Improper design of Instrumentation & Control (I&C) systems is one of the main reasons for human errors during the operation and maintenance phase of Nuclear reactors. It is very important to carry out detailed failure/safety analysis of I & C systems. The design shall be such that any single failure of I&C system should not unnecessarily shut down commercial nuclear reactor. It is necessary to provide sufficient redundancy to ensure the specified high reliability of I&C systems. On-line testability shall be provided during the design stage itself for I&C systems. Fast Breeder Nuclear Reactor uses plutonium oxide as fuel and liquid sodium as coolant. Due to high power density (500 KW/litre) in the reactor core, computer based supervision and control systems are used to detect flow blockage in the fuel subassemblies. Physically and functionally distributed computer systems process nearly 15000 process signals in the nuclear reactor. The processed information is routed to the control room through optical fibre based plant area network. This paper explains distributed embedded systems, neutronic systems, diverse safety logic systems, etc. The on-line diagnostics to detect both safe failure and unsafe failure are explained with illustrations. The architecture of safety instrumentation and reliability analysis are detailed in this paper. The criteria for selecting the testing interval of I&C system is explained for neutronic system, safety logic system and real time computer system. The plant operator should be well trained in both normal and transient behaviour of various subsystems of nuclear reactors. Abnormal behaviour of subsystems is categorized based on probability of occurrence. Architecture of Training Simulator for nuclear reactor shall also take into account simulation of failure modes of I & C systems. Modeling of both normal and failure mode of operation of I&C systems of Fast Breeder Nuclear reactor are explained with typical examples. Format for display of fault messages in Large Video display units at control room should take into account psychology of plant operator. Details of typical comfortable formats of display, which are developed in consultation with Nuclear Power Plant operators, are illustrated.

Key words: Fast breeder nuclear reactor, Real time computer system, Neutronic system, Safety logic system, Safe and
unsafe failure,Testing interval failure rate