ML14127A400

Request for Technical Specification Interpretation Regarding the Offsite Power Supplies to the Onsite Class 1E Alternating Current Power Distribution System

ML14127A400
Person / Time
Site:	Columbia
Issue date:	06/13/2014
From:	Lyon C Plant Licensing Branch IV
To:	Reddemann M Energy Northwest
Lyon C
References
TAC MF1010
Download: ML14127A400 (14)

Text

UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 Mr. Mark E. Reddemann Chief Executive Officer Energy Northwest P.O. Box 968 (Mail Drop 1 023)

Richland, WA 99352-0968 June 13, 2014

SUBJECT:

COLUMBIA GENERATING STATION-RESPONSE TO REQUEST FOR TECHNICAL SPECIFICATION INTERPRETATION REGARDING THE OFFSITE POWER SUPPLIED TO THE ONSITE CLASS 1 E ALTERNATING CURRENT POWER DISTRIBUTION SYSTEM (TAC NO. MF1010)

Dear Mr. Reddemann:

By letter dated March 13, 2013 (Agencywide Document Access and Management System (ADAMS) Accession No. ML13080A257), Energy Northwest (the licensee) requested the U.S. Nuclear Regulatory Commission (NRC) staff's interpretation of the licensee's position regarding alignment of the offsite power supplies in meeting Technical Specification (TS) 3.8.1, "AC [Alternating Current] Sources - Operating," and TS 3.8.2, "AC Sources - Shutdown," at Columbia Generating Station (CGS). The NRC staff evaluated your request based on the guidance in NRC's Information Notice 97-80, "Licensee Technical Specification Interpretations,"

dated November 21, 1997 (ADAMS Accession No. ML031050052), as supported by NRC Inspection Manual, Part 9900: Technical Guidance, Chapter STSINTR, "Licensee Technical Specification Interpretations."

The NRC staff agrees that the two CGS TS-qualified circuits from offsite are from the Ashe substation and the Benton substation, via transformers TR-S and TR-B, respectively. The staff also agrees that the TR-B offsite circuit must be capable of providing power to the 4.16 kiloVolt (kV) engineered safety features (ESF) buses, both Division 1 and Division 2, as the second TS-qualified offsite electrical power source.

The NRC staff disagrees with the licensee's interpretation of the CGS TS Section 3.8.1 regarding the electrical power source Operability of TR-S. Specifically, Limiting Condition for Operation (LCO) 3.8.1, "AC Sources Operating," requires that TR-S must be capable of providing power to the Division 3 ESF Class 1 E bus and the Division 1 and Division 2 4.16 kV ESF Class 1 E buses as one of the two qualified offsite electrical power sources. In addition, TR-B must also be capable of providing power to the 4.16 kV ESF buses, both Division 1 and Division 2, as the other TS-qualified offsite electrical power source in order to satisfy LCO 3.8.1 (a), "Two qualified circuits between the offsite transmission network and the onsite Class 1 E AC Electric Power Distribution System."

For LCO 3.8.2, "AC Sources-Shutdown," the single source can be provided by either of the two qualified circuits via transformer TR-S or transformer TR-B. Enclosed is the NRC staff's evaluation of the licensee's position regarding the intent of the TSs, as requested in your letter dated March 13, 2013.

If you have any questions regarding this matter, I may be reached at (301) 415-2296 or via e-mail at fred.lyon@nrc.gov.

Docket No. 50-397

Enclosure:

Staff Evaluation cc w/encl: Distribution via Listserv Sincerely, Carl F. Lyon, Project Manager Plant Licensing Branch IV-1 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation

UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION INTERPRETATION OF TECHNICAL SPECIFICATIONS 3.8.1 AND 3.8.2 ENERGY NORTHWEST COLUMBIA GENERATING STATION DOCKET NO. 50-397

1.0 INTRODUCTION

By letter dated March 13, 2013 (Agencywide Document Access and Management System (ADAMS) Accession No. ML13080A257), Energy Northwest (the licensee) requested the U.S. Nuclear Regulatory Commission (NRC) staff's interpretation of the licensee's position regarding alignment of the offsite power supplies in meeting Technical Specification (TS) 3.8.1, "AC [Alternating Current] Sources-Operating," and TS 3.8.2, "AC Sources-Shutdown," at Columbia Generating Station (CGS). The NRC staff evaluated your request based on the guidance in NRC's Information Notice 97-80, "Licensee Technical Specification Interpretations,"

dated November 21, 1997 (ADAMS Accession No. ML031050052), as supported by NRC Inspection Manual, Part 9900: Technical Guidance, Chapter STSINTR, "Licensee Technical Specification Interpretations."

The licensee requested that the NRC provide a written interpretation regarding TS requirements found in TS 3.8.1 and TS 3.8.2. Specifically, the licensee requested agreement with the following position regarding alignment of the offsite power supplies. The licensee interprets the required alignment of offsite power supplies to be:

The two circuits from offsite are from the Ashe substation and the Benton substation (via transformers TR-S and TR-B, respectively). The TR-S offsite circuit must be capable of providing power to the Division 3 4.16 kV Engineered Safety Feature ( ESF) bus and either the Division 1 or [emphasis added}

Division 2 4.16 kV ESF bus. The TR-B offsite circuit must be capable of providing power to both Divisions 1 and 2 4.16 kV ESF buses.

The licensee considers this interpretation to be consistent with CGS' licensing basis and Part 50 of Title 10 of the Code of Federal Regulations (1 0 CFR 50), Appendix A, General Design Criterion (GDC) 17, "Electric power systems," as documented in the CGS Final Safety Analysis Report (FSAR).

1.1 Background

The following is excerpted from the CGS TS Bases, Section B 3.8.1, "AC Sources - Operating":

Enclosure The unit Class 1 E AC Electrical Power Distribution System AC sources consist of the offsite power sources and the onsite standby power sources (diesel generators (DGs) 1, 2, and 3). As required by 10 CFR 50, Appendix A, GDC 17 (Ref. 1 }, the design of the AC electrical power system provides independence and redundancy to ensure an available source of power to the Engineered Safety Feature (ESF) systems.

The Class 1 E AC distribution system supplies electrical power to three divisional load groups, Divisions 1, 2, and 3, with each division powered by an independent Class 1 E 4.16 kV ESF bus (refer to LCO 3.8.7, "Distribution Systems-Operating"). Divisions 1 and 2 4.16 kV ESF buses have two separate and independent offsite sources of power. Division 3 4.16 kV ESF bus has one offsite source of power. Each 4.16 kV ESF bus has a dedicated onsite DG. The ESF systems of any two of the three divisions provide for the minimum safety functions necessary to shut down the unit and maintain it in a safe shutdown condition.

Offsite power is supplied to the switchyard from the transmission network. From the switchyard two qualified, electrically and physically separated circuits provide AC power to the Divisions 1 and 2 4.16 kV ESF buses (SM-7 and SM-8), while only one qualified circuit provides AC power to the Division 3 4.16 kV ESF bus (SM-4). One qualified circuit (to all 4.16 kV ESF buses) is from the 230 kV Ashe substation stepped down through the 230 kV/4.16 kV windings of a 230 kV/6.9

• kV/4.16 kV transformer (the startup transformer, TR-S). The other qualified circuit (to Divisions 1 and 2 4.16 kV ESF buses only} is from the 115 kV Benton substation stepped down through a 115 kV/4.16 kV transformer (the backup transformer, TR-B). The offsite AC electrical power sources are designed and located so as to minimize to the extent practicable the likelihood of their simultaneous failure under operating and postulated accident and environmental conditions. A detailed description of the offsite power network and circuits to the onsite Class 1 E 4.16 kV ESF buses is found in FSAR, Chapter 8 (Ref. 2).

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2.0 REGULATORY EVALUATION

The following NRC requirements and guidance documents were applicable to the staff's review of the licensee's TS interpretation request:

The CGS FSAR Section 8.1.5.1, "Offsite Electrical Power System," states that the offsite power system conforms to Title 1 0 of the Code of Federal Regulations (10 CFR), Part 50, Appendix A, "[GDC] for Nuclear Power Plants."

Paragraph 50.36(c)(2)(ii) of 10 CFR, "Technical Specifications," requires that a technical specification limiting condition for operation (LCO) of a nuclear reactor must be established for each item meeting one or more of the criteria set forth in 10 CFR 50.36(c)(2)(ii)(A)-(D).

GDC 17, "Electric power systems," requires, in part, that An onsite electric power system and an offsite electric power system shall be provided to permit functioning of structures, systems, and components important to safety.

The onsite electric power supplies, including the batteries, and the onsite electric distribution system, shall have sufficient independ~nce, redundancy, and testability to perform their safety functions assuming a single failure.

Electric power from the transmission network to the onsite electric distribution system shall be supplied by two physically independent circuits... designed and located so as to minimize to the extent practical the likelihood of their simultaneous failure under operating and postulated accident and environmental conditions... One of these circuits shall be designed to be available within a few seconds following a loss-of-coolant accident to assure that core cooling, containment integrity, and other vital safety functions are maintained.

Provision shall be included to minimize the probability of losing electric power from any of the remaining supplies as a result of, or coincident with, the loss of power generated by the nuclear power unit, the loss of power from the transmission network, or the loss of power from the onsite electric power supplies.

GDC 18, "Inspection and testing of electric power systems," requires, in part, that Electric power systems important to safety shall be designed to permit appropriate periodic inspection and testing of important areas and features, such as wiring, insulation, connections, and switchboards, to assess the continuity of the systems and the condition of their components. The systems shall be designed with a capability to test periodically (1) the operability and functional performance of the components of the systems, such as onsite power sources, relays, switches, and buses, and (2) the operability of the systems as a whole and, under conditions as close to design as practical, the full operation sequence that brings the systems into operation, including operation of applicable portions of the protection system, and the transfer of power among the nuclear power unit, the offsite power system, and the onsite power system.

Regulatory Guide 1.32, Revision 0, " Criteria for Safety-Related Electric Power Systems for Nuclear Power Plants," August 1972 (not in ADAMS), describes a method acceptable to the NRC staff for complying with GDC 17 and 18 with respect to the design, operation, and testing of safety-related electric power systems in all types of nuclear power plants.

CGS TS 3.8.1 and 3.8.2 require the operability of the offsite power system as a part of the LCO and specify actions to be taken when the offsite power system is less than required.

The TSs for operating nuclear power plants include the operational restrictions resulting from the loss of power sources. In general, plant TSs require the operability of the offsite power system as a part of the LCO and specify actions to be taken when the offsite power system is inoperable. CGS LCOs for TSs 3.8.1 and TS 3.8.2 are consistent with NUREG-1434, "Standard Technical Specifications General Electric BWR/6 Plants" (STS), and state the following:

TS 3.8.1, "AC Sources - Operating" LCO 3.8.1 The following AC electrical power sources shall be OPERABLE:

a.

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

b.

Three diesel generators (DGs).

TS 3.8.2, "AC Sources - Shutdown" LCO 3.8.2 The following AC electrical power sources shall be OPERABLE:

a.

One qualified circuit between the offsite transmission network and the on site Class 1 E AC electrical power distribution subsystem(s) required by LCO 3.8.8, "Distribution Systems-Shutdown;"

b.

One diesel generator (DG) capable of supplying one division of the Division 1 or 2 onsite Class 1 E AC electrical power distribution subsystem(s) required by LCO 3.8.8; and

c.

The Division 3 DG capable of supplying the Division 3 onsite Class 1 E AC electrical power distribution subsystem, when the Division 3 onsite Class 1 E electrical power distribution subsystem is required by LCO 3.8.8.

The TS Bases for CGS TS 3.8.1 are CGS-specific and state, in part, the following:

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

The two circuits from offsite are from the Ashe substation and the Benton substation (via transformers TR-S and TR-B, respectively). To ensure the requirements of Reference 1 are met, the TR-S offsite circuit must be capable of providing power to the Division 3 4.16 kV ESF bus (SM-4) and either the Division 1 (SM-7) or Division 2 (SM-8) 4.16 kV ESF bus [emphasis added]. The TR-B offsite circuit must be capable of providing power to both Divisions 1 and 2 4.16 kV ESF buses. The qualified offsite circuits include the circuit path and disconnect to the respective transformers, the circuit path and breakers to the respective non-Class 1 E 4.16 kV switchgear, SM-1, SM-2, and SM-3 (for the TR-S offsite circuit only), and the circuit path and breakers to the respective Class 1 E switchgear (SM-4, SM-7, and SM-8).

Each offsite circuit must be capable of maintaining rated frequency and voltage, and accepting required loads during an accident, while connected to the ESF buses.

3.0 TECHNICAL EVALUATION

The NRC staff has reviewed the licensee's interpretation of TS 3.8.1 and 3.8.2 and the supporting regulatory and technical analyses. The offsite and onsite power system at CGS is designed to comply with the requirements of GDC 17. The CGS FSAR, Section 8.1.5.1, describes that the existing onsite power system consists of two physically independent sources of offsite power that are brought to the onsite Class 1 E AC distribution system. The two sources are designed and located so as to minimize the likelihood of simultaneous failure. Each of these independent circuits has the capability to safely shut down the unit. The Preferred source is through the Startup Transformer (TR-S) supplied from the 230 kV Ashe substation stepped down through the 230 kV/4.16 kV windings of a 230 kV /6.9 kV/4.16 kV transformer, and the Backup Transformer (TR-B) is the other qualified source from the 115 kV Benton substation stepped down through a 115 kV/4.16 kV transformer. The 500-kV plant output and 230-kV plant startup lines originating at the Ashe Switchyard are geographically isolated from the backup 115-kV line from Benton Switchyard. The physical separation from the 500-kV and 230-kV lines minimizes the likelihood of a simultaneous outage of all offsite sources. One additional offsite power source is available to each division (Division 1, 2, and 3) by disconnecting the main generator bus links and backfeeding the safety-related buses from the 500 kV network. This source is not credited for satisfying TS or GDC 17 requirements. The CGS FSAR, Section 8.1.5.2, describes that two immediate access (offsite) power sources are provided for the Division 1 and Division 2 ESF systems; one immediate access (offsite) power source is provided for the Division 3 (high pressure core spray; HPCS) system. The onsite power system includes a diesel generator (DG) for each of the 4.16 kV safety buses, SM-7, SM-8, and SM-4 (Division 1, 2, and 3, respectively).

The licensee requested the NRC provide an interpretation regarding the TS requirement.

Specifically, the licensee requested agreement with its interpretation regarding alignment of the offsite power supplies in meeting TS 3.8.1 and TS 3.8.2.

The two circuits from offsite are from the Ashe substation and the Benton substation (via transformers TR-S and TR-B, respectively.) The TR-S offsite circuit must be capable of providing power to the Division 3 4.16 kV Engineered Safety Feature (ESF) bus and either the Division 1 or [emphasis addedl Division 2 4.16 kV ESF bus. The TR-B offsite circuit must be capable of providing power to both Divisions 1 and 2 4.16 kV ESF buses.

The licensee considers this position to be consistent with the licensing basis of the plant.

The NRC staff reviewed the licensing basis and design of CGS and concludes that the licensee's interpretation as stated above does not comply with GDC 17. The CGS FSAR, Section 8.1.5.1, states, in part, that the "normal power supply to plant auxiliary loads is provided through the normal auxiliary transformers connected to the generator bus." The two offsite power sources are in standby mode when unit is operating at power. On a unit trip, the auxiliary loads on Divisions 1, 2, and 3 are automatically fast transferred (simultaneous open/close) to the startup transformer TR-S for supply of offsite power. All non-safety related and safety-related electrical buses are powered through TR-S and the plant can be brought to a safe shutdown condition. Therefore, the NRC staff concludes that the 230 kV offsite power source from TR-S satisfies the immediate source requirement of GDC 17.

Based on its review of the CGS FSAR and the information provided by the licensee, the NRC staff concludes that, if the TR-S electrical power source is not immediately available, then within a few seconds, the bus transfer scheme allows the backup source, through transformer TR-B, to supply power to safety related Class 1 E electrical buses SM-7 and SM-8 only. The delay in transfer results in a momentary loss of offsite electrical power to the safety-related buses, which is detected by loss-of-voltage (LOV) relays. The LOV relays start the onsite diesel generators DG-1, DG-2, and DG-3. The loss of TR-S will also separate the non-safety related and safety-related electrical buses SM-1, SM-2, SM-3 (non-safety related 4.16 kV buses), and SM-7, SM-4 and SM-8 (safety-related 4.16 kV buses), respectively. DG-3 will supply safety related electrical bus SM-4 loads, and Backup Transformer TR-B will supply safety related electrical bus SM-7 and SM-8 loads following the separation of buses. The 115 kV offsite power source, through transformer TR-B, powers limited station buses and satisfies the delayed or second power source requirement of GDC 17. Therefore, CGS has two offsite power sources to meet the GDC 17 requirements.

The NRC staff reviewed changes made to applicable portions of the CGS licensing basis since initial licensing, in order to verify that there had been no change in NRC staff position. The following sections summarize the NRC staff's review.

TS LCO 3.8.1 and LCO 3.8.2 Operability TS LCO 3.8.1 Operability is met when aligned to the two qualified circuits between the offsite transmission network and the onsite Class 1 E AC electric power distribution system. TS LCO 3.8.2 Operability is met with one qualified circuit between the offsite transmission network and the onsite Class 1 E AC electrical power distribution subsystem(s) required by LCO 3.8.8, "Distribution Systems - Shutdown."

The CGS TS requirement for two qualified offsite power sources (or circuits) refers to the circuits from the transmission network described above in Section 1.1. Specifically, one of the two qualified TS "offsite circuits" from the TR-S transformer includes the first inter-tie breaker at the TR-S transformer, and all the equipment downstream such as breakers, transformers, switches, interrupting devices, cabling, and controls up to and including SM-4, SM-7, and SM-8 Class 1 E buses. Similarly, the other qualified TS "offsite circuit" from the 115 kV/4.16 kV transformer (TR-B) to the onsite Class 1 E buses includes all devices from the first intertie to the safety-related buses SM-7 and SM-8.

Compliance with CGS TS LCO 3.8.1.a requires that the station have two qualified sources of offsite power to the Division 1 and the Division 2 Class 1 E buses. The immediate source of offsite power to the class 1 E buses is provided by the TR-S as discussed above. The equipment associated with TR-S offsite circuit (also referred to as the "preferred" source) and the TR-B offsite power circuit (also referred to as the "backup" source) is described in the CGS TS Bases and FSAR Chapter 8, "Electric Power." The CGS TS 3.8.1 and 3.8.2 Bases description of the offsite circuit is CGS-specific and generally consistent with STS 3.8.1 and 3.8.2 Bases, with the exception that the CGS TS 3.8.1 Bases considers the LCO to be met when either Division 1 or Division 2 is capable of being powered by TR-S.

TS 3.8.1 Bases The current TS Bases, which describe that the LCO is met when Division 3 and either Division 1 or Division 2 are capable of being powered by TR-S, were included in the CGS (formally known as Washington Public Power Supply System Nuclear Project Number 2; WPPSS WNP-2) license amendment request (LAR) forTS conversion to NUREG-1434, Revision 1 (STS). The NRC staff reviewed the pre-conversion TS 3/4.8 and TS 3/4.8 Bases (License Amendment No.

136 and Revision 0, respectively) and confirmed that the pre-conversion TS and TS Bases did not include the current language, or other similar language, stating or otherwise implying that LCO 3.8.1.a is met when either Division 1 or Division 2 is capable of being powered by TR-S.

Furthermore, the LAR for the TS conversion to NUREG-1434, Revision 1 (Amendment No. 149 dated March 4 1997; ADAMS Accession No. ML031290340), did not include any technical discussion regarding why the pre-conversion TS Bases were not retained. The TS conversion changed the pre-conversion TS Bases by adding the following insert:

INSERT B 3.8-1 LCO-A The two circuits from offsite are from the Ashe substation and the Benton substation (via transformers TR-S and TR-B, respectively). To insure the requirements of Reference 1 [GDC-17] are met, the TR-S offsite circuit must be capable of providing power to the Division 3 4.16 kV ESF bus (SM-4) and either the Division 1 (SM-7) or Division 2 (SM-8) 4.16 kV ESF bus. The TR-B offsite circuit must be capable of providing power to both the Divisions 1 and 2 4.16 kV ESF buses. The qualified offsite circuits include the circuit path and disconnect to the respective transformers, the circuit path and breakers to the respective non-class 1 E 4.16 kV switchgear, SM-1, SM-2, and SM-3 (for the TRS offsite circuit only), and the circuit path and breakers to the respective Class 1 E switchgear (SM-4, SM-7, and SM-8).

The LAR provided the following justification for the above CGS TS 3.8.1 Bases deviation from the NUREG-1434, Revision 1, STS 3.8.1 Bases:

Changes have been made (additions, deletions, and/or changes to the NUREG) to reflect the plant specific nomenclature, number, reference, system description, or analysis description.

The NRC staff safety evaluation related to license Amendment No. 149, dated March 4, 1997, approving the CGS TS 3.8.1 conversion to STS, did not include any discussion of the above proposed TS Bases change regarding the licensee's TS Bases interpretation of LCO 3.8.1, "AC Sources-Operating" (i.e., "... the TR-S offsite circuit must be capable of providing power to the Division 3 4.16 kV ESF bus (SM-4) and either the Division 1 (SM-7) or Division 2 (SM-8) 4.16 kV ESF bus").

1982 FSAR Power System Description and Safety Evaluation Report The NRC staff reviewed Chapter 8 of FSAR Amendment No. 33, dated February 1982, which was the revision in effect at the time the operating license was issued for CGS. The NRC staff did not identify any description or other wording in FSAR Sections 8.1, 8.2, and 8.3 descriptions of the onsite and offsite power systems that indicate that the TR-S offsite circuit must be capable of providing power to the Division 3 4.16 kV ESF bus and either the Division 1 or Division 2 4.16 kV ESF Bus. The following is excerpted from the 1982 FSAR offsite electrical power system description and describes, in part, the offsite power supplies to CGS:

Two immediately available sources of power from the utility grid are provided to supply offsite power, one from the BPA 230 kV grid and one from the BPA

[Bonneville Power Administration] 115 kV grid. The 230 kV source is from the 230 kV bus at the BPA H.J. Ashe Switchyard via a 3000-foot long 230 kV tie line, the startup transformer and the 4.16 kV non-Class 1 E switchgear buses to the Class 1 E switchgear buses.

An automatic fast transfer system is provided to transfer the 4.16 kV non-Class 1 E buses from the generator source to the 230 kV offsite grid source if the generator source is lost. This source [TR-S] has sufficient capacity to carry both the plant normal auxiliary loads and the plant ESF loads.

The 115 kV source is from the BPA 115 kV Benton Switchyard via a four-mile long 115 kV tie line and the backup transformer to the Class 1 E switchgear buses. If power is not available from either the generator source or the 230 kV source, Class IE buses SM-7 and SM-8 will be automatically transferred to the 115 kV system source. This source [TR-B] has sufficient capacity to carry the Division 1 and 2 ESF loads only; the tie breakers between the 4.16 kV Class 1 E and non-Class IE buses are, therefore, automatically opened when the backup source breakers close.

The system startup transformer [TR-S] supplied by the H. J. Ashe 230 kV Switchyard supplies power for the startup and ESF loads.

The backup offsite ac power source [TR-B] is capable of providing power to all Division 1 and 2 ESF loads. It is used to supply these ESF auxiliary loads during diesel-generator testing or when the main generator is shut down and the offsite startup source [TR-S] is unavailable.

The NRC staff also reviewed the Safety Evaluation Report (SER) Section 8.2, "Offsite Power System," for the application filed by the WPPSS, as applicant, for a license to operate WNP-2 (Docket No. 50-397), dated March 1982. Regarding the offsite power system, the SER states the following:

Two physically independent and redundant sources of offsite power are available for startup and safe shutdown of the unit. Safety-related 4.16-kV buses are powered from the two independent startup transformers through the non-safety 4.16-kV buses. During normal plant operation, 4.16-kV power is supplied by the unit's auxiliary transformer. Power for plant startup and shutdown is supplied by the preferred startup transformer. In the event the preferred startup transformer is unavailable, an automatic transfer scheme connects the backup (alternate) startup transformer to the Class 1 E buses.

The startup transformer (TR-S) has the capacity to supply full startup, normal running, and engineered safety features (ESF) shutdown loads for Divisions 1, 2, and 3. The backup startup transformer [TR-B] has the capacity to supply the full power requirements of the ESF system for both Division 1 and Division 2.

Upon loss of both normal and startup sources, the tie breakers between the 4.16-kV Class 1 E and the 4. 16-kV non-Class 1 E switchgear buses are automatically opened, thereby shedding all loads supplied through the 4.164kV non-Class 1 E buses. The 4.16-kV Class 1 E bus under voltage relays cause a trip of all the 4.16-kV feed breakers except those breakers supplying the 480-V substations (transformers). The Division 1 and 2, 4.16-kV Class 1 E buses are then automatically transferred to the 115/4.16-kV backup transformer.

The NRC staff did not identify in the 1982 FSAR or the 1982 SER any information to support the licensee's position that the TR-S offsite circuit must be capable of providing power to the Division 3 4.16 kV ESF bus and either the Division 1 or Division 2 4.16 kV ESF bus.

The licensee's stated interpretation of TS LCO 3.8.1 would allow plant operation with either the Division 1 or Division 2 bus completely disconnected from the immediate source through transformer TR-S with no automatic or manual connection capability requirement. Furthermore, with the electrical system in this configuration, a normal plant trip with offsite power available from transformers TR-S and TR-B would result in the transfer of Division 1, 2, and 3 safety buses to TR-S. However, with Division 1 (Division 2) not aligned to TR-S, the safety bus relays will detect a LOV, start the corresponding DG-1 (DG-2) and initiate a transfer to the delayed or second offsite source through TR-B after several seconds. This sequence of events is not identified in the licensing basis of the plant and is not consistent with the description stated in FSAR 8.1.5.2, Amendment No. 59, dated December 2007, which states that two immediate access (offsite) power sources are provided for the Division 1 and Division 2 ESF systems, and one immediate access (offsite) power source is provided for the Division 3 (HPCS) system.

In summary, the NRC staff interprets that the CGS TS 3.8.1 (a) requirement for two qualified offsite electrical power sources (or circuits) refers to the circuits from the transmission network via the Ashe 230 kV line and the from the Benton 115 kV line via transformers TR-S and TR-B, respectively, to the Division 1 and Division 2 Class 1 E ESF buses. These offsite power sources must be aligned or capable of automatically being aligned to the Class 1 E ESF buses to satisfy TS LCO 3.8.1 (a), "Two qualified circuits between the offsite transmission network and the onsite Class 1E AC Electric Power Distribution System." TS LCO 3.8.2(a) requires one qualified circuit between the offsite transmission network and the onsite Class 1 E AC electrical power distribution subsystem(s) required by LCO 3.8.8, "Distribution Systems-Shutdown;" this single source can be provided by the qualified circuit via transformer TR-S transformer or transformer TR-B.

4.0 CONCLUSION

The NRC staff agrees that the two CGS TS-qualified circuits from offsite are from the Ashe substation and the Benton substation, via transformers TR-S and TR-B, respectively. The staff also agrees that the TR-B offsite circuit must be capable of providing power to the 4.16 kV ESF buses, both Division 1 and Division 2, as the second TS-qualified offsite electrical power source.

The NRC staff disagrees with the licensee's interpretation of the CGS TS Section 3.8.1 regarding the electrical power source Operability of TR-S. Specifically, LCO 3.8.1, "AC Sources Operating," requires that TR-S must be capable of providing power to the Division 3 ESF Class 1 E bus and the Division 1 and Division 2 4.16 kV ESF Class 1 E buses as one of the two qualified offsite electrical power sources. In addition, TR-8 must also be capable of providing power to the 4.16 kV ESF buses, both Division 1 and Division 2, as the other TS-qualified offsite electrical power source in order to satisfy LCO 3.8.1 (a), "Two qualified circuits between the offsite transmission network and the onsite Class 1E AC Electric Power Distribution System."

For LCO 3.8.2, "AC Sources-Shutdown," the single source can be provided by either of the two qualified circuits via transformer TR-S or transformer TR-B.

Principal Contributors: G. Waig, NRR/DSS/STSB G. Matharu, NRR/DE/EEEB Date: June 13, 2014

ML14127A400

• via memo OFFICE NRR/DORULPL4-1/PM NRR/DORULPL4-1/LA NRR/DE/EEEB/BC*

NAME Fly on JBurkhardt JZimmerman DATE 5/16/14 5/13/14 4/30/14 OFFICE OGC-NLO NRR/DORULPL4-1/BC NRR/DORULPL4-1/PM NAME BHarris MMarkley Fly on DATE 6/5/14 6/13/14 6/13/14