VICNIS, a new safety-related radiation monitoring channel for checking vessel boundary integrity

BUGEY-3 feedback and mechanical analyses have both shown the possibility of occurrence of leaks through alloy 600 penetration cracks. At the beginning of 1993, at least 4% of the 1,000 inspected penetrations demonstrated evidence of purely longitudinal cracks at various stages of evolution. This relatively new problem is a major problem for EDF since about 4 points of PWR availability were lost in 1992. Although cracking is not considered by EDF as presenting near term risks for Safety, EDFs strategy heavily relies on efficient leak-detection devices. A couple of days after the BUGEY-3 leak discovery, in October 1991, EDF started testing or at least carrying out investigations on a number of various devices to set up an industrial device for reliable and efficient leak detection systems. VICNIS monitoring equipment based on detection of nitrogen 13 has been granted French Safety Authority approval. A series of tests conducted on EDF plants in 1992 confirm VICNIS vessel integrity monitoring capabilities