Influence of Surface Treatment on the Corrosion of the Pipes of Fuel Elements Made of Zr1Nb and È110 Zirconium Alloys

We study the long-term corrosion resistance in water for the samples of pipes used as protective shells of the fuel element and made of Zr1Nb calcium thermal alloy (earlier, it was called KTTs-110) and È110 alloy applicable in contemporary water-cooled, water-moderated reactors WWÉR-1000 and WWÉR-400. The tests were carried out in water whose composition was close to the composition of the water coolant of WWÉR reactors at a working temperature of the shells of fuel element equal to 350°C. It was discovered that the process of oxidation is first described by the regularity close to a cubic function. However, after a certain period of time, this dependence suddenly changes into the accelerated oxidation (“kink”) running according to a power law approaching the linear dependence. We analyzed the kinetics of corrosion and the structures of oxide films and alloys after 50,000 h of testing. The influence of the concentration of oxygen, as an admixture in alloys, and the procedures of treatment of the surfaces of the samples of pipes on the corrosion processes is discussed, as well as the long-term corrosion resistance of alloys. It is shown that Zr alloys with niobium (1 wt.% Nb), such as È110 and Zr1Nb experimental alloy developed in Ukraine are capable of preserving the high corrosion resistance and protective properties for at least seven fuel reactor campaigns.