05000313/LER-2021-002, Automatic Reactor Trip Due to High Reactor Coolant System Pressure
| ML22027A731 | |
| Person / Time | |
|---|---|
| Site: | Arkansas Nuclear  |
| Issue date: | 01/27/2022 |
| From: | Keele R Entergy Operations |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| 1CAN012202 LER 2021-002-00 | |
| Download: ML22027A731 (6) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 3132021002R00 - NRC Website | |
text
-~ Entergy 1CAN012202 January 27, 2022 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, DC 20555-0001 Entergy Operations, Inc.
1448 S.R. 333 Russellville, AR 72802 Tel 479-858-7826 Riley D. Keele, Jr.
Manager, Regulatory Assurance Arkansas Nuclear One 10 CFR 50.73
Subject:
Licensee Event Report 50-313/2021-002-00, Automatic Reactor Trip Due to High Reactor Coolant System Pressure Arkansas Nuclear One - Unit 1 NRC Docket No. 50-313 Renewed Facility Operating License No. DPR-51 Entergy Operations, Inc. (Entergy) submits the enclosed Licensee Event Report (LER) 50-313/2021-002-00 for Arkansas Nuclear One, Unit 1. This event is reportable in accordance with 10 CFR 50.73(a)(2)(iv)(A) as any event or condition that resulted in manual or automatic actuation of the Reactor Protection System (RPS). The LER describes an Automatic Reactor Trip Due to High Reactor Coolant System Pressure which occurred on November 29, 2021.
This letter contains no new commitments and no revisions to existing commitments.
Should you have any questions concerning this issue, please contact Riley D. Keele Jr.,
Manager Regulatory Assurance, at 4 79-858-7826.
Respectfully, R~~i~*
RDK/ble Attachment: Licensee Event Report 50-313/2021-002-00
1CAN012202 Page 2 of 2 cc:
NRC Region IV Regional Administrator NRC Senior Resident Inspector - Arkansas Nuclear One NRC Project Manager - Arkansas Nuclear One Designated Arkansas State Official
Attachment to 1CAN012202 Licensee Event Report 50-313/2021-002-00
Abstract
On November 29, 2021, at 1458 Central Standard Time (CST), while operating in Mode 1 at 100% power, Arkansas Nuclear One, Unit 1, (ANO-1) automatically tripped due to high Reactor Coolant System pressure following a Main Feedwater System transient. All control rods fully inserted and all systems responded as designed. The plant was stabilized in Mode 3 (Hot Standby).
The cause of the Main Feedwater System transient was the failure of the A MFP High Pressure (HP) governor to respond to lowering A MFP speed. The initiating event was a failure of the A MFP LP governor servo drive and actuator. When the LP governor servo drive failed, the HP governor did not respond to restore A MFP speed.
Proper program values had not been input in the HP governor controller during previous maintenance in 2015. The HP governor failure to respond resulted in underfeeding the A Steam Generator and an automatic reactor trip due to high Reactor Coolant System pressure.
PLANT STATUS Arkansas Nuclear One, Unit 1, (ANO-1) was operating at 100% rated thermal power. There were no other structures, systems, or components (SSCs) that were inoperable at the time that contributed to the event.
EVENT DESCRIPTION
On November 29, 2021, at 1458 CST, ANO-1 automatically tripped due to high Reactor Coolant System (RCS) (AB) pressure following a Main Feedwater System (SJ) transient. The transient was initiated by failure of the A Main Feedwater Pump (MFP) (JK) to maintain proper speed and a subsequent underfeed of the A Steam Generator (AD).
The plant was stabilized in MODE 3 (Hot Standby) by maintaining pressure and temperature with Main Feedwater and steaming to the Main Condenser (SG). No radiological releases occurred due to this event.
This event was reported under 10 CFR 50.72(b)(2)(iv)(B) and 10 CFR 50.72(b)(3)(iv)(A) for the Reactor Protection System (RPS) (JC) actuation (EN 55614).
This report is made pursuant to 10 CFR 50.73(a)(2)(iv)(A), any event or condition that resulted in manual or automatic actuation of the Reactor Protection System.
SAFETY ASSESSMENT
The automatic reactor trip was due to high RCS pressure caused by the Main Feedwater System transient. Following the reactor trip, the Main Feedwater system (MFW) (SJ) responded properly and supplied feedwater to both Steam Generators (SG) (AD). This allowed for the MFW system to provide normal post trip heat removal via the SGs and did not result in actual consequences to safety of the general public, nuclear safety, industrial safety, or radiological safety.
The safety significance of this event is determined to be low.
EVENT CAUSE(S)
The cause for the A MFP lowering speed was a failure of the low pressure (LP) governor servo drive and actuator (65).
This was the initiating event.
During normal plant operation, the HP governor (JK) should sense lowering MFP speed and restore it to a normal value based on controller program values. The HP governor did not respond however due to a failure to input proper program parameters in the HP governor controller during previous maintenance in 2015. This resulted in an underfeed condition in the A Steam Generator and a subsequent reactor trip due to high RCS pressure before Operations could trip the A MFP and initiate a plant runback.
CORRECTIVE ACTIONS
The LP servo drive and actuator for the A MFP were replaced and the pump was returned to service. The incorrect program values were corrected on the HP governor valve control system.
An extent of condition review determined the B MFP HP governor valve control system also contained incorrect program values. This condition was corrected on the B MFP control system prior to reactor startup.
Page 3 of 3 (08-2020)
U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 08/31/2023 LICENSEE EVENT REPORT (LER)
CONTINUATION SHEET (See NUREG-1022, R.3 for instruction and guidance for completing this form https://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr1022/r3/)
- 3. LER NUMBER Arkansas Nuclear One, Unit 1 05000-313 YEAR SEQUENTIAL NUMBER REV NO.
2021 002 0
Corrective actions have also been issued to provide verification and validation of MFP governor control parameters in implementing procedures and preventative maintenance work orders.
PREVIOUS SIMILAR EVENTS
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