In a nuclear power plant, what is used to change water into steam

In a nuclear power plant, heat released from nuclear fission reactions is used to change water into steam. The conversion of water into steam and using steam to be able to turn a propulsion shaft includes the process of producing and the expanding phase of the steam cycle.  In order to understand the steam cycle, it is very important to also properly comprehend the characteristics and properties of both water and steam especially during the most crucial phase of conversion.