05000400/LER-2014-002
| Shearon Harris Nuclear Power Plant, Unit 1 | |
| Event date: | 06-12-2014 |
|---|---|
| Report date: | 08-11-2014 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition |
| 4002014002R00 - NRC Website | |
Background
On June 12, 2014, while operating at 100 percent power in Mode 1, Harris plant personnel determined that inadequate cable protection existed in the control cables for the Turbine Emergency Oil Pump (EOP) [P] during an evaluation of an Operational Experience (OE).
DP-1-250-3 is a circuit breaker [BKR] which feeds the motor of the direct current (DC) Lube Oil Backup pump [P]. Directly off the motor starter are control switch cables [CBL] which had no electrical protection devices (fuses) other than the circuit breaker. Since the control cable is routed through several fire areas, including the main control room, postulated conditions could have allowed fires to ignite in multiple areas. Because the control cable is routed through cable trays that contain safe shutdown cables, the configuration creates a common enclosure situation. Additionally, failure of the EOP could cause significant main turbine damage.
This event is reportable in accordance with 10 CFR 50.73(a)(2)(ii)(B), “The nuclear power plant being in an unanalyzed condition that significantly degraded plant safety.” On June 12, 2014, at approximately 1247 EDT, Harris plant personnel determined that inadequate cable protection existed in the control cables for the Turbine EOP. The cable protection was being reviewed as a result of an extent of condition identified in an OE evaluation.
The DC motor power is supplied through cables. Directly off the motor starter are control switch cables.
There were no electrical protection devices (fuses) other than the circuit breaker protecting these cables. The large breaker did not provide adequate cable protection in case of a fault and did not meet Harris Nuclear Plant (HNP) design requirements. The installed cables were sized consistently with the original EBASCO specification for control cables, but because they are tied directly to a 250V DC bus [BU], they were actually installed like power cables.
Control cables that are not protected from electrical faults could become a fire ignition source.
Event Description
In the event of an over-current situation, the cables could have heated up anywhere along their path, including at the switches. This could have caused and/or propagated fires in multiple fire areas.
Energy Industry Identification System (EIIS) and component codes are identified in the text as [XX].
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 (T-5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by internet 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.
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 (T-5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by internet 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.
An extent of condition (EOC) evaluation was performed that was limited to DC powered motors, including safe shutdown (SSD) motors, and vendor-supplied motor control skids. The EOC evaluation concluded that the Air Side Back-up Pump Motor [MO] circuit has the same unfused condition.
However, it was not a fire protection concern since the cable remains in one area and would not allow fire propagation to other fire areas.
These cables were designed and installed without proper electrical fault protection. This lack of fault protection could have created a common enclosure fire hazard in certain situations. This design is an historical issue that was part of the original plant design, and no discrepancies have been found that would indicate this should have been identified earlier than now.
Causal Factors The apparent cause is the historical installation of an unfused section of cable in the control circuit of the Emergency Oil Pump.
Corrective Actions
Completed Corrective Actions
Immediate Compensatory Action – Established hourly fire watches in multiple areas.
Installed fuses in each leg of the 250V DC control circuit for the EOP motor as per Engineering Change 96989.
Safety Analysis
There were no safety consequences associated with this event, as the equipment did not fail (the unfused cables did not burn). These cables were designed and installed without proper electrical fault protection. This lack of fault protection could have created a common enclosure fire hazard under postulated situations.
NFPA 805 has two requirements to ensure that the fire damage is limited to one fire area. The first is having rated fire barriers between different divisions of equipment. The second is that fire damage cannot propagate outside the fire area due to electrical faults in the Common Enclosures. Those circuits that share enclosures with circuits required to achieve the nuclear safety performance criteria 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 (T-5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by internet 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.
and whose fire-induced failure could cause the loss of the required components must be identified to prevent propagating fires outside of the immediate fire area due to fire-induced electrical faults on inadequately protected cables or via inadequately sealed fire area boundaries. This creates a condition where the cable is not electrically protected such that a high impedance fault could cause the cable to overheat. If the cable reaches 400 degrees F, cable damage may occur to adjacent cables (Common Enclosure Concern). A temperature of 400 degrees F is the conservative value used for KERITE Fire Resistant cable, used in the Zone Of Influence calculations as specified in the HNP Safety Evaluation Report (SER) for the transition to NFPA 805. If the cable reaches the ignition temperature, a secondary fire can be created in areas anywhere along the cable path. Since these cables are routed through multiple fire areas, the secondary fire could be outside of the area where the original postulated fire occurs. This could expose the plant to cross train cable damage and is contrary to the requirements of NFPA 805.
Other than the risks associated with fire and safe shutdown in the affected areas, there are no additional chemical, radiological, industrial, production, Emergency Preparedness, or Security impacts due to this condition. The nuclear safety significance lies in the potential for a fire to damage safe shutdown equipment in multiple fire areas, which would put the plant in an unanalyzed condition.
No Operating Experience was found that would indicate the unfused cables should have been identified earlier. HNP became aware of the issue on January 9, 2014.
This report contains no regulatory commitments.
Commitments
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