Ageing and safety

Ageing is a continuous process which cannot be reversed but which can be controlled by replacing components. However, the replacement of some components may be impossible or uneconomical; therefore, monitoring and in-service inspections must be increased. The combination of replacement of components and increased monitoring should make possible the total control of ageing. In this connection, it can be said that it is necessary to produce components and systems which are appropriate to the useful life of the facility, otherwise safety will be affected; that the materials used should be carefully selected so as to reduce activation problems; that in any new design, the need for components, systems and programmes for decontamination of the facility must be taken into account; that in order to control ageing, the increase in the level of monitoring and the replacement of components should be planned as a function of time; and that maintaining a constant level of design monitoring and increasing the rate of component replacement alone does not constitute control of ageing. It is not possible to replace all the components and those which cannot be replaced (reactor vessel, steam generators, pressurizer, heat exchangers, etc.) would present a high risk of failure if the monitoring of them were not stepped up so as to allow timely corrective action to be taken. (author)