1CAN022503, Response to Request for Additional Information - Request for Review and Approval of Changes to the Safety Analysis Report and to a Confirmatory Order Clarifying an Alternate Means of Compliance for Pressurizer Heaters Emerge

Response to Request for Additional Information - Request for Review and Approval of Changes to the Safety Analysis Report and to a Confirmatory Order Clarifying an Alternate Means of Compliance for Pressurizer Heaters Emerge

ML25057A318
Person / Time
Site:	Arkansas Nuclear
Issue date:	02/26/2025
From:	Couture P Entergy Operations
To:	Office of Nuclear Reactor Regulation, Document Control Desk
References
1CAN022503, EPID L-2024-LLA-0092
Download: ML25057A318 (1)

Text

Entergy Operations, Inc., 1340 Echelon Parkway, Jackson, MS 39213 1CAN022503 10 CFR 50.90 February 26, 2025 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, DC 20555-0001

Subject:

Response to Request for Additional Information - Request for Review and Approval of Changes to the Safety Analysis Report and to a Confirmatory Order Clarifying an Alternate Means of Compliance for Pressurizer Heaters Emergency Power Supply Arkansas Nuclear One - Unit 1 NRC Docket Nos. 50-313 Renewed Facility Operating License No. DPR-51

References:

1. Entergy letter to NRC, "Request for Review and Approval of Changes to the Safety Analysis Report and to a Confirmatory Order Clarifying an Alternate Means of Compliance for Pressurizer Heaters Emergency Power Supply,"

(ADAMS Accession No. ML24184B775), (1CAN072401), dated July 2, 2024.

2. NRC (Dennis Galvin) electronic correspondence to Entergy (Riley Keele, Jr.),

"Arkansas Nuclear 1 - Request for Additional Information - Request for Review and Approval Changes to SAR and to a Confirmatory Order - PZR HTR Emergency Power Supply (EPID L-2024-LLA-0092," (ADAMS Accession No. ML25029A006), (1CNA012502), dated January 28, 2025.

Pursuant to 10 CFR 50.90, Entergy Operations, Inc. (Entergy), requested an amendment to the Renewed Facility Operating License Number DPR-51 for Arkansas Nuclear One, Unit 1 (ANO-1) (Reference 1). Entergy requested the Nuclear Regulatory Commissions (NRC's) review and approval of a change to the ANO-1 Safety Analysis Report (SAR) and to the Confirmatory Order to implement all "Category A" lessons learned requirements by January 31, 1980, for ANO-1. The changes address manual actions outside the control room to restore emergency power to the pressurizer heaters. These actions are required due to the plant's design.

Phil Couture Senior Manager Fleet Regulatory Assurance - Licensing Tel 601-368-5102

1CAN022503 Page 2 of 2 The NRC staff provided Entergy a Request for Additional Information (RAI) in Reference 2.

Enclosed is the response to the RAI.

This letter contains no new regulatory commitments.

If there are any questions or if additional information is needed, please contact Riley Keele, Manager, Regulatory Assurance, Arkansas Nuclear One, at 479-858-7826.

I declare under penalty of perjury that the foregoing is true and correct. Executed on February 26, 2025.

Respectfully, Phil Couture PC/rwc

Enclosure:

Response to Request for Additional Information

Attachment:

Single line description of the ANO-1 Electrical Distribution System

- For Information Only cc:

NRC Region IV Regional Administrator NRC Senior Resident Inspector - Arkansas Nuclear One NRC Project Manager - Arkansas Nuclear One Digitally signed by Philip Couture DN: cn=Philip Couture, c=US, o=Entergy, ou=Regulatory Assurance, email=pcoutur@entergy.com Date: 2025.02.26 07:39:14 -06'00' Philip Couture

ENCLOSURE 1CAN022503 RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION

1CAN022503 Enclosure Page 1 of 7 RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION

=

Background===

By application dated July 2, 2024 (Agencywide Documents Access and Management System (ADAMS) Accession Number ML24184B775 Entergy Operations, Inc. (Entergy, the licensee) requested an amendment to the Renewed Facility Operating License Number DPR-51 for Arkansas Nuclear One, Unit 1 (ANO-1). The proposed changes would modify the ANO-1 Safety Analysis Report (SAR) and the Confirmatory Order to implement all Category A lessons learned requirements by January 31, 1980, for ANO-1. The proposed changes would add to the SAR and the confirmatory order statements for performing manual actions at 120 VAC instrument panels Y01 and Y02 outside the control room to restore power to the pressurizer low-low level interlock.

ANO-1 SAR section 4.2.4.4, "Pressurizer Heaters," states Each diesel generator [DG]

emergency bus supplies emergency power to 168 kW [kilowatts] of pressurizer heaters. Two separate sets of heaters totaling 84 kW each are supplied by the diesel generators. The remaining 84 kW is powered from a swing bus which can be supplied by either diesel generator.

This ensures emergency power redundancy to sufficient heater capacity to establish and maintain pressure control at hot standby during a loss of offsite power [LOOP].

ANO-1 SAR, section 8.3.1.1.4, "480-Volt Auxiliary System," states "As a result of NUREG-0578, Item 2.1.1, an additional 42 kW of pressurizer heater capacity was added. These heaters are powered from the 480-volt swing bus using a safety grade breaker."

Technical Specification (TS) 3.4.9, "Pressurizer," Limiting Condition of Operation (LCO) requires a minimum of 126 kW of Engineered Safeguards (ES) bus powered pressurizer heaters to be operable in Modes 1-3.

Regulatory Basis The staff applied the following NRC regulations to review the license amendment request (LAR):

Title 10 of the Code of Federal Regulations (10 CFR) Part 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 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.

1CAN022503 Enclosure Page 2 of 7 The staff used the following NRC guidance to review the LAR:

NUREG-0737, Clarification of TMI Action Plan Requirements," section II.E.3.1, "Emergency Power Supply for Pressurizer Heaters," provides positions and clarifications to the recommendations in section 2.1.1 of NUREG-0578. The positions and clarifications NUREG-0737, section II.E.3.1 are as follows:

Positions Consistent with satisfying the requirements of General Design Criteria 10 ["Reactor design"], 14

["Reactor coolant pressure boundary"], 15 ["Reactor coolant system design"], 17 ["Electric power systems"], and 20 ["Protection systems functions"] of Appendix A to 10 CFR Part 50 for the event of loss of offsite power, the following positions shall be implemented:

The pressurizer heater power supply design shall provide the capability to supply, from either the offsite power source or the emergency power source (when offsite power is not available), a predetermined number of pressurizer heaters and associated controls necessary to establish and maintain natural circulation at hot standby conditions. The required heaters and their controls shall be connected to the emergency buses in a manner that will provide redundant power supply capability.

Procedures and training shall be established to make the operator aware of when and how the required pressurizer heaters shall be connected to the emergency buses. If required, the procedures shall identify under what conditions selected emergency loads can be shed from the emergency power source to provide sufficient capacity for the connection of the pressurizer heaters.

The time required to accomplish the connection of the preselected pressurizer heater to the emergency buses shall be consistent with the timely initiation and maintenance of natural circulation conditions.

Pressurizer heater motive and control power interfaces with the emergency buses shall be accomplished through devices that have been qualified in accordance with safety-grade requirements.

NUREG-0737, section II.E.3.1 provides the following clarifications to the recommendations in section 2.1.1 of NUREG-0578.

Clarifications:

(1) Redundant heater capacity must be provided, and each redundant heater or group of heaters should have access to only one Class 1E division power supply.

(2) The number of heaters required to have access to each emergency power source is that number required to maintain natural circulation in the hot standby condition.

1CAN022503 Enclosure Page 3 of 7 (3) The power sources need not necessarily have the capacity to provide power to the heaters concurrently with the loads required for loss-of-coolant accident.

(4) Any changeover of the heaters from normal offsite power to emergency onsite power is to be accomplished manually in the control room.

(5) In establishing procedure to manually load the pressurizer heaters onto the emergency power sources, careful consideration must be given to:

(a) which ESF loads may be appropriately shed for a given situation.

(b) reset of the safety injection actuation signal to permit the operation of the heaters; and (c) instrumentation and criteria for operator use to prevent overloading a diesel generator.

(6) The Class 1E interfaces for main power and control power are to be protected by safety grade circuit breakers (see also Regulatory Guide 1.75).

(7) Being non-Class 1E loads, the pressurizer heaters must be automatically shed from the emergency power sources upon the occurrence of a safety injection actuation signal (see item 5.b. above).

Issue:

In the LAR, the staff notes that the 84-kW of pressurizer heaters on the swing bus, which includes the remaining 42-kW for a redundant group of heaters, and the pressurizer low-low level interlock, which permits the operation of the heaters, have access to both DGs even if its not simultaneously. Also, if the 480-volt swing bus or the 120-volt bus feeding the low-low level interlock fails, the required 126-kW pressurizer heater capacity in each redundant group would not be available. Furthermore, it appears that the safety classification of the circuit breakers used to power the pressurizers from the trains 480-volt buses and the low-low level interlock from the 12-volt bus Y02 are not provided in the SAR.

Question 1

1. Explain how a redundant group of pressurizer heaters that consist of 84 kW on a train and 42 KW on the swing bus has access to only one Class 1E division power supply that satisfies NUREG-0737, section II.E.3.1, clarifications (1) and (2).

Response

As noted by the NRC, NUREG-0737, Recommendation II.E.3.1, Clarifications (1) and (2) state that:

(1) Redundant heater capacity must be provided, and each redundant heater or group of heaters should have access to only one Class 1E division power supply.

1CAN022503 Enclosure Page 4 of 7 (2) The number of heaters required to have access to each emergency power source is that number required to maintain natural circulation in the hot standby condition.

Following the 1979 TMI event, Babcock & Wilcox (B&W) determined that 126 kW of pressurizer heater capacity was necessary within 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> following the loss of offsite power to assure proper control for natural circulation.

In Reference 1, ANO committed to provide the capability to power 126 kW of pressurizer heater capacity from redundant emergency power sources for Unit 1. The power source alone would be safety grade with appropriate qualified, safety grade interface devices to isolate the remainder of the non-safety grade system.

Since the receipt of the Reference 2 letter (transmitting NUREG-0578), ANO reviewed the NRCs additional clarifications for compliance with NUREG-0578 requirements. Based on the review of Reference 2, specifically Item 2.1.1, "Emergency Power Supply Pressurizer Heaters,"

Entergy revised Reference 1. It should be noted that the NRC position provided in NUREG-0578, Item 2.1.1 is the same as presented in NUREG-0737, Item II.E.3.1, Clarifications 1 and 2.

ANO-1 was originally designed with two separate sets of heaters totaling 84 kW each supplied by the diesel generators. One of the revisions to Reference 1 was related to providing emergency power to the pressurizer heaters. ANO-1 decided to power the required additional 42 kW of heaters from the "swing bus" (can be connected to either diesel generator, separately) and energized manually from the control room (Reference 3). See ANO-1 Safety Analysis Report (SAR) Section 8.3.1.1.4.

The current configuration of emergency powered pressurizer heaters includes 84 kW supplied by #1 Emergency Diesel Generator (EDG), a separate set of 84 kW heaters supplied by

1. 2 EDG, and another set of 84 kW heaters powered from the safety-related "swing bus" (which includes the required 42 kW). The "swing bus" cannot be simultaneously connected to both Engineering Safeguard (ES) buses supplied by the EDGs. If the "swing bus" is aligned to be supplied from #1 EDG, there is a total of 168 kW of emergency powered pressurizer heaters available independent of the #2 EDG train. Likewise, if the "swing bus" is aligned to be supplied from #2 EDG, 168 kW of emergency powered pressurizer heaters are available independent of

1. 1 EDG train. This ensures there is > 126 kW of emergency powered pressurizer heaters available as required by ANO-1 Technical Specification (TS) if either EDG is out of service for any reason.

The NRC issued a Confirmatory Order to implement all Category A lessons learned requirements by January 31, 1980, for ANO-1 in Reference 4.

Based upon the review of Reference 3, the NRC concluded that ANO was in compliance with the emergency power supply requirements for the pressurizer heaters as outlined in NUREG-0578 (Reference 5, Enclosure 1).

In accordance with 10 CFR 50.54(f), the NRC requested licensees to furnish confirmation that the implementation dates included in the NUREG-0737 would be met. Reference 6 provides the requested information for ANO.

1CAN022503 Enclosure Page 5 of 7 For ANO-1, Item II.E.3.1, the response provided in Reference 7 states:

As a result of NUREG-0578, item 2.1.1, AP&L installed an additional 42 KW of pressurizer heater capacity. The pressurizer heaters, which are powered from the Engineered Safeguards (ES) buses, are now capable of providing 126 KW of pressurizer heater capacity from either ES bus. The additional heaters are powered from the 480 volt swing bus using a qualified combination starter of the circuit breaker type. This circuit is controlled from the control room by means of an on-off switch and is not tripped on ESAS but on pressurizer low level. This design is consistent with similar application at ANO-1. It also should be noted that ANO-1 was not designed to meet Reg.

Guide 1.75.

Reference 6 also required the TSs be revised for Item 2.1.1. In letter dated July 2, 1980, the NRC provided model TSs for NUREG-0578 items. One of the model TS was for Item 2.1.1 (Reference 8). The ANO-1 TSs were amended via Reference 9 to include the following specification:

The reactor shall not be made critical until at least 2 of the 3 emergency-powered pressurizer heater groups are operable. With less than 2 of the 3 required heater groups operable, restore the required heater groups to operable status within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />. If the required heater groups are not restored to operable status within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />, be in hot shutdown within the following 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />.

This requirement remains as an ANO-1 TS requirement (Reference 10).

Based on the discussion provided above, the ANO-1 emergency power sources for the pressurizer heaters are compliant with NUREG-0578, Item 2.1.1 and therefore, NUREG-0737, Recommendation II.E.3.1, Clarifications (1) and (2).

2. Provide the safety classification of the circuit breakers that are used to power the pressurizer heaters and the low-low level interlock from the Class 1E 480-volt buses and 120-volt Y2 to satisfy NUREG-0737, section II.E.3.1, clarification (6).

Response

As noted by the NRC, NUREG-0737, Recommendation II.E.3.1, Clarification (6) states that the Class 1E interfaces for main power and control power are to be protected by safety-grade circuit breakers. This is the same as the NRC's position 4 of NUREG-0578, Item 2.1.1.

A single-line depiction of the ANO-1 electrical power distribution system is attached for reference. As shown in the attachment, the electrical power distribution systems are divided by train (red and green). As noted above, the emergency power source for the pressurizer heaters for ANO-1 was implemented in accordance with NUREG-0578, Item 2.1.1.

As described in SAR Section 8.3.1.1.4, the two load centers, which supply ES (vital) loads (B5 and B6), have two tie breakers between buses. The engineered safeguards 480-volt load

1CAN022503 Enclosure Page 6 of 7 centers (vital buses) are located within a Class 1 structure (Seismic Category 1) area to minimize exposure to mechanical, fire, and water damage. This equipment is properly coordinated electrically to permit safe operation of the equipment under normal and short circuit conditions.

The main incoming breakers and motor starter breakers of the load centers can be controlled from the control room and the switchgear. This is also true of all the load center crosstie breakers except the B2-B7 crosstie (non-safety) which can only be operated at the switchgear.

The ES 480-volt distribution equipment is designed to meet the seismic requirements for Class 1E electric equipment as discussed in ANO-1 SAR Section 5.1. All load center transformers, load center buses, and motor control center buses have adequate capacity to supply the momentary and continuous loads connected to the 480-volt buses.

Specifically, the 84-kW red train powered pressurizer heaters are connected to the vital safety-related bus B-51 through breaker B-5144. The 84-kW green train powered pressurizer heaters are connected vital safety-related bus B61 through breaker B-6144.

The "swing bus", Bus B-56, receives its power from either EDG-backed ES 480 VAC bus (manually selected by Operations from the Control Room), which provides power to an additional 84 kW of pressurizer heaters (including the required 42 kW).

All the breakers used to power the pressurizer heaters are safety-related.

The power source for the red train 120-volt vital AC distribution panel Y-01 is from breaker B-5143B. The green train 120V vital AC distribution panel power source is from breaker B-6143B. Both breakers are safety related.

The crosstie breakers between Y-01 and Y-02, Y-01-24/CB and Y-01-52/CB, are safety-related.

Based on the discussion above, the ANO-1 emergency power sources for the pressurizer heaters are compliant with NUREG-0737, Recommendation II.E.3.1, Clarification (6).

References

1. Arkansas Power & Light Company (now Entergy) letter to the Nuclear Regulatory Commission (NRC), "Lessons Learned Task Force Recommendations," ADAMS Accession No. ML19275A856), dated October 17, 1979.

2. NRC to All Operating Nuclear Power Plants, "Discussion of Lessons Learned Short Term Requirements," (ADAMS Accession No. ML112990312), dated October 30, 1979.

3. Entergy letter to NRC, "Lessons Learned Task Force Short-Term Recommendations,"

(ADAMS Accession No. ML19250C346), dated November 20, 1979.

1CAN022503 Enclosure Page 7 of 7

4. NRC letter to Entergy, "Confirmatory Order, Order Confirms Your Commitment as Stated in Your Letters to Implement All Category A Lessons Learned Requirements Prior to Plant Operations After 1/31/80," ADAMS Accession Number ML021220215, (1CNA018003), dated January 2, 1980.

5. NRC letter to Entergy, (ADAMS Accession No. ML19309B770, dated March 10, 1980.

6. NRC letter to All Licensees of Operating Plants and Applicants for Operating Licenses and Holders of Construction Permits, "Post TMI-Requirements," (ADAMS Accession No. ML082970268), dated October 31, 1980.

7. Entergy letter to NRC, "NUREG-0737," (ADAMS Accession No. ML19340E088), dated December 31, 1980.

8. NRC letter to All Pressurized Water Reactor Licensees, (ADAMS Accession No. ML093430163), dated July 2, 1980.

9. NRC letter to Entergy, (ADAMS Accession No. ML021220268), dated February 2, 1980.

10. Arkansas Nuclear One, Unit 1 Technical Specification 3.4.9, "Pressurizer," ACTION C, Amendment 254.

Enclosure, Attachment 1CAN022503 Single line description of the ANO-1 Electrical Distribution System For Information Only

1CAN022503 Enclosure, Attachment Page 1 of 2 Red Train 6900 VAC Green Train 6900 VAC Green Train 4160 Volt Vital AC Green Train 4160 Volt Non-Vital AC Green Train 480 Volt Vital AC (contd on next page)

Red Train 480 Volt Vital AC (contd on next page)

Red Train 4160 Volt Non-Vital AC Red Train 4160 Volt Vital AC

1CAN022503 Enclosure, Attachment Page 2 of 2 Red Train 480 Volt Vital AC Green Train 480 Volt Vital AC Red Train Pzr Htr Proportional Bank #1 B-5144 Green Train Pzr Htr Proportional Bank #1 B-6144 Red Train 120 Volt Vital AC Panel Y01 Green Train 120 Volt Vital AC Panel Y02 (Pzr Htr Interlock Pwr)

Pzr Htr Group 5 from B56 swing bus B-5663