05000387/LER-2021-005-01, Automatic Reactor Scram Due to Turbine Control Valve Fast Closure

Automatic Reactor Scram Due to Turbine Control Valve Fast Closure

ML22089A238
Person / Time
Site:	Susquehanna
Issue date:	03/30/2022
From:	Cimorelli K Susquehanna, Talen Energy
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
PLA-7992 LER 2021-005-01
Download: ML22089A238 (4)

LER-2021-005, Automatic Reactor Scram Due to Turbine Control Valve Fast Closure

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(iv)(A), System Actuation 10 CFR 50.73(a)(2)(iv)(B), System Actuation 10 CFR 50.73(a)(2)
3872021005R01 - NRC Website

text

Kevin Cimorelli Susquehanna Nuclear, LLC Site Vice President 769 Salem Boulevard Be1wick, PA 18603 TALEN~

Tel. 570,542.3795 Fax 570.542.1504 Kevin.Cimorelli@TalenEnergy.com ENERGY

March 30, 2022

Attn: Document Control Desk 10 CPR 50.73 U. S. Nuclear Regulatory Commission Washington, DC 20555-0001

SUSQUEHANNA STEAM ELECTRIC STATION LICENSEE EVENT REPORT 50-387/2021-005-01 UNIT 1 LICENSE NO. NPF-14 PLA-7992 Docket No. 50-387

Attached is Licensee Event Report (LER) 50-3 87/2021-005-01. The LER supplement reports an event involving an automatic scram due to a Reactor Protection System actuation as a result of Turbine Valve fast closure and subsequent Electro-hydraulic Control Fluid pressure petturbation. The condition is being rep01ied in accordance with 10 CPR 50.73(a)(2)(iv)(A) as an event that resulted in automatic actuation of a system listed in 10 CFR 50.73(a)(2)(iv)(B).

There were no actual consequences to the health and safety of the public as a result of this event.

This letter contains no new or revised regulatory commitments.

K. Cimorelli

Attachment: LER 50-387/2021-005-0l

Copy: NRC Region I Mr. C. Highley, NRC Senior Resident Inspector Ms. A. Klett, NRC Project Manager Mr. M. Shields, PA DEP/BRP U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY 0MB: NO. 3150-0104 EXPIRES: 08/31/2023

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Susquehanna Steam Electric Station, Unit 1 05000387 1 of 3

4. Title Automatic Reactor Scram due to Turbine Control Valve Fast Closure

5. Event Date 6. LER Number 7. Report Date 8. Other Facilities Involved Rev Month Day Docket Number Month Year Year Sequential Day Number No. Year Facility Name 05000 Facility Name Docket Number 11 30 2021 2021 - 005 - 01 03302022 05000

9. Operating Mode 10. Power Level 1 080

Abstract

At approximately 12:54 on November 30, 2021, Susquehanna Steam Electric Station, Unit 1, experienced an automatic reactor scram during Turbine Valve Cycling surveillance testing. During the fast closure portion of the surveillance test on Main Stop Valve 4 (MSV-4), a closure of Turbine Control Valve 4 (CV-4) occurred, resulting in a Division II Reactor Protection System (RPS) actuation.

While the Division II half scram signal was actuated, a Division I RPS actuation occurred, resulting in a full reactor scram. All control rods inserted and operators placed mode switch to shut down.

Event Notification 55616 reported this event in accordance with 10 CFR 50.72(b)(2)(iv)(B) and 10 CFR 50.72{b)(3)(iv)(A). This event is also reportable in accordance with 10 CFR 50.73(a)(2){iv)(A) as an event that resulted in automatic actuation of a system in 10 CFR 50.73(a)(2)(iv)(B).

The CV-4 fast closed due to transient voltage from a ground fault on the CV-4 Fast Acting Solenoid (FASV) field wiring. The previous single point vulnerability review for the system failed to identify and mitigate this failure mechanism. The Electro-hydraulic Control fluid pressure perturbation from the simultaneous closure of MSV-4 and CV-4 resulted in the Division II RPS actuation. Further review identified a recommended modification to dampen pressure in the system was never installed based on vendor recommendation. Key corrective actions include, in part, replacement of the CV-4 FASV wire and installation of orifices in accordance with the General Electric Technical Information Letter 1212-2 guidance.

There were no actual consequences to the health and safety of the public as a result of this event.

U. 5. NUCLEAR REGULATORY COMMISSION APPROVED BY 0MB: NO. 3150-0104 EXPIRES: 08/31/2023 Susquehanna Steam Electric Station, 05000-387 NUMBER NO, Unit 1 2021 - 005 - 01

NARRATIVE

CONDITIONS PRIOR TO EVENT

Unit 1 - Mode 1, approximately 80 percent Rated Thermal Power (RTP)

Unit 2 - Mode 1, approximately 100 percent RTP

Unit 1 Turbine Valve Cycling surveillance testing was in progress at the time of the event.

EVENT DESCRIPTION

At approximately 12:54 on November 30, 2021, Susquehanna Steam Electric Station, Unit 1, experienced an automatic scram due to a Reactor Protection System (RPS) [EIIS System Code: JC] actuation during Turbine Valve Cycling surveillance testing. During the fast closure portion of the surveillance test on Main Stop Valve 4 (MSV-4) [EIIS System/Component Codes: TA/SHV], Control Valve 4 (CV-4) [TA/FCV] unexpectedly fast closed, thereby generating a Turbine Control Valve fast closure on Division II RPS. Fast closure of CV-4 and MSV-4 caused an Emergency Trip System (ETS) pressure perturbation in the Electro-hydraulic Control (EHC) [TG] system which actuated one of the two Division I RPS low pressure switches. The Division I signal combined with the Division II signal resulted in a full scram. All control rods inserted, and operators placed mode switch to shut down. Reactor water level was maintained at the normal operating band using the Reactor Feed Water system [SJ]. All safety systems responded properly during the event.

Event Notification 55616 reported this event in accordance with 10 CFR 50.72(b)(2)(iv)(B) and 10 CFR 50.72(b)(3)(iv)(A). This event is also reportable in accordance with 10 CFR 50.73(a)(2)(iv)(A) as an event that resulted in automatic actuation of a system listed in 10 CFR 50.73(a)(2)(iv)(B).

CAUSE OF EVENT

Transient voltage from a ground fault on the CV-4 Fast Acting Solenoid, SV10150D, field wiring energized the solenoid causing CV-4 to unexpectedly fast close. The EHC Single Point Vulnerability Assessment did not identify failure modes necessary to develop bridging and mitigation strategies on a passive component (i.e., wiring) located in a severe service environment and ultimately contributed to a reactor scram.

ETS header pressure drop from simultaneous fast closure of CV-4 and MSV-4 actuated one of the two Division I RPS control valve ETS low pressure switches (PSLC721 N005A/C) [JJ/PS]. Operating Experience General Electric Technical Information Letter (TIL) 1212-2, which provided recommendations for controlling ETS pressure/flow via installation of orifices [OR], was previously evaluated with an inadequate conclusion resulting in the orifices not being installed as recommended.,

ANALYSIS/SAFETY SIGNIFICANCE

The actual consequence of this event was a Unit 1 Reactor scram. The scram did not require or result in the actuation of Emergency Core Cooling System and no main steam relief valves [SB/RV] opened. Reactor Core Isolation Cooling system [BN] initiated as designed. All safety systems responded properly during the event. The condition described herein did not result in a safety system functional failure. Accordingly, this

event will not be counted as a safety system functional failure in the Reactor Oversight Process Performance Indicators. There were no actual consequences to the health and safety of the public as a result of this event.

CORRECTIVE ACTIONS

Key Corrective Actions Included:

1. Replace damaged wiring for CV-4.

2. Install orifices in accordance with General Electric TIL 1212-2 guidance.

3. Perform Extent of Condition, as required, for Unit 1 and 2 main turbine steam valves.

4. Develop preventative maintenance tasks for critical wiring on main turbine steam valves.

5. Revise, as required, the EHC Single Point Vulnerability Mitigation Plan to address any vulnerabilities and associated mitigation strategies on passive components (e.g. wiring).

COMPONENT FAILURE INFORMATION

Component Identification - SV10150D Wiring Component Name - Control Valve 4 Fasting Acting Solenoid Component Model Number - D3W4BVY13X1555 Manufacturer - Parker Hannifin

PREVIOUS OCCURRENCES

None.