Functional design approach to PWR safety

The present work in the US nuclear industry directed towards improving response during emergency conditions consists of improvement in emergency procedures, post-accident instrumentation, alarm presentation, and the development of operator aids. This paper contains work in progress for the formulation of a possible basis for such an effort. The basis consists of using a functional relationship chart for PWR safety as a conceptual model for the plant. The functional relationship identifies elements important to safety starting from the abstract concepts of fission product barrier maintenance and proceeding to equipment details. The interactions have been structured by using a multilevel flow model of the plant which formulates the purpose, function and supporting systems in terms of mass and energy transport and storage processes, and their functional interrelationship by critical, controllable variables. The methodology for developing a set of critical safety function restoration procedures is also presented to demonstrate application of these concepts