The site licence requires the licensee to produce a maintenance schedule, which is submitted to the Nu­clear Installations Inspectorate for approval. The schedule consists of a number of items of plant and equipment which are directly connected with the sate operation of reactor systems, and which are in need of a regular system of maintenance at a prescribed interval. The items listed are those which if not func — tioning correctly could contribute to an unsafe con­dition during reactor operation:

• Testing of reactor guard lines.

• Maintenance of emergency boiler feed pumps,

• Maintenance of valves in the boiler feed mains.

• Testing of reactor vessel safety valves.

• Maintenance of burst cartridge detection gear, etc.

The schedule will show the prescribed frequency which will be at least two years so that it appears between the biennial overhauls. Some of the items may only be carried out on a complete shut down of the re­actor with the reactor pressure vessel at atmosphe­ric pressure, and therefore may only be done during the biennial overhaul, e. g., CCb make-up isolating valves.