Physical science: how does a nuclear reactor convert nuclear energy into thermal energy?

I'm not sure if nuclear energy is turned into thermal energy using this method, but it definitely makes energy; the reactor fissions a uranium-235 isotope into multiple pieces and controls the energy. The reactor core sits inside a steel pressure vessel, so that water around it remains liquid even at the operating temperature of over 320°C.  Steam is formed either above the reactor core or in separate pressure vessels, and this drives the turbine to produce electricity.  The steam is then condensed and the water recycled.

A nuclear reactor produces and controls the release of energy from splitting the atoms of uranium. Uranium-fuelled nuclear power is a clean and efficient way of boiling water to make steam which drives turbine generators.