Ex-Vessel Delayed Neutron Detection Systems for the ASTRID Sodium-Cooled Fast Reactor

Monitoring fuel integrity during sodium-cooled fast reactor operation becomes a crucial issue when sodium uranoplutonate formed consecutively to a clad aperture will foster cooling defaults. Delayed neutron detection (DND) systems are the key tools allowing to prevent and to mitigate such an accident by monitoring the concentration of delayed neutron precursors contained into the coolant. DND systems operate in hard gamma-rays fluxes and low-neutron activity levels. They have to be carefully optimized in order to detect, as early as possible, potentially harmful failures. A discussion is conducted on privileged ways to design DND systems, and some conclusions are stated.