NPP steam generators ageing and related actions to assure safety and reliability

Nuclear safety assurance and nuclear power plant availability represent an important target for Plant Owner and Regulatory Authority. In time NPP components ageing appears. This is a continuous degradation of materials due to operating conditions (which include normal operations and transients). Ageing has significant impact to the safety through: a. degradation towards safety margins; b. decrease of component integrity; c. decrease of active component functionality; d. increase of failure probability of components; e. decrease of the defence in-depth. An important component which could affect safety through its ageing are the tubes of steam generators. The most important phenomena which affect the steam generators are corrosion and wear damage. This document analyses in detail their effects and identifies adequate counter measures as for instance: a. designed-related measures; b. choice of materials; c. the concept for the secondary system; d. monitoring of the water/steam cycle. (Author) 1 Fig