12.67. As a result of quality assurance programs for reactor components and inspection during operation, the probability of mechanical failures is low. Nevertheless, the consequences of possible failures must be considered in the safety analysis. Among the more important events of low probability in the nuclear steam supply system, which could conceivably cause some fuel cladding damage, are the following: (1) a small-scale break in the reactor coolant circuit, steam-generator feedwater lines, or steam lines, and (2) complete loss of ac power leading to a loss of the normal flow of reactor coolant.