05000333/LER-2013-003
| James A. Fitzpatrick Nuclear Power Plant | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition |
| Initial Reporting | |
| ENS 49491 | 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition |
| 3332013003R00 - NRC Website | |
Background
Preceding events Unit: 1 Mode: 1 Event Date: 10/31/2013 Event Time: 17:22 EST Mode Name: Power Operation Reactor Power: 100 percent
EVENT DESCRIPTION
During James A. Fitzpatrick's (JAF) review of OE INPO ICES-305419, JAF identified a similar condition. The station's review determined that the plant wiring design for the station batteries (71SB-1 and 71SB-2) [EllS Identifier: BTRY] ammeter [II] circuits contains a shunt in the current flow from each direct current (DC) battery, with leads to an ammeter in the main control room (MCR). The small difference in voltage between the two taps on the shunt is enough to deflect the ammeter in the MCR when current flows from the battery through the shunt. The ammeter wiring attached to the shunt does not have fuses, and if one of the ammeter wires shorts to ground during a fire, at the same time another DC wire from the opposite polarity on the same battery also shorts to ground during the fire, a ground loop through the unfused ammeter cable could occur. With enough current going through the cable, the potential exists that the overloaded ammeter wiring could damage other wiring in direct physical contact with the cable resulting in a loss of the associated safe shutdown function/capability or a secondary fire in another fire area.
This event was reported to the NRC (ENS 49491) on October 31, 2013 per 10 CFR 50.72(b)(3)(ii)(B). The required actions of the Technical Requirement Manual for fire barrier penetrations were implemented. This report is being submitted in accordance with 10 CFR 50.73(a)(2)(ii)(B), a condition that resulted in the plant being in an unanalyzed condition that significantly degraded plant safety.
EVENT ANALYSIS & CAUSE The premise for this event to occur requires two concurrent extremely low resistance (hard) grounds (i.e., one on the positive side of the battery through the ammeter circuit wiring routed to the control room and one on the negative side of the battery through a second ground on the same battery system). The ammeter circuit only contains one pole of the battery and the event requires an unrelated circuit (of opposite polarity) shorting to ground. Furthermore, this circuit must contain an overcurrent protective device not adequately rated for the ammeter wiring. The DC distribution system is floating with no established ground other than the high resistance ground provided through the ground detector [GDET]. It is designed in this manner to allow the system to withstand one hard ground (zero resistance) with no adverse effect on the operation of any equipment fed from the DC system. Since this is a very low probability event, it was likely not considered during the development of the original Appendix R analysis and related Institute of Electrical and Electronics Engineers (IEEE) standards.
EXTENT OF CONDITION
An extent of condition review determined that this issue applies to Divisions 1 and 2 ammeter circuit wiring. The areas with the deficient fire barriers are the DC Switchgear Room 1A and 1B, Cable Spreading Room, Relay Room and Control Room.
FAILED COMPONENT IDENTIFICATION:
None
Completed Actions
The required actions of the Technical Requirement Manual for fire barrier penetrations were implemented. The Operability of fire detectors on both sides of the subject penetrations was verified.
Open Actions The condition is being tracked by the corrective action process; an analysis is underway to determine the appropriate resolution.
SAFETY SIGNIFICANCE
Nuclear Safety There were no actual consequences for this event. The potential consequences of this event are that the overloaded ammeter wiring could damage other wiring in direct physical contact with the cable resulting in a loss of the associated safe shutdown function/capability or a secondary fire in another fire area.
Radiological Safety No radiological impact or dose associated with this condition.
Industrial Safety No safety events or abnormal increases to personnel risk.
SIMILAR EVENTS
A review was performed and it was determined that there are no similar historical cases at JAF.
REFERENCES
- October 31, 2013 - CR-JAF-2013-05546