Performance and functioning of active systems can be tested during oper­ation and can be ensured via maintenance under maintenance rule (MR), that is evaluation and assessment of the effectiveness of the maintenance along safety criteria, and/or via implementation of the programme for main­taining the environmental qualification (EQ).

For I&C components operating under harsh conditions environmen­tal qualification should be implemented. When the older VVER-440 and

VVER-1000 NPPs were built, a large part of the originally installed elec­trical and I&C equipment did not have initial qualification or the qualifica­tion was not certified properly. The issue was recognized in the first safety reviews (see IAEA, 1992; 1996a; 1996b; 2000). The issue can be resolved in two steps:

• Restoring the initial qualification.

• Maintaining the qualified state of equipment.

The maintenance of the qualification means:

• Control of the capability of equipment to fulfil its safety function through:

◦ periodic testing of systems and components

◦ testing of the equipment following maintenance

◦ results of service routes by maintenance personnel

◦ diagnostics measurements.

• Development and implementation of a scheduled replacement pro­gramme taking into account the requirements for environmental quali­fication in purchasing the new equipment.

• Preventive maintenance of the equipment.

The environmental qualification should be reviewed and validated for the extended operational lifetime. There are different possible outcomes of the review:

• The qualification remains valid for the period of LTO.

• The qualification has been projected to the end of the period of long-term operation.

• The effects of ageing on the intended function(s) have to be adequately managed for the period of LTO via introducing new ageing management programmes.

• Replacement of the equipment.