Reactor core make-up water tank is one vertical cylindrical carbon steel vessel lined with stainless steel with hemispherical upper and lower glands, serving as the equipment to discharge the non-dynamic residual heat of AP1000 nuclear island. When there occurs non-LOCA accident, in case the normal make-up water is not available or insufficient, Reactor core make-up water tank will provide make-up and boronizing for the RCS.