Irradiation effects in helium implanted silicon carbide measured by X-ray absorption spectrometry

Silicon carbide (SiC) is investigated as a possible structural material for future nuclear power plants. It is utilized as fibre and/or as matrix in ceramic composite materials. The fibre reinforcement is necessary to provide the required ductility. In this work, the behaviour of pure SiC under irradiation by He implantation is studied. Samples are investigated by means of the extended X-ray absorption fine structure (EXAFS) spectroscopy, performed at the Si K-edge. The Fourier transforms of the EXAFS data indicate a decrease of the Si–Si bond related shells around the absorbing Si. The possible damage features are discussed and the three most probable ones for the irradiation conditions are selected for future modelling work.

An X-ray absorption spectroscopy study of an oxide dispersion strengthened steel

Wolfgang Hoffelner, Manuel Alexandre Pouchon

Oxide dispersion strengthened (ODS) steels are being investigated as possible structural material for components of future nuclear power plants. The dispersoids in the matrix (yttria particles) serve as pinning points for moving dislocations, and thereby improve the creep behavior of the material. Depending on the product, the dimension of the particles is in the range from a few nm up to 100 nm. The material properties depend on the size distribution. It is also expected that other parameters of the dispersoids may influence the materials behavior. An extended X-ray absorption fine structure (EXAFS) study has been conducted on PM2000 (ferritic ODS steel) samples, in order to determine the structure of the yttria inclusions. A PM2000 sample, which had been irradiated with He ions of 1.5 MeV up to a matrix-damage of not, vert, similar1 displacement per atom (dpa) in a surface layer of 2.7 μm in depth was measured. A multi angle implantation was performed, in order to avoid damage peaks as function of depth. A direct comparison of the EXAFS spectra and of the Fourier transformations shows no major difference between the irradiated samples and the non-irradiated one. Therefore any potential radiation induced damage or phase transformation of the dispersoids must be minor, which indicates good radiation stability under the given circumstances.

Elsevier2007

Synchrotron Light Techniques for the Investigation of Advanced Nuclear Reactor Structural Materials

Didier Gavillet, Wolfgang Hoffelner, Manuel Alexandre Pouchon

In the frame of the Generation IV initiative, different structural material candidates are investigated at the Paul Scherrer Institute. These are oxide dispersion strengthened (ODS) steels, intermetallic materials and ceramic composite materials. The response of the material to different potential loads (irradiation, temperature …) is addressed in a multi-scale approach, both, modelling wise and also experimentally. The investigation of each scale delivers at least a qualitative understanding of possibly evolving damage in the material and also delivers a validation of the corresponding scale on the modelling side. From the experimental side, the lower end of the scale, the atomistic and structural level, can be investigated by conventional techniques, as for example transmission electron microscopy (TEM) and X-ray diffraction (XRD). However, the use of synchrotron radiation techniques offers an ideal, complementary way to investigate the material structure and other properties. This paper presents applications in the field of the ODS research, where the structural behaviour of the nanoscopic dispersoids can selectively be investigated, although only being present with roughly 5 wt % in the matrix. A study showing the structural behaviour of these oxide particles as a function of irradiation illustrates the potential of the extended X-ray absorption fine structure (EXAFS) technique. Using X-ray magnetic circular dichroism (XMCD), which is a difference-signal of two X-ray absorption spectra recorded for positive and negative helicities of the beam, the magnetic structure and some magnetic parameters, can be resolved. An example shows, how this can be applied to understand (Fe,Cr) systems, which is the base alloy of the investigated ODS steel. The results deliver an important crosscheck for modelling. Beside the presentation of these techniques, this paper shows how beamline techniques can serve nuclear research, with possibly activated materials. At the Paul Scherrer Institute, a sample holder for highly active materials has been developed, and has already served for EXAFS measurements at the Swiss Light Source (SLS). The set-up of this sample holder is briefly presented here.

Nuclear Energy Agency, Organisation for Economic Co-operation and Development2007

EXAFS Study on Irradiated ODS Ferritic Steel

Manuel Alexandre Pouchon

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.

2007

Synchrotron Light Techniques for the Investigation of Advanced Nuclear Reactor Structural Materials

Didier Gavillet, Wolfgang Hoffelner, Manuel Alexandre Pouchon

Nuclear Energy Agency, Organisation for Economic Co-operation and Development2007