PURPOSE: To drain the pool water stored in the lower parts of a pressure suppression chamber and a pedestal within a short time by providing an incline surface and a water collecting pit to the floor part of a reactor container and arranging a drain pump outside the reactor container.

CONSTITUTION: At first, the pool water 10 stored in the lower parts of a pressure suppression chamber 7 and a pedestal 3 is drained out of a reactor container using a drain pump 20 and piping 19. Since the pool water 10 passes through the lower opening 11a provided to the pedestal 3 from the inclined surface 16 of the floor part of the reactor container 2 in a stage advancing in drainage and flows in a water collecting pit 17 to be gathered therein, the pool water is drained out of the reactor container 2 through the piping 19 by continuously driving the pump 20. After the pool water 10 in the pressure suppression chamber 7 and the pedestal 3 is drained, the lower parts of the pressure suppression chamber 7 and the pedestal 3 are cleaned and the inspection, repairing and painting of a vent pipe 9 and a column support 8 are performed. By forcibly draining pool water using this drain equipment, the time for drainage can be shortened.