After its successful deployment in the railroad, the CLEARSY RS4 safety relay makes its debut in the nuclear power industry by successfully passing the Belgian Nuclear Safety Authority tests. The modernization of the BR2 High Flux Reactor located in Mole (Belgium) is carried out in compliance with the post-Fukushima safety requirements, and the SCK-CEN (Center for Nuclear Studies) has selected CLEARSY’s range of RS4 relays to realize a new emergency reactor shutdown system, a major safety function also called extreme device, for the safe operation of the reactor. The technical characteristics of the RS4, certified SIL4, allow a simple and scalable integration on all chassis and all industrial environmental constraints, while being compliant with the functional requirements of nuclear safety. The emergency shutdown system of a reactor is classified in Category A.