On November 28, 2007, the inspectors observed licensee actions in response to a
scram with complications. The digital
feedwater level control system experienced a loss of two power supplies. This caused a loss of
feedwater, main
turbine trip, and reactor
scram due to an erroneous
reactor vessel water level 8 signal. The loss of
feedwater caused an actual
reactor vessel water level 2, which initiated both
RCIC and
high pressure core spray (
HPCS) for
reactor vessel water level control.
RCIC tripped approximately 13 seconds after initiation due to low suction pressure, and reactor vessel control was maintained using
HPCS. The inspectors observed licensee personnel shutdown the plant to Mode 4. A Special Inspection Team was chartered to investigate this event, and the results are documented in
IR 05000440/2007010. At the end of the inspection period, the inspectors continued to evaluate the adequacy of
RCIC surveillance test procedures. A contributing cause of the November 28, 2007,
RCIC failure was determined to be an improperly tuned flow controller. The controller settings were established in January 2006 and the
RCIC system had passed routine surveillance testing criteria since that time without identification of the condition.
RCIC testing typically relied on a suction and return flow path to the condensate storage tank. On November 28, 2007,
RCIC failed to perform as designed when called upon to inject from the suppression pool to the reactor vessel.
