Patent ID: 7245689

Claim:
A nuclear reactor internal structure of a nuclear reactor, comprising: a coolant inlet nozzle that receives a coolant; a pressure vessel defining a lower plenum at a bottom portion thereof; a reactor core arranged in said pressure vessel; a reactor core tank arranged around said reactor core; a downcomer portion of an annular shape defined between said pressure vessel and said reactor core tank, such that the coolant introduced from said coolant inlet nozzle flows down said downcomer portion perpendicularly from said coolant inlet nozzle without dispersing in a circumferential direction of said downcomer portion; a radial key portion provided in said downcomer portion for fixing said reactor core tank relative to said pressure vessel; and a connecting plate provided in said lower plenum below said downcomer portion, said connecting plate having a rim portion, provided with a plurality of holes, and a ring portion provided outside the rim portion, an outermost peripheral edge of said ring portion including an arcuate portion, having a constant radius from a center of the connecting plate as to an entire length of the arcuate portion, and a cut-off portion, provided adjacent said arcuate portion, such that the coolant that has passed through said downcomer portion, between said connecting plate and said pressure vessel, and into said lower plenum forms a main flow flowing toward the center of said lower plenum.