JP2550134B

PURPOSE:To prevent an increase of pressure drop without losing the reinforcing effect by reinforcing beams by installing a gap, many holes or windows to the flow passage around the inflow port of a control rod guide pipe inserted between the reinforcing beams to expand the flow passage. CONSTITUTION:The reactor coolant flowing into the control rod guide pipe 6 from an inflow port 5 thereof passes upward toward the orifice of a fuel supporting fitting 7. While the one beam 4 of the orthogonal reinforcing beams 3, 4 has the height up to the rear face of a core supporting plate 2, the other beam 3 is lowered in the height to form the gap 11 to allow passage of the reactor coolant between the top end thereof and the supporting plate 2. An equally good alternative is to form both the beams 3, 4 to the height reaching the supporting plate 2 and to provide the many holes 9 allowing the passage of the reactor coolant to the one beam 4 or both the beams 3, 4. Further, provision of the square windows 10 allowing the passage of the reactor coolant in the upper area of the height of the beams 3, 4 to one or both of the beams is equally good.