supplement 22, Appendix HH, 'Watts Bar Unit 2 Action Items Table," Open Item 27 (Reference 1).

History The WBN Auxiliary Power System (APS) was originally designed for two unit operation. However, due to the deferral of completion of Unit 2 prior to 2007, a detailed analysis of the adequacy of the APS was performed for Unit 1 only during the Unit 1 licensing effort. Therefore, the APS analysis supported Unit 1 operation only, although it took into account Unit 2 busses, boards and loads required for Unit 1 operation and safe shutdown. As TVA has continued to prepare for WBN Unit 2 licensing and the plans to place the unit into commercial operation, the APS will be required to support a two unit operation.

Open Item 27 originated as a result of the NRC staffs review of the WBN Unit 2 FSAR. In Reference 2, TVA received an RAI from NRC regarding the WBN Unit 2 FSAR amendment related to electrical engineering systems. The NRC requested additional information describing all such transmission system grid conditions and a E1-2

detailed description of the operating characteristics of the offsite power supply at the Watts Bar Hydro Plant Switchyard (WBHS) (for dual-unit operation at WBN Units 1 and 2) including operating voltage range, post-contingency voltage drops (including bounding values and post-unit trip values), operating frequency range, etc.

TVA provided the RAI response (Reference 3) that included the results of grid studies that showed that, under the worst case scenario, the maximum voltage drop would not exceed 5 kV. TVA stated that the auxiliary power system analysis for two unit operation was performed using a 161 kV grid voltage drop of 11 kV when powered from CSSTs C and D and 9 kV when powered from CSSTs A and B. Furthermore, TVA stated that CSSTs A and B would be used to substitute for CSSTs D and C, respectively, in case of CSST C or D outage.

On February 2011, the NRC issued NUREG-0847, Supplement 22, Safety Evaluation Report Related to the Operation of Watts Bar Nuclear Plant, Unit 2, which contained a summary of the NRC staff review related to the WBN Unit 2, FSAR Section 8 Electric Power Systems and the TVA RAI responses. In its review to determine compliance with General Design Criteria 17 and 18, the NRC in its summary of SER Supplement 22, Section 8.2.2, stated:

During its previous review in support of the operation of WBN Unit 1, the NRC staff concluded that TVA met the requirements of GDC 17 with respect to the offsite power systems having the (1) capacity and capability to permit functioning of SSCs important to safety; (2) provisions to minimize the probability of losing electric power from any of the remaining supplies as a result of, or coincident with, the loss of power generated by the nuclear power unit or loss of power from the onsite electric power supplies; (3) physical independence of circuits; and (4) availability of circuits.

However, in SER supplement 22, the NRC staff further requested that TVA evaluate the capability of the CSSTs for a dual-unit shutdown resulting from an abnormal operating occurrence (a summary of similar margin studies based on a dual-unit trip as a result of an abnormal operational occurrence and an accident in one unit concurrent with a spurious ESF actuation, These should be based on the completed analysis for uprating CSSTs A and B). The NRC identified the follow up action as Open Item 27 (Appendix HH) in SER Supplement 22.

In a letter dated December 6, 2010 (Reference 4), for question RAI 8.2.2-1, TVA stated, The loading for a dual unit trip (item a) is slightly less than the loading with one unit in accident and a spurious accident signal in the other unit. Therefore, a separate load flow was not performed. The NRC staff then requested that TVA provide a summary of margin studies based on scenarios described in FSAR Section 8.1 for CSSTs A, B, C, and D.

In a follow up letter dated April 6, 2011 (Reference 5), TVA stated, A separate load flow was performed for a dual unit shutdown resulting from an abnormal operational occurrence with and without offsite power. TVA provided a summary of resulting loading on the CSSTs. The NRC staff reviewed the loading and margins available and concluded that the CSSTs are adequately rated for postulated conditions. As a result, the NRC closed Open Item 27 in NUREG-0847, SER Supplement 24 (Reference 6).

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Conclusion TVA has concluded that based on the upgrades to CSST A and B supported by the electrical studies and engineering calculations, as discussed above and in the references, there exists reasonable assurance that TVA has demonstrated that the requirements of GDC 17 are satisfied and that CSSTs A or B may be used as proposed in the LAR.

NRC RAI No. 2 The LAR proposes new TS SRs for transfers (automatic and manual to and from the maintenance feeds) associated with CSST A, B 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.

TVA Response As delineated in the TVA LAR associated with this RAI, Reference 7, there is no automatic transfer associated with maintenance feeder (CSST A or B feeding the shutdown boards) such as those that exist between normal and alternate supplies (CSST C and D feeding the shutdown boards). All transfer to and from the maintenance feed are manual only. The Proposed change to TS SR 3.8.1.8 is to test Manual Transfer Surveillance between C or D and B or A CSSTs. LAR page E-1 17 of 48 has been revised in order to provide clarity for the manual transfer surveillance between CSST C or D and CSST B or A. The revised page is included as Enclosure 2 to the cover letter for this RAI response.

NRC RAI No. 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.

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TVA Response TVAs position is that the use of CSST A and B satisfies the requirements of GDC 17 and no additional compensatory actions are required during the LCO period when these CSSTs are being used as a substitute for CSST C or D. As part of managing plant risk for maintenance activities, CSST C or D would be protected equipment when one of these CSSTs was taken out of service. This control of protective equipment action is delineated in plant procedure 1-PI-OPS-1-PE, Protected Equipment.

NRC RAI No. 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 B using the same methodology as approved for the normal source.

TVA Response The WBN 2 DVR setpoints for the shutdown boards is under review by NRC. TVA has requested a meeting with NRC to discuss the DVR setpoints and conformance to NRC requirements and guidance. This meeting is currently scheduled for April 24, 2014. The DVR relays are physically located on the shutdown boards, thus the DVR settings when approved by the NRC, will be valid whether CSSTs C and D or combinations of CSSTs C or D with CSSTs A or B supplying power to the boards.

The same methodology for validating the DVR setpoints is used for the various combinations of CSSTs supplying the boards described in the LAR.

NRC RAI No. 5 The LAR states that the CSST A or B 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 C or D 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.

TVA Response TVA will not consider the maintenance source (CSST A or B) to be an operable source until one of them is made available to the shutdown board.

If CSST A or B is being used as the manual (delayed) source (which has been limited to a period of 14 days), then CSST A or B would be used to unload the diesel after the loads are automatically transferred to the diesel upon loss of both CSSTs C and D.

The operation would be performed from the control room in the same manner that the diesel would be unloaded from the Normal or Alternate supply. This action would take less than 10 minutes; however, there is no time requirement to take this action.

After one train is aligned to CSST A or B (i.e., aligned as an immediate source) no other manual action is required. The transfer from the USST to the CSST is an E1-5

automatic transfer. The boards would only be de-energized for the period required for the breakers to cycle during the fast transfer.

Note: Although the transfer can be made immediately to CSST A or B, when first entering the LCO, this would cause the plant to make multiple board transfers which would increase the likelihood of a loss of power.

NRC RAI No. 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 competition 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:

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 D, 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 GDC 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 GDC 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.

TVA Response

a. During the 14 day LCO, all four Shutdown Boards would be supplied by CSST C or D. Either of these sources is able to supply power for both units within specified limits to components and systems required to ensure that fuel design limits, reactor coolant pressure boundary design conditions, vital functions are maintained, and the core is cooled during:

a. A dual-unit trip as a result of abnormal operational occurrence

c. An accident in one unit and concurrent shutdown of the second unit

d. An accident in one unit and spurious Engineered Safety Feature actuation in the other unit (Spurious Accident Signal)

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There is no operational differences to the plant, during any mode of operation or during the events specified above, when the plant is normally configured (with the A train supplied from CSST C, and the B train supplied from CSST D), versus both the A and B train supplied by CSST C or D.

b. When Unit 1 is in power operation, the Shutdown Boards, via the unit boards, can be supplied from the Main Generator through the USSTs. Upon a load rejection, the unit boards are:

Transferred immediately, if the rejection is caused by a generator protective function, or Transferred after 30 seconds by reverse power detection. During the 30 second delay, the generator is motored from offsite and acts as a VAR source to maintain voltage at the terminals.

In order to ensure that CSST A and/or B are able to supply power for both units within specified limits to components and systems required to ensure that fuel design limits and reactor coolant pressure boundary design conditions and the core is cooled and vital functions are maintained, the transformers were analyzed for a full load sequence With the Unit boards supplied from the CSSTs at the beginning of the event, and With the Unit Boards supplied from the USSTs for 30 Seconds and then transferred to either CSST A or B.

This analysis evaluated:

a. A dual-unit trip as a result of 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 actuation in the other unit (Spurious Accident Signal)

The final alignment would result in the following possible configurations:

1. If CSST C is out of service, 6.9 KV Shutdown Board 1B-B and 2B-B will be supplied by CSST A. CSST D will supply 6.9 KV Shutdown Board 1A-A and 2A-A.

2. If CSST D is out of service, 6.9 KV Shutdown Board 1A-A and 2A-A will be supplied by CSST B. CSST C will supply 6.9 KV Shutdown Board 2B-B and 2B-B.

In either case, each train will be supplied by a different GDC-17 compliant immediate offsite source.

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NRC RAI No. 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 D 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.

TVA Response The breaker trip logic from the Unit Board (Maintenance Feeders) is similar to the Normal and Alternate supplies breaker logics from C and D CSSTs, and would not preclude automatic actions associated with supplying power from onsite diesel generators, during an emergency start.

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References

1. USNRC NUREG-0847, Supplement 22, Safety Evaluation Report Related to the Operation of Watts Bar Nuclear Plant, Unit 2, Docket Number 50-391, published February 2011 (ML110390197)

2. NRC to TVA letter dated July 12, 2010, Watts Bar Nuclear Plant, Unit 2 - Request for Additional Information Regarding Licensee's Final Safety Analysis Report Amendment Related to Electrical Engineering Systems (TAC No. ME2731) (ADAMS Accession No. ML101530354)

3. TVA Letter to NRC, Watts Bar Nuclear Plant (WBN) Unit 2 - Final Safety Analysis Report (FSAR) - Response to Request for Additional Information, dated November 9, 2010

4. TVA letter to NRC dated December 6, 2010, "Watts Bar Nuclear Plant (WBN) Unit 2 -

Safety Evaluation Report Supplement 22 (SSER22) - Response to Requests for Additional Information" [ML103420569]

5. TVA letter to NRC dated April 6, 2011, Watts Bar Nuclear Plant (WBN) Unit 2 - Safety Evaluation Report Supplement 22 (SSER22) - Response to NRC Required Action Items [ML110980637]

6. USNRC NUREG-0847, Supplement 24, Safety Evaluation Report Related to the Operation of Watts Bar Nuclear Plant, Unit 2, Docket Number 50-391, published September 2011 (ML11277A148)

7. Letter from TVA to NRC to Submit Application to Modify Watts Bar Nuclear Plant, Unit 1 Technical Specifications Regarding AC Sources - Operating (TS-WBN-13-02), dated August 1, 2013 (ML13220A103)

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L44 140421 004 ENCLOSURE 2 Revised License Amendment Request WBN-13-02, Page E-1 17 of 48 E2-1

ATTACHMENT 1 Proposed TS Changes (Mark-Ups) for WBN Unit 1 AC Sources-Operating 3.8.1 SURVEILLANCE FREQUENCY SR 3.8.1.7 Verify each DG starts from standby condition 184 days and achieves in ~ 10 seconds, voltage ~ 6800 V, and frequency ~ 58.8 Hz. Verify after DG fast start from standby conditions that the DG achieves steady state voltage ~ 6800 V and ~

7260 V, and frequency ~ 58.8 Hz and ~ 61.2 Hz.

SR 3.8.1.8 * - - - - * -NOTE--------*

For the 1A-A and 18-B Shutdown Boards, this Surveillance shall not be performed in MODE 1 or 2.

However, credit may be taken for unplanned events that satisfy this SR.

18 months VeFify a1:1tematis and man1:1al tFansfeF ef eash e.Q kV sl=l1:1tdewn t>eaFd peweF s1:1pply fFem the ner:mal effsite siFG1:1it te easl=I altemate effsite siFG1:1it.

Verifv the following:

a. Automatic and manual transfer of each 6.9 kV shutdown board power supply from the normal offsite circuit to the alternate offsite circuit;

b. Automatic transfer of the associated 6.9 kV shutdown board power supply from the USST to the associated CSST A or B. when USST is powering the associated shutdown board and CSST A or B is credited with meeting LCO 3.8.1.a requirements; and between

c. Manual transfer of the associated 6.9 kV shutdown board power supply from the associated CSST A or B to the normal offsite circuit fCSST C or D. as applicable), when CSST A or B is credited with and meeting LCO 3.8.1.a requirements.

(continued)

E-1 17 of 48