JP2791077B

PURPOSE:To facilitate control of a void rate of a reactor core by providing a fuel assembly with a coolant passage connected to a coolant discharge opening, a coolant climb passage connected to a lower region and a coolant drop passage connected to the coolant passage. CONSTITUTION:A great part of cooling water fed to a fuel assembly 20 is introduced to a passage 23 of the fuel assembly 20 through a through hole 18 provided in a fuel hold part 16 of a lower tie plate, and the residual cooling water is allowed to flow in a water rod 31. Part of the cooling water allowed to flow in an inflow port 19 is introduced in a coolant passage 8 from a flow opening 7 to reach a space 12. The residual cooling water allowed to flow in an inflow opening 19 is allowed to flow in a coolant climb passage part 2 through a coolant climb passage part inlet 4 to be discharged in the passage 8 from a drop passage discharge opening 5 through a reversion part 15 and a coolant drop passage part 3 further. The cooling water discharged from the discharge opening 5 becomes liquid or gas in accordance with the flow amount of the cooling water allowed to flow in the passage 8 from a passage opening 7.