A self-revealing event identified a finding of low to moderate safety significance, because Calvert Cliffs Nuclear Power Plant (CCNPP) did not perform a modification design review, as required by station procedures. Following a Unit 2
reactor trip on January 23, 2004, the atmospheric dump valves and
turbine bypass valves automatically Quick Opened, as designed. However, the Quick Open signal did not clear when the
reactor coolant temperature dropped below the Quick Open setpoint, because of a reactor regulating system relay failure. As a result, an uncontrolled cooldown of the
reactor coolant system occurred, which in turn caused a loss of the normal heat removal system. This finding was more than minor because it was considered to be a precursor to a more significant event. A
Significance Determination Process Phase-3 risk analysis determined that this finding was of low to moderate safety significance, based on the change in core damage frequency.
