[en] Despite being a vital issue, the performance of computer systems and networks is often not adequately addressed until late in a project's lifecycle, when the discovery of inadequacies can have significant cost and time penalties. One way to help avoid this is to use simulation modelling at varying stages during a system's lifecycle to assess performance and to identify potential problems. It is generally accepted that there is no realistic alternative to computers carrying out essential tasks in the operation of nuclear power stations. It is essential, therefore, that there is a high degree of confidence that these computer systems will perform as required once installed and set to work. Simulation modelling provides a convenient and cost-effective way of assessing the performance of such computer-based systems. (Author)