TEM-studies of the dislocation loops and niobium-based precipitates in E110 alloy after operation in VVER-type reactor conditions

Abstract Microstructural studies of fuel cladding (made of E110 alloy based on sponge zirconium) after operation in VVER-1000 conditions (up to ~13 dpa) were carried out. The essential microstructural elements, which are responsible for the degradation of this material under the influence of operational factors, are established. It is known that in the process of irradiation, beta‑niobium needle-shaped precipitates are formed (in addition to the dislocation structures), which, upon reaching a specific fluence of fast neutrons, form periodic structures (with a bulk density of ~2–3∙10 22  m −3 ). However, for the first time in this work, it was shown that relatively low doses of irradiation (~1.5 dpa) are characterized by the formation of needle-like phases with the high bulk density of ~4∙10 22  m −3 , which decreases with increasing of irradiation dose. This indicates the coagulation process of these particles during further operation of the fuel rods as a part of the VVER-1000 Fuel Assembly (FA). It is also shown in this work that the threshold dose for the formation of -type dislocation loops in alloy E110 (under the specified irradiation conditions) does not exceed 5.6 dpa.