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| number = ML13220A103 | | number = ML13220A103 | ||
| issue date = 08/01/2013 | | issue date = 08/01/2013 | ||
| title = | | title = Application to Modify Technical Specifications Regarding AC Sources - Operating (TS-WBN-13-02) | ||
| author name = Shea J | | author name = Shea J | ||
| author affiliation = Tennessee Valley Authority | | author affiliation = Tennessee Valley Authority | ||
| addressee name = | | addressee name = | ||
| Line 15: | Line 15: | ||
=Text= | =Text= | ||
{{#Wiki_filter:Tennessee Valley Authority, 1101 Market Street, Chattanooga, Tennessee | {{#Wiki_filter:Tennessee Valley Authority, 1101 Market Street, Chattanooga, Tennessee 37402 August 1, 2013 10 CFR 50.90 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, D.C. 20555-0001 Watts Bar Nuclear Plant Unit 1 Facility Operating License No. NPF-90 NRC Docket No. 50-390 | ||
==Subject:== | ==Subject:== | ||
Application to Modify Watts Bar Nuclear Plant, Unit I Technical Specifications Regarding AC Sources - Operating (TS-WBN-13-02) | |||
References 1. NUREG-0847, "Safety Evaluation Report Related to the Operation of Watts Bar Nuclear Plant, Unit 2," Supplement 22, dated February 2011 (ADAMS Accession No. ML110390197) | |||
: 2. NUREG-0847, "Safety Evaluation Report Related to the Operation of Watts Bar Nuclear Plant, Unit 2," Supplement 24, dated September 2011 (ADAMS Accession No. ML11277A148) | |||
In accordance with the provisions of 10 CFR 50.90, "Application for amendment of license, construction permit, or early site permit," the Tennessee Valley Authority (TVA) is submitting a request for an amendment to Facility Operating License No. NPF-90 for Watts Bar Nuclear Plant (WBN), Unit 1. | |||
TVA proposes this license amendment request (LAR) to the WBN, Unit 1 Technical Specifications (TS) to modify the Limiting Condition for Operation (LCO) for the AC Sources Operating in LCO 3.8.1, provide additional time to restore an inoperable offsite circuit, modify Surveillance Requirement (SR) 3.8.1.8, and modify the current licensing basis, as described in the Updated Final Safety Analysis Report (UFSAR), for the available maintenance feeder for the Common Station Service Transformers (CSST) A and B. The proposed LAR credits upgrades made to CSST A and B to provide two new sources of preferred Class 1 E power supply feeds in addition to the two normal Class 1 E power supply feeds. The TS change is needed to support dual unit operations without requiring a dual unit shutdown during maintenance on either preferred power CSST C or D. This proposed request also achieves licensing basis commonality for the current Operating Unit 1 license with respect to those approved elements of the Unit 2 application as docketed in NUREG-0847, Supplements 22 and 24 (References 1 and 2). | |||
Printed on recycled paper | |||
U.S. Nuclear Regulatory Commission Page 2 August 1, 2013 The enclosure provides the description, technical evaluation, regulatory evaluation, and environmental consideration of the proposed changes. Attachments 1 and 2 to the enclosure provide the existing TS and Bases pages marked-up to show the proposed changes. | |||
Attachments 3 and 4 to the enclosure provide the existing TS and Bases pages retyped with the proposed changes incorporated. Attachment 5 to the enclosure provides a summary of the proposed UFSAR changes. | |||
TVA requests approval of this LAR no later than April 30, 2014, to support preparations for fuel load activities at Watts Bar Unit 2. | |||
TVA has determined that there are.no significant hazards considerations associated with the proposed change and that the change qualifies for a categorical exclusion from environmental review pursuant to the provisions of 10 CFR 51.22(c)(9). | |||
The WBN Plant Operations Review Committee and the WBN Nuclear Safety Review Board have reviewed the proposed changes and determined that operation of WBN in accordance with the proposed change will not endanger the health and safety of the public. | |||
Additionally, in accordance with 10 CFR 50.91 (b)(1), TVA is sending a copy of this letter and the enclosure to the Tennessee Department of Environment and Conservation. | |||
Attachments 1 and 2 to the enclosure provide the existing TS and Bases pages marked-up to show the proposed changes.Attachments 3 and 4 to the enclosure provide the existing TS and Bases pages retyped | There are no regulatory commitments associated with this submittal. Please address any questions regarding this request to Mr. E. D. Schrull at 423-751-3850. | ||
Attachment 5 to the enclosure provides a summary of | I declare under penalty of perjury that the foregoing is true and correct. Executed on this 1 st day of August 2013. | ||
The WBN Plant Operations Review Committee and the WBN Nuclear Safety Review | Resp hly, J W Shea, cresident, Nuclear Licensing | ||
There are no regulatory commitments associated with this submittal. | |||
Please address | |||
I declare under penalty of perjury that the foregoing is true and correct. | |||
Executed on | |||
==Enclosure:== | ==Enclosure:== | ||
Evaluation of Proposed | Evaluation of Proposed Change cc (Enclosure): | ||
NRC Regional Administrator | NRC Regional Administrator - Region II NRC Senior Resident Inspector- Watts Bar Nuclear Plant, Unit 1 Director, Division of Radiological Health - Tennessee State Department of Environment and Conservation | ||
-Region | |||
ENCLOSURE TENNESSEE VALLEY AUTHORITY WATTS BAR NUCLEAR PLANT UNIT I EVALUATION OF PROPOSED CHANGE | |||
==Subject:== | ==Subject:== | ||
Application to Modify Watts Bar Nuclear Plant, Unit I Technical Specifications Regarding AC Sources - Operating (TS-WBN-13-02) 1.0 | |||
==SUMMARY== | |||
DESCRIPTION 2.0 DETAILED DESCRIPTION 2.1 Proposed Changes 2.2 Need for Proposed Changes | |||
==3.0 TECHNICAL EVALUATION== | |||
3.1 System Description 3.2 Evaluation | |||
== | ==4.0 REGULATORY EVALUATION== | ||
4.0 REGULATORY EVALUATION | |||
4.1 Applicable Regulatory Requirements and Criteria 4.2 Precedent 4.3 Significant Hazards Consideration 4.4 Conclusions | |||
==6.0 REFERENCES== | ==5.0 ENVIRONMENTAL CONSIDERATION== | ||
==6.0 REFERENCES== | |||
ATTACHMENTS | ATTACHMENTS | ||
: 1. Proposed TS Changes (Mark-Ups) for WBN Unit | : 1. Proposed TS Changes (Mark-Ups) for WBN Unit 1 | ||
by adding a note | : 2. Proposed TS Bases Changes (Mark-Ups) for WBN Unit 1 (For Information Only) | ||
: 3. Proposed TS Changes (Final Typed) for WBN Unit 1 | |||
to allow the use of Common Station | : 4. Proposed TS Bases Changes (Final Typed) for WBN Unit 1 (For Information Only) | ||
Attachments 1 and 2 to this enclosure provide the existing WBN, Unit 1 TS and | : 5. Proposed UFSAR Changes (Mark-Ups) for WBN Unit 1 (For Information Only) | ||
Attachments 3 and 4 to this enclosure provide the existing TS and Bases pages retyped to show the proposed changes.Attachment 5 to this enclosure provides a summary of the proposed UFSAR changes.2.0 DETAILED DESCRIPTION | E-1 I of 48 | ||
1.0 | |||
==SUMMARY== | |||
DESCRIPTION This evaluation supports a request to amend Watts Bar Nuclear Plant (WBN), Unit 1, Facility Operating License No. NPF-90. The proposed change will modify WBN, Unit 1 Technical Specification (TS) 3.8.1, "AC Sources - Operating," by adding a note to Limiting Condition for Operation (LCO) 3.8.1, adding additional required actions to LCO 3.8.1 Action A, and adding requirements to Surveillance Requirement (SR) 3.8.1.8. The proposed change will also revise the current licensing basis, as described in the Updated Final Safety Analysis Report (UFSAR), to allow the use of Common Station Service Transformers (CSSTs) A and B as qualified sources of power. | |||
This amendment proposes to revise Technical Specification 3.8.1 and Technical Specification Bases 3.8.1 to add an allowance to use Common Station Service Transformer (CSST) A or B to meet the requirements of LCO 3.8.1, with respect to qualified offsite circuits, provide additional time to operate with an offsite circuit inoperable when CSST C or D is inoperable, and add testing of the manual transfers of the shutdown boards to and from the maintenance feeds (i.e., CSSTs A and B). Testing of the manual transfers is required to show that these transfers are functional and can be used to supply power to the shutdown boards during conditions when either CSST C or D is out of service for maintenance or to restore power if CSST C or D fails. The proposed changes result from upgrades made to CSSTs A and B to provide two new sources of preferred Class 1 E power supply feeds in addition to the two normal Class 1 E power supply feeds. The upgrades to CSSTs A and B were completed as part of actions to address NUREG-0847, "Safety Evaluation Report Related to the Operation of Watts Bar Nuclear Plant, Unit 2," Supplement 22, Appendix HH, | |||
'Watts Bar Unit 2 Action Items Table," Open Item 27 (Reference 1). | |||
In addition, this amendment proposes to modify the current licensing basis, as described in the UFSAR, to remove the statements restricting the use of the CSSTs A and B maintenance feed during dual unit operations. | |||
Attachments 1 and 2 to this enclosure provide the existing WBN, Unit 1 TS and Bases pages marked-up to show the proposed changes. Attachments 3 and 4 to this enclosure provide the existing TS and Bases pages retyped to show the proposed changes. | |||
Attachment 5 to this enclosure provides a summary of the proposed UFSAR changes. | |||
2.0 DETAILED DESCRIPTION | |||
===Background=== | ===Background=== | ||
The WBN Alternating Current (AC) Electrical Power Distribution System AC sources | The WBN Alternating Current (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 Code of Federal Regulations (CFR) 50, Appendix A, General Design Criterion (GDC) 17 (Reference 2), 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. | ||
and | Offsite power is supplied to the 161 kiloVolt (kV) transformer yard by two dedicated lines from the WBN Hydro Plant switchyard. From the 161 kV transformer yard, two electrically and physically separated circuits provide AC power, through stepdown CSSTs C and D, 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 E-1 2 of 48 | ||
From the 161 kV transformer yard, two electrically and physically separated circuits provide AC power, through stepdown CSSTs C and D, | |||
A | 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 are found in WBN UFSAR Section 8 (Reference 3). | ||
The WBN Auxiliary Power System (APS) was originally designed for two unit operation. | |||
Currently TVA continues to prepare for WBN Unit 2 licensing and plans to place the unit | 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. | ||
By letter dated July 12, 2010, (Reference 4), the NRC requested that | Therefore, the APS analysis supported Unit 1 operation only, although it took into account Unit 2 buses, boards and loads required for Unit 1 operation and safe shutdown. | ||
" Dual-unit trip as a result of an abnormal operational occurrence; | Currently TVA continues to prepare for WBN Unit 2 licensing and plans to place the unit into commercial operation in the near future. Thus, the APS will be required to support a two unit operation. By letter dated July 12, 2010, (Reference 4), the NRC requested that TVA provide an executive summary of the two unit analysis to support the following design requirements: | ||
* Accident in one unit and concurrent shutdown of the second unit (with and without | " Dual-unit trip as a result of an abnormal operational occurrence; | ||
* Accident in one unit and concurrent shutdown of the second unit (with and without offsite power); and | |||
The study specifically evaluated existing CSSTs A and B to determine their acceptability | * Accident in one unit and spurious Engineered Safety Feature (ESF) actuation in the other unit (with and without offsite power). | ||
Additionally, it concluded that the voltage criteria are met for WBN | WBN performed a study (Reference 5) to evaluate the existing WBN APS to determine its adequacy for two unit operation, including the design requirements requested in the Reference 4 NRC letter. As stated in the TVA letter to the NRC dated July 31, 2010 (Reference 6), the scope of this study included the CSSTs A, B, C, and D; 6.9-kV shutdown boards; 6.9-kV start buses; 6.9-kV common boards; 6.9-kV unit boards; downstream 6.9-kV-480-volt (V) transformers; 480-V distribution systems loads, and all interconnections. | ||
This License Amendment Request (LAR) requests to revise the WBN, Unit 1 Technical Specifications (TS) by modifying the Limiting Condition for Operation (LCO) for | The study specifically evaluated existing CSSTs A and B to determine their acceptability as qualified offsite power sources for the safety related boards when used for safe shutdown of the units under a design basis Loss of Coolant Accident (LOCA). The study recommended adding an automatic On Load Tap Changer (OLTC) on the primary side of CSST A and B. | ||
: a. Number the current LCO 3.8.1 Note as "Note 1" and add a Note 2 to LCO 3.8.1 | The study also concluded that WBN Units 1 and 2 are stable for all 3-phase fault scenarios with normal clearing. Additionally, it concluded that the voltage criteria are met for WBN Unit 2 coming on line and for other future system changes. | ||
: b. Renumber Required Action A.3 to "A.3.1" and add additional required actions to | As a result of the above study, TVA upgraded CSSTs A and B to functionally perform as alternate sources of offsite power in order to increase defense in depth and add increased reliability to the offsite power sources. | ||
A.3.1 Restore offsite circuit to OPERABLE status. | The WBN Design Change Notices (DCNs) that facilitated the use of CSSTs A and B as qualified offsite sources for the 6.9 kV shutdown boards to support safe shutdown of the unit during a design basis event have been completed. | ||
: a. Automatic and manual | This License Amendment Request (LAR) requests to revise the WBN, Unit 1 Technical Specifications (TS) by modifying the Limiting Condition for Operation (LCO) for the AC Sources Operating in LCO 3.8.1, providing additional time to restore an inoperable offsite circuit, modifying Surveillance Requirement (SR) 3.8.1.8, and modifying the current licensing basis, as described in the UFSAR, for the available maintenance feeder for CSSTs A and B. | ||
when CSST A or B is | E-1 3 of 48 | ||
UFSAR | |||
Sections 8.2.1, 8.2.1.3,8.2.1.5, 8.2.1.6 and 8.2.1.8. | 2.1 Proposed Changes Technical Specification Changes TVA proposes the following changes to the WBN, Unit 1 Technical Specifications. | ||
In addition, UFSAR Figures 8.1-2, 8.1-2B, 8.3-5, 8.3-16,8.3-17, 8.3-18 and 8.3-19 are affected by the proposed change and will be updated | : a. Number the current LCO 3.8.1 Note as "Note 1" and add a Note 2 to LCO 3.8.1 to provide guidance and conditions for using CSST A or B to meet one of the two qualified offsite circuits, to read: | ||
"Maintenance of records, making of reports." | : 2. Common Station Service Transformer(CSST) A or B may be used to meet one of the two qualified offsite circuitrequirements of LCO 3.8.1, provided CSST A or B is only providinq power to its normal unit and reactorcoolant pump boards, and: | ||
The referenced figures are based on TVA drawings 1-15E500-1, 1-15E500-3, 1-45W724-1, 1-45W724-2, 1-45W724-3 and 1-45W724-4 respectively. | : a. CSST A or B is providinq power to the associatedshutdown board; or | ||
Refer to Enclosure Attachment 5 for the currently planned UFSAR text changes.2.2 Need for Proposed | : b. The associatedshutdown board is beinq powered by the Unit Station Service Transformer(USST) and automatic transfercapabilityfrom the USST to CSST A or B (as applicable)is OPERABLE. | ||
). From a plant operational flexibility standpoint, this condition has been adequate for single unit operation. | : b. Renumber Required Action A.3 to "A.3.1" and add additional required actions to LCO 3.8.1 Condition A to provide alternate requirements for using CSST A or B to meet LCO requirement, to read (renumbered Required Action A.3.1 shown for clarity): | ||
Maintenance on either CSST C or D | A.3.1 Restore offsite circuit to OPERABLE status. | ||
Thus, performing maintenance | OR A.3.2.1 Aliqn backup offsite circuit CSST A or CSST B to requiredshutdown board. | ||
Furthermore, performing the | AND A.3.2.2 Restore offsite circuit to OPERABLE status | ||
: c. Revise SR 3.8.1.8 to add additional surveillance requirements for verifying automatic and manual function of 6.9 kV power supplies, to read: | |||
Verify the followincq: | |||
: a. Automatic and manual transferof each 6.9 kV shutdown boardpower supply from the normal offsite circuit to the alternateoffsite circuit; | |||
: b. Automatic transferof the associated6.9 kV shutdown boardpower suppl, from the USST to the associatedCSSTA or B, when USST is powerinq the associatedshutdown board and CSST A or B is credited with meetinq LCO 3.8.1.a requirements;and | |||
: c. Manual transferof the associated6.9 kV shutdown boardpower suppli from the associatedCSST A or B to the normaloffsite circuit(CSST C or D. | |||
E-1 4of48 | |||
as applicable), when CSST A or B is creditedwith meeting LCO 3.8.1.a requirements. | |||
UFSAR Changes In order to credit upgrades made to CSSTs A and B, to provide four new sources of preferred Class 1E power supply feeds in addition to the two normal Class 1 E power supply feeds, the following UFSAR sections will be revised: Sections 8.2.1, 8.2.1.3, 8.2.1.5, 8.2.1.6 and 8.2.1.8. In addition, UFSAR Figures 8.1-2, 8.1-2B, 8.3-5, 8.3-16, 8.3-17, 8.3-18 and 8.3-19 are affected by the proposed change and will be updated as part of the amendment implementation phase to be included in the subsequent UFSAR update as required by 10 CFR 50.71(e), "Maintenance of records, making of reports." | |||
The referenced figures are based on TVA drawings 1-15E500-1, 1-15E500-3, 1-45W724-1, 1-45W724-2, 1-45W724-3 and 1-45W724-4 respectively. Refer to Enclosure Attachment 5 for the currently planned UFSAR text changes. | |||
2.2 Need for Proposed Changes Watts Bar Nuclear Plant (WBN) is currently configured with four CSSTs that provide offsite power. CSSTs C and D are qualified and used to supply the safety related class 1E power system; CSSTs A and B are used for non-safety loads. During operation in Mode 1, 2, 3, or 4 with either CSST C or D out of service, the plant is required to enter LCO 3.8.1 Condition A for not having two qualified offsite power sources available (i.e., one of the two qualified offsite sources are inoperable ). From a plant operational flexibility standpoint, this condition has been adequate for single unit operation. Maintenance on either CSST C or D during single unit operation mode can be performed in Modes other than Modes 1, 2, 3, and 4, i.e., | |||
when only one of the two qualified offsite circuits are required to be OPERABLE in accordance with LCO 3.8.2, "AC Sources - Shutdown." Thus, performing maintenance at this time does not require entry into LCO 3.8.1. | |||
However, once Unit 2 begins power operations, it will be desirable to have one unit running while the other unit is in an outage. Therefore, one unit will be in Mode 1, 2, 3, or 4 when it is desired to perform maintenance on CSST C or D. To support performing maintenance on either of these two CSSTs when one unit is operating will require increased operational flexibility from the offsite power system to ensure that two offsite sources can be maintained even when a CSST is removed from service. Furthermore, performing the required maintenance can take more time than the currently allowed 72 hours to restore an inoperable qualified offsite circuit to OPERABLE status when the unit is in MODE 1, 2, 3, or 4, as required by LCO 3.8.1, Action A. Therefore, this technical specification change is necessary to allow this maintenance to be performed without requiring a dual unit shutdown including those times when the maintenance or repairs may require up to 14 days or longer. | |||
==3.0 TECHNICAL EVALUATION== | |||
====3.2.1 Introduction | ===3.1 System Description=== | ||
Design studies have concluded that CSSTs A and B are appropriately sized to | The WBN plant electric power system consists of the main generators, USSTs, CSSTs, diesel generators, batteries, and the electrical distribution system. Under normal operating conditions, the main generators supply electrical power through isolated-phase buses to the main step-up transformers and through the unit station service transformers to the non-safety auxiliary power system. Offsite electrical power supplies Class 1 E circuits through the 161-kV system via CSSTs C and D. The primaries of the unit station service E-1 5of48 | ||
With CSSTs A and B meeting the requirements of GDC 17, these transformers may be | |||
Several design changes were required in order to qualify the existing CSSTs A and B | 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 CSSTs. | ||
In conformance with GDC 17, the design function of the preferred offsite power system is 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. | |||
The preferred power lines from the existing Watts Bar Hydro 161-kV switchyard, provides power to all four CSSTs (A, B, C, and D) and are routed to minimize the likelihood of their simultaneous failure. | |||
The safety-related plant distribution system receives AC power from CSSTs C and D through the shutdown boards (which are powered from the offsite power system), or four 4400 kW diesel-generator standby power sources, and distributes it to both safety-related and non-safety-related loads in the plant. The two preferred circuits have access to the TVA transmission network which in turn has multiple interties with other transmission networks. | |||
Each line (CSST C and D) is the normal feed for one train of shutdown boards and the alternate feed for the other train of shutdown boards. The other transformer (CSST A and B) on each line supplies power to the 6.9kV unit boards and can indirectly power the shutdown boards if they are tied to the unit boards through the maintenance feeder. This maintenance feeder path is not a qualified source for the shutdown boards and can only be used in Mode 5 or below (i.e., when LCO 3.8.1 is not applicable). | |||
Currently, UFSAR Section 8.2.1.8 describes automatic fast transfer of the 6.9kV shutdown boards to their alternate source (CSST C or D) when the normal source (CSST C or D) trips. | |||
When CSST C or D trips and CSST A or B is manually aligned in place of the tripped CSST C or D, the fast transfer for the alternate is lost. Also, due to loading and separation requirements alignment restrictions are required when CSST A or B is used as an offsite supply for the 6.9kV Shutdown Boards. | |||
The 6.9kV common switchgear C and D are connected to the 6.9kV shutdown boards by cables arranged to provide two physically independent sources of offsite power. | |||
The CSSTs and buses are connected and arranged to provide two physically independent offsite power (OSP) circuits to the onsite (Class 1E) distribution system. One OSP circuit that is connected to CSSTs A and D is designated P while the other OSP circuit that is connected to CSSTs B and C is designated R. Circuits designated P and R are routed in separate conduits and trays to assure physical independence with any exceptions and their justifications documented in the design criteria. Non-segregated phase buses are used to connect the secondary of CSSTs C and D to 6.9-kV common switchgear C and switchgear D, respectively. During startup and shutdown, all auxiliary power is supplied from the 161 -kV system through CSSTs A, B, C and D. | |||
E-1 6 of 48 | |||
Two offsite power circuits are required to be operational with one available within a few seconds following a loss of coolant accident (as specified in GDC 17). The proposed amendment improves the ability of the plant to meet these design requirements during dual unit operation. A simplified diagram of the proposed change is provided below. | |||
IL CSST B ILLIi CSST A CSST B IL CSST A 1B i 1C i 2B 2C Unit Boards i iCSST 0 . . 0 0B., | |||
* r. | |||
L:I Shutdown lA-A lB-B 2A-A 2B-B Boards Maintenance feeder proposed by this license amendment. | |||
3.2 Evaluation 3.2.1 Introduction Design studies have concluded that CSSTs A and B are appropriately sized to carry required Balance of Plant (BOP) loads as well as one train of Class 1 E loads for each unit during normal and accident conditions provided both CSSTs A and B are in service (Reference 8). In addition, the analysis demonstrated that power and control cables associated with CSSTs A and B and the maintenance feeders meet separation requirements provided only CSST A or CSST B is used to power one train of shutdown boards, but not both. These restrictions have been incorporated into the WBN Unit 1 UFSAR and Design Criteria. | |||
With CSSTs A and B meeting the requirements of GDC 17, these transformers may be used as qualified sources of offsite power. A description of the changes to CSSTs A and B needed for them to considered qualified sources is provided below. This amendment proposes to revise Technical Specification 3.8.1 by adding a note to Limiting Condition for Operation (LCO) 3.8.1 allowing the use of CSST A or B to meet the requirements of LCO 3.8.r.a under certain circumstances, adding additional required actions to LCO 3.8.1 Action A to allow one qualified offsite circuit to be inoperable for up to 14 days, and adding requirements to Surveillance Requirement (SR) 3.8.1.8 to add testing of the manual transfers of the shutdown boards to and from the maintenance feeds (i.e., CSSTs A and B) in order to show that these transfers are functional and can be used to supply power to the shutdown boards in the case that either CSST C or D is out of service for maintenance or for other reasons. | |||
E-1 7 of 48 | |||
3.2.2 Technical Basis The existing CSSTs A and B were upgraded to provide an additional source of qualified power to the safety related class 1 E system. This upgrade allows either CSST A or B to power the shutdown boards while either CSST C or D is out of service for maintenance. | |||
Several design changes were required in order to qualify the existing CSSTs A and B for offsite power sources to the safety related class 1 E system. On-load tap changers (OLTCs) were installed on CSST A and B to meet the required stable voltage requirements for the 6.9kV Shutdown Boards. "P" and "R" train designations were added to power and control cables associated with CSSTs A and B and cables were re-routed as necessary to maintain GDC 17 separation requirements. | |||
Additional new features from the physical work completed under DCN 52336, have installed: | Additional new features from the physical work completed under DCN 52336, have installed: | ||
" cables and raceways to provide OLTC position indication; | " cables and raceways to provide OLTC position indication; | ||
* OLTC trouble alarm;* manual/automatic operation of the OLTC in the Main Control Room;* control switch and tap position indicator, for CSST A and B in the Electrical | * OLTC trouble alarm; | ||
: 2. All power and control circuits associated with CSSTs A and B as well as | * manual/automatic operation of the OLTC in the Main Control Room; | ||
The offsite source via CSST A or B has been analyzed to demonstrate that the sources | * control switch and tap position indicator, for CSST A and B in the Electrical Control Board (ECB) Panel 2; | ||
" Loss of the largest capacity being supplied to the grid;* Loss of the largest load from the grid;* Loss of the most critical transmission line; and* Loss of both | * Alarm for CSST A and B tap changer abnormal in annunciator window box XA 42A, window number 502B/503B, located in ECB Panel 3; and | ||
(Reference | * Alarm input combined with other alarm inputs from CSST A and B. | ||
The use of CSSTs A and B as offsite power sources to the safety related class 1 E system requires compliance with several restrictions to ensure loading and separation requirements are met before either of these CSSTs can be aligned to the shutdown boards. Some restrictions include: | |||
When the plant is normally aligned with CSSTs C and D powering the shutdown boards, | : 1. Only CSST A or B can be used as a qualified offsite power at any given time (i.e., either CSST C or D must be Operable); | ||
: 2. All power and control circuits associated with CSSTs A and B as well as the maintenance feeders must be normally aligned; and | |||
Furthermore, alignment of the shutdown boards to | : 3. The CSST being used to meet LCO 3.8.1.a cannot be providing power to unit and reactor coolant pump (RCP) boards other than its normal boards. The unit and RCP boards not normally powered by the CSST being used to meet LCO 3.8.1.a must be powered by the other CSST (A or B) or the USST. | ||
The modifications created operational differences that affect actions by | These restrictions are required in order to maintain the GDC 17 separation requirements because the original design did not consider these separation requirements. | ||
In addition there is no automatic | The offsite source via CSST A or B has been analyzed to demonstrate that the sources can support shutdown in the event of an accident in one unit and an orderly shutdown of the other unit, including a spurious ESF actuation in the non-accident unit. The Transmission System Study considered the following: | ||
The WBN simulator was modeled to show that the proposed lineups can be performed | " Loss of the largest capacity being supplied to the grid; | ||
When one of the two normal CSSTs (i.e., CSST C or D) becomes inoperable, | * Loss of the largest load from the grid; | ||
Furthermore, during this extended time, | * Loss of the most critical transmission line; and | ||
(< 1 E-6 IDCP, 1 E-7 ILERP). Therefore, power to the shutdown boards (at least one train)could be manually transferred to CSST A or B, whichever has been aligned as required | * Loss of both units E-1 8 of 48 | ||
This situation is similar to the condition currently allowed during the first 72 hours | |||
Therefore, TVA considers the extension of | The analysis demonstrated that CSST A or B has sufficient capacity and voltage to adequately supply the 1E loads. Electrical Calculation EDQ00099920070002, "Auxiliary Power System Analysis for Two Unit Operation," (Reference 8) evaluated and determined the use of CSSTs A and B as substitutes for CSSTs C and D acceptable provided CSSTs A and B are equipped with automatic OLTCs under certain documented operational restrictions. | ||
To ensure CSSTs A and B are operable, SR 3.8.1.8 has been modified to require | When the plant is normally aligned with CSSTs C and D powering the shutdown boards, the loss of a CSST results in the automatic transfer of the two shutdown boards it powers to the other CSST, D or C. This proposed TS change provides an alternate path to offsite power via CSST A or B to one train of safety buses. Realignment is performed manually from the Main Control Room using a permanently installed transfer scheme, with no requirement on actions outside the Main Control Room (can also be done locally in AUX Position). Upon detecting a loss of offsite power from C or D, the operable Maintenance Supply is available for restoration of the preferred source to safety related loads. The restoration of power to the Safety Related Boards can be performed within a few minutes of detection, which is well within the four hour coping period established for station blackout, loss of all offsite and onsite AC power. | ||
Furthermore, if the USSTs are tied to the unit boards, then the proposed | As stated in proposed Note 2 to LCO 3.8.1, the use of CSSTs A and B as a qualified backup is limited to one CSST only (i.e., only one train per unit can be supplied by CSST A or B at any given time). If CSST C or D is out of service, train A or B for both units will be required to be manually aligned to CSST B or A, respectively, when CSST A or B is being used to meet LCO 3..8.1.a requirements. Furthermore, alignment of the shutdown boards to the USST is allowed by Note 2 since an automatic transfer capability from the USST to CSSTs A and B exists. Thus, if the USST trips, power to the applicable unit boards is automatically transferred to CSSTs A and B, thereby maintaining power to the shutdown boards, if they are directly tied to the units boards. In addition, the CSST being used is restricted to powering only its normal unit and RCP boards. This ensures the CSST is not overloaded when supplying power to the shutdown boards. | ||
To ensure the CSST | Plant modifications resulted in the acceptable alignments for the shutdown boards, allowing CSST A or B to be placed in service in any operating mode while CSST D or C respectively is out of service. The modifications created operational differences that affect actions by the Operations staff. The ability to use CSST A or B as a qualified offsite power source will be added to operations procedures and training. In addition there is no automatic transfer associated with the maintenance feeders such as those that exist between the normal and alternate supplies to the shutdown boards. All transfers to and from the maintenance feeds are manual. It is also possible to make the transfer by local control if in the AUX position. | ||
This is detailed in References 1 and 7,which are NRC Safety Evaluations related to the operation of WBN, Unit 2. These | The WBN simulator was modeled to show that the proposed lineups can be performed and plant operators will be able to execute the procedures and meet the times that are in the proposed TS Amendment. | ||
Qualification of CSSTs A and B | When one of the two normal CSSTs (i.e., CSST C or D) becomes inoperable, existing TS 3.8.1 Required Action A.3 requires the offsite circuit to be restored within 72 hours. | ||
Furthermore, the request to provide additional time | Proposed Required Actions A.3.2.2 will allow up to 14 days to restore the inoperable circuit to operable status. This time is allowed only if CSST A or B is aligned to be capable of providing power to the respective shutdown board within the same 72 hours as is currently allowed to restore an inoperable offsite circuit. Furthermore, during this extended time, the DGs remain operable (if they were inoperable, another Action would be required to be entered - Action D - and Action D does not allow this extended Completion Time). The additional time from 72 hours to 14 days for proposed LCO Required Action A.3.2.2 allows E-1 9of48 | ||
Two offsite power circuits are required to | |||
completing maintenance and/or major repairs and also limits the number of transients required during this period. A PRA risk review identified the extension of time where a second offsite power source is not automatically available has less risk significance than multiple transients to maintain an automatically available second offsite power source (Reference 9). If the other CSST C or D is lost during this time (i.e., the time between the current 72 hours and the proposed 14 days), the shutdown boards powered by that CSST (C or D) would be automatically re-energized from the associated DGs. The PRA analysis concluded that the planned alternate alignments could be maintained for an entire annual evaluation period and the changes in CDF and LERF would be minimal and would remain below industry guidelines for risk associated with online maintenance | |||
The proposed changes described in this Technical Specification (TS) amendment request,do not alter or revise offsite Alternating Current power systems at Watts Bar Nuclear Plant(WBN) Unit 1, which are designed to comply with the following applicable regulations | (< 1 E-6 IDCP, 1 E-7 ILERP). Therefore, power to the shutdown boards (at least one train) could be manually transferred to CSST A or B, whichever has been aligned as required by proposed Required Action A.3.2.1, and the DGs placed back into the standby condition. | ||
* 10 CFR 50, Appendix A, General Design Criterion (GDC) 17, "Electric | This situation is similar to the condition currently allowed during the first 72 hours after CSST C or D becomes inoperable. Therefore, TVA considers the extension of the restoration time to be acceptable. | ||
specifies that an offsite electric power system shall be provided to | To ensure CSSTs A and B are operable, SR 3.8.1.8 has been modified to require similar testing as is currently performed for CSSTs C and D. Specifically, the manual transfer capability is required to be tested when CSST A or B is used to meet the LCO 3.8.1.a requirements. Furthermore, if the USSTs are tied to the unit boards, then the proposed SR also requires testing of the automatic transfer between the USSTs and CSSTs A and B. | ||
This will ensure CSSTS can be properly aligned to provide power to the shutdown boards, when they are being used to meet the LCO 3.8.1.a requirements. To ensure the CSST is only providing power to its normal unit and RCP boards, the Bases of SR 3.8.1.1, which verifies correct breaker alignment and power availability for each offsite circuit, will be modified to provide clarification that when the CSST A or B is being used to meet LCO 3.8.1.a requirements, the breaker alignment check will include verifying the CSST is only providing power to its normal unit and RCP boards. | |||
specifies that electric power systems important to safety shall be designed to | In addition, the NRC has previously reviewed and approved the above design changes for CSSTs A and B to support dual unit operation. This is detailed in References 1 and 7, which are NRC Safety Evaluations related to the operation of WBN, Unit 2. These proposed changes achieve licensing basis commonality for both units, with respect to using CSSTs A and B. | ||
* Regulatory Guide 1.32, Revision 1, "Criteria for Safety-Related Electric | 3.2.3 Conclusion The physical modifications upgraded CSSTs A and B to be in conformance with the requirements of GDC 17 for use as an offsite power source. The manual transfer to CSSTs A and B can be performed directly from the Main Control Room. The proposed TS Amendment Will improve the availability of the offsite power system to the safety related electrical buses and provide the necessary flexibility for two unit operation without necessitating the simultaneous shutdown of both units for maintenance of either CSST C or D. | ||
describes acceptable designs for the availability | Proposed changes to the UFSAR, tech specs, tech spec bases, and design criteria have been prepared and are waiting implementation upon approval of this amendment request to reflect this change as well as to outline the requirements which must be met in order for CSSTs A and B to be used as offsite power sources. Qualification of CSSTs A and B as offsite power sources will allow maintenance to be performed on CSSTs C and D without requiring a dual unit outage which is necessary for WBN to operate as a dual unit plant. | ||
describes the operating procedures and restrictions with respect to the availability | E-1 10 of 48 | ||
provides criteria for the determination of Class 1 E power system design features | |||
As stated above, these changes, related to utilizing CSSTs A and B as qualified offsite sources, have been previously approved by the NRC for WBN, Unit 2. | |||
The proposed revision to Unit 1 TS 3.8.1 to establish licensing basis commonality for WBN Units 1 and 2 is based on previously approved elements of the Unit 2 Safety Evaluation documented in References 1 and 7. The extension of the Completion Time from 72 hours to 14 days is acceptable because during the additional time, a qualified second circuit is available to be manually tied to provide power to at least one shutdown board train, and the DGs remain fully operable. Furthermore, the request to provide additional time to operate with an offsite circuit inoperable when CSST C or D is inoperable helps reduce the number of times that the transfers are performed and allow additional time to complete maintenance and/or repairs while also limiting the number of transients required during this period. The PRA risk review identified the extension of time where a second offsite power source is not automatically available has less risk significance than multiple transients to maintain an automatically available second offsite power source. | |||
The revision to add the automatic (USST only) and manual transfer testing of the associated shutdown power to the associated CSST A or B is to ensure functionality of the associated equipment and maintain an appropriate level of quality. | |||
==4.0 REGULATORY EVALUATION== | |||
4.1 Applicable Regulatory Requirements and Criteria Per GDC 17 the purpose of the offsite power system is to provide a source of power for all equipment required to assure that fuel design limits and design conditions of the reactor coolant pressure boundary are not exceeded. Two offsite power circuits are required to be operational with one available within a few seconds of a loss of coolant accident. The proposed amendment improves the ability of the plant to meet these design requirements. | |||
The proposed changes described in this Technical Specification (TS) amendment request, do not alter or revise offsite Alternating Current power systems at Watts Bar Nuclear Plant (WBN) Unit 1, which are designed to comply with the following applicable regulations and requirements: | |||
* 10 CFR 50, Appendix A, General Design Criterion (GDC) 17, "Electric power systems," specifies that an offsite electric power system shall be provided to permit functioning of structures, systems, and components important to safety. | |||
* 10 CFR 50, Appendix A, GDC 18, "Inspection and testing of electric power systems," | |||
specifies that electric power systems important to safety shall be designed to permit appropriate periodic inspection and testing of important areas and features. | |||
* Regulatory Guide 1.32, Revision 1, "Criteria for Safety-Related Electric Power Systems for Nuclear Plants," describes acceptable designs for the availability of offsite power. | |||
& Regulatory Guide 1.93, Revision 0, "Availability of Electric Power Sources,'" | |||
describes the operating procedures and restrictions with respect to the availability of electric power sources. | |||
E-1 11 of 48 | |||
Institute of Electrical and Electronics Engineers (IEEE) Standard 308-1971, "Criteria for Class 1E Power Systems for Nuclear Power Generating Stations," | |||
provides criteria for the determination of Class 1 E power system design features and the requirements for their testing, surveillance, and documentation. | |||
With the implementation of the proposed change, WBN will continue to meet the applicable regulations and requirements. | With the implementation of the proposed change, WBN will continue to meet the applicable regulations and requirements. | ||
4.2 Precedent TVA did not identify any applicable regulatory precedent regarding the changes proposed by TVA in this license amendment request. | |||
4.3 Significant Hazards Consideration IVA has concluded that the changes to WBN Unit 1 TS 3.8.1 and the licensing basis, as described in the Updated Final Safety Analysis Report (UFSAR), do not involve a significant hazards consideration. TVA's conclusion is based on its evaluation in accordance with 10 CFR 50.91 (a)(1) of the three standards set forth in 10 CFR 50.92, "Issuance of Amendment," as discussed below: | |||
: 1. Does the proposedamendment involve a significantincreasein the probability or consequence of an accidentpreviously evaluated? | |||
Response: No The proposed changes described in this TS amendment request, do not alter the safety functions of the WBN Offsite Power system. Design calculations document that CSSTs A and B have adequate capacity to supply all connected loads including one train of shutdown boards in all allowable alignments and meet the separation requirements for offsite power sources. The consequences of an accident are not changed when using CSST A or B to power the shutdown boards because these CSSTs are rated to carry all required loads for any design basis accidents. The failure of a CSST is not considered to be an initiator of a plant accident and therefore the probability or consequences of accidents or events previously evaluated, as described in the UFSAR, is not changed. | |||
Therefore, this proposed amendment does not involve a significant increase in the probability or consequences of an accident previously evaluated. | |||
: 2. Does the proposed amendment create the possibility of a new or different kind of accidentfrom any accidentpreviously evaluated? | |||
Response: No. | |||
As stated above, malfunctions of the CSSTs are not considered to be an initiator for plant accidents and the modifications to the offsite power system do not create a new or different kind of accident. The purpose of the offsite power system is to provide a source of power to the safety related equipment required to mitigate a design basis accident. CSSTs A and B have been physically upgraded and proven by design calculation to meet all required GDC 17 requirements for separation and voltage E-1 12 of 48 | |||
stability. Using CSSTs A and B as alternate sources of shutdown power does not negatively affect the offsite power systems ability to meet its design function. | |||
Therefore, the proposed amendment does not create the possibility of a new or different kind of accident from any accident previously evaluated. | |||
: 3. Does the proposed amendment involve a significant reduction in a margin of safety? | |||
Response: No. | |||
CSSTs A and B have adequate design margin to meet all possible loading scenarios as long as both CSSTs A and B are operational prior to one being used as a source of offsite power. This requirement is added to the control room drawings, plant design criteria and the UFSAR in order to ensure acceptable margin is always available prior to CSSTs A or B being used as a source of offsite power. | |||
Therefore, the proposed changes do not involve a significant reduction in a margin of safety. | |||
4.3 Conclusions In conclusion, based on the considerations discussed above, (1) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, (2) such activities will be conducted in compliance with the Commission's regulations, and (3) the issuance of the amendment will not be inimical to the common defense and security or to the health and safety of the public. | |||
==5.0 ENVIRONMENTAL CONSIDERATION== | |||
A review has determined that the proposed amendment would change a requirement with respect to installation or use of a facility component located within the restricted area, as defined in 10 CFR 20, or would change an inspection or surveillance requirement. | |||
However, the proposed amendment does not involve (i) a significant hazards consideration, (ii) a significant change in the types or significant increase in the amounts of any effluents that may be released offsite, or (iii) a significant increase in individual or cumulative occupational radiation exposure. Accordingly, the proposed amendment meets the eligibility criterion for categorical exclusion set forth in 10 CFR 51.22(c)(9). Therefore, pursuant to 10 CFR 51.22(b), no environmental impact statement or environmental assessment need be prepared in connection with the proposed amendment. | |||
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Accordingly, the proposed amendment meets the eligibility criterion for categorical exclusion set forth in 10 CFR 51.22(c)(9). | |||
Therefore, pursuant | |||
no environmental impact statement or environmental assessment need | |||
E-1 13 of 48 | |||
==6.0 REFERENCES== | ==6.0 REFERENCES== | ||
: 1. NUREG-0847, "Safety Evaluation Report Related to the Operation of Watts | : 1. NUREG-0847, "Safety Evaluation Report Related to the Operation of Watts Bar Nuclear Plant, Unit 2," Supplement 22, dated February 2011 (ML110390197). | ||
: 2. 10 CFR 50 Appendix A, General Design Criterion (GDC) 17, "Electric | : 2. 10 CFR 50 Appendix A, General Design Criterion (GDC) 17, "Electric Power Systems" | ||
dated July 12, 2010 (ADAMS Accession No. ML101530354). | : 3. WBN Unit 1, UFSAR, Section 8. | ||
: 5. WBN-AC-Study-001, "Offsite Power Feasibility Study for the AC Auxiliary | : 4. NRC letter, '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)," dated July 12, 2010 (ADAMS Accession No. ML101530354). | ||
: 6. TVA letter, "Watts Bar Nuclear Plant (WBN) Unit 2 -Final Safety Analysis Report(FSAR) -Response to Preliminary Requests for Additional Information and | : 5. WBN-AC-Study-001, "Offsite Power Feasibility Study for the AC Auxiliary Power System to Determine Its Acceptability for Unit 2 Completion." | ||
dated July 31, 2010 (ADAMS Accession No. | : 6. TVA letter, "Watts Bar Nuclear Plant (WBN) Unit 2 - Final Safety Analysis Report (FSAR) - Response to Preliminary Requests for Additional Information and Requests for Additional Information," dated July 31, 2010 (ADAMS Accession No. ML102290258). | ||
: 7. NUREG-0847, "Safety Evaluation Report Related to the Operation of Watts | : 7. NUREG-0847, "Safety Evaluation Report Related to the Operation of Watts Bar Nuclear Plant, Unit 2," Supplement 24, dated September 2011 (ML11277A148). | ||
: 8. Watts Bar NPG Calculation No. EDQ00099920070002, "AC Auxiliary Power | : 8. Watts Bar NPG Calculation No. EDQ00099920070002, "AC Auxiliary Power System Analysis," Revision 028, dated May 30, 2011. | ||
Revision 028, dated May 30, 2011.9. TVA PRA Evaluation Response No. WBN-1-11-094, Revision 0, approved | : 9. TVA PRA Evaluation Response No. WBN-1-11-094, Revision 0, approved November 10, 2011, to support license amendment request to permit the use of CSST A or B to function as alternate to CSST C or D. | ||
: a. Two qualified circuits between the offsite transmission network and | E-1 14 of 48 | ||
----------- | |||
NOTES--------------------- | ATTACHMENT I Proposed TS Changes (Mark-Ups) for WBN Unit I AC Sources-Operating 3.8.1 3.8 ELECTRICAL POWER SYSTEMS 3.8.1 AC Sources - Operating LCO 3.8.1 The following AC electrical sources shall be OPERABLE: | ||
-----1. The C-S DG may be substituted for any of the required DGs.2. Common Station Service Transformer (CSST) A | : a. Two qualified circuits between the offsite transmission network and the onsite Class 1E AC Electrical Power Distribution System; and | ||
APPLICABILITY:MODES 1, 2, 3, and 4. | : b. Four diesel generators (DGs) capable of supplying the onsite Class 1E AC Electrical Power Distribution System. | ||
LCO 3.0.4.b is not applicable to DGs.E-1 15of48 ATTACHMENT | --------------------- - ---------- NOTES--------------------- ----- | ||
A. | : 1. The C-S DG may be substituted for any of the required DGs. | ||
: 2. Common Station Service Transformer(CSST) A orB may be used to meet one of the two qualified offsite circuitrequirements of LCO 3.8.1. Provided CSST A or B is only Providinqpower to its normal unit and reactorcoolantpump boards,and: | |||
> 58.8 Hz. Verify after DG | : a. CSST A or B is providinq power to the associatedshutdown board: or | ||
_ 58.8 Hz and _< 61.2 Hz.SR 3.8.1.8--------------------- | : b. The associatedshutdown board is beinq powered by the Unit Station Service Transformer(USST) and automatictransfercapabilityfrom the USST to the CSST A or B (as applicable)is OPERABLE. | ||
NOTE ----------------- | APPLICABILITY:MODES 1, 2, 3, and 4. | ||
For the 1A-A and 1 B-B Shutdown Boards, | ACTIONS NOTE--------------------------------- | ||
: a. Automatic and manual | LCO 3.0.4.b is not applicable to DGs. | ||
E-1 15of48 | |||
when CSST A or B is | |||
ATTACHMENT 1 Proposed TS Changes (Mark-Ups) for WBN Unit I AC Sources-Operating 3.8.1 CONDITION IREQUIRED ACTION COMPLETION TIME CONDITION__IREQUIRED__ACTION A. One offsite circuit A.1 Perform SR 3.8.1.1 for 1 hour inoperable. OPERABLE offsite circuit. | |||
AND Once per 8 hours thereafter AND A.2 Declare required 24 hours from feature(s) with no offsite discovery of no power available offsite power to one inoperable when it's train concurrent with redundant required inoperability of feature(s) is inoperable. redundant required feature(s) | |||
AND 72 hours A.3.1 Restore offsite circuit to OPERABLE status. AND 6 days from discovery of failure to meet LCO OR A.3.2.1 Align backup offsite 72 hours circuit CSST A or CSST B to requiredshutdown AND board. | |||
6 days from discovery of failure to meet LCO AND A.3.2.2 Restore offsite circuit to 14 days OPERABLE status. | |||
E-1 16 of 48 | |||
ATTACHMENT I Proposed TS Changes (Mark-Ups) for WBN Unit I AC Sources-Operating 3.8.1 SURVEILLANCE FREQUENCY SR 3.8.1.7 Verify each DG starts from standby condition 184 days and achieves in _<10 seconds, voltage _>6800 V, and frequency > 58.8 Hz. Verify after DG fast start from standby conditions that the DG achieves steady state voltage _>6800 V and < | |||
7260 V, and frequency _Ž58.8 Hz and _< 61.2 Hz. | |||
SR 3.8.1.8 --------------------- NOTE ----------------- | |||
For the 1A-A and 1 B-B Shutdown Boards, this Surveillance shall not be performed in MODE 1 or 2. | |||
However, credit may be taken for unplanned events that satisfy this SR. | |||
18 months Verify automatic and manual tranisfor of "Ach 6.9 W, s-hutd-own board power supply fromn the normal offsite crutto eac-h -alternateoffeito circuit. | |||
Verify the followingi: | |||
: a. Automatic and manual transferof each 6.9 kV shutdown boardpower supply from the normal offsite circuitto the alternateoffsite circuit; | |||
: b. Automatic transferof the associated6.9 kV shutdown boardpower supply from the USST to the associatedCSST A or B, when USST is powerina the associatedshutdown boardand CSST A or B is credited with meeting LCO 3.8. 1.a requirements:and | |||
: c. Manual transferof the associated6.9 kV shutdown boardpower supply from the associatedCSST A or B to the normal offsite circuit (CSST C or D. as applicable), when CSST A or B is creditedwith meeting LCO 3.8.1.a requirements. | |||
(continued) | |||
E-1 17 of 48 | |||
ATTACHMENT 2 Proposed TS Bases Changes (Mark-Ups) for WBN Unit 1 AC Sources - Operating B 3.8.1 BASES (continued) | |||
APPLICABLE The initial conditions of DBA and transient analyses in the SAFETY ANALYSES 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. | |||
LCO 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 DBA. | |||
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 normally from two independent immediate access circuits. | |||
Each of the two circuits is routed from the switchyard through a 161 kV transmission line and 161 to 6.9 kV transformer (common station service transformers) to the onsite Class 1E distribution system. The medium voltage power system starts at the low-side of the common station service transformers. | |||
E-1 18 of 48 | |||
ATTACHMENT 2 Proposed TS Bases Changes (Mark-Ups) for WBN Unit I AC Sources - Operating B 3.8.1 BASES (continued) | |||
LCO Each DG must be capable of starting, accelerating to rated speed and voltage, (continued) 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. | |||
Proper sequencing of loads, including tripping of nonessential loads, is a required function for DG OPERABILITY. | |||
Note I 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. | |||
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. | |||
A second Note has been added to allow common station service transformer(CSST) A or B to be used to meet one of the two qualified offsite circuit requirementsof LCO 3.8. l.a. CSSTs A and B directly power the unit boards,and throuwh feeder breakers between the unit boardsand the shutdown boards, can provide power to the shutdown boards required by LCO 3.8.9, "AC Distribution." The Note allows one of the two CSSTs (A or B) to replace the normal qualified offsite circuit supply (CSST C or D), | |||
provided the CSST is only providinaDower to its normal unit and reactor coolant pump (RCP) boards and either a) CSST A or B (as applicable)is providinq power to the associatedshutdown board; or b) the associated shutdown boardis beinq powered by the unit station service transformer (USST) and automatic transfercapability from the USST to CSST A or B (as applicable)is OPERABLE. This allowance is acceptable since CSSTA and B are capable of providinq the propervoltage and frequency to the class 1E shutdown boards. In addition,all necessary unit boards and breakers necessary to provide power to the requiredshutdown boards are required to be OPERABLE and are part of the CSST A or B qualified circuit. | |||
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ATTACHMENT 2 Proposed TS Bases Changes (Mark-Ups) for WBN Unit I AC Sources - Operating B 3.8.1 BASES (continued) | |||
ACTIONS A.3.1. A.3.2.1. and A.3.2.2 (continued) | |||
According to Regulatory Guide 1.93 (Ref. 6), operation may continue in Condition A for a period that should not exceed 72 hours. With one 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 hour 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 DBA 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 hours. This could lead to a total of 144 hours, 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 hours (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 B are entered concurrently. The "AND" connector between the 72 hour 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. | |||
Alternately,in lieu of restoring the inoperablecircuit to OPERABLE status in 72 hours. requiredAction A.3.2.1 requires aligning the backup offsite circuit CSST A or B to the requiredshutdown board within 72 hours. This is accomplishedby ensuring power is available to CSST A or B. and that the breakers from CSST A or B to the associatedunit boards are OPERABLE and can be closed from the control room, and the breakers from the associatedunit boards to the associatedshutdown boards are OPERABLE and can be closed from the control room. This action is allowed since the remainingqualified offsite circuit continues to provide Power to all the shutdown boards. In addition. once CSST A or B is "alianed."it E-1 20 of 48 | |||
ATTACHMENT 2 Proposed TS Bases Changes (Mark-Ups) for WBN Unit I AC Sources - Operating B 3.8.1 BASES (continued) is capable of beinq manually connected to the associatedshutdown boards (eitherTrain A or Train B shutdown boards)by control room personnel Furthermore,the inoperable offsite circuitmust be restoredto OPERABLE status within 14 days. This can be accomplishedb' either restoring the normal circuit (CSST C or D) to OPERABLE status, or by utilizing the LCO Note 2 allowance. LCO Note 2 allows CSST A or B to replace one of the normal qualified offsite circuits, provided either: a) CSST A or B is providing power to the associated shutdown board(i.e., it is physically tied, througqh the unit boards,to the associatedshutdown boards);or the associatedshutdown boards are powered from the associatedUSST (throucih the unit boards)and the automatic transfercapabilityfrom the USST to the CSST is OPERABLE. Once this LCO Note 2 requirementis met, CSST A or B is allowed to meet the LCO 3.8. l.a requirement and thus, the requirementfor two qualified circuitsis being met. The 14-day completion time is acceptable durinq this additionaltime period since the remaining OPERABLE qualified circuitcontinues to provide offsite power to the shutdown boardsand either CSST A or B is available to provide a second source of qualified offsite power, througjh the manual operation of circuit breakers from the control room. | |||
E-1 21 of 48 | |||
ATTACHMENT 2 Proposed TS Bases Changes (Mark-Ups) for WBN Unit 1 AC Sources - Operating B 3.8.1 BASES (continued) | |||
I ACTIONS H.1 and 1.1 (continued) | |||
Condition H and Condition I corresponds to a level of degradation in which all redundancy in the AC electrical power supplies cannot be guaranteed. At this severely degraded level, any further losses in the AC electrical power system will cause a loss of function. Therefore, no additional time is justified for continued operation. The plant is required by LCO 3.0.3 to commence a controlled shutdown. | |||
SURVEILLANCE The AC sources are designed to permit inspection and testing of all important REQUIREMENTS areas and features, especially those that have a standby function, in accordance with 10 CFR 50, Appendix A, GDC 18 (Ref. 8). Periodic component tests are supplemented by extensive functional tests during refueling outages (under simulated accident conditions). The SRs for demonstrating the OPERABILITY of the DGs are in accordance with the recommendations of Regulatory Guide 1.9 (Ref. 3) and Regulatory Guide 1.137 (Ref. 9), as addressed in the FSAR. | |||
Where the SRs discussed herein specify voltage and frequency tolerances, the following is applicable. 6800 volts is the minimum steady state output voltage and the 10 second transient value. 6800 volts is 98.6% of the nominal bus voltage of 6900 V corrected for instrument error and is the upper limit of the minimum voltage required for the DG supply breaker to close on the 6.9 kV shutdown board. The specified maximum steady state output voltage of 7260 V is 110% of the nameplate rating of the 6600 V motors. The specified 3 second transient value of 6555 V is 95% of the nominal bus voltage of 6900 V. The specified maximum transient value of 8880 V is the maximum equipment withstand value provided by the DG manufacturer. The specified minimum and maximum frequencies of the DG are 58.8 Hz and 61.2 Hz, respectively. These values are equal to +/- 2% of the 60 Hz nominal frequency and are derived from the recommendations given in Regulatory Guide 1.9 (Ref. 3). | |||
SR 3.8.1.1 This SR ensures proper circuit continuity for the offsite AC electrical power supply to the onsite distribution network and availability of offsite AC electrical power. The breaker alignment verifies that each breaker is in its correct position to ensure that distribution buses and loads are connected to their preferred power source, and that appropriate independence of offsite circuits is maintained. | |||
When the allowance of LCO Note 2 is being used, this SR also includes verifying CSSTA or B (as applicable)is only aligned to provide power to its normal unit and RCP boards. The 7 day Frequency is adequate since breaker position is not likely to change without the operator being aware of it and because its status is displayed in the control room. | |||
E-1 22 of 48 | |||
ATTACHMENT 2 Proposed TS Bases Changes (Mark-Ups) for WBN Unit I AC Sources - Operating B 3.8.1 BASES (continued) | |||
SURVEILLANCE SR 3.8.1.7 REQUIREMENTS (continued) See SR 3.8.1.2. | |||
SR 3.8.1.8 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. Similarly, if CSST A or B is beinq used to meet LCO 3.8.1.a as allowed by LCO Note 2. | |||
then the manual transferfrom CSST A or B (whichever is being used) to the normal offsite circuit (CSST C or D (as applicable), demonstrates the OPERABILITY of the associatedCSST A or B offsite circuit to power the shutdown loads. In addition, if the USST is bein-g used to provide power to the shutdown boards, then automatic transfercapabilityfrom the USST to the associatedCSST (A or B) must also be tested. This requiredportion of the Surveillance Requirement demonstratespower can be provided by the required CSST A or B (as applicable),if power is being initiallyprovided by the USST (i.e., the provision described in part b of LCO Note 2). | |||
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 a Note. The reason for the Note is that, during operation with the reactor critical, performance of this SR could cause perturbations to the electrical distribution systems that could challenge continued steady state operation and, as a result, plant safety systems. 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. | |||
E-1 23 of 48 | |||
ATTACHMENT 3 Proposed TS Changes (Final Typed) for WBN Unit I AC Sources - Operating 3.8.1 3.8 ELECTRICAL POWER SYSTEMS 3.8.1 AC Sources - Operating LCO 3.8.1 The following AC electrical sources shall be OPERABLE: | |||
: a. Two qualified circuits between the offsite transmission network and the onsite 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. | |||
---------------------- NOTES -------------------------- | |||
: 1. The C-S DG may be substituted for any of the required DGs. | |||
: 2. Common Station Service Transformer (CSST) A or B may be used to meet one of the two qualified offsite circuit requirements of LCO 3.8.1, provided CSST A or B is only providing power to its normal unit and reactor coolant pump (RCP) boards, and: | |||
: a. CSST A or B is providing power to the associated shutdown board division; or | |||
: b. The associated shutdown board is being powered by the Unit Station Service Transformer (USST) and automatic transfer capability from the USST to CSST A or B (as applicable) is OPERABLE. | |||
APPLICABILITY:MODES 1, 2, 3, and 4. | |||
ACTIONS | |||
------------------------------------------ NOTE-------------------------------------------------- | |||
LCO 3.0.4.b is not applicable to DGs. | |||
CONDITION I REQUIRED ACTION I COMPLETION TIME A. One offsite circuit A.1 Perform SR 3.8.1.1 for 1 hour inoperable. OPERABLE offsite circuit. | |||
AND Once per 8 hours thereafter AND (continued) | |||
E-1 24 of 48 | |||
ATTACHMENT 3 Proposed TS Changes (Final Typed) for WBN Unit I AC Sources - Operating 3.8.1 CONDITION I REQUIRED ACTION I COMPLETION TIME A.2 Declare required 24 hours from feature(s) with no offsite discovery of no offsite power available power to one train inoperable when it's concurrent with redundant required inoperability of feature(s) is inoperable. redundant required feature(s) | |||
AND A.3.1 Restore offsite circuit to 72 hours OPERABLE status. | |||
AND 6 days from discovery of failure to meet LCO OR A. 3.2.1 Align backup offsite circuit 72 hours CSST A or CSST B to required shutdown board. AND 6 days from discovery of failure to meet LCO AND A.3.2.2 Restore offsite circuit to 14 days OPERABLE status. | |||
(continued) | (continued) | ||
E-1 | E-1 25 of 48 | ||
ATTACHMENT 3 Proposed TS Changes (Final Typed) for WBN Unit I AC Sources - Operating 3.8.1 SURVEILLANCE FREQUENCY SR 3.8.1.7 Verify each DG starts from standby condition 184 days and achieves in < 10 seconds, voltage _>6800 V, and frequency >_58.8 Hz. Verify after DG fast start from standby conditions that the DG achieves steady state voltage > 6800 V and < | |||
7260 V, and frequency _>58.8 Hz and <_61.2 Hz. | |||
SR 3.8.1.8 ------------------- NOTE----------------- | |||
For the 1A-A and 1B-B Shutdown Boards, this Surveillance shall not be performed in MODE 1 or 2. | |||
However, credit may be taken for unplanned events that satisfy this SR. | |||
18 months Verify the following: | |||
: a. Automatic and manual transfer of each 6.9 kV shutdown board power supply from the normal offsite circuit to the alternate offsite circuit; | |||
: b. Automatic transfer of the associated 6.9 kV shutdown board power supply from the USST to the associated CSST A or B, when USST is powering the associated shutdown board and CSST A or B is credited with meeting LCO 3.8.1.a requirements; and | |||
: c. Manual transfer of the associated 6.9 kV shutdown board power supply from the associated CSST A or B to the normal offsite circuit (CSST C or D, as applicable), | |||
when CSST A or B is credited with meeting LCO 3.8.1.a requirements. | |||
> | |||
_> 58.8 Hz and < | |||
NOTE----------------- | |||
For the 1A-A and 1B-B Shutdown Boards, | |||
: a. Automatic and manual transfer of each 6.9 | |||
when CSST A or B is credited with meeting LCO 3.8.1. | |||
(continued) | (continued) | ||
E-1 26 of 48 | |||
ATTACHMENT 4 Proposed TS Bases Changes (Final Typed) for WBN Unit I AC Sources - Operating B 3.8.1 BASES (continued) | |||
APPLICABLE The initial conditions of DBA and transient analyses in the SAFETY ANALYSES 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 | |||
6.9kV Start Board Breaker Controls: | 6.9kV Start Board Breaker Controls: | ||
The breaker control cables for 6.9kV Start Bus A normal feeder breaker 1512 are routed separately | The breaker control cables for 6.9kV Start Bus A normal feeder breaker 1512 are routed separately from those for 6.9kV Start Bus B normal feeder breaker 1612. | ||
6.9kV start bus alternate feeder | 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 1614 and 1514 are not credited for supply of offsite power. | ||
The breaker control cables for circuit breakers 1714, 1622 (NO) and 1114 (NC) at 6.9kV Unit Board | 6.9kV Unit Board lB, IC, 2B, 2C Breaker Controls: | ||
El 41 of 48 WBNP- | The breaker control cables for circuit breakers 1714, 1622 (NO) and 1114 (NC) at 6.9kV Unit Board lB are routed separately from those for breakers 1722, 1524 (NO) and 1122 (NC) at 6.9kV Unit Board 1C. | ||
Similarly, the breakers control cables for circuit breakers 1814, 1632 (NO) and 1214 (NC) at 6.9kV Unit Board 2B are routed separately from those for breakers 1822, 1534 (NO) and 1222 (NC) at 6.9kV Unit Board 2C. | |||
Control cables associated with breakers 1114, 1214, 1622, 1632, 1714 and 1814 are designated as R and control cables associated with breakers 1122, 1222, 1524, 1534, 1722 and 1822 are designated as P for separation identification. | |||
Thus, a ground fault | El 41 of 48 | ||
By reclosing the WBH 161 kV switchyard | WBNP-7 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 10 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. | |||
supply ean .. | 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 161 kV switchyard. An automatic transfer of the loads fed from the faulted CSST will be initiated to the unfaulted CSST. | ||
Delete | The faulted circuits can be isolated by opening the 6.9kV common switchgear C and D breakers. | ||
Common station service buses A and B maintain 61 feet centerline-to-centerline separation, | By reclosing the WBH 161 kV switchyard breakers, power can be restored to the nuclear plant 6.9kV shutdown boards through the unfaulted secondaries of CSST C and/or D. An alternate path is available to the shutdown boards from the 161kV circuits by way of CSST A and/or CSST B through the maintenance supply circuit from the 6.9kV unit boards to the 6.9kV shutdown boards. -Thc u.s. ofthe mtaintn.an. supply. ean .nlyb ..usi hen .ihcca. h unit is in ..l. shutdom.-...h........... Delete text 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. | ||
The | 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 B and 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. | ||
The supply and | El 42 of 48 8.2-15 | ||
The unit start board consists of a normal feeder breaker and | WBNP-9 From the feeder breakers of the 6.9kV unit start board, the two 6.9kV unit start buses A and B and RCP start buses A and B run on separate support structures. These buses are outdoor, non-segregated, and the conductors are fully insulated with flame-retardant material. At the penetration of the outside building wall, the unit buses are provided with fire- and moisture-resistant barriers. The RCP start buses enter the outdoor metal-clad switchgear and connect to the RCP board supply breakers. These breakers are electrically operated, vertical lift draw out type, with stored energy mechanisms. | ||
These buses are outdoor, non-segregated, and the conductors are fully insulated with flame-retardant material. | The 6.9kV start buses enter the turbine building spaced 8 feet 6 inches centerline-to-centerline and maintain this spacing through the building. The start buses are tapped at appropriate places and routed to the appropriate supply breakers in the 6.9kV unit and 6.9kV common boards. The start buses enter the unit board supply breakers through the top of the boards. The unit board normal supply breaker and alternate supply breaker for each board are separated along the length of the board by several feeder breakers, thereby preventing a fault in one supply breaker from damaging the other. All buses are provided with gas-resistant seals at entry to the switchgear. | ||
At | Functional Measures Compliance with GDC 17 is discussed in the following paragraphs. | ||
The RCP start buses enter the outdoor metal-clad switchgear and connect | Each of the two 161kV circuits providing offsite power to Watts Bar Nuclear Plant is supplied through two power circuit breakers connecting with separate sections of the main bus in the WBH Plant switchyard. The two overhead transmission lines are routed to minimize the probability of their simultaneous failure. Each 161 kV line terminates at a pair of 161 - 6.9-kV common station service transformers (A and D, and B and C, respectively). Each pair of transformers, as well as the buses and cables that are used to connect them to the onsite power (standby) distribution system at the 6.9kV shutdown boards are physically and electrically independent. | ||
These breakers are electrically | Each of the 6.9kV shutdown boards is connected to the offsite power circuits via common station service transformer (CSST) C or D through the 6.9-kV shutdown boards normal or alternate supply breakers. For a loss of power from either CSST C or D not due to a fault in the CSST differential zone of protection, under this alignment, the affected 6.9kV shutdown board loads will be disconnected from offsite power and sequentially loaded onto their respective diesel generator. | ||
For an acceptable range of 161 -kV grid conditions, either offsite power circuit can start and supply all electrical equipment that would be supplied from the Class 1E distribution systems for a design basis accident in Unit 1 and no fuel in Unit 2 (via transformers C or D), and a simultaneous single worst case transmission system contingency. For this event, transformer C or D would be operating within its OA rating and adequate voltage would be supplied to the safety-related buses. | |||
The 6.9kV start buses enter the turbine building spaced 8 feet 6 inches centerline-to-centerline and maintain this spacing through the building. | /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. | ||
The start buses are tapped at appropriate | -* insert text on next page here. | ||
Functional | El 43 of 48 8.2-16 | ||
Each of the two 161kV circuits providing offsite power to Watts Bar Nuclear Plant is | |||
The two overhead transmission lines are routed to minimize | insert for Page 8.2-16 CSSTs A and B have the capability to provide qualified offsite power in the event that CSST D or C respectively is out of service. CSST A and B can only be aligned to the 6.9kV shutdown boards through manual operations and do not offer automatic transfer capability to the other offsite source. CSST A and B each have a 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. Due to independence limitations, CSST A and B cannot be credited for supply of both offsite power sources simultaneously. | ||
Each 161 kV line terminates at a pair of 161 -6.9- | El 44 of 48 | ||
Each pair | |||
Each of the 6.9kV shutdown boards is connected to the offsite power circuits via common | WBNP-9 The BOP load-shedding scheme trips selected loads if both Unit 1 and 2 generators are tripped and either CSST A or B is out of service. Initiation of load shedding is accomplished automatically by undervoltage at transformer secondary Y-winding of either CSST A or B, and both Unit 1 and 2 generators tripped. Two reactor coolant pumps per unit are tripped when the above conditions exist. Tripping of these loads results in a signification reduction (50% if the reactor coolant pumps) of the station load. | ||
For a loss of power from either CSST C or D not due to a fault in the | The load-shedding scheme consists of two redundant trip and lockout circuits for each circuit breaker receiving a load-shed command. The redundant load- shedding circuits are located in different 6.9kV start boards. One load- shedding circuit associated with CSST A is in 6.9-kV start board A, and the other which is associated with CSST B is in 6.9kV start board B. Control power to the redundant auxiliary power system (APS) load-shedding circuits is provided from separated 250V dc batteries and battery boards. APS load- shedding circuit 1 receives control power from 250V DC Battery 1 via 250V Turbine Building Board 1, and APS circuit 2 from 250V DC Battery 2 via 250V Turbine Building Board 2. Loss of control power to either 250V Turbine Building Board initiates automatic transfer from the normal dc supply to the alternate dc supply with annunciation that auto transfer has occurred. This maximizes the ability of the load-shedding scheme to operate if grid and generator conditions warrant such operation. | ||
For an acceptable range of 161 -kV grid conditions, either offsite power circuit can start | The 6.9kV shutdown boards are provided with loss-of-voltage and degraded- voltage relays that initiate transfer from the normal supply, to the standby (diesel generator) power supply. If the standby supply is paralleled with one of the offsite supplies for testing, loss of the standby supply would cause reverse power relays to trip the standby circuit breaker. or maintenance For a loss of offsite power during diesel generator testing, the diesel generator wi switch to the emergency mode of operation with one exception. The diesel generator will re ain in the testing mode if the 6.9kV shutdown board's offsite power feed is through the alternatefeeder. In this case, the diesel generator's overcurrent relays are active to prevent the diesel generator from being overloaded. 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. | ||
For this event, transformer | 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. | ||
CSST A and B can only be aligned to the 6.9kV shutdown boards | El 45 of 48 8.2-17 | ||
El 44 of 48 WBNP- | |||
Initiation of load shedding is accomplished automatically by undervoltage at transformer secondary Y-winding of either CSST A or B, | WBNP-1 The non-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-lE and Class IE circuits that are fed from each of the vital battery boards. Thus, failure of all of the non-1E control power circuits on the vital battery boards will not have any effect on the IE circuits or battery boards. WBNP is in full compliance wt< GDCl?. add -firstinsert on next page herej. | ||
Two reactor coolant pumps per unit are tripped when | 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 redundant load- shedding circuits are located | Regulatory Guide 1.32 has been implemented by providing two immediate access circuits +e the transmission network Figures 8.1-2, 8.1-2a, 8.1-2b, and 8.2-1 indicate the functional arrangement of these ontinuously energized circuits. | ||
This maximizes the ability of the load-shedding scheme to operate if grid and generator conditions warrant such operation. | jadd text from second insert on next page, here. I 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. | ||
The 6.9kV shutdown boards are provided with loss-of-voltage and degraded-voltage relays | CSSTs A and B supply power to the 6.9kV unit boards and 6.9kV common boards A and B during startup or shutdowr._ IAdditionally, CSST A or B may supply power to 6.9kVshutdown boards | ||
or maintenance For a loss of offsite power during diesel generator | - .dunng maintenance of CSST D or C respectively in any operating mode. | ||
-- r------------------------- ----------- - - - | |||
The diesel generator will re ain in the | K' - | ||
In | smbire%,v V.lwge., msjfe.ptrtmAOsJ1Imflr hay a*f UtSnAmqJiA *fr8gn speedJ fleftl tapJ '.J11h1 5 0"*fi A1 Ot".flWflitW1.7 -A:,ASA W.J WUOL V 1JUU.Y | ||
If an accident signal is initiated during testing of the standby supply, | - -IAt' yýt ý,,' fl.J týh4*1 %,tJMh1X3.'Lý 0flIAIAý VTý11J1.'O *XS autoemati epcrtiatt is the normftl mede. | ||
El 45 of | l1te | ||
Selective coordination exists between the non-lE and Class IE circuits that are fed from each of the | . . ig 4Tho 6.9k-W shutode" boards may also be powered from the unit boards;- however-, thi: | ||
Figure 8.1-2 indicates that redundant power trains | limited admintistratively ontly to Oeeur w~ith bOth un~its in eeld ghutodoer or noet fu6od In addition to compliance with the above standards for portions of the offsite power s,ystem, the 6.9kV start board, 6.9kV unit boards, 6.9kV RCP boards, and the associated 6.9kV btises were procured in accordance with certain TVA standards and industry standards. TVA spe*cifications require conformance of this equipment to such standards as the following: the overal 1 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 tflirough C37.9 and NEMA SG-4; associated relays are specified to conform to ANSI C37. 1, iiistrument transformers to ANSI C57.13 and NEMA EI-2, and wiring to IPCEA S-61-402 and N1EMA WC5. | ||
Regulatory Guide 1.32 has been implemented by providing two immediate access circuits | ireplace the crossed out text with text from third insert on next page I | ||
+e | El 46 of 48 8.2-19 | ||
jadd text from second insert on next page, here. | |||
CSSTs A and B supply power to the 6.9kV unit boards and 6.9kV common boards A and | Ifirst insert for Page 8.2-19 1 From four of the 6.9kV unit boards located in the turbine building maintenance feeder cables are routed to the 6.9kV shutdown boards located in the auxiliary building where they connect to the supply breakers. | ||
IAdditionally, CSST A or B may supply power to 6.9kVshutdown boards-.dunng maintenance of CSST D or C respectively in any operating mode.--r------------------------- | These feeder cables are routed in divisional raceway to maintain separation between the two offsite power sources. | ||
----------- | Isecond insert for Page 8.2-19 under normal plant alignments and either two immediate access circuits or one immediate access circuit and one delayed access circuit under maintenance alignments | ||
---K' -smbire%,v V.lwge., | [third insert for Page 8.2-19 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 which adjust voltage based on the normally connected shutdown boards. | ||
msjfe.ptrtmAOsJ1Imflr hay a*f UtSnAmqJiA | During maintenance of common station service transformer C or D, power continuity to the normally connected train of 6.9kV shutdown boards is provided by the boards' maintenance feeds which connect to unit boards with access to common station service transformers B or A respectively. Use of transformers A and B is restricted such that they are not simultaneously credited as an independent source of offsite power for the Class 1E power system. Common station service transformers A and B have automatic load tap changers on the primary winding which adjust voltage based on the normally connected start board. | ||
*fr8gn speedJ fleftl tapJ '. | 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. | ||
-A:,ASA W.J WUOL V 1JUU.Y --IAt' yýt ý,,' fl.J týh4*1 %,tJMh1X3.'Lý 0flIAIAý VTý 11J1.'O * | El 47 of 48 | ||
however-, | |||
thi:limited admintistratively ontly to Oeeur w~ith bOth un~its in eeld ghutodoer or noet | WBNP-9 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. | ||
TVA | 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 normal 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. | ||
the | 8.2.2 Analysis lits associated CSSTs Each 161kV circuit and C89 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 (1) an SI in a WBN nuclear unit with an electrical fault in the generator step-up transformer, or (2) an SI in a WBN nuclear unit and either the loss of SQN Unit 2, the loss of the largest load on the grid (Bowater 161 -kV substation), or the loss of the most critical transmission line. | |||
These feeder cables are routed in divisional raceway to maintain separation between the two offsite | 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. | ||
[third insert for Page 8.2- | 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. | ||
Use of transformers A and B is restricted such that they are not simultaneously credited as an independent source of | 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 transformers C and D through the 6.9kV common switchgear C and D circuits. The normal supply breakers are shown normally closed on Figure 8.1-2a. 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. | ||
In accordance with GDC 18 requirements, the offsite power system has been designed to | El 48 of 48 8.2-20}} | ||
Transfers from the normal (offsite) supply to | |||
Testing of these transfers while the nuclear unit is at power could result | |||
For this reason, testing of | |||
Provisions | |||
Physical separation of lines, primary and backup protection | |||
Results | |||
or the loss of the most critical transmission line.Transient unit stability studies were performed to show that the WBN unit and the Watts | |||
These studies were performed to | |||
For normal operation, power is supplied from the common station | |||
The | |||
Latest revision as of 03:41, 6 February 2020
| ML13220A103 | |
| Person / Time | |
|---|---|
| Site: | Watts Bar  |
| Issue date: | 08/01/2013 |
| From: | James Shea Tennessee Valley Authority |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| Download: ML13220A103 (50) | |
Text
Tennessee Valley Authority, 1101 Market Street, Chattanooga, Tennessee 37402 August 1, 2013 10 CFR 50.90 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, D.C. 20555-0001 Watts Bar Nuclear Plant Unit 1 Facility Operating License No. NPF-90 NRC Docket No. 50-390
Subject:
Application to Modify Watts Bar Nuclear Plant, Unit I Technical Specifications Regarding AC Sources - Operating (TS-WBN-13-02)
References 1. NUREG-0847, "Safety Evaluation Report Related to the Operation of Watts Bar Nuclear Plant, Unit 2," Supplement 22, dated February 2011 (ADAMS Accession No. ML110390197)
- 2. NUREG-0847, "Safety Evaluation Report Related to the Operation of Watts Bar Nuclear Plant, Unit 2," Supplement 24, dated September 2011 (ADAMS Accession No. ML11277A148)
In accordance with the provisions of 10 CFR 50.90, "Application for amendment of license, construction permit, or early site permit," the Tennessee Valley Authority (TVA) is submitting a request for an amendment to Facility Operating License No. NPF-90 for Watts Bar Nuclear Plant (WBN), Unit 1.
TVA proposes this license amendment request (LAR) to the WBN, Unit 1 Technical Specifications (TS) to modify the Limiting Condition for Operation (LCO) for the AC Sources Operating in LCO 3.8.1, provide additional time to restore an inoperable offsite circuit, modify Surveillance Requirement (SR) 3.8.1.8, and modify the current licensing basis, as described in the Updated Final Safety Analysis Report (UFSAR), for the available maintenance feeder for the Common Station Service Transformers (CSST) A and B. The proposed LAR credits upgrades made to CSST A and B to provide two new sources of preferred Class 1 E power supply feeds in addition to the two normal Class 1 E power supply feeds. The TS change is needed to support dual unit operations without requiring a dual unit shutdown during maintenance on either preferred power CSST C or D. This proposed request also achieves licensing basis commonality for the current Operating Unit 1 license with respect to those approved elements of the Unit 2 application as docketed in NUREG-0847, Supplements 22 and 24 (References 1 and 2).
Printed on recycled paper
U.S. Nuclear Regulatory Commission Page 2 August 1, 2013 The enclosure provides the description, technical evaluation, regulatory evaluation, and environmental consideration of the proposed changes. Attachments 1 and 2 to the enclosure provide the existing TS and Bases pages marked-up to show the proposed changes.
Attachments 3 and 4 to the enclosure provide the existing TS and Bases pages retyped with the proposed changes incorporated. Attachment 5 to the enclosure provides a summary of the proposed UFSAR changes.
TVA requests approval of this LAR no later than April 30, 2014, to support preparations for fuel load activities at Watts Bar Unit 2.
TVA has determined that there are.no significant hazards considerations associated with the proposed change and that the change qualifies for a categorical exclusion from environmental review pursuant to the provisions of 10 CFR 51.22(c)(9).
The WBN Plant Operations Review Committee and the WBN Nuclear Safety Review Board have reviewed the proposed changes and determined that operation of WBN in accordance with the proposed change will not endanger the health and safety of the public.
Additionally, in accordance with 10 CFR 50.91 (b)(1), TVA is sending a copy of this letter and the enclosure to the Tennessee Department of Environment and Conservation.
There are no regulatory commitments associated with this submittal. Please address any questions regarding this request to Mr. E. D. Schrull at 423-751-3850.
I declare under penalty of perjury that the foregoing is true and correct. Executed on this 1 st day of August 2013.
Resp hly, J W Shea, cresident, Nuclear Licensing
Enclosure:
Evaluation of Proposed Change cc (Enclosure):
NRC Regional Administrator - Region II NRC Senior Resident Inspector- Watts Bar Nuclear Plant, Unit 1 Director, Division of Radiological Health - Tennessee State Department of Environment and Conservation
ENCLOSURE TENNESSEE VALLEY AUTHORITY WATTS BAR NUCLEAR PLANT UNIT I EVALUATION OF PROPOSED CHANGE
Subject:
Application to Modify Watts Bar Nuclear Plant, Unit I Technical Specifications Regarding AC Sources - Operating (TS-WBN-13-02) 1.0
SUMMARY
DESCRIPTION 2.0 DETAILED DESCRIPTION 2.1 Proposed Changes 2.2 Need for Proposed Changes
3.0 TECHNICAL EVALUATION
3.1 System Description 3.2 Evaluation
4.0 REGULATORY EVALUATION
4.1 Applicable Regulatory Requirements and Criteria 4.2 Precedent 4.3 Significant Hazards Consideration 4.4 Conclusions
5.0 ENVIRONMENTAL CONSIDERATION
6.0 REFERENCES
ATTACHMENTS
- 1. Proposed TS Changes (Mark-Ups) for WBN Unit 1
- 2. Proposed TS Bases Changes (Mark-Ups) for WBN Unit 1 (For Information Only)
- 3. Proposed TS Changes (Final Typed) for WBN Unit 1
- 4. Proposed TS Bases Changes (Final Typed) for WBN Unit 1 (For Information Only)
E-1 I of 48
1.0
SUMMARY
DESCRIPTION This evaluation supports a request to amend Watts Bar Nuclear Plant (WBN), Unit 1, Facility Operating License No. NPF-90. The proposed change will modify WBN, Unit 1 Technical Specification (TS) 3.8.1, "AC Sources - Operating," by adding a note to Limiting Condition for Operation (LCO) 3.8.1, adding additional required actions to LCO 3.8.1 Action A, and adding requirements to Surveillance Requirement (SR) 3.8.1.8. The proposed change will also revise the current licensing basis, as described in the Updated Final Safety Analysis Report (UFSAR), to allow the use of Common Station Service Transformers (CSSTs) A and B as qualified sources of power.
This amendment proposes to revise Technical Specification 3.8.1 and Technical Specification Bases 3.8.1 to add an allowance to use Common Station Service Transformer (CSST) A or B to meet the requirements of LCO 3.8.1, with respect to qualified offsite circuits, provide additional time to operate with an offsite circuit inoperable when CSST C or D is inoperable, and add testing of the manual transfers of the shutdown boards to and from the maintenance feeds (i.e., CSSTs A and B). Testing of the manual transfers is required to show that these transfers are functional and can be used to supply power to the shutdown boards during conditions when either CSST C or D is out of service for maintenance or to restore power if CSST C or D fails. The proposed changes result from upgrades made to CSSTs A and B to provide two new sources of preferred Class 1 E power supply feeds in addition to the two normal Class 1 E power supply feeds. The upgrades to CSSTs A and B were completed as part of actions to address NUREG-0847, "Safety Evaluation Report Related to the Operation of Watts Bar Nuclear Plant, Unit 2," Supplement 22, Appendix HH,
'Watts Bar Unit 2 Action Items Table," Open Item 27 (Reference 1).
In addition, this amendment proposes to modify the current licensing basis, as described in the UFSAR, to remove the statements restricting the use of the CSSTs A and B maintenance feed during dual unit operations.
Attachments 1 and 2 to this enclosure provide the existing WBN, Unit 1 TS and Bases pages marked-up to show the proposed changes. Attachments 3 and 4 to this enclosure provide the existing TS and Bases pages retyped to show the proposed changes.
Attachment 5 to this enclosure provides a summary of the proposed UFSAR changes.
2.0 DETAILED DESCRIPTION
Background
The WBN Alternating Current (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 Code of Federal Regulations (CFR) 50, Appendix A, General Design Criterion (GDC) 17 (Reference 2), 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.
Offsite power is supplied to the 161 kiloVolt (kV) transformer yard by two dedicated lines from the WBN Hydro Plant switchyard. From the 161 kV transformer yard, two electrically and physically separated circuits provide AC power, through stepdown CSSTs C and D, 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 E-1 2 of 48
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 are found in WBN UFSAR Section 8 (Reference 3).
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 buses, boards and loads required for Unit 1 operation and safe shutdown.
Currently TVA continues to prepare for WBN Unit 2 licensing and plans to place the unit into commercial operation in the near future. Thus, the APS will be required to support a two unit operation. By letter dated July 12, 2010, (Reference 4), the NRC requested that TVA provide an executive summary of the two unit analysis to support the following design requirements:
" Dual-unit trip as a result of an abnormal operational occurrence;
- Accident in one unit and concurrent shutdown of the second unit (with and without offsite power); and
- Accident in one unit and spurious Engineered Safety Feature (ESF) actuation in the other unit (with and without offsite power).
WBN performed a study (Reference 5) to evaluate the existing WBN APS to determine its adequacy for two unit operation, including the design requirements requested in the Reference 4 NRC letter. As stated in the TVA letter to the NRC dated July 31, 2010 (Reference 6), the scope of this study included the CSSTs A, B, C, and D; 6.9-kV shutdown boards; 6.9-kV start buses; 6.9-kV common boards; 6.9-kV unit boards; downstream 6.9-kV-480-volt (V) transformers; 480-V distribution systems loads, and all interconnections.
The study specifically evaluated existing CSSTs A and B to determine their acceptability as qualified offsite power sources for the safety related boards when used for safe shutdown of the units under a design basis Loss of Coolant Accident (LOCA). The study recommended adding an automatic On Load Tap Changer (OLTC) on the primary side of CSST A and B.
The study also concluded that WBN Units 1 and 2 are stable for all 3-phase fault scenarios with normal clearing. Additionally, it concluded that the voltage criteria are met for WBN Unit 2 coming on line and for other future system changes.
As a result of the above study, TVA upgraded CSSTs A and B to functionally perform as alternate sources of offsite power in order to increase defense in depth and add increased reliability to the offsite power sources.
The WBN Design Change Notices (DCNs) that facilitated the use of CSSTs A and B as qualified offsite sources for the 6.9 kV shutdown boards to support safe shutdown of the unit during a design basis event have been completed.
This License Amendment Request (LAR) requests to revise the WBN, Unit 1 Technical Specifications (TS) by modifying the Limiting Condition for Operation (LCO) for the AC Sources Operating in LCO 3.8.1, providing additional time to restore an inoperable offsite circuit, modifying Surveillance Requirement (SR) 3.8.1.8, and modifying the current licensing basis, as described in the UFSAR, for the available maintenance feeder for CSSTs A and B.
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2.1 Proposed Changes Technical Specification Changes TVA proposes the following changes to the WBN, Unit 1 Technical Specifications.
- a. Number the current LCO 3.8.1 Note as "Note 1" and add a Note 2 to LCO 3.8.1 to provide guidance and conditions for using CSST A or B to meet one of the two qualified offsite circuits, to read:
- 2. Common Station Service Transformer(CSST) A or B may be used to meet one of the two qualified offsite circuitrequirements of LCO 3.8.1, provided CSST A or B is only providinq power to its normal unit and reactorcoolant pump boards, and:
- a. CSST A or B is providinq power to the associatedshutdown board; or
- b. The associatedshutdown board is beinq powered by the Unit Station Service Transformer(USST) and automatic transfercapabilityfrom the USST to CSST A or B (as applicable)is OPERABLE.
- b. Renumber Required Action A.3 to "A.3.1" and add additional required actions to LCO 3.8.1 Condition A to provide alternate requirements for using CSST A or B to meet LCO requirement, to read (renumbered Required Action A.3.1 shown for clarity):
A.3.1 Restore offsite circuit to OPERABLE status.
OR A.3.2.1 Aliqn backup offsite circuit CSST A or CSST B to requiredshutdown board.
AND A.3.2.2 Restore offsite circuit to OPERABLE status
- c. Revise SR 3.8.1.8 to add additional surveillance requirements for verifying automatic and manual function of 6.9 kV power supplies, to read:
Verify the followincq:
- a. Automatic and manual transferof each 6.9 kV shutdown boardpower supply from the normal offsite circuit to the alternateoffsite circuit;
- b. Automatic transferof the associated6.9 kV shutdown boardpower suppl, from the USST to the associatedCSSTA or B, when USST is powerinq the associatedshutdown board and CSST A or B is credited with meetinq LCO 3.8.1.a requirements;and
- c. Manual transferof the associated6.9 kV shutdown boardpower suppli from the associatedCSST A or B to the normaloffsite circuit(CSST C or D.
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as applicable), when CSST A or B is creditedwith meeting LCO 3.8.1.a requirements.
UFSAR Changes In order to credit upgrades made to CSSTs A and B, to provide four new sources of preferred Class 1E power supply feeds in addition to the two normal Class 1 E power supply feeds, the following UFSAR sections will be revised: Sections 8.2.1, 8.2.1.3, 8.2.1.5, 8.2.1.6 and 8.2.1.8. In addition, UFSAR Figures 8.1-2, 8.1-2B, 8.3-5, 8.3-16, 8.3-17, 8.3-18 and 8.3-19 are affected by the proposed change and will be updated as part of the amendment implementation phase to be included in the subsequent UFSAR update as required by 10 CFR 50.71(e), "Maintenance of records, making of reports."
The referenced figures are based on TVA drawings 1-15E500-1, 1-15E500-3, 1-45W724-1, 1-45W724-2, 1-45W724-3 and 1-45W724-4 respectively. Refer to Enclosure Attachment 5 for the currently planned UFSAR text changes.
2.2 Need for Proposed Changes Watts Bar Nuclear Plant (WBN) is currently configured with four CSSTs that provide offsite power. CSSTs C and D are qualified and used to supply the safety related class 1E power system; CSSTs A and B are used for non-safety loads. During operation in Mode 1, 2, 3, or 4 with either CSST C or D out of service, the plant is required to enter LCO 3.8.1 Condition A for not having two qualified offsite power sources available (i.e., one of the two qualified offsite sources are inoperable ). From a plant operational flexibility standpoint, this condition has been adequate for single unit operation. Maintenance on either CSST C or D during single unit operation mode can be performed in Modes other than Modes 1, 2, 3, and 4, i.e.,
when only one of the two qualified offsite circuits are required to be OPERABLE in accordance with LCO 3.8.2, "AC Sources - Shutdown." Thus, performing maintenance at this time does not require entry into LCO 3.8.1.
However, once Unit 2 begins power operations, it will be desirable to have one unit running while the other unit is in an outage. Therefore, one unit will be in Mode 1, 2, 3, or 4 when it is desired to perform maintenance on CSST C or D. To support performing maintenance on either of these two CSSTs when one unit is operating will require increased operational flexibility from the offsite power system to ensure that two offsite sources can be maintained even when a CSST is removed from service. Furthermore, performing the required maintenance can take more time than the currently allowed 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> to restore an inoperable qualified offsite circuit to OPERABLE status when the unit is in MODE 1, 2, 3, or 4, as required by LCO 3.8.1, Action A. Therefore, this technical specification change is necessary to allow this maintenance to be performed without requiring a dual unit shutdown including those times when the maintenance or repairs may require up to 14 days or longer.
3.0 TECHNICAL EVALUATION
3.1 System Description
The WBN plant electric power system consists of the main generators, USSTs, CSSTs, diesel generators, batteries, and the electrical distribution system. Under normal operating conditions, the main generators supply electrical power through isolated-phase buses to the main step-up transformers and through the unit station service transformers to the non-safety auxiliary power system. Offsite electrical power supplies Class 1 E circuits through the 161-kV system via CSSTs C and D. The primaries of the unit station service E-1 5of48
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 CSSTs.
In conformance with GDC 17, the design function of the preferred offsite power system is 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.
The preferred power lines from the existing Watts Bar Hydro 161-kV switchyard, provides power to all four CSSTs (A, B, C, and D) and are routed to minimize the likelihood of their simultaneous failure.
The safety-related plant distribution system receives AC power from CSSTs C and D through the shutdown boards (which are powered from the offsite power system), or four 4400 kW diesel-generator standby power sources, and distributes it to both safety-related and non-safety-related loads in the plant. The two preferred circuits have access to the TVA transmission network which in turn has multiple interties with other transmission networks.
Each line (CSST C and D) is the normal feed for one train of shutdown boards and the alternate feed for the other train of shutdown boards. The other transformer (CSST A and B) on each line supplies power to the 6.9kV unit boards and can indirectly power the shutdown boards if they are tied to the unit boards through the maintenance feeder. This maintenance feeder path is not a qualified source for the shutdown boards and can only be used in Mode 5 or below (i.e., when LCO 3.8.1 is not applicable).
Currently, UFSAR Section 8.2.1.8 describes automatic fast transfer of the 6.9kV shutdown boards to their alternate source (CSST C or D) when the normal source (CSST C or D) trips.
When CSST C or D trips and CSST A or B is manually aligned in place of the tripped CSST C or D, the fast transfer for the alternate is lost. Also, due to loading and separation requirements alignment restrictions are required when CSST A or B is used as an offsite supply for the 6.9kV Shutdown Boards.
The 6.9kV common switchgear C and D are connected to the 6.9kV shutdown boards by cables arranged to provide two physically independent sources of offsite power.
The CSSTs and buses are connected and arranged to provide two physically independent offsite power (OSP) circuits to the onsite (Class 1E) distribution system. One OSP circuit that is connected to CSSTs A and D is designated P while the other OSP circuit that is connected to CSSTs B and C is designated R. Circuits designated P and R are routed in separate conduits and trays to assure physical independence with any exceptions and their justifications documented in the design criteria. Non-segregated phase buses are used to connect the secondary of CSSTs C and D to 6.9-kV common switchgear C and switchgear D, respectively. During startup and shutdown, all auxiliary power is supplied from the 161 -kV system through CSSTs A, B, C and D.
E-1 6 of 48
Two offsite power circuits are required to be operational with one available within a few seconds following a loss of coolant accident (as specified in GDC 17). The proposed amendment improves the ability of the plant to meet these design requirements during dual unit operation. A simplified diagram of the proposed change is provided below.
IL CSST B ILLIi CSST A CSST B IL CSST A 1B i 1C i 2B 2C Unit Boards i iCSST 0 . . 0 0B.,
- r.
L:I Shutdown lA-A lB-B 2A-A 2B-B Boards Maintenance feeder proposed by this license amendment.
3.2 Evaluation 3.2.1 Introduction Design studies have concluded that CSSTs A and B are appropriately sized to carry required Balance of Plant (BOP) loads as well as one train of Class 1 E loads for each unit during normal and accident conditions provided both CSSTs A and B are in service (Reference 8). In addition, the analysis demonstrated that power and control cables associated with CSSTs A and B and the maintenance feeders meet separation requirements provided only CSST A or CSST B is used to power one train of shutdown boards, but not both. These restrictions have been incorporated into the WBN Unit 1 UFSAR and Design Criteria.
With CSSTs A and B meeting the requirements of GDC 17, these transformers may be used as qualified sources of offsite power. A description of the changes to CSSTs A and B needed for them to considered qualified sources is provided below. This amendment proposes to revise Technical Specification 3.8.1 by adding a note to Limiting Condition for Operation (LCO) 3.8.1 allowing the use of CSST A or B to meet the requirements of LCO 3.8.r.a under certain circumstances, adding additional required actions to LCO 3.8.1 Action A to allow one qualified offsite circuit to be inoperable for up to 14 days, and adding requirements to Surveillance Requirement (SR) 3.8.1.8 to add testing of the manual transfers of the shutdown boards to and from the maintenance feeds (i.e., CSSTs A and B) in order to show that these transfers are functional and can be used to supply power to the shutdown boards in the case that either CSST C or D is out of service for maintenance or for other reasons.
E-1 7 of 48
3.2.2 Technical Basis The existing CSSTs A and B were upgraded to provide an additional source of qualified power to the safety related class 1 E system. This upgrade allows either CSST A or B to power the shutdown boards while either CSST C or D is out of service for maintenance.
Several design changes were required in order to qualify the existing CSSTs A and B for offsite power sources to the safety related class 1 E system. On-load tap changers (OLTCs) were installed on CSST A and B to meet the required stable voltage requirements for the 6.9kV Shutdown Boards. "P" and "R" train designations were added to power and control cables associated with CSSTs A and B and cables were re-routed as necessary to maintain GDC 17 separation requirements.
Additional new features from the physical work completed under DCN 52336, have installed:
" cables and raceways to provide OLTC position indication;
- OLTC trouble alarm;
- manual/automatic operation of the OLTC in the Main Control Room;
- control switch and tap position indicator, for CSST A and B in the Electrical Control Board (ECB) Panel 2;
- Alarm for CSST A and B tap changer abnormal in annunciator window box XA 42A, window number 502B/503B, located in ECB Panel 3; and
- Alarm input combined with other alarm inputs from CSST A and B.
The use of CSSTs A and B as offsite power sources to the safety related class 1 E system requires compliance with several restrictions to ensure loading and separation requirements are met before either of these CSSTs can be aligned to the shutdown boards. Some restrictions include:
- 1. Only CSST A or B can be used as a qualified offsite power at any given time (i.e., either CSST C or D must be Operable);
- 2. All power and control circuits associated with CSSTs A and B as well as the maintenance feeders must be normally aligned; and
- 3. The CSST being used to meet LCO 3.8.1.a cannot be providing power to unit and reactor coolant pump (RCP) boards other than its normal boards. The unit and RCP boards not normally powered by the CSST being used to meet LCO 3.8.1.a must be powered by the other CSST (A or B) or the USST.
These restrictions are required in order to maintain the GDC 17 separation requirements because the original design did not consider these separation requirements.
The offsite source via CSST A or B has been analyzed to demonstrate that the sources can support shutdown in the event of an accident in one unit and an orderly shutdown of the other unit, including a spurious ESF actuation in the non-accident unit. The Transmission System Study considered the following:
" Loss of the largest capacity being supplied to the grid;
- Loss of the largest load from the grid;
- Loss of the most critical transmission line; and
- Loss of both units E-1 8 of 48
The analysis demonstrated that CSST A or B has sufficient capacity and voltage to adequately supply the 1E loads. Electrical Calculation EDQ00099920070002, "Auxiliary Power System Analysis for Two Unit Operation," (Reference 8) evaluated and determined the use of CSSTs A and B as substitutes for CSSTs C and D acceptable provided CSSTs A and B are equipped with automatic OLTCs under certain documented operational restrictions.
When the plant is normally aligned with CSSTs C and D powering the shutdown boards, the loss of a CSST results in the automatic transfer of the two shutdown boards it powers to the other CSST, D or C. This proposed TS change provides an alternate path to offsite power via CSST A or B to one train of safety buses. Realignment is performed manually from the Main Control Room using a permanently installed transfer scheme, with no requirement on actions outside the Main Control Room (can also be done locally in AUX Position). Upon detecting a loss of offsite power from C or D, the operable Maintenance Supply is available for restoration of the preferred source to safety related loads. The restoration of power to the Safety Related Boards can be performed within a few minutes of detection, which is well within the four hour coping period established for station blackout, loss of all offsite and onsite AC power.
As stated in proposed Note 2 to LCO 3.8.1, the use of CSSTs A and B as a qualified backup is limited to one CSST only (i.e., only one train per unit can be supplied by CSST A or B at any given time). If CSST C or D is out of service, train A or B for both units will be required to be manually aligned to CSST B or A, respectively, when CSST A or B is being used to meet LCO 3..8.1.a requirements. Furthermore, alignment of the shutdown boards to the USST is allowed by Note 2 since an automatic transfer capability from the USST to CSSTs A and B exists. Thus, if the USST trips, power to the applicable unit boards is automatically transferred to CSSTs A and B, thereby maintaining power to the shutdown boards, if they are directly tied to the units boards. In addition, the CSST being used is restricted to powering only its normal unit and RCP boards. This ensures the CSST is not overloaded when supplying power to the shutdown boards.
Plant modifications resulted in the acceptable alignments for the shutdown boards, allowing CSST A or B to be placed in service in any operating mode while CSST D or C respectively is out of service. The modifications created operational differences that affect actions by the Operations staff. The ability to use CSST A or B as a qualified offsite power source will be added to operations procedures and training. In addition there is no automatic transfer associated with the maintenance feeders such as those that exist between the normal and alternate supplies to the shutdown boards. All transfers to and from the maintenance feeds are manual. It is also possible to make the transfer by local control if in the AUX position.
The WBN simulator was modeled to show that the proposed lineups can be performed and plant operators will be able to execute the procedures and meet the times that are in the proposed TS Amendment.
When one of the two normal CSSTs (i.e., CSST C or D) becomes inoperable, existing TS 3.8.1 Required Action A.3 requires the offsite circuit to be restored within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />.
Proposed Required Actions A.3.2.2 will allow up to 14 days to restore the inoperable circuit to operable status. This time is allowed only if CSST A or B is aligned to be capable of providing power to the respective shutdown board within the same 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> as is currently allowed to restore an inoperable offsite circuit. Furthermore, during this extended time, the DGs remain operable (if they were inoperable, another Action would be required to be entered - Action D - and Action D does not allow this extended Completion Time). The additional time from 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> to 14 days for proposed LCO Required Action A.3.2.2 allows E-1 9of48
completing maintenance and/or major repairs and also limits the number of transients required during this period. A PRA risk review identified the extension of time where a second offsite power source is not automatically available has less risk significance than multiple transients to maintain an automatically available second offsite power source (Reference 9). If the other CSST C or D is lost during this time (i.e., the time between the current 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> and the proposed 14 days), the shutdown boards powered by that CSST (C or D) would be automatically re-energized from the associated DGs. The PRA analysis concluded that the planned alternate alignments could be maintained for an entire annual evaluation period and the changes in CDF and LERF would be minimal and would remain below industry guidelines for risk associated with online maintenance
(< 1 E-6 IDCP, 1 E-7 ILERP). Therefore, power to the shutdown boards (at least one train) could be manually transferred to CSST A or B, whichever has been aligned as required by proposed Required Action A.3.2.1, and the DGs placed back into the standby condition.
This situation is similar to the condition currently allowed during the first 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> after CSST C or D becomes inoperable. Therefore, TVA considers the extension of the restoration time to be acceptable.
To ensure CSSTs A and B are operable, SR 3.8.1.8 has been modified to require similar testing as is currently performed for CSSTs C and D. Specifically, the manual transfer capability is required to be tested when CSST A or B is used to meet the LCO 3.8.1.a requirements. Furthermore, if the USSTs are tied to the unit boards, then the proposed SR also requires testing of the automatic transfer between the USSTs and CSSTs A and B.
This will ensure CSSTS can be properly aligned to provide power to the shutdown boards, when they are being used to meet the LCO 3.8.1.a requirements. To ensure the CSST is only providing power to its normal unit and RCP boards, the Bases of SR 3.8.1.1, which verifies correct breaker alignment and power availability for each offsite circuit, will be modified to provide clarification that when the CSST A or B is being used to meet LCO 3.8.1.a requirements, the breaker alignment check will include verifying the CSST is only providing power to its normal unit and RCP boards.
In addition, the NRC has previously reviewed and approved the above design changes for CSSTs A and B to support dual unit operation. This is detailed in References 1 and 7, which are NRC Safety Evaluations related to the operation of WBN, Unit 2. These proposed changes achieve licensing basis commonality for both units, with respect to using CSSTs A and B.
3.2.3 Conclusion The physical modifications upgraded CSSTs A and B to be in conformance with the requirements of GDC 17 for use as an offsite power source. The manual transfer to CSSTs A and B can be performed directly from the Main Control Room. The proposed TS Amendment Will improve the availability of the offsite power system to the safety related electrical buses and provide the necessary flexibility for two unit operation without necessitating the simultaneous shutdown of both units for maintenance of either CSST C or D.
Proposed changes to the UFSAR, tech specs, tech spec bases, and design criteria have been prepared and are waiting implementation upon approval of this amendment request to reflect this change as well as to outline the requirements which must be met in order for CSSTs A and B to be used as offsite power sources. Qualification of CSSTs A and B as offsite power sources will allow maintenance to be performed on CSSTs C and D without requiring a dual unit outage which is necessary for WBN to operate as a dual unit plant.
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As stated above, these changes, related to utilizing CSSTs A and B as qualified offsite sources, have been previously approved by the NRC for WBN, Unit 2.
The proposed revision to Unit 1 TS 3.8.1 to establish licensing basis commonality for WBN Units 1 and 2 is based on previously approved elements of the Unit 2 Safety Evaluation documented in References 1 and 7. The extension of the Completion Time from 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> to 14 days is acceptable because during the additional time, a qualified second circuit is available to be manually tied to provide power to at least one shutdown board train, and the DGs remain fully operable. Furthermore, the request to provide additional time to operate with an offsite circuit inoperable when CSST C or D is inoperable helps reduce the number of times that the transfers are performed and allow additional time to complete maintenance and/or repairs while also limiting the number of transients required during this period. The PRA risk review identified the extension of time where a second offsite power source is not automatically available has less risk significance than multiple transients to maintain an automatically available second offsite power source.
The revision to add the automatic (USST only) and manual transfer testing of the associated shutdown power to the associated CSST A or B is to ensure functionality of the associated equipment and maintain an appropriate level of quality.
4.0 REGULATORY EVALUATION
4.1 Applicable Regulatory Requirements and Criteria Per GDC 17 the purpose of the offsite power system is to provide a source of power for all equipment required to assure that fuel design limits and design conditions of the reactor coolant pressure boundary are not exceeded. Two offsite power circuits are required to be operational with one available within a few seconds of a loss of coolant accident. The proposed amendment improves the ability of the plant to meet these design requirements.
The proposed changes described in this Technical Specification (TS) amendment request, do not alter or revise offsite Alternating Current power systems at Watts Bar Nuclear Plant (WBN) Unit 1, which are designed to comply with the following applicable regulations and requirements:
- 10 CFR 50, Appendix A, General Design Criterion (GDC) 17, "Electric power systems," specifies that an offsite electric power system shall be provided to permit functioning of structures, systems, and components important to safety.
- 10 CFR 50, Appendix A, GDC 18, "Inspection and testing of electric power systems,"
specifies that electric power systems important to safety shall be designed to permit appropriate periodic inspection and testing of important areas and features.
- Regulatory Guide 1.32, Revision 1, "Criteria for Safety-Related Electric Power Systems for Nuclear Plants," describes acceptable designs for the availability of offsite power.
& Regulatory Guide 1.93, Revision 0, "Availability of Electric Power Sources,'"
describes the operating procedures and restrictions with respect to the availability of electric power sources.
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Institute of Electrical and Electronics Engineers (IEEE) Standard 308-1971, "Criteria for Class 1E Power Systems for Nuclear Power Generating Stations,"
provides criteria for the determination of Class 1 E power system design features and the requirements for their testing, surveillance, and documentation.
With the implementation of the proposed change, WBN will continue to meet the applicable regulations and requirements.
4.2 Precedent TVA did not identify any applicable regulatory precedent regarding the changes proposed by TVA in this license amendment request.
4.3 Significant Hazards Consideration IVA has concluded that the changes to WBN Unit 1 TS 3.8.1 and the licensing basis, as described in the Updated Final Safety Analysis Report (UFSAR), do not involve a significant hazards consideration. TVA's conclusion is based on its evaluation in accordance with 10 CFR 50.91 (a)(1) of the three standards set forth in 10 CFR 50.92, "Issuance of Amendment," as discussed below:
- 1. Does the proposedamendment involve a significantincreasein the probability or consequence of an accidentpreviously evaluated?
Response: No The proposed changes described in this TS amendment request, do not alter the safety functions of the WBN Offsite Power system. Design calculations document that CSSTs A and B have adequate capacity to supply all connected loads including one train of shutdown boards in all allowable alignments and meet the separation requirements for offsite power sources. The consequences of an accident are not changed when using CSST A or B to power the shutdown boards because these CSSTs are rated to carry all required loads for any design basis accidents. The failure of a CSST is not considered to be an initiator of a plant accident and therefore the probability or consequences of accidents or events previously evaluated, as described in the UFSAR, is not changed.
Therefore, this proposed amendment does not involve a significant increase in the probability or consequences of an accident previously evaluated.
- 2. Does the proposed amendment create the possibility of a new or different kind of accidentfrom any accidentpreviously evaluated?
Response: No.
As stated above, malfunctions of the CSSTs are not considered to be an initiator for plant accidents and the modifications to the offsite power system do not create a new or different kind of accident. The purpose of the offsite power system is to provide a source of power to the safety related equipment required to mitigate a design basis accident. CSSTs A and B have been physically upgraded and proven by design calculation to meet all required GDC 17 requirements for separation and voltage E-1 12 of 48
stability. Using CSSTs A and B as alternate sources of shutdown power does not negatively affect the offsite power systems ability to meet its design function.
Therefore, the proposed amendment does not create the possibility of a new or different kind of accident from any accident previously evaluated.
- 3. Does the proposed amendment involve a significant reduction in a margin of safety?
Response: No.
CSSTs A and B have adequate design margin to meet all possible loading scenarios as long as both CSSTs A and B are operational prior to one being used as a source of offsite power. This requirement is added to the control room drawings, plant design criteria and the UFSAR in order to ensure acceptable margin is always available prior to CSSTs A or B being used as a source of offsite power.
Therefore, the proposed changes do not involve a significant reduction in a margin of safety.
4.3 Conclusions In conclusion, based on the considerations discussed above, (1) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, (2) such activities will be conducted in compliance with the Commission's regulations, and (3) the issuance of the amendment will not be inimical to the common defense and security or to the health and safety of the public.
5.0 ENVIRONMENTAL CONSIDERATION
A review has determined that the proposed amendment would change a requirement with respect to installation or use of a facility component located within the restricted area, as defined in 10 CFR 20, or would change an inspection or surveillance requirement.
However, the proposed amendment does not involve (i) a significant hazards consideration, (ii) a significant change in the types or significant increase in the amounts of any effluents that may be released offsite, or (iii) a significant increase in individual or cumulative occupational radiation exposure. Accordingly, the proposed amendment meets the eligibility criterion for categorical exclusion set forth in 10 CFR 51.22(c)(9). Therefore, pursuant to 10 CFR 51.22(b), no environmental impact statement or environmental assessment need be prepared in connection with the proposed amendment.
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6.0 REFERENCES
- 1. NUREG-0847, "Safety Evaluation Report Related to the Operation of Watts Bar Nuclear Plant, Unit 2," Supplement 22, dated February 2011 (ML110390197).
- 2. 10 CFR 50 Appendix A, General Design Criterion (GDC) 17, "Electric Power Systems"
- 4. NRC letter, '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)," dated July 12, 2010 (ADAMS Accession No. ML101530354).
- 5. WBN-AC-Study-001, "Offsite Power Feasibility Study for the AC Auxiliary Power System to Determine Its Acceptability for Unit 2 Completion."
- 6. TVA letter, "Watts Bar Nuclear Plant (WBN) Unit 2 - Final Safety Analysis Report (FSAR) - Response to Preliminary Requests for Additional Information and Requests for Additional Information," dated July 31, 2010 (ADAMS Accession No. ML102290258).
- 7. NUREG-0847, "Safety Evaluation Report Related to the Operation of Watts Bar Nuclear Plant, Unit 2," Supplement 24, dated September 2011 (ML11277A148).
- 8. Watts Bar NPG Calculation No. EDQ00099920070002, "AC Auxiliary Power System Analysis," Revision 028, dated May 30, 2011.
- 9. TVA PRA Evaluation Response No. WBN-1-11-094, Revision 0, approved November 10, 2011, to support license amendment request to permit the use of CSST A or B to function as alternate to CSST C or D.
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ATTACHMENT I Proposed TS Changes (Mark-Ups) for WBN Unit I AC Sources-Operating 3.8.1 3.8 ELECTRICAL POWER SYSTEMS 3.8.1 AC Sources - Operating LCO 3.8.1 The following AC electrical sources shall be OPERABLE:
- a. Two qualified circuits between the offsite transmission network and the onsite Class 1E AC Electrical Power Distribution System; and
- b. Four diesel generators (DGs) capable of supplying the onsite Class 1E AC Electrical Power Distribution System.
- ---------- NOTES--------------------- -----
- 2. Common Station Service Transformer(CSST) A orB may be used to meet one of the two qualified offsite circuitrequirements of LCO 3.8.1. Provided CSST A or B is only Providinqpower to its normal unit and reactorcoolantpump boards,and:
- a. CSST A or B is providinq power to the associatedshutdown board: or
- b. The associatedshutdown board is beinq powered by the Unit Station Service Transformer(USST) and automatictransfercapabilityfrom the USST to the CSST A or B (as applicable)is OPERABLE.
APPLICABILITY:MODES 1, 2, 3, and 4.
ACTIONS NOTE---------------------------------
LCO 3.0.4.b is not applicable to DGs.
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ATTACHMENT 1 Proposed TS Changes (Mark-Ups) for WBN Unit I AC Sources-Operating 3.8.1 CONDITION IREQUIRED ACTION COMPLETION TIME CONDITION__IREQUIRED__ACTION A. One offsite circuit A.1 Perform SR 3.8.1.1 for 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> inoperable. OPERABLE offsite circuit.
AND Once per 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> thereafter AND A.2 Declare required 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> from feature(s) with no offsite discovery of no power available offsite power to one inoperable when it's train concurrent with redundant required inoperability of feature(s) is inoperable. redundant required feature(s)
AND 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> A.3.1 Restore offsite circuit to OPERABLE status. AND 6 days from discovery of failure to meet LCO OR A.3.2.1 Align backup offsite 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> circuit CSST A or CSST B to requiredshutdown AND board.
6 days from discovery of failure to meet LCO AND A.3.2.2 Restore offsite circuit to 14 days OPERABLE status.
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ATTACHMENT I Proposed TS Changes (Mark-Ups) for WBN Unit I AC Sources-Operating 3.8.1 SURVEILLANCE FREQUENCY SR 3.8.1.7 Verify each DG starts from standby condition 184 days and achieves in _<10 seconds, voltage _>6800 V, and frequency > 58.8 Hz. Verify after DG fast start from standby conditions that the DG achieves steady state voltage _>6800 V and <
7260 V, and frequency _Ž58.8 Hz and _< 61.2 Hz.
SR 3.8.1.8 --------------------- NOTE -----------------
For the 1A-A and 1 B-B Shutdown Boards, this Surveillance shall not be performed in MODE 1 or 2.
However, credit may be taken for unplanned events that satisfy this SR.
18 months Verify automatic and manual tranisfor of "Ach 6.9 W, s-hutd-own board power supply fromn the normal offsite crutto eac-h -alternateoffeito circuit.
Verify the followingi:
- a. Automatic and manual transferof each 6.9 kV shutdown boardpower supply from the normal offsite circuitto the alternateoffsite circuit;
- b. Automatic transferof the associated6.9 kV shutdown boardpower supply from the USST to the associatedCSST A or B, when USST is powerina the associatedshutdown boardand CSST A or B is credited with meeting LCO 3.8. 1.a requirements:and
- c. Manual transferof the associated6.9 kV shutdown boardpower supply from the associatedCSST A or B to the normal offsite circuit (CSST C or D. as applicable), when CSST A or B is creditedwith meeting LCO 3.8.1.a requirements.
(continued)
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ATTACHMENT 2 Proposed TS Bases Changes (Mark-Ups) for WBN Unit 1 AC Sources - Operating B 3.8.1 BASES (continued)
APPLICABLE The initial conditions of DBA and transient analyses in the SAFETY ANALYSES 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.
LCO 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 DBA.
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 normally from two independent immediate access circuits.
Each of the two circuits is routed from the switchyard through a 161 kV transmission line and 161 to 6.9 kV transformer (common station service transformers) to the onsite Class 1E distribution system. The medium voltage power system starts at the low-side of the common station service transformers.
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ATTACHMENT 2 Proposed TS Bases Changes (Mark-Ups) for WBN Unit I AC Sources - Operating B 3.8.1 BASES (continued)
LCO Each DG must be capable of starting, accelerating to rated speed and voltage, (continued) 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.
Proper sequencing of loads, including tripping of nonessential loads, is a required function for DG OPERABILITY.
Note I 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.
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.
A second Note has been added to allow common station service transformer(CSST) A or B to be used to meet one of the two qualified offsite circuit requirementsof LCO 3.8. l.a. CSSTs A and B directly power the unit boards,and throuwh feeder breakers between the unit boardsand the shutdown boards, can provide power to the shutdown boards required by LCO 3.8.9, "AC Distribution." The Note allows one of the two CSSTs (A or B) to replace the normal qualified offsite circuit supply (CSST C or D),
provided the CSST is only providinaDower to its normal unit and reactor coolant pump (RCP) boards and either a) CSST A or B (as applicable)is providinq power to the associatedshutdown board; or b) the associated shutdown boardis beinq powered by the unit station service transformer (USST) and automatic transfercapability from the USST to CSST A or B (as applicable)is OPERABLE. This allowance is acceptable since CSSTA and B are capable of providinq the propervoltage and frequency to the class 1E shutdown boards. In addition,all necessary unit boards and breakers necessary to provide power to the requiredshutdown boards are required to be OPERABLE and are part of the CSST A or B qualified circuit.
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ATTACHMENT 2 Proposed TS Bases Changes (Mark-Ups) for WBN Unit I AC Sources - Operating B 3.8.1 BASES (continued)
ACTIONS A.3.1. A.3.2.1. and A.3.2.2 (continued)
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 <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />. With one 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 <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> 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 DBA 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 <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />. This could lead to a total of 144 hours0.00167 days <br />0.04 hours <br />2.380952e-4 weeks <br />5.4792e-5 months <br />, 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 <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> (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 B are entered concurrently. The "AND" connector between the 72 hour8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> 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.
Alternately,in lieu of restoring the inoperablecircuit to OPERABLE status in 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />. requiredAction A.3.2.1 requires aligning the backup offsite circuit CSST A or B to the requiredshutdown board within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />. This is accomplishedby ensuring power is available to CSST A or B. and that the breakers from CSST A or B to the associatedunit boards are OPERABLE and can be closed from the control room, and the breakers from the associatedunit boards to the associatedshutdown boards are OPERABLE and can be closed from the control room. This action is allowed since the remainingqualified offsite circuit continues to provide Power to all the shutdown boards. In addition. once CSST A or B is "alianed."it E-1 20 of 48
ATTACHMENT 2 Proposed TS Bases Changes (Mark-Ups) for WBN Unit I AC Sources - Operating B 3.8.1 BASES (continued) is capable of beinq manually connected to the associatedshutdown boards (eitherTrain A or Train B shutdown boards)by control room personnel Furthermore,the inoperable offsite circuitmust be restoredto OPERABLE status within 14 days. This can be accomplishedb' either restoring the normal circuit (CSST C or D) to OPERABLE status, or by utilizing the LCO Note 2 allowance. LCO Note 2 allows CSST A or B to replace one of the normal qualified offsite circuits, provided either: a) CSST A or B is providing power to the associated shutdown board(i.e., it is physically tied, througqh the unit boards,to the associatedshutdown boards);or the associatedshutdown boards are powered from the associatedUSST (throucih the unit boards)and the automatic transfercapabilityfrom the USST to the CSST is OPERABLE. Once this LCO Note 2 requirementis met, CSST A or B is allowed to meet the LCO 3.8. l.a requirement and thus, the requirementfor two qualified circuitsis being met. The 14-day completion time is acceptable durinq this additionaltime period since the remaining OPERABLE qualified circuitcontinues to provide offsite power to the shutdown boardsand either CSST A or B is available to provide a second source of qualified offsite power, througjh the manual operation of circuit breakers from the control room.
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ATTACHMENT 2 Proposed TS Bases Changes (Mark-Ups) for WBN Unit 1 AC Sources - Operating B 3.8.1 BASES (continued)
I ACTIONS H.1 and 1.1 (continued)
Condition H and Condition I corresponds to a level of degradation in which all redundancy in the AC electrical power supplies cannot be guaranteed. At this severely degraded level, any further losses in the AC electrical power system will cause a loss of function. Therefore, no additional time is justified for continued operation. The plant is required by LCO 3.0.3 to commence a controlled shutdown.
SURVEILLANCE The AC sources are designed to permit inspection and testing of all important REQUIREMENTS areas and features, especially those that have a standby function, in accordance with 10 CFR 50, Appendix A, GDC 18 (Ref. 8). Periodic component tests are supplemented by extensive functional tests during refueling outages (under simulated accident conditions). The SRs for demonstrating the OPERABILITY of the DGs are in accordance with the recommendations of Regulatory Guide 1.9 (Ref. 3) and Regulatory Guide 1.137 (Ref. 9), as addressed in the FSAR.
Where the SRs discussed herein specify voltage and frequency tolerances, the following is applicable. 6800 volts is the minimum steady state output voltage and the 10 second transient value. 6800 volts is 98.6% of the nominal bus voltage of 6900 V corrected for instrument error and is the upper limit of the minimum voltage required for the DG supply breaker to close on the 6.9 kV shutdown board. The specified maximum steady state output voltage of 7260 V is 110% of the nameplate rating of the 6600 V motors. The specified 3 second transient value of 6555 V is 95% of the nominal bus voltage of 6900 V. The specified maximum transient value of 8880 V is the maximum equipment withstand value provided by the DG manufacturer. The specified minimum and maximum frequencies of the DG are 58.8 Hz and 61.2 Hz, respectively. These values are equal to +/- 2% of the 60 Hz nominal frequency and are derived from the recommendations given in Regulatory Guide 1.9 (Ref. 3).
SR 3.8.1.1 This SR ensures proper circuit continuity for the offsite AC electrical power supply to the onsite distribution network and availability of offsite AC electrical power. The breaker alignment verifies that each breaker is in its correct position to ensure that distribution buses and loads are connected to their preferred power source, and that appropriate independence of offsite circuits is maintained.
When the allowance of LCO Note 2 is being used, this SR also includes verifying CSSTA or B (as applicable)is only aligned to provide power to its normal unit and RCP boards. The 7 day Frequency is adequate since breaker position is not likely to change without the operator being aware of it and because its status is displayed in the control room.
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ATTACHMENT 2 Proposed TS Bases Changes (Mark-Ups) for WBN Unit I AC Sources - Operating B 3.8.1 BASES (continued)
SURVEILLANCE SR 3.8.1.7 REQUIREMENTS (continued) See SR 3.8.1.2.
SR 3.8.1.8 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. Similarly, if CSST A or B is beinq used to meet LCO 3.8.1.a as allowed by LCO Note 2.
then the manual transferfrom CSST A or B (whichever is being used) to the normal offsite circuit (CSST C or D (as applicable), demonstrates the OPERABILITY of the associatedCSST A or B offsite circuit to power the shutdown loads. In addition, if the USST is bein-g used to provide power to the shutdown boards, then automatic transfercapabilityfrom the USST to the associatedCSST (A or B) must also be tested. This requiredportion of the Surveillance Requirement demonstratespower can be provided by the required CSST A or B (as applicable),if power is being initiallyprovided by the USST (i.e., the provision described in part b of LCO Note 2).
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 a Note. The reason for the Note is that, during operation with the reactor critical, performance of this SR could cause perturbations to the electrical distribution systems that could challenge continued steady state operation and, as a result, plant safety systems. 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.
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ATTACHMENT 3 Proposed TS Changes (Final Typed) for WBN Unit I AC Sources - Operating 3.8.1 3.8 ELECTRICAL POWER SYSTEMS 3.8.1 AC Sources - Operating LCO 3.8.1 The following AC electrical sources shall be OPERABLE:
- a. Two qualified circuits between the offsite transmission network and the onsite 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.
NOTES --------------------------
- 2. Common Station Service Transformer (CSST) A or B may be used to meet one of the two qualified offsite circuit requirements of LCO 3.8.1, provided CSST A or B is only providing power to its normal unit and reactor coolant pump (RCP) boards, and:
- a. CSST A or B is providing power to the associated shutdown board division; or
- b. The associated shutdown board is being powered by the Unit Station Service Transformer (USST) and automatic transfer capability from the USST to CSST A or B (as applicable) is OPERABLE.
APPLICABILITY:MODES 1, 2, 3, and 4.
ACTIONS
NOTE--------------------------------------------------
LCO 3.0.4.b is not applicable to DGs.
CONDITION I REQUIRED ACTION I COMPLETION TIME A. One offsite circuit A.1 Perform SR 3.8.1.1 for 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> inoperable. OPERABLE offsite circuit.
AND Once per 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> thereafter AND (continued)
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ATTACHMENT 3 Proposed TS Changes (Final Typed) for WBN Unit I AC Sources - Operating 3.8.1 CONDITION I REQUIRED ACTION I COMPLETION TIME A.2 Declare required 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> from feature(s) with no offsite discovery of no offsite power available power to one train inoperable when it's concurrent with redundant required inoperability of feature(s) is inoperable. redundant required feature(s)
AND A.3.1 Restore offsite circuit to 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> OPERABLE status.
AND 6 days from discovery of failure to meet LCO OR A. 3.2.1 Align backup offsite circuit 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> CSST A or CSST B to required shutdown board. AND 6 days from discovery of failure to meet LCO AND A.3.2.2 Restore offsite circuit to 14 days OPERABLE status.
(continued)
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ATTACHMENT 3 Proposed TS Changes (Final Typed) for WBN Unit I AC Sources - Operating 3.8.1 SURVEILLANCE FREQUENCY SR 3.8.1.7 Verify each DG starts from standby condition 184 days and achieves in < 10 seconds, voltage _>6800 V, and frequency >_58.8 Hz. Verify after DG fast start from standby conditions that the DG achieves steady state voltage > 6800 V and <
7260 V, and frequency _>58.8 Hz and <_61.2 Hz.
SR 3.8.1.8 ------------------- NOTE-----------------
For the 1A-A and 1B-B Shutdown Boards, this Surveillance shall not be performed in MODE 1 or 2.
However, credit may be taken for unplanned events that satisfy this SR.
18 months Verify the following:
- a. Automatic and manual transfer of each 6.9 kV shutdown board power supply from the normal offsite circuit to the alternate offsite circuit;
- b. Automatic transfer of the associated 6.9 kV shutdown board power supply from the USST to the associated CSST A or B, when USST is powering the associated shutdown board and CSST A or B is credited with meeting LCO 3.8.1.a requirements; and
- c. Manual transfer of the associated 6.9 kV shutdown board power supply from the associated CSST A or B to the normal offsite circuit (CSST C or D, as applicable),
when CSST A or B is credited with meeting LCO 3.8.1.a requirements.
(continued)
E-1 26 of 48
ATTACHMENT 4 Proposed TS Bases Changes (Final Typed) for WBN Unit I AC Sources - Operating B 3.8.1 BASES (continued)
APPLICABLE The initial conditions of DBA and transient analyses in the SAFETY ANALYSES 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.
LCO Two qualified circuits between the Watts Bar Hydro 161 kV switchyard and the onsite Class 1E 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 DBA.
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 normally from two independent immediate access circuits.
Each of the two circuits is routed from the switchyard through a 161 kV I transmission line and 161 to 6.9 kV transformer (common station service transformers) to the onsite Class 1 E distribution system. The medium voltage power system starts at the low-side of the common station service transformers.
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ATTACHMENT 4 Proposed TS Bases Changes (Final Typed) for WBN Unit I AC Sources - Operating B 3.8.1 BASES (continued)
LCO Each DG must be capable of starting, accelerating to rated speed and voltage, (continued) 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.
Proper sequencing of loads, including tripping of nonessential loads, is a required function for DG OPERABILITY.
Note 1 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.
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.
A second Note has been added to allow common station service transformer (CSST) A or B to be used to meet one of the two qualified offsite circuit requirements of LCO 3.8. 1.a. CSSTs A and B directly power the unit boards, and through feeder breakers between the unit boards and the shutdown boards, can provide power to the shutdown boards required by LCO 3.8.9, "AC Distribution." The Note allows one of the two CSSTs (A or B) to replace the normal qualified offsite circuit supply (CSST C or D), provided the CSST is only providing power to its normal unit and reactor coolant pump (RCP) boards, and either a) CSST A or B (as applicable) is providing power to the associated shutdown board; or b) the associated shutdown board is being powered by the unit station service transformer (USST) and automatic transfer capability from the USST to CSST A or B (as applicable) is OPERABLE. This allowance is acceptable since CSST A and B are capable of providing the proper voltage and frequency to the class 1 E shutdown boards. In addition, all necessary unit boards and breakers necessary to provide power to the required shutdown boards are required to be OPERABLE and are part of the CSST A or B qualified circuit.
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ATTACHMENT 4 Proposed TS Bases Changes (Final Typed) for WBN Unit I AC Sources - Operating B 3.8.1 BASES (continued)
ACTIONS A.3.1, A.3.2.1, and A.3.2.2 (continued)
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 <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />. With one 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 1E Distribution System.
The 72 hour8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> 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 DBA 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 <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />. This could lead to a total of 144 hours0.00167 days <br />0.04 hours <br />2.380952e-4 weeks <br />5.4792e-5 months <br />, 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 <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> (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 B are entered concurrently. The "AND" connector between the 72 hour8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> 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.
Alternately, in lieu of restoring the inoperable circuit to OPERABLE status in 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />, required Action A.3.2.1 requires aligning the backup offsite circuit CSST A or B to the required shutdown board within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />. This is accomplished by ensuring power is available to CSST A or B, and that the breakers from CSST A or B to the associated unit boards are OPERABLE and can be closed from the control room, and the breakers from the associated unit boards to the associated shutdown boards are OPERABLE and can be closed from the control room. This action is allowed since the remaining qualified offsite circuit continues to provide power to all the shutdown boards. In addition, once CSST A or B is "aligned," it is capable of being manually connected to the associated shutdown boards (either Train A or Train B shutdown boards) by control room personnel.
Furthermore, the inoperable offsite circuit must be restored to OPERABLE status within 14 days. This can be accomplished by either restoring the normal circuit (CSST C or D) to OPERABLE status, or by utilizing the LCO Note 2 allowance.
LCO Note 2 allows CSST A or B to replace one of the normal qualified offsite E-1 29 of 48
ATTACHMENT 4 Proposed TS Bases Changes (Final Typed) for WBN Unit I AC Sources - Operating B 3.8.1 BASES (continued) circuits, provided either: a) CSST A or B is providing power to the associated shutdown board (i.e., it is physically tied, through the unit boards, to the associated shutdown boards); or the associated shutdown boards are powered from the associated USST (through the unit boards) and the automatic transfer capability from the USST to the CSST is OPERABLE. Once this LCO Note 2 requirement is met, CSST A or B is allowed to meet the LCO 3.8.1.a requirement and thus, the requirement for two qualified circuits is being met. The 14-day completion time is acceptable during this additional time period since the remaining OPERABLE qualified circuit continues to provide offsite power to the shutdown boards and either CSST A or B is available to provide a second source of qualified offsite power, through the manual operation of circuit breakers from the control room.
E-1 30 of 48
ATTACHMENT 4 Proposed TS Bases Changes (Final Typed) for WBN Unit I AC Sources - Operating B 3.8.1 BASES (continued)
ACTIONS H.1 and 1.1 (continued)
Condition H and Condition I corresponds to a level of degradation in which all redundancy in the AC electrical power supplies cannot be guaranteed. At this severely degraded level, any further losses in the AC electrical power system will cause a loss of function. Therefore, no additional time is justified for continued operation. The plant is required by LCO 3.0.3 to commence a controlled shutdown.
SURVEILLANCE The AC sources are designed to permit inspection and testing of all important REQUIREMENTS areas and features, especially those that have a standby function, in accordance with 10 CFR 50, Appendix A, GDC 18 (Ref. 8). Periodic component tests are supplemented by extensive functional tests during refueling outages (under simulated accident conditions). The SRs for demonstrating the OPERABILITY of the DGs are in accordance with the recommendations of Regulatory Guide 1.9 (Ref. 3) and Regulatory Guide 1.137 (Ref. 9), as addressed in the FSAR.
Where the SRs discussed herein specify voltage and frequency tolerances, the following is applicable. 6800 volts is the minimum steady state output voltage and the 10 second transient value. 6800 volts is 98.6% of the nominal bus voltage of 6900 V corrected for instrument error and is the upper limit of the minimum voltage required for the DG supply breaker to close on the 6.9 kV shutdown board. The specified maximum steady state output voltage of 7260 V is 110% of the nameplate rating of the 6600 V motors. The specified 3 second transient value of 6555 V is 95% of the nominal bus voltage of 6900 V. The specified maximum transient value of 8880 V is the maximum equipment withstand value provided by the DG manufacturer. The specified minimum and maximum frequencies of the DG are 58.8 Hz and 61.2 Hz, respectively. These values are equal to +/- 2% of the 60 Hz nominal frequency and are derived from the recommendations given in Regulatory Guide 1.9 (Ref. 3).
SR 3.8.1.1 This SR ensures proper circuit continuity for the offsite AC electrical power supply to the onsite distribution network and availability of offsite AC electrical power. The breaker alignment verifies that each breaker is in its correct position to ensure that distribution buses and loads are connected to their preferred power source, and that appropriate independence of offsite circuits is maintained.
When the allowance of LCO Note 2 is being used, this SR also includes verifying CSST A or B (as applicable) is only aligned to provide power to its normal unit and RCP boards. The 7 day Frequency is adequate since breaker position is not likely to change without the operator being aware of it and because its status is displayed in the control room.
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ATTACHMENT 4 Proposed TS Bases Changes (Final Typed) for WBN Unit 1 AC Sources - Operating 3.8.1 SURVEILLANCE SR 3.8.1.7 REQUIREMENTS (continued) See SR 3.8.1.2.
SR 3.8.1.8 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. Similarly, if CSST A or B is being used to meet LCO 3.8.1.a as allowed by LCO Note 2, then the manual transfer from CSST A or B (whichever is being used) to the normal offsite circuit (CSST C or D (as applicable), demonstrates the OPERABILITY of the associated CSST A or B offsite circuit to power the shutdown loads. In addition, if the USST is being used to provide power to the shutdown boards, then automatic transfer capability from the USST to the associated CSST (A or B) must also be tested. This required portion of the Surveillance Requirement demonstrates power can be provided by the required CSST A or B (as applicable), if power is being initially provided by the USST (i.e., the provision described in part b of LCO Note 2).
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 a Note. The reason for the Note is that, during operation with the reactor critical, performance of this SR could cause perturbations to the electrical distribution systems that could challenge continued steady state operation and, as a result, plant safety systems. 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.
E-1 32 of 48
ATTACHMENT 5 Proposed UFSAR Changes for WBN Unit I E-1 33 of 48
WBNP-9 8.2 OFFSITE (PREFERRED) POWER SYSTEM 8.2.1 Description Preferred offsite power is supplied from TVA's 161 kV 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 1E 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 1E power systems be used only Mien the li, 6,-!i Q -when CSST C or D is out of service Fwhich can . m qduring any operating mode.
The ilass lE power system can be transferred from the offsite no durin any oper in mod.
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 161 kV 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 1 and no fuel in Unit-2 The analyses assumed that equipment started by a safety injection signal (SIS) started at the s e time unless the load's control circuitry has sequential time delay, that all equipment that is ped off by a SIS was tripped, and that all continuous loads that could be operating mediately 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.
Additionally, studies have shown that one transmission line and CSST A, or one transmission line and CSST B are capable of starting and running the minimum required safety-related loads for one train in each unit.
El 34 of 48 8.2-1
WBNP-1 8.2.1.3 Arrangement of the Start Boards, Unit Boards, Common Boards, and Reactor Coolant Pump (RCP) 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 13.8kV, 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 B and the two 6.9kV RCP start buses A and B run 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.
linsert this new text here 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 feeders cables are routed in divisional raceway to maintain separation between the two offsite power sources.
El 35 of 48 8.2-5
WBNP-1 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 120V 1-phase heaters to maintain the temperature inside the housing at least 5PC 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 8.2-11 show the electrical control area where the relay, control, 250V dc 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 dc supply via circuit breakers on the turbine building dc distribution boards. Physical isolation of control power supplies is achieved by metal barriers between adjacent panels. Two separate 250V dc 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 dc 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 dc 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.
8.2.1.5 Switchyard Control and Relaying The design of the offsite (preferred) power system with its 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 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.
The CSST maintenance configurations can be aligned to provide either two immediate access circuits or one immediate and one delayed access circuit in accordance with Regulatory Guide 1.32, position C.1.a, requirements for acceptable designs.
El 36 of 48 8.2-6
WBNP-0 lAutomatic transfers are not provided for CSST maintenance alignments.
Automatic transfers of the Class 1E 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.
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 8.2-1B and 8.2-1C show the single line diagrams for the two panels at Watts Bar Hydro Plant.
Two separate 250V dc 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 dc 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 dc distribution buses.
8.2.1.6 6.9kV Start Boards Control and Relaying 6.9kV Start Buses The secondaries of common station service transformers A and B feed into two start boards containing four circuit breakers each. Two of the circuit breakers, 1512 and 1614, are the normal 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 normal and alternate feeders for RCP start bus A, and breakers 2612 and 2514 are the normal 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 dc normal control power for the pair of breakers feeding start bus A is supplied from a separate battery and dc distribution board from that of the normal 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:
- 1. Start Bus Fan Failure
- 2. Start Bus Transfers
- 3. Start Bus Failures or Undervoltage El 37 of 48 8.2-9
WBNP-1 Annunciation No. 3 is composed of bus differential relay operation, bus a.c. voltage failure, and control bus dc 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 B is the normal feeder to 6.9kV common board B and the alternate feeder to 6.9kV unit boards lB, ID, 2B, and 2D.
6.9kV Common Switchpear C and D I and Start Board A and B I The secondaries of common station service transformers C and D feed into 6.9kV common switchgear C and D (Figure 8.1-2a). Each switchgear contains two circuit breakers which are aligned to the common station service transformers as follows:
I. Common station service transformer C:
This transformer provides normal (offsite) power from the secondary Y winding to 6.9kV shutdown board lA-A through circuit breaker 1712 and from the secondary X winding to 6.9kV shutdown board 2A-A through circuit breaker 2714. In addition, this transformer provides alternate (offsite) power from the secondary X winding to 6.9kV shutdown board IB-B through circuit breaker 2714 and from the secondary Y winding to 6.9kV shutdown board 2B-B through circuit breaker 1712. 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 lB-B through circuit breaker 2814 and from the secondary Y winding to 6.9kV shutdown board 2B-B through circuit breaker 1812. In addition, this transformer provides alternate (offsite) power from the secondary Y winding to 6.9kV shutdown board lA-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 add text on normally closed.
insert on next hese circuits are designated as P for separation identification.
page, here 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 .. ' b used................. i ....e (e........
..ad hutl...n or fint fucled).
. All transfe] tween the normal, alternate and maintenance feeders take place at the 6.9kV shutdown boarHs.
can be used to provide a second qualified offsite power source to the 6.9 kV shutdown boards when required.
El 38 of 48 8.2-10
linsert for Page 8.2-10 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:
- 1. 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 1A, 1C, 2A and 2C. When CSST D 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 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 2B-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 B and alternate power to 6.9kV unit boards IB, 1D, 2B and 2D. 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 IA-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 of 6.9kV class 1E power. Additionally, CSST A and B only have the capacity to supply one train of 6.9kV shutdown boards for each unit.
El 39 of 48
WBNP-1 6.9kV Common Station Switchgear C and D Control The normal control power for circuit breakers 1712 and 2714 is supplied from the existing 125V dc vital Battery Board I; the normal control power for circuit breakers 1812 and 2814 is supplied from the existing 125V dc vital Battery Board II. 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 125V dc vital Battery Board III; the alternate control power for circuit breakers 1812 and 2814 is supplied from existing 125V dc 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 Add text on insert
< Ion next page, here.
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 transformer.
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 dc distribution system.
El 40 of 48 8.2-11
linsert for Page 8.2-11 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 IB, 1C, 2B, 2C and Common Board A and B are supplied from 250VDC Turbine Distribution Boards 1 and 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 IB 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.
6.9kV Start Board Breaker Controls:
The breaker control cables for 6.9kV Start Bus A normal feeder breaker 1512 are routed separately from those for 6.9kV Start Bus B normal 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 1614 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 1714, 1622 (NO) and 1114 (NC) at 6.9kV Unit Board lB are routed separately from those for breakers 1722, 1524 (NO) and 1122 (NC) at 6.9kV Unit Board 1C.
Similarly, the breakers control cables for circuit breakers 1814, 1632 (NO) and 1214 (NC) at 6.9kV Unit Board 2B are routed separately from those for breakers 1822, 1534 (NO) and 1222 (NC) at 6.9kV Unit Board 2C.
Control cables associated with breakers 1114, 1214, 1622, 1632, 1714 and 1814 are designated as R and control cables associated with breakers 1122, 1222, 1524, 1534, 1722 and 1822 are designated as P for separation identification.
El 41 of 48
WBNP-7 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 10 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 161 kV 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 of CSST C and/or D. An alternate path is available to the shutdown boards from the 161kV circuits by way of CSST A and/or CSST B through the maintenance supply circuit from the 6.9kV unit boards to the 6.9kV shutdown boards. -Thc u.s. ofthe mtaintn.an. supply. ean .nlyb ..usi hen .ihcca. h unit is in ..l. shutdom.-...h........... Delete text 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 B and 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.
El 42 of 48 8.2-15
WBNP-9 From the feeder breakers of the 6.9kV unit start board, the two 6.9kV unit start buses A and B and RCP start buses A and B run on separate support structures. These buses are outdoor, non-segregated, and the conductors are fully insulated with flame-retardant material. At the penetration of the outside building wall, the unit buses are provided with fire- and moisture-resistant barriers. The RCP start buses enter the outdoor metal-clad switchgear and connect to the RCP board supply breakers. These breakers are electrically operated, vertical lift draw out type, with stored energy mechanisms.
The 6.9kV start buses enter the turbine building spaced 8 feet 6 inches centerline-to-centerline and maintain this spacing through the building. The start buses are tapped at appropriate places and routed to the appropriate supply breakers in the 6.9kV unit and 6.9kV common boards. The start buses enter the unit board supply breakers through the top of the boards. The unit board normal supply breaker and alternate supply breaker for each board are separated along the length of the board by several feeder breakers, thereby preventing a fault in one supply breaker from damaging the other. All buses are provided with gas-resistant seals at entry to the switchgear.
Functional Measures Compliance with GDC 17 is discussed in the following paragraphs.
Each of the two 161kV circuits providing offsite power to Watts Bar Nuclear Plant is supplied through two power circuit breakers connecting with separate sections of the main bus in the WBH Plant switchyard. The two overhead transmission lines are routed to minimize the probability of their simultaneous failure. Each 161 kV line terminates at a pair of 161 - 6.9-kV common station service transformers (A and D, and B and C, respectively). Each pair of transformers, as well as the buses and cables that are used to connect them to the onsite power (standby) distribution system at the 6.9kV shutdown boards are physically and electrically independent.
Each of the 6.9kV shutdown boards is connected to the offsite power circuits via common station service transformer (CSST) C or D through the 6.9-kV shutdown boards normal or alternate supply breakers. For a loss of power from either CSST C or D not due to a fault in the CSST differential zone of protection, under this alignment, the affected 6.9kV shutdown board loads will be disconnected from offsite power and sequentially loaded onto their respective diesel generator.
For an acceptable range of 161 -kV grid conditions, either offsite power circuit can start and supply all electrical equipment that would be supplied from the Class 1E distribution systems for a design basis accident in Unit 1 and no fuel in Unit 2 (via transformers C or D), and a simultaneous single worst case transmission system contingency. For this event, transformer C or D would be operating within its OA rating and adequate voltage would be supplied to the safety-related buses.
/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.
-* insert text on next page here.
El 43 of 48 8.2-16
insert for Page 8.2-16 CSSTs A and B have the capability to provide qualified offsite power in the event that CSST D or C respectively is out of service. CSST A and B can only be aligned to the 6.9kV shutdown boards through manual operations and do not offer automatic transfer capability to the other offsite source. CSST A and B each have a 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. Due to independence limitations, CSST A and B cannot be credited for supply of both offsite power sources simultaneously.
El 44 of 48
WBNP-9 The BOP load-shedding scheme trips selected loads if both Unit 1 and 2 generators are tripped and either CSST A or B is out of service. Initiation of load shedding is accomplished automatically by undervoltage at transformer secondary Y-winding of either CSST A or B, and both Unit 1 and 2 generators tripped. Two reactor coolant pumps per unit are tripped when the above conditions exist. Tripping of these loads results in a signification reduction (50% if the reactor coolant pumps) of the station load.
The load-shedding scheme consists of two redundant trip and lockout circuits for each circuit breaker receiving a load-shed command. The redundant load- shedding circuits are located in different 6.9kV start boards. One load- shedding circuit associated with CSST A is in 6.9-kV start board A, and the other which is associated with CSST B is in 6.9kV start board B. Control power to the redundant auxiliary power system (APS) load-shedding circuits is provided from separated 250V dc batteries and battery boards. APS load- shedding circuit 1 receives control power from 250V DC Battery 1 via 250V Turbine Building Board 1, and APS circuit 2 from 250V DC Battery 2 via 250V Turbine Building Board 2. Loss of control power to either 250V Turbine Building Board initiates automatic transfer from the normal dc supply to the alternate dc supply with annunciation that auto transfer has occurred. This maximizes the ability of the load-shedding scheme to operate if grid and generator conditions warrant such operation.
The 6.9kV shutdown boards are provided with loss-of-voltage and degraded- voltage relays that initiate transfer from the normal supply, to the standby (diesel generator) power supply. If the standby supply is paralleled with one of the offsite supplies for testing, loss of the standby supply would cause reverse power relays to trip the standby circuit breaker. or maintenance For a loss of offsite power during diesel generator testing, the diesel generator wi switch to the emergency mode of operation with one exception. The diesel generator will re ain in the testing mode if the 6.9kV shutdown board's offsite power feed is through the alternatefeeder. In this case, the diesel generator's overcurrent relays are active to prevent the diesel generator from being overloaded. 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.
El 45 of 48 8.2-17
WBNP-1 The non-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-lE and Class IE circuits that are fed from each of the vital battery boards. Thus, failure of all of the non-1E control power circuits on the vital battery boards will not have any effect on the IE circuits or battery boards. WBNP is in full compliance wt< GDCl?. add -firstinsert on next page herej.
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.
Regulatory Guide 1.32 has been implemented by providing two immediate access circuits +e the transmission network Figures 8.1-2, 8.1-2a, 8.1-2b, and 8.2-1 indicate the functional arrangement of these ontinuously energized circuits.
jadd text from second insert on next page, here. I 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.
CSSTs A and B supply power to the 6.9kV unit boards and 6.9kV common boards A and B during startup or shutdowr._ IAdditionally, CSST A or B may supply power to 6.9kVshutdown boards
- .dunng maintenance of CSST D or C respectively in any operating mode.
-- r------------------------- ----------- - - -
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- -IAt' yýt ý,,' fl.J týh4*1 %,tJMh1X3.'Lý 0flIAIAý VTý11J1.'O *XS autoemati epcrtiatt is the normftl mede.
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. . ig 4Tho 6.9k-W shutode" boards may also be powered from the unit boards;- however-, thi:
limited admintistratively ontly to Oeeur w~ith bOth un~its in eeld ghutodoer or noet fu6od In addition to compliance with the above standards for portions of the offsite power s,ystem, the 6.9kV start board, 6.9kV unit boards, 6.9kV RCP boards, and the associated 6.9kV btises were procured in accordance with certain TVA standards and industry standards. TVA spe*cifications require conformance of this equipment to such standards as the following: the overal 1 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 tflirough C37.9 and NEMA SG-4; associated relays are specified to conform to ANSI C37. 1, iiistrument transformers to ANSI C57.13 and NEMA EI-2, and wiring to IPCEA S-61-402 and N1EMA WC5.
ireplace the crossed out text with text from third insert on next page I
El 46 of 48 8.2-19
Ifirst insert for Page 8.2-19 1 From four of the 6.9kV unit boards located in the turbine building maintenance feeder cables are routed to the 6.9kV 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 two offsite power sources.
Isecond insert for Page 8.2-19 under normal plant alignments and either two immediate access circuits or one immediate access circuit and one delayed access circuit under maintenance alignments
[third insert for Page 8.2-19 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 which 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 6.9kV shutdown boards is provided by the boards' maintenance feeds which connect to unit boards with access to common station service transformers B or A respectively. Use of transformers A and B is restricted such that they are not simultaneously credited as an independent source of offsite power for the Class 1E power system. Common station service transformers A and B have automatic load tap changers on the primary winding which 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.
El 47 of 48
WBNP-9 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 normal 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 lits associated CSSTs Each 161kV circuit and C89 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 (1) an SI in a WBN nuclear unit with an electrical fault in the generator step-up transformer, or (2) an SI in a WBN nuclear unit and either the loss of SQN 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 transformers C and D through the 6.9kV common switchgear C and D circuits. The normal supply breakers are shown normally closed on Figure 8.1-2a. 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.
El 48 of 48 8.2-20