Safety assessment for computerized nuclear reactor protection systems: The Markov approach

In reactor protection systems based on minicomputers a central role is played by the diagnostic capability of selfchecking programs. It is thus of great importance to determine the efficiency that such programs must have with respect to fault detection in order to meet a certain reliability goal. Even though the content of this report is part of the safety study on a particular plant (Tapiro Research Reactor in service at C.S.N. Casaccia) it allows one to reach more general conclusions about the reliability of computerized protection systems. Another major aim of this paper is to point out the methodological difficulties met in the safety qualification of these systems.