05000219/LER-2013-005
| Oyster Creek, Unit 1 | |
| Event date: | 12-17-2013 |
|---|---|
| Report date: | 04-11-2014 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(B), System Actuation |
| 2192013005R01 - NRC Website | |
Reported lessons learned are incorporated into the licensing process and fed back to industry.
Send comments regarding burden estimate to the FOIA, Privacy and Information Collections Branch (1-5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by intemet e-mail to Infocollects.Resource@nrc.gov, and to the Desk Officer, Office of Information and Regulatory Affairs, NEOB-10202, (3150-0104), Office of Management and Budget, Washington, DC 20503. If a means 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.
Plant Conditions Prior To Event
Event Date: December 17, 2013 Event Time: 1958 EST Unit 1 Mode: Hot Shutdown Power Level: 0%
Description of Event
On December 17, 2013 at 1958 EST, while shut down, the plant experienced a reactor SCRAM when taking the Mode Switch from REFUEL to SHUTDOWN. The jumpers required to prevent a full SCRAM for this Mode Switch change were not installed as required by procedure.
The Unit Supervisor (US) and Reactor Operators (ROs) did not physically verify these jumpers were removed as required by the pre-critical check off and assumed they were installed. The US mistakenly believed the Mode Switch had to be in SHUTDOWN to remove the jumpers, even though these jumpers had already been removed by procedure. Believing that the jumpers were installed, the US ordered the Mode Switch placed in SHUTDOWN, which initiated a full SCRAM.
Cause of Event
The actuation was a result of the reactor mode switch being placed from the refuel position to the shutdown position without the scram bypass jumpers installed. The jumpers required to prevent a full SCRAM for this Mode Switch change were not installed as required by procedure. The Unit Supervisor (US) and Reactor Operators (ROs) did not physically verify these jumpers were removed as required by the pre-critical check off and assumed they were installed.
The root cause determined that an unvalidated assumption by the supervisors resulted in a reactor scram while shut down.
Analysis of Event
The Reactor Protection System processed the full SCRAM signal and the Control Rod Drive (CRD) system operated as designed, with hydraulic pressure attempting to drive in rods that were already fully inserted. This action can introduce corrosion products from the guide tubes into the drive seals, which causes excessive leakage leading to increased drive speeds and increased drive pressure necessary to break the rods free from the fully inserted position. Thorough rod exercising and flushing is necessary to mitigate these effects. Since this event occurred during the final preparations for reactor startup, complete rod exercising was not accomplished. The plant startup was delayed by approximately four hours, and some additional delays due to having to break free rods during the startup, as well as increased potential for double notching events, could be attributed to this event.
There were no safety consequences impacting the plant or public safety as a result of this event. The reactor was subcritical with all rods inserted at the time of the actuation. All systems functioned as designed. This event is being reported pursuant to 10CFR50.73(a)(2)(iv)(B) due to a valid actuation of the Reactor Protection System (RPS).
Corrective Actions
The root cause determined that an unvalidated assumption by the supervisors resulted in a reactor scram while shut down.
Corrective actions include evaluation on requirements, through an Out-of-box Evaluation, to ensure operators understand and can demonstrate the proper use of the human performance fundamental tools that broke down in this instance. In addition, procedures will be enhanced to clarify verification requirements.
Operations management will reinforce the clear standard for zero deviations to procedure use and adherence requirements. All Operators and Operations Supervisors will perform a read and sign documenting that they understand and will comply with the requirements.
Previous Occurrences
There have been no similar Licensee Event Reports associated with this component failure submitted at OCNGS in the last two years.