Trip To A Nuclear Reactor

My son's homeschool group toured the Breazeale Nuclear Reactor at Penn State University. My older kid took the day off school to take advantage of the opportunity. They offer some hands on activities and a wealth of information. I didn't get to go. I wish I had!

What causes the "blue glow" around the nuclear reactor core while it is operating?

This bluish light is caused by charged particles that are traveling through water at a very high speed which causes a shock wave to form. This shock wave is similar to the sonic boom caused when a jet exceeds the speed of sound in air. In the case of breaking the sound barrier, a wall of sound is formed in the shape of a pointed cone with the jet's nose located at the tip. This wall of sound results in a sonic boom. A similar situation occurs for the charged particle in water, but instead of a wall of sound it is a wall of light. The blue glow is called Cerenkov Radiation.