This is a video of a General Atomics TRIGA (Training, Research, Isotopes, General Atomics — the most common non-power nuclear reactor in the world) starting up. Some more info while I watch it again and flinch again like it was just about to melt my face off, which it totally wanted to, I could tell:

The blue light is from electrons moving through the water causing Cherenkov [electromagnetic] radiation.

“The reactor is brought to criticality and then the transient control rod is forced out. This causes a power pulse of about 500-1000 MW.”

Per some insightful Youtube comments: “And that’s how I found out I am sexually attracted to nuclear reactors,” and “The fountain of youth has been discovered I see, might just dip the ol’pecker in and see if it grows bigger, I mean it can’t get any smaller right?” Ahahahhaha, admittedly, I did forget writing those.

Keep going for the worthwhile video (the audio really makes it 10x better).

Source: Geekologie – Just Like In The Movies!: Video Of A Nuclear Reactor Starting Up