Neutron diffraction study of samples of fuel element claddings made of austenitic steel

•Massive samples of fuel claddings prepared from steel EK-164 after their operation life in the BN-600 reactor have been investigated using neuron diffraction technique.•The FCC crystal structure of EK-164 is shown to be preserved up to the maximal damage dose of 73 dpa applied.•It is shown that the dislocation density change at high doses depends on irradiation temperature.•Lattice parameter of steel EK-164 is also correlated with irradiation temperature, indicating the competitive processes with radiated effects. The paper presents the results of investigation of the performance of industrial fuel elements operating in the active zone of a fast–neutron reactor BN-600. As a continuation of previous works, we have studied fuel elements made of austenitic steel EK-164 after their irradiation under a maximal dose of 72.3 dpa at temperatures ranging from 370 to 628 °C. As in the earlier work on studying spent fuel elements fabricated from standard steel ChS-68, neutron-diffraction method was used that demonstrates a number of advantages over traditional methods, in particular, it is the least-exposing workers to radiation hazards and most suitable for studying bulk irradiated materials. Based on the experience gained, some quite typical microstructure distortions arisen under irradiation were revealed, changes in the density and type of dislocations depending on the dose and temperature were determined, and the dominant role of temperature at high doses of fast neutrons was confirmed. The behavior of EK-164 steel samples selected from different series is shown to depend on their initial structural state.