Reliability of nuclear power installations

The causes of subcritical crack propagation in materials are discussed: subcritical crack propagation caused by material fatigue; propagation of the crack caused by long-term effects of high temperatures (creep); crack propagation caused by corrosion under stress. The most complex information on damage to bodies is provided by an analysis of the emission of stress waves which is caused by sudden changes both on the front of the crack and in the surrounding area. With regard to the initiation of fatigue cracks it was found that the surface layer is least resistant. The initial dimension of cracks is in the order of 10-4 cm. Important are not so much individual cracks as their critical density and critical configuration. (E.F.)