05000341/LER-2016-002

LER-2016-002, Both Residual Heat Removal Low Pressure Coolant Injection Divisions Inoperable Due to Inoperable Injection Valve

Fermi 2
Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability
Initial Reporting
ENS 51676	10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident
3412016002R00 - NRC Website

LER 16-002-00 for Fermi 2, Regarding Both Residual Heat Removal Low Pressure Coolant Injection Divisions Inoperable Due to Inoperable Injection Valve

ML16082A458
Person / Time
Site:	Fermi
Issue date:	03/22/2016
From:	Polson K J DTE Electric Company, DTE Energy
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
NRC-16-0016 LER 16-002-00
Download: ML16082A458 (6)

There were no inoperable Structures, Systems, or Components at the start of the event that contributed to the event.

Description of the Event

On January 22, 2016, at 1923 EST, both divisions of Residual Heat Removal (RHR) [BO] were declared inoperable for the Low Pressure Coolant Injection (LPCI) mode of operation due to a failure of the division 1 LPCI outboard injection motor operated valve [ISV], El 1 50F017A. While performing the division 1 RHR pump and valve operability surveillance test, El 150F017A closed properly but failed to open during its required stroke time test.

The Fermi 2 accident analysis takes credit for the proper operation of the LPCI loop select logic during a loss of coolant accident (LOCA). The loss of coolant event involves the postulation of a spectrum of piping breaks inside the primary containment, varying in size, type, and location. The most severe nuclear system effects and the greatest release of material to the primary containment result from a complete circumferential break of one of the two reactor recirculation loop [AD] pipe lines. This is the design basis accident (DBA). Since the LPCI system injects water into the reactor vessel [RPV] through the discharge piping of one of the recirculation loops, a loop selection logic is provided to ensure that the water is injected into an unbroken loop. The loop selection logic compares pressure on the two recirculation loops. A broken loop will indicate a lower pressure than an unbroken loop. The loop selection logic directs the LPCI injection into the high pressure (unbroken) loop. The loop selection is effected through the operation of the RHR injection valves.

Valve E1150F017A is a normally open RHR injection valve in series with the inboard El 1 50F015A valve.

These valves control the RHR LPCI flow into reactor recirculation loop A. Because the valve failed in the closed position, flow would be inhibited into the A recirculation loop for scenarios where a break is detected in loop B.

Therefore, both divisions of RHR were declared inoperable for the LPCI function at 1923 EST on January 22, 2016. Technical Specification 3.5.1, Condition K was invoked and limiting condition for operation (LCO) 3.0.3 was immediately entered.

Trouble shooting determined that the control power [JS] closing contactor did not have full freedom of movement because of foreign material. The contactor was removed from the Motor Control Center (MCC) and was manually cycled on a workbench. While manually cycling the contactor, a screw fell out of the contactor.

The screw apparently fell into the contactor from a Control Relay (CR) located above the contactor in the MCC.

At approximately 2143 EST, the El 150F017A valve was re-tested satisfactorily. The valve properly closed and opened, meeting required Inservice Inspection (ISI) stroke time acceptance criteria. At 2145 EST, both divisions of RHR were declared operable for the LPCI and LCO 3.5.1, Condition K and. LCO 3.0.3 were exited.

January 23, 2016, 0020 EST, to the NRC Operations Center. Reactor Power was maintained at 100 percent throughout the event.

This report is being made pursuant to I OCFR50.73(a)(2)(v)(D) as a condition that could have prevented the fulfillment of a system safety function needed to mitigate the consequences of an accident. In addition, this report is being made pursuant to 10CFR50.73(a)(2)(vii) as an event where a single cause or condition caused at least one independent train or channel to become inoperable in multiple systems or two independent trains or channels to become inoperable in a single system designed to mitigate the consequences of an accident.

Significant Safety Consequences and Implications The safety function of the LPCI mode of the RHR system is to inject water from the suppression pool into the reactor vessel via injection lines connected to the reactor recirculation piping following a large break LOCA.

Since a large break LOCA could occur in either one of the two reactor recirculation loops, the LPCI loop select logic function is designed to select the undamaged reactor recirculation loop for LPCI injection. Under the conditions of this event, with the Loop A outboard injection valve closed and unable to open, had a LOCA occurred in recirculation loop B or elsewhere in the reactor connected piping systems in containment, the automatic LPCI injection to the reactor vessel would have been prevented.

Inoperability of the E1150FO1 7A valve, for approximately one hour and 50 minutes, rendered both divisions of LPCI inoperable. However, during that period of time the core spray and standby feedwater systems were available to address large break LOCA events. The high pressure coolant injection, reactor core isolation cooling, and standby feedwater systems were also available to address any small break LOCA scenarios that could have occurred at that time. The event was of low safety significance considering the short duration; therefore, the health and safety of the general public were not adversely impacted.

Cause of the Event

A Root Cause Evaluation determined that the technical requirements to check all fasteners for looseness were not adequately implemented into Maintenance work instructions (procedures) for MCC inspections during Preventative Maintenance. Additionally, the General Electric (GE) CR305 contactor orientation inside the MCC created a susceptibility to foreign material. When the contactor is mounted horizontally, an opening is created where foreign material can fall into the contactor.

The contributing cause was that previous Corrective Action Program documents/products did not adequately identify the cause of similar previous events and did not effectively implement corrective actions to minimize recurrence.

Corrective Actions

The foreign material was removed and the MCC bucket was restored and tested satisfactorily. The MCC was independently inspected for additional foreign material and all other screws on the relay were tightened. Four procedures will be revised to include instructions to check accessible spare terminal screws for tightness. The revisions will be complete by May 31, 2016.

Additional corrective actions include personnel training and the inspection of Engineered Safety Feature (ESF) MCC positions with CR120B relays for loose or missing screws and for susceptible contactor orientation. All screws will be tightened during the inspections and a Design Change will be implemented to modify the susceptible MCC contactors with a permanent FME barrier. Initial visual inspections are complete. All corrective actions will be completed by the next refueling outage (RF18), scheduled for spring 2017.

Additional Information:

A. Failed Component Data:

None.

B. Previous Similar Events:

Inoperable Due to Valve Failure," was submitted when the E1150F017B, the Division 2 LPCI outboard injection valve, failed to open. The cause of the failure was high resistance on the open contactor auxiliary interlock contact. Therefore, the corrective actions for LER 2005-004 would not have prevented the current event.

Actions taken in response to Condition Assessment Resolution Document 06-22311, which identified a foreign material that impacted the operation of a similar contactor were not effective to prevent the occurrence of this event.