Integrated energy systems, such as for use in green industrial processes that produce few or no carbon emissions, and associated devices and methods are described herein. A representative integrated energy system can include a power plant system having multiple modular nuclear reactors. The nuclear reactors can generate steam for direct industrial use or for use in an electrical power conversion system to generate electricity. Individual ones of the nuclear reactors can be configured to flexibly generate differing outputs of steam or electricity based on the vary requirements of the industrial processes of the integrated energy system. The industrial processes can include, for example, the production of hydrogen, oxygen, nitrogen, ammonia, urea, sulfur, sulfuric acid, and/or other useful chemicals.