Reactivity control rod for core, core of nuclear reactor, nuclear reactor and nuclear power plant

Abstract

In a nuclear reactor in which a primary coolant is contained, the primary coolant moves upwardly from the core by an operation thereof. An annular steam generator is arranged in an upper side of the core into which the upwardly moving primary coolant flows and transfers heat in the primary coolant into water therein to generate a steam. A passage structure defines a coolant passage for the primary coolant to an outside of the core. The heat-transferred primary coolant in the annular steam generator flows downwardly in the coolant passage so as to flow into the core, thereby moving upwardly. A reactor vessel is arranged to surround the coolant passage so as to contain the core, the annular steam generator and the passage means therein.

1 . A reactor core in a core barrel of a nuclear reactor, comprising:
 a plurality of fuel assemblies contained in the core barrel; and   a mixture contained in the core barrel,   wherein said mixture is made of a neutron absorber that absorbs a neutron in the core and a neutron moderator that moderates a neutron therein so that a reactivity of the core is controlled.   
     
     
         2 . The reactor core according to  claim 1 , further comprising:
 a reactivity control assembly arranged at a predetermined portion in the fuel assemblies, said reactivity control assembly having a tube portion; and   a neutron absorber rod assembly contained in the tube portion and having the mixture made of the neutron absorber and the neutron moderator,   wherein said neutron absorber rod assembly has a plurality of neutron absorber rods each having a cladding tube and the mixture filled therein,   said mixture is made of the neutron absorber and the neutron moderator,   said absorber rod assembly is arranged at the center portion of the fuel assemblies,   said neutron absorber and the neutron moderator is mixed according to a volume percent ratio,   said volume percent ratio of the neutron moderator and the neutron absorber is X to Y, said X percent being bigger than the Y percent; and   said volume percent ratios of the neutron moderator and the neutron absorber in the neutron absorber rod in the axial direction are different according to different positions in the axial direction of the core.