RA-24-0283, Manual Reactor Trip and Auxiliary Feedwater Actuation Due to Water Intrusion

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Manual Reactor Trip and Auxiliary Feedwater Actuation Due to Water Intrusion
ML24330A060
Person / Time
Site: Catawba Duke Energy icon.png
Issue date: 11/25/2024
From: Flippin N
Duke Energy Carolinas
To:
Office of Nuclear Reactor Regulation, Document Control Desk
References
RA-24-0283 LER 024-002-00
Download: ML24330A060 (1)
v • d • e


Text

el_-, DUKE

~ ENERGY~

RA-24-0283 November 25, 2024 U.S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, D.C. 20555

Subject:

Duke Energy Carolinas, LLC Catawba Nuclear Station, Unit 2 Docket No. 50-414 Licensee Event Report (LER) 414/2024-002-00 Nicole Flippin Vice President Catawba Nuclear Station Duke Energy CN01VP I 4800 Concord Road York, SC 29745 o: 803.701.3340 10 CFR 50.73 Pursuant to 10 CFR 50.73(a)(1) and (d), attached is LER 414/2024-002-00, entitled "Unit 2 Manual Reactor Trip and Auxiliary Feedwater Actuation Due to Water Intrusion". This report is being submitted in accordance with 10 CFR 50. 73(a)(2)(iv)(A).

There are no regulatory commitments contained in this letter or its attachment.

This event is considered to be of no significance with respect to the health and safety of the public.

If questions arise regarding this LER, please contact Sherry Andrews of Regulatory Affairs at (803) 701-3424.

Sincerely, Nicole Flippin Vice President, Catawba Nuclear Station Attachment

United States Nuclear Regulatory Commission Page2 November 25, 2024 xc (with attachment):

Laura Dudes Regional Administrator U.S. Nuclear Regulatory Commission - Region II Jack Minzer-Bryant NRG Project Manager (CNS)

U.S. Nuclear Regulatory Commission David Rivard Senior Resident Inspector, Catawba Nuclear Station U.S. Nuclear Regulatory Commission

NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY 0MB: NO. 3150-0104 EXPIRES: 04/30/2027 (04-02-2024)

Estimated burden per response to comply with this mandalofy collection request 80 hours9.259259e-4 days <br />0.0222 hours <br />1.322751e-4 weeks <br />3.044e-5 months <br />. Reported lessons

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LICENSEE EVENT REPORT (LER) learned are inc:orpocated into the licensing process and fed back to industry. Send comments rega*ding burden

  1. ¥~

estimate to the FOIA, Library, and Information Colklctions Branch (T-6 A10M), U.S. Nuclear Regulatory Commission,

(See Page 2 for required number of digits/characters for each block)

Washington, QC 20555--0001, or by email to lnfocollects.Resot.rce@nrc.gov, and the 0MB reviewer at 0MB Office

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of Information and Regulatory Affars, (3150-0104), Attn: Desk Officer for the Nuclea-Regulalofy Commission, 725 (See NUREG-1022, R.3 for instruction and guidance for completing this form 17th Street NW, Washington, QC 20503. The NRC may not conduct or sponsor, and a person is not requred to htt~://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr1022/r3(J respond to, a collection of information unless the document requesting or requiring the collection displays a currently valid 0MB control number.

1. Facility Name IB]

050

2. Docket Number
3. Page Catawba Nuclear Station, Unit 2 00414 1 OF 4 052
4. Title Unit 2 Manual Reactor Trip and Auxiliary Feedwater Actuation Due to Water Intrusion
5. Event Date
6. LER Number
7. Report Date
8. other Facilities Involved Month Day Year Year Sequential Revision Month Day Year Facility Name Docket Number Number No.

050 09 27 2024 2024 00 11 25 24 Facility Name Docket Number 002 -

052

9. Operating Mode
10. Power Level 1

100

11. This Report is Submitted Pursuant to the Requirements of 1 0 CFR §: (Check all that apply) 10 CFR Part 20 20.2203(a)(2)(vi) 10 CFR Part 50
50. 73(a)(2)(ii)(A)
50. 73(a)(2)(viii)(A) 73.1200(a) 20.2201(b) 20.2203(a)(3)(i) 50.36(c)(1 )(i)(A)
50. 73(a)(2)(ii)(B)
50. 73(a)(2)(viii)(B) 73.1200(b) 20.2201(d) 20.2203(a)(3)(ii) 50.36(c)(1 )(ii)(A)
50. 73(a)(2)(iii)
50. 73(a)(2)(ix)(A) 73.1200(c) 20.2203(a)(1) 20.2203(a)(4) 50.36(c)(2)

~ 50. 73(a)(2)(iv)(A)

50. 73(a)(2)(x) 73.1200(d) 20.2203(a)(2)(i) 10 CFR Part 21 50.46(a)(3)(ii)
50. 73(a)(2)(v)(A) 10 CFR Part 73 73.1200(e) 20.2203(a)(2)(ii) 21.2(c) 50.69(g)
50. 73(a)(2)(v)(B) 73.77(a)(1) 73.1200(f) 20.2203(a)(2)(iii)
50. 73(a)(2)(i)(A)
50. 73(a)(2)(v)(C)
73. 77(a)(2)(i) 73.1200(9) 20.2203(a)(2)(iv)
50. 73(a)(2)(i)(B)
50. 73(a)(2)(v)(D)
73. 77(a)(2)(ii) 73.1200(h) 20.2203(a)(2)(v)
50. 73(a)(2)(i)(C)
50. 73(a)(2)(vii)

OTHER (Specify here, in abstract, or NRC 366A).

12. Licensee Contact for this LER Licensee Contact Phone Number (Include area code)

Sherry Andrews, Lead Regulatory Affairs Specialist (803) 701-3424

13. Complete One Line for each Component Failure Described in this Report Cause System Component Manufacturer Reportable to IRIS Cause System Component Manufacturer Reportable to IRIS B

EA SWGR G080 y

14. Supplemental Report Expected Month Day Year

!xi No I

15. Expected Submission Date Yes (If yes, complete 15. Expected Submission Date)
16. Abstract (Limit to 1326 spaces, i.e., approximately 13 single-spaced typewritten lines)

On 9/27/2024 at 0748 EDT, with Unit 2 in Mode 1 at approximately 100% power, the reactor was manually tripped due to a loss of condenser vacuum. The trip was not complicated with all systems responding normally post-trip.

The Unit 2 auxiliary feedwater system started automatically as expected.

During tropical storm Helene, Catawba experienced water intrusion into the 2HTA switchgear room located in the service building. The wind driven rain saturated exposed service building block walls allowing water to migrate into the rooms, resulting in the de-energization of 2HTA which tripped all cooling tower fans on Unit 1 and Unit 2. The loss of all cooling tower fans degraded main condenser vacuum on both units. The Unit 2 reactor was manually tripped due to approaching the low condenser vacuum trip setpoint. Operations was able to stabilize Unit 1 at 32 percent power. This event is being reported pursuant to 10 CFR 50. 73(a)(2)(iv)(A). There was no impact to the health and safety of the public.

NRC FORM 366A (04-02-2024)

U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY 0MB: NO. 3150-0104 EXPIRES: 04/30/2027 LICENSEE EVENT REPORT (LER)

CONTINUATION SHEET (See NUREG-1022, R.3 for instruction and guidance for completing this form http://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr1022/r3Q

1. FACILITY NAME

.--------------,1[R]

050 Catawba Nuclear Station, Unit 2 052 NARRATIVE BACKGROUND Estimated burden per response to comply with this mandatory collection request: 80 hours9.259259e-4 days <br />0.0222 hours <br />1.322751e-4 weeks <br />3.044e-5 months <br />. Reported lessons learned are incorporated into the licensing process and fed back to industry. Send comments regarding burden estimate to the FOIA, Library, and Information Collections Branch (T-6 A 1 OM), U. S.

Nuclear Regulatory Commission, Washington, DC 20555-0001,

or by email to lnfocollects.Resource@nrc.gov, and the 0MB reviewer at: 0MB Office of Information and Regulatory Affairs, (3150-0104), Attn: Desk Officer for the Nuclear Regulatory Commission, 725 17th Street NW, Washington, DC 20503. The NRC may not conduct or sponsor, and a person is not required to respond to, a collection of information unless the document requesting or requiring the collection displays a currently valid 0MB control number.

2. DOCKET NUMBER 00414 3, Lt:K NUMHt:K YEAR SEQUENTIAL

~ NUMBER

-1 002 REV NO.

1-0 The following information is provided to assist readers in understanding the event described in this LER.

Applicable Energy Industry Identification [EIIS] system and component codes are enclosed within brackets.

Catawba Nuclear Station unique system and component identifiers are contained within parentheses.

This event is being reported under the following criterion:

This event was reported to the NRC on September 27, 2024, in Event Notification 57344, as a 4-hour notification under 10 CFR 50.72(b)(2)(iv)(B) for the Unit 2 Reactor Protection System Actuation, and as an 8-hour notification under 1 O CFR 50.72(b)(3)(iv)(A) for the automatic start of the Unit 2 Auxiliary Feedwater system actuation. It is also reportable as a 60-day written report under 10 CFR 50. 73(a)(2)(iv)(A), "Any event or condition that resulted in manual or automatic actuation of any of the systems listed in paragraph (a)(2)(iv)(B)."

The applicable 10 CFR 50.73(a)(2)(iv)(B) systems include the Reactor Protection System and the Auxiliary Feedwater System.

EN 57344 also reported a loss of safety function due to all trains of the Unit 1 Auxiliary Feedwater System were inoperable when the Unit 1 Hotwell Temperature exceeded the operability limit for the system. After additional review, it has been determined that a loss of safety function did not occur as the available Auxiliary Feedwater System trains suction source, at the time, was from the upper surge tanks and the nuclear service water system, which had an acceptable operating temperature. As such, this event is not reportable on Unit 1 per 10 CFR

50. 72(b)(3)(v) or 10 CFR 50. 73(a)(2)(v).

Reactor Protection System [JC] (IPE)

The Reactor Trip System automatically limits reactor operation to within a safe region by shutting down the reactor whenever the limits of the region are approached. Whenever a direct process or calculated variable exceeds a setpoint the reactor will be shutdown in order to protect against either gross damage to fuel cladding or loss of system integrity which could lead to release of radioactive fission products into the containment. The various reactor trip circuits automatically open the reactor trip breakers whenever a condition monitored by the Reactor Trip System reaches a preset level. In addition to the automatic monitoring and actuation of the protection system, a manual actuation circuit is also available to initiate a reactor shutdown. The manual trip consists of two switches (one for Train A and one for train B) in the control room. There are no interlocks that can block this trip.

Auxiliary Feedwater System [BA] (CA)

The Auxiliary Feedwater System is the assured source of feedwater to the steam generators during accident conditions. The CA System is designed to start automatically in the event of loss of offsite electrical power, trip o both main feedwater pumps, safety injection signal, or low-low steam generator water level; any of which may result in, coincide with, or be caused by a reactor trip. The CA System will supply sufficient feedwater to maintain the reactor at hot standby for two hours followed by cooldown of the Reactor Coolant System to the temperature at which the Residual Heat Removal System may be operated.

NRC FORM 366A (04-02-2024)

Page 2

of 4

NRC FORM 366A (04-02-2024)

U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY 0MB: NO. 3150-0104 EXPIRES: 04/30/2027 LICENSEE EVENT REPORT (LER)

CONTINUATION SHEET (See NUREG-1022, R.3 for instruction and guidance for completing this form http://www.nrc.gov/reading-rm/doc-colleclions/nuregs/staff/sr1022/r3D

1. FACILITY NAME

[K) 050 Catawba Nuclear Station, Unit 2 0

052 NARRATIVE Condenser Circulating Water [KE] (RC)

Estimated burden per response to comply with this mandatory collection request: 80 hours9.259259e-4 days <br />0.0222 hours <br />1.322751e-4 weeks <br />3.044e-5 months <br />. Reported lessons learned are incorporated into the licensing process and fed back to industry. Send comments regarding burden estimate to the FOIA, Library, and Information Collections Branch (T-6 A 1 OM), U. S.

Nuclear Regulatory Commission, Washington, DC 20555-0001, or by email to lnfocollects.Resource@nrc.gov, and the 0MB reviewer at: 0MB Office of Information and Regulatory Affairs, (3150-0104), Attn: Desk Officer for the Nuclear Regulatory Commission, 725 17th Street NW, Washington, DC 20503. The NRC may not oonduct or sponsor, and a person is not required to respond to, a collection of information unless the document requesting or requiring the collection displays a currently valid 0MB oontrol number.

2. DOCKET NUMBER YEAR SEQUENTIAL 00414

~ NUMBER

-1 002 REV NO.

I-~

The Condenser Circulating Water System supplies cooling water to the main and feedwater pump turbine condensers to condense the turbine exhaust steam. The rejected heat from the condensers is dissipated to the ambient surroundings by the cooling towers while meeting all applicable chemical and thermal effluent criteria.

Auxiliary Power System [EA] (EPM)

The 13.8kV Normal Auxiliary Power System load center switchgear (HTA) is provided to supply the cooling tower fan motors, and the associated cooling tower loads. The 600-volt Cooling Tower Auxiliary Power System supplies power to the cooling tower fan motors and auxiliaries via the cooling tower motor control centers. This 600VAC system is supplied from the 13.8kV Normal Auxiliary Power System.

EVENT DESCRIPTION The 1 HT A bus is normally powered from the 1 A train of offsite power and the 2HT A bus from the 2A train of offsite power. The 1 HTA and 2HTA buses can be electrically cross connected so that either Unit can power the buses. In preparation for planned work during refueling outage C1 R28, Catawba had aligned the 2A train of offsite power to supply 1 HTA via the electrical cross connection with 2HT A. This resulted in all Unit 1 and Unit 2 cooling tower fans being powered via 2HT A.

During Tropical Storm Helene, Catawba experienced water intrusion into the 2HTA switchgear room located in the service building due to wind driven rain. The wind driven rain saturated exposed service building block walls and saturated the block wall allowing water to migrate vertically downward into the 2HTA switchgear room. The water intrusion resulted in the de-energization of 2HTA which tripped all the cooling tower fans on Unit 1 and Unit 2. Operations entered the off-normal procedures for Loss of Condenser Vacuum for both Units. Operations manually tripped Unit 2 reactor due to approaching the low condenser vacuum trip setpoint. Because Unit 1 was at a lower starting power level due to end of cycle coast down prior to outage C1 R28, Operators were able to stabilize Unit 1 at approximately 32% power.

CAUSAL FACTORS Field walkdowns occurring after the event identified the direct cause was associated with water intrusion into 2HTA switchgear room during Tropical Storm Helene. The wind driven rain saturated exposed service building block walls allowing water to migrate vertically downward into the 2HTA switchgear room. The water intrusion resulted in the de-energization of 2HTA which tripped all the cooling tower fans on Unit 1 and Unit 2.

NRG FORM 366A (04-02-2024)

Page 3

of 4

NRC FORM 366A (04-02-2024)

U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY 0MB: NO. 3150-0104 EXPIRES: 04/30/2027 LICENSEE EVENT REPORT (LER)

CONTINUATION SHEET (See NUREG-1022, R.3 for instruction and guidance for completing this form http://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr1022/r3D

1. FACILITY NAME r-------------,1[K]

050 Catawba Nuclear Station, Unit 2 052 NARRATIVE CORRECTIVE ACTIONS Immediate:

Estimated burden per response to comply with this mandatory collection request: 80 hours9.259259e-4 days <br />0.0222 hours <br />1.322751e-4 weeks <br />3.044e-5 months <br />. Reported lessons learned are incorporated into the licensing process and fed back to industry. Send comments regarding burden estimate to the FOIA, Library, and lnfomiation Collections Branch (T-6 A10M), U.S.

Nuclear Regulatory Commission, Washington, DC 20555-0001, or by email to lnfooollects.Resource@nrc.gov, and the 0MB reviewer at: 0MB Office of Information and Regulatory Affairs, (3150-0104), Attn: Desk Officer for the Nuclear Regulatory Commission, 725 17th Street NW, Washington, DC 20503. The NRG may not oonduct or sponsor, and a person is not required to respond to, a oollection of infom,ation unless the document requesting or requiring the collection displays a currenUy valid 0MB oontrol number.

2. DOCKET NUMBER 00414
3. Lt:.K NUMtst:.K YEAR SEQUENTIAL

~ NUMBER

-1 002 REV NO.

I-~

1. Power was restored to Unit 2 HTA, and Unit 2 was restored to full power operation
2. Temporary covers were installed over Unit 1 and Unit 2 HTA as an interim measure until permanent actions are implemented to prevent future water intrusion Planned:
1. Permanent actions will be identified and implemented to prevent future water intrusion into the Units 1 HTA and 2HTA service building locations SAFETY ANALYSIS At 07 48 [EDT] hours on October 27, 2024, with Unit 2 in Mode 1 at approximately 100 percent power, water intrusion during heavy rainfall caused 13.8kv switchgear 2HTA to deenergize, causing the loss of all Unit 1 and Unit 2 recirculated cooling water fans. Subsequently, Unit 2 was manually tripped by operators due to a loss of condenser vacuum. This resulted in an automatic actuation of the Unit 2 auxiliary feedwater system. The Unit 2 reactor trip did not impact the health and safety of the public and there was no safety or radiological consequence to this event. The trip was uncomplicated with all systems responding normally post-trip. No equipment deficiencies were observed during the reactor trip.

This event did not result in a Safety System Functional Failure. All safety systems were capable of performing their safety function at all times during this event.

ADDITIONAL INFORMATION There have been no previous Licensee Event Reports at Catawba Nuclear Station in the last three years with the same causal factor as this issue.

NRG FORM 366A (04-02-2024)

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