05000338/LER-2024-001-01, Automatic Reactor Trip Due to PRNI High Negative Rate

Automatic Reactor Trip Due to PRNI High Negative Rate

ML24268A312
Person / Time
Site:	North Anna
Issue date:	09/24/2024
From:	Hilbert L Virginia Electric & Power Co (VEPCO)
To:	Office of Nuclear Reactor Regulation, Document Control Desk
References
24-249A LER 2024-001-01
Download: ML24268A312 (1)

LER-2024-001, Automatic Reactor Trip Due to PRNI High Negative Rate

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(iv)(A), System Actuation
3382024001R01 - NRC Website

text

VIRGINIA ELECTRIC AND POWER COMPANY RICHMOND, VIRGINIA 23261 10CFR50.73 Virginia Electric and Power Company North Anna Power Station 1022 Haley Drive Mineral, Virginia 23117 September 24, 2024 Attention: Document Control Desk U. S. Nuclear Regulatory Commission Washington, DC 20555-0001 Dear Sir or Madam:

Serial No.:

24-249A NAPS:

RAP Docket Nos.: 50-338 License Nos.: NPF-4 Pursuant to 1 0CFR50.73, Virginia Electric and Power Company hereby submits the following Licensee Event Report applicable to North Anna Power Station Unit 1.

Report No. 50-338/2024-001-01 This report has been reviewed by the Facility Safety Review Committee and will be forwarded to the Management Safety Review Committee for its review.

Sincerely, Lisa Hilbert Site Vice President North Anna Power Station Enclosure Commitments contained in this letter: None cc:

United States Nuclear Regulatory Commission Region II Marquis One Tower 245 Peachtree Center Ave., NE, Suite 1200 Atlanta, Georgia 30303-1257 NRC Senior Resident Inspector North Anna Power Station

Abstract

On May 29, 2024, at 0624 hours0.00722 days <br />0.173 hours <br />0.00103 weeks <br />2.37432e-4 months <br /> with Unit 1 in Mode 1, 100% power, an automatic reactor trip occurred due to power range nuclear instrument high negative rate. The cause of the negative rate was due to control rod K4 dropping into the core. Control rod K4 dropped due to a relaxing of pin prongs that caused the Stationary Coil circuit to open. A 4-hour report was made per 10 CFR 50.72(b)(2)(iv)(B) for a Reactor Protection System (RPS) Actuation and an 8-hour report was made per 10 CFR 50.72(b)(3)

(iv)(A) for a valid Engineered Safety Feature actuation for the Auxiliary Feedwater (AFW) Pumps actuating as designed during the event.

Unit 2 was not impacted by this event. This event is reportable per 10 CFR 50.73(a)(2)(iv)(A) for RPS actuation and valid AFW actuation. The health and safety of the public were not affected by this event.

1.0 Description of Event

2. DOCKET NUMBER

3. LER NUMBER I

00338 D

NUMBER NO.

I YEAR SEQUENTIAL REV

~ -I 001 1-0 On May 29, 2024, at 0624 hours0.00722 days <br />0.173 hours <br />0.00103 weeks <br />2.37432e-4 months <br /> with Unit 1 in Mode 1, 100% power, an automatic reactor trip occurred due to power range nuclear instrument (EIIS Component DET, System_ IG) high negative rate. The cause of the negative rate was due to control rod (EIIS Component ROD, System AA) K4 dropping into the core. The Auxiliary Feedwater (AFW) Pumps (EIIS Components P, System BA) actuated as designed during this event. The reactor trip and AFW pumps starting are reportable per 10 CFR 50.73(a)(2)(iv)(A) as System Actuations.

The direct cause of this event was the loss of continuity to the stationary gripper coil for control rod K4. The cause of K4 dropping into the core was a relaxing of the pin prongs resulting in reduced pin spread on the " E" Pin. This resulted in a poor connection on the plug side of the Patch Panel connection inside of containment. The poor connection caused the Stationary Coil circuit to open. This resulted in the Stationary Coil losing its holding current. The Stationary Gripper then opened, dropping K4. K4 dropping created a change in flux that was picked up by nuclear instruments N41 and N43. This satisfied the 2/4 NI High Negative Flux Rate Trip, which opened the Reactor Trip Breakers (EIIS Component BKR, System AA).

2.0 Significant Safety Consequences and Implications No significant safety consequences resulted from this event due to plant equipment performing as designed. The health and safety of the public were not affected by this event.

3.0 Cause of the Event rThe direct cause of this event was the loss of continuity to the stationary gripper coil for control rod K4. The cause of K4 dropping into the core was a relaxing of the pin prongs resulting in reduced pin spread on the " E" Pin. This resulted in a poor connection on the plug side of the JB-672 Patch Panel connection inside of containment. The poor connection caused the Stationary Coil circuit to open.

4.0 Immediate Corrective Action The plug for control rod K4 was replaced.

5.0 Additional Corrective Actions

2. DOCKET NUMBER

3. LER NUMBER I

00338 D

NUMBER NO.

I YEAR SEQUENTIAL REV

~-I 001 1-0 Update 1/2-ECM-1901-01," Disconnecting and Connecting CROM, RPI, and Head Vent Valves and CROM and RPI Resistance Testing," Section 6.5, CROM Coil Resistance Testing, to require manipulating the CROM Connectors during resistance checks to ensure no poor connections exist. This will consist of all the JB-671 and JB-672 Patch Panel CROM Connectors and any Reactor Head CROM Connectors that were disconnected. Manipulating the connectors during resistance checks will result in erratic or high resistance readings for any plugs that are not able to make a good connection. A step will also be added to clean the plug and receptacle as necessary.

6.0 Actions to Prevent Recurrence Engineering to work with Westinghouse to design, procure, and implement a pin spread testing tool for the CROM Patch Panel Connectors for Unit 1 and Unit 2. Update 1/2-ECM-1901-01 to provide guidance for use of these tools prior to reconnecting the CROM Cables.

7.0 Similar Events No similar events have been noted at North Anna.

8.0 Additional Information Unit 2 was not impacted by this event. The health and safety of the public were not affected by this event. Page 3

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