Nuclear reactor

Abstract

A nuclear reactor includes a reflector and a flow path. The reflector reflects neutrons, contains graphite and a moderator having a smaller moderating power than the graphite, and is sectioned into plural parts along a direction of flow of fuel pebbles. The flow path is surrounded by the reflector, and the fuel pebbles flow through the flow path and undergo nuclear reaction to generate power. Volume ratio of the graphite to the moderator having a smaller moderating power than the graphite in each part of the reflector is determined based on a power distribution in the reactor core in the direction of flow of the fuel pebbles.

1 . A nuclear reactor of a Block-type High Temperature Gas Reactor comprising:
 a reactor core;   a fuel block arranged in the reactor core, the fuel block having a coolant flow path through which a coolant flows to cool the fuel block; and   a reflector arranged inside the reactor core and sectioned into plural parts along a flow direction of the coolant, the reflector containing graphite and a moderator having a smaller moderating power than the graphite, wherein   a volume ratio of the graphite to the moderator having a smaller moderating power than the graphite in each part of the reflector is determined based on a power distribution in the reactor core in the flow direction of the coolant, and   a volume fraction of the moderator having the smaller moderating power than the graphite in each part of the reflector is determined so that the volume fraction increases from an upstream side to a downstream side of the coolant flow path.   
     
     
         2 . The nuclear reactor according to  claim 1 , wherein
 the reflector is sectioned into five parts along the flow direction of the coolant, so that the volume fraction of the moderator having the smaller moderating power than the graphite increases by 25% in each part from the upper side toward the lower side of the reactor core.