What is the direct function of the energy released from the nuclear chain reaction in a nuclear power plant?

turning the blades of the turbine

heating water to produce steam

powering the condenser

carrying electricity from the plant to consumers

The answer is heating water to produce steam.

The design of a nuclear energy plant and a plant that works with fossil fuel are similar in the sense that both use the heat of a reaction to produce steam. After that, the steam is used to move turbines, which produce electricity.

In a nuclear plant the heat is produced by the nuclear fission reaction, while in a typical energy plant the heat is produced by the chemical reaction (combustion) of the fossil fuel (carbon, oil, gas).