05000341/LER-2016-001

LER-2016-001, Turbine Stop Valve Closure and Turbine Control Valve Fast Closure Reactor Protection System Functions Considered Inoperable Due to Open Turbine Bypass Valves

Fermi 2
Event date:	01-06-2016
Report date:	01-23-2017
Reporting criterion:	10 CFR 50.73(a)(2)(vii), Common Cause Inoperability 10 CFR 50.73(a)(2)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(v)(A), Loss of Safety Function - Shutdown the Reactor
LER closed by
IR 05000341/2017001 (1 May 2017)
3412016001R01 - NRC Website

LER 16-001-01 for Fermi 2 Regarding Turbine Stop Valve Closure and Turbine Control Valve Fast Closure Reactor Protection System Functions Considered Inoperable Due to Open Turbine Bypass Valves

ML17024A304
Person / Time
Site:	Fermi
Issue date:	01/23/2017
From:	Polson K J DTE Energy
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
NRC-17-0003 LER-16-001-01
Download: ML17024A304 (6)

comments regarding burden estimate to the FOIA, Privacy and Information Collections Branch (T-5 F53), 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.

05000- Fermi 2 341 Initial Plant Conditions Mode 1 Reactor Power 100 percent There were no structures, components, or systems that were inoperable at the start of the event that contributed to the event.

Description of the Event

At 1514 EST on January 6, 2016, while operating at 100 percent Reactor Thermal Power (RTP) the East and West Turbine Bypass Valves (TBV) V automatically opened as expected for 3 minutes and 32 seconds in response to the number one High Pressure Turbine Stop Valve (TSV) drifting from full open to 25 percent open due to an actuator malfunction.

Per Technical Specification (TS) Bases 3.3.1.1, TBVs must remain shut while RTP is at or above 29.5 percent to consider all channels of the TSV closure and Turbine Control Valve (TCV) fast closure Reactor Protection System (RPS) [JD] functions operable.

A failure analysis revealed that the valve actuator malfunction and TSV position drift was caused by faulty connectors CON within the actuator. Reactor Operators lowered RTP to 91.0 percent and at 1518 EST, the TBVs automatically closed and the TSV closure and TCV fast closure RPS functions were no longer considered inoperable.

TS 3.3.1.1 requires that the TSV closure and TCV fast closure RPS functions be operable at or above 29.5 percent RTP.

An event notification and follow up notification (No. 51755) were made to the NRC based on meeting the reporting criteria of 10 CFR 50.72(b)(3)(v)(A) and (D).

This event is reportable under 10 CFR 50.73(a)(2)(v), as an event or condition that could have prevented the fulfillment of the safety function of systems that are needed to: (A) shut down the reactor and maintain it in a safe shutdown condition and (D) mitigate the consequences of an accident.

In addition, since this event affected all channels of the TSV closure and TCV fast closure RPS functions, this event is reportable under 10 CFR 50.73(a)(2)(vii), as an event where a single cause or condition caused two independent channels to become inoperable in a single system designed to: (A) shut down the reactor and maintain it in a safe shutdown condition and (D) mitigate the consequences of an accident.

There were no radiological releases associated with this event.

Significant Safety Consequences and Implications There were no significant safety consequences associated with this event. At no time during this event was there a potential for endangering the public health and safety.

comments regarding burden estimate to the FOIA, Privacy and Information Collections Branch (T-5 F53), 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.

05000- Fermi 2 341 Per Chapter 15 of the Fermi 2 Updated Final Safety Analysis Report (UFSAR), the TCV fast closure function is the primary scram signal for the generator load rejection event. For this event, the reactor scram reduces the amount of energy required to be absorbed and ensures that the Minimum Critical Power Ratio (MCPR) Safety Limit (SL) is not exceeded. TCV fast closure signals are initiated by the de-energization of the solenoid dump valve at each control valve.

This function must be enabled at RTP greater than or equal to 29.5 percent.

Per Chapter 15 of the Fermi 2 UFSAR, the TSV closure function is the primary scram signal for the turbine trip event. For this event, the reactor scram reduces the amount of energy required to be absorbed and ensures that the MCPR SL is not exceeded. TSV closure signals are initiated from position switches located on each of the four TSVs. This function must be enabled at RTP greater than or equal to 29.5 percent.

Four Turbine First Stage Pressure (TFSP) transmitters PT are provided to initiate the automatic bypass of the TCV fast closure and TSV closure scrams, when the first stage pressure is below a preset fraction of rated pressure corresponding to approximately 29.5 percent of rated power.

The TBVs, if open at power levels above 29.5 percent RTP, may cause the TSV closure and TCV fast closure RPS functions to be inadvertently bypassed due to the diversion of steam flow away from the TFSP transmitters. In this event, during the period of time while TBVs were open, reactor power was maintained above 91 percent and the RPS functions were confirmed to be enabled. Therefore, there was no actual impact on safety.

Cause of the Event

The valve actuator malfunction and TSV position drift was caused by a failed Valve Control Module (VCM) servo driver to Unitized Actuator (UA) servo valve loop initiating a valve close position signal. The apparent cause was faulty connectors in the UA due to wear and fatigue. The contributing cause was circuit resistance measurement of the VCM to UA servo loop was not being performed.

Corrective Actions

The faulty connectors were replaced.

Additional corrective actions included: testing continuity of the servo valve circuit to identify and repair degraded conditions, developing a Preventative Maintenance (PM) task to address Extent of Condition on other modulating valves during refueling outages, and adjusting the maintenance frequency on the actuators to limit service time to 6 refueling outages.

This event was documented and evaluated in the Fermi 2 Corrective Action Program. All corrective actions have been completed.

Additional Information

A. Failed Component: UA connectors/wiring Function: Route position demand signal to the servo valve Manufacturer: Amphenol Model Number: MS3106E14S-6P Primary Failure Cause: Wear and fatigue comments regarding burden estimate to the FOIA, Privacy and Information Collections Branch (T-5 F53), 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.

05000- Fermi 2 341 B. Previous Licensee Event Reports (LERs) or Similar Events:

There are no previous similar events for UA connectors or wiring failing due to wear and fatigue.