The inspectors identified a finding of very low safety significance (Green) with an associated
NCV of
10 CFR Part 50, Appendix B, Criterion V, for the licensees failure to accomplish quality activities in accordance with the prescribed procedures. Specifically, the licensee failed to adequately evaluate and document the generic implications of the cause of the 2012 cracking identified in CRDM-24 in accordance with a quality procedure, Procedure,
EN-LI-118, Root Cause Evaluation. This issue was entered into the licensees Corrective Action Program (
CAP) under
CR-PLP-2013-01500. Subsequently, the licensee decided to revise the inspection plan to add additional corrective actions to inspect a sample of
welds No. 3 and No. 4 for
TGSCC during the upcoming refueling outage. The inspectors determined that this issue was more than minor in accordance with
IMC 0612, Appendix B, Issue Screening, because if left uncorrected, the performance deficiency would have the potential to
lead to a more significant safety concern. Specifically, absent NRC identification, the licensee would not have completed further evaluations or inspections of
CRDM housing
welds, which could have resulted in additional
CRDM housing failure and leakage by
TGSCC. In accordance with Table 2, Cornerstones Affected by Degraded Condition or Programmatic Weakness, of
IMC 609, Attachment 4, Initial Characterization of Findings, the inspectors determined that the finding was associated with the
Initiating Events Cornerstone because the failure of a
CRDM housing is a Primary System
LOCA initiator contributor. Using Exhibit 1,
Initiating Events Screening Questions, in
IMC 0609, Attachment A, The
Significance Determination Process (
SDP) for Findings At-Power, the inspectors determined this finding was of very low safety significance because the leak would not exceed the
reactor coolant system leak rate for a small
LOCA and would not have likely affected other systems used to mitigate a
LOCA resulting in a total loss of their function. Specifically, the slow rate of change for leakage for
TGSCC in type 316 stainless steel will experience leakage rates well below a small break
LOCA, which would be observed through the crack, alerting operators to take action to shut down the plant prior to experiencing a component rupture. The inspectors determined that the primary cause of the failure to adequately consider
welds No. 3 and No. 4 in the generic implications section of the root cause report (
RCR) related to the decision making cross-cutting component in the human performance area because licensee staff did not use conservative assumptions in decision making. Specifically, the licensee did not use conservative assumptions when excluding
welds No. 3 and No. 4 as being susceptible to
TGSCC when there was not enough information to exclude them from consideration.
