Before fuel loading, the operators must be trained and qualified to operate the fuel handling equipment. Detailed procedures and operating instruc­tions must be prepared and exercised during the training period with dummy fuel assemblies. Strict attention to criticality such as boron concen­tration levels in pressurized water reactors (PWR) is essential at this stage. Once fuel is loaded, for light water reactors (LWRs) the upper vessel inter­nals and the pressure vessel head are installed. At this point, the operator carries out additional mechanical and electrical tests to verify that the reactivity control systems are functioning properly and reliably. The initial core monitoring system data will familiarize the operator with some practi­cal reactor core experience.

Some additional tests are normally performed just before initial critical­ity to provide further assurance that the plant systems and components required for plant operation perform as expected. The plant is then brought from cold shutdown to hot shutdown to initial criticality for the start of low-power physics testing. A variety of tests are performed to confirm the core design values as used in the FSAR and other technical analyses. Reactor power is then raised through steps with test programmes at each step. The tests include physics measurements, plant shutdown and heat removal capabilities, power transients, loss of site power tests, and instru­mentation and control checks.

After full power is reached and maintained for a period of time, the plant should be shut down and thoroughly inspected, and the commissioning data assessed. Any changes to the plant would be evaluated thoroughly to ensure that safety margins meet the design specifications and that the plant can perform reliably. Finally, plant acceptance testing is performed to ensure that the plant meets the contractual output. The plant operating staff typi­cally become proficient in the operation and maintenance of components and systems during the commissioning activity.

During operation, the licensee is required to maintain detailed records concerning operations, and the nature of these records is stated in the operating license. These can include the results of effluent and environmen­tal monitoring programmes, operating and maintenance procedures, results of the commissioning programme, results of inspection and maintenance programmes, and the nature and amount of radiation, nuclear substances and hazardous substances within the nuclear facility.

The operator must also manage plant configuration changes and the status of the SSCs over the life of the plant. A key aspect of this is the management of ageing, including both degradation and obsolescence, par­ticularly for those SSCs important for safety. It is likely that the licensee will have to demonstrate to the regulator that it has a comprehensive and systematic management programme to address SSC ageing. The IAEA has published recommendations for the establishment, implementation, and improvement of ageing management programmes that can be used to develop an effective strategy (IAEA, 2009d). According to this guide: ‘Evaluation of the cumulative effects of both physical ageing and obsoles­cence on the safety of nuclear power plants is a continuous process and is assessed in a periodic safety review or an equivalent systematic safety reas­sessment programme.’ The science, technology and regulatory aspects of ageing in nuclear power plants are considered in detail in Tipping (2010).