A nuclear reactor holds enormous power under careful control. It is read as intense energy or emotion that must be contained, and as the fear of what happens if containment fails.
When this appeared in your dream, what were you feeling?
My Cosmic Code has a private dream journal. Write a dream down and the app picks out the symbols in it, shows what dream books say about them and, over time, which words recur across your entries. The journal is stored on your device only.