Prolonged life of collectors of WWER-440 steam generators by nickel overlaying

Collectors of steam generators at the Mochovce nuclear power plant which will be furnished with WWER-440 reactors are to be protected with an austenitic overlay in places where there is a fluctuation of the water-steam level. The purpose of the protective overlay is to provide the resistance of the collector material to corosion cracking under increased thermal and mechanical load. For the overlay, welding materials have been suggested with a high nickle content and an increased chromium content. The results are discussed of tests of overlays carried out using various strip electrodes and fluxing agents. The tests were aimed at detecting the resistance of the material to inter-crystalline corrosion, corrosion cracking and low-cycle fatigue. On the basis of the tests a production technology was chosen for the overlay using the UTP UP 068 HH strip manufactured by the West German firm Universal Tiefpunkt which is characterized by a high content of niobium and the fluxing agent VUZ T1N developed for this purpose in the CSSR. (Z.M.). 5 figs., 3 tabs., 1 ref