The following IAEA terminology and definitions have been adopted throughout the TECDOC:

• Ageing is defined as the continuous time dependent degradation of SSC-materials due to normal service conditions, which include normal operation and transient conditions; postulated accident and post-accident conditions are excluded. It is emphasized here that ageing is a wide term, and may even be extended to include the extent and current level of personnel training and even the status of updated documentation used in the NPP.

• Ageing management (AM) is defined as engineering, operations and maintenance actions to control within acceptable limits ageing degradation of systems, structures and components (SSCs).

• Ageing management programme (AMP) is defined as any programme or activity that adequately manages the effect of ageing on SSCs (e. g. maintenance programme, chemistry programme, inspection or surveillance activities, etc.).

• Condition assessment (CA) is defined as an ageing assessment methodology applied to systems, as well as components and structures, or groups of components with similar characteristics (commodities).

• Life assessment (LA) is defined as an ageing assessment methodology applied to critical and/or complex components and structures that involve mainly passive functions and typically are not expected to be replaced within the original design life of the plant.

• Plant life management (PLiM) is the integration of ageing and economic planning to:

• Maintain a high level of safety

• Optimize the operation, maintenance and service life of SSCs;

• Maintain an acceptable level of performance;

• Maximize return on investment over the service life of the NPP; and

• Provide NPP utilities/owners with the optimum pre-conditions for long term operation (LTO).

• LTO of an NPP so long as all safety requirements are fulfilled and that economic viability, taking into account all costs, including PLiM measures is guaranteed. LTO is a utility/owner policy of intent to operate beyond the original design life.

Therefore, PLiM for NPPs is a methodology whereby all expenses are optimized to favour commercial profitability and competitiveness, while providing safe and reliable supplies of electrical power. In general, PLiM may be defined as the continuous operation of the plant, with an acceptable level of safety, beyond a licensing period established following a safety assessment.