9.1 Reactor inspection and repairs

A condition attached to the Site Licence of a nuclear power station requires the biennial inspection of each reactor and its associated conventional plant. As well as an internal assessment of the reactor, the inspec­tion includes the maintenance and assessment of the various reactor systems. Included in these systems are such items as the burst cartridge detection equipment, control rod system, cooling and ventilation plant. In general, these items do not present unique problems of maintenance or inspection nor do they require specialised techniques or equipment to assess their condition. The outcome of the inspections, and any maintenance deemed necessary, is to provide the Nu­clear Installation Inspectorate (Nil) with an assess­ment of the continued safe and satisfactory service of the whole plant. Such assessment enables the In­spectorate to issue a ‘start-up Certificate’ allowing the continued operation of the reactor for a further two years.

The inspection and maintenance of the conventional plant follows well established electromechanical tech­niques and in many cases the examinations are more frequent than on a biennial basis. For example, the refuelling machinery, considered to be part of the reactor system, is usually subject to frequent checks of its control system to ensure that no untoward incidents may occur whilst attached to the reactor. Similarly, the reactor’s guard line trip circuitry is checked several times per year. All such external features of the reactor are readily available for routine check procedures. However, the internal items of the reactor are not so accessible and are only available during the extended period of a shutdown. It is the special requirements of the reactor internal inspection and repair that are dealt with in this section.

9.1.1 Inspection requirements

Internal reactor inspection includes all those proce­dures devised to establish the component quality and condition. In this sense metallurgical samples, quan­titative material analysis and metrology techniques are considered to be part of the inspection procedure. The procedure is required to:

• Confirm component behaviour predictions.

• Provide back-up data of material quality.

• Establish a base line of component condition.

• Monitor the condition of any installed items

resulting from maintenance procedures.