[en] We are presently participating in a program to optimize the functional man-machine interface for Liquid Metal-Cooled Fast Breeder Reactors. The overall objective of this program is to enhance operational safety; that is, to accommodate plant incidents through optimal integration of man and machine in performing the functions required to safely control a plant during both normal and off-normal conditions. Purpose of this talk is to describe an approach to determine the optimal roles of man and computer in the control of nuclear power plants. Purpose of this session was to get together people that are working in the areas of understanding of how operators control plants, and working on developing new aids for these operators. We were asked to explain how our modeling and approach we're taking will lead us to an optimization of the roles of the man and the computer in the control of nuclear power plants. Our emphasis was to be on the functions required for plant control, and how the attributes of the human operator and the attributes of the computer can be optimally used to enhance operational safety in performing these functions