05000219/LER-2017-002

LER-2017-002, Manual Reactor Scram due to Degrading Main Condenser Vacuum

Oyster Creek Nuclear Generating Station
Event date:	07-03-2017
Report date:	08-31-2017
2192017002R00 - NRC Website

LER 17-002-00 for Oyster Creek Regarding Manual Scram due to Degraded Main Condenser Vacuum

ML17249A124
Person / Time
Site:	Oyster Creek
Issue date:	08/31/2017
From:	Gillin M F Exelon Generation Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
RA-17-052 LER 17-002-00
Download: ML17249A124 (4)

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.

Oyster Creek Nuclear Generating Station

3. LER NUMBER

2017 - 00 002

Plant Conditions Prior To Event

Event Date:

Unit 1 Mode:

July 3, 2017 Event Time: 10:15 hours ET Power Operation Power Level: 100%

Description of Event

On July 3, 2017 at 1015 hours0.0117 days <br />0.282 hours <br />0.00168 weeks <br />3.862075e-4 months <br /> a manual reactor scram was initiated due to degrading condenser vacuum. The loss of vacuum was initiated by the operations department failure to execute the procedural requirement to align the AOG system into a shutdown lineup. The SJAE discharge line was blocked by water from the AOG system. The AOG system tripped eleven hours earlier following a grid disturbance. During the trip, operations personnel failed to re-align the AOG system to a shutdown lineup resulting in the AOG Flame Arrestor siphoning into the lower section of the off-gas delay pipe.

Cause of Event

Operations failed to enter stop work criteria, made a non-conservative decision and did not execute a procedure in response to a trip of AOG. After the AOG system trip from the electrical transient, operations personnel misdiagnosed the AOG system lineup. The AOG system had partially isolated as designed with the recombiner blower still in service. To place the AOG system in a shutdown lineup, the system isolation valve had to be closed to separate the AOG building from the off-gas delay pipe. This isolation valve was left open and flame arrestor water siphoned back into the off-gas delay pipe causing a stall of the SJAEs and a subsequent loss of main condenser vacuum.

Analysis of Event

Following the manual scram actuation, all systems responded as expected; therefore, this event is of low safety significance.

An analysis did not determine an area where early detection via plant observable parameters would have stopped the event. An analysis of water usage and design is below.

A known operating characteristic on the system results in the flame arrestor getting pressurized on the process side up to 5 psig, (stem pressurization air sub-system). This pressure will cause the flame arrestor to siphon back into the AOG inlet line. A siphon will continue to backfill the suction lines due to the automatic makeup from the demineralized water system. Failure to isolate the inlet line to the flame arrestor with the system not in service allows water back flow to the off-gas process piping and fill the delay pipe. The delay pipe is the discharge piping from the SJAE process gas flow. Water filling the line resulted in the stall of the SJAE's that started at 0919 hours0.0106 days <br />0.255 hours <br />0.00152 weeks <br />3.496795e-4 months <br /> on July 3, 2017.

To block SJAE flow this line would have to fill up the lowest elevation of piping. This is approximately 8100 gallons of water. The earliest detection of changes in the plant would occur just as the pipe is filled with water blocking the flow and is consistent with operations observations at approximately 0825 hours0.00955 days <br />0.229 hours <br />0.00136 weeks <br />3.139125e-4 months <br /> on July 3, 2017.

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.

Oyster Creek Nuclear Generating Station

3. LER NUMBER

2017 - 00 002

Corrective Actions

Exelon took the following corrective actions:

1. Immediate procedure changes to alarm response and operating procedures were performed to provide clear direction for a trip of the AOG system.

2. Industry Benchmarking was completed and the Operations department has implemented an integrated decision-making model.

3. Reinforcement of key operations fundamentals and human performance boards with each operator.

Previous Occurrences

A previous event occurred on July 26, 2012 during startup from Forced Outage 1 F29. The delay pipe filled with water prior to or during plant startup resulting in a six-hour delay in establishing condenser vacuum. A procedure change was put in place to verify the delay pipe is draining correctly prior to every plant start up.

Component Data Component IEEE 805 System ID IEEE 803A Component N/A N/A N/A