The inspectors identified a finding of very low safety significance and an associated
NCV of
10 CFR 50, Appendix B, Criterion III, ?Design Control,? when licensee personnel failed to perform an adequate thermal-mechanical analysis to support operation with a missing Unit 2 head stud. Specifically, the licensee did not perform a complete set of analyses under operating, faulted, and design conditions to confirm the associated stud and
flange stresses would remain within the Code allowable limits. Consequently, the licensee did not recognize that the bearing stress under the head stud nuts at the vessel
flange face exceeded the Code allowable stress. The licensee entered this issue into their
CAP as
IR 01578717, ?Unit 2 RV [Reactor Vessel] Closure Stud Bearing Stress is Above
ASME Allowed.? The inspectors determined that the performance deficiency was more than minor because it was associated with the Design Control attribute of the
Initiating Events cornerstone and adversely affected the cornerstone objective of limiting the likelihood of those events that upset plant stability and challenge critical safety functions. The inspectors also answered ?Yes? to the more-than-minor screening question, ?If left uncorrected, would the performance deficiency have the potential to
lead to a more
significant safety concern?? Specifically, the inspectors determined that this issue was more than minor because, if left uncorrected, the failure to perform an adequate thermal-mechanical analysis could result in the inability of the reactor vessel to meet the design basis operating
transient without a
LOCA. The inspectors performed a Phase 1
SDP Screening and evaluated this issue by application of Questions 1 and 2. Questions 1 and 2 asked: ?If after a reasonable assessment of degradation, could the finding result in exceeding the
reactor coolant leak rate for a small
LOCA or could the finding have likely affected other systems used to mitigate a
LOCA resulting in a total loss of their function (e.g., Interfacing System
LOCA)?? In this case, because of the available margins in the
flange material strength, the inspectors answered these questions ?No? and this issue screened as having very low safety significance. This finding had a cross-cutting aspect in the Resources component of the Human Performance cross-cutting area because the licensee did not have complete, accurate, and up-to-date design documentation, procedures, and work packages. Specifically, the licensee failed to ensure the applicable
ASME Code Section III design limit for bearing stress (design basis) was correctly translated into design document
EC 379850