05000285/LER-2014-003

LER-2014-003, Reactor Trip Due to Stator Water Cooling Leak During Maintenance

Fort Calhoun Station
Event date:	3-17-2014
Report date:	5-14-2014
Reporting criterion:	10 CFR 50.73(a)(2)(iv)(A), System Actuation
2852014003R00 - NRC Website

Reported lessons learned are incorporated into the licensing process and fed back to industry.

Send comments regarding burden estimate to the FOIA, Pnvacy and Information Collections Branch (T-5 F53). U.S Nuclear Regulatory Commission, Washington, DC 20555-0001 or by internet e-mail to Infocollects.Resource@nrcigov, and to the Desk Officer, Office of Information and Regulatory Affairs, NEOB 10202, (3150-0104), Office of Management and Budget, Washington, DC 20503. a means ,,sec to impose an information collection does not display a currently valid CMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the informatior collection

BACKGROUND

Fort Calhoun Station (FCS) is a two-loop reactor coolant system of Combustion Engineering design.

EVENT DESCRIPTION

On March 17, 2014, at 12:02 Central Daylight Time (CDT), a turbine trip and subsequent reactor trip occurred while operating at nominal 100 percent power. Maintenance was in progress on the main generator stator water cooling system when system inventory was lost resulting in an automatic turbine trip due to low system pressure. Immediate response by operations personnel included implementing procedure EOP-00, Standard Post Trip Actions, and subsequent entry into procedure EOP-01, Reactor Trip Recovery. Based on plant system response this is considered an uncomplicated trip.

The loss of stator water cooling system inventory occurred during the removal of generator stator water cooling conductivity electrode number CE-5043-1 for calibration. The installed safety knob did not prevent the probe from being removed from the system causing a stator water cooling leak. The technicians were unable to isolate the leak in time to prevent a turbine trip. The leak was isolated shortly after the trip by fully removing the probe and closing the isolation valve.

At 1455 Central Daylight Time (CDT), the Headquarter Operations Officer (H00) was informed of the event per 10 CFR 50.72(b)(2)(iv)(B) (RPS Actuation) and 50.72(b)(3)(iv)(A) (Specified System Actuation (RPS)). This report is being submitted pursuant to 10 CFR 50.73(a)(2)(iv)(A), Specified System Actuation (RPS).

CONCLUSION

Fort Calhoun Station's (FCS's) risk management processes and individual behaviors/mindsets were investigated to determine the root and contributing causes of this event. The RCA team reviewed FCS procedures, standards, and expectations regarding operational risk assessment. Interviews were then conducted to determine if individual behaviors/mindsets and station culture was in line with established expectations.

The investigation concluded that there were shortfalls in individuals' mindsets and in the level of detail in the Station's risk management procedures. Mindsets and accountability contributed to the cause of this event, and current Station procedures and guidelines are not sufficiently detailed to ensure workers are not in a knowledge based performance mode when assessing risk just prior to job execution. Individual behaviors, mindset, and knowledge levels, as well as Station procedures and processes need to be at a level to ensure risk identification and mitigation actions are adequately evaluated prior to the job scheduled start time.

The Station determined that the root cause of the plant trip was that operational risk was not effectively identified or mitigated by individuals throughout the organization.

Fort Calhoun Station Reported lessons learned are incorporated into the licensing process and fed back to industry Send comments regarding burden estimate to the FOIA, Pnvacy and Information Collections Branch (T-5 F53), U.S Nuclear Regulatory Commission Washington, DC 20555-0001, or by Internet e-mail to Infocotlects.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 requ'red to respond to, the information collection Fort Calhoun Station

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CORRECTIVE ACTIONS

The leak was isolated shortly after the trip by fully removing the probe and closing the isolation valve.

Long Term Corrective Actions To correct the root cause Fort Calhoun Station will be implementing the Exelon risk management procedure, WC-AA-104, Integrated Risk Management. This procedure provides direction consistent with industry best practices, and requires individual review of each category of risk identification and mitigation.

SAFETY SIGNIFICANCE

The loss of stator water cooling pressure caused a turbine trip to protect the main generator as designed. Plant safety systems shutdown the reactor plant and support systems operated as designed. One non-safety bus was wetted and then deenergized as a precautionary measure. No equipment was damaged. The plant trip is considered uncomplicated.

SAFETY SYSTEM FUNCTIONAL FAILURE

This does not represent a safety system functional failure in accordance with NEI 99-02, revision 7.

PREVIOUS EVENTS

None.