6. Conclusion

Following a detailed study of the ultrasonically relevant parameters for fuel characterization, we developed a specific acoustic microscope which is now used in its "routine use" version at the JRC-ITU European center in Karlsruhe.

Completely new conclusions on the evolution of the elastic properties of UO ₂ fuels as a function of the burnup rate have been drawn for fuels that have spent up to 10 years in the reactor.

The basic assumption of reducing everything to a global effect of the rate of combustion, without distinguishing between thermal, chemical and other effects, seems coherent and has enabled us to define simple equations that make the device usable in an almost plug-and-play version.

Today's microscopes make it possible to obtain both Young's modulus and density...