ML22062B664

Request for Additional Information 120V Inverter LAR from the Electrical Branch

ML22062B664
Person / Time
Site:	Seabrook
Issue date:	02/07/2022
From:	Justin Poole Plant Licensing Branch 1
To:	Levander M NextEra Energy Seabrook
Poole J, NRR/DORL/LPLI, 415-2048
References
EPID L-2021-LLA-0131
Download: ML22062B664 (6)

Text

From: Poole, Justin To: Levander, Matthew Cc: Mack, Jarrett; Danna, James

Subject:

RE: Request for Additional Information RE: 120V Inverter LAR from the Electrical Branch Date: Monday, February 07, 2022 11:13:00 AM Attachments: L-2021-LLA-0131 Electrical RAIs final.pdf

Matt,

By letter dated July 21, 2021, as supplemented by letter dated September 22, 2021 (Agencywide Documents Access and Management System (ADAMS) Accession Number ML21202A238 and ML21278A309, respectively), NextEra Energy Seabrook, LLC (NextEra, the licensee) requested changes to the Technical Specifications (TSs) for Renewed Facility Operating License NPF-86 for Seabrook Station, Unit No. 1 (Seabrook). The proposed changes would revise TS 3/4.8.3, Onsite Power Distribution - Operating, by increasing the Allowed Outage Time (AOT) for the 120-volt (V) alternating current (AC) vital instrument panel inverters, establishing a new required action for two inoperable 120 VAC vital instrument panel inverters of the same electrical train and related administrative changes.

The Supplement dated September 22, 2021 superseded the July 21, 2021, application. In reviewing the submitted information, the U.S. Nuclear Regulatory Commission (NRC) staff has determined that additional information is necessary to complete its review.

On January 7, 2022, the NRC staff sent NextEra the DRAFT RAIs to ensure that the questions are understandable, the regulatory basis is clear, there is no proprietary information contained in the RAIs, and to determine if the information was previously docketed. On January 24, 2022, the NRC and NextEra held a clarifying call. During the call, it was decided that the second question needed to be rewritten. This revised version of the DRAFT RAIs were sent to NextEra on February 4, 2022. On February 7, 2022, NextEra notified the staff that no clarification of the revised question was needed and requested a response date of 30 days from the date of this email. The NRC staff informed NextEra that this timeframe is acceptable. The attached is the final version of the RAIs.

These RAIs will be put in ADAMS as a publicly available document.

Justin C. Poole Project Manager NRR/DORL/LPL I U.S. Nuclear Regulatory Commission (301)415-2048

REQUESTS FOR ADDITIONAL INFORMATION (RAIs) REGARDING THE LICENSE AMENDMENT REQUEST TO REVISE TECHNICAL SPECIFICATION 3/4.8.3, ONSITE POWER DISTRIBUTION - OPERATING SEABROOK STATION, UNIT NO. 1 DOCKET NO. 50-443

By application dated July 21, 2021, and as supplemented by letter dated September 22, 2021 (Agencywide Documents Access and Management System (ADAMS) Accession Number ML21202A238 and ML21278A309, respectively), NextEra Energy Seabrook, LLC (NextEra, the licensee) requested changes to the Technical Specifications (TSs) for Renewed Facility Operating License NPF -86 for Seabrook Station, Unit No. 1 (Seabrook). The proposed changes would revise TS 3/4.8.3, Onsite Power Distribution - Operating, by increasing the Allowed Outage Time (AOT) for the 120- volt (V) alternating current (AC) vital instrument panel inverters, establishing a new required action for two inoperable 120 VAC vital instrument panel inverters of the same electrical train and related administrative changes. The Supplement dated September 22, 2021 superseded the July 21, 2021, application.

The NRC staff has determined that the following additional information is needed to complete the review of the Seabrook license amendment request ( LAR) supplement dated September 21, 2021.

Regulatory Requirements and Guidance

The NRC staff used the following regulatory requirements to review the LAR:

Title 10 of the Code of Federal Regulations, Part 50 (10 CFR 50), Section 36, Technical specifications, requires, in part, that the applicants for a license authorizing operation of a production or utilization facility must include in their application proposed TSs. 10 CFR 50.36(c) requires that TS include items in five specific categories related to station operation. These categories are (1) Safety limits, limiting safety system settings, and limiting control settings, (2)

Limiting conditions for operation (LCOs), (3) Surveillance requirements (SRs), (4) Design features, and (5) Administrative controls. The proposed change to the Seabrook TS relates to the LCO category.

10 CFR 50.36(c)(2)(i), in part, stated that LCOs 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, Appendix A, General Design Criterion (GDC) 17, Electric power systems, states, in part:

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 independence, redundancy, and testability to perform their safety functions assuming a single failure.

Provisions 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.

Seabrook TS LCO 3.8.3.1 requires, in part, the following electrical busses to be energized in the specified manner:

c. 120-volt A.C. Vital Panel #1A energized from its associated inverter connected to D.C. Bus #11A,*

d. 120-volt A.C. Vital Panel #1 B energized from its associated inverter connected to D.C. Bus #11 B,*

e. 120-volt A.C. Vital Panel #1 C energized from its associated inverter connected to D.C. Bus #11C,*

f. 120- volt A.C. Vital Panel #1D energized from its associated inverter connected to D.C. Bus #11 D,*

g. 120-volt A.C. Vital Panel #1E energized from its associated inverter connected to D.C. Bus #11A,*

h. 120-volt A.C. Vital Panel #1F energized from its associated inverter connected to D.C. Bus #11 B,*

• Two inverters may be disconnected from their D.C. bus for up to 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> as necessary, for the purpose of performing an equalizing charge on their associated battery bank provided: (1) their vital busses are energized, and (2) the vital busses associated with the other battery bank are energized from their associated inverters and connected to their associated D.C. bus.

Section 2.1, System Design and Operation, of the LAR states:

The 120 Vital AC Instrumentation and Control Power System (120 VAC Vital Instrument System) is composed of six independent AC buses designated as 1A through 1F, each having its own uninterruptible power supply (UPS). The 120 VAC Vital Instrument System is the source of AC power for the reactor protection, reactor control and balance of plant instrument systems that are essential to the operation of the plant during normal operations and postulated accident conditions.

The 120 VAC Vital Instrument System is comprised of the UPS units and the 120-volt vital instrument distribution panels.

Four of the vital UPS units provide separate and independent power supplies to the four NSSS [Nuclear Steam Supply System] instrumentation channels (designated as channels I, II, Ill and IV). These four UPS units are powered either from the 480V distribution system or 125-volt [direct current] DC system (station batteries/chargers) depending on the available 480V bus voltage. The two additional vital UPS units provide redundant power supplies to the balance of plant Train A and Train B vital instrument panels. These two UPS units are normally powered from the 480V system and can also convert 125-volt DC power from station batteries to 120V AC Power. Each vital UPS unit has adequate capacity to carry the associated load continuously.

The UPS units consist of a rectifier section which converts three-phase 460V AC power to a nominal 125 VDC power and an inverter section which inverts the DC power to single phase 120 VAC power

The 120 VAC Vital Instrument System has a normal, emergency and maintenance mode of operation. Circuit breaker lineup, switch position and the supplying source of power are the key factors in determining the operational mode.

• For maintenance purposes, each vital distribution panel is provided with a connection to a non-safety-related 120 VAC supply powered by a diesel backed 460 VAC MCC. When the UPSs need to be isolated, the maintenance supply circuit breaker to the vital distribution panel is closed and the normal circuit breaker is opened. The UPS distribution configuration for NSSS UPS units 1A and 1B (1-EDE-l-1A and 1-EDE-I-1B) can transfer power from the vital instrument bus inverters to the maintenance supply either automatically or manually without interruption to the connecting loads. Presently, when NSSS UPS units 1C and 1D (1-EDE-I-1C and 1-EDE-I-1D) are required to be isolated for maintenance, the normal main circuit breaker must be opened before the maintenance breaker can be closed resulting in a brief connecting load interruption. For balance-of-plant UPS units 1 E and 1 F (1-EDE-I-1E and 1-EDE-I-1F), power transfer from the associated instrument bus inverters to the maintenance supply can be automatic or manual without interruption to the connecting loads.

Seabrook Updated Safety Analysis Report (UFSAR) Table 8.3 -3, Engineered Safety Features, sheet 7 of 9 and Figure 8.3-3, Separation of Instrument and Control Power Sources, show that the UPSs 1A, 1C, and 1E provide 120 VAC power to Channels I and III and Train A instrumentation and the UPSs 1B, 1D, and 1F provides 120 VAC power to Channels II and IV and Train B instrumentation.

NRC Staff RAIs

EEE B RAI - 1

The licensee proposed to revise Seabrook TS 3.8.3.1, ACTION b, by increasing from 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> to 7 days the AOT to reenergize 120 VAC Vital Instrument Panels 1A, 1B 1 C, 1 D, 1 E or 1 F from its associated inverter connected to its associated DC bus.

The staff notes that the LAR did not provide a deterministic justification for the proposed 7-day AOT.

Provide a technical justification for the proposed 7-day AOT extension (actual hours plus margin) based on plant-specific past operating experience and vendor recommendations.

EEEB RAI - 2

The licensee proposed a new TS 3.8.3.1, ACTION d, for the condition of two 120 VAC vital instrument panels of the same electrical train either not energized from their associated inverter or with their inverters not connected to their associated DC bus (i.e., inoperable). The proposed completion time for restoring at least one AC vital panel from its associated inverter connected to its associated DC bus is within 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br />.

The licensee proposed a new TS 3.8.3.1, ACTION d, as follows:

With two A.C. vital panels of the same electrical train either not energized from their associated inverter, or with their inverters not connected to their associated D.C. bus: (1) reenergize both A.C. vital panels within 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> or be in at least HOT STANDBY within the next 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and in COLD SHUTDOWN within the following 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br />; and (2) reenergize at least one A.C. vital panel from its associated inverter connected to its associated D.C. bus within 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> or be in at least HOT STANDBY within the next 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and in COLD SHUTDOWN within the following 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br />.

The staff notes the following:

- A footnote to the LCO 3.8.3.1 denoted by the asterisk next to the DC Bus numbering allows two inverters to be disconnected from their DC bus for the purpose of performing an equalizing charge on their associated battery bank. Thus, the proposed new Action d would apply when two inverters in the same train are not connected to their associated DC supply for reasons other than performing an equalizing charge on their associated battery bank.

- Seabrook TS LCO 3.8.3.1 requires the AC vital panels to be energized from their associated inverters. In the proposed new Action d.2, it appears that one of the AC vital panels would not to be reenergized from its associated inverter connected to its associated DC bus.

This would result in the proposed new Action d not meeting the LCO. The licensee would have to enter LCO 3.0.3 to shut down the reactor for two inoperable AC vital panels of the same train in the proposed new Action d, as it would be the case under the current TS 3.8.3.1.

- The LAR did not appear to provide a plant-specific justification for the 8-hour AOT proposed for the new Action d.

The NRC staff has the following questions:

a) Clarify if the proposed Action d will apply to all three vital AC panels/inverters of the same electrical train.

b) Discuss how the proposed new Action d meet the LCO 3.8.3.1 requirements for the 120- volt AC vital panels in accordance with 10 CFR 50.36(c)(2)(i).

c) Provide a technical justification for the proposed 8-hour AOT for two inoperable inverters in the new Action d based on plant -specific past operating experience and/or timeline for reenergizing an AC vital panel from its associated inverter connected to its associated DC bus.

EEEB RAI - 3

The licensee stated that the enclosure and attachments provided in its supplement dated September 22, 2021, superseded and replaced the corresponding enclosure and attachments of its initial application dated July 21, 2021. Attachment 1, Proposed Technical Specification Pages (Markup), to the enclosure provides revised Seabrook TS pages marked up to show the proposed changes.

The NRC staff notes that Attachment 1 does not show all the proposed changes.

Provide a markup to the TS that shows the proposed 1) deletion of 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> AOT with the associated asterisk and footnote and 2) the proposed 7-day AOT.

EEEB RAI - 4

Section 2.1 of the LAR states:

Should a UPS become unavailable, an alternate supply is available by an automatic/manual transfer switch for 120 VAC instrument busses 1A, 1B, 1E and 1F

For balance-of-plant UPS units 1E and 1F (1-EDE-I-1E and 1-EDE-I-1F), power transfer from the associated instrument bus inverters to the maintenance supply can be automatic or manual without interruption to the connecting loads.

The 120 VAC Vital Instrument System inverters I -EDE-I-IE and I-EDE-I-IF associated with instrument buses IE and IF supply power to balance-of-plant instrumentation. UPS IE, designated for the "A" train, and UPS IF, for the "B" train, derive their AC and DC input power from train "A" and train "B" safety-related power supplies. Each of the two balance of-plant vital instrument buses are provided with a static transfer switch for automatic, fast transfer of these buses to a maintenance supply from a 480/120-volt AC transformer connected to a non-safety-related power source (with a backup power supply from the emergency diesel generator) in the event of unavailability of the associated UPS.

The NRC staff notes that the names of the balance of plant vital instrument buses and associated UPSs and inverters are not consistent within the LAR.

Clarify the names and/or designation of the UPSs, inverters, and vital instrument buses associated with the balance of plant Train A and Train B vital instrument panels.