After a nuclear accident, why need two emergency actions: insertion of control rods inside the reactor & continuous spraying of cold water?

The insertion of control rods aims to stop the fission reaction. When the fission reaction slows down, there is still residual heat produced in the reactor core. Hence, continuous spraying of cold water is essential in order to remove the residual heat and lower the temperature of the reactor core. If not, the temperature of the reactor core would keep rising and might eventually lead to a core-melt accident, as in the cases of Three Mile Island nuclear accident that happened in 1979 in the US and the Fukushima accident occurred in 2011 in Japan.
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