Reactor main systems are those important for the safe operation of research reactors. They may be divided into safety and support systems. Support systems are often not considered as safety systems but their failure may cause indirect effects on reactor safety Therefore, experienced operators must realize that these support systems require routine, periodic maintenance with the same care as any other safety related system. The most important components or functions of the described main systems are inspected or evaluated at regular intervals following a maintenance and inspection manual or procedures as approved by the respective Regulatory Body which licensed the reactor.