In the fall of 2001, North Anna Unit 2 conducted a visual inspection of the outer surface of its reactor vessel head (RVH), looking for evidence of leakage. Three of 69 control rod drive mechanism (CRDM) penetrations were identified as suspect, based on the presence of boric acid crystals encircling the three penetrations. Supplemental inspections from underneath the ferritic steel RVH revealed crack-like indications in the vicinity of the J-groove weld/butter region of each of the three penetration attachment welds. To characterize the flaws, a representative portion of one of the welds was removed for metallographic analysis. The results of the analysis formed the technical basis for a root cause evaluation (RCE), conducted to determine the origin of cracking. This report summarizes the findings of that RCE. It also briefly discusses the inspection/repair strategy implemented by Dominion to comply with US Nuclear Regulatory Commission Bulletin 2001–01.

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