Study of corrosion mechanism of new zircaloys

The present thesis focus on the corrosion mechanism of new zircaloys, those Zr-rich alloys more recently synthesized, expected to exhibit a superior resistance due to their specific doping with a few at% of niobium. Better and better, series of different zirconium alloys were developed successively to improve the life time of the nuclear plants, where those alloys are used to build the critical tubing's around the core and the nuclear fuel. In Part 1 (Introduction) the main problems of zirconium alloys cladding are situated. Then in Part 2, knowledge on the corrosion of zirconium alloys is refreshed from literature. The experimental methods used during preparation of the present thesis are described in part 3. More in details, corrosion resistance principles of zirconium alloys are reported in Chapter 4 as experimented either in pressurized water or in high temperature steam. Chapter 5 is devoted to the impacts of the microstructure on the corrosion process, more particularly with the new alloys. In the following part, the role of the surface oxide film is questioned for two new alloys. Chapter 7 focus on the parallel impacts of residual stresses and crystal structure of surface zirconia, that is more addressed to the Nb-containing alloys (Part 7). Cubic and monoclinic oxides are questioned in Chapter 8, before to write Main Conclusions. (author)