05000313/LER-2023-002, Reactor Protection System Underpower Relay Test Failure Resulting in Condition Prohibited by Technical Specifications
| ML23160A212 | |
| Person / Time | |
|---|---|
| Site: | Arkansas Nuclear  (DPR-051) |
| Issue date: | 06/09/2023 |
| From: | Keele R Entergy Operations |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| 1CAN062303 LER 2023-002-00 | |
| Download: ML23160A212 (1) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 3132023002R00 - NRC Website | |
text
- ) entergy 1CAN062303 June 9, 2023 ATTN : Document Control Desk U. S. Nuclear Regulatory Commission Washington, DC 20555-0001 Riley D. Keele, Jr.
Manager, Regulatory Assurance Arkansas Nuclear One Tel 479-858-7826 10 CFR 50.73
Subject:
Licensee Event Report 50-313/2023-002-00, Reactor Protection System Underpower Relay Test Failure Resulting in Condition Prohibited by Technical Specifications Arkansas Nuclear One - Unit 1 NRC Docket No. 50-313 Renewed Facility Operating License No. DPR-51 Pursuant to the reporting requirements of 10 CFR 50. 73, attached is the subject Licensee Event Report concerning the Arkansas Nuclear One, Unit 1, Reactor Protection System underpower relay test failure that resulted in a condition prohibited by Technical Specifications.
There are no new commitments contained in this submittal. Should you have any questions concerning this issue, please contact me at 479-858-7826.
Sincerely, Riley Keele RDK/bka Digitally signed by Riley Keele ON: ro=Riley Keele, c=US, emai1=rkeele@entergy.com Reason: I am app-oving this document Date: 2023.06.09 08:36:59 -05'00'
Attachment:
Licensee Event Report 50-313/2023-002-00 Entergy Operations, Inc. 1448 SR 333, Russellville, AR 72802
1CAN062303 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 1CAN062303 Licensee Event Report 50-313/2023-002-00
Abstract
On April 11, 2023 during evaluation of the Reactor Protection System (RPS) and associated Reactor Coolant Pump (RCP) 'D' underpower relay, Arkansas Nuclear One, Unit 1 (ANO-1) identified the RCP 'D' underpower relay was past inoperable, which is a condition prohibited by Technical Specifications (TS).
The cause of this event was a failure of the RCP underpower relay to open during testing due to a failure to disable a holding coil internal to the relay prior to installation during the ANO-1 fall 2022 refueling outage (1 R30).
The RCP 'D' underpower relay has been replaced with a relay that has the holding coil disabled.
There were no consequences to the general safety of the public, nuclear safety, industrial safety or radiological safety. No radiological releases occurred due to this event.
PLANT STATUS
- 2. DOCKET NUMBER
- 3. LER NUMBER I
313 NUMBER NO.
I YEAR SEQUENTIAL REV a-I 002 1-G At the time the condition was discovered, Arkansas Nuclear One, Unit 1 (ANO-1) was operating in Mode 1 at 100 percent rated thermal power (RTP). There were no other structures, systems, or components that were inoperable at the time that contributed to this condition.
EVENT DESCRIPTION
On February 8, 2023 at 0846 CST, the ANO-1 Reactor Coolant Pump (RCP) 'D' Reactor Protection System (RPS) underpower relay failed Preventive Maintenance (PM) testing.
On February 9, 2023 a temporary modification was implemented to remove the 125 volt DC source from the time delay relays feeding all RPS channels for the 'D' RCP. This temporary modification generated a signal to all four channels of RPS showing the 'D' RCP as being tripped, which was a conservative configuration. This placed ANO-1 in a conditional single point vulnerability until the failed underpower relay could be replaced and the temporary modification removed.
On February 14, 2023 the 'D' RCP underpower relay was replaced with a relay that has the holding coil disabled.
Subsequently, the temporary modification was removed.
On April 11, 2023 ANO-1 completed a Past Operability evaluation of the RPS and associated 'D' RCP underpower relay as a result of failed PM testing.
The result of the Past Operability evaluation found the RCP 'D' underpower relay was Past Inoperable from the time it was replaced on October 11, 2022 during the fall 2022 refueling outage (1 R30) until February 9, 2023 when a temporary modification was installed to bypass the failed relay. The replacement RCP 'D' underpower relay was not capable of performing its safety function due to the failure to disable a holding coil. ANO-1 TS 3.3.1 RPS Instrumentation requires four channels of RPS instrumentation for each Function in TS Table 3.3.1-1 to be Operable. The failure of the RCP 'D' underpower relay would have inhibited the "Reactor Coolant Pump to Power" Function for RCP 'D' during the time period listed above and is a Condition Prohibited by TS.
However, the result of the Past Operability evaluation found the RPS was Past Operable. The RPS safety function is the generation of a reactor trip signal when monitored variables exceed their setpoints to protect the reactor core against fuel rod cladding damage. The failure of the RCP 'D' underpower relay would not prevent RPS from initiating a reactor trip signal during a four pump coast down, the event for which this trip function is credited, because the trip occurs at any power level if the trip of 3 RCP's is detected. The underpower relays for the remaining 3 RCP's tested satisfactory and were operable for the period of time the 'D' RCP was inoperable. Since a reactor trip will occur at any power for loss of 3 RCP's, each RPS channel would have detected conditions requiring a reactor trip in the event of a loss of all RCP's, despite the erroneous input for RCP 'D'.
No radiological releases occurred due to this condition.
This report is made pursuant to 10 CFR 50.73(a)(2)(i)(B), any operation or condition which was prohibited by the plant's Technical Specifications.
SAFETY ASSESSMENT
- 2. DOCKET NUMBER
- 3. LER NUMBER I
313 NUMBER NO.
I YEAR SEQUENTIAL REV a-I 002 1-G The RCP 'D' underpower relay was inoperable for a total of 121 days from the time it was installed on October 11, 2022 until February 9, 2023 when a temporary modification was installed to bypass the failed relay. According to ANO-1 TS Table 3.3.1-1, the "Reactor Coolant Pump to Power" RPS Function is only required in Modes 1 and 2. ANO-1 was in a Mode of Applicability for approximately 7 4 days over that period of time. Given the RPS remained Operable and capable of performing it's Safety Function during this period of time, the safety significance of this event is determined to be low.
This condition did not result in actual consequences to safety of the general public, nuclear safety, industrial safety or radiological safety.
EVENT CAUSE(S)
The ANO-1 'D' RCP underpower relay failed PM testing. The underpower relay test failure direct cause was a failure to disable the internal holding coil which resulted in the failure of the underpower relay to open when the relay coil was de-energized via the test push button. The holding coil being enabled allowed the circuitry for the RCP underpower indication lights to induce a current on the relay contact such that the relay would not trip open during the push button test. It was later identified that the original design of the system requires that the holding coils, internal to the respective RCP underpower relays, be disabled for proper functionality.
Failure to maintain design of the RCP underpower relay due to a lack of documentation on the relay's internal holding coil design configuration was identified as a contributing casual factor.
Also, failure to perform adequate Post Maintenance Testing (PMT) upon installation of the replacement RCP underpower relay for verification of satisfactory operation was identified as a contributing casual factor.
CORRECTIVE ACTIONS
This event was entered into the station's corrective action program.
The initial corrective action to be implemented was to install a temporary modification to generate a signal to all four channels of RPS showing the 'D' RCP as being tripped.
Later the 'D' RCP underpower relay was replaced with a relay that has the holding coil disabled and the temporary modification was removed.
Additional corrective actions are planned to update the appropriate procedure, calculation and vendor technical manual to capture the requirement to disable the underpower relay holding coils. In addition, corrective actions are planned to ensure future PMT will include the pushbutton surveillance testing as part of relay replacement to verify the holding coil is disabled to allow the relay to perform its design function. In addition, the existing inventory of RCP underpower relays in stock at ANO will have the holding coil disabled.
PREVIOUS SIMILAR EVENTS
I
- 2. DOCKET NUMBER
- 3. LER NUMBER I
YEAR SEQUENTIAL REV 120231 NUMBER NO.
313
- - I 1-G 002 ANO-1 LER 2021-002-00, "Automatic Reactor Trip Due to High Reactor Coolant System Pressure" was identified. This reactor trip was due to the failure of the 'A' Main Feedwater Pump (MFP) High Pressure (HP) governor to respond to lowering 'A' MFP speed which was caused by a failure to input proper program values in the HP governor controller during previous maintenance activities. A causal factor of this event involved the failure to identify that the original design of the system requires that the RCP underpower relay holding coil be disabled for proper functionality. Page 4
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