05000348/LER-2013-004
| Joseph M. Farley Nuclear Plant, Unit 1 | |
| Event date: | 12-16-2013 |
|---|---|
| Report date: | 02-14-2014 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition |
| 3482013004R00 - NRC Website | |
Westinghouse — Pressurized Water Reactor Energy Industry Identification Codes are identified in the text as [XX]
Description of Event
While Farley Units 1 and 2 were operating at 100 percent power in Mode 1 at 1627 CST on December 16, 2013, an engineering review of recent industry operating experience regarding unf used direct current (DC) ammeter [II] circuits was concluded. The review determined that certain DC ammeter circuits at Farley lacked overcurrent protection. A postulated fire in a fire area containing DC ammeter circuit cabling could result in concurrent shorts to ground of a DC ammeter cable and a DC cable of opposite polarity. Due to a lack of overcurrent protection, the resultant excessive current flow in the ammeter cable could result in a secondary fire in another fire area. Due to the cable routing and the location of safe shutdown equipment at Farley, the two fires could adversely affect alternate safe shutdown capability contrary to 10 CFR 50, Appendix R. There were no structures, components, or systems that were inoperable at the time of this determination that contributed to the conclusion.
The following Farley Unit 1 and 2 components have the vulnerability identified.
Auxiliary Building safety related DC system Batteries [BTRY] Auxiliary Building safety related DC system Battery Chargers [BYC] Turbine Building non-safety related DC system Batteries Service Water Structure safety related DC system Battery Chargers Multiple fire areas in the Turbine Building, Service Water Structure, and Auxiliary Building, including the common control room and the cable spreading rooms are potentially affected.
This represents an unanalyzed condition that significantly degraded plant safety and is reportable pursuant to 10 CFR 50.73(a)(2)(ii)(B).
Cause of Event
The cause of the condition was a latent design error that was made during plant construction. The original design of the ammeter circuits did not provide for overcurrent protection.
Safety Assessment There are no actual safety consequences. The event did not adversely affect the safe operation of the plant or the health and safety of the public. A secondary fire from this condition is considered improbable since two grounds of opposite polarity must be established from a single fire such that the fault current is sufficient to overheat the grounded ammeter cabling or adjacent material to the point of ignition. Additionally, the fault current must be low enough so as not to actuate overcurrent protection in the grounded cabling that is opposite in polarity to the grounded ammeter cable.
Corrective Action Compensatory measures have been established in all affected fire areas per Farley fire protection procedures. These compensatory measures will remain in effect until permanent resolution of this condition. Plant modifications are being developed to provide overcurrent protection for the affected DC ammeter circuitry.
Additional Information
A review of past LERs at Farley from 2008 to present identified no similar design deficiencies impacting alternate safe shutdown capability.