As part of the renovation project of the Phénix plant, the modular-type steam generators were the subject of an expert evaluation program in order to verify their condition after ~100 000 h of power operation and demonstrate their ability to continue operation for the planned lifetime extension (30 000 h).

This evaluation, based on the destructive examination of several modules, showed that some parts of the superheater and reheater were affected by some delayed reheat cracking of 321 H stainless steel. Thus, the extension of the operation of the units for the prolonged lifetime of the plant could not be justified.

A major repair operation was undertaken. Every superheater and reheater module was disassembled. A cleaning process was developed for removal of residual sodium inside the modules, based on the water vapor nitrogen method, and adapted to the special geometry of the component. The potentially defective parts were replaced by new ones. A specific procedure was used for welding of aged to new materials. The nonreplaced parts were controlled by a specially developed ultrasonic technique; 47 modules were successfully repaired within 1 yr.