05000387/LER-2016-008

LER-2016-008, Inoperability of Diesel Generator Due to Misalignment of MOC Switch Contacts Due to Inadequate Post Maintenance Testing

Susquehanna Steam Electric Station Unit 1
Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident
3872016008R00 - NRC Website

LER 16-008-00 for Susquehanna, Unit 1, Regarding Inoperability of Diesel Generator Due to Misalignment of MOC Switch Contacts Due to Inadequate Post Maintenance Testing

ML16144A022
Person / Time
Site:	Susquehanna
Issue date:	05/19/2016
From:	Franke J A Susquehanna
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
PLA-7477 LER 16-008-00
Download: ML16144A022 (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 internet 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.

CONDITIONS PRIOR TO EVENT

Unit 1 — Mode 5, 0 percent Rated Thermal Power Unit 2 — Mode 1, 100 percent Rated Thermal Power There were no structures, systems, or components that were inoperable at the start of the event that contributed to the event other than the failed component itself.

EVENT DESCRIPTION

On April 1, 2016 at 20:24, Unit 2 entered Technical Specification (TS) 3.8.1 due to the A Diesel generator (DG) [EIIS System/Component Identifier: EK/DG] being inoperable due to the misaligned contacts [EIIS Component Identifier: CNTR] on the Mechanism-Operated Cell (MOC) switch. Based upon review of the history and cause, the condition likely existed since the supply breaker [EIIS Component Identifier: BKR] was replaced on July 19, 2010. A detailed timeline is provided below:

On July 19, 2010, Supply Breaker 1A20104 for the A DG was replaced during routine preventive maintenance activities.

On May 12, 2012, the timer (62X1A20104) [EIIS Component Identifier: TMR] associated with the Emergency Switchgear and Load Center Cooling Supply Fan (1V222A) [EIIS Component Identifier: FAN] immediately went to run without a time delay during performance of the Unit 1 Division I LOCA/LOOP test.

The acceptance criterion for this timer is greater than or equal to 54 seconds. The timer was replaced.

Post maintenance testing (PMT) was an abbreviated test performed by simulating the LOOP logic via a jumper and confirming the fan started after an appropriate time delay.

On April 17, 2014, during performance of Unit 1 Division I LOCA/LOOP testing, 1V222A started without a time delay. The timer was replaced. PMT was an abbreviated test to ensure the timer's delay was correct.

On April 25, 2014, during re-performance of LOCA/LOOP testing, 1V222A failed to give proper indication during bus stripping and bus re-energization, but the timing acceptance criterion was met. Possible wiring issues were investigated but none were found.

On March 23, 2016 at 13:36, Timer 62X1A20104 failed acceptance criteria during LOCA/LOOP testing as a result of 1V222A starting without a time delay. In accordance with the TS Bases, operability of the associated AC sources can be restored by rendering the affected load inoperable; Fan 1V222A was shut down by taking the hand switch to STOP. Extensive troubleshooting was performed to determine the cause, and on April 1, 2016, it was determined that the contacts on MOC Switch S1 in Breaker 1A20104 were not properly aligned.

On April 1, 2016 at 20:24, Unit 2 entered TS 3.8.1 due to the A DG being inoperable due to the misaligned contacts on the MOC switch. Unit 1 was in a refuel outage (Mode 5) and did not require the A DG; therefore, TS 3.8.2 was not entered on Unit 1.

On April 2, 2016 at 19:37, the A DG was declared Operable and Unit 2 exited TS 3.8.1 after MOC switch linkage adjustments were made and the contacts were cleaned.

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 internet 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.

Based upon review of the history and cause, there is firm evidence that the condition existed since the supply breaker was replaced on July 19, 2010. As noted in the safety significance section, the A DG was still able to perform its intended safety function; however, since the condition results in inability to meet Surveillance Requirement 3.8.1.18, the A DG must be considered inoperable during periods when 1V222A would have been available to start (without a time delay). As a result, this event is reportable as a condition prohibited by Technical Specifications, in accordance with 10CFR50.73(a)(2)(i)(B), since the inoperability is assumed to have existed for a period of time greater than allowed by the Technical Specifications. A review of historical information for the last three years identified instances in which one of the other DGs (B, C, or D) was inoperable. Based on this information, this condition is also reportable as a condition that could have prevented fulfillment of a safety function in accordance with 10CFR50.73(a)(2)(v)(D).

CAUSE OF EVENT

The direct cause of the MOC switch contacts not aligning properly was mis-adjustment of the MOC switch linkage. The apparent cause of the MOC switch contacts not aligning properly is inadequate post maintenance testing (PMT) for the breaker swap because PMT did not check MOC switch contact alignment.

ANALYSIS/SAFETY SIGNIFICANCE

Actual Consequences:

As a result of declaring the A DG inoperable, Unit 2 entered a 72 hour8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> shutdown action in accordance with TS 3.8.1. This TS entry caused Unit 2 EOOS to be Yellow. Unit 1 was in Mode 5 and the A DG was not required for Unit 1; therefore TS 3.8.2 was not entered. Due to the minimal loading resulting from 1V222A, there was no impact on the ability of the A DG to perform its safety function. Other loads such as Core Spray and RHR were proven to have the correct time delay during the performance of Unit 1 Division I LOCA/LOOP testing on March 23, 2016.

Potential Consequences:

If the issue was not resolved within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />, Unit 2 would have had to initiate shutdown activities.

CORRECTIVE ACTIONS

Key corrective actions will include the following:

1. Revising procedures to include visual inspection to ensure the MOC switch contacts are properly aligned during post maintenance testing.

COMPONENT FAILURE INFORMATION

Westinghouse Porcelain Metal Clad Switchgear Type DH-P Housing 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 internet 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.

PREVIOUS SIMILAR EVENTS

The following are Susquehanna MOC switch issues identified within the past 10 years:

CR-1071573 — On September 9, 2008, 13.8kV Bus 10 failed to transfer due to an open contact in the circuit, which was a MOC switch on the 13kV Breaker. Troubleshooting found that the MOC switches were preloaded and that the pantograph was not moving freely. The linkage was adjusted; pantograph was cleaned, adjusted and lubricated so that it would not bind and so that all contacts were making up properly.

CR-1308123 — On September 28, 2010, a minimum flow valve did not auto open due to MOC switch contacts not fully making up. The condition was corrected by adjusting the MOC switch operating rod in order to have the contacts make up.