SAFETY ENHANCED FAST REACTOR

PURPOSE:To obtain a safety-enhanced fast reactor in which natural stopping capability of fast reactor enhanced by such a structure that the negative reaction due to bending of fuel assembly toward the outer peripheral side of reactor core is accelerated. CONSTITUTION:A fuel assembly is split into upper and lower assemblies 20, 40 where the lower assembly is constituted of an reactor core fuel part at the uppermost part, a plenum part at the lower part, and a blanket part between them, whereas the upper assembly 40 is constituted of an upper shield body. The lower assembly 20 is irected while being supported, at the lower end thereof, by reactor core lower supporting boards 50a, 50b with the upper end thereof being set free. The upper assembly is suspended from the lower end of a reactor core upper mechanism 51 thus arranging the upper and lower assemblies in the reactor core with an interval S being set between the upper end of the lower assembly and the lower end of the upper assembly. Upon temperature rise of coolant due to abnormality, uppermost fuel part of the lower assembly 20 bends significantly to the outer peripheral side of reactor core thus inducing negative reaction automatically. Density coefficient of coolant sodium can be suppressed low by setting a wide interval S.