05000219/LER-2017-001

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LER-2017-001, Automatic SCRAM due to APRM High Flux during Turbine Valve Testing
Oyster Creek, Unit 1
Event date:
Report date:
Reporting criterion: 10 CFR 50.73(a)(2)(iv)(A), System Actuation
2192017001R01 - NRC Website
LER 17-001-01 for Oyster Creek, Regarding Transfer of Automatic SCRAM due to APRM High Flux during Turbine Valve Testing
ML17129A602
Person / Time
Site: Oyster Creek Exelon icon.png
Issue date: 05/03/2017
From: Gillin M F
Exelon Generation Co
To:
Document Control Desk, Office of Nuclear Reactor Regulation
References
RA-17-028
Download: ML17129A602 (4)


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 Infocollects.Resource@nrc gov, and to the Desk Officer, Office of Information and Regulatory Affairs, used to impose an informahon collechdn 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

2017 - 01 001

Plant Conditions Prior To Event

Event Date: November 20, 2016 Event Time: 0342 EST Unit 1 Mode: Power Operation Power Level: 92%

Description of Event

On 11/20/2016, the Main Control Room (MCR) Operators were conducting quarterly Main Turbine surveillance testing. At 0326 EST, the MCR Operators commenced testing the Turbine Master Trip Solenoid Valve (MTS-3) at 95% reactor power in accordance with plant procedures. After actuating the Turbine Master Trip Solenoid Valve, the MCR Operators observed fluctuations in control valve and bypass valve position indication. The Control Room Operators also identified a transfer between the EPR and MPR and fluctuations in reactor pressure. Field Operators were dispatched to the turbine front standard to inspect for any abnormalities. The Field Operators reported vibration and high frequency oscillations of the control linkages contained in the front standard. In response to the field report, the MCR Operators commenced a controlled power reduction in an effort to arrest the oscillations.

At approximately 0342 EST, an automatic reactor SCRAM occurred at 92% power due to Average Power Range Monitor (APRM) high flux. The turbine control valves failed to properly control reactor pressure during the power reduction due to a malfunction of the Mechanical Hydraulic Control (MHC) System. After the plant scram, the_ vibration and oscillations at the front standard ceased, and the bypass valves responded to regulate reactor pressure. An inspection of the front standard and the turbine control valve hydraulic enclosure was performed following the plant shutdown. The inspection identified that the hydraulic feedback linkage for the number 2 turbine control valve had come disconnected and the fastener for the hydraulic feedback linkage on the number 4 control valve was loose due to the vibration that was experienced. The feedback linkage degradation resulted in the unexpected change in control valve position during the power reduction and the subsequent reactor scram.

Cause of Event

The root cause investigation determined that the performance of the Turbine Master Trip Solenoid Valve operability test with the plant at power challenged the stability of the MHC system due to unrecognized design vulnerability in the configuration of the hydraulic tubing. The hydraulic tubing for the Turbine Master Trip Solenoid Valve is routed to the bypass valve loading piston. The design function of the bypass valve loading piston is to dampen vibration on the control linkages contained in the front standard. During the Turbine Master Trip Solenoid Valve Operability Test, a pressure pulse is placed on the bypass pilot valve loading piston that can lead to an oscillation of the MHC system. The design vulnerability was unrecognized because the OEM drawings did not identify the function or location of the loading piston with respect to the location of the Master Trip Solenoid hydraulic supply.

The root cause investigation also determined that degradation of the bypass valve loading piston contributed to the oscillation of the MHC System.

Analysis of Event

Infocollects.Resource@nrc 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

2017 - 01 001 This issue resulted in an automatic reactor SCRAM. There were no equipment problems noted related to placing the reactor in a safe Cold Shutdown Condition.

There were no safety consequences impacting the plant or public safety as a result of this event. All control rods fully inserted and plant response was as expected. This event is being reported pursuant to 10CFR50.73(a)(2)(iv)(A) due to an actuation of the Reactor Protection System (RPS).

Corrective Actions

The following corrective actions were taken:

  • The hydraulic linkage for the number 2 and number 4 control valves were repaired.
  • The bypass valve loading piston was replaced.
  • The turbine master trip solenoid valve test will no longer be performed online. The test will be performed during unit outage only.

Previous Occurrences

Oyster Creek Nuclear Generating Station experienced a similar event on December 14, 2013. During quarterly turbine valve testing with reactor power at 100% of rated thermal power, the plant experienced reactor pressure control abnormalities. The hydraulic feedback linkage for the number 2 and number 3 control valves failed, thereby requiring a scram. Operators initiated a manual reactor scram due to reactor pressure rising to 1042 psig which approached the automatic scram set point. That event was reported under LER 2013-004-00 in February 2014.

Component Data Component IEEE 805 System ID IEEE 803A Component Control Valve Hydraulic Enclosure TG XC