Instead of that energy being directed to the turbines to convert the thermal energy into rotational energy (and thus it to electricity), the reactor begins cooling from the primary reactions (but not completely since secondary reactions/decay still are going) since there is no reaction heat (reactor idled). All of that excess residual heat contained in the mass of the fuel and reactor water is carried away by the cooling water loop, and either out to the cooling tower where it evaporates and releases its energy, or through the next stages of the loop into the cooling supply, most likely a neighboring river or lake.