Small reactors are already used in environments where the unit is self contained with no environmental impact during operation (passive cooling). The discussion

Small reactors are already used in environments where the unit is self contained with no environmental impact during operation (passive cooling). The discussion of environmental impact of those units are generally about decommissions once they are removed from the environment where they have been operating. Large generators are not self contained and usually need a lot of water for cooling, and they have waste heat. They are also very large concrete buildings, so environmental considerations are needed there.