Text

Response to NRC Request for Additional Information Related to Application to Modify Technical Specifications Regarding AC Sources - Operating (TS-WBN-13-02)
	ML15041A732
Person / Time
Site:	Watts Bar
Issue date:	01/29/2015
From:	James Shea; Tennessee Valley Authority
To:	; Document Control Desk, Office of Nuclear Reactor Regulation
References
	CNL-14-107, TS-WBN-13-02
	Download: ML15041A732 (91)
	v • d • e

[iE Tennessee Valley Authority. 1101 Market Street. Chattanooga. Tennessee 37402 January 29. 2015 CNL-14-107 10 CFR 50.90 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, D.C. 20555-0001

Subject:

Watts Bar Nuclear Plant, Unit 1 Facility Operating License No. NPF-90 NRC Docket No. 50-390 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)

[ML14056A525]

3. Letter from TVA to NRC, "Response to Request for Additional Information Related to Application to Modify Watts Bar Nuclear Plant, Unit 1 Technical Specifications Related to AC Sources - Operating (TS WBN 13-02)," dated April 21, 2014 (TAC No. MF2549) [ML14112A341]

4. Electronic mail from Jeanne Dion (NRC) to Gordon Arent (TVA},

"Request for Additional Information for Watts Bar Nuclear Plant Unit 1 Common Station Service Transformer License Amendment Request,"

dated June 2, 2014 (TAC No. MF2549) [ML14168A613]

5. Letter from NRC to TVA, "Watts Bar Nuclear Plant, Unit 1 - Issuance of Amendment Regarding the Completion Time for the Inoperable Emergency Diesel Generator(S) (TAC No. ME2985)," dated July 6, 2010. [ML101390154)

U.S. Nuclear Regulatory Commission CNL-14-107 Page2 January 29, 2015 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 for Technical Specification (TS) 3.8.1, "AC Sources Operating," Surveillance Requirement 3.8.1.8, and 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 A and 8.

On February 26, 2014, the Nuclear Regulatory Commission (NRC) transmitted a request for additional information (RAI) by electronic mail (email) (Reference 2).

TVA responded to the Reference 2 RAI by letter dated April 21, 2014 (Reference 3). On April 24, 2014, the NRC conducted a public meeting where TVA responses provided in Reference 3 were discussed.

Subsequently, on June 2, 2014, the NRC transmitted an additional RAI (Reference 4). This RAI requested further explanation of the information provided in the Reference 3 response, as was discussed during the public meeting held on April 24, 2014.

The enclosures to this letter provide the TVA response to the Reference 4 RAI, revising and superseding in its entirety the RAI response submitted in Reference 3. Enclosure 1 provides TVA's response to the June 2, 2014 email. Enclosure 2 provides TVA's revised response to TVA's April 21, 2014 RAI response. Attached to Enclosure 2 are revised proposed TS pages, TS Bases pages, and UFSAR pages.

Note that Attachment 3, "Clean Typed" TS pages, is labeled "For Information Only." These pages reflect the changes requested in this LAR using the TS pages currently implemented at WBN. In License Amendment (LA) 84 (Reference 5) the NRC approved changes to WBN Unit 1, TS Section 3.8.1, to be implemented after the issuance of the Facility Operating License for WBN Unit 2 and prior to WBN Unit 2 entry into Mode 4, "Hot Shutdown." Because WBN Unit 2 is under construction with the projected approval of the Facility Operating License in the first half of 2015, LA 84 may be implemented before approval of this LAR. Therefore, the "Clean Typed" TS pages may require changes to reflect implementation of WBN Unit 1, LA 84.

Consistent with the standards set forth in Title 10 of the Code of Federal Regulations (10 CFR) 50.92(c), TVA has determined that TVA's response, as provided in this letter, does not affect the no significant hazards considerations associated with the proposed license amendment previously provided in Reference 1. Tennessee Valley Authority has further determined that the proposed amendment still qualifies for a categorical exclusion from environmental review pursuant to the provisions of 10 CFR 51.22(c)(9). Additionally, in accordance with 10 CFR 50.91 (b)(1), TVA is sending a copy of this letter, the enclosures, and the attachments to the Tennessee Department of Environment and Conservation.

U.S. Nuclear Regulatory Commission CNL-14-107 Page 3 January 29, 2015 There are no new regulatory commitments included in this submittal. Please address any questions regarding this submittal to Gordon Arent at (423) 365-2004.

I declare under penalty of perjury that the foregoing is true and correct. Executed on the 29th day of January 2015.

~**

hea ic esident, Nuclear Licensing

Enclosures:

1.

Response to Request for Additional Information, Offsite Power Availability Requirements via June 2, 2014 email

2.

Revised Response to NRC RAls dated February 26, 2014 cc (w Enclosures):

NRC Regional Administrator - Region II NRC Senior Resident Inspector - Watts Bar Nuclear Plant, Unit 1 NRC Project Manager - Watts Bar Nuclear Plant, Unit 1 Director - Division of Radiological Health - Tennessee State Department of Environment and Conservation

U.S. Nuclear Regulatory Commission CNL-14-107 Page4 January 29, 2015 CSK/EDS bee (w Enclosures)*

G. P. Arent R.R. Baron M.A. Balduzzi L.B. Belvin G. A. Boerschig J.M. Casner C.R. Church E.W. Cobey S. M. Connors G. M. Cook D. M. Czufin D. L. Daniels R. E. Detwiler C. P. Dieckmann S. M. Douglas B. M. Duckett M. J. Durr J.P. Grimes K. R. Jones G. W. Mauldin M. M. McBrearty R. G. Perez J. T. Polickoski M. A. Purcell C. J. Riedl G. 0. Riste C. M. Robinette E. D. Schrull T. L. Scott R. Seipel J. W. Shea M. D. Skaggs S. A. Vance K. T. Walsh B. A. Wetzel K. W. Whittenburg R. E. Wiggall

0. J. Zeringue ECM EDMS, WT 3B-K

ENCLOSURE 1 TENNESSEE VALLEY AUTHORITY WATTS BAR NUCLEAR PLANT, UNIT 1 RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION OFFSITE POWER AVAILABILITY REQUIREMENTS

[ADAMS Accession No. ML14168A613]

NRC Request for Additional Information [(RAIU

Background:

Assuming Watts Bar [Nuclear Plant] Unit 1 and Unit 2 are operating in Mode 1, the current (l]icensing basis of the plant is:

The Class 1 E power system is normally supplied from offsite power through [Common Service Station Transformers (CSSTs)] C and D. For flexibility, there is also a maintenance feed available from CSSTs A and B to the Class 1E power systems to be used only when the unit is in cold shutdown.

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 Following a dual unit trip the plant alignment would result in the following configuration as described in the [Updated Final Safety Analysis Report (UFSAR)]:

1. CSST C will supply 6.9 KV Shutdown Board 1A-A and 2A-A. Shutdown Boards 18-8 and 28-8 will be supplied by CSST D.

2. This arrangement provides two immediate sources to redundant trains of Units 1 and 2 and EACH source provides assurance that specified acceptable fuel design limits and design conditions of the reactor coolant pressure boundary are not exceeded (a [General Design Criterion (GDC)] 17 requirement) because there is adequate capacity in each source AND no delay in providing power to plant shutdown loads.

3. As a defense-in-depth measure, the plant design affords a transfer to the alternate path (with fast transfer) through CSST D (if CSST C is unavailable) or CSST C (if CSST Dis unavailable). This configuration results in a SINGLE

'immediate' source to redundant trains of Units 1 and 2 and is not in compliance GDC 17 requirements. Hence, a dual unit plant [Limiting Condition of Operation (LCO)] is imposed by Technical [S]pecifications.

E1-1

RAI questions 1 and 6 The [License Amendment Request (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 LCO 3.8.1, with respect to qualified offsite circuits that satisfy GDC 17 requirements, i.e. to compensate for item 3 above. CSST A (or CSST 8) is considered the "delayed" second source for GDC 17 source.

[The] RAI Questions 1 and 6 are related to the time delay associated with using CSST A and B as GDC 17 source.

GDC 17 requires two sources of offsite power, one immediate source and one source can be delayed. The GDC does not define the requirement for allowable delay time in the second source. However, the GDC states that "The safety function for each system (assuming the other system is not functioning) shall be to provide sufficient capacity and capability to assure that (1) specified acceptable fuel design limits (SAFDLs) and design conditions of the reactor coolant pressure boundary are not exceeded as a result of anticipated operational occurrences and (2) the core is cooled and containment integrity and other vital functions are maintained in the event of postulated accidents".

The LAR proposes CSST A (or CCST B) to be "available" but not connected to the shutdown busses. The staff has noted that CSST A and B have adequate capacity to support safe shutdown of the [WBN] units. The staff requested information on how this proposed delayed path with CSST A (or B) in 'available mode' is able to support GDC 17 requirements (1) and (2) noted above. The RAI responses in letter dated April 21, 2014 did not provide a clear answer related to the proposed delay in the second GDC 17 source.

Summary

'The staff is concerned that the proposed amendment would deviate from the current license basis because sources would not be immediately connected to safe shutdown busses. Allowing the delayed [Alternating Current] sources to be unconnected for a period of 14 days, as stated in the LAR, would not meet GDC 17."

NOTE: The staff considers the proposed change to be non-conservative when compared to the current licensing basis as indicated in the RAls based on;

1.

the time delay associated with CSST A and B,

2.

CSSTs A and B are not automatically aligned to the shutdown busses,

3.

CSSTs A and B do not have the capacity to supply loads on both units during limiting Design Basis Events, and

4.

CSSTs A and B cannot be aligned to more than one shutdown bus for dual unit shutdown.

E1-2

Tennessee Valley Authority (TV Al Response TVA is revising its response to the NRC's request for additional information contained in TVA's letter dated April 21, 2014. The change is to align the shutdown boards of the Common Station Service Transformer (CSST) that is out-of-service to the associated unit board and power the unit board from the Unit Station Service Transformer (USST) with either CSST A or B in standby or power the unit board directly from either CSST A or B through the start bus. The revised response is contained in Enclosure 2.

E1-3

ENCLOSURE2 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 [Nuclear Plant (WBN)] Unit 1 includes the capability to power each of the Shutdown Boards 1 A-A and 1 B-B from Common Station Service Transformer[s] (CSST[s]) 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 1 B-B and an automatic transfer to the alternate source CSST D for 1A-A and CSST C for 1 B-B. When [WBN] Unit 2 is in commercial operation, Shutdown Boards 2A-A and 28-B will have [a] similar configuration from CSST C and CSST D. The CSST[s] C and Dare 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 [boards],

b) CSSTs A and B do not have the capacity to supply loads on both units during limiting [d]esign [b]asis [e]vents, [and]

c) CSSTs A and B cannot be aligned to more than one shutdown[board) for [a] dual[-

]unit shutdown.

NRC RAI No.1 The [License Amendment Request (LAR)] proposes to revise [Technical Specification (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 [Updated Final Safety Analysis Report (UFSAR)], to allow the use of CSST[s]

A and Bas qualified sources of power. In addition to the differences in capabilities of transformers CSST[s] A, B, C and D identified above, the LAR does not delineate the capability of offsite power through CSST[s] 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 Q[ B as a temporary backup source of power for the shutdown busses and part of overall compensatory actions for the following E2-1

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 o to allow one qualified offsite circuit to be inoperable for up to 14 days for the operating unit.

TV A Response TVA is not proposing to use CSST A or Bas a temporary back up power source. The proposed TS change credits upgrades made to CSSTs A and B to provide two new qualified offsite power circuits, in addition to the current qualified offsite power circuits. The TS change is needed to support dual unit operations without requiring a dual unit shutdown during maintenance on either preferred power source 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, and add testing of the automatic transfers of Unit Boards 1 B, 1 C, 2B, and 2C from the Unit Station Service Transformer (USST) to the start bus. The start bus would be powered from either CSST A or B.

TVA determined that testing of the automatic transfer was required to show that these transfers are functional and could be used to supply power to the shutdown boards, via the unit 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, described in Section 3.2.2, Technical Analysis, of Reference 1, made to CSSTs A and B to provide two new offsite power circuits in addition to the two current offsite power circuits.

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 two-unit operation.

In Reference 2, TVA received a request for additional information (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 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.

In a letter dated December 6, 2010 (Reference 3), for question RAI 8.2.2-1, TVA stated, "The E2-2

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." In Supplemental Safety Evaluation Report (SSER) 22, the NRC staff referenced this letter and 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.

TVA provided the RAI response (Reference 4) 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.

In February 2011, the NRC issued NUREG-0847, Supplement 22, "Safety Evaluation Report Related to the Operation of Watts Bar Nuclear Plant, Unit 2," (Reference 5) 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 GDCs 17 and 18, the NRC in its summary of Safety Evaluation Report (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 GOG 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 requesting 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 SSER 22.

In a follow up letter dated April 6, 2011 (Reference 6), 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, SSER 24 (Reference 7).

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

E2-3

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.

TV A Response TVA is proposing to change the original LAR to return to requiring two qualified circuits to be operable for unrestricted operation, allowing for one required offsite circuit to be inoperable for a maximum of 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months . If CSST C or Dis out-of-service, TVA is proposing to use either CSST B or A, respectively, as a replacement qualified offsite circuit to supply the affected 6.9 kV shutdown boards. The replacement qualified circuit would be from the 161 kV WBHS to CSST A or B to the associated start bus, through the associated unit board to the affected 6.9 kV shutdown boards. This qualified circuit would be considered operable when the breakers needed for the lineup are closed. Therefore, no surveillance to verify manual operation is required because manual operation is not needed once the qualified circuit is operable.

Alternatively, the automatic fast transfer from the unit board's normal supply to its alternate supply is also proposed for operability. The normal at-power supply lineup of the 6.9 kV unit boards is from the USSTs. An automatic unit board power supply fast transfer occurs on a USST fault and on a main generator trip. TVA is proposing to allow for maintaining an operable offsite circuit using the normal at-power unit board power supply, requiring the unit board power supply automatic fast transfer to the start bus to be operable. With the automatic fast transfer operable, the USST supplying power to the unit board, the unit board supplying power to the shutdown board, and CSST A or B aligned to the unit board, the CSST would be supplying power to the 6.9 kV shutdown board(s) within a few seconds of a loss of the USST.

Therefore, this automatic transfer requires periodic verification that it will perform its intended function and surveillance requirement (SR) 3.8.1.22 is proposed to be added to reflect this verification.

Currently WBN Unit 1 SR 3.8.1.8 requires verification of automatic and manual transfer of each 6.9 kV shutdown board power supply from the normal offsite circuit to each alternate offsite circuit. Verification of this automatic and manual transfer supports operability of the offsite circuits when the 6.9 kV shutdown boards require their normal and alternate power supplies.

By requiring an operable fast transfer interlock mechanism, the circuit that is not connected to at least two 6.9 kV shutdown boards through the normal supply is maintained operable.

TVA is proposing two changes to SR 3.8.1.8, both associated with the note. The first change is to modify the note to allow the Surveillance to be performed for reestablishing E2-4

OPERABILITY, provided an assessment determines plant safety is maintained or enhanced.

This change would allow the surveillance to be performed for post work testing following corrective maintenance, corrective modification, deficient or incomplete surveillance testing, and other unanticipated OPERABILITY concerns. This change is consistent with NUREG-1431, Standard Technical Specifications - Westinghouse Plants, Revision 4 as approved by the NRC under Technical Specification Task Force (TSTF) traveler TSTF-283-A, "Modify Section 3.8 Mode Restriction Notes." A second note is proposed to limit the conditions under which the surveillance requirement is required to be met.

The purpose of SR 3.8.1.8 is to demonstrate the OPERABILITY of the alternate circuit distribution network to power the shutdown loads. The second note limits the conditions that the surveillance requirement is required to be met to when the transfer to the alternate circuit is needed. With the four 6.9 kV shutdown boards aligned to their normal offsite circuit, if a loss of one offsite circuit occurred; one load group will remain energized by offsite power, no transfer is required. With one or more 6.9 kV shutdown boards aligned to their alternate source, a transfer will align those 6.9 kV shutdown boards aligned to their normal offsite circuit to their alternate circuit, maintaining one load group energized following a loss of one offsite circuit. If all four 6.9 kV shutdown boards are aligned to their alternate source, the SR is not required to be met, because no shutdown board requires normal and alternate supply.

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 §!Lonsite 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.

TVA Response TVA position is that the use of CSST A or B satisfies the requirements of GDC 17. However, the use of CSST A or B as an offsite source requires that CSST A and B be available to prevent overloading the credited circuit. In addition, the associated power and control feeders must be in their normal positions to ensure independence. Due to independence limitations, CSST A and B cannot be credited as offsite power circuits simultaneously. No additional compensatory actions are required 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 will be protected equipment when one of these CSSTs is taken out of service. This control of protective equipment action is delineated in plant procedure 1-Pl-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.

E2-5

TV A Response The WBN Unit 2 DVR setpoints for the shutdown boards is under review by the NRC. 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 CSST C or D with CSST A or B are 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.

TV A Response TVA will not consider CSST A or Bas a qualified circuit until the shutdown board is aligned to the unit board. The unit board will be aligned to either CSST A or B, or the CSST will be available through automatic transfer of the unit board from the USST to the CSST. When aligned to the USST, automatic transfer occurs immediately if the rejection is caused by a generator protective function or after 30 seconds, by reverse power detection. During the 30-second delay, the generator is motored from offsite power and the USST remains energized.

Although CSST A or B cannot be credited as a qualified offsite circuit until the maintenance path is aligned, operator actions are required to align the maintenance feed. These actions are required to be completed within LCO 3.8.1, Required Action A.3, "Restore required offsite circuit to OPERABLE status," Completion Time of 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months or Condition G is entered and a unit shutdown is required. During the 72 hour8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months Completion Time of Required Action A.3 the operators must transfer the 6.9 kV shutdown board power source from either CSST C or D to the associated unit board via the maintenance feed. The actions to transfer the 6.9 kV shutdown board power supply to the maintenance circuit are directed by operating procedures.

In addition, if the automatic transfer verification, required by SR 3.8.1.22, between the unit board's normal power supply (USST) and its alternate power supply (CSST) has not been performed within its required frequency, this verification must also be performed. This verification must be performed within the 72 hour8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months Completion Time of Required Action A.3 or unit board power supply aligned to the alternate power supply (CSST A or B), also directed by operating procedures.

NRC RA! 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 0.02 hours 1.190476e-4 weeks 2.7396e-5 months when one offsite power source (through CSST C or D) is not available. The LAR proposes to extend the CT to E2-6

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.

TV A Response

a. TVA is no longer proposing a Required Action with a 14-day completion time.

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 maintains 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, the transformers were analyzed for a full load sequence. The analysis demonstrates that 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 with; the unit boards supplied from the CSSTs at the beginning of the event, and 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; and E2-7

c. Accident in one unit and spurious ESF actuation in the other unit (Spurious Accident Signal).

The final alignment would result in the following possible configurations:

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

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

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

Relevant excerpts of the analysis were provided to the NRC in Reference 8.

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.

TV A Response The breaker trip logic from the unit board (maintenance feeders} is similar to the normal and alternate supplies breaker logics from CSSTs C and D, and would not preclude automatic actions associated with supplying power from onsite diesel generators during an emergency start.

Additional Information Prior to the NRC staff listing their specific requests for information, the staff made a statement noting limitations for CSSTs A and B compared to CSSTs C and D that included:

a} CSSTs A and Bare 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.

In response to these listed limitations, TVA provides the following response.

Limitation a) CSSTs A and B are not automatically aligned to the shutdown busses TVA has changed its original requested lineup such that to exit the 72-hour completion time for LCO 3.8.1, Action A, the affected shutdown boards must be aligned to the unit board that would be supplied power either from the associated USST or from CSST A or B through the E2-8

start bus. On a loss of the USST, the unit board's power supply automatically shifts to the start bus that is powered from the CSST.

Limitation bl CSSTs A and B do not have the capacity to supply loads on both units during limiting Design Basis Events Individually, CSSTs A and B do not have the capacity to supply all four 6.9 kV shutdown boards, but do have the capacity to supply two 6.9 kV shutdown boards, one from each unit, in the same train. CSST A or B, individually, has a higher capacity than CSST C or D, individually. Because CSST A and B would potentially be supplying other loads powered from the 6.9 kV units boards, 6.9 kV reactor coolant pump boards, or 6.9 kV common boards, they are limited to supplying two 6.9 kV shutdown boards. Normally CSST C supplies 6.9 kV Shutdown Boards 1A-A (Unit 1) and 2A-A (Unit 2) while CSST D supplies 6.9 kV Shutdown Boards 1 B-B (Unit 1) and 2B-B (Unit 2).

The CSST A would be used to replace CSST D. The qualified offsite circuit using CSST A would be from the 161 kV WBHS (Bay 4) through CSST A, through CSST A breaker 1512 (normally closed), through 6.9 kV Start Bus A to 6.9 kV Unit Boards 1C and 2C. The 6.9 kV Unit Boards 1 C and 2C would then supply power to 6.9 kV Shutdown Boards 1 B-8 (Unit 1) and 2B-B (Unit 2). These are the same 6.9 kV shutdown boards CSST D normally supplies. A similar configuration exists when CSST B is replacing CSST C.

Therefore, either CSST A or B has the capacity to supply one train of loads on both units during limiting design basis events, but not both trains.

Limitation cl CSSTs A and B cannot be aligned to more than one shutdown bus for dual unit shutdown.

As described in Limitation b), CSSTs A and B can be aligned to two 6.9 kV shutdown boards, one from each unit, thus able to support a dual unit shutdown.

REFERENCES

1. TVA letter to NRC, "Application to Modify Watts Bar Nuclear Plant, Unit 1 Technical Specifications Regarding AC Sources -

Operation (TS-WBN-13-02)," dated August 1, 2013(ML13220A103)

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 dated December 6, 2010, 'Watts Bar Nuclear Plant (WBN) Unit 2 -

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

4. 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, E2-9

2010 [ML103200146]

5. 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 (ML1103901973

6. 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]

7. 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)

8. TVA letter to NRC, "Watts Bar Nuclear Plant (WBN) Unit 2 - Final Safety Analysis Report (FSAR) -

Response to Requests for Additional Information," dated November 9, 2010(ML103200146 and ML103200150)

E2-10

ENCLOSURE2 ATTACHMENT 1 Proposed TS Changes (Mark-Ups)

Watts Bar Nuclear Plant-Unit 1

AC Sources - Operating 3.8.1 3.8 ELECTRICAL POWER SYSTEMS 3.8.1 AC Sources - Operating LCO 3.8.1 APPLICABILITY:

ACTIONS The following AC electrical sources shall be OPERABLE:

a.

Two qualified circuits between the offsite transmission network and the onsile Class 1 E AC Electrical Power Distribution System; and

b.

Four diesel generators (DGs) capable of supplying the onsite Class 1E AC Electrical Power Distribution System.

NOTE The C-S DG may be substituted for any of the required DGs.

MODES 1, 2, 3, and 4.

NOTE--------------------------

LCO 3.0.4.b is not applicable to DGs.

CONDITION A.

One required offsite circuit A. 1 inoperable.

Watts Bar-Unit 1 AND A.2 REQUIRED ACTION COMPLETION TIME Perform SR 3.8.1.1 for required 1 hour1.157407e-5 days 2.777778e-4 hours 1.653439e-6 weeks 3.805e-7 months OPERABLE offsite circuit.

Declare required feature(s) with no offsite power available inoperable when its redundant required feature(s) is inoperable.

3.8-1 Once per 8 hours9.259259e-5 days 0.00222 hours 1.322751e-5 weeks 3.044e-6 months thereafter 24 hours2.777778e-4 days 0.00667 hours 3.968254e-5 weeks 9.132e-6 months from discovery of no offsite power to one train concurrent with inoperability of redundant required feature(s)

(continued)

Amendment 39

ACTIONS CONDITION A.

(continued)

A.3 B.

One required DG B.1 inoperable.

AND B.2 AND B.3.1 B.3.2 AND Watts Bar-Unit 1 REQUIRED ACTION Restore requjred offsite circuit to OPERABLE status.

Perform SR 3.8.1.1 for the required offsite circuits.

Declare required feature(s) supported by the inoperable DG inoperable when its required redundant feature(s) is inoperable.

Determine OPERABLE DGs are not inoperable due to common cause failure.

OR Perform SR 3.8.1.2 for OPERABLE DGs.

3.8-2 AC Sources - Operating 3.8.1 COMPLETION TIME 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months AND 6 days from discovery of failure to meetLCO 1 hour1.157407e-5 days 2.777778e-4 hours 1.653439e-6 weeks 3.805e-7 months AND Once per 8 hours9.259259e-5 days 0.00222 hours 1.322751e-5 weeks 3.044e-6 months thereafter 4 hours4.62963e-5 days 0.00111 hours 6.613757e-6 weeks 1.522e-6 months from discovery of Condition B concurrent with inoperability of redundant required feature(s) 12 hours1.388889e-4 days 0.00333 hours 1.984127e-5 weeks 4.566e-6 months 12 hours (continued)

Amendment 39

ACTIONS CONDITION REQUIRED ACTION B.

(continued)

B.4 Restore required DG to OPERABLE status.

c.

Two required DGs in Train C.1 Perform SR 3.8.1.1 for the A inoperable.

required offsite circuits.

OR Two required DGs in Train B inoperable.

AND C.2 Declare required feature(s) supported by the inoperable OGs inoperable when its required redundant feature(s) is inoperable.

AND C.3.1 Determine OPERABLE DGs are not inoperable due to common cause failure.

OR C.3.2 Perform SR 3.8.1.2 for OPERABLE DGs.

AND Watts Bar-Unit 1 3.8-2a AC Sources - Operating 3.8.1 COMPLETION TIME 14 days AND 17 days from discovery of failure to meetLCO 1 hour1.157407e-5 days 2.777778e-4 hours 1.653439e-6 weeks 3.805e-7 months AND Once per 8 hours9.259259e-5 days 0.00222 hours 1.322751e-5 weeks 3.044e-6 months thereafter 4 hours4.62963e-5 days 0.00111 hours 6.613757e-6 weeks 1.522e-6 months from discovery of Condition C concurrent with inoperability of redundant required feature(s) 12 hours1.388889e-4 days 0.00333 hours 1.984127e-5 weeks 4.566e-6 months 12 hours (continued)

Amendment 39

CONDITION REQUIRED ACTION

c.

(continued)

C.4 Restore at least one required DG to OPERABLE status.

D.

Two required offsite circuits D.1 Declare required feature(s) inoperable.

inoperable when its redundant required feature(s) is inoperable.

AND D.2 Restore one required offsite circuit to OPERABLE status.

Watts Bar-Unit 1 3.8-3 AC Sources-Operating 3.8.1 COMPLETION TIME 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months AND 6 days from discovery of failure to meetLCO 12 hours1.388889e-4 days 0.00333 hours 1.984127e-5 weeks 4.566e-6 months from discovery of Condition D concurrent with inoperability of redundant required features 24 hours2.777778e-4 days 0.00667 hours 3.968254e-5 weeks 9.132e-6 months (continued)

Amendment 30, 39

ACTIONS (continued)

CONDITION E.

One required offsite circuit inoperable.

AND One or more required DG(s) in Train A inoperable.

OR One or more required DG(s) in Train B inoperable.

F.

One or more required DG(s) in Train A inoperable.

AND One or more required DG(s) in Train B inoperable.

G.

Required Action and Associated Completion Time of Condition A, B, C, D, E, or F not met.

Watts Bar-Unit 1 REQUIRED ACTION

NOTE Enter applicable Conditions and Required Actions of LCO 3.8.9, "Distribution Systems-Operating,"

when Condition E is entered with no AC power source to any train.

E.1 Restore required offsite circuit to OPERABLE status.

OR E.2 Restore required DG(s) to OPERABLE status.

F.1 Restore required DGs in Train A to OPERABLE status.

OR F.2 Restore required DGs in Train B to OPERABLE status G.1 Bein MODE3.

AND G.2 Bein MODES.

3.84 AC Sources-Operating 3.8.1 COMPLETION TIME 12 hours1.388889e-4 days 0.00333 hours 1.984127e-5 weeks 4.566e-6 months 12 hours 2 hours2.314815e-5 days 5.555556e-4 hours 3.306878e-6 weeks 7.61e-7 months 2 hours 6 hours6.944444e-5 days 0.00167 hours 9.920635e-6 weeks 2.283e-6 months 36 hours (continued)

Amendment 39

ACTIONS (continued)

CONDITION H.

Two required offsite circuits inoperable.

AND One or more required DG(s) in Train A inoperable.

OR One or more required DG(s) in Train B inoperable.

I.

One required offsite circuit inoperable.

AND One or more required DG(s) in Train A inoperable.

AND One or more required DG(s) in Train B inoperable.

Watts Bar-Unit 1 REQUIRED ACTION H.1 Enter LCO 3.0.3.

1.1 Enter LCO 3.0.3.

3.8-5 AC Sources-Operating 3.8.1 COMPLETION TIME Immediately Immediately Amendment 39

SURVEILLANCE REQUIREMENTS SURVEILLANCE AC Sources-Operating 3.8.1 FREQUENCY SR 3.8.1.1 Verify correct breaker alignment and indicated power 7 days SR 3.8.1.2 Watts Bar-Unit 1 availability for each reauired offsite circuit.

1.

NOTES---------

Performance of SR 3.8.1. 7 satisfies this SR.

2.

A modified DG start involving idling and gradual acceleration to synchronous speed may be used for this SR as recommended by the manufacturer. When modified start procedures are not used, the time, voltage, and frequency tolerances of SR 3.8.1.7 must be met.

Verify each DG starts from standby conditions and achieves steady state voltage ~ 6800 V and s 7260 V, and frequency~ 58.8 Hz ands 61.2 Hz.

3.8-6 As specified in Table 3.8.1-1 (continued)

AC Sources-Operating 3.8.1 SURVEILLANCE REQUIREMENTS (continued)

SR 3.8.1.7 SR3.8.1.8 Watts Bar-Unit 1 SURVEILLANCE FREQUENCY Verify each DG starts from standby condition and 184 days achieves in :S 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 :S 7260 V, and frequency~ 58.8 Hz and :S 61.2 Hz.

-NOTE§--

!:. For the 1 A-A and 1 B-B Shutdown Boards, this Surveillance shall not normally be performed in MODE 1 or 2. However, this Surveillance may be performed to reestablish OPERABILITY provided an assessment determjnes the safety of the plant js majntajned or enhanced. ~redit may be taken for unplanned events that satisfy this SR.

2.

Transfer capability is only reauired to be met for 6.9 kV shutdown boards that require normal and alternate power supplies.

Verify automatic and manual transfer of each 6.9 kV 18 months shutdown board power supply from the normal offsite circuit to theeaei::. alternate offsite circuit.

(continued) 3.8-8 Amendment 89

SURVEILLANCE REQUIREMENTS (continued)

SR 3.8.1.21 SR 3.8.1.22 Watts Bar-Unit 1 SURVEILLANCE Verify when started simultaneously from standby condition, each DG achieves, in s 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 s 7260 V, and frequency~ 58.8 Hz and s 61.2 Hz.

NOTES----------

.1. For the 1B and 1C Unit Boards. this Surveillance shall not normally be pertormed in MODE 1 or 2.

However. this surveillance mav be performed to reestablish OPERABILITY provided an assessment determines the safetv of the plant is maintained or enhanced. Credit may be taken for unplanned events that satisfy this SR.

~ Transfer capabi!itv is only regujred to be met for 6.9 kV unit boards that reauire normal and alternate power supplies.

Verify automatic transfer of each 6.9 kV Unit Board

18. 1C. 28. and 2C power supply from the normal oower supply to the alternate power supply.

3.8-16 AC Sources-Operating 3.8.1 FREQUENCY 10 years 18 months

ENCLOSURE2 ATTACHMENT 2 Proposed TS Bases Changes (Mark-Ups)

Watts Bar Nuclear Plant - Unit 1

AC Sources - Operating B 3.8.1 B 3.8 ELECTRICAL POWER SYSTEMS B 3.8.1 AC Sources-Operating BASES BACKGROUND Watts Bar-Unit 1 The plant AC Electrical Power Distribution System AC sources consist of the offsite power sources (preferred power sources, normal and alternate(s)), and the onsite standby power sources (Train A and Train B diesel generators (DGs)). As required by 10 CFR 50, Appendix A, GDC 17 (Ref. 1 ), the design of the AC electrical power system provides independence and redundancy to ensure an available source of power to the Engineered Safety Feature (ESF) systems.

The onsite Class 1 E AC Distribution System supplies electrical power to four power trains, shared between the two units, with each train powered by an independent Class 1 E 6.9 kV shutdown board. Power trains 1A and 2A comprise load group A, and power trains 1 B and 2B comprise load Group B. Two DGs associated with one load group can provide all safety related functions to mitigate a loss-of-coolant accident (LOCA) in one unit and safely shutdown the opposite unit. Each 6.9 kV shutdown board has two separate and independent offsite sources of power as well as a dedicated onsite DG source. The A and B train ESF systems each provide for the minimum safety functions necessary to shut down the plant and maintain it in a safe shutdown condition. Power can be supplied to each Class 1 E 6.9 kV shutdown board from a normal offsite circuit (either CSST C or Dl an alternate offsite circuit (either CSST C or Dl. a majntenance offsite cjrcuit (ejther CSST A or Bl. or a DG.

Offsite power is supplied to the Watts Bar 161 kV transformer yard by two dedicated lines from the Watts Bar Hydro Plant switchyard. This is described in more detail in FSAR Section 8 (Ref.2). From the 161 kV transformer yard, two electrically and physically separated circuits provide AC power, through step-down common station service transformers, to the 6.9 kV shutdown boards. The two offsite AC electrical power sources are designed and located so as to minimize to the extent practical the likelihood of their simultaneous failure under operating and postulated accident and environmental conditions. A detailed description of the offsite power network and the circuits to the Class 1E shutdown boards is found in Reference 2.

An offsite circuit consists of all breakers, transformers, switches, interrupting devices, cabling, and controls required to transmit power from the offsite transmission network (i.e., Watts Bar Hydro Plant switchyard) to the onsite Class 1E ESF buses (i.e., 6.9 kV shutdown boards).

(continued) 8 3.8-1

BASES BACKGROUND (continued)

Watts Bar-Unit 1 AC Sources - Operating B 3.8.1 A single offsite circuit is capable of providing the ESF loads. Two8elA of these circuits are required to meet the Limiting Condition for Operation.

The onsite standby power source for each 6.9 kV shutdown board is a dedicated DG. WBN uses 4 DG sets for Unit 1 operation. These same DGs will be shared for Unit 2 operation. WBN may utilize a C-S DG that can be manually aligned (electrically and mechanically) to any 6.9 kV shutdown board to replace an existing DG. A DG starts automatically on a safety injection (SI) signal (i.e., low pressurizer pressure or high containment pressure signals) or on an 6.9 kV shutdown board degraded voltage or loss-of-voltage signal (refer to LCO 3.3.5, "Loss of Power (LOP) Diesel Generator (DG) Start Instrumentation"). After the DG has started, it will automatically tie to its respective 6.9 kV shutdown board after offsite power is tripped as a consequence of 6.9 kV shutdown board loss-of-voltage or degraded voltage, independent of or coincident with an SI signal. The DGs will also start and operate in the standby mode without tying to the 6.9 kV shutdown board on an SI signal alone. Following the trip of offsite power, a loss-of-voltage signal strips all nonpermanent loads from the 6.9 kV shutdown board.

When the DG is tied to the 6.9 kV shutdown board, loads are then sequentially connected to its respective 6.9 kV shutdown board by the automatic sequencer.

The sequencing logic controls the permissive and starting signals to motor breakers to prevent overloading the DG by automatic load application.

In the event of a loss of preferred power, the 6.9 kV shutdown boards are automatically connected to the DGs in sufficient time to provide for safe reactor shutdown and to mitigate the consequences of a Design Basis Accident (OBA) such as a LOCA.

Certain required plant loads are returned to service in a predetermined sequence in order to prevent overloading the DG in the process. Within the required interval (FSAR Table 8.3-3) after the initiating signal is received, all automatic and permanently connected loads needed to recover the plant or maintain it in a safe condition are returned to service.

Ratings for Train 1A, 1 B, 2A and 2B DGs satisfy the requirements of Regulatory Guide 1.9 (Ref. 3). The continuous service rating of each DG is 4400 kW with 10% overload permissible for up to 2 hours2.314815e-5 days 5.555556e-4 hours 3.306878e-6 weeks 7.61e-7 months in any 24 hour2.777778e-4 days 0.00667 hours 3.968254e-5 weeks 9.132e-6 months period. The ESF loads that are powered from the 6.9 kV shutdown boards are listed in Reference 2.

(continued)

B 3.8-2

BASES APPLICABLE SAFETY ANALYSES LCO Watts Bar-Unit 1 AC Sources - Operating B 3.8.1 The initial conditions of OBA and transient analyses in the FSAR, Section 6 (Ref. 4) and Section 15 (Ref. 5), assume ESF systems are OPERABLE. The AC electrical power sources are designed to provide sufficient capacity, capability, redundancy, and reliability to ensure the availability of necessary power to ESF systems so that the fuel, Reactor Coolant System (RCS), and containment design limits are not exceeded. These limits are discussed in more detail in the Bases for Section 3.2, Power Distribution Limits; Section 3.4, Reactor Coolant System (RCS); and Section 3.6, Containment Systems.

The OPERABILITY of the AC electrical power sources is consistent with the initial assumptions of the Accident analyses and is based upon meeting the design basis of the plant. This results in maintaining at least two DG's associated with one load group or one offsite circuit OPERABLE during Accident conditions in the event of:

a.

An assumed loss of all offsite power or all onsite AC power; and

b.

A worst case single failure.

The AC sources satisfy Criterion 3 of NRC Policy Statement.

Two qualified circuits between the Watts Bar Hydro 161 kV switchyard and the onsite Class 1 E Electrical Power System and separate and independent OGs for each train ensure availability of the required power to shut down the reactor and maintain it in a safe shutdown condition after an anticipated operational occurrence (AOO) or a postulated OBA.

Qualified offsite circuits are those that are described in the FSAR and are part of the licensing basis for the plant.

Each offsite circuit must be capable of maintaining acceptable frequency and voltage, and accepting required loads during an accident, while connected to the 6.9 kV shutdown boards.

Offsite power from the Watts Bar Hydro 161 kV switchyard to the onsite Class 1 E distribution system is from two independent immediate access circuits. Each of the two reauired circuits are routed from the switchyard through a 161 kV transmission line and one of fourtwe 161 to 6.9 kV transformer§ (common station service transformers CCSSTsl) to the onsite Class 1E distribution system.

Normally the two reauired circuits are aligned to power the 6.9 kV shutdown boards through CSST C and CSST 0. However. one of the two required circuits may also be aligned to power two shutdown boards in the same load group through either CSST A or CSST B and its associated Unit Boards. either directly from the CSST through the Unit Board or by automatic transfer from the Unit Station Service Transformer CUSST> to the CSST. Use of CSST A or B as an offsjte source reaujres that CSST A and B both be available and that the (continued)

B 3.8-3

BASES LCO (continued)

Watts Bar-Unit 1 AC Sources - Operating B 3.8.1 associated power and control feeders be in thejr normal positions to ensure independence. Due to independence limitations. CSST A and B cannot be credited for supply of both offsite oower sources simultaneously. The medium voltage power system starts at the low-side of the common station service transformers.

Each regujred offsite circujt is that combination of power sources described below that are either connected to the Class 1 E AC Electrical Power Distribution Svstem. or is available to be connected to the Class 1E AC Electrical Power Distribution Svstem through automatic transfer at the 6.9 kV Shutdown or Unit Boards within a few seconds. as reauired.

The following offsite oower configurations meet the requirements of the LCO:

1.

Normal Operation Ci.e.. all 6.9 kV shutdown boards aligned to their normal offsite circuit) - Two offsite circuits consisting of Ca> AND Cb> Cno board transfers required: a loss of either circuit will not prevent the minimum safety functions from being performed);

a.

From the 161 kV Watts Bar Hydro Switchvard CBay 13). through CSST C (winding Y) to 6.9 kV Shutdown Board 1A-A and (winding X) to 6.9 kV Shutdown Board 2A-A: AND

b.

From the 161 kV Watts Bar Hvdro Switchyard <Bay 4 ). through CSST D (winding X> to 6.9 kV Shutdown Board 1 B-B and (winding Y> to 6.9 kV Shutdown Board 28-B.

2.

Alternate Operation (i.e.. one or more 6.9 kV shutdown boards aligned to their alternate offsite circuit) -Two offsite circuits consisting of Cal AND (b)

AND (cl (as needed) (Note: 6.9 kV shutdown board(s) aligned to normal circuit reauire an OPERABLE automatic transfer: a loss of either circuit will not prevent the minimum safety functions from being performed);

a.

From the 161 kV Watts Bar Hydro Switchvard (Bay 13). through CSST C (winding Y> to 6.9 kV Shutdown Board 1A-A (normal) AND/OR Shutdown Board 2B-B (alternate) and (winding X> to 6.9 kV Shutdown Board 2A-A Cnormall AND/OR Shutdown Board 1B-B <alternate>:

b.

From the 161 kV Watts Bar Hvctro Switchvard <Bay 4). through CSST D (winding X> to 6.9 kV Shutdown Board 1 B-B (normal) ANO/OR Shutdown Board 2A-A <alternate) and (winding Yl to 6.9 kV Shutdown Board 28-B (normal> AND/OR Shutdown Board 1A-A (alternate); AND

c.

An OPERABLE transfer from the normal circuit to the alternate circuit for those 6.9 kV shutdown boards aligned to their normal circuit.

(continued)

B 3.8-4

BASES LCO (continued)

Watts Bar-Unit 1 AC Sources - Operating B 3.8.1

3.

Unjt Board Operation - Normal Supply (i.e.. one offsite circuit includes a unit board supplied by its normal power supply. the USST) - Two offsite circuits consisting of (a) OR Cb) (relies on automatic transfer of Unit Board power supply alignment from its normal supply CUSSTl to its alternate supply CCSST via the Start Bus):

a. CSST C out-of-service:

1) From the 161 kV Watts Bar Hvctro Switchyard (Bay 4 ). through CSST 0 (winding Xl to 6.9 kV Shutdown Board 1B-B and (winding Yl to 6.9 kV Shutdown Board 28-B:

2) From the 161 kV Watts Bar Hydro SWitchyard CBay 13). through CSST B (winding Y) to the 6.9 kV Unit Board 1 B and Unit Board 2B (Breakers 1622 & 1632 open):

3) From Unit Board 1B to 6.9 kV Shutdown Board 1A-A (Breaker 1718 closed);

4) From Unit Board 2B to 6.9 kV Shutdown Board 2A-A (Breaker 1818 closed); ANO

5) Unit Board 1 B and Unit Board 2B normal to alternate automatic transfer circuit OPERABLE.

b. CSST D out-of-service;

1) From the 161 kV Watts Bar Hydro Switchyard (Bay 13). through CSST C (winding Xl to 6.9 kV Shutdown Board 1A-A and (winding Yl to 6.9 kV Shutdown Board 2A-A:

2) From the 161 kV Watts Bar Hydro Switchyard (Bay 4). through CSST A (winding Yl to the 6.9 kV Unit Board 1C and Unit Board 2C (Breakers 1524 and 1534 open);

3) From Unit Board 1 C to 6.9 kV Shutdown Board 1 B-B <Breaker 1726 closed);

4) From Unit Board 2C to 6.9 kV Shutdown Board 2B-B (Breaker 1826 closed); ANO

5) Unit Board 1C and Unit Board 2C normal to alternate automatic transfer circuit OPERABLE.

(continued)

B3.8-5

BASES LCO (continued)

Watts Bar-Unit 1 AC Sources - Operating B 3.8.1

4) Unit Board Operation - Alternate Supply (i.e.. one offsite circuit includes a unit board supplied by its alternate power supply. the CSST via the Start Busl -

Two offsite circuits consisting of Cal OR Cbl (no board transfers reauiredl:

a. CSST C out-of-service:

1) From the 161 kV Watts Bar Hydro Switchyard CBay 4). through CSST D Cwjndjng Xl to 6.9 kV Shutdown Board 1B-B and (winding Yl to 6.9 kV Shutdown Board 2B-B: AND

2) From the 161 kV Watts Bar Hydro Switchvard CBay 13). through CSST B Cwindjng Yl to the 6.9 kV Unit Board 1 B and Unit Board 2B

<Breakers 1622 and 1632 closed) to 6.9 kV Shutdown Board 1A-A and to 6.9 kV Shutdown Board 2A-A (Breakers 1718 and 1818 closed).

respectively.

b. CSST D out-of-service 1l From the 161 kV Watts Bar Hydro Switchyard <Bay 13). through CSST C (winding Xl to 6.9 kV Shutdown Board 1A-A and (winding Yl to 6.9 kV Shutdown Board 2A-A: AND 2l From the 161 kV Watts Bar Hydro Switchvard CBay 4l. through CSST A (winding Yl to the 6.9 kV Unit Board 1C and Unit Board 2C

<Breakers 1524 and 1534 closed) to 6.9 kV Shutdown Board 1B-B and to 6.9 kV Shutdown Board 2B-B (Breakers 1726 and 1826 closed).

respectively.

Note: When using either CSST A or B as a qualified offsite circuit. the CSST CA or Bl not jn use as a qualified circujt must be available.

Each DG must be capable of starting, accelerating to rated speed and voltage, and connecting to its respective 6.9 kV shutdown board on detection of loss-of-voltage. This will be accomplished within 10 seconds. Each DG must also be capable of accepting required loads within the assumed loading sequence intervals, and continue to operate until offsite power can be restored to the 6.9 kV shutdown boards. These capabilities are required to be met from a variety of initial conditions such as DG in standby with the engine hot and DG in standby with the engine at ambient conditions. Additional DG capabilities must be demonstrated to meet required Surveillances, e.g., capability of the DG to revert to standby status on an accident signal while operating in parallel test mode.

(continued)

B 3.8-6

BASES LCO (continued)

Watts Bar-Unit 1 AC Sources - Operating B 3.8.1 Proper sequencing of loads, including tripping of nonessential loads, is a required function for DG OPERABILITY.

A Note has been added to indicate that the C-S DG may be substituted for any of the required DGs. However, the C-S DG cannot be declared OPERABLE until it is connected electrically in place of another DG, and it has satisfied applicable Surveillance Requirements.

The AC sources in one train must be separate and independent (to the extent possible) of the AC sources in the other train. For the DGs, separation and independence are complete. However. CSST A or B can onlv supply two 6.9 kV shutdown boards in the same load group. to ensure the separation criteria is met.

For the offsite AC sources, separation and independence are to the extent practical. A circuit may be connected to more than one ESF bus, with fast transfer capability to the other circuit OPERABLE, and not violate separation criteria. A circuit that is not connected to an ESF bus is required to have OPERABLE fast transfer inter1ock mechanisms to at least two ESF buses to support OPERABILITY of that circuit.

(continued)

B 3.8-7

BASES (continued)

APPLICABILITY ACTIONS Watts Bar.Unit 1 AC Sources

Operating B 3.8.1 The AC sources are required to be OPERABLE in MODES 1, 2, 3, and 4 to ensure that:

a.

Acceptable fuel design limits and reactor coolant pressure boundary limits are not exceeded as a result of AOOs or abnormal transients; and

b.

Adequate core cooling is provided and containment OPERABILITY and other vital functions are maintained in the event of a postulated OBA.

The AC power requirements for MODES 5 and 6 are covered in LCO 3.8.2, "AC Sources* Shutdown."

A Note prohibits the application of LCO 3.0.4.b to an inoperable DG. There is an increased risk associated with entering a MODE or other specified condition in the Applicability with an inoperable DG and the provisions of LCO 3.0.4.b, which allow entry into a MODE or other specified condition in the Applicability with the LCO not met after performance of a risk assessment addressing inoperable systems and components, should not be applied in this circumstance.

To ensure a highly reliable power source remains with one required offsite circuit inoperable, it is necessary to verify the OPERABILITY of the remaining required offsite circuit on a more frequent basis. Since the Required Action only specifies "perform," a failure of SR 3.8.1.1 acceptance criteria does not result in a Required Action not met. However, if a second required circuit fails SR 3.8.1.1, the second offsite circuit is inoperable, and Condition 0, for two required offsite circuits inoperable, is entered.

Required Action A.2, which only applies if the train cannot be powered from a requjredi:. offsite source, is intended to provide assurance that an event coincident with a single failure of the associated DG will not result in a complete loss of safety function of critical redundant required features. These features are powered from the redunaant AC electrical power trains. This includes motor driven auxiliary feedwater pump. Single train systems, such as the turbine driven auxiliary feedwater pump, may not be included.

B 3.8-8 (continued)

Revision 68, 116 Amendment 55

BASES ACTIONS (continued)

Watts Bar-Unit 1 AC Sources - Operating 83.8.1 According to Regulatory Guide 1.93 (Ref. 6), operation may continue in Condition A for a period that should not exceed 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months . With one required offsite circuit inoperable, the reliability of the offsite system is degraded, and the potential for a loss of offsite power is increased, with attendant potential for a challenge to the plant safety systems. In this Condition, however, the remaining OPERABLE offsite circuit and OGs are adequate to supply electrical power to the onsite Class 1 E Distribution System.

The 72 hour8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months Completion Time takes into account the capacity and capability of the remaining AC sources, a reasonable time for repairs, and the low probability of a OBA occurring during this period.

The second Completion Time for Required Action A.3 establishes a limit on the maximum time allowed for any combination of required AC power sources to be inoperable during any single contiguous occurrence of failing to meet the LCO. If Condition A is entered while, for instance, a DG is inoperable and that OG is subsequently returned OPERABLE, the LCO may already have been not met for up to 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months . This could lead to a total of 144 hours0.00167 days 0.04 hours 2.380952e-4 weeks 5.4792e-5 months , since initial failure to meet the LCO, to restore the offsite circuit. At this time, a DG could again become inoperable, the circuit restored OPERABLE, and an additional 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months (for a total of 9 days) allowed prior to complete restoration of the LCO. The 6 day Completion Time provides a limit on the time allowed in a specified condition after discovery of failure to meet the LCO. This limit is considered reasonable for situations in which Conditions A and Bare entered concurrently. The "At::IQ" connector between the 72 hour8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months and 6 day Completion Times means that both Completion Times apply simultaneously, and the more restrictive Completion Time must be met.

As in Required Action A.2, the Completion Time allows for an exception to the normal "time zero" for beginning the allowed outage time "clock." This will result in establishing the "time zero" at the time that the LCO was initially not met, instead of at the time Condition A was entered.

(continued)

B 3.8-10

BASES ACTIONS (continued)

Watts Bar-Unit 1 B.1 and C.1 AC Sources - Operating B 3.8.1 To ensure a highly reliable power source remains with one or more DGs inoperable in Train A OR with one or more DGs inoperable in Train B, it is necessary to verify the availability of the required offsite circuits on a more frequent basis. Since the Required Action only specifies "perform," a failure of SR 3.8. 1.1 acceptance criteria does not result in a Required Action being not met.

However, if a circuit fails to pass SR 3.8. 1.1, it is inoperable. Upon required offsite circuit inoperability, additional Conditions and Required Actions must then be entered.

B.2and C.2 Required Actions B.2 and C.2 are intended to provide assurance that a loss of offsite power, during the period that a DG is inoperable, does not result in a complete loss of safety function of critical systems. These features are designed with redundant safety related trains. This includes motor driven auxiliary feedwater pumps. Single train systems, such as the turbine driven auxiliary feedwater pump, are not included. Redundant required feature failures consist of inoperable features associated with a train, redundant to the train that has inoperable DG(s).

The Completion Time for Required Actions 8.2 and C.2 are intended to allow the operator time to evaluate and repair any discovered inoperabilities. This Completion Time also allows for an exception to the normal "time zero" for beginning the allowed outage time Kclock." In this Required Action, the Completion Time only begins on discovery that both:

a.

An inoperable DG exists; and

b.

A required feature on the other train (Train A or Train B) is inoperable.

If at any time during the existence of this Condition (one or more DGs inoperable) a required feature subsequently becomes inoperable, this Completion Time would begin to be tracked.

Discovering one or more required DGs in Train A or one or more DGs in Train B inoperable coincident with one or more inoperable required support or supported features, or both, that are associated with the OPERABLE DGs, results in starting the Completion Time for the Required Action. Four hours from the discovery of these events existing concurrently is Acceptable because it minimizes risk while allowing time for restoration before subjecting the plant to transients associated with shutdown.

B 3.8-11 (continued)

Revision 50 Amendment 39

BASES ACTIONS (continued)

Watts Bar-Unit 1 p.1 and D.2 AC Sources - Operating B 3.8.1 Required Action 0.1, which applies when two required offsite circuits are inoperable, is intended to provide assurance that an event with a coincident single failure will not result in a complete loss of redundant required safety functions.

The Completion Time for this failure of redundant required features is reduced to 12 hours1.388889e-4 days 0.00333 hours 1.984127e-5 weeks 4.566e-6 months from that allowed for one train without offsite power (Required Action A.2). The rationale for the reduction to 12 hours1.388889e-4 days 0.00333 hours 1.984127e-5 weeks 4.566e-6 months is that Regulatory Guide 1.93 (Ref. 6) allows a Completion Time of 24 hours2.777778e-4 days 0.00667 hours 3.968254e-5 weeks 9.132e-6 months for two required offsite circuits inoperable, based upon the assumption that two complete safety trains are OPERABLE. When a concurrent redundant required feature failure exists, this assumption is not the case, and a shorter Completion Time of 12 hours1.388889e-4 days 0.00333 hours 1.984127e-5 weeks 4.566e-6 months is appropriate. These features are powered from redundant AC safety trains. This includes motor driven auxiliary feedwater pumps. Single train features, such as the turbine driven auxiliary pump, are not included in the list.

The Completion Time for Required Action 0.1 is intended to allow the operator time to evaluate and repair any discovered inoperabilities. This Completion Time also allows for an exception to the normal "time zero" for beginning the allowed outage time "clock." In this Required Action the Completion Time only begins on discovery that both:

a.

All required offsite circuits are inoperable; and

b.

A required feature is inoperable.

If at any time during the existence of Condition D (two offsite circuits inoperable) a required feature becomes inoperable, this Completion Time begins to be tracked.

According to Regulatory Guide 1.93 (Ref. 6), operation may continue in Condition 0 for a period that should not exceed 24 hours2.777778e-4 days 0.00667 hours 3.968254e-5 weeks 9.132e-6 months . This level of degradation means that the offsite electrical power system does not have the capability to effect a safe shutdown and to mitigate the effects of an accident; however, the onsite AC sources have not been degraded. This level of degradation generally corresponds to a total loss of the immediately accessible offsite power sources.

Because of the normally high availability of the offsite sources, this level of degradation may appear to be more severe than other combinations of two AC sources inoperable (e.g., combinations that involve an offsite circuit and one OG inoperable, or one or more OGs in each train inoperable). However, two factors tend to decrease the severity of this level of degradation:

B 3.8-12 (continued)

Revision 50 Amendment 39

BASES ACTIONS Watts Bar-Unit 1 Q.1 and 0.2 (continued)

AC Sources - Operating B 3.8.1

a.

The configuration of the redundant AC electrical power system that remains available is not susceptible to a single bus or switching failure; and

b.

The time required to detect and restore an unavailable reauired offsite power source is generally much less than that required to detect and restore an unavailable onsite AC source.

With both of the required offsite circuits inoperable, sufficient onsite AC sources are available to maintain the plant in a safe shutdown condition in the event of a OBA or transient. In fact, a simultaneous loss of offsite AC sources, a LOCA, and a worst case single failure were postulated as a part of the design basis in the safety analysis. Thus, the 24 hour2.777778e-4 days 0.00667 hours 3.968254e-5 weeks 9.132e-6 months Completion Time provides a period of time to effect restoration of one of the offsite circuits commensurate with the importance of maintaining an AC electrical power system capable of meeting its design criteria.

According to Reference 6, with the available offsite AC sources, two less than required by the LCO, operation may continue for 24 hours2.777778e-4 days 0.00667 hours 3.968254e-5 weeks 9.132e-6 months . If two offsite sources are restored within 24 hours2.777778e-4 days 0.00667 hours 3.968254e-5 weeks 9.132e-6 months , unrestricted operation may continue. If only one offsite source is restored within 24 hours2.777778e-4 days 0.00667 hours 3.968254e-5 weeks 9.132e-6 months , power operation continues in accordance with Condition A.

E.1 and E.2 Pursuant to LCO 3.0.6, the Distribution System ACTIONS would not be entered even if all AC sources to it were inoperable, resulting in de-energization.

Therefore, the Required Actions of Condition E are modified by a Note to indicate that when Condition E is entered with no AC source to any train, the Conditions and Required Actions for LCO 3.8.9, "Distribution Systems - Operating," must be immediately entered. This allows Condition E to provide requirements for the loss of one offsite circuit and one or more DGs in a train, without regard to whether a train is de-energized. LCO 3.8.9 provides the appropriate restrictions for a de-energized train.

According to Regulatory Guide 1.93 (Ref. 6), operation may continue in Condition E for a period that should not exceed 12 hours1.388889e-4 days 0.00333 hours 1.984127e-5 weeks 4.566e-6 months .

B 3.8-13 (continued)

Revision 50 Amendment 39

BASES SURVEILLANCE REQUIREMENTS (continued)

Watts Bar-Unit 1 SR 3.8.1.7 See SR 3.8.1.2.

SR 3.8.1.8 AC Sources - Operating B 3.8.1 Transfer of each 6.9 kV shutdown board power supply from the normal offsite circuit to the alternate offsite circuit demonstrates the OPERABILITY of the alternate circuit distribution network to power the shutdown loads. The 18 month Frequency of the Surveillance is based on engineering judgment, taking into consideration the plant conditions required to perform the Surveillance, and is intended to be consistent with expected fuel cycle lengths. Operating experience has shown that these components usually pass the SR when performed at the 18 month Frequency. Therefore, the Frequency was concluded to be acceptable from a reliability standpoint.

This SR is modified by twoa Note_!. The reason for the first Note is that, during operation with the reactor critical, performance of this SR for the 1A-A or 1 B-B Shutdown Board could cause perturbations to the electrical distribution systems that could challenge continued steady state operation and, as a result, plant safety systems. This restriction from normally performing the Surveillance in MODE 1 or 2 is further amplified to allow the Surveillance to be performed for the purpose of reestablishing OPERABILITY (e.g.. post work testing following corrective maintenance. corrective modification. deficient or incomplete surveillance testing. and other unanticioated OPERABILITY concerns) provided an assessment determjnes plant safety js majntained or enhanced. This assessment shall. as a minimum. consider the potential outcomes and transients associated with a failed Surveillance. a successful Surveillance. and a perturbation of the offsite or onsite svstem when they are tied together or operated independently for the Surveillance: as well as the operator procedures available to cope with these outcomes. These shall be measured against the avoided risk of a plant shutdown and startup to detennjne that plant safety is maintained or enhanced when the Surveillance is performed in MODE 1 or 2.

Risk insights or deterministic methods may be used for this assessment. Credit may be taken for unplanned events that satisfy this SR. Examples of unplanned events may include:

1)

Unexpected operational events which cause the equipment to perform the function specified by this Surveillance, for which adequate documentation of the required performance is available; and

2)

Post corrective maintenance testing that requires performance of this Surveillance in order to restore the component to OPERABLE, provided the maintenance was required, or performed in conjunction with maintenance required to maintain OPERABILITY or reliability.

(continued)

B 3.8-19

BASES SURVEILLANCE REQUIREMENTS Watts Bar-Unit 1 SR 3.8.1.8 (continued)

AC Sources - Operating B 3.8.1 Note 2 specifies that the transfer capability is only required to be met when one or more 6.9 kV shutdown boards require normal and alternate power supplies.

When all the 6.9 kV shutdown boards are supplied power by their normal power supply the alternate power supply is not reauired. When one or more of the 6.9 kV shutdown boards are supplied power from their alternate power supply the automatic transfer for those 6.9 kV shutdown boards required to transfer from their normal to alternate power supply is required to be OPERABLE. If one or more of the 6.9 kV shutdown boards are aligned to its alternate source CCSST C or CSST 0) this SR verifies that at least two 6.9 kV shutdown boards in the same load group will be powered from an offsite circuit if a fault occurs on either circuit.

SR 3.8.1.9 Each DG is provided with an engine overspeed trip to prevent damage to the engine. Recovery from the transient caused by the loss of a large load could cause diesel engine overspeed, which, if excessive, might result in a trip of the engine. This Surveillance demonstrates the DG load response characteristics and capability to reject the largest single load without exceeding predetermined voltage and frequency and while maintaining a specified margin to the overspeed trip. The largest single load for each DG is the essential raw cooling water pump at 800 HP. This Surveillance may be accomplished by: 1) tripping the DG output breaker with the DG carrying greater than or equal to its associated single largest post accident load while paralleled to offsite power or while solely supplying the bus, or 2) tripping its associated single largest post accident load with the DG solely supplying the bus. As required by Regulatory Guide 1.9, C1.4 (Ref. 3), the load rejection test is acceptable if the increase in diesel speed does not exceed 75% of the difference between synchronous speed and the overspeed trip setpoint, or 15% above synchronous speed, whichever is lower.

The time, voltage, and frequency tolerances specified in this SR are derived from Regulatory Guide 1.9 (Ref. 3) recommendations for response during load sequence intervals. The 3 seconds specified is equal to 60% of a typical 5 second load sequence interval associated with sequencing of the largest load.

The voltage and frequency specified are consistent with the design range of the equipment powered by the DG. SR 3.8. 1.9.a corresponds to the maximum frequency excursion, while SR 3.8.1.9.b and SR 3.8.1.9.c are steady state voltage and frequency values to which the system must recover following load rejection.

The 18 month Frequency is consistent with the recommendation of Regulatory Guide 1.9 (Ref. 3).

(continued}

B 3.8-20

BASES SURVEILLANCE REQUIREMENTS Watts Bar-Unit 1 SR 3.B.1.21 (continued)

AC Sources - Operating B 3.8.1 The Frequency for accelerated testing is 7 days, but no less than 24 hours2.777778e-4 days 0.00667 hours 3.968254e-5 weeks 9.132e-6 months . Tests conducted at intervals of less than 24 hours2.777778e-4 days 0.00667 hours 3.968254e-5 weeks 9.132e-6 months may be credited for compliance with Required Actions. However, for the purpose of re-establishing the normal 31-day Frequency, a successful test at an interval of less than 24 hours2.777778e-4 days 0.00667 hours 3.968254e-5 weeks 9.132e-6 months should be considered an invalid test and not count towards the 7 consecutive failure free starts, and the consecutive test count is not reset.

A test interval in excess of 7 days (or 31 days as appropriate) constitutes a failure to meet the SRs and results in the associated DG being declared inoperable. It does not, however, constitute a valid test or failure of the DG, and any consecutive test count is not reset.

SR 3.8.1.22 Transfer of the 6.9 kV Unit Boards 1 B. 1 C. 2B. and 2C power supply from the normal power supply (USST> to the alternate power supply (CSST via the 6.9 kV Start Bus) demonstrates the OPERABILITY of the maintenance offsite circuit to power the shutdown loads wben tbe shutdown board is powered from the USST.

The 18-month Freauencv of the Surveillance is based on engineerjng judgment.

taking into consideration the plant conditions required to perform the Surveillance.

and is intended to be consistent with expected fuel cycle lengths. Operating experience has shown that these components usually pass the SR when performed at the 18 month Frequency. Therefore. the Frequency is acceptable from a reliabilitv standpoint.

This SR is modified by two Notes. The reason for the first Note is that. during operation with the reactor critical. performance of this SR for the 1 B or 1 C Unit Board could cause perturbations to the electrical distribution svstems that could challenge continued steadv state operation and. as a result. plant safetv svstems.

This restriction from normally performing the Surveillance in MODE 1 or 2 is further amplified to allow the Surveillance to be perfornJed for the pumose of reestablishing OPERABILITY (e.g., post work testing following corrective maintenance. corrective modification. deficient or incomplete surveillance testing.

and other unanticipated OPERABILITY concerns) provided an assessment determines olant safety is maintained or enhanced. This assessment shall. as a minimum, consider the potential outcomes and transients associated with a failed Surveillance, a successful Surveillance. and a perturbation of the offsite or onsite svstem when they are tied together or operated jndeoendently for the Surveillance: as well as the operator procedures available to cope with these outcomes. These shall be measured against the avoided risk of a plant shutdown and startup to determine that plant safety is maintained or enhanced when the Surveillance is performed in MODE 1 or 2. Risk insights or deterministic methods may be used for this assessment. Credit may be taken for unplanned events that satisfy this SR. Examples of unplanned events may include:

1} Unexpected operational events which cause the equipment to perform the function specified by this Surveillance. for which adequate documentation of the required performance is available: and B 3.8-34 Revision 50 Amendment 39

BASES SURVEILLANCE REQUIREMENTS REFERENCES Watts Bar-Unit 1 AC Sources - Operating B 3.8.1 SR 3.8.1.22 (continued)

~ Post corrective maintenance testing that requires performance of this Surveillance in order to restore the component to OPERABLE. provided the maintenance was required. or performed in conjunction with maintenance required to maintain OPERABILITY or reliabilitv.

Note 2 specifies that transfer capability is only required to be met for 6.9 kV Unit Boards that require normal and alternate power supplies. If the unit board is not a part of the required qualified circuit or the qualified circuit is powered from the CSST through the unit board to the 6.9 kV shutdown board. the automatic transfer is not required.

1.

Title 10, Code of Federal Regulations, Part 50, Appendix A, General Design Criterion (GDC) 17, "Electrical Power Systems."

2.

Watts Bar FSAR, Section 8.2, "Offsite Power System," and Tables 8.3-1 to 8.3-3, "Safety-Related Standby Power Sources and Distribution Boards," "Shutdown Board Loads Automatically Tripped Following a Loss of Nuclear Unit and Preferred Power," and "Diesel Generator Load Sequentially Applied Following a Loss of Nuclear Unit and Preferred Power."

3.

Regulatory Guide 1.9, Rev. 3, "Selection, Design, Qualification and Testing of Emergency Diesel Generator Units Used as Class 1E Onsite Electric Power Systems at Nuclear Power Plants," July 1993.

4.

Watts Bar FSAR Section 6, "Engineered Safety Features."

5.

Watts Bar FSAR, Section 15.4, "Condition IV-Limiting Faults."

6.

Regulatory Guide 1.93, Rev. 0, "Availability of Electric Power Sources,"

December 1974.

7.

Generic Letter 84-15, "Proposed Staff Actions to Improve and Maintain Diesel Generator Reliability," July 2, 1984.

8.

Title 10, Code of Federal Regulations, Part 50, Appendix A, GDC 18, "Inspection and Testing of Electric Power Systems."

9.

Regulatory Guide 1.137, Rev. 1, "Fuel Oil Systems for Standby Diesel Generators," October 1979.

10.

Watts Bar Drawing 1-47W605-242, "Electrical Tech Spec Compliance Tables.

11.

TVA's letter to NRC dated August 7, 2001, Technical Specification Change TS-01-04, Diesel Generator (DG) Risk Informed Allowed Outage Time (AOT) Extension B 3.8-35 Revision 50 Amendment 39

Distribution Systems - Operating B 3.8.9 B 3.8 ELECTRICAL POWER SYSTEMS B 3.8.9 Distribution Systems - Operating BASES BACKGROUND Watts Bar-Unit 1 The onsite Class 1 E AC electrical power distribution system is divided by train into two redundant and independent AC electrical power distribution subsystems.

The AC electrical power subsystem includes four 6.9 kV shutdown boards. Each 6.9 kV shutdown board has access to the two separate and independent preferred offsite sources of power as well as a dedicated onsite diesel generator (DG) source. Usually. oOne of the two offsite sources will be the normal power source for a 6.9 kV shutdown board, and the other offsite source will be the alternate power source. Transfers from the normal source to the alternate source may be manual or automatic. Automatic transfers only occur when the relay logic is tripping a transmission line and the associated common station service transformers. Only manual transfers are permitted from alternate to normal.

Additionally. the maintenance source to the 6.9 kV shutdown board can be used as an offsite power source." Transferring the 6.9 kV shutdown board to the maintenance power source is done manually from the normal or alternate power source. For a loss of offsite power to the 6.9 kV shutdown boards, the onsite emergency power system supplies power to the 6.9 kV shutdown boards. Control power for the 6.9 kV breakers is supplied from the Class 1 E batteries. Additional description of this system may be found in the Bases for LCO 3.8.1, "AC Sources-Operating," and the Bases for LCO 3.8.4, "DC Sources - Operating."

The AC Distribution System includes the 480 V shutdown boards and associated supply transformers, load centers, and protective devices shown in Table B 3.8.9-1.

The 120 VAC vital buses are arranged in four load groups and are normally powered from the unit inverters or spare inverters and DC Boards I, II, Ill, and IV.

An alternate power supply for the vital buses is a regulated transformer bypass source powered from the same train as the associated unit inverter, and its use is governed by LCO 3.8.7, "Inverters - Operating."

There are four independent 125 VOC electrical power distribution buses. Each bus receives normal power from an independent 480 VAC shutdown board via its associated battery charger. Upon loss of 480 VAC shutdown board power, the DC buses are energized by their connected battery banks.

The list of all required distribution buses is presented in Table B 3.8.9-1.

(continued)

B 3.8-89 Revision 67, 75, 76, n. 78

ENCLOSURE2 ATIACHMENT3 Clean Typed TS Pages Watts Bar Nuclear Plant - Unit 1 For Information Only Check with the TVA Nuclear Licensing contact listed on the cover letter prior to issuing TS pages. Current TS may have changed due to implementation of License Amendments implemented after these TS pages were submitted (e.g., WBN Unit 1 License Amendment 84

[ML101390154]).

AC Sources - Operating 3.8.1 3.8 ELECTRICAL POWER SYSTEMS 3.8.1 AC Sources - Operating LCO 3.8.1 APPLICABILITY:

ACTIONS The following AC electrical sources shall be OPERABLE:

a.

Two qualified circuits between the offsite transmission network and the onsite Class 1E AC Electrieal Power Distribution System; and

b.

Four diesel generators (DGs) capable of supplying the onsite Class 1 E AC Electrical Power Distribution System.

NOTE------------------------

The C-S DG may be substituted for any of the required DGs.

MODES 1, 2, 3, and 4.

NOTE---------------------

LCO 3.0.4.b is not applicable to DGs.

CONDITION A.

One required offsite circuit A.1 inoperable.

Watts Bar-Unit 1 AND A.2 REQUIRED ACTION COMPLETION TIME Perform SR 3.8.1.1 for required 1 hour1.157407e-5 days 2.777778e-4 hours 1.653439e-6 weeks 3.805e-7 months OPERABLE offsite circuit.

Declare required feature(s) with no offsite power available inoperable when its redundant required feature(s) is inoperable.

3.8-1 Once per 8 hours9.259259e-5 days 0.00222 hours 1.322751e-5 weeks 3.044e-6 months thereafter 24 hours2.777778e-4 days 0.00667 hours 3.968254e-5 weeks 9.132e-6 months from discovery of no offsite power to one train concurrent with inoperability of redundant required feature(s)

(continued)

Amendment 39

ACTIONS CONDITION A.

(continued)

A.3 B.

One required DG B.1 inoperable.

AND B.2 AND B.3.1 B.3.2 AND Watts Bar-Unit 1 REQUIRED ACTION Restore required offsite circuit to OPERABLE status.

Perform SR 3.8.1.1 for the required offsite circuits.

Declare required feature(s) supported by the inoperable DG inoperable when its required redundant feature(s) is inoperable.

Determine OPERABLE DGs are not inoperable due to common cause failure.

OR Perform SR 3.8.1.2 for OPERABLE DGs.

3.8-2 AC Sources - Operating 3.8.1 COMPLETION TIME 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months AND 6 days from discovery of failure to meetLCO 1 hour1.157407e-5 days 2.777778e-4 hours 1.653439e-6 weeks 3.805e-7 months AND Once per 8 hours9.259259e-5 days 0.00222 hours 1.322751e-5 weeks 3.044e-6 months thereafter 4 hours4.62963e-5 days 0.00111 hours 6.613757e-6 weeks 1.522e-6 months from discovery of Condition B concurrent with inoperability of redundant required feature(s) 12 hours1.388889e-4 days 0.00333 hours 1.984127e-5 weeks 4.566e-6 months 12 hours (continued)

Amendment 39

ACTIONS CONDITION B.

(continued)

B.4

c.

Two required DGs in Train C.1 A inoperable.

OR Two required DGs in Train B inoperable.

AND C.2 AND C.3.1 C.3.2 AND Watts Bar-Unit 1 REQUIRED ACTION Restore required DG to OPERABLE status.

Perfonn SR 3.8.1.1 for the required offsite circuits.

Declare required feature(s) supported by the inoperable DGs inoperable when its required redundant feature(s) is inoperable.

Detennine OPERABLE DGs are not inoperable due to common cause failure.

OR Perfonn SR 3.B.1.2 for OPERABLE DGs.

3.8-2a AC Sources - Operating 3.8.1 COMPLETION TIME 14 days AND 17 days from discovery of failure to meetLCO 1 hour1.157407e-5 days 2.777778e-4 hours 1.653439e-6 weeks 3.805e-7 months AND Once per B hours thereafter 4 hours4.62963e-5 days 0.00111 hours 6.613757e-6 weeks 1.522e-6 months from discovery of Condition C concurrent with inoperability of redundant required feature(s) 12 hours1.388889e-4 days 0.00333 hours 1.984127e-5 weeks 4.566e-6 months 12 hours (continued)

Amendment 39

CONDITION REQUIRED ACTION C.

(continued)

C.4 Restore at least one required DG to OPERABLE status.

D.

Two required offsite circuits D.1 Declare required feature(s) inoperable.

inoperable when its redundant required feature(s) is inoperable.

AND D.2 Restore one required offsite circuit to OPERABLE status.

Watts Bar-Unit 1 3.8-3 AC Sources-Operating 3.8.1 COMPLETION TIME 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months AND 6 days from discovery of failure to meet LCO 12 hours1.388889e-4 days 0.00333 hours 1.984127e-5 weeks 4.566e-6 months from discovery of Condition D concurrent with inoperability of redundant required features 24 hours2.777778e-4 days 0.00667 hours 3.968254e-5 weeks 9.132e-6 months (continued)

Amendment 30, 39

ACTIONS (continued)

CONDITION E.

One required offsite circuit inoperable.

AND One or more required DG(s) in Train A inoperable.

OR One or more required OG(s) in Train B inoperable.

F.

One or more required DG(s) in Train A inoperable.

AND One or more required DG(s) in Train B inoperable.

G.

Required Action and Associated Completion Time of Condition A, B, C, 0, E, or F not met.

Watts Bar-Unit 1 REQUIRED ACTION

NOTE------

Enter applicable Conditions and Required Actions of LCO 3.8.9, "Distribution Systems - Operating,"

when Condition E is entered with no AC power source to any train.

E.1 Restore required offsite circuit to OPERABLE status.

OR E.2 Restore required OG(s) to OPERABLE status.

F.1 Restore required DGs in Train A to OPERABLE status.

OR F.2 Restore required OGs in Train B to OPERABLE status G.1 Bein MODE3.

AND G.2 Bein MODES.

3.8-4 AC Sources-Operating 3.8.1 COMPLETION TIME 12 hours1.388889e-4 days 0.00333 hours 1.984127e-5 weeks 4.566e-6 months 12 hours 2 hours2.314815e-5 days 5.555556e-4 hours 3.306878e-6 weeks 7.61e-7 months 2 hours 6 hours6.944444e-5 days 0.00167 hours 9.920635e-6 weeks 2.283e-6 months 36 hours (continued)

Amendment 39

ACTIONS (continued)

CONDITION H.

Two required offsite circuits inoperable.

AND One or more required DG(s) in Train A inoperable.

QB One or more required DG(s) in Train B inoperable.

I.

One required offsite circuit inoperable.

AND One or more required DG(s) in Train A inoperable.

AND One or more required DG(s) in Train B inoperable.

Watts Bar-Unit 1 REQUIRED ACTION H.1 Enter LCO 3.0.3.

1.1 Enter LCO 3.0.3.

3.6-5 AC Sources-Operating 3.6.1 COMPLETION TIME Immediately Immediately Amendment 39

SURVEILLANCE REQUIREMENTS SURVEILLANCE AC Sources-Operating 3.8.1 FREQUENCY SR 3.8.1.1 Verify correct breaker alignment and indicated power 7 days SR 3.8.1.2 Watts Bar-Unit 1 availability for each required offsite circuit.

NOTES-------

1.

Performance of SR 3.8.1. 7 satisfies this SR.

2.

A modified DG start involving idling and gradual acceleration to synchronous speed may be used for this SR as recommended by the manufacturer. When modified start procedures are not used, the time, voltage, and frequency tolerances of SR 3.8.1. 7 must be met.

Verify each DG starts from standby conditions and achieves steady state voltage ~ 6800 V and s 7260 V, and frequency~ 58.8 Hz ands 61.2 Hz.

3.8-6 As specified in Table 3.8.1-1 (continued)

AC Sources-Operating 3.8.1 SURVEILLANCE REQUIREMENTS (continued)

SR 3.8.1.7 SR3.8.1.8 Watts Bar-Unit 1 SURVEILLANCE FREQUENCY Verify each DG starts from standby condition and 184 days achieves in s 10 seconds, voltage ~ 6800 V, and frequency ~ 56.6 Hz. Verify after DG fast start from standby conditions that the DG achieves steady state voltage~ 6600 V ands 7260 V, and frequency~ 56.8 Hz ands 61.2 Hz.

NOTES----------

1.

For the 1A-A and 1 B-B Shutdown Boards, this Surveillance shall not normally be performed in MODE 1 or 2. However, this Surveillance may be performed to reestablish OPERABILITY provided an assessment determines the safety of the plant is maintained or enhanced. Credit may be taken for unplanned events that satisfy this SR.

2. Transfer capability is only required to be met for 6.9 kV shutdown boards that require normal and alternate power supplies.

Verify automatic and manual transfer of each 6.9 kV 16 months shutdown board power supply from the normal offsite circuit to the alternate offsite circuit.

(continued) 3.8-8 Amendment 69

SURVEILLANCE REQUIREMENTS (continued)

SR 3.8.1.21 SR 3.8.1.22 Watts Bar-Unit 1 SURVEILLANCE Verify when started simultaneously from standby condition, each DG achieves, ins 10 seconds, voltage 2: 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 s 7260 V, and frequency 2: 58.8 Hz and s 61.2 Hz.

NOTES-------

1. For the 1 B and 1 C Unit Boards, this Surveillance shall not normally be performed in MODE 1 or 2.

However, this surveillance may be performed to reestablish OPERABILITY provided an assessment determines the safety of the plant is maintained or enhanced. Credit may be taken for unplanned events that satisfy this SR.

2. Transfer capability is only required to be met for 6.9 kV unit boards that require normal and alternate power supplies.

Verify automatic transfer of each 6.9 kV Unit Board 1 B, 1C, 2B, and 2C power supply from the normal power supply to the alternate power supply.

3.8-16 AC Sources-Operating 3.8.1 FREQUENCY 10 years 18 months

ENCLOSURE2 ATTACHMENT 4 Proposed TS Bases Changes (Clean Typed)

Watts Bar Nuclear Plant - Unit 1

AC Sources - Operating B 3.8.1 B 3.8 ELECTRICAL POWER SYSTEMS B 3.8.1 AC Sources-Operating BASES BACKGROUND Watts Bar-Unit 1 The plant AC Electrical Power Distribution System AC sources consist of the offsite power sources (preferred power sources, normal and alternate(s)), and the onsite standby power sources (Train A and Train B diesel generators (DGs)). As required by 10 CFR 50, Appendix A, GDC 17 (Ref. 1 ), the design of the AC electrical power system provides independence and redundancy to ensure an available source of power to the Engineered Safety Feature (ESF) systems.

The onsite Class 1 E AC Distribution System supplies electrical power to four power trains, shared between the two units, with each train powered by an independent Class 1 E 6.9 kV shutdown board. Power trains 1A and 2A comprise load group A, and power trains 1 B and 28 comprise load Group B. Two DGs associated with one load group can provide all safety related functions to mitigate a loss-of-coolant accident (LOCA) in one unit and safely shutdown the opposite unit. Each 6.9 kV shutdown board has two separate and independent offsite sources of power as well as a dedicated onsite DG source. The A and B train ESF systems each provide for the minimum safety functions necessary to shut down the plant and maintain it in a safe shutdown condition. Power can be supplied to each Class 1 E 6.9 kV shutdown board from a normal off site circuit (either CSST C or D) an alternate offsite circuit (either CSST C or D), a maintenance offsite circuit (either CSST A or B), or a DG.

Offsite power is supplied to the Watts Bar 161 kV transformer yard by two dedicated lines from the Watts Bar Hydro Plant switchyard. This is described in more detail in FSAR Section 8 (Ref.2). From the 161 kV transformer yard, two electrically and physically separated circuits provide AC power, through step-down common station service transformers, to the 6.9 kV shutdown boards. The two offsite AC electrical power sources are designed and located so as to minimize to the extent practical the likelihood of their simultaneous failure under operating and postulated accident and environmental conditions. A detailed description of the offsite power network and the circuits to the Class 1 E shutdown boards is found in Reference 2.

An offsite circuit consists of all breakers, transformers, switches, interrupting devices, cabling, and controls required to transmit power from the offsite transmission network (i.e., Watts Bar Hydro Plant switchyard) to the onsite Class 1E ESF buses (i.e., 6.9 kV shutdown boards).

(continued)

B 3.8-1

BASES BACKGROUND (continued)

Watts Bar-Unit 1 AC Sources - Operating B 3.8.1 A single offsite circuit is capable of providing the ESF loads. Two of these circuits are required to meet the Limiting Condition for Operation.

The onsite standby power source for each 6.9 kV shutdown board is a dedicated DG. WBN uses 4 DG sets for Unit 1 operation. These same DGs will be shared for Unit 2 operation. WBN may utilize a C-S DG that can be manually aligned (electrically and mechanically) to any 6.9 kV shutdown board to replace an existing DG. A DG starts automatically on a safety injection (SI) signal (i.e., low pressurizer pressure or high containment pressure signals) or on an 6.9 kV shutdown board degraded voltage or loss-of-voltage signal (refer to LCO 3.3.5, "Loss of Power (LOP) Diesel Generator (DG) Start Instrumentation"). After the DG has started, it will automatically tie to its respective 6.9 kV shutdown board after offsite power is tripped as a consequence of 6.9 kV shutdown board loss-of-voltage or degraded voltage, independent of or coincident with an SI signal. The DGs will also start and operate in the standby mode without tying to the 6.9 kV shutdown board on an SI signal alone. Following the trip of offsite power, a loss-of-voltage signal strips all nonpermanent loads from the 6.9 kV shutdown board.

When the DG is tied to the 6.9 kV shutdown board, loads are then sequentially connected to its respective 6.9 kV shutdown board by the automatic sequencer.

The sequencing logic controls the permissive and starting signals to motor breakers to prevent overloading the DG by automatic load application.

In the event of a loss of preferred power, the 6.9 kV shutdown boards are automatically connected to the DGs in sufficient time to provide for safe reactor shutdown and to mitigate the consequences of a Design Basis Accident (OBA) such as a LOCA.

Certain required plant loads are returned to service in a predetermined sequence in order to prevent overloading the DG in the process. Within the required interval (FSAR Table 8.3-3) after the initiating signal is received, all automatic and permanently connected loads needed to recover the plant or maintain it in a safe condition are returned to service.

Ratings for Train 1A, 1 B, 2A and 2B DGs satisfy the requirements of Regulatory Guide 1.9 {Ref. 3). The continuous service rating of each DG is 4400 kW with 10% overload permissible for up to 2 hours2.314815e-5 days 5.555556e-4 hours 3.306878e-6 weeks 7.61e-7 months in any 24 hour2.777778e-4 days 0.00667 hours 3.968254e-5 weeks 9.132e-6 months period. The ESF loads that are powered from the 6.9 kV shutdown boards are listed in Reference 2.

(continued)

B 3.8-2

BASES APPLICABLE SAFETY ANALYSES LCO Watts Bar-Unit 1 AC Sources - Operating B 3.8.1 The initial conditions of OBA and transient analyses in the FSAR, Section 6 (Ref. 4) and Section 15 (Ref. 5), assume ESF systems are OPERABLE. The AC electrical power sources are designed to provide sufficient capacity, capability, redundancy, and reliability to ensure the availability of necessary power to ESF systems so that the fuel, Reactor Coolant System (RCS), and containment design limits are not exceeded. These limits are discussed in more detail in the Bases for Section 3.2, Power Distribution Limits; Section 3.4, Reactor Coolant System (RCS); and Section 3.6, Containment Systems.

The OPERABILITY of the AC electrical power sources is consistent with the initial assumptions of the Accident analyses and is based upon meeting the design basis of the plant. This results in maintaining at least two DG's associated with one load group or one offsite circuit OPERABLE during Accident conditions in the event of:

a.

An assumed loss of all offsite power or all onsite AC power; and

b.

A worst case single failure.

The AC sources satisfy Criterion 3 of NRC Policy Statement.

Two qualified circuits between the Watts Bar Hydro 161 kV switchyard and the onsite Class 1 E Electrical Power System and separate and independent DGs for each train ensure availability of the required power to shut down the reactor and maintain it in a safe shutdown condition after an anticipated operational occurrence (AOO) or a postulated OBA.

Qualified offsite circuits are those that are described in the FSAR and are part of the licensing basis for the plant.

Each offsite circuit must be capable of maintaining acceptable frequency and voltage, and accepting required loads during an accident, while connected to the 6.9 kV shutdown boards.

Offsite power from the Watts Bar Hydro 161 kV switchyard to the onsite Class 1E distribution system is from two independent immediate access circuits. Each of the two required circuits are routed from the switchyard through a 161 kV transmission line and one of four 161 to 6.9 kV transformers (common station service transformers (CSSTs)) to the onsite Class 1 E distribution system.

Normally the two required circuits are aligned to power the 6.9 kV shutdown boards through CSST C and CSST D. However, one of the two required circuits may also be aligned to power two shutdown boards in the same load group through either CSST A or CSST B and its associated Unit Boards, either directly from the CSST through the Unit Board or by automatic transfer from the Unit Station Service Transformer (USST) to the CSST. Use of CSST A or B as an offsite source requires that CSST A and B both be available and that the (continued)

B 3.8-3

BASES LCO (continued)

Watts Bar-Unit 1 AC Sources - Operating B 3.8.1 associated power and control feeders be in their normal positions to ensure independence. Due to independence limitations, CSST A and B cannot be credited for supply of both offsite power sources simultaneously. The medium voltage power system starts at the low-side of the common station service transformers.

Each required offsite circuit is that combination of power sources described below that are either connected to the Class 1 E AC Electrical Power Distribution System, or is available to be connected to the Class 1E AC Electrical Power Distribution System through automatic transfer at the 6.9 kV Shutdown or Unit Boards within a few seconds, as required.

The following offsite power configurations meet the requirements of the LCO:

1.

Normal Operation (i.e., all 6.9 kV shutdown boards aligned to their normal offsite circuit) - Two offsite circuits consisting of (a) ANO (b) (no board transfers required; a loss of either circuit will not prevent the minimum safety functions f ram being performed);

a.

From the 161 kV Watts Bar Hydro Switchyard (Bay 13), through CSST C (winding Y) to 6.9 kV Shutdown Board 1A-A and (winding X) to 6.9 kV Shutdown Board 2A-A: ANO

b.

From the 161 kV Watts Bar Hydro Switchyard (Bay 4 ), through CSST D (winding X) to 6.9 kV Shutdown Board 1B-B and (winding Y) to 6.9 kV Shutdown Board 2B-B.

2.

Alternate Operation (i.e., one or more 6.9 kV shutdown boards aligned to their alternate offsite circuit)- Two offsite circuits consisting of (a) AND (b)

AND (c) (as needed) (Note: 6.9 kV shutdown board(s) aligned to normal circuit require an OPERABLE automatic transfer; a loss of either circuit will not prevent the minimum safety functions from being performed);

a.

From the 161 kV Watts Bar Hydro Switchyard (Bay 13), through CSST C (winding Y) to 6.9 kV Shutdown Board 1A-A (normal) ANO/OR Shutdown Board 2B-B (alternate) and (winding X) to 6.9 kV Shutdown Board 2A-A (normal) AND/OR Shutdown Board 1B-B (alternate);

b. From the 161 kV Watts Bar Hydro Switchyard (Bay 4 ), through CSST O (winding X) to 6.9 kV Shutdown Board 1B-B (normal) ANO/OR Shutdown Board 2A-A (alternate) and (winding Y) to 6.9 kV Shutdown Board 2B-B (normal) AND/OR Shutdown Board 1A-A (alternate); AND

c. An OPERABLE transfer from the normal circuit to the alternate circuit for those 6.9 kV shutdown boards aligned to their normal circuit.

(continued)

B 3.8-4

BASES LCO (continued)

Watts Bar-Unit 1 AC Sources - Operating B 3.8.1

3. Unit Board Operation - Normal Supply (i.e., one offsite circuit includes a unit board supplied by its normal power supply, the USST) - Two offsite circuits consisting of (a) OR (b) (relies on automatic transfer of Unit Board power supply alignment from its normal supply (USST) to its alternate supply (CSST via the Start Bus):

a. CSST C out-of-service;

1) From the 161 kV Watts Bar Hydro Switchyard (Bay 4 ). through CSST D (winding X) to 6.9 kV Shutdown Board 1B-B and (winding Y) to 6.9 kV Shutdown Board 28-B;

2) From the 161 kV Watts Bar Hydro Switchyard (Bay 13), through CSST B (winding Y) to the 6.9 kV Unit Board 1 B and Unit Board 2B (Breakers 1622 & 1632 open);

3) From Unit Board 1 B to 6.9 kV Shutdown Board 1A-A (Breaker 1718 closed);

4) From Unit Board 2B to 6.9 kV Shutdown Board 2A-A (Breaker 1818 closed); AND

5) Unit Board 1 Band Unit Board 2B normal to alternate automatic transfer circuit OPERABLE.

b. CSST D out-of-service;

1) From the 161 kV Watts Bar Hydro Switchyard (Bay 13), through CSST C (winding X) to 6.9 kV Shutdown Board 1A-A and (winding Y) to 6.9 kV Shutdown Board 2A-A;

2) From the 161 kV Watts Bar Hydro Switchyard (Bay4), through CSST A (winding Y) to the 6.9 kV Unit Board 1C and Unit Board 2C (Breakers 1524 and 1534 open);

3) From Unit Board 1C to 6.9 kV Shutdown Board 18-B (Breaker 1726 closed);

4) From Unit Board 2C to 6.9 kV Shutdown Board 2B-B (Breaker 1826 closed); AND

5) Unit Board 1C and Unit Board 2C normal to alternate automatic transfer circuit OPERABLE.

(continued)

B3.8-5

BASES LCO (continued)

Watts Bar-Unit 1 AC Sources - Operating B 3.8.1

4) Unit Board Operation - Alternate Supply (i.e., one offsite circuit includes a unit board supplied by its alternate power supply, the CSST via the Start Bus)-

Two offsite circuits consisting of (a) OR (b) (no board transfers required):

a. CSST C out-of-service;

1) From the 161 kV Watts Bar Hydro Switchyard (Bay 4 ), through CSST D (winding X) to 6.9 kV Shutdown Board 1B-B and (winding Y) to 6.9 kV Shutdown Board 2B-B; AND

2) From the 161 kV Watts Bar Hydro Switchyard (Bay 13), through CSST B (winding Y) to the 6.9 kV Unit Board 1 B and Unit Board 2B (Breakers 1622 and 1632 closed) to 6.9 kV Shutdown Board 1A-A and to 6.9 kV Shutdown Board 2A-A (Breakers 1718 and 1818 closed),

respectively.

b. CSST D out-of-service

1) From the 161 kV Watts Bar Hydro Switchyard (Bay 13), through CSST C (winding X) to 6.9 kV Shutdown Board 1A-A and (winding Y) to 6.9 kV Shutdown Board 2A-A; AND

2)

From the 161 kV Watts Bar Hydro Switchyard (Bay 4), through CSST A (winding Y) to the 6.9 kV Unit Board 1 C and Unit Board 2C (Breakers 1524 and 1534 closed) to 6.9 kV Shutdown Board 1B-B and to 6.9 kV Shutdown Board 2B-B (Breakers 1726 and 1826 closed),

respectively.

Note: When using either CSST A or B as a qualified offsite circuit, the CSST (A or B) not in use as a qualified circuit must be available.

Each DG must be capable of starting, accelerating to rated speed and voltage, and connecting to its respective 6.9 kV shutdown board on detection of loss-of*

voltage. This will be accomplished within 10 seconds. Each DG must also be capable of accepting required loads within the assumed loading sequence intervals, and continue to operate until offsite power can be restored to the 6.9 kV shutdown boards. These capabilities are required to be met from a variety of initial conditions such as DG in standby with the engine hot and DG in standby with the engine at ambient conditions. Additional DG capabilities must be demonstrated to meet required Surveillances, e.g., capability of the DG to revert to standby status on an accident signal while operating in parallel test mode.

(continued)

B 3.8-6

BASES LCO (continued)

Watts Bar-Unit 1 AC Sources - Operating B 3.8.1 Proper sequencing of loads, including tripping of nonessential loads, is a required function for DG OPERABILITY.

A Note has been added to indicate that the C-S DG may be substituted for any of the required DGs. However, the C-S DG cannot be declared OPERABLE until it is connected electrically in place of another DG, and it has satisfied applicable Surveillance Requirements.

The AC sources in one train must be separate and independent (to the extent possible) of the AC sources in the other train. For the OGs, separation and independence are complete. However, CSST A or B can only supply two 6.9 kV shutdown boards in the same load group, to ensure the separation criteria is met.

For the offsite AC sources, separation and independence are to the extent practical. A circuit may be connected to more than one ESF bus, with fast transfer capability to the other circuit OPERABLE, and not violate separation criteria. A circuit that is not connected to an ESF bus is required to have OPERABLE fast transfer interlock mechanisms to at least two ESF buses to support OPERABILITY of that circuit.

(continued) 83.8-7

BASES (continued)

APPLICABILITY ACTIONS Watts Bar-Unit 1 AC Sources - Operating B 3.8.1 The AC sources are required to be OPERABLE in MODES 1, 2, 3, and 4 to ensure that:

a.

Acceptable fuel design limits and reactor coolant pressure boundary limits are not exceeded as a result of AOOs or abnormal transients; and

b.

Adequate core cooling is provided and containment OPERABILITY and other vital functions are maintained in the event of a postulated OBA.

The AC power requirements for MODES 5 and 6 are covered in LCO 3.8.2, "AC Sources - Shutdown."

A Note prohibits the application of LCO 3.0.4.b to an inoperable DG. There is an increased risk associated with entering a MODE or other specified condition in the Applicability with an inoperable DG and the provisions of LCO 3.0.4.b, which allow entry into a MOOE or other specified condition in the Applicability with the LCO not met after performance of a risk assessment addressing inoperable systems and components, should not be applied in this circumstance.

To ensure a highly reliable power source remains with one required offsite circuit inoperable, it is necessary to verify the OPERABILITY of the remaining required offsite circuit on a more frequent basis. Since the Required Action only specifies "perform," a failure of SR 3.8.1.1 acceptance criteria does not result in a Required Action not met. However, if a second required circuit fails SR 3.8.1.1, the second offsite circuit is inoperable, and Condition D, for two required off site circuits inoperable, is entered.

Required Action A.2, which only applies if the train cannot be powered from a required offsite source, is intended to provide assurance that an event coincident with a single failure of the associated DG will not result in a complete loss of safety function of critical redundant required features. These features are powered from the redundant AC electrical power trains. This includes motor driven auxiliary feedwater pump. Single train systems, such as the turbine driven auxiliary feedwater pump, may not be included.

B 3.8-8 (continued)

Revision 68, 116 Amendment 55

BASES ACTIONS (continued)

Watts Bar-Unit 1 AC Sources - Operating B 3.8.1 According to Regulatory Guide 1.93 (Ref. 6), operation may continue in Condition A for a period that should not exceed 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months . With one required offsite circuit inoperable, the reliability of the offsite system is degraded, and the potential for a loss of offsite power is increased, with attendant potential for a challenge to the plant safety systems. In this Condition, however, the remaining OPERABLE offsite circuit and DGs are adequate to supply electrical power to the onsite Class 1 E Distribution System.

The 72 hour8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months Completion Time takes into account the capacity and capability of the remaining AC sources, a reasonable time for repairs, and the low probability of a OBA occurring during this period.

The second Completion Time for Required Action A.3 establishes a limit on the maximum time allowed for any combination of required AC power sources to be inoperable during any single contiguous occurrence of failing to meet the LCO. If Condition A is entered while, for instance, a DG is inoperable and that DG is subsequently returned OPERABLE, the LCO may already have been not met for up to 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months . This could lead to a total of 144 hours0.00167 days 0.04 hours 2.380952e-4 weeks 5.4792e-5 months , since initial failure to meet the LCO, to restore the offsite circuit. At this time, a DG could again become inoperable, the circuit restored OPERABLE, and an additional 72 hours8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months (for a total of 9 days) allowed prior to complete restoration of the LCO. The 6 day Completion Time provides a limit on the time allowed in a specified condition after discovery of failure to meet the LCO. This limit is considered reasonable for situations in which Conditions A and Bare entered concurrently. The "AND" connector between the 72 hour8.333333e-4 days 0.02 hours 1.190476e-4 weeks 2.7396e-5 months and 6 day Completion Times means that both Completion Times apply simultaneously, and the more restrictive Completion Time must be met.

As in Required Action A.2, the Completion Time allows for an exception to the normal "time zero" for beginning the allowed outage time "clock." This will result in establishing the "lime zero" at the time that the LCO was initially not met, instead of at the time Condition A was entered.

(continued)

B 3.8-10

BASES ACTIONS (continued)

Watts Bar-Unit 1 B.1 and C.1 AC Sources - Operating B 3.8.1 To ensure a highly reliable power source remains with one or more DGs inoperable in Train A OR with one or more DGs inoperable in Train B, it is necessary to verify the availability of the required offsite circuits on a more frequent basis. Since the Required Action only specifies "perform," a failure of SR 3.8.1.1 acceptance criteria does not result in a Required Action being not met.

However, if a circuit fails to pass SR 3.8.1.1, it is inoperable. Upon required offsite circuit inoperability, additional Conditions and Required Actions must then be entered.

B.2and C.2 Required Actions B.2 and C.2 are intended to provide assurance that a loss of offsite power, during the period that a DG is inoperable, does not result in a complete loss of safety function of critical systems. These features are designed with redundant safety related trains. This includes motor driven auxiliary feedwater pumps. Single train systems, such as the turbine driven auxiliary feedwater pump, are not included. Redundant required feature failures consist of inoperable features associated with a train, redundant to the train that has inoperable DG(s).

The Completion Time for Required Actions B.2 and C.2 are intended to allow the operator time to evaluate and repair any discovered inoperabilities. This Completion Time also allows for an exception to the normal "time zero" for beginning the allowed outage time "clock." In this Required Action, the Completion Time only begins on discovery that both:

a.

An inoperable CG exists; and

b.

A required feature on the other train (Train A or Train B) is inoperable.

If at any time during the existence of this Condition (one or more DGs inoperable) a required feature subsequently becomes inoperable, this Completion Time would begin to be tracked.

Discovering one or more required DGs in Train A or one or more DGs in Train B inoperable coincident with one or more inoperable required support or supported features, or both, that are associated with the OPERABLE DGs, results in starting the Completion Time for the Required Action. Four hours from the discovery of these events existing concurrently is Acceptable because it minimizes risk while allowing time for restoration before subjecting the plant to transients associated with shutdown.

B 3.8-11 (continued)

Revision 50 Amendment 39

BASES ACTIONS (continued)

Watts Bar-Unit 1 D.1 and D.2 AC Sources - Operating B 3.8.1 Required Action 0.1, which applies when two required offsite circuits are inoperable, is intended to provide assurance that an event with a coincident single failure will not result in a complete loss of redundant required safety functions.

The Completion Time for this failure of redundant required features is reduced to 12 hours1.388889e-4 days 0.00333 hours 1.984127e-5 weeks 4.566e-6 months from that allowed for one train without offsite power (Required Action A.2). The rationale for the reduction to 12 hours1.388889e-4 days 0.00333 hours 1.984127e-5 weeks 4.566e-6 months is that Regulatory Guide 1.93 (Ref. 6) allows a Completion Time of 24 hours2.777778e-4 days 0.00667 hours 3.968254e-5 weeks 9.132e-6 months for two required offsite circuits inoperable, based upon the assumption that two complete safety trains are OPERABLE. When a concurrent redundant required feature failure exists, this assumption is not the case, and a shorter Completion Time of 12 hours1.388889e-4 days 0.00333 hours 1.984127e-5 weeks 4.566e-6 months is appropriate. These features are powered from redundant AC safety trains. This includes motor driven auxiliary feedwater pumps. Single train features, such as the turbine driven auxiliary pump, are not included in the list.

The Completion Time for Required Action 0.1 is intended to allow the operator time to evaluate and repair any discovered inoperabilities. This Completion Time also allows for an exception to the normal "time zero" for beginning the allowed outage time "clock.* In this Required Action the Completion nme only begins on discovery that both:

a.

All required offsite circuits are inoperable; and

b.

A required feature is inoperable.

If at any time during the existence of Condition 0 (two offsite circuits inoperable) a required feature becomes inoperable, this Completion Time begins to be tracked.

According to Regulatory Guide 1.93 (Ref. 6), operation may continue in Condition 0 for a period that should not exceed 24 hours2.777778e-4 days 0.00667 hours 3.968254e-5 weeks 9.132e-6 months . This level of degradation means that the offsite electrical power system does not have the capability to effect a safe shutdown and to mitigate the effects of an accident; however, the onsite AC sources have not been degraded. This level of degradation generally corresponds to a total loss of the immediately accessible offsite power sources.

Because of the normally high availability of the offsite sources, this level of degradation may appear to be more severe than other combinations of two AC sources inoperable (e.g., combinations that involve an offsite circuit and one OG inoperable, or one or more OGs in each train inoperable). However, two factors tend to decrease the severity of this level of degradation:

B 3.8-12 (continued)

Revision 50 Amendment 39

BASES ACTIONS Watts Bar-Unit 1 D.1 and D.2 (continued)

AC Sources - Operating B 3.8.1

a.

The configuration of the redundant AC electrical power system that remains available is not susceptible to a single bus or switching failure; and

b.

The time required to detect and restore an unavailable required offsite power source is generally much less than that required to detect and restore an unavailable onsite AC source.

With both of the required offsite circuits inoperable, sufficient onsite AC sources are available to maintain the plant in a safe shutdown condition in the event of a OBA or transient. In fact, a simultaneous loss of offsite AC sources, a LOCA, and a worst case single failure were postulated as a part of the design basis in the safety analysis. Thus, the 24 hour2.777778e-4 days 0.00667 hours 3.968254e-5 weeks 9.132e-6 months Completion Time provides a period of time to effect restoration of one of the offsite circuits commensurate with the importance of maintaining an AC electrical power system capable of meeting its design criteria.

According to Reference 6, with the available offsite AC sources, two less than required by the LCO, operation may continue for 24 hours2.777778e-4 days 0.00667 hours 3.968254e-5 weeks 9.132e-6 months . If two offsite sources are restored within 24 hours2.777778e-4 days 0.00667 hours 3.968254e-5 weeks 9.132e-6 months , unrestricted operation may continue. If only one offsite source is restored within 24 hours2.777778e-4 days 0.00667 hours 3.968254e-5 weeks 9.132e-6 months , power operation continues in accordance with Condition A.

E.1 and E.2 Pursuant to LCO 3.0.6, the Distribution System ACTIONS would not be entered even if all AC sources to it were inoperable, resulting in de-energization.

Therefore, the Required Actions of Condition E are modified by a Note to indicate that when Condition E is entered with no AC source to any train, the Conditions and Required Actions for LCO 3.8.9, "Distribution Systems - Operating," must be immediately entered. This allows Condition E to provide requirements for the loss of one offsite circuit and one or more DGs in a train, without regard to whether a train is de-energized. LCO 3.8.9 provides the appropriate restrictions for a de-energized train.

According to Regulatory Guide 1.93 (Ref. 6), operation may continue in Condition E for a period that should not exceed 12 hours1.388889e-4 days 0.00333 hours 1.984127e-5 weeks 4.566e-6 months .

B 3.8-13 (continued)

Revision 50 Amendment 39

BASES SURVEILLANCE REQUIREMENTS (continued)

Watts Bar-Unit 1 SR 3.8.1.7 See SR 3.8.1.2.

SR 3.8.1.8 AC Sources - Operating B 3.8.1 Transfer of each 6.9 kV shutdown board power supply from the normal off site circuit to the alternate offsite circuit demonstrates the OPERABILITY of the alternate circuit distribution network to power the shutdown loads. The 18 month Frequency of the Suiveillance is based on engineering judgment, taking into consideration the plant conditions required to perform the Surveillance, and is intended to be consistent with expected fuel cycle lengths. Operating experience has shown that these components usually pass the SR when performed at the 18 month Frequency. Therefore, the Frequency was concluded to be acceptable from a reliability standpoint.

This SR is modified by two Notes. The reason for the first Note is that, during operation with the reactor critical, performance of this SR for the 1A-A or 1 B-B Shutdown Board could cause perturbations to the electrical distribution systems that could challenge continued steady state operation and, as a result, plant safety systems. This restriction from normally performing the Surveillance in MODE 1 or 2 is further amplified to allow the Surveillance to be performed for the purpose of reestablishing OPERABILITY (e.g., post work testing following corrective maintenance, corrective modification, deficient or incomplete surveillance testing, and other unanticipated OPERABILITY concerns) provided an assessment determines plant safety is maintained or enhanced. This assessment shall, as a minimum, consider the potential outcomes and transients associated with a failed Suiveillance, a successful Surveillance, and a perturbation of the off site or onsite system when they are tied together or operated independently for the Surveillance; as well as the operator procedures available to cope with these outcomes. These shall be measured against the avoided risk of a plant shutdown and startup to determine that plant safety is maintained or enhanced when the Suiveillance is performed in MODE 1 or 2.

Risk insights or deterministic methods may be used for this assessment. Credit may be taken for unplanned events that satisfy this SR. Examples of unplanned events may include:

1)

Unexpected operational events which cause the equipment to perform the function specified by this Suiveillance, for which adequate documentation of the required performance is available; and

2)

Post corrective maintenance testing that requires performance of this Surveillance in order to restore the component to OPERABLE, provided the maintenance was required, or performed in conjunction with maintenance required to maintain OPERABILITY or reliability.

(continued)

B 3.8-19

BASES SURVEILLANCE REQUIREMENTS Watts Bar-Unit 1 SR 3.8.1.8 (continued)

AC Sources - Operating B 3.8.1 Note 2 specifies that the transfer capability is only required to be met when one or more 6.9 kV shutdown boards require normal and alternate power supplies.

When all the 6.9 kV shutdown boards are supplied power by their normal power supply the alternate power supply is not required. When one or more of the 6.9 kV shutdown boards are supplied power from their alternate power supply the automatic transfer for those 6.9 kV shutdown boards required to transfer from their normal to alternate power supply is required to be OPERABLE. If one or more of the 6.9 kV shutdown boards are aligned to its alternate source (CSST C or CSST 0) this SR verifies that at least two 6.9 kV shutdown boards in the same load group will be powered from an offsite circuit if a fault occurs on either circuit.

SR 3.8.1.9 Each DG is provided with an engine overspeed trip to prevent damage to the engine. Recovery from the transient caused by the loss of a large load could cause diesel engine overspeed, which, if excessive, might result in a trip of the engine. This Surveillance demonstrates the DG load response characteristics and capability to reject the largest single load without exceeding predetermined voltage and frequency and while maintaining a specified margin to the overspeed trip. The largest single load for each DG is the essential raw cooling water pump at 800 HP. This Surveillance may be accomplished by: 1) tripping the DG output breaker with the DG carrying greater than or equal to its associated single largest post accident load while paralleled to offsite power or while solely supplying the bus, or 2) tripping its associated single largest post accident load with the DG solely supplying the bus. As required by Regulatory Guide 1.9, C1.4 (Ref. 3), the load rejection test is acceptable if the increase in diesel speed does not exceed 75% of the difference between synchronous speed and the overspeed trip setpoint. or 15% above synchronous speed, whichever is lower.

The time, voltage, and frequency tolerances specified in this SR are derived from Regulatory Guide 1.9 (Ref. 3) recommendations for response during load sequence intervals. The 3 seconds specified is equal to 60% of a typical 5 second load sequence interval associated with sequencing of the largest load.

The voltage and frequency specified are consistent with the design range of the equipment powered by the DG. SR 3.8.1.9.a corresponds to the maximum frequency excursion, while SR 3.8.1.9.b and SR 3.8.1.9.c are steady state voltage and frequency values to which the system must recover following load rejection.

The 18 month Frequency is consistent with the recommendation of Regulatory Guide 1.9 (Ref. 3).

(continued)

B 3.8-20

BASES SURVEILLANCE REQUIREMENTS Watts Bar-Unit 1 SR 3.8.1.21 (continued)

AC Sources - Operating B 3.8.1 The Frequency for accelerated testing is 7 days, but no less than 24 hours2.777778e-4 days 0.00667 hours 3.968254e-5 weeks 9.132e-6 months . Tests conducted at intervals of less than 24 hours2.777778e-4 days 0.00667 hours 3.968254e-5 weeks 9.132e-6 months may be credited for compliance with Required Actions. However. for the purpose of re-establishing the normal 31-day Frequency, a successful test at an interval of less than 24 hours2.777778e-4 days 0.00667 hours 3.968254e-5 weeks 9.132e-6 months should be considered an invalid test and not count towards the 7 consecutive failure free starts, and the consecutive test count is not reset.

A test interval in excess of 7 days (or 31 days as appropriate) constitutes a failure to meet the SRs and results in the associated DG being declared inoperable. It does not, however, constitute a valid test or failure of the DG, and any consecutive test count is not reset.

SR 3.8.1.22 Transfer of the 6.9 kV Unit Boards 1 B, 1 C, 28, and 2C power supply from the normal power supply (USST) to the alternate power supply (CSST via the 6.9 kV Start Bus) demonstrates the OPERABILITY of the maintenance offsite circuit to power the shutdown loads when the shutdown board is powered from the USST.

The 18-month Frequency of the Surveillance is based on engineering judgment, taking into consideration the plant conditions required to perform the Surveillance, and is intended to be consistent with expected fuel cycle lengths. Operating experience has shown that these components usually pass the SR when performed at the 18 month Frequency. Therefore, the Frequency is acceptable from a reliability standpoint.

This SR is modified by two Notes. The reason for the first Note is that, during operation with the reactor critical, performance of this SR for the 1 B or 1 C Unit Board could cause perturbations to the electrical distribution systems that could challenge continued steady state operation and, as a result, plant safety systems.

This restriction from normally performing the Surveillance in MODE 1 or 2 is further amplified to allow the Surveillance to be performed for the purpose of reestablishing OPERABILITY (e.g., post work testing following corrective maintenance, corrective modification, deficient or incomplete surveillance testing, and other unanticipated OPERABILITY concerns) provided an assessment determines plant safety is maintained or enhanced. This assessment shall, as a minimum, consider the potential outcomes and transients associated with a failed Surveillance, a successful Surveillance, and a perturbation of the offsite or onsite system when they are tied together or operated independently for the Surveillance; as well as the operator procedures available to cope with these outcomes. These shall be measured against the avoided risk of a plant shutdown and startup to determine that plant safety is maintained or enhanced when the Surveillance is performed in MODE 1 or 2. Risk insights or deterministic methods may be used for this assessment. Credit may be taken for unplanned events that satisfy this SR. Examples of unplanned events may include:

1) Unexpected operational events which cause the equipment to perform the function specified by this Surveillance, for which adequate documentation of the required performance is available; and B 3.8-34 Revision 50 Amendment 39

BASES SURVEILLANCE REQUIREMENTS REFERENCES Watts Bar-Unit 1 AC Sources - Operating B 3.8.1 SR 3.8.1.22 (continued)

2) Post corrective maintenance testing that requires performance of this Surveillance in order to restore the component to OPERABLE, provided the maintenance was required, or performed in conjunction with maintenance required to maintain OPERABILITY or reliability.

Note 2 specifies that transfer capability is only required to be met for 6.9 kV Unit Boards that require normal and alternate power supplies. If the unit board is not a part of the required qualified circuit or the qualified circuit is powered from the CSST through the unit board to the 6.9 kV shutdown board, the automatic transfer is not required.

1.

Title 10, Code of Federal Regulations, Part 50, Appendix A, General Design Criterion (GDC) 17, "Electrical Power Systems."

2.

Watts Bar FSAR, Section 8.2, "Offsite Power System," and Tables 8.3-1 to 8.3-3, "Safety-Related Standby Power Sources and Distribution Boards," "Shutdown Board Loads Automatically Tripped Following a Loss of Nuclear Unit and Preferred Power," and "Diesel Generator Load Sequentially Applied Following a Loss of Nuclear Unit and Preferred Power."

3.

Regulatory Guide 1.9, Rev. 3, "Selection, Design, Qualification and Testing of Emergency Diesel Generator Units Used as Class 1E Onsite Electric Power Systems at Nuclear Power Plants," July 1993.

4.

Watts Bar FSAR Section 6, "Engineered Safety Features."

5.

Watts Bar FSAR, Section 15.4, "Condition IV-Limiting Faults."

6.

Regulatory Guide 1.93, Rev. 0, "Availability of Electric Power Sources,"

December 1974.

7.

Generic Letter 84-15, "Proposed Staff Actions to Improve and Maintain Diesel Generator Reliability," July 2, 1984.

8.

Title 10, Code of Federal Regulations, Part 50, Appendix A, GDC 18, "Inspection and Testing of Electric Power Systems."

9.

Regulatory Guide 1.137, Rev. 1, "Fuel Oil Systems for Standby Diesel Generators," October 1979.

10.

Watts Bar Drawing 1-47W605-242, "Electrical Tech Spec Compliance Tables.

11.

TVA's letter to NRC dated August 7, 2001, Technical Specification Change TS-01-04, Diesel Generator (DG) Risk Informed Allowed Outage Time (AOT) Extension B 3.8-35 Revision 50 Amendment 39

Distribution Systems - Operating B3.8.9 B 3.8 ELECTRICAL POWER SYSTEMS B 3.8.9 Distribution Systems - Operating BASES BACKGROUND Watts Bar-Unit 1 The onsite Class 1 E AC electrical power distribution system is divided by train into two redundant and independent AC electrical power distribution subsystems.

The AC electrical power subsystem includes four 6.9 kV shutdown boards. Each 6.9 kV shutdown board has access to the two separate and independent preferred offsite sources of power as well as a dedicated onsite diesel generator (DG) source. Usually, one of the two offsite sources will be the normal power source for a 6.9 kV shutdown board, and the other offsite source will be the alternate power source. Transfers from the normal source to the alternate source may be manual or automatic. Automatic transfers only occur when the relay logic is tripping a transmission line and the associated common station service transformers. Only manual transfers are permitted from alternate to normal.

Additionally, the maintenance source to the 6.9 kV shutdown board can be used as an offsite power source." Transferring the 6.9 kV shutdown board to the maintenance power source is done manually from the normal or alternate power source. For a loss of offsite power to the 6.9 kV shutdown boards, the onsite emergency power system supplies power to the 6.9 kV shutdown boards. Control power for the 6.9 kV breakers is supplied from the Class 1 E batteries. Additional description of this system may be found in the Bases for LCO 3.8.1, RAC Sources-Operating," and the Bases for LCO 3.8.4, "DC Sources - Operating."

The AC Distribution System includes the 480 V shutdown boards and associated supply transformers, load centers, and protective devices shown in Table B 3.8.9-1.

The 120 VAC vital buses are arranged in four load groups and are normally powered from the unit inverters or spare inverters and DC Boards I, II, Ill, and IV.

An alternate power supply for the vital buses is a regulated transformer bypass source powered from the same train as the associated unit inverter, and its use is governed by LCO 3.8.7, "Inverters-Operating."

There are four independent 125 VDC electrical power distribution buses. Each bus receives normal power from an independent 480 VAC shutdown board via its associated battery charger. Upon loss of 480 VAC shutdown board power, the DC buses are energized by their connected battery banks.

The list of all required distribution buses is presented in Table B 3.8.9-1.

(continued)

B 3.8-89 Revision 67, 75, 76, n, 78

ENCLOSURE2 ATIACHMENT5 Proposed Updated Final Safety Analysis Report (Marked-Up)

Watts Bar Nuclear Plant-Unit 1

WBNP-xx 8.0 ELECTRIC POWER

8.1 INTRODUCTION

8.1. l Utility Grid and Interconnections The Tennessee Valley Authority (TVA) is a corporation of the United States Government serving the State of Tennessee and parts of six other States in the southeast on the boundaries of Tennessee. TV A is interconnected with electric power companies to the north, west, south, and east of its service area. As shown in Figure 8.1-l, the TV A grid consists of interconnected hydro plants, fossil-fueled plants, combustion turbine plants, and nuclear plants supplying electric energy over a transmission system consisting of various voltages up to 500 kV.

The Watts Bar Nuclear Plant is located 48 miles northeast of Chattanooga, Tennessee, on the west bank of the Tennessee River. The plant is connected into a strong 500kV transmission grid.

The 500kV Switchyard is a double breaker - double bus configuration. Each unit and each of five 500k V transmission lines can be connected to either or both buses through a single 500k V breaker. Preferred power is supplied from the existing Watts Bar Hydro 161-kV Switchyard over two radial lines located entirely on TV A property. The Watts Bar Hydro 161-kV Switchyard is interconnected with the TV A power system through six 161-k V transmission lines and five hydro generators.

8.1.2 Plant Electrical Power System The plant electric power system consists of the main generator, the unit station service transformers, the common station service transformers, the diesel generators, the batteries, and the electric distribution system as shown on Figures 8.1-2, 8. l-2a, 8. l-2b, and 8.1-3. Under normal operating conditions, the main generator supplies electrical power through isolated-phase buses to the main step-up transformers and through the unit station service transformers (located adjacent to the Turbine Building) to the non:safety auxiliary power system. Offsite electrical power normally supplies Class IE circuits through the 161-kV system via Common Station Service Transformers (CSSTs) C and D. Alternatively. offsite power to the Class IE system can also be supplied through CSSTs B or A. but not both simultaneously. if the normal CSST is unavailable. The primaries of the unit station service transformers are connected to the isolated-phase bus at a point between the generator terminals and the low-voltage connection of the main transformers. During normal operation. station auxiliary power is taken from the main generator through the unit station service transformers and from the 161-kV system through the common station service transformers. During startup and shutdown, all auxiliary power is supplied from the 161-kV system through CSSTs A, B, C and D. The standby (onsite) power is supplied by four diesel generators. An additional diesel generator unit (ADGU, not required for Unit I operation1) has been provided (equivalent to the existing diesel generators) to replace any one of the four existing diesel generator units.

1 The ADGU, as described in WBN's UFSAR and design bases, is not functional. Pending the outcome of ongoing analysis, this SSC may he deleted from UFSAR.

8.1-l

WBNP-xx 8.2 OFFSITE (PREFERRED) POWER SYSTEM 8.2. l Description Preferred offsite power is supplied from TV A's 16 lkV transmission grid at Watts Bar Hydro Plant (WBH) switchyard over two separate transmission lines, each connecting to two 161-6.9-kV common station service transformers (CSSTs) at Watts Bar Nuclear Plant (WBN).

The Class 1 E power system is normally supplied from offsite power through CSSTs C and D.

For flexibility, there is also a maintenance feed available from CSSTs A and B to the Class 1 E power systems.. which cante be used when CSST C or D is out-of-service during any Operating Modeeely whee the ltftit is ie eelel shutElewe.

The Class 1 E power system can be transferred from the offsite normal power supply to the offsite alternate power supply to demonstrate operability of the board transfer. Transfers from the normal supply to the alternate supply may be manual or automatic. Automatic transfers from the normal power supply to the alternate power supply are initiated by any transformer or line failure relays.

Manual (routine) transfers are initiated at the discretion of the operator for test or normal operation. Manual transfers may be effected from the main control room by placing the "auto-manual" transfer switch in manual, then placing the control switch for the selected supply breaker in the "close" position and the control switch for the supply breaker in the "trip" position.

For all unit generator trips except those caused by electrical faults that open 1 and/or 2 main generator 500kV circuit breakers, the Balance of Plant (BOP) ac auxiliary power system remains connected to its unit sources for 30 seconds, then fast transfers to offsite power supplied through common transformers A and B. If the unit trip is caused by an electrical fault, the BOP system transfer is not delayed.

Transmission system studies (TSS) have been made that show for an acceptable range of transmission grid conditions, one offsite power circuit consisting of one 16lkV transmission line and transformer C, or the other transmission line and transformer D is capable of starting and running all required safety-related loads, for a design basis accident in Unit l and no fuel in Unit-2. Additionally. studies haye shown that one transmission line and CSST A. or one transmission line and CSST B. are capable of starting and running the minimum required safetv-related loads for one train in each unit. The analyses assumed that equipment started by a safety injection signal (SIS) started at the same time unless the load's control circuitry has sequential time delay, that all equipment that is tripped off by a SIS was tripped, and that all continuous load~ that could be operating immediately after the SIS, whether safety-related or not, were running.

A load shedding feature is provided for part of the BOP loads in the event of a two Unit trip with either CSST A or B out of service. Load shedding was not considered in the TSS.

8.2-l

WBNP-xx 8.2.1.2 Transmission Lines, Switchyard. and Transformers The two 16lkV and the five 500kV lines connecting the nuclear plant with the TV A transmission network are indicated functionally on Figure 8.2-1. The onsite transmission line arrangement is shown on Figure 8.2-3. Preferred power is supplied from the existing Watts Bar Hydro 16lkV switchyard over two radial 16lkV overhead lines approximately 1.5 miles long. These transmission lines provide power to the nuclear plants CSSTs A and D and CSSTs B and C and are routed to the east and north of the nuclear plant transformer yard respectively. These lines are routed to minimize the likelihood of their simultaneous failure.

The location of common station service transformers A and B is shown on Figures 8.2-3 and 8.2-5. Each transformer has a single primary and two secondary windings. The primary voltage is 16lkV with the winding rated 57/76/95 MV A. OAIFAIFOA (Future). The secondary voltage is 6.9 kV and each winding is rated 36/48/60 MV A. OAIFAIFOA (Future). The primary winding of each transformer has an automatic load-tap changer unit which will adjust voltage based on the normally connected start bus.

The location of common station service transformers C and Dis also shown on Figures 8.2-3.

Each transformer has a single primary winding and two secondary windings with automatic load-tap changer units. which will adjust voltage based on the normally connected shutdown board.

The primary voltage is 16lkV, and the winding is rated 33/44/55 MVA. OA/FOA/FOA. The secondary voltage is 6.9 kV. and each winding is rated 24/32/40 MVA. OA/FOA/FOA.

Calculated loads for common station service transformers A, B. C and D are well below winding ratings for all conditions.

Fire protection is provided for each common station service transformer by a deluge type water sprinkler system which can be automatically activated by thermostats or the transformer electrical protection devices.

8.2-4

8.2. l.3 WBNP-xx Arrangement of the Start Boards. Unit Boards. Common Boards. and Reactor Coolant Pump CRCP) Boards From the low-voltage side of common station service transformers A and B, 6.9kV station service buses supply the 6.9kV common, unit, and RCP boards via the 6.9kV start boards. The station service (start) buses are outdoor, nonsegregated, partially ventilated. metal-clad structures and are shown on Figure 8.2-5. At the 6.9kV startboard, these buses enter the outdoor metal-clad switchgear and connect to supply breakers. The design of the 6.9kV start boards and RCP boards conforms to ANSI, C37.20 (Standard for Switchgear Assemblies including Metal-Enclosed Bus) and is classified as outdoor metal-clad switchgear. Section 20, 6.2.2 of this standard defines the requirements for barriers. The circuit breakers at the 6.9kV start boards are electrically operated, vertical lift drawout type, with stored energy mechanisms. These circuit breakers have a continuous rating of 3,000 and 3,750 amperes for the RCP Start Bus breakers and Start Buses A and B breakers, respectively, an insulation system for l3.8kV, interrupting rating of 1,000 MVA, and a momentary rating of 80,000 amperes. The circuit breakers are utilized at 6.9kV.

Therefore, there is sufficient margin between the application and the rating of these circuit breakers.

From the 6.9-kV start board the two 6.9kV start buses A and Band the two 6.9kV RCP start buses A and Brun on separate support structures as outdoor, nonsegregated, partially ventilated metal-clad assemblies (Figure 8.2-5). The bus bars are fully insulated with flame-retardant material. bus supports are flame-retardant, and the metal enclosures are such that arcing faults in one bus will not endanger the other. The 6.9kV RCP start buses enter the RCP outdoor metal-clad switchgear and connect to supply breakers.

The four unit station service transformers are located in the transformer yard, south of the Turbine Building and directly under the delta section of the main generator isolated-phase bus.

Location of the unit station service transformers is shown on Figure 8.2-5. From each of the unit station service transformer low-voltage sides two 6.9kV buses originate, one running in the switchyard parallel to the south wall of the Turbine Building and connecting to the RCP switchgear, and the other entering the south Turbine Building wall for routing to the unit and common boards. The unit station service buses are outdoor, nonsegregated, partially ventilated, metal-clad construction until they enter the Turbine Building, where the construction changes to indoor type. After entering the Turbine Building, the unit station service buses are routed to the appropriate supply breakers in the 6.9kV unit and 6.9kV common boards, entering through the tops of the 6.9kV unit boards and the bottoms of the 6.9kV common boards. The 6.9kV unit and common boards are indoor, metal-clad switchgear with electrically operated, vertical lift drawout breakers with stored energy mechanisms.

From four of the 6.9 kV unit boards located in the Turbine Building. maintenance feeder cables are routed to the 6.9 kV shutdown boards located in the Auxiliary Building. where they connect to the supply breakers. These feeder cables are routed in divisional raceway to maintain separation between the offsite power sources.

8.2-5

WBNP-xx CSSTs C and D are connected to 6.9kV common switchgear C and D via a bus similar to 6.9kV start buses A and B (Figure 8.2-5A). The 6.9kV common switchgear C and D are then connected to the 6.9kV shutdown boards via cables which are routed through conduit banks and cable trays.

All of the indoor station service buses are non-ventilated, non-segregated, metal-clad, drip proof construction. In addition, the outdoor portions are weatherproof and equipped with l 20V I -phase heaters to maintain the temperature inside the housing at least 5°C above outside temperature.

All buses are provided with gas-resistant seals at entry to switchgear. At the penetration of an outside building wall, the buses are provided with a fire-resistant and moisture-resistant barrier.

8.2.1.4 Arrangement of Electrical Control Area (Nuclear Plant)

Figures 8.2-7 and 8.2-l l show the electrical control area where the relay, control, 250V de control power distribution panels and battery boards are located. Control power for start board power circuit breakers and associated protective relays is distributed from the 250V de supply via circuit breakers on the turbine building de distribution boards. Physical isolation of control power supplies is achieved by metal barriers between adjacent panels. Two separate 250V de buses are provided in these panels. Each bus can be fed from one of the two 250V battery boards (Figures 8.2-12 and 8.2-13) through manual, mechanically interlocked, nonautomatic circuit interrupters. The power circuit breaker and associated relay control circuits are allocated to these two de buses on the basis of switchyard connections. This allocation of control circuits ensures that the common station service transformer control and relay circuits are fed from two independent de distribution buses. Each circuit is protected by a circuit breaker and supervised by an amber indicating light located on the recording and instrument board. These indicating lights are grouped on the panel on the basis of the de buses they are connected to, and their wiring is physically separated on the panel on the same basis.

8.2.l.5 Switchvard Control and Relaying The design of the offsite (preferred) power system with its normal provision of two immediate access circuits from the transmission network via Watts Bar Hydro Plant complies with the NRC regulatory position expressed in Regulatory Guide 1.32 for the preferred design of such a system._

The CSST maintenance configurations can also be aligned to provide immediate access circuits.

The transmission line relay protection circuits at the hydro plant continuously monitor the conditions of the offsite power system and are designed to detect and isolate the faults with maximum speed and minimum disturbance to the system.

8.2-6

WBNP-xx Automatic transfers of the Class IE power system from the normal power supply to the alternate power supply only occur when the relay logic is tripping a transmission line and the associated common station service transformers. Automatic transfers of the Class IE power svstem are not provided for CSST maintenance alignments.

Control power for power circuit breakers and associated protective relays is supplied by two independent 250V batteries and is distributed via circuit breakers on separate panels. Figures 8.2-1 B and 8.2-1 C show the single line diagrams for the two panels at Watts Bar Hydro Plant.

Two separate 250V de buses are provided in these panels. Each bus can be fed from one of the two 250V battery boards through manual. mechanically interlocked, nonautomatic circuit interrupters. The power circuit breaker and associated relay control circuits are allocated to these two de buses on the basis of switchyard connections. This allocation of control circuits ensures that the control and relay circuits of the two nuclear plant lines are fed from two independent de distribution buses.

8.2.1.6 6.9kV Start Boards Control and Relaying 6.9kV Start Buses The secondaries of common station service transfonners A and B feed into two start boards containing four circuit breakers each. Two of the circuit breakers, 1512 and 1614, are the nonnal and alternate feeders for start bus A while breakers 1612 and 1514 are the normal and alternate feeders for start bus B. Two other breakers, 2512 and 2614, are the nonnal and alternate feeders for RCP start bus A, and breakers 2612 and 2514 are the nonnal and alternate feeders for RCP start bus B. The two circuit breakers feeding each start bus from a different common station service transformer are interlocked and the control circuits arranged in such a manner that manually-initiated high-speed (six cycles or less) transfers can be made from either breaker to the other breaker. Automatic transfers can only be made from the normal breaker to the alternate breaker and are delayed until the bus residual voltage reduces to 30% of nominal. All automatic transfers are initiated by undervoltage on the bus. The 250V de normal control power for the pair of breakers feeding start bus A is supplied from a separate battery and de distribution board from that of the nonnal control power for the two breakers feeding start bus B. Alternate control power feeders are similarly segregated.

Manual control of the circuit breakers is provided on the electrical control board in the Main Control Room where the operator has instrumentation showing the voltage on each of the two buses and current flowing in each of the four CSST secondary windings. The following annunciation is provided:

I.

Start Bus Fan Failure

2.

Start Bus Transfers

3.

Start Bus Failures or Undervoltage 8.2-9

WBNP-xx Annunciation No. 3 is composed of bus differential relay operation, bus a.c. voltage failure, and control bus de voltage failure. Start bus A is the normal feeder to 6.9kV common board A and the alternate feeder to 6.9kV unit boards IA, IC. 2A, and 2C. Start bus 8 is the normal feeder to 6.9kV common board 8 and the alternate feeder to 6.9kV unit boards 18, ID, 2B, and 20.

6.9kV Common Switchgear C and D. and Start Boards A and B The secondaries of common station service transformers C and D feed into 6.9kV common switchgear C and D (Figure 8. l-2a). Each switchgear contains two circuit breakers which are aligned to the common station service transformers as follows:

1.

Common station service transformer C:

This transformer provides normal (offsite) power from the secondary Y winding to 6.9kV shutdown board IA-A through circuit breaker 1712 and from the secondary X winding to 6.9kV shutdown board 2A-A through circuit breaker 2714. ln addition, this transformer provides alternate (offsite) power from the secondary X winding to 6.9kV shutdown board lB-B through circuit breaker 2714 and from the secondary Y winding to 6.9kV shutdown board 28-8 through circuit breaker 17I2. These feeders are protected by overcurrent and ground overcurrent relays. All of these switchgear circuit breakers are normally closed.

These circuits are designated as R for separation identification.

2.

Common station service transformer D:

This transformer provides normal (offsite) power from the secondary X winding to 6.9kV shutdown board IB-B through circuit breaker 28I4 and from the secondary Y winding to 6.9kV shutdown board 28-B through circuit breaker 18I2. In addition, this transformer provides alternate (offsite) power from the secondary Y winding to 6.9kV shutdown board IA-A through circuit breaker 1812 and from the secondary X winding to 6.9kV shutdown board 2A-A through circuit breaker 2814. These feeders are protected by overcurrent and ground overcurrent relays. All of these switchgear circuit breakers are normally closed.

These circuits are designated as P for separation identification.

8.2-10

WBNP-xx The secondaries of common station service transformers A and B feed into the 6.9kV start boards A and B. The start boards can be aligned to the 6.9kV shutdown boards through the unit boards as follows:

I. Common station service transformer A:

This transformer provides offsite power. from the secondary Y winding through circuit breaker 1512. for normal power to 6.9kV common board A and alternate power to 6.9kV unit boards IA. IC. 2A. and 2C. When CSST Dis not available. this transformer can be aligned manually to provide power to the 6.9kV shutdown boards. Normal (offsite) power from the transformer secondary Y winding can be aligned to 6.9kV shutdown board lB-B via 6.9kV start board A through circuit breaker 1512 to 6.9kV unit board IC through circuit breakers 1524 & 1722 and to 6.9kV shutdown board lB-B through circuit breaker 1726. Similarly. normal (offsite) power from transformer secondary Y winding can be aligned to 6.9kV shutdown board 2B-B via 6.9kV start board A through circuit breaker 1512 to 6.9kV unit board 2C through circuit breakers 1534 & 1822 and to 6.9kV shutdown board 28-B through circuit breaker 1826.

These circuits are identified as P separation designation.

2. Common station service transformer B:

This transformer provides offsite power. from the secondary Y winding through circuit breaker 1612. for normal power to 6.9kV common board Band alternate power to 6.9kV unit boards lB. ID. 28 and 20. When CSST C is not available this transformer can be aligned manually to provide power to the 6.9kV shutdown boards. Normal (offsite) power from the transformer secondary Y winding can be aligned to 6.9kV shutdown board IA-A via 6.9kV start board B through circuit breaker 1612 to 6.9kV unit board lB through circuit breakers 1622 & 1714 and to 6.9kV shutdown board lA-A through circuit breaker 1718. Similarly. normal (offsite) power from transformer secondary Y winding can be aligned to 6.9kV shutdown board 2A-A via 6.9kV start board B through circuit breaker 1612 to 6.9kV unit board 2B through circuit breakers 1632 & 1814 and to 6.9kV shutdown board 2B-B through circuit breaker 1818.

These circuits are identified as R separation designation.

The provisions made for independence of offsite sources are limited such that CSST A and B cannot be credited simultaneously for supply of6.9kV Class IE power. Additionally. CSST A and B only have the capacity to supply one train of 6.9kV shutdown boards for each unit.

All alternate and maintenance feeder circuit breakers located on the 6.9kV shutdown boards are open during normal plant operation and are utilized only when the normal power supply is not available. The maintenance supplies can be used to provide a second qualified offsite power source to the 6.9 kV shutdown boards when reguiredere eely te he useEI whee eeitker t:tBit is epef&fiag (either ia eelEI sktttdev.'ft er eet Rieled). All transfers between the normal, alternate and maintenance feeders take place at the 6.9kV shutdown boards.

8.2-11

WBNP-xx 6.9kV Common Station Switchgear C and D Control The normal control power for circuit breakers 1712 and 2714 is supplied from the existing l 25V de vital Battery Board I; the normal control power for circuit breakers 1812 and 2814 is supplied from the existing l 25V de vital Battery Board Il. This arrangement provides physically and electrically independent supplies. Control power circuits have been uniquely identified as P and R. P-designated cables are routed in separate raceways from R-designated cables with any exceptions and their justifications documented in the design criteria. The alternate control power for circuit breakers 1712 and 2714 is supplied from existing l 25V de vital Battery Board 111; the alternate control power for circuit breakers 1812 and 2814 is supplied from existing l 25V de vital Battery Board IV. These cables have been routed such that with either breakers 1712 and 2714 or breakers 1812 and 2814 receiving control power from the designated alternate source (and with the other breaker pair receiving control power from the normal source) physical and electrical independence of control power for each switchgear is maintained.

Manual control of the circuit breakers is provided on the electrical control board in the main control room where the operator has instrumentation showing the voltage on each of the two buses and the current flowing in each of the four feeder breakers.

The following annunciation is provided: Loss of Control Power 6.9kV Start Boards A & B. Unit Boards and Common Boards Control Power The normal control power for circuit breaker used to supply offsite power from CSST A and B to the 6.9kV shutdown boards is arranged to provide physically and electrically independent supplies.

The normal and alternate control power feeds to the 250VDC control buses for 6.9kV Start Boards A and B. Unit Boards I B. 1 C. 2B. 2C and Common Board A and B are supplied from 250VDC Turbine Distribution Boards land 2. The normal power feeder cables for 6.9kV Start Board control bus A are routed separately from those for control bus B. The normal power feeder cables for the 6.9kV Common Board A control bus are routed separately from those for 6.9kV Common Board B. The normal power feeder cables for the 6.9kV Unit Board lB control bus are routed separately from those for 6.9kV Unit Board IC. The normal power feeder cables for the 6.9kV Unit Board 2B control bus are routed separately from those for 6.9kV Unit Board 2C Control cables associated with CSST A normal alignments are designated as P and control cables associated with CSST B normal alignments are designated as R for separation identification.

8.2-12

WBNP-xx 6.9kV Start Board Breaker Controls:

The breaker control cables for 6.9kV Start Bus A nonnal feeder breaker 1512 are routed separately from those for 6.9kV Start Bus B nonnal feeder breaker 1612.

Control cables associated with breaker 1512 are designated as P and control cables associated with breaker 1612 are designated as R for separation identification. 6.9kV start bus alternate feeder breakers 16 l 4 and 1514 are not credited for supply of offsite power.

6.9kV Unit Board lB. IC. 2B. 2C Breaker Controls:

The breaker control cables for circuit breakers l 714. 1622 (NO) and 1114 CNC) at 6.9kV Unit Board lB are routed separately from those for brea!cers 1722. 1524 CNOl and l 122 CNC) at 6.9kV Unit Board IC. Similarly. the breakers control cables for circuit breakers 1814. 1632 (NO) and 1214 (NC) at 6. 9k V Unit Board 28 are routed separately from those for breakers l 822. l 534 CNO) and 1222 (NC) at 6.9kV Unit Board 2C.

Control cables associated with breakers l 114. 1214. 1622. 1632. l 714 and 1814 are designated as R and control cables associated with breakers 1122. 1222. l 524. 1534. 1722 and 1822 are designated as P for separation identification.

8.2.1.7 6.9kV Unit and RCP Board Control and Relaying The alternate feeder to each 6.9kV unit and RCP board is from one of the start buses with the normal feeder being from a unit station service transfonner.

Each 6.9kV unit and RCP board can be selected for automatic or manual transfer between the normal and alternate supply breakers. Manual transfers are high speed (6 cycles or less) and can be made from the normal to the alternate supply or from the alternate to the normal supply.

Automatic transfers can only be made from the normal to the alternate supply. Automatic transfers initiated by loss of voltage on the unit board are delayed until the bus residual voltage decreases to 30% of nominal. Those transfers initiated by reactor trip or turbine trip signals on the unit or RCP boards are high speed transfers. Control power is from the 250V de distribution system.

8.2-13

WBNP-xx These cables (designated P and R) are routed in close proximity to each other in the conduit vault as they transition from the cable trays to their respective common switchgear ductbank, and in the Turbine Building as they transition from the cable trays to their respective conduits. These cables routed in free air, where they are in close proximity in the conduit vault and Turbine Building, are fire-wrapped to preclude one faulted circuit from affecting the other circuit.

A chain link fence separates the cable tray supports from a maintenance access road. In addition, there is a 4-foot slope from the base of the pedestal-type supports to the road which is l 0 feet away. Due to the size and quantity of insulated cables in each tray, it is very unlikely that either circuit would be lost due to a collapse of a support for any reason. Since cables for each circuit are separated as 3-phase bundles in the respective P or R designated tray, phase-to-phase faults between normal or alternate circuits are considered extremely unlikely. Thus, a ground fault on one circuit is the most likely type of fault.

A ground fault or a short circuit on the secondary side of either CSST C or CSST D is cleared by operation of its respective breaker in the Watts Bar Hydro Plant l61kV switchyard. An automatic transfer of the loads fed from the faulted CSST will be initiated to the unfaulted CSST.

The faulted circuits can be isolated by opening the 6.9kV common switchgear C and D breakers.

By reclosing the WBH 161 kV switchyard breakers, power can be restored to the nuclear plant 6.9kV shutdown boards through the unfaulted secondaries ofCSST C and/or D. An alternate path is available to the shutdown boards from the 16lkV circuits by way ofCSST A and/or CSST B through the maintenance supply circuit from the 6.9kV unit boards to the 6.9kV shutdown boards. The ese efthe maiRteR&nee sepply ean eat~* he eseel vlheR eaeh eRit is either iR eelEI shetele*Nft er has ee fuel.

The offsite circuits are designed and located so as to minimize to the extent practical the likelihood of their simultaneous failure under operating and postulated accident conditions.

Common station service buses A and B maintain 61 feet centerline-to-centerline separation, until they converge at the unit start board. The buses run on separate support structures and run approximately 15 feet before entering the unit start board. At the unit start board, these buses enter the outdoor, metal-clad switchgear and connect to the board supply breakers. The buses are provided with gas resistant seals at the entry to the switchgear. The supply and feeder breakers at the 6.9kV unit start board are electrically operated, vertical lift draw out type, with stored energy mechanisms. The unit start board consists of a normal feeder breaker and an alternate feeder breaker for each of the 6.9kV start buses A and Band the RCP start buses A and B. The normal feeder breaker and the alternate feeder breaker obtain their supply from separate buses and separate common station service transformers, thereby giving each start bus two possible and independent sources of power.

8.2-17

WBNP-xx CSST A or B may be used as a replacement for CSSTs Dor C. respectively. through the 6.9kV shutdown board maintenance supply breakers. CSST A and B each have sufficient FA-rated capability to maintain adequate voltage for one train of shutdown boards for each unit while supplying required BOP loads for a design basis accident in one unit and safe shutdown of the other unit. When the USST is used. the affected shutdown board maintenance feeders are supplied from the USSTs through the Unit Boards and are automatically transferred to CSST A or B in the event of a unit trip. Use of CSST A or Bas an off site source requires that CSST A and B both be available and that the associated power and control feeders be in their normal positions to ensure independence. Due to independence limitations. CSST A and B cannot be credited for supply of both offsite power sources simultaneously. Feeders for CSST A are indeoendent of those for CSST C and feeders for CSST Bare independent of those for CSST D.

Supply of Class 1 E oower by CSST A or B requires manual breaker operations to align the CSST source to the applicable shutdown board maintenance feeders.

A load-shedding scheme is provided to reduce the BOP loads under certain conditions, but no credit is taken for load shedding in the TSS.

8.2-19

WBNP-xx The 6.9kV shutdown boards are provided with loss-of-voltage and degraded-voltage relays that initiate transfer from the nonnal supply. to the standby (diesel generator) power supply. If the standby supply is paralleled with one of the off site supplies for testing, loss of the standby supply would cause reverse power relays to trip the standby circuit breaker.

For a loss of offsite power during diesel generator testing, the diesel generator will switch to the emergency mode of operation with ene eJteeptien. The diesel geneFateF 'Nill Femain ie the testieg mede if the e.9kV sk1:1tde*+'lft eeard's etisite pevleF feed is UtFeHgk the altemate feedeF. IB this ease, the diesel geeemter's e¥eret:1FFeet rele}'5 ere eeti¥e te pFeveet the diesel geeemter frem eeieg e*;erleeEleEl. If an accident signal is initiated during testing of the standby supply, the standby breaker is tripped and the emergency loads are automatically energized by the offsite power supply. Should a LOCA and a loss of offsite power occur when a diesel generator is paralleled with the grid under test, its 6.9kV shutdown board standby and supply breakers are tripped, load shedding occurs and the diesel generator sequencer will load the accident loads.

Only one diesel generator will be in the test mode (i.e.* operated in parallel with the offsite power supply) at any given time unless the unit is in cold shutdown or not fueled: then, both diesels of the same train may be in test. Therefore, loss of any onsite power generation will not prevent the distribution system from being powered from the offsite circuits.

8.2-21

WBNP-xx The non-Class lE control power circuits from the vital battery boards to 6.9kV common switchgear C and D have redundant protection (breaker and fuse) in the event of a failure.

Selective coordination exists between the non-Class lE and Class lE circuits that are fed from each of the vital battery boards. Thus, failure of all of the non-Class l E control power circuits on the vital battery boards will not have any effect on the Class lE circuits or battery boards.

WBNP is in full compliance with GDC 17.

Use ofCSST Bas a replacement for CSST C reauires control of breakers on 6.9kV start board B and 6.9kV unit boards lB and 2B. Similarly. use of CSST A as a replacement for CSST D requires control of breakers on 6.9kV start board A and 6.9kV unit boards lC and 2C. These breakers are controlled with non-Class lE 250Vdc supplied by 250Vdc Turbine Building Distribution Boards l and 2. The normally aligned 250Vdc power sources and control power feeders to the start boards and unit boards meet the requirements for independence of offsite sources in accordance with GDC-17.

Regulatory Guide 1.6 has been implemented by providing each ac load group with a connection to each of the preferred source circuits. Figure 8.1-2 indicates that redundant power trains in each unit are fed from different preferred source circuits. The two preferred source circuits are.

however. shared between the two nuclear units.

Regulatory Guide 1.32 has been implemented by providing two immediate access circuits fromte the transmission network. Figures 8.1-2, 8. l-2a, 8. l-2b, and 8.2-1 indicate the functional arrangement of these continuously energized circuits.

Normal power is supplied to the 6.9kV unit boards by the unit station service transformers; to the 6.9kV common boards A and B by CSSTs A and B, and to the 6.9kV shutdown boards by the CSSTs C and D during normal plant operation.

8.2-24

WBNP-xx CSSTs A and B supply power to the 6.9kV unit boards and 6.9kV common boards A and B during startup or shutdown. Additionally. CSST A or B may supply power to the 6.9 kV shutdown boards during maintenance of CSST D or C. respectively. in any Operating Mode.

Power continuity to the 6.9kV shutdown boards is normally provided from common station service transformers C and D. To provide a stable voltage. these transformers have automatic load tap changers on each secondary that adjust voltage based on the normally connected shutdown boards.

During maintenance of common station service transformer C or D. power continuity to the normally connected train of 6. 9k V shutdown boards is provided by the boards' maintenance feeds that connect to unit boards with access to common station service transformers B or A.

respectively. Use of transformers A and Bis restricted such that they are not simultaneously credited as an independent source of offsite power for the Class l E power svstem. Common station service transformers A and B have automatic load tap changers on the primary winding that adjust voltage based on the normally connected start board.

The automatic load tap changers for all common station service transformers are normally controlled in the automatic mode with the capability for manual adjustment from the main control room pf0*1ielee fi:e1B CSSTs C &Ha D. Te pFe*1iee a steele 'leltege, these traesfeffHers have eute1Batie high Sfleed lead tefl eh&HgeFS ea eeeh seeeadery, whieh eajust Yeltege hesed ea the neffHelly eeaneeted shuteewa heefds. The lead t&fl eheegers else h&¥e the eepehility te he IB&BU&lly adjusted ffelB the eeaa:el FeelB, eut &Htematie ef)efEKieft is the BeffH&l IBede.

The 6.9k'l shutElevre heards 1Bey else he fleweFee ff:elB the unit heenls; hewe¥eF, this line ttfl is lilBited edmieislf'eti'<*ely eRly te eeeHF with hath tiaits Hi eels shtitee'ffll er eet fuelee.

In addition to compliance with the above standards for portions of the offsite power system, the 6.9kV start board, 6.9kV unit boards, 6.9kV RCP boards, and the associated 6.9kV buses were procured in accordance with certain TV A standards and industry standards. TV A specifications require conformance of this equipment to such standards as the following: the overall construction, ratings, tests, service conditions, etc. are required to be in conformance to ANSI C37.20 and NEMA SG-5; the power circuit breakers are referenced to ANSI C37.4 through C37.9 and NEMA SG-4; associated relays are specified to conform to ANSI C37. l, instrument transformers to ANSI C57.13 and NEMA EI-2, and wiring to IPCEA S-61-402 and NEMA WC5.

8.2-25

WBNP-xx The design of the equipment arrangement was also implemented to comply with GDC 3 for fire protection and with GDC 18 and Regulatory Guide 1.22 for each of periodic tests and inspections.

In accordance with GDC 18 requirements, the offsite power system has been designed to permit appropriate periodic inspection and testing. Transfers from the normal (offsite) supply to the alternate (offsite) supply, or from the nonnal or alternate supply to the standby supply, may be manual or automatic. Testing of these transfers while the nuclear unit is at power could result in transients that could cause tripping of the reactor or turbine. For this reason, testing of the manual and automatic sequence will be performed when the unit is shutdown. Provisions exist for individual testing of the BOP load shedding circuits while maintaining the load-shedding capability of the circuit not being tested.

8.2.2 Analysis Each l6lkV circuit and its associated CSSTs C BRe D have sufficient capacity and adequate voltage to supply the essential safety auxiliaries of a unit under loss of coolant accident conditions concurrent with a simultaneous worst-case single transmission system contingency.

Physical separation of lines, primary and backup protection systems, and a strong transmission grid minimize the probability of simultaneous failures of offsite power sources. Results of steady-state and transient stability studies show that the offsite power sources remain intact and are reliable sources to supply the onsite electric power system for (I) an SI in a WBN nuclear unit with an electrical fault in the generator step-up transfonner, or (2) an SI in a WBN nuclear unit and either the loss ofSQN Unit 2, the loss of the largest load on the grid (Bowater 161-kV substation), or the loss of the most critical transmission line.

Transient unit stability studies were performed to show that the WBN unit and the Watts Bar Hydro Plant units would maintain synchronism for a line-to-ground fault and a stuck breaker.

Transient voltage stability studies were performed on the 500-kV and 161-kV system by simulating a line-to-ground fault with a stuck breaker. These studies were performed to ensure relay coordination, unit stability, and voltage recovery requirements were met.

System Operation Each 6.9kV shutdown board can be powered through any one of four shutdown board supply breakers. For normal operation, power is supplied from the common station service transfonners C and D through the 6.9kV common switchgear C and D circuits. The normal supply breakers are shown normally closed on Figure 8. l-2a. Shown normally open are the breakers that connect the alternate offsite power circuits to the shutdown boards (via CSSTs C or D), the emergency supply breakers that connect each shutdown board to a separate standby diesel generator, and the maintenance supply breakers that can provide power to the shutdown boards via the unit boards.

8.2-26

WBNP-xx Automatic fast-bus transfers from the normal to the alternate source are initiated by CSST protection devices. Return to the normal supply is manual only. Manual transfers are fast transfers completed in approximately six cycles. Manual transfer may be effected between any incoming feeder breakers.

Each 6.9kV shutdown board is equipped with loss-of-voltage and degraded-voltage relaying.

When a shutdown board is connected to either its normal or alternate power source, loss-of-voltage or degraded-voltage initiates bus transfers to the standby diesel generator supply.

The degraded-voltage relays (27 DAT, DBT. OCT) have a voltage setpoint of 96% of 6.9kV (nominal, decreasing). These relays are arranged in a two-out-of-three coincidence logic (Figure 8.3-5A) to initiate a IO-second (nominal) time delay. If the voltage is still low at the end of 10 seconds, an alarm will be fillenunciated in the Control Room, a trip of the 6.9kV shutdown-board supply breaker will occur, load shedding from the 6.9kV and 480V shutdown boards and diesel generator start will be initiated, and the 480V shutdown-board current-limiting reactor-bypass breaker will close.

The undervoltage protection consists of three sets of relays. The first set of these relays (27L VA, LVB, LVC) has a voltage setpoint of87% of6.9kV (nominal, decreasing). These relays are arranged in a two-out-of-three coincidence logic (Figure 8.3-5A) to initiate a time delay that is set at 0.75 seconds. At the end of this time delay, if the voltage is still low, a trip of the 6.9kV shutdown-board supply breaker will occur. Once the supply breakers have been opened, a second set of induction disk-type undervoltage relays, 270, which has a voltage setpoint of 70%

of 6.9kV (nominal, decreasing) and an internal time delay of0.5 seconds (nominal) at zero volts, will start the diesel generator. A third set of induction disk-type undervoltage relays, 27S, which has a voltage setpoint of70% of 6.9kV (nominal, decreasing) and an internal time delay of 3 seconds (nominal) at zero volts, will initiate load shedding of the loads on the 6.9kV shutdown board, selected loads on the 480V shutdown board, and closure of the 480V shutdown-board current-limiting reactor bypass breaker.

The time delays associated with the 27 DAT, DBT, OCT and with the 27 L VA, L VB, L VC relays are designed to allow for normal voltage transients on the system.

Voltage relays monitor the circuits to each 6.9kV shutdown board's alternate and emergency supply breakers and permit automatic transfer to those sources only when adequate voltage is available. A typical transfer scheme is shown schematically in Figure 8.3-5 for 6.9kV shutdown board IA-A.

To protect the Class IE equipment from a sustained overvoltage, each 6.9kV shutdown board is provided with a set of two instantaneous solid-state overvoltage relays, 59-0. These relays are arranged in a one-out-of-two logic which annunciates in the main control room after a short time delay. The relays have a nominal voltage setpoint of 7260 volts +/- 1 % ( 110% of motor rated voltage). Upon receipt of the overvoltage alarm, the operator takes the necessary action to reduce the voltage.

8.2-27

v t e Letter Sequence Response to RAI
TAC:MF2549, (Approved, Closed)
Initiation Request, Request, Request Acceptance... Administration Questions 31 March 2015 26 February 2014 16 June 2014 15 April 2015 Answers 21 April 2014 29 January 2015 12 June 2015 Results Approval, Approval Other: ML15232A113, ML15232A116
MONTHYEAR2015-01-29 [Table View]

CNL-14-107, Response to NRC Request for Additional Information Related to Application to Modify Technical Specifications Regarding AC Sources - Operating (TS-WBN-13-02)

Text

Subject:

References:

Enclosures:

Background:

8.1 INTRODUCTION

Navigation menu

CNL-14-107, Response to NRC Request for Additional Information Related to Application to Modify Technical Specifications Regarding AC Sources - Operating (TS-WBN-13-02)

Text

Subject:

References:

Enclosures:

Background:

8.1 INTRODUCTION

Navigation menu

Search