In any nuclear power plant safety is assured by well defined procedures & practices and by implementing redundant & diverse technology. Procedures concern to the component/system will vary from state to state. Prototype Fast Breeder Reactor (PFBR) is a 500 MWe capacity, pool type reactor utilizing liquid sodium as a coolant and fuel as Mixed Oxide (Plutonium and Uranium). In general there are two reactor states inPFBR i.e. Transition state and Stable state. Wherein steady state indicates stable operating or shutdown state of reactor and transition state indicates an intermediate state between two stable states and this state ensures the healthiness of redundant/diverse system and its auxiliary system. This paper discusses about control logic simulation & implementation of Reactor Start-Up (RSU) system i.e. one of the transition state of PFBR which comes in-between Reactor in Shutdown (RSD) and Reactor in Operation (ROP). It elaborates about interfacing of various process conditions, authorization for reactor startup, inter connection of safety shutdown system, integration and testing of the simulated startup logic.