05000458/LER-2020-004, Inadvertent Initiation and Injection of High Pressure Core Spray (HPCS)
| ML20302A456 | |
| Person / Time | |
|---|---|
| Site: | River Bend  |
| Issue date: | 10/29/2020 |
| From: | Vercelli S Entergy Operations |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| RBG-48053 LER 2020-004-00 | |
| Download: ML20302A456 (5) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v), Loss of Safety Function |
| 4582020004R00 - NRC Website | |
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Entergy Operations, Inc.
Enteigy Bend 61 N
© St. Francisville, LA 70775 Tel 225-381-4374 Steve Vercelli Site Vice President 10 CFR 50.73 RBG-48053 October 29, 2020 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, DC 20555-0001
Subject:
Licensee Event Report 50-458 I 2020-004-00, Inadvertent Initiation and Injection of High Pressure Core Spray (HPCS)
River Bend Station Unit 1 NRC Docket Nos. 50-458 Renewed Facility Operating License No. NPF-47 In accordance with 10 CFR 50.73, enclosed is the subject Licensee Event Report. This document contains no commitments. If you have any questions, please contact Mr. Tim Schenk, Regulatory Assurance Manager, at 225-381-4177.
Respectfully, SPVIdjp
Enclosure:
Licensee Event Report 50-458 I 2020-004-00, Inadvertent Initiation Injection of High Pressure Core Spray (HPCS) cc:
NRC Regional Administrator - Region IV NRC Project Manager - River Bend Station NRC Senior Resident Inspector
- - River Bend Station Louisiana Department of Environmental Quality Public Utility Commission of Texas
Enclosure RBG-48053 Licensee Event Report 50-458 I 2020-004-00, Inadvertent Initiation Injection of High Pressure Core Spray (HPCS)
Abstract
On September 03, 2020 at 2048 CT, River Bend Station (RBS) experienced a High Pressure Core Spray (HPCS) system inadvertent initiation and injection into the core while the station was at 92 percent power. Control Room Operators took manual control of Feedwater Level Control to maintain a stable reactor water level. Once it was verified that feedwater was not needed for level control, Operations manually closed the injection isolation valve and performed an override of the HPCS system.
Closure of the HPCS Injection Valve rendered this system incapable of responding to an automatic actuation and was declared inoperable.
This report is made in accordance with 10 CFR 50.73(a)(2)(v)(D) for any event or condition that could have prevented the fulfillment of the safety function of structure or system that is needed to mitigate the consequences of an accident.
EVENT DESCRIPTION
On September 03, 2020 at 2048 CT, the High Pressure Core Spray System (HPCS) inadvertently initiated and injected into the reactor vessel causing a rise in reactor water level. No related activity was in progress at the time of the event.
The Main Control Room (MCR) operators took the following immediate actions to restore normal reactor vessel water level:
- Ensured HPCS was not needed for reactor water level control
- Took manual control of HPCS and terminated injection
- Took manual control of the Feed-Water Level Control system (FWLC)
- Restored reactor water level to within the normal operating band
- Placed Feedwater Level Control (FWLC) back in automatic The Division 3 Diesel Generator started automatically as expected with HPCS initiation and was subsequently secured by Operations. Upon initial investigation, the Control Room Operators observed that an entire row of HPCS trip unit circuit cards had failed low on the trip unit rack. When the back panel back door was opened, a strong acrid odor was present.
SAFETY ASSESSMENT
The actual consequence as stated was a High Pressure Core Spray (HPCS) inadvertent initiation and injection into the reactor pressure vessel. There were no other actual consequences to general safety of the public, nuclear safety, industrial safety or radiological safety for this event. The core was not adversely impacted by this event, and the option to initiate a manual SCRAM was always available to Operations. The HPCS pump was manually overridden, rendering the system INOPERABLE, but still available to mitigate the consequences of an accident if needed.
The MCR was able to take manual control of the RPV water level and return it to normal conditions. From a nuclear safety perspective, this event had no adverse impacts on the core. All core responses were as expected and remain bounded by the current licensing basis. Therefore, it has been determined there was no Safety System Functional Failure.
EVENT CAUSE
A trip unit card located on rack Z2 developed an electrical short and caused an amperage spike. This amperage spike caused voltage to lower across rack Zi. Once this voltage lowered beyond a certain point, an invalid Level 2 signal was generated and caused a HPCS actuation.
The voltage across rack Zi fell below 22 VDC but remained above 19 VDC. When this happened, unit input voltage at the rack did not go low enough for the card rack to completely lose power, but it was low enough for the card to incorrectly interpret the low voltage as a low voltage signal from the field. Since the trip unit is programmed in reverse (meaning it acts on a low/de-energized voltage signal from a field transmitter), it still had enough power to be operational and was able to generate a false (or invalid) Level 2 signal.
CORRECTIVE ACTIONS
Completed Action
- - As an immediate corrective action, replaced three failed trip unit cards along with the power supply.
PREVIOUS SIMILAR EVENTS
LER 2018-002 On April 26, 2018 at 15:31 CT, I&C technicians were restoring Reactor Vessel Water Level Transmitter BZ1-LTNO81C to service with the reactor operating at 100% power. During this transmitter restoration, the station experienced an invalid initiation of High Pressure Core Spray (HPCS) with injection into the reactor vessel.
NRC FORM 368A (08-2020)
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