05000373/LER-2017-005

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LER-2017-005, Manual Reactor Scram Resulting From Feedwater Regulating Valve Failure Causing High Reactor Water Level
Lasalle County Station, Unit 1
Event date: 02-17-2017
Report date: 04-18-2017
Reporting criterion: 10 CFR 50.73(a)(2)(iv)(A), System Actuation
LER closed by
IR 05000373/2017004 (13 February 2018)
3732017005R00 - NRC Website
LER 17-005-00 for LaSalle County, Unit 1, Regarding Manual Reactor Scram Resulting From Feedwater Regulating Valve Failure Causing High Reactor Water Level
ML17108A430
Person / Time
Site: LaSalle, Lasalle Exelon icon.png
Issue date: 04/18/2017
From: Trafton W J
Exelon Generation Co
To:
Document Control Desk, Office of Nuclear Reactor Regulation
References
RA17-037
Download: ML17108A430 (4)


comments regarcing burden ezlimate to the Information Services Branch (T-2 F43), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by e-mail to Infocollects.Resourceilinro.gov, and to the Desk Officer, Office of Information and Regulatory Affairs, used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.

3. LER NUMBER 2. DOCKET NUMBER - 00

PLANT AND SYSTEM IDENTIFICATION

LaSalle County Station Unit 1 is a General Electric Boiling Water Reactor with 3546 Megawatts Thermal Rated Core Power.

The Feedwater (FW) system provides a source of processed water to the reactor pressure vessel (RPV) to maintain the desired water level during normal plant operating conditions. The affected component was the Feedwater Regulating Valve (FRV), which is used to control the flow of FW to the RPV for water level control when the motor-driven reactor feed pump is used.

CONDITION PRIOR TO EVENT

Unit(s): 1 Reactor Mode(s): 1 Event Date:

February 17, 2017 Event Time: 2353 CST Mode(s) Name: Power Operation Power Level: 30 percent

DESCRIPTION OF EVENT

On February 17, 2017, Unit 1 was in the process of power ascension at approximately 30 percent power from a previous forced shutdown. At 23:53 CST, the Main Control Room received a FW control RPV high level alarm. Operators quickly diagnosed an abrupt change in reactor water level and that level was rapidly increasing. The operators entered the abnormal procedures in parallel with setting manual scram criteria of greater than 50 inches reactor water level and not in control, as directed by station procedures. The manual scram was initiated as level was approaching the turbine trip set point of 55.5 inches in order to terminate the transient. The scram was not complicated, and all equipment performed as designed. The plant was placed in a stable condition, with reactor pressure maintained by the turbine bypass valves. Reactor water level was controlled with FW through the low-flow regulating valve. All control rods fully inserted, and decay heat was removed via steam to the main condenser using bypass valves.

CAUSE OF EVENT

The high reactor water level trip occurred due to a failure of the RN regulating valve (FRV) positioner arm, which caused the regulating valve to be driven to the full open position and resulted in a rapid increase in RPV level. Field observations at FRV 1FW005 revealed that the valve positioner feedback drive arm had broken cleanly into two pieces at the junction between the arm and shaft. The feedback drive arm extension was also found to be severely bent. The FRV positioner feedback assembly was a standard vendor design when installed as part of the hydraulics for the upgrade of the air-operated valve (AOV) performed in 2002. This design of the valve position feedback assembly has proven not to be robust enough for the FRV application.

Contributing to this event were FRV cycling during operations caused by the inherent dead-band of the valve positioner and the positioner feedback assembly.

REPORTABILITY AND SAFETY ANALYSIS

The event was reportable to the NRC in accordance with 10 CFR 50.72(b)(2)(iv)(B) for any event or condition that results in actuation of the reactor protection system (RPS) when the reactor is critical. An Emergency Notification System (ENS) report number 52564 was made on February 18, 2017.

This event is also reportable in accordance with 10 CFR 50.73(a)(2)(iv)(A) as an event or condition that resulted in manual or automatic actuation of the reactor protection system (RPS). The safety significance of this condition was minimal, as plant equipment responded as expected for the event; therefore, there were no impacts to plant safety or design margins.

2017 005 comments regarding burden estimate to the Information Services Branch (T-2 F43), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by e-mail to used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.

3. LER NUMBER 2. DOCKET NUMBER - 00 005 2017

CORRECTIVE ACTIONS

A replacement feedback positioner arm and a new positioner were installed on the Unit 1 FRV. A calibration of the FRV positioner arm and a FlowScan diagnostic test were performed to verify proper operation. Additional corrective actions are to evaluate the design of the Motor Driven Reactor Feed Pump (MDRFP) FRV positioner and its feedback assembly for potential improvements that could make the feedback arm more robust and have less dead-band to reduce the valve cycling.

PREVIOUS OCCURRENCES

A review of past events in the last three years identified no previous occurrences that related to FW valve or reactor water level control events. Examples of reactor scrams included Unit 2 LER 374-2014-001-00 (Reactor Scram Due to Main Steam Isolation Valve Stem-Disk Separation) and Unit 2 LER 374-2017-001-00 (Manual Reactor Scram due to Turbine-Generator Run-Back Caused by Stem-Disc Separation in Stator Water Cooling Heat Exchanger Inlet Valve), and Unit 1 LER 373-2017-003-00 (Automatic Reactor Scram due to Main Generator Trip on Differential Current During Back-Feed Operations). However, none of these were applicable to the subject event. Searches were also performed of the station's corrective action program and INPO operating experience databases, which did not identify information or a similar occurrence to this event.

COMPONENT FAILURE DATA

Manufacturer: Control Components International (C600) Device (Model): Air-Operated Valve Regulator Assembly (922401010, Self-Drag Element) Component ID: 1FW005, Motor Driven Reactor Feed Regulating Valve "C"