[CalChris]

My dad worked for TVA (in Knoxville) on their nuclear plants. I got a tour of Oak Ridge including a test reactor where you could look into a reactor core … through about 20 feet of flowing water, an early unforgettable blue.

[chasil]

I am assuming the blue glow was due to Cherenkov radiation.

https://en.m.wikipedia.org/wiki/Cherenkov_radiation