A review of industry operating experience regarding the impact of unfused [safety-related] direct current ammeter circuits in the main control room has determined the described condition [having the ammeters installed] to be applicable to River Bend Station, resulting in a potentially
unanalyzed condition with respect to
10 CFR 50 Appendix R analysis requirements. River Bend Station does have unfused ammeter leads. This normally is not a concern, since two failures are required to cause the problem described in the document referenced above; an ammeter lead must short to ground, and another lead of the opposite polarity must also short to ground. Either of these events by itself will set an alarm, but not cause equipment damage. This allows for locating and repairing the problem before the second failure occurs. However, during a fire, there is a greater chance that these two failures could happen simultaneously, or before a single failure can be repaired.
This condition is being reported in accordance with 10 CFR 50.72(b)(3)(ii)(B). Interim compensatory measures have been implemented.
The NRC Resident Inspector has been notified.
