Papers by Author: Claude Degueldre

Abstract: 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.

Abstract: The toxicity of the UO2 spent fuel is dominated by plutonium and minor actinides (MA): Np, Am and Cm, after decay of the short live fission products. Zirconia ceramics containing Pu and MA in the form of an Inert Matrix Fuel (IMF) could be used to burn these actinides in Light Water Reactors. Optimisation of the fuel designs dictated by properties such as thermal, mechanical, chemical and physical must be performed with attention for their behaviour under irradiation. Zirconia must be stabilised by yttria to form a solid solution such as AnzYyPuxZr1-yO2-y where minor actinide oxides are also soluble. Burnable poison may be added if necessary such as Gd, Ho, Er, Eu or Np, Am them-self. These cubic solid solutions are stable under heavy ion irradiation. The retention of fission products in zirconia, under similar thermodynamic conditions, is a priori stronger, compared to UO2, the lattice parameter being larger for UO2 than for (Y,Zr)O2-x. (Er,Y,Pu,Zr)O2-x in which Pu contains 5% Am was successfully irradiated in the Proteus reactor at PSI, in the HFR facility, Petten as well as in the Halden Reactor. These irradiations make the Swiss scientists confident to irradiate such IMF in a commercial reactor that would allow later a commercial deployment of such a fuel for Pu and MA utilisation in a last cycle. The fuel forms namely pellet of solid solution, cercer or cermet fuel are discussed considering the once through strategy. For this strategy, low solubility of the inert matrix is required for geological disposal. As spent fuels these IMF’s are demanding materials from the solubility point of view, this parameter was studied in detail for a range of solutions corresponding to groundwater under near field conditions. Under these conditions the IMF solubility is 106 times smaller than glass, which makes the zirconia material very attractive for deep geological disposal. The desired objective would be to use IMF to produce energy in reactors, opting for an economical and ecological solution.