In time, plant components become outdated and they cannot be adequately maintained without compensatory actions to mitigate the effects of their obsolescence. From this perspective when key components from process systems are obsolete, the system health is at high risk of deterioration. A systematic obsolescence mitigation programme comprises 3 phases:

• Preliminary identification of equipment obsolescence

• Obsolescence assessment and resolution (evaluation, identification of alternatives, definition of implementation strategies and resolution)

• Develop a replacement programme and prioritize upgrade/replacement solutions.

Many NPPs are currently operating using programmemable electronic systems and equipment. Future NPPs and retrofit projects will also use these types of devices, which are the state of science and technology solution for I&C. The life cycle of such equipment has to be considered, taking into account the specific characteristics of electronic information technology (IT), and not be limited to the aspect of ageing of components (hardware).

Analog and digital electronics used to convert the sensor signals should be included in the management of I&C ageing. This equipment has not, in the past, been the subject of ageing concerns because they are normally located in instrument cabinets in the easily accessible and environmentally benign areas of the plant and consequently age very slowly. However, obsolescence of this equipment is important, especially when it relates to LTO.

Obsolescence is more of a problem with this equipment than ageing, because electronic components and digital systems are frequently upgraded by manufacturers, and older equipment is no longer available. Consequently, in the focus of ageing management for such systems, it is necessary to ensure that the required functions are met independently of the I&C technology applied.

Thus, the ageing of programmable electronic devices is to be considered within the concept of LTO, and maintenance of equipment, considering both hardware and software facets, and the human/organizational associated consequences.