Extended scope and responsibility in large component replacements

The replacement of large components from the reactor coolant system was initiated in the early eighties to face the degradation of alloy-600. First to be replaced were the steam generators followed in the nineties by the reactor vessel head. Till now Areva has succeeded in replacing 44 steam generators and 76 reactor vessel heads. Since 2003 the plant operators have been considering the, simultaneous or not, replacement of other large components like pressurizer or pipe segments from the reactor cooling system, in order to extent the operation life of the unit. A critical constraint for the plant operator is the time required to obtain the necessary materials. A good example is given in Ringhals-4, for which 3 steam generators and the pressurizer will be replaced simultaneously in 2011, forgings and tubing should be ordered in early 2007. This paper give details on 2 major projects performed by Areva: -) reactor vessel head and pressurizer simultaneous replacement at St-Lucie, in addition to the replacement of both components, the scope included the opening and closure of the reactor containment building for access; -) 2 steam generators replacement with extended scope at Bugey-4. (A.C.)