To provide a draining system for S/P water of a nuclear power plant and a water supply system for an auxiliary fuel pool with a simple system by sharing an SPCU system.

By installing a piping 6 communicating an F/D 3 downstream side of the SPCU system to an SAP waste water tank 4 or the auxiliary fuel pool 15, the S/P water passed from an S/P 1 to the F/D 3 by a pump 2 and purified can be transferred to the S/P waster water tank 4 or the auxiliary fuel pool 15 with maintained or improved water quality. By utilizing facilities of an existing SPCU system during the transfer, increase of costs can be minimized by a simple system.