ML19091A194

Safety Evaluation Input for License Amendment Request to Revise the Technical Specifications 3.8.1, AC Sources - Operating.

ML19091A194
Person / Time
Site:	McGuire, Mcguire
Issue date:	04/17/2019
From:	Office of Nuclear Reactor Regulation
To:
Foli A
Shared Package
ML19108A285	List: ML19091A194 ML19108A317
References
CAC MF9673, CAC MF9674, EPID L-2017-LLA-0256
Download: ML19091A194 (29)

Text

MCGUIRE NUCLEAR STATION UNITS 1 AND 2 - SAFETY EVALUATION INPUT REGARDING LICENSE AMENDMENT REQUEST TO REVISE TECHNICAL SPECIFICATIONS 3.8.1 TO EXTEND DIESEL GENERATOR COMPLETION TIMES DOCKET NOS. 50-369 AND 50-370 (CAC NOS. MF9673 AND MF9674; AND EPID: L-2017-LLA-0256)

1.0 INTRODUCTION

By letter dated May 2, 2017 (Agencywide Documents Access management System (ADAMS)

Accession No. ML17122A116), as supplemented by letters dated July 20, 2017 (ADAMS Accession No. ML17201Q132), November 21, 2017 (ADAMS ML17325A588), July 10, 2018 (ADAMS Accession No. ML18192A002), December 3, 2018 (ADAMS Accession No. ML18337A277), and April 8, 2019 (ADAMS Accession No. ML19099A046), Duke Energy Carolinas, LLC (Duke Energy, the licensee), requested an amendment to Renewed License Nos. NPF-9 and NPF-17 for McGuire Nuclear Station (MNS), Units 1 and 2. In the license amendment request (LAR), the licensee proposed revising the MNS Technical Specifications (TS) 3.8.1, AC [Alternating Current] Sources - Operating, to allow the extension of the Completion Time (CT) for an inoperable emergency diesel generator (DG) from 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> to 14 days, and to ensure that at least one train of shared components has an operable emergency power supply. To support the extended 14-day CT request, MNS would add an emergency supplemental power source (ESPS) with the capability to power any emergency bus. The proposed changes to TS 3.8.1 in the December 3, 2018 letter superseded the proposed TS 3.8.1 changes in the May 2, 2017, November 21, 2017, and July 10, 2018 letters.

2.0 REGULATORY EVALUATION

2.1 System Description According to Chapter 8, Electric Power, of the MNS Updated Safety Analysis Report (UFSAR),

and Section 3.2, McGuire AC power System Description, of the May 2, 2017 letter, the MNS offsite power system, which is the preferred power supply, consists of the main step-up transformers, the switching station and the transmission system. Each MNS unit is provided with two independent immediate access circuits of offsite power from the transmission system.

For Unit 1, each circuit consists of a connection from the 230 kilo volts (KV) switching station over an independent 230 KV overhead transmission line through one of the two half-sized step-up transformers to one of the two-unit auxiliary transformers. For Unit 2, each circuit consists of a connection from the 525-KV switching station over an independent 525 KV overhead transmission line through one of the two half-sized step-up transformers to one of the two-unit auxiliary transformers.

The boundary between the offsite power system and the onsite power system is the main step-up transformer terminations on the low voltage side. The onsite power system consists of all sources of electric power and their associated distribution systems in the generating unit. These sources are the main generator, two DGs and the batteries.

ENCLOSURE

The normal onsite power supply for each MNS unit onsite AC power system is the 24-KV unit generator which feeds power to the auxiliary power transformers through isolated phase bus.

Each MNS unit is provided with two full size auxiliary power transformers that are sized to carry all of the auxiliaries of one operating unit plus the safety shutdown loads of the other unit. Each auxiliary power transformer has two secondary windings, with each winding normally energizing one 6900 VAC normal auxiliary power system switchgear assembly. The 6900 VAC normal auxiliary power system furnishes power to all the large station auxiliary loads such as the reactor coolant pumps, condenser circulating water pumps and hotwell pumps. In addition, the system furnishes normal power to the redundant 4160 VAC essential auxiliary power system through unit auxiliary switchgear breakers and 6900/4160 V transformers. Two redundant and independent 4160 VAC essential auxiliary power system trains supply power to all engineered safety equipment in each MNS unit such that the failure of components in one of the two trains does not affect the other train.

Each MNS unit has two 600 VAC essential auxiliary power system trains, each of which includes two 600 VAC load centers. Each 600 V load center is normally fed by a separate 4160/600 V load center transformer connected to the 4160 VAC essential auxiliary power system buses. The 600 V load centers supply power to large loads such as heater loads and 600 V motor control centers (MCCs). The 600 V MCCs connect to all the 600 volt loads which require power during station blackout (SBO) or accident conditions.

Each MNS unit includes two independent emergency DGs that supply power to the redundant 4160 VAC essential auxiliary power system trains. Each DG is rated at 4000 kilo watts electric (KWe), 0.8 power factor (PF), 4160 V. Each DG is rated for continuous operation at 4000 KWe with added capacity to operate between 4200-4400 KWe for a period of two hours out of every twenty-four hours of operation without adversely affecting the life of the unit. All Class 1E switchgear and load center breakers that are required to function automatically following a safety injection actuation signal and/or SBO condition are controlled by a load sequencer associated with each DG.

MNS includes a standby shutdown facility (SSF) DG as an alternate AC (AAC) power source to cope with an SBO. The SSF DG is available within 10 minutes of a SBO event. The SBO scenario assumes that both units experience loss of offsite Power (LOOP) and that one units emergency DGs completely fail to start. At least one emergency DG is assumed to start for the non-SBO unit. MNS is subject to a minimum SBO coping capability of 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> with emergency DG reliability target of 0.95 (consistent with the requirements of NUMARC 87-00). The SSF has the capability to maintain the plant in hot standby conditions for a period of approximately 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> following the loss of plant power, which exceeds the SBO required coping duration of 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />.

In its May 2, 2017 letter, the licensee stated that the normal power system and the emergency DGs can supply the MNS shared systems, which consist of components shared between the units. The MNS shared systems are: Nuclear Service Water System (NSWS), Control Room Area Ventilation System (CRAVS), Control Room Area Chilled Water System (CRACWS) and Auxiliary Building Filtered Ventilation Exhaust System (ABFVES).

The MNS TS 3.8.1 provide the requirements for the offsite circuit(s) and DG(s) during operation.

The CT for returning an inoperable DG to operable status is 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />. In addition, the current MNS TS 3.8.1 have no requirements for the AC power sources for the shared systems.

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2.2 Description of Proposed Changes 2.2.1 Shared Systems:

In its May 2, 2017 letter, the licensee stated that the AC power source operability requirements for the MNS shared systems are currently located in the TS Bases and specify that both normal and emergency power sources are required for the operability of the shared systems.

However, the MNS TS definition of operable/ operability only requires normal or emergency power. The licensee proposed to use the MNS TS definition of operable/operability for the MNS shared systems AC power source operability requirements, and to add these requirements to the MNS TS 3.8.1.

In its December 3, 2018 letter, the licensee proposed to incorporate the opposite units AC power sources that are necessary to support the shared systems operability into TS 3.8.1. The proposed change would add new LCOs with associated applicability note, Conditions, RAs, and CTs to MNS TS 3.8.1.

2.2.2 Emergency DG 14-day CT Extension:

In its May 2, 2017 letter, the licensee proposed to extend the current MNS TS CT for an inoperable unit-specific emergency DG from 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> to 14 days provided that the ESPS is available and functional. The ESPS would be the backup power supplies for the 4160 VAC bus whose emergency DG is removed from service.

The ESPS will be a permanently installed, non-safety related, commercial grade system consisting of the following major components: 1) two 6.9 KV Caterpillar C175-16 supplemental DG sets (SDGs), each rated at 2500 KWe at 0.8 PF continuous power and 2750 KWe @ 0.8 PF prime power, 2) ABBs ADVAC switchgear product line to allow the power output of the two SDGs to be synchronized to a common ESPS bus, individual output breakers are provided for connection to the 6900 VAC Normal Auxiliary Power Systems of each unit, 3) A 6.9 KV/480 VAC dry transformer for supplying auxiliary power while the SDGs are running, and 4) a 4000 KWe, 6.9 KV resistive load bank for periodic testing of the SDGs. The ESPS major components will be physically separated from the existing emergency DGs, the offsite and onsite power systems and the safety-related Class 1E 4160 V essential busses. Each SDG will be located in its own weather enclosure mounted on top of an above grade sub-base fuel tank. The sub-base fuel tanks are specified to contain sufficient usable fuel to allow for 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br /> of continuous operation at rated load. The total power output from the two SDGs will be 5000 KWe (5500 KWe at the prime rating).

The licensee stated that the primary reason for the request to extend the CT for an inoperable DG is to allow sufficient time to perform planned reliability improvement modifications and adequate preventative maintenance to ensure emergency DG reliability and availability.

Additionally, should conditions occur requiring emergency DG corrective maintenance, the proposed change also provides flexibility to resolve emergency DG deficiencies and avoid potential unplanned shutdowns, along with any potential attendant challenges to safety systems during an unplanned shutdown. In its July 20, 2017 letter, the licensee clarified that the 14-day extended CT will be entered for only one emergency DG to avoid loss of safety functions for shared systems.

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In its December 3, 2018 letter, the licensee stated that MNS has completed the installation of the ESPS equipment and facility tie-ins. In addition, the licensee proposed revising the existing TS 3.8.1 Required Actions (RAs) and associated CTs for an inoperable unit-specific emergency DG (Condition B) to allow the 14-day CT extension for restoring the inoperable unit-specific emergency DG.

2.2.3 Proposed TS Changes The licensee proposed the following changes to current MNS Units 1 and 2 TS 3.8.1 in its December 3, 2018 letter:

Current TS LCO 3.8.1 and Applicability states:

Revised TS LCO 3.8.1 and Applicability would state:

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Current TS 3.8.1, Condition A and Required Action A.1 currently state:

Revised TS 3.8.1 Condition A and Required Action A.1 would state:

urrent TS 3.8.1 CT for Required Action A.3 state:

Revised TS 3.8.1 CT for Required Action A.3 would state:

Current TS LCO 3.8.1, Condition B states:

Revised TS LCO 3.8.1, Condition B would state:

New TS 3.8.1 Required Action B.1 would state:

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Current TS LCO 3.8.1 Required Actions B.1, B.2, B.3.1, and B.3.2 state:

Revised and renumbered Required Actions B.2, B.3, B.4.1, and B.4.2 would state:

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New TS 3.8.1 Required Action B.5 and CTs would state:

Current TS 3.8.1, Required Action B.4 (revised and renumbered as Required Action B.6) and CTs state:

Revised and renumbered Required Action B.6 and CTs would state:

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New TS 3.8.1 Condition C, Required Actions C.1, C.2, and C.3 would state:

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New TS 3.8.1 Condition D, Required Actions D.1, D.2, D.3, D.4.1, D.4.2, D.5.1, and D.5.2 would be added and would state:

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Current TS 3.8.1 Condition C (revised and renumbered as Condition E), Required Actions C.1 and C.2, and CTs state:

Revised and Renumbered TS 3.8.1 Condition E, Required Action E.1 and E.2, and CTs would state:

Current TS 3.8.1, Condition D (revised and renumbered as Condition F) and Required Actions D.1 and D.2 state:

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Revised and Renumbered TS 3.8.1 Condition F and Required Actions F.1 and F.2 would state:

Current TS LCO 3.8.1, Condition E (revised and renumbered as Condition G) and Required Action D.1 state:

Revised and Renumbered TS 3.8.1, Condition G and Required Action G.1 would state:

Current TS 3.8.1, Condition F (renumbered as Condition H) and Required Action F.1 state:

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Renumbered TS 3.8.1 Condition H and Required Action H.1 would state:

Current TS 3.8.1 Condition G (revised and renumbered as Condition I) and Required Actions G.1 and G.2 state:

Revised and Renumbered Condition I and Required Action I.1 and I.2 would state:

Current TS 3.8.1, Condition H (revised and renumbered as Condition H) and Required Action H.1 states:

Revised and Renumbered TS 3.8.1 Condition H and Required Action H.1 would state:

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2.3 Regulatory Acceptance Criteria The NRC staff applied the following U.S. Nuclear Regulatory Commission (NRC) requirements to evaluate the LAR:

Title 10 of the Code of Federal Regulations (10 CFR) Section 50.36, Technical Specifications, requires, in part, that the operating license of a nuclear production facility include technical specifications (TS). 10 CFR 50.36(c)(2)(i) requires that the TS limiting conditions for operation (LCOs), which are the lowest functional capability or performance levels of equipment required for safe operation of the facility. When a limiting condition for operation of a nuclear reactor is not met, the licensee shall shut down the reactor or follow any remedial action permitted by the technical specifications until the condition can be met."

10 CFR 50.36(c)(2)(ii)(C) Criterion 3 requires that a TS LCO be established for a structure, system, or component that is part of the primary success path and which functions or actuates to mitigate a design basis accident or transient that either assumes the failure of or presents a challenge to the integrity of a fission product barrier.

10 CFR, Appendix A of Part 50, General Design Criterion (GDC) 17, Electric Power Systems, requires that an onsite electric power system and an offsite electric power system be provided to permit functioning of structures, systems, and components important to safety. The safety function for each system (assuming the other system is not functioning) shall be to provide sufficient capacity and capability to assure that (1) specified acceptable fuel design limits and design conditions of the reactor coolant pressure boundary are not exceeded as a result of anticipated operational occurrences and (2) the core is cooled and containment integrity and other vital functions are maintained in the event of postulated accidents. The onsite electric power supplies, including the batteries, and the onsite electric distribution system, shall have sufficient independence, redundancy, and testability to perform their safety functions assuming a single failure.

10 CFR 50 Appendix A, GDC 18, Inspection and testing of electric power systems, requires, in part, that electric power systems important to safety be designed to permit appropriate periodic inspection and testing of important areas and features to assess the continuity of the systems and the condition of their components. The systems shall be, in part, designed with a capability to test periodically (1) the operability and functional performance of the components of the systems, 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.

The staff considered the following NRC guidance documents to evaluate the LAR:

NUREG-0800 (Standard Review Plan) Branch Technical Position BTP 8-8, Onsite (Emergency Diesel Generators) and Offsite Power Sources Allowed Outage Time Extension. The BTP 8-8 provides guidance for reviewing requests for the allowed outage time extensions for the onsite and offsite electrical power sources to perform online maintenance of the power sources.

Regulatory Guide (RG) 1.93, Availability of Electric Power Sources, Revision 0, which provides guidelines that the NRC staff considers acceptable when the number of available electric power sources are less than the number of sources required by the LCOs for a facility.

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3.0 TECHNICAL EVALUATION

3.1 Staff Evaluation 3.1.1 Shared Systems - Existing TS LCO 3.8.1 and Applicability - Revised The existing MNS TS LCO 3.8.1 requires two offsite circuits and two DGs capable of supplying power to the unit Onsite Essential Auxiliary Power Systems.

In letter dated June 30, 2017 (ADAMS Accession No. ML17167A317), the NRC staff requested the licensee to provide a detailed justification on how the proposed TS changes would satisfy 10 CFR 50.36(c)(2)(ii)(C), Criterion 3. In its letter dated July 10, 2018, the licensee stated that, to continue to meet Criterion 3 of 10 CFR 50.36, the existing TS LCO 3.8.1 for each MNS unit will be revised to include both normal and emergency power required from the opposite unit to maintain operability of the MNS shared systems. Specifically, two new LCO 3.8.1.c (normal power) and LCO 3.8.1.d (emergency power) from the opposite unit necessary to supply power to the MNS shared systems between the two units would be added to the existing TS LCO 3.8.1. The new LCO 3.8.1.c would state: "The qualified circuit(s) between the offsite transmission network and the opposite unit's Onsite Essential Auxiliary Power System necessary to supply power to the Nuclear Service Water System (NSWS), Control Room Area Ventilation System (CRAVS), Control Room Area Chilled Water System (CRACWS) and Auxiliary Building Filtered Ventilation Exhaust System (ABFVES). The new LCO 3.8.1.d would state: "The DG(s) from the opposite unit necessary to supply power to the NSWS, CRAVS, CRACWS and ABFVES.

The NRC staff reviewed the proposed new LCO 3.8.1.c and LCO 3.8.1.d and finds that these new LCO requirements, in conjunction with the requirements for the applicable unit (or unit-specific) AC electrical power sources in LCO 3.8.1.a and LCO 3.8.1.b, ensure that power is available to two trains of the shared systems (i.e., NSWS, CRAVS, CRACWS and ABFVES).

The NRC staff concludes that the licensee has identified the minimum components to be operable in LCO 3.8.1 when either MNS unit is in Mode 1-4, as required by 10 CFR 50.36(c)(2)(ii) C) Criterion 3.

The licensee also proposed to add a new Note to the Applicability of TS LCO 3.8.1 to take exception to the requirements for the opposite units AC power sources in the new TS LCO 3.8.1.c and LCO 3.8.1.d when the associated shared systems are inoperable. The NRC staffs evaluation for the proposed new Applicability Note, and further discussion on the new LCO 3.8.1.c and LCO 3.8.1.d, is provided by the Containment and Plant Systems Branch.

3.1.2 Emergency DG 14-day CT Extension - Existing Condition B - Revised The NRC staff reviewed the proposed extended 14-day extended CT for an inoperable unit-specific emergency DG (TS 3.8.1 existing Condition B) in accordance with the BTP 8-8 guidance. The existing Condition B with associated RAs and CTs would be revised to allow the verification of an opposite unit DG and the extended 14-day CT.

The existing Condition B (one DG is inoperable) would be revised by adding LCO 3.8.1.b to existing condition statement. The licensee stated that the "LCO 3.8.1.b" is added to Condition B to clarify that the condition pertains to a unit-specific emergency DG rather than a DG from the opposite unit. The NRC staff finds the revised Condition B acceptable since the addition of LCO 3.8.1.b to the existing Condition B does not change the intent of the condition.

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A new RA B.1 would be added to verify the operability of the opposite units LCO 3.8.1.d DG(s) necessary to supply power to the shared systems within a CT of 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> and once per 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> thereafter when an LCO 3.8.1.b DG is inoperable. In its December 3, 2018 letter, the licensee stated that the new RA B.1 would be an administrative verification of the operability for the LCO 3.8.1.d DG(s). The licensee further stated that the 1-hour CT would allow sufficient time to perform RA B.1 if the inoperability of the LCO 3.8.1.b DG was unplanned; and the 12-hour CT was based on the MNS operator shift of 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />. If the verification in RA B.1 resulted in the LCO 3.8.1.d DG(s) being inoperable in Condition B (one LCO 3.8.1.b DG inoperable), MNS would enter either the proposed new Condition D and/or renumbered Condition G, as applicable (see sections 3.1.3.3 and 3.1.3.6 of this SE for the staffs evaluations of the proposed new Condition D and renumbered Condition G, respectively). The NRC staff finds the new RA B.1 with associated CTs acceptable since it will help ensure that at least one train of shared systems has an operable DG.

The existing RAs B.1, B.2, B.3.1, B.3.2 would be renumbered as RAs B.2, B.3, B.4.1, and B.4.2, respectively; the term required would be added to offsite circuits in the renumbered RA B.2; and (s) would be added to DG in the renumbered RAs B.4.1 and B.4.2. Adding required to offsite circuits in the renumbered RA B.2 would indicate that the RA would be performed for all offsite circuits required by the LCO 3.8.1. In its July 10, 2018 letter, the licensee stated that changing DG to DG(s) in the renumbered RAs B.4.1 and B.4.2 would allow the RAs to be performed for the operable LCO 3.8.1.b DG and LCO 3.8.1.d DG(s). The NRC staff finds that the proposed changes to existing B.1, B.2, B.3.1, B.3.2 are editorial in nature and are, therefore, acceptable.

A new RA B.5 with associated CT would be added to the revised Condition B; and the existing RA B.4 with associated CT would be revised and renumbered as RA B.6 to allow the extension of the CT for an inoperable LCO 3.8.1.b DG from 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> to 14 days.

BTP 8-8 recommends that a supplemental power source capable of supplying all LOOP loads to bring the unit to a cold shutdown be provided as a backup to a single inoperable DG in case of a LOOP event concurrent with a failure of the remaining DG during the extended CT. In Section 3.4, Station Blackout, and Section 3.5, Emergency Supplemental Power Source (ESPS) of its May 2, 2017 letter, the license proposed to use the ESPS as the supplemental AC power source that would be the backup to the inoperable unit-specific emergency DG (LCO 3.8.1.b DG) during the proposed extended 14-day CT. Furthermore, the licensee stated that the ESPS is designed to be connected to any of the four 4160 VAC essential busses and will provide 4800 KWe continuous to the selected 4160 VAC essential bus. The licensee clarified that the 4800-KWe power output of the ESPS exceeds the 4000-KWe maximum rating of any existing emergency DG (which would normally supply power the LOOP loads); and, thus, the ESPS would give the SBO unit (i.e., unit with inoperable DG and LOOP event concurrent with failure of the remaining DG) the capability to power one train of essential equipment to achieve and maintain the unit in cold shutdown (i.e., Mode 5). The licensee also stated that a cold shutdown at MNS can be achieved with one train of shared components. The NRC staff finds that since the ESPS power output exceeds the rating of the current MNS emergency DG, the ESPS has sufficient capacity to supply the LOOP loads to bring the affected MNS unit to a cold shutdown during the extended CT as recommended by BTP 8-8 and, is therefore, acceptable.

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BTP 8-8 recommends that the availability of the supplemental AC power source be verified within the last 30 days before entering extended CT by operating or bringing the power source to its rated voltage and frequency and ensuring all its auxiliary support systems are available or operational. In its July 10, 2018 letter, the licensee stated that the availability of the ESPS would require 1) performance of the load test within 30 days of entry into the extended CT; 2) verification of the fuel tank locally to be greater than or equal to a 24-hour supply; and 3) verification of the ESPS supporting system parameters for starting and operating to be within limits for functional availability. The NRC staff noted that the performance of the load test for the ESPS will involve bringing the ESPS to its rated voltage and frequency, and the verification of the ESPS supporting systems parameters within limits will ensure that the support systems are functional. The NRC staff finds that since the availability of the ESPS and its auxiliary support systems will be verified within the last 30 days before entering extended CT, as recommended by BTP 8-8 and is, therefore, acceptable.

BTP 8-8 recommends that the time to make the supplemental power source available to supply the loads, including cross-connection, should be approximately 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> to enable restoration of battery chargers and control reactor coolant system inventory. BTP 8-8 also recommends that plants have approved procedures for connecting the supplemental power source to the safety buses. In its May 2, 2017 letter, the licensee stated that, to meet the approximately one hour criterion, MNS will utilize an existing Emergency Procedure (ECA-0.0, Loss of All AC Power) that guides the control room operators through the appropriate steps to systematically cope with a total loss of AC Power (i.e., SBO). The licensee also stated that observations of the operators on the plant simulator showed that it would take about 20 minutes for the operators to get to the point in the procedure to attempt to restore power from any of the normal and emergency power sources (i.e., restoring an emergency DG, cross-tying the units or restoring offsite power). In letter dated November 2, 2018 (ADAMS Accession No. ML18306A937), in a request for additional information (RAI) 3a, the NRC staff requested the licensee to clarify the estimated time it would take to connect the ESPS power source (i.e., the two supplemental DGs) to the stations safety bus from the start of an SBO event. In its December 3, 2018 letter, in response to RAI 3a, the licensee clarified that the time it would take to restore power to a 4160 V safety bus using the ESPS from the time power would be lost to the 4160 V safety buses was validated at 70 minutes including margin. The NRC staff finds that MNS meets the intent of the BTP 8-8 guidance regarding the timeframe for making the supplemental power source available to supply the loads since the 70-minute timeframe to re-energize a 4160 VAC safety bus using the ESPS is within approximately 1 (60 minutes) hour timeframe.

To support the timeframe for making the supplemental power source available, BTP 8-8 recommends that plants assess their ability to cope with loss of all AC power (i.e., SBO) for this timeframe independent of a supplemental power source. In its November 2, 2018 letter, in RAI 3b, the NRC staff requested the licensee to provide a discussion that summarizes the calculations or analysis performed to assess the MNS ability to cope with the loss of all AC power (i.e., SBO) for one hour or the plant specific period until the ESPS is connected to the shutdown buses. In its December 3, 2018 letter, in response to RAI 3b, the licensee stated that Duke Energy has performed a calculation for MNS that assessed its ability to cope with an SBO event without taking credit for the SSF. The licensee further stated that 1) the calculation included a reactor coolant pump seal leakage, no primary mass addition, no secondary heat sink and assumed that the SSF is unavailable; and 2) the calculation concluded that the length of time between the SBO event initiation and the onset of significant core uncover is approximately 2.4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />. In Attachment 1 of its April 8, 2019 letter, the licensee provided a figure of core collapsed water level versus time from the calculation to support their initial response to RAI 3b.

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The figure shows that the core remains covered with minimal voiding until approximately 115 minutes (greater than 70 minutes) at which point the core collapsed level begins to decrease.

Since MNSs SBO calculation takes no credit for the SSF and shows that the core will remain covered within the first 115-minute of an SBO event, the NRC staff finds that MNS has sufficient time to cope with an SBO event without a supplemental AC power source for the 70-minute duration as noted above in response to RAI 3a until the ESPS is connected to a 4160V safety bus. Therefore, the NRC staff finds that MNSs ability to cope with an SBO event without a supplemental AC power source for the 70-minute duration credited to connect the ESPS to a 4160V safety bus is consistent with the recommendations of BTP 8-8, and is therefore, acceptable.

BTP 8-8 recommends that the TS contains RAs and CTs to verify that the supplemental AC source is available before entering the extended CT and every 8-12 hours (once per shift). The MNS 14-day extended CT begins after 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> of continuous DG inoperability. In its December 3, 2018 letter, the licensee proposed to add a new RA B.5 to the TS 3.8.1 revised Condition B (inoperable LCO 3.8.1.b DG) to evaluate the availability of the ESPS within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> and once per 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> thereafter. The licensee stated that the 12-hour CT was chosen because the MNS operator shifts are 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />. In its May 2, 2017 letter, the licensee stated that the extended 14-day CT for one inoperable LCO 3.8.1.b DG will be applied only if there is a suitable ESPS available and functional. The NRC staff finds that the proposed 1-hour and 12-hour thereafter CTs for RA B.5 will allow the licensee to ensure that the ESPS is available before entering the time greater than 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> of continuous DG inoperability. Therefore, the NRC staff finds that the proposed RA B.5 and associated CTs are consistent with the recommendation provided in BTP 8-8, and are, therefore, acceptable.

BTP 8-8 recommends that if the supplemental power source becomes unavailable any time during the extended CT, the unit shall enter the LCO 3.8.1 and start shutting down within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />. The MNS 14-day extended CT for restoring an inoperable LCO 3.8.1.b DG to operable status begins from the time greater than the existing 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> up to 14 days. In its December 3, 2018 letter, the licensee proposed to revise the existing RA B.4 (restore DG to operable status) and associated CTs to allow the proposed 14-day CT extension.

The existing RA B.4 would be renumbered as RA B.6. The NRC staff finds the renumbering of RA B.4 as RA B.6 is editorial in nature and is, therefore, acceptable.

The renumbered RA B.6 (restore DG to operable status) would have 4 CTs that state: 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> from discovery of unavailable ESPS AND 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> from discovery of Condition B entry 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> concurrent with unavailability of ESPS AND 14 days AND 17 days from discovery of failure to meet LCO 3.8.1.a or LCO 3.8.1.b. The 4 CTs for the renumbered RA B.6 are joined by an AND connector to indicate that all CTs apply simultaneously, and the more restrictive CT must be met.

The first two CTs (i.e., 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> from discovery of unavailable ESPS AND 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> from discovery of Condition B entry 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> concurrent with unavailability of ESPS) would limit the time to restore the unit-specific emergency DG (i.e., LCO 3.8.1.b DG) to operable status without an available ESPS. The third CT (i.e., 14 days) would extend the total time to restore the LCO 3.8.1.b DG from the existing 72-hour CT up to 14 days provided that the ESPS is available. If the ESPS is found unavailable any time from initial entry into Condition B up to 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br />, the first two CTs (72-hour CT and 24-hour CT) will limit the time to restore the LCO 3.8.1.b DG to operable status to 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> from entry into Condition B.

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If the ESPS becomes unavailable sometime after 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> from initial entry into Condition B, the licensee has 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> to restore the LCO 3.8.1.b DG to operable status. But, before entering the time greater than 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />, the licensee must ensure that the ESPS is available per RA B.5, as recommended by the BTP 8-8. Otherwise, if the ESPS remains unavailable per RA B.5 up to 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> from initial entry into Condition B, the remaining time to restore the LCO 3.8.1.b DG to operable status is limited to 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> from initial entry into Condition B. If the ESPS becomes unavailable sometime after 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> from initial entry into Condition B (assuming that the ESPS was available prior to entering the time greater than 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />), the time to restore the LCO 3.8.1.b DG to operable status is limited to 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> provided that the total time does not exceed 14 days. If the LCO 3.8.1.b DG is not restored to operable status within this 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> and/or within the 14-day CT, the licensee will enter the renumbered Condition I (revised Condition G) to shut down the affected MNS unit (see section 3.1.3.8 of this SE for the staffs evaluation of the proposed renumbered Condition I). Based on the above discussion, the NRC staff finds that the proposed 72-hour, 24-hour, and 14-day CTs for the renumbered RA B.6 are consistent with the guidance provided in the BTP 8-8 since the CTs will allow 1) 72-hour limit to restore the DG if the ESPS is unavailable during the first 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> of DG inoperability, and 2) 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> to restore the DG if the ESPS is unavailable during the extended CT.

The fourth CT (i.e., 17 days from discovery of failure to meet LCO 3.8.1.a or LCO 3.8.1.b) would limit the maximum time that LCO 3.8.1.a or LCO 3.8.1.b is not met while concurrently or simultaneously in the TS 3.8.1 revised Condition A (inoperable LCO 3.8.1.a offsite circuit) and revised Condition B (inoperable LCO 3.8.1.b DG). In its July 10, 2018 letter, the licensee clarified that the maximum 17 days would be the sum of the 72-hour CT for restoring an inoperable offsite circuit and the extended 14-day CT for restoring an inoperable LCO 3.8.1.b DG (renumbered RA B.6). The NRC staff finds the maximum 17-day CT for the renumbered RA B.6 acceptable since it limits the allowable total time that any combination or required AC power sources will be inoperable at the same time.

BTP 8-8 recommends that a justification be provided for the duration of the requested extended CT (i.e., 14 days for MNS) based on plant-specific past operating experience. In its July 20, 2017 letter, the licensee provided a summary of projected major maintenance work hours for the emergency DGs in both units on a per-calendar year basis. The NRC staff finds that, based on the projected maintenance work hours, the proposed 14-day CT is acceptable because it is consistent with the BTP 8-8 guidance.

In its December 3, 2018 letter, the licensee also provided the following Regulatory Commitments (which superseded the commitments made in the May 2, 2017 letter) that pertain to the NRC staffs deterministic evaluation:

• The preplanned DG maintenance will not be scheduled if severe weather conditions are anticipated. Weather conditions will be evaluated prior to intentionally entering the extended DG CT and will not be entered if official weather forecasts are predicting severe weather conditions (i.e., thunderstorm, tornado or hurricane warnings). Operators will monitor weather forecasts each shift during the extended DG CT. If severe weather or grid instability is expected after a DG outage begins, station managers will assess the conditions and determine the best course for returning the DG to operable status.

• Component testing or maintenance of safety systems and important non-safety equipment in the offsite power systems that can increase the likelihood of a plant transient (unit trip) or LOOP will be avoided during the extended DG CT.

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• No discretionary switchyard maintenance will be performed during the extended DG CT.

• The turbine-driven auxiliary feed water pump will not be removed from service for elective maintenance activities during the extended CT. The turbine-driven auxiliary feed water pump will be controlled as "protected equipment" during the extended DG CT. The Non-CT EDGs, ESPS, Component Cooling System, Safe Shutdown Facility, Nuclear Service Water System, Chemical and Volume Control System, Diesel Air Compressors, Residual Heat Removal System, motor driven auxiliary feed water pumps, and the switchyard will also be controlled as "protected equipment."

• During the extended DG CT, the ESPS will be routinely monitored during operator rounds, with monitoring criteria identified in the operator rounds. The ESPS will be monitored for fire hazards during operator rounds.

• Licensed Operators and Auxiliary Operators will be trained on the purpose and use of the ESPS and the revised emergency procedure (EP) actions. Personnel performing maintenance on the ESPS will be trained.

• The system load dispatcher will be contacted once per day to ensure no significant grid perturbations (high grid loading unable to withstand a single contingency of line or generation outage) are expected during the extended DG CT.

• TS required systems, subsystems, trains, components and devices that depend on the remaining power sources will be verified to be operable and positive measures will be provided to preclude subsequent testing or maintenance activities on these systems, subsystems, trains, components and devices during the extended DG CT.

• Prior to entering the extended CT for an inoperable DG, when both units are in the TS 3.8.1 Modes of APPLICABILITY, the station will ensure that each train of shared systems is powered by an operable Class 1E AC Distribution System with an operable DG, from opposite units.

The NRC staff determined that the above-mentioned commitments are consistent with the staff's position in BTP 8-8, which identified commitments expected to ensure maintenance of defense-in-depth during an extended CT.

In summary, the NRC staff determined that licensee provided adequate justification for the proposed extended 14-day CT for an inoperable DG because the ESPS will be available prior to entering the extended CT and will be capable of supplying power to the loads necessary to bring the affected MNS unit to a cold shutdown in the event of a LOOP concurrent with a single failure. The NRC staff also finds that the licensee has provided acceptable commitments for maintaining overall defense-in-depth to assure safe shutdown of the affected MNS unit.

Therefore, based on the above evaluation, the NRC staff finds that the proposed change in the CT for one inoperable unit-specific emergency DG (revised Condition B) 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.

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3.1.3 Additional TS 3.8.1 Changes 3.1.3.1 Existing Condition A - Revised The existing Condition A applies when one of the two qualified offsite circuits between the offsite transmission network and the onsite essential auxiliary power system in LCO 3.8.1.a is inoperable.

The existing Condition A would be revised by adding LCO 3.8.1.a to existing statement; and the existing RA A.1 would be revised by adding required to operable and (s) to circuit. In its July 10, 2018 letter, the licensee stated that the addition of LCO 3.8.1.a to Condition A would clarify that the condition pertains to a qualified circuit between the offsite transmission network and the affected units onsite essential auxiliary power system. The licensee further stated that required and (s) would be added to RA A.1 to indicate that it could be necessary to verify the operability of more than one offsite circuit if the LCO 3.8.1.c offsite circuit was supplying power to a train of the shared systems when in Condition A. The NRC staff noted that the proposed changes to existing Condition A and RA A.1 reflect the addition of the new LCO 3.8.1.c offsite circuit to the TS 3.8.1 and do not change the intent of the existing requirements. Therefore, the NRC staff finds the proposed revised Condition A with associated RA A.1 acceptable since the proposed changes do not change the intent of the existing requirements.

The existing maximum CT of 6 days from discovery of failure to meet LCO for RA A.3 (restore offsite circuit to operable status) would be revised to 17 days from discovery of failure to meet LCO 3.8.1.a or LCO 3.8.1.b. Changing LCO to LCO 3.8.1.a or LCO 3.8.1.b would clarify the 17-day CT pertain to the unit-specific AC power sources. In its July 10, 2018 letter, the licensee stated that the maximum 17-day CT for RA A.3 would limit the total time that the LCO 3.8.1 is not met while concurrently or simultaneously in the revised Condition A and revised Condition B (LCO 3.8.1.b DG). The CT for restoring the units DG to operable status (renumbered RA B.6) is being extended from 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> up to 14 days (see section 3.1.2 of this SE for the staffs evaluation of the 14-day CT for the revised Condition B). Thus, the proposed new maximum 17-day CT for RA A.3 would be the sum of the existing 72-hour CT for RA A.3 and the proposed 14-day CT for RA B.6. The NRC staff finds the proposed maximum 17-day CT for RA A.3 acceptable since it will limit the time for restoring the inoperable unit-specific AC power sources to meet the LCO 3.8.1 or take other remedial actions for the safe operation of the plant.

3.1.3.2 New Condition C - Added The proposed new Condition C would apply when LCO 3.8.1.c offsite circuit is inoperable. The proposed new RAs C.1, C.2, C.3 for new Condition C would be modified by a Note.

The proposed Note would state: Enter applicable Conditions and Required Actions of LCO 3.8.9, Distribution Systems - Operating, when Condition C is entered with no AC power source to a train. In its July 10, 2018 letter, the licensee stated that the note would allow the new Condition C to provide requirements for the loss of a LCO 3.8.1.c offsite circuit and LCO 3.8.1.d DG without regard to whether a train is de-energized, as the MNS TS LCO 3.8.9, Distribution Systems - Operating, provides the appropriate restrictions for a de-energized train. In its December 3, 2018 letter, the licensee further clarified that in the case where one LCO 3.8.1.c offsite circuit would be inoperable (proposed new Condition C) concurrently with one inoperable LCO 3.8.1.d DG (proposed new Condition D) associated with the same train of shared systems, the proposed Note would allow MNS to enter the applicable TS LCO 3.8.9 actions to re-energize the affected train of shared systems. The NRC staff noted that the proposed Note is 20

consistent with the MNS current TS Note for the condition (i.e., existing TS 3.8.1 Condition D) in which both the offsite circuit and the DG supplying the same train of distribution systems are inoperable. Therefore, the NRC staff finds that the proposed Note for the new Condition C is acceptable since it will allow actions to be taken for the safe operation of the MNS, and it is consistent with the MNS current TS requirement for the concurrent inoperability of a unit DG and offsite circuit.

The proposed new RA C.1 would require the performance of SR 3.8.1.1 for the required offsite circuit(s) within CT of 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> AND Once per 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> thereafter. The SR 3.8.1.1 verifies the operability of a required offsite circuit. In its July 10, 2018 letter, the licensee stated that the new RA C.1 would ensure that a highly reliable power source remains operable with one required LCO 3.8.1.c offsite circuit inoperable. The licensee also stated that the CTs (i.e., 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> AND Once per 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> thereafter) for the new RA C.1 is consistent with the CT for the existing RA A.1 (perform SR 3.8.1.1 for operable offsite circuit). If a required offsite circuit failed the SR 3.8.1.1, MNS would enter the revised Condition A and/or the proposed revised Condition E, as applicable. The NRC staff finds that the proposed new RA C.1 and associated CTs for the new Condition C are acceptable because they are consistent with the MNS TS requirements (i.e., RA A.1 with CT) for an inoperable required offsite circuit (i.e., Condition A).

The proposed new RA C.2 would state declare NSWS, CRAVS, CRACWS or ABFVES with no offsite power available inoperable when the redundant NSWS, CRAVS, CRACWS or ABFVES is inoperable within a CT of 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> from discovery of no offsite power to one train concurrent with inoperability of redundant required feature(s). In its July 10, 2018 letter, the licensee stated that the new RA C.2 would provide assurance that an event coincident with a single failure of the DG that is associated with the affected train would not result in a complete loss of safety function for the NSWS, CRAVS, CRACWS or the ABFVES. The licensee stated the 24-hour CT would allow time for restoration before subjecting the unit to transients associated with shutdown, and it takes into account factors such as the component operability of the redundant counterpart to the inoperable shared system, the capacity and capability of the remaining AC sources, and a reasonable time for repairs. The NRC staff noted that the proposed new RA C.2 and associated 24-hour CT for the new Condition C are consistent with the intent of the existing RA A.2 and associated CT for one inoperable LCO 3.8.1.a offsite circuit (revised Condition A).

In addition, the proposed RA C.2 will allow MNS to enter the applicable TS conditions and RAs for the shared systems to take appropriate actions for the safe operation of the plant.

Therefore, the NRC staff finds that the proposed RA C.2 and associated CT are acceptable because they meet the intent of the MNS current TS requirements for an inoperable required offsite circuit.

The proposed new RA C.3 would require restoring the LCO 3.8.1.c offsite circuit to operable status within a CT of 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />. In its December 3, 2018 letter, the licensee stated that the proposed new RA C.3 would allow MNS to meet the LOC 3.8.1.c to comply with 10 CFR 50.36(c)(2). The licensee further stated that with one required LCO 3.8.1.c offsite circuit inoperable, the reliability of the offsite power is degraded and the potential for a LOOP is increased; however, the remaining operable offsite circuits and DGs are adequate to supply electrical power to the onsite Class 1E distribution system. RG 1.93 recommends power operation not to exceed 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> if one TS required offsite circuit is inoperable. Thus, the NRC staff finds the proposed new RA C.3 and associated 72-hour CT acceptable since they are consistent with the recommendations of RG 1.93 and allow the LCO 3.8.1.c to be met, as required by 10 CFR 5036(c)(2).

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3.1.3.3 New Condition D - Added The proposed new Condition D would apply when LCO 3.8.1.d DG inoperable. A new Note and new RAs D.1, D.2, D.3, D.4.1, D.4.2, D.5.1 and D.5.2 with associated CTs are proposed for the new Condition D.

The proposed Note would state: Enter applicable Conditions and Required Actions of LCO 3.8.9, Distribution Systems - Operating, when Condition D is entered with no AC power source to a train. In its July 10, 2018 letter, the licensee stated that the proposed Note would allow the new Condition D to provide requirements for the loss of an LCO 3.8.1.d DG and an LCO 3.8.1.c offsite circuit without regard to whether a train is de-energized, as MNS TS LCO 3.8.9 provides the appropriate restrictions for a de-energized train. In its December 3, 2018 letter, the licensee clarified that in the case the proposed one LCO 3.8.1.d DG would be inoperable (proposed new Condition D) concurrently with one inoperable LCO 3.8.1.c offsite circuit (proposed new Condition C) associated with the same train of shared systems, the proposed Note would allow MNS to enter the applicable TS 3.8.9 actions to re-energize the affected train of shared systems. The NRC staff noted that the proposed Note is consistent with the MNS current TS Note for the condition (i.e., existing TS 3.8.1 Condition D) in which both the offsite circuit and the DG supplying the same train of safety-related systems are inoperable. Therefore, the NRC staff finds that the proposed Note for the new Condition D is acceptable since it will allow actions to be taken for the safe operation of the MNS, and it is consistent with the MNS current TS requirement for the concurrent inoperability of a unit DG and offsite circuit.

The proposed new RA D.1 would verify both LCO 3.8.1.b DGs operable within a CT of 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> AND once per 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> thereafter. In its December 3, 2018 letter, the licensee stated that the new RA D.1 would be an administrative verification of the operability for the LCO 3.8.1.d DG(s).

In addition, the licensee stated that the 1-hour CT would allow sufficient time to perform RA D.1 if the inoperability of the LCO 3.8.1.b DG was unplanned, and the 12-hour CT was based on the MNS operator shifts of 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />. The NRC staff noted that if the verification in RA D.1 would result in one or two LCO 3.8.b DG(s) being inoperable, the plant would enter either the revised Condition B and/or the renumbered Condition G, as applicable (see sections 3.1.2 and 3.1.3.6 for the staffs evaluation of the revised Condition B and the renumbered Condition G, respectively). The NRC staff finds the new RA D.1 with associated CTs acceptable since it will provide assurance that the LCO 3.8.1.b DGs are capable of supplying the safety-related equipment.

The proposed new RA D.2 would require the performance of SR 3.8.1.1 for the required offsite circuit(s) within a CT of 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> AND once per 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> thereafter. In its July 10, 2018 letter, the licensee stated that the new RA D.2 would ensure that a highly reliable power source remains with one required LCO 3.8.1.d DG inoperable. The licensee also stated that the CTs (i.e., 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> AND Once per 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> thereafter) for the new RA D.2 is consistent with the CTs for the existing RA A.1 as well as the existing RA B.1 (renumbered as RA B.2) for an inoperable LCO 3.8.1.b DG. If a required offsite circuit failed the SR 3.8.1.1, MNS would enter the revised Condition A and/or the revised Condition E, as applicable. The NRC staff finds that the new RA D.2 and associated CTs are acceptable because they are consistent with the MNS TS requirements (i.e., renumbered RA B.2 with CT) for an inoperable required DG.

The proposed new RA D.3 would declare NSWS, CRAVS, CRACWS or ABFVES supported by the inoperable DG inoperable when the redundant NSWS, CRAVS, CRACWS or ABFVES is inoperable within a CT of 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> from discovery of Condition E concurrent with inoperability of redundant required feature(s).

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In its July 10, 2018 letter, the licensee stated that the new RA D.3 would provide assurance that a LOOP event concurrent with the inoperability of the LCO 3.8.1.d DG does not result in a complete loss of safety function for the NSWS, CRAVS, CRACWS or the ABFVES. The licensee further stated the 24-hour CT would allow time for restoration before subjecting the unit to transients associated with shutdown, and it takes into account factors such as the capacity and capability of the affected shared system and a reasonable time for repairs. The NRC staff noted that the proposed RA D.3 and associated 4-hour CT for the new Condition D are consistent with the intent of the existing RA B.2 (renumbered as RA B.3) and associated CT for one inoperable LCO 3.8.1.b DG (revised Condition B). In addition, the proposed RA D.3 will allow MNS to enter the applicable conditions and RAs for the affected shared systems TS LCO to take appropriate actions for the safe operation of the plant. Therefore, the NRC staff finds that the proposed RA D.3 and associated CT are acceptable since they meet the intent of the MNS current TS requirements for an inoperable required DG.

The proposed new RA D.4.1 and RA D.4.2 are joined by an OR connector so that either one or the other would apply. The proposed new RA D.4.1 would state: determine operable DG(s) is not inoperable due to common cause failures, within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />. The proposed RA D.4.2 would state Perform SR 3.8.1.2 for OPERABLE DG(s) within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />. The SR 3.8.1.2 ensures the operability of the DG(s) by verifying that each DG can start from standby conditions and achieve required steady state voltage and frequency. In its July 10, 2018 letter, the licensee stated that the new RA D.4.1 would allow MNS to avoid unnecessary testing of the operable DGs if the cause of the inoperability of the LCO 3.8.1.d DG could be determined not to exist on the operable DGs. The licensee further stated that if the cause of the inoperability of the LCO 3.8.1.d DG could not be confirmed not to exist on the operable DG(s), then the proposed new RA D.4.2 would be performed. The NRC staff noted that the proposed RA D.4.1 and RA D.4.2 with associated CTs for the new Condition D (one LCO 3.8.1.d DG) are consistent with the existing RA B.3.1 (renumbered as RA B.4.1) and RA B.3.2 (renumbered as RA B.4.2) for one inoperable LCO 3.8.1.b DG (revised Condition B). Therefore, the NRC staff finds that the proposed RA D.4.1 and RA D.4.2 and associated CTs are acceptable since they are consistent with the MNS current TS requirements for verifying the operability of the remaining DGs when a required DG is inoperable.

The proposed new RA D.5.1 and RA D.5.2 are joined by an OR connector so that either one or the other would apply. The proposed new RA D.5.1 would state restore LCO 3.8.1.d DG to operable status within a CT of 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />. In its December 3, 2018 letter, the licensee stated that the proposed new RA D.5.1 would allow LOC 3.8.1.d to be met to comply with 10 CFR 50.36(c)(2). The licensee further stated that with one required LCO 3.8.1.d DG inoperable, the remaining operable DGs and offsite power circuits are adequate to supply electrical power to the onsite Class 1E distribution system. When one TS required DG is inoperable, RG 1.93 recommends continue power operation not to exceed 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />, provided that the redundant DG is assessed within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> to be free from common-cause failure or is verified to be operable in accordance with plant-specific technical specifications. The proposed RA D.4.1 will assess the operable DG(s) to be free from common-cause failure within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> and the proposed RA D.4.2 will verify the operability of the remaining DG(s) within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />, as recommended by RG 1.93. The NRC staff finds that the proposed RA D.4.1 and RA D.4.2 will provide the prerequisite actions for 72-hour power operation in Condition D, as recommended by RG 1.93.

Therefore, the NRC staff finds the proposed RA D.5.1 and associated 72-hour CT acceptable since they are consistent with the recommendations of RG 1.93 and allow the LCO 3.8.1.c to be met, as required by 10 CFR 5036(c)(2).

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The proposed new RA D.5.2 would state: align NSWS, CRAVS, CRACWA and ABFVES supported by the inoperable LCO 3.8.1.d DG to an operable DG within a 72-hour CT. The NRC staff noted that in case the LCO 3.8.1.d would require only one opposite units DG, the shared systems supported by the inoperable required LCO 3.8.1.d DG would be realigned to the non-required operable LCO 3.8.1.d DG within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />. This will meet the LCO 3.8.1.d requirements for an operable DG and satisfy the RG 1.93 allowance for continued power operation of 72-hours. Therefore, the NRC staff finds the proposed RA D.5.2 with associated 72-hour CT acceptable since it will allow the LCO 3.8.1.d to be met, as required by 10 CFR 5036(c)(2).

3.1.3.4 Existing Condition C - Revised and Renumbered as Condition E The existing Condition C is applicable to two inoperable offsite circuits. The existing Condition C would be revised by renumbering it as Condition E, and by adding LCO 3.8.1.a to the existing condition statement and two new alternative conditions.

The existing RA C.1 and RA C.2 would be renumbered as RA E.1 and RA E.2, respectively; and Condition C in the existing CT for RA C.1 would be renumbered as Condition E in the CT for renumbered RA E.1. The NRC staff finds that the renumbering of existing Condition C, RA C.1, and RA C.2 as Condition E, RA E.1, and RA E.2, respectively, is an editorial change which is consistent with the addition of proposed new Conditions to the TS, and is, therefore, acceptable.

The renumbered Condition E would have three options joined by an OR connector so that either one of them would apply. The first option of Condition E would state two LCO 3.8.1.a offsite circuits inoperable. In its July 10, 2018 letter, the licensee stated that the addition of LCO 3.8.1.a to the existing Condition C clarifies that the portion of the condition pertains to the qualified circuits between the offsite transmission network and the unit-specifics onsite essential auxiliary power system. The NRC staff finds that the first option of the renumbered Condition E is acceptable since adding LCO 3.8.1.a to specify the units offsite circuit is consistent with the existing Condition C.

The second option of the renumbered Condition E would apply when one LCO 3.8.1.a offsite circuit that provides power to the shared systems and one LCO 3.8.1.c offsite circuit are inoperable. The third option of the renumbered Condition E would apply when two LCO 3.8.1.c offsite circuits are inoperable. In its July 10, 2018 letter, the licensee stated that the third option of the renumbered Condition E would be applicable when both trains of shared systems are aligned to receive power from the same unit. The NRC staff noted that the second and third options of the renumbered Condition E pertain to two offsite circuits that are credited to supply power to the redundant trains of shared systems, and also reflect the addition of the opposite unit LCO 3.8.1.c offsite circuits to the TS LCO 3.8.1. Therefore, the NRC staff finds that the second and third options of the renumbered Condition E satisfy the intent of the existing Condition C for two inoperable offsite circuits, and are, therefore, acceptable.

3.1.3.5 Existing Condition D - Revised and Renumbered as Condition F The existing Condition D is applicable to one offsite circuit inoperable and one DG inoperable.

The existing Condition D would be revised by adding LCO 3.8.1.a and LCO 3.8.1.b to the condition.

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The revised Condition D would be renumbered as Condition F. In addition, the existing RA D.1 and RA D.2 would be renumbered as RA F.1 and RA F.2, respectively; and Condition D in the existing note would be renumbered as Condition F. The NRC staff finds that the renumbering of existing Condition D, RA D.1, and RA D.2 as Condition F, RA F.1, and RA F.2, respectively, is an editorial change which is consistent with the addition of proposed new Conditions to the TS, and is, therefore, acceptable.

The renumbered Condition F would state one LCO 3.8.1.a offsite circuit inoperable and one LCO 3.8.1.b DG inoperable. In its July 10, 2018 letter, the licensee stated that the addition of LCO 3.8.1.a and LCO 3.8.1.b to the existing Condition D clarifies that the condition pertains to a qualified circuit between the offsite transmission network and the unit-specifics onsite essential auxiliary power system and to a unit-specific DG capable of supplying the units onsite essential auxiliary power systems. The NRC staff finds the renumbered Condition F acceptable since adding LCO 3.8.1.a and LCO 3.8.1.b to the existing condition to specify the units offsite circuit and DG is consistent with the existing Condition D.

3.1.3.6 Existing Condition E - Revised and Renumbered as Condition G The existing Condition E applies to two inoperable DGs. The existing Condition E would be revised by adding LCO 3.8.1.b to existing condition statement and two new alternative conditions.

The revised Condition E would be renumbered as Condition G. In addition, the existing RA E.1 (restore one DG to operable status) would be renumbered as RA G.1. The NRC staff finds that the renumbering of existing Condition E and RA E.1 as Condition G and RA G.1, respectively, is an editorial change which is consistent with the addition of proposed new Conditions to the TS, and is, therefore, acceptable.

The renumbered Condition G would have three options joined by an OR connector so that either one of them would apply. The first option would state two LCO 3.8.1.b DGs inoperable.

In its July 10, 2018 letter, the licensee stated that the addition of the LCO 3.8.1.b to the existing Condition E clarifies that the condition pertains to the unit-specific emergency DGs.

The TS requirement to restore one DG to operable status (renumbered RA G.1) within 2 hour-CT remains unchanged. The NRC staff finds the first option of the renumbered Condition G acceptable since adding LCO 3.8.1.b to specify the units DG is consistent with the existing Condition E.

The second option of the renumbered Condition G would apply when one LCO 3.8.1.b DG that provides power to the shared systems and one LCO 3.8.1.d DG are inoperable. The third option of the renumbered Condition G would state two LCO 3.8.1.d DGs inoperable. In its July 10, 2018 letter, the licensee stated that the third option would be applicable when both trains of shared systems would be aligned to receive power from the same unit. Since the second and third options of the renumbered Condition G pertain to two DGs that are credited to supply power to the trains of shared systems, the NRC staff finds that the second and third options for the renumbered Condition G satisfy the intent of the existing Condition E for two inoperable DGs, and are, therefore, acceptable.

The renumbered RA G.1 to restore one DG to operable status within a 2-hour CT would also apply to the second and third options of the renumbered Condition G. According to RG 1.93, power operation may continue for a period that should not exceed 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> if two required onsite AC power sources that supply power to redundant trains of safety systems are not available.

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Within these 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br />, one or both onsite AC power source(s) may be restored. Since the second and third options of the renumbered Condition G address the inoperability of two DGs that supply power to the redundant trains of shared systems, the NRC staff finds that the RA G.1 (restore one DG to operable status) and associated 2-hour CT are consistent with RG 1.93, and are therefore, acceptable.

3.1.3.7 Existing Condition F - Renumbered as Condition H The existing Condition F applies when one automatic load sequencer is inoperable. The existing Condition F and RA F.1 would be renumbered as Condition H and RA H.1, respectively.

The NRC staff finds that the renumbering of existing Condition F and RA H.1 as Condition H and RA H.1 is an editorial change which is consistent with the addition of proposed new Conditions to the TS, and is, therefore, acceptable.

3.1.3.8 Existing Condition G - Revised and Renumbered as Condition I The existing Condition G applies when the RA and associated CT of Condition A, B, C, D, E, or F are not met. The existing Condition G would be revised by modifying the list of conditions in the statement, and by adding two new alternative conditions.

The revised Condition G would be renumbered as Condition I. In addition, the existing RA G.1 and RA G.2 would be renumbered as RA I.1 and RA I.2, respectively. The requirements in RA I.1 and RA I.2 and associated CTs remain unchanged. The NRC staff finds that the renumbering of existing Condition G, RA G.1, and RA G.2 as Condition I, RA I.1, and RA I.2, respectively, is an editorial change which is consistent with the addition of proposed new Conditions to the TS, and is, therefore, acceptable.

The renumbered Condition I would have three options joined by an OR connector so that either one of them would apply. The first option of the renumbered Condition I would apply when the RA and associated CT of Condition A (revised), C (new), E (revised Condition C), F (revised Condition D), G (revised Condition E), or H (existing Condition F) are not met. The second option of Condition I would state Required Action and associated Completion Time of Required Action B.2, B.3, B.4.1, B.4.2, or B.6 not met. The third option of the renumbered Condition I would state Required Action and associated Completion Time of Required Action RA D.2, D.3, D.4.1, D.4.2, D.5.1, or D.5.2 not met.

In any of the above mentioned three options of the renumbered Condition I, if an RA and associated CT (except RA B.1 and RA D.1) would not be met, the renumbered RA I.1 and RA I.2 would require that the unit be brought to mode 3 in 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and mode 5 in 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br />, respectively. According to MNS TS LCO 3.0.3, if an LCO and associated actions are not met, the unit shall be placed in a mode or other specified condition in which the LCO is not applicable, and action shall be initiated within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> to place the unit, as applicable, in mode 3 within 7 hours8.101852e-5 days <br />0.00194 hours <br />1.157407e-5 weeks <br />2.6635e-6 months <br /> and in mode 5 within 37 hours4.282407e-4 days <br />0.0103 hours <br />6.117725e-5 weeks <br />1.40785e-5 months <br />. The NRC staff noted when an RA and CT in the renumbered Condition I were not met, the LCO 3.8.1 would not be met. Since the LCO 3.8.1 and associated actions in the renumbered Condition I will not be met and the LCO 3.8.1 is applicable in Mode 1-4, the NRC staff finds that placing the unit in Mode 3 (RA I.1) in 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and in Mode 5 (RA I.2) in 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br /> is consistent with the WBN TS LCO 3.0.3 requirements.

Therefore, the NRC staff finds that the renumbered Condition I and associated RA I.1, RA I.2, and CTs are acceptable since they will allow the affected unit to be place in safe shutdown conditions when the inoperable AC power sources cannot be restored within the required CTs.

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The NRC staff noted that the new RA B.1 (verify LCO 3.8.1.d DG(s) operable), new RA B.5 (ensure availability of ESPS), and new RA D.1 (verify both LCO 3.8.1.b DGs operable) with their respective associated CTs are not included in the renumbered Condition I. If the RA B.1 and associated CT or RA D.2 and associated CT are not met (i.e., LCO 3.8.d DG(s) and LCO 3.8.1.b DGs are not operable), the affected WBN unit would enter applicable conditions (i.e.,

Conditions D, B, and G) to restore the inoperable DGs to operable status to meet the LCO 3.8.1. If RA B.5 and associated CT are not met (i.e., ESPS is unavailable), actions would be taken to restore the affected DG within the applicable CT of RA B.6. Since the failure to meet RA B.1, RA B.5, and RA D.1 and associated CTs would not be failure to meet the LCO 3.8.1, the NRC staff finds that excluding the RA B.1 and D.1 and associated CTs from the Condition I is acceptable.

3.1.3.9 Existing Condition H - Revised and Renumbered as Condition J The existing Condition H applies to three or more AC sources inoperable. The existing Condition H would be revised by adding LCO 3.8.1.a and LCO 3.8.1.b to the existing condition statement and one new alternate condition.

The revised Condition H would be renumbered as Condition J. In addition, the existing RA H.1 (enter LCO 3.0.3) would be renumbered as RA J.1. The NRC staff finds that the renumbering of existing Condition H and RA H.1 as Condition J and RA J.1, respectively, is an editorial change and is, therefore, acceptable.

The renumbered Condition J would have two options. The first option of the renumbered Condition J would state three or more LCO 3.8.1.a and LCO 3.8.1.b AC sources inoperable.

In its July 10, 2018 letter, the licensee stated that the addition of LCO 3.8.1.a and LCO 3.8.1.b to the existing Condition H statement clarifies that the condition would correspond to a level of degradation in which all redundancy in the unit-specific AC electrical power supplies (i.e., LCO 3.8.1.a and LCO 3.8.1.b) would be lost. Since the existing Condition H applies to the unit-specific AC power sources, the NRC staff finds that adding LCO 3.8.1.a and LCO 3.8.1.b to the existing Condition H does not change the intent of the condition. Therefore, the NRC staff finds the first option of the renumbered Condition J acceptable since the first option is consistent with the existing Condition H.

The second option of the renumbered Condition J would state Three or more LCO 3.8.1.c and LCO 3.8.1.d AC sources inoperable. In this condition, the RA J.1 (enter LCO 3.0.3) would be implemented immediately to shut down the plant. In its July 10, 2018 letter, the licensee stated that the second option of the renumbered Condition J would correspond to a level of degradation in which all redundancy in LCO 3.8.1.c and LCO 3.8.1.d AC electrical power supplies would be lost. The NRC staff noted that this condition could entail the loss of all power to both trains of shared systems in case of failure of the remaining operable LCO 3.8.1.c offsite circuit or LCO 3.8.1.d DG. Thus, it will be reasonable to enter LCO 3.0.3 to commence an orderly shutdown to place the affected unit in a safe shutdown condition. In addition, the RA to enter LCO 3.0.3 immediately for this condition are consistent with the MNS current TS requirements to enter LCO 3.0.3 for three or more AC power sources inoperable (existing Condition H). Therefore, the NRC staff finds that the second option for the renumbered Condition J and associated RA J.1 and CT are acceptable because they satisfy the intent of the existing Condition H for three or more inoperable AC power sources.

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3.2 Deterministic Conclusion The NRC staff reviewed the proposed changes to TS 3.8.1, "AC Sources - Operating," to extend the CT for one inoperable DG from 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> to 14 days based on the availability of the ESPS against the guidance in the BTP 8-8 and to add actions for inoperable AC power sources required for the MNS shared systems. The NRC staff also reviewed the proposed TS 3.8.1 actions for inoperable opposite units AC power sources required to supply power to the MNS shared systems.

The NRC staff finds that the MNS use of ESPS during maintenance of one safety related DG meets the staffs position in BTP 8-8 since the ESPS provides an acceptable supplemental power source to the inoperable DG during the extended CT. The NRC staff also finds that the proposed remedial actions to meet the LCO 3.8.1 provide reasonable assurance that the activities as authorized (e.g., the longer CTs) will not endanger the health and safety of the public. Therefore, the NRC staff concludes that the proposed MNS TS changes are acceptable because 1) they provide acceptable remedial actions that allow the MNS units to restore inoperable AC power sources within acceptable times to meet the TS LCOs 3.8.1, as required by 10 CFR 50.36(c)(2), and 2) they ensure that the required AC power sources are returned to service to perform their safety functions and to meet the redundancy of the AC vital system, as required by GDC 17.

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