When any plant is put to work it generates the re­quirement for maintenance. On a nuclear site, main­tenance is considered in two separate philosophies, these are:

• The commercial risk in not doing it, e. g., loss of generation from failure of plant.

• Maintenance which is part of ensuring that plant operates safely (safety of the public and persons engaged on the site).

In the first item a programme of maintenance has to be designed to ensure that the risk of failure is acceptable. Advantage can be taken of the provision of standby plant where this exists to do regular main­tenance, and most major plant auxiliaries are dupli­cated. The problems occur with those major equipment items, such as the main turbine-generators and gas circulators, that need the unit shut down for access to carry out the repairs and maintenance.

The requirement under conditions of the site li­cence to shut the reactor down for inspection purposes within a maximum period of two years from the time it was previously given consent to start-up, provides a window for the overhaul and maintenance of these major items. Unfortunately, this gives a very ‘peaky’ resource requirement for maintenance during this win­dow of about three months. Most nuclear sites keep the maintenance in-house rather than using contract labour. The reason for this is that the work requires specialist knowledge and expertise coupled with (in many instances) a good knowledge of health physics procedures and practices.