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,    said mixture being 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.    
   
   
       3 . The reactor core according to  claim 2 , 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 being made of the neutron absorber and the neutron moderator, and wherein said absorber rod assembly is arranged at the center portion of the fuel assemblies.  
   
   
       4 . The reactor core according to  claim 1 , further comprising a reflector surrounding an outer periphery of the core barrel and formed at its upper portion with a cavity; and a mixture filled in the cavity of the reflector, said mixture being made of a neutron absorber that absorbs a neutron and a neutron moderator that moderates a neutron.  
   
   
       5 . The reactor core according to  claim 1 , wherein said mixture is made by mixing gadolinium as the neutron absorber and zirconium hydride as the neutron moderator.  
   
   
       6 . The reactor core according to  claim 2 , wherein said neutron moderator has a distribution in a diametrical direction of the tube portion, said distribution being gradually dense toward an inside of the tube portion.  
   
   
       7 . The reactor core according to  claim 1 , wherein said mixture is made by mixing gadolinium as the neutron absorber and graphite as the neutron moderator.  
   
   
       8 . The reactor core according to  claim 3 , wherein said neutron absorber and the neutron moderator are molded to be granules, and said granules of the neutron moderator and neutron absorber are filled in the cladding tube by using a vibration compaction process.  
   
   
       9 . The reactor core according to  claim 3 , wherein at least one of said cladding tube and the tube portion is formed at its inner surface with an inside cote for preventing hydrogen from being transmitted.  
   
   
       10 . The reactor core according to  claim 3 , wherein said neutron absorber of the mixture is formed with a fission product.  
   
   
       11 . The reactor core according to  claim 13 , wherein said neutron absorber and the neutron moderator are mixed according to a volume percent ratio and wherein, assuming that the volume percent ratio of the neutron moderator and the neutron absorber is X to Y, said X percent is bigger than the Y percent.  
   
   
       12 . The reactor core according to  claim 11 , wherein 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.  
   
   
       13 . A reactor core in a core barrel of a nuclear reactor, comprising: 
 a plurality of fuel assemblies contained in the core barrel;    a mixture contained in the core barrel, said mixture being made of gadolinium as a neutron absorber that absorbs a neutron in the core and zirconium hydride as a neutron moderator that moderates a neutron therein so that a reactivity of the core is controlled;    a reactivity control assembly arranged at a predetermined portion in the fuel assemblies, and having a tube portion; and    a neutron absorber rod assembly contained in the tube portion and having a mixture made of the neutron absorber and the neutron moderator, said neutron absorber rod assembly being arranged at a central portion of the fuel assemblies.