A self-revealing finding of very low safety significance (Green) with associated
NCV of
10 CFR Part 50, Appendix B, Criterion XVI, and
Technical Specification (TS) 3.4.13, Primary Coolant System (
PCS)
Operational Leakage, was identified for failure to take corrective actions to prevent recurrence of
Control Rod Drive Mechanism (
CRDM) cracking and leakage, a significant
condition adverse to quality (
SCAQ). Specifically, for Criterion XVI the licensee failed to include the internal
CRDM housing weld build-up area within the scope of corrective actions taken for a 2001
CRDM through wall leak on CRDM-21, caused by transgranular
stress corrosion cracking (
TGSCC). Subsequently, a
through wall leak recurred in the weld build-up area on CRDM-24 in 2012 due to
TGSCC. As a result, the licensee operated with
PCS pressure boundary leakage, which is not allowed by
TS 3.4.13. Further, because the licensee was not aware that the leakage was
PCS pressure boundary leakage, the licensee did not implement the associated TS action statement. The licensee replaced CRDM-24 upper housing and entered the issue into their corrective action program as
CR-PLP-2013-01134. Additional corrective actions are described in NRC
Inspection Report 05000255/2012012. The inspectors determined that this issue was more than minor in accordance with
IMC 0612, Appendix B, Issue Screening, because it was associated with the
Initiating Events Cornerstone attribute of equipment performance and adversely affected the cornerstone objective to limit the likelihood of events that upset plant stability. Specifically, the licensee did not take adequate corrective actions to prevent recurrence of leakage in
CRDM housings, which represents
pressure boundary leakage. The inspectors determined this finding was of very low safety significance (Green) because the leak would not have exceeded the
reactor coolant system leak rate for a small
LOCA and could 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 cause of this finding, non-conservative decision making, occurred over 10 years ago and is well outside of the nominal 3 year period in
IMC 0612 for cross-cutting aspects. Therefore, this is not indicative of current performance, because no other opportunities to identify the issue occurred during the previous 3-year period. However more recently, the licensee exhibited non-conservative decision making with respect to addressing the potential for
CRDM housing cracking and leakage during the recent root cause (Section 4OA2.4 (b.2) of this report), resulting in another finding. This cross-cutting aspect will be captured through the other finding.
