Safe-End Replacement on Pressurizer Upper Nozzles

Following the occurrence of cracking in various nozzle Dissimilar Metal (DM) butt welds in different PWR plants around the world (VC Summer, Ringhals, Tsugura and more recently Wolf Creek), an integrated approach to develop a material degradation management program was adopted for the Belgian PWR Units. Electrabel, together with Tractebel Engineering and Vinc¸otte have qualified enhanced nondestructive examination procedures and extended in-service inspections. Over the last decade, a very effective monitoring of the potential cracking in the pressurizer nozzles to safe-ends DM welds has been conducted. Electrabel and Tractebel Engineering are now initiating a mitigation process. Within this frame, Westinghouse Electric Company has developed a replacement solution of the pressurizer (PRZ) upper nozzle safe-ends of the 4^″ and 6^″ lines with implementations at Doel Units 3 & 4 and Tihange Units 2 & 3. This paper outlines the development of the replacement solution. It provides an overview of the replacement process itself. It outlines the comprehensive qualification program developed to achieve approval for implementation.