Design of the 4S Reactor

The Super-Safe, Small and Simple (4S) sodium-cooled fast reactor plant incorporates innovative design features, such as a nonrefueling reactor, passive safety, low maintenance requirements, and inherent security. Major components such as the reflector drive mechanisms, the electromagnetic pumps, and the double-wall tube steam generator have been optimized for efficient and safe operation.

The nonrefueling reactor concept is made possible by incorporating a 30-yr refueling interval for the reflector-controlled metallic fuel core. Sodium-cooled, metallic-fueled fast reactors have a good conversion ratio due to fast neutron usage, thus extending the core life. Passive safety is achieved with redundant residual heat removal systems that function using only natural circulation, and a metallic core with a negative reactivity coefficient. Low maintenance requirements are achieved by simplifying the design and minimizing the use of active components, and by using electromagnetic pumps, which have no moving parts. The inherent security of the nuclear materials is significantly enhanced by the nonrefueling reactor concept and the minimal maintenance requirements. In addition, the reactor building is located below ground level, providing substantial protection against an aircraft impact and thus further enhancing the security of the design.

The demonstration of key components such as the electromagnetic pumps and the steam generator is part of an ongoing testing program that has already confirmed many of the 4S engineering solutions.

This paper describes the current status of design and component tests for the 4S reactor.