Microanalytical characterization of as-fabricated and irradiated oxide nuclear fuels

The application of quantitative scanning electron microscopy and Vickers microhardness measurement for the characterization of as-fabricated and irradiated uranium and uranium-plutonium oxide fissile materials originally lead to a great variety of results. Even after identical operational procedures the results were equivocal. Consequently a classification was set up under aspect of as-fabricated structural phenomena, within the calcium fluorite crystal system. The type A-class includes material data, which are attributed to an originally highly crystallized homogeneous state. The type B-class is related to incompletely sintered as-fabricated structures with a high degree of discontinuities. After these efforts general conclusions appeared to be possible: 1. The local process of nuclear fission exerts restructuring forces on the surrounding environment. 2. Restructuring does not occur instantaneously; it is determined by relaxation processes; this means, that it is dependent on time. 3. Restructuring occurs discontinuously with temperature, i.e. under various mechanisms in different zones. 4. In the final structural state, after a long period of operation, there is no special far distance crystalline orientation left; the structure does not show morphological discontinuities, any longer. 5. In this final state, which is far from thermodynamic equilibrium, the materials instantaneously react on nuclear fission impacts by energy dissipation. 6 refs., 7 figs