A Green self revealing finding was identified for inadequate implementation of corrective actions regarding vibration induced failures of socket welds. This finding resulted in an August 11, 2011, Nine Mile Unit 2
scram due to a failed socket weld on the vent line for the \'A\'
feedwater pump (FWP) minimum flow line.
NMPNS did not properly consider the impact of high vibration levels on a vent line attached to the \'A\' FWP mini-flow recirculation line.
NMPNS corrective actions included upgrading the socket weld to the requirements outlined in industry operating experience (
OE). The inspectors determined that the finding was of very low safety significance (Green) through performance of a Phase 1
SOP in accordance with
IMC 0609.04, Table 4a, Characterization Worksheet for
Initiating Events,
Mitigating Systems (MS) and
Barrier Integrity Cornerstones. Specifically, the finding did not contribute to both the likelihood of a
reactor trip and the likelihood that mitigation equipment or functions will not be available. This finding has a cross-cutting aspect in the area of problem identification and resolution in that
NMPNS did not implement and institutionalize
OE through changes to station processes, procedures, equipment and training programs. Specifically in 1998 and again in 2010,
NMPNS did not institutionalize external and internal
OE to reduce the probability of a socket weld failure.
