PHYSICS AND TECHNOLOGY FACULTY

At the present time, a zirconium-based alloy with 1% niobium (E110) is used as the main material for shells of fuel elements of VVER-type reactors because it has good processability, acceptable radiation resistance, and a quite small thermal neutron capture cross section.

In the course of reactor operation, the radiation-induced structural elements (dislocation loops, second phases (for example, phases based on niobium and zirconium, which form periodic structures), vacancy voids) are formed in alloys based on zirconium. This causes the degradation of mechanical properties - reduced plasticity, an increase in the yield strength, etc. However, at present, there is practically no quantitative the contribution assessment of various radiation-induced structural components to the degradation of mechanical properties.

In this work, studies of zirconium samples (from fuel claddings) in different states were carried out (in the initial state and after irradiation under VVER-1000 conditions).

Microstructural studies were carried using transmission (FEI Titan 80-300) and scanning electron microscopy (Zeiss Merlin), as well as atomic-probe tomography (Camceca LEAP 4000 HR): the phase composition (density, size and composition of the second phases) is determined, the dislocation structure is assessed (the density of dislocations and dislocation loops, the plane and the Burgers vector are established).

Thus, the basic degradation mechanisms of the E110 alloy under the influence of operational factors were established.