Examination of Austenitic Steels Microstructure Change Induced Neutron Irradiation by Using of Neutron Scattering Methods

Two cladding pin austenitic steels ChS68 and EK164 irradiated in the BN-600 reactor up to maximum dose ∼80 dpa were examined by methods: neutron diffraction; small angle neutron scattering; X ray and electron microscopy. The formation and growth of both dislocation loops and radiation voids, as well as formation of segregation profiles, second phase precipitates, and chemical composition changes in a crystalline matrix were revealed in the steels after irradiation. All these resulted in growth of micro deformations in the crystalline matrix and changes of texture of the cladding pin steels, which were fixed by neutron diffraction and X ray methods. Texture decreasing more clearly occurred after low irradiation temperature (370°C) then after higher temperature irradiation (520°C). Observing of small angle neutron scattering increasing with dose growth is probably caused in He-v voids nucleus and segregations formed along dislocations and grain boundaries. At the present time the nature of scattering centers were not uniquely established. It is connected with an insufficiently adequate calculation model of small angle neutron scattering. Therefore solving of this problem requires additional development of calculation models. On the whole the examination shows that neutron scattering methods are very effective for research radiation induced structure changes. (author)