05000338/LER-2022-001-01, Automatic Reactor Trip During Control Rod Operability Testing
| ML22270A020 | |
| Person / Time | |
|---|---|
| Site: | North Anna  |
| Issue date: | 09/06/2022 |
| From: | Hilbert L Virginia Electric & Power Co (VEPCO) |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| 22-133A LER 2022-001-01 | |
| Download: ML22270A020 (4) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 3382022001R01 - NRC Website | |
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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 6, 2022 Attention: Document Control Desk U. S. Nuclear Regulatory Commission Washington, DC 20555-0001
Dear Sir or Madam:
Serial No.:
22-133A NAPS:
CNC Docket Nos.: 50-338 License Nos.: NPF-4 Pursuant to 10CFR50.73, Virginia Electric and Power Company hereby submits the following Licensee Event Report applicable to North Anna Power Station Unit 1.
Report No. 50-338/2022-001-01 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: /J /)
~-CtWJr Lisa Hilbert Site Vice President North Anna Power Station Enclosure Cor:nmitments contained in this letter: None cc:... L.Jnited States Nu9lear 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 April 14, 2022, at 0928 hours0.0107 days <br />0.258 hours <br />0.00153 weeks <br />3.53104e-4 months <br /> with Unit 1 in Mode 1, 100 percent power, an automatic reactor trip occurred during the performance of the control rod operability periodic test. The reactor trip occurred during the manipulation of the rod control selector switch as part of the rod operability testing. A 4-hour and 8-hour non-emergency report was made per 10 CFR 50. 72(8)
(2)(iv)(B) for RPS actuation (trip) and 10 CFR 50.72(b)(3)(iv)(A) for a valid actuation of an ESF system, respectively.
The cause of the event was inadequate current to the Shutdown Bank "B" Group 2 rods via a failed 1/0 AC Amplifier card.
I Unit 2 continued to operate at 99 percent power, Mode 1, during the event. The health and safety of the public were not affected by this event.
This event is reportable in accordance with 10 CFR 50.73(a)(2)(iv)(A) for RPS actuation (trip) and a valid actuation of the auxiliary feedwater system.
Plant Operating Conditions Prior to the Event Unit 1 - Mode 1, 100 percent Rated Thermal Power Unit 2 - Mode 1, 99 percent Rated Thermal Power
1.0 Description of Event
On April 14, 2022, at 0928 hours0.0107 days <br />0.258 hours <br />0.00153 weeks <br />3.53104e-4 months <br /> with Unit 1 in Mode 1, 100 percent power, an automatic reactor trip occurred during the performance of the control rod operability periodic test due to Power Range High Negative Flux Rate. The reactor trip occurred during the manipulation of the rod control selector switch (EIIS Component HS, System AA) as part of the rod operability testing. Shutdown Bank "B" Group 2 rods (EIIS Component ROD, System AA) fell into the core during the performance of the control rod operability periodic test which caused the Power Range High Negative Flux Rate.
A 4-hour and 8-hour non-emergency report was made per 10 CFR 50.72(b)(2)(iv)(B) for RPS actuation (trip) and 10 CFR 50.72(b)(3)(iv)(A) for a valid actuation of an ESF system, respectively.
Following the Unit 1 trip, the turbine drain valves 1-SD-MOV-102A/B/C/D (EIIS Component 20, System TF) opened then repeatedly cycled closed. The MOV's were deenergized in the Open position by opening the associated breakers and a Condition Report was submitted. Additionally, one of the two Intermediate Range Nuclear Instruments (NI), N-36 (EIIS Component DET, System JG), was found to be undercompensated during the reactor trip.
2.0 Significant Safety Consequences and Implications
No significant safety consequences resulted from this event. During this time frame, North Anna Unit 2 operated at 99 percent power. The health and safety of the public were not affected by this event.
3.0 Cause of the Event
The Shutdown Bank "B" (SBB) Group 2 rods dropping into the core caused a Power Range High Negative Flux Rate.
Testing by the Original Equipment Manufacturer (OEM), Westinghouse, has verified that the cause of the dropped rods was inadequate current to the Shutdown Bank "B" Group 2 rods via a failed 1/0 AC Amplifier card in the Logic Cabinet.
The failure on the 1/0 A813 Amplifier card caused stationary and movable zero current orders to the SBB Group 2 coils at the same time_ The resulting failure provided reduced holding current to both coils to prevent dropping the rods. An additional failure on the card caused a Multiplexing Alarm, which resulted in the reduced holding current dividing between two groups of rods; the selected (SBB Group 2) and previously selected banks (CBS Group 2). This resulted in minimal current being applied to the movable coils and thus dropped the SBB Group 2 rods. Additional testing will be performed by the OEM to identify the subcomponent(s) that caused the failure of the 1/0 A813 Amplifier card.
4.0 Immediate Corrective Action
The immediate corrective action was to replace the failed 1/0 Amplifier card as well as several other cards initially identified during troubleshooting.
5.0 Additional Corrective Actions
Perform an evaluation to decrease the frequency of the Rod Operability Periodic testing from a Fleet perspective to have less wear on the Rod Control System and an increase in system reliability.
A work order was issued to address the relay that was found to be mechanically bound resulting in the 1-SD-MOV-102A/
B/C/D valves cycling. Work and associated testing were completed satisfactorily.
Compensating voltages were adjusted for the N-36 Intermediate Range Nuclear Instrumentation satisfactorily.
6.0 Actions to Prevent Recurrence After the vendor provides data regarding the failed subcomponent on the 1/0 AC Amplifier Card (A813), follow on actions will be created to address vulnerabilities identified in Rod Control System. This will include Work Orders and new Preventative Maintenance activities as appropriate for time-based replacements.
7.0 Similar Events
A review of internal operating experience was performed, and one similar event was identified:
On August 27, 1996, North Anna Unit 1 experienced an automatic reactor trip from 100 percent power with the initiating signal being "Hi Flux Rate - Reactor Trip" during Rod Operability testing when the Operator at the Controls started to insert Control Bank "B." Multiple rods in Control Bank "B" Group 2 fell into the core. The cause was a faulty input/output isolation amplifier card in the Control Rod Drive System which failed to supply a full current - stationary current order to Control Bank "B" Group 2.
8.0 Additional Information
Unit 2 continued to operate at 99 percent power, Mode 1 during this event.
There were no releases of radioactive materials, radiation exposures or personnel injuries associated with this event. Page 3
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