Annick Froideval

EXAFS Study on Irradiated ODS Ferritic Steel

The commercial material PM2000 is investigated as a representative for the material class of Oxide Dispersion Strengthened (ODS) steels. ODS steels are envisaged as substance of structural components in Very High Temperature Reactors (VHTR). The VHTR concept is considered by the Generation IV International Forum, an initiative researching the next generation of nuclear power plants. The chosen ODS is mainly used for non-nuclear applications. In order to justify the applicability of this material within a neutron irradiative environment, the evolution of radiation damage must be investigated. PM2000 samples are therefore exposed to 4He2+ irradiation at different temperatures. The potential structural change is measured as a function of the radiation parameters, using Extended X-Ray Absorption Fine Structure (EXAFS) spectroscopy on the yttrium K-edge and on the iron K-edge. A degradation of the dispersoids or the steel matrix would show the limitation of this material candidate.

Condition Monitoring of High Temperature Components With Sub-Sized Samples

Advanced nuclear plants are designed for long-term operation in quite demanding environments. Limited operation experience with the materials used in such plants necessitate a reliable assessment of damage and residual life of components. Non-destructive condition monitoring of damage is difficult, if not impossible for many materials. Periodic investigation of small samples taken from well defined locations in the plant could provide an attractive tool for damage assessments. This paper will discuss possibilities of using very small samples taken from plant locations for complementary condition monitoring. Techniques such as micro/nano-indentation, micropillar compression, micro bending, small punch and thin strip testing can be used for the determination of local mechanical properties. Advanced preparation techniques such as focused ion beam (FIB) allow the preparation of samples from these small volumes for micro-structural analyses with transmission electron microscope (TEM) and advanced X-ray synchrotron techniques. Modeling techniques (e.g. dislocation dynamics DD) can provide a quantitative link between microstructure and mechanical properties. Using examples from ferritic oxide dispersion strengthened materials the DD approach is highlighted to understand component life assessments.