PURPOSE: To provide improvement of safety and relieve the shock when reaching the bottom by increasing the resistance of water during the vessel descending within the pool by providing for the cooling fins of the spent fuel transfer vessel to position with downward rake.

CONSTITUTION: Multiple cooling fins 2 are provided for periphery direction at the outside surface of the spent fuel vessel made of stainless steel cylinder with downward rake being lower than the horizontal direction. For descending the vessel 1 within the pool 10, the air bubble 12 is developed under the cooling fins 2, which increases buoyancy and increases ascending resistance of water. The descending speed of the vessel 1 may be reduced enabling to relieve the shock when reaching the bottom.