05000219/LER-2016-005

LER-2016-005, Technical Specification Prohibited Condition Caused by One Electromatic Relief Valve Inoperable for Greater than Allowed Outage Time

Oyster Creek, Unit 1
Event date:	09-19-2016
Report date:	11-17-2016
Reporting criterion:	10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications
2192016005R00 - NRC Website

LER 16-005-00 for Oyster Creek Nuclear Generating Station Regarding Technical Specification Prohibited Condition Caused by One Electromatic Relief Valve Inoperable for Greater than Allowed Outage Time

ML16336A636
Person / Time
Site:	Oyster Creek
Issue date:	11/17/2016
From:	Gillin M Exelon Generation Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
RA-16-095 LER 16-005-00
Download: ML16336A636 (5)

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.

3. LER NUMBER 2. DOCKET NUMBER - 00

Plant Conditions Prior To Event

Event Date: September 19, 2016 Event Time: 1500 EDT Unit 1 Mode: Cold Shutdown Power Level: 0%

Description of Event

On September 19, 2016 after achieving Cold Shutdown for the 1R26 Refuel Outage, as found testing was performed on all five (5) Electromatic Relief Valves (EMRVs). The "E" EMRV did not open from the Main Control Room (MCR), and no change in indication was observed. Per the work activity, technicians were dispatched to the Drywell to validate that the valve did not move upon receiving an open signal from the MCR. Troubleshooting was developed and determined that the cutout switch in the valve actuator was stuck in the open position, thereby preventing the actuator pickup solenoid from energizing to open the valve. The cutout switch did not operated as required due to the hinge pin washers not installed in the cutout switch assembly. Without the washers installed, the hinge pins interfered with the solenoid frame holes creating mechanical binding.

During each refueling outage, all five (5) EMRV actuators are removed from the plant, refurbished, and reinstalled during the following refueling outage. By Oyster Creek Nuclear Generating Station (OCNGS) process, the EMRV actuators are refurbished with new springs, posts, guides, and microswitches every 24 months during refueling outages. The actuator inspection/refurbishment frequency of 24 months is more frequent than the manufacturer's (Dresser Industries) recommended frequency of 36 months (per Vendor Manual VM-OC-0030, Installation and Maintenance Manual for Electromatic Relief Valves, Revision 1,Section VII, Ref. 4.5).

Equipment Description

The EMRVs are Type 6" 1525-VX relief valves manufactured by Dresser Industries. They are installed on the two (2) main steam lines that carry steam from the reactor vessel to the main turbine. Actuation signals from either the Automatic Depressurization System or the individual EMRV pressure switches, as well as from the manual control switches will open the valves to relieve vessel pressure, thereby allowing the low pressure Core Spray System to provide makeup water to the reactor core during accident / transient conditions.

The main valve is operated by a pilot valve that is controlled by energizing a DC operated solenoid actuator. When energized, the solenoid develops an electromagnetic field that enables the downward travel of a plunger, which strikes the pilot valve lever pushing it down. In that position, the lever opens the exhaust/venting path of the main valve, which subsequently opens the EMRV. The solenoid actuator is equipped with two solenoid coils (a pickup, low resistance - 50 coil, and a hold, high resistance - 3000 coil) in series. The hold coil has a parallel cutout switch, which is normally closed, thus bypassing the hold coil during the initial solenoid actuation. The initial pickup current in that configuration (-20 amps) is capable of developing the force required by the plunger for striking down the pilot valve lever and opening the EMRV. During its downward travel, the plunger tail will also strike down the cutout switch lever, which opens the cutout switch and connects the hold coil into the circuit. The low current developed (- 0.5 Amps) in that configuration is required to allow the EMRV to remain open, as needed, without the risk of burning out the pickup coil.

2016 005 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.

Analysis of Event

There was no actual safety consequence associated with this event.

Based on the failure mechanism, it has been determined that the "E" EM RV was inoperable for longer than the Technical Specification Allowed Out of Service time of 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />.

When the EM RV is no longer required to be open, the solenoid coils are de-energized, and the plunger travels upward pulled by the actuator springs. As it travels upward, the plunger releases the cutout switch lever, which retracts to its initial (closed) position helped by the combination of a tension and torsional springs. The failure of the cutout switch to retract to its normal (closed) position would result in the pickup and hold coil simultaneously energized during an EMRV actuation, which would subsequently prevent the solenoid from developing the required force to overcome the actuator spring force, inhibiting the EMRV from opening.

The results of the analysis performed substantiate that the cause of the event was isolated to the "E" EMRV only.

Cause of Event

The "E" EMRV failure was caused due to the failure to install the hinge pin washers in the cutout switch assembly.

Without the washers installed, the hinge pins interfered with the solenoid frame holes creating binding and rotational forces that resulted in a deformation of the cutout switch lever arm. The lever arm deformation allowed the lever arm to bind on the solenoid frame and could not be overcome by the spring force. This condition resulted in the cutout switch being held open and the "E" EMRV unable to actuate.

Immediate Actions

1. Extent of Condition Inspections were performed to the other four (4) EMRV actuators that were removed during 1R26 Refuel Outage. Only "E" EMRV, no discrepancies were identified.

Corrective Actions

1. Inspected all five (5) EMRV solenoid actuators prior to installation in the plant to verify critical parameters as well as installation of the hinge star washers.

2. An investigation is being performed to identify why the washers were not installed. Any additional corrective actions will be determined through the investigation.

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.

Assessment of Safety Consequences

There was no actual safety consequences associated with this event. All EMRVs were operable at the time of installation during 1R25 Refuel Outage (2014) as proven by operability surveillance testing during start-up from the outage. During Cycle 25, OCNGS did not have any transients or events which required the "E" EMRV to operate. Additionally, OCNGS UFSAR Chapter 15, assumes four out of the five EMRVs are available for any of the accident analyses requiring EMRV operation/actuation.

The Electromatic Relief Valves (EMRVs) have three modes of operation that were evaluated for Design Basis.

These three modes are:

1) Automatic operation under Small Break Loss of Coolant Accident (SBLOCA) conditions 2) Automatic operation under high Reactor Pressure Vessel (RPV) Pressure condition 3) Manual operation under conditions dictated by the Emergency Operating Procedures (EOPs) The 'B', 'C', and `E' EMRV have a setpoint to open at 1085 psig, which is higher than the setpoints for the 'A' and `D' EMRV of 1065 psig. Time delay relays prevent the simultaneous opening of the EMRVs. The failure of the EMRV cutout switch lever arm would have precluded the "E" EMRV assembly from being able to cycle open in the event of an automatic or manual actuation. The remaining four (4) of the five (5) EMRVs would have continued to operate and would have cycled as required to ensure operations under a SBLOCA or RPV high pressure condition. The 'A' through EMRVs were evaluated to not be susceptible to the same failure and were maintained in an operable condition in accordance with station procedures.

Previous Occurrences

In 2014 the station experienced an event in which two (2) actuators were found to be inoperable during the refurbishment process, after removal from the plant in September 2012 during the 1R24 Refuel Outage. The station performed the corrective actions to change the design of the EMRV solenoid actuators to prevent recurrence The new designed actuators were installed in September 2014 during OCNGS 1R25 Refuel Outage.

Additionally, a corrective action was implemented to perform as found testing during subsequent refuel outages prior to replacing the actuators. The performance of these modifications was not a contributing cause to the failure experienced in the "E" EMRV on September 19, 2016.

Component Data Component IEEE 805 System ID IEEE 803A Component Relief Valve SB RV