Experience with corrosion damage of primary circuits of nuclear power plants

Approximately 70% of the materials of primary circuits of WWER type nuclear power plants are manufactured from stabilized austenitic steel of the 08Kh18N10T type. The rest is produced from materials surfaced with a lining of a stainless austenitic steel. The stainless steels are of approximately the same composition but different production. In addition to thin metal sheets of 4 to 7 mm in thickness, the materials include rough forged pieces of the primary circuit or of steam generator collectors (up to 80 mm) and also overlay metals for the anticorrosion reactor lining. Each component causes special technological problems, which are briefly discussed. For instance, in casting high-weight ingots the danger arises of local material contamination. The component corrosion resistance is affected not only by the basic steel composition but also by the steel purity and the conditions of its heat treatment. A major role is played by the surface roughness and the method of chip machining of components. The materials used are not resistant to corrosion cracking or pitting corrosion. It is thus necessary to carefully check the chemical water regimen and other parameters of primary circuit operation. Checking the components during power unit shutdowns, however, makes it necessary to deactive the components; this may lead to undesirable disturbance of the passivation film on their surfaces. (Z.M.). 8 figs