The double-meaning of the word “startup” might throw people off, but when the other items from the list in the quote are “trials” and “construction” you can imagine they are talking about an action rather than an entity. Here a “reactor startup” would be the process of a reactor going from subcritical, extremely low power state to the point where it can heat water on its own through fission. This is a standard term in the nuclear power industry, and this confusion seems like one more reason reactors should not exist in an unregulated venture capital environment.