The invention provides a lower
pipe seat of a light-water reactor
nuclear fuel assembly. The lower
pipe seat comprises a frame body, a plurality of first main ribs, a plurality of second main ribs, and a plurality of
pipe fitting installation parts, wherein the first main ribs are arranged in the frame body in parallel at intervals, the second main ribs are arranged in the frame body in parallel at intervals, the frame body comprises a first
diagonal line and a second
diagonal line which is intersected with the first
diagonal line, a plurality of first main ribs and / or a plurality of second main ribs are parallel to the first diagonal line and / or the second diagonal line, a plurality of first main ribs and a plurality of second main ribs are intersected to divide the interior of the frame body into a plurality of through drain holes; and a plurality of
pipe fitting installation parts are respectively arranged at positions where a plurality of first main ribs and a plurality of second main ribs are intersected. The invention further provides a bottom device of the light-water reactor
nuclear fuel assembly. According to the lower pipe seat, a plurality of first main ribs and / or a plurality of second main ribs are parallel to the first diagonal line and / or the second diagonal line respectively, so that the performance of the lower pipe seat can be effectively prompted.