Reactor Shutdown and Control Systems

Abstract

The control rods are an essential element so as to control the reactor reactivity. At Superphenix, twenty-one of them were enabling the control, even the automatic control for three of them, of the reactor power during operations, and its shutdown so as to put it in a safe state. These systems consisted in three distinct parts:A hexagonal sheath, externally identical to surrounding sub-assemblies, within which slides the control rod (unlike at Phenix, the rod is interdependent with the sheath).The control rod, whose body contains pins formed of boron carbide pellet stacks.The rod mechanism located on the core cover plug, having both to adjust the rod position during operations and drop it, if necessary, so as to shutdown the reactor.In addition to these twenty-one rods (system said as SCP or RBC), there was a Back-up Shutdown System (said as SAC or RBS), constituted of three rods, whose unique function was to stop the reactor, even in the event of the reactor block significant distortions, via a simple de-energization of the in-sodium electromagnets holding this system three rods. These device experience feedback was positive, with few significant problems during operations and with real enhancements in terms of safety.