What role does near-pure water play in nuclear power plants in the United States?

Near-pure water is utilized in nuclear power plants primarily as a moderator in the fission process. Its role involves slowing down neutrons that are produced during fission events. Slower (or thermal) neutrons are more likely to collide with fissile nuclei, such as uranium-235 or plutonium-239, effectively increasing the likelihood of further fission reactions.

As water moderates the neutrons, it also absorbs some of the heat generated from the fission process. This heat is critical because it is subsequently used to generate steam that drives turbines for electricity generation. Therefore, while the water slows down the neutrons, it also heats up in the process, which is essential for the overall energy generation mechanism of the power plant.

The other options do not accurately reflect the scientific principles involved in nuclear fission. Fusion does not occur in typical nuclear power plants, and the functions described regarding inhibition of neutrons do not align with the role of water, which is to enhance the fission process rather than inhibit it.