There was an emergency core shutdown which sounded like our tour guide had just gotten a phone call. He left for a moment to check with the office and then came back to say "don't worry, the core has just had an emergency shutdown which is fairly routine, we can go on with our tour."
That was sometime back around early 1980s when I went on a guided tour of Washington State University's research reactor in Pullman. We had just visited the pool room where the reactor resides 20 feet down toward the bottom of a deep pool. This faint blue glow around the reactor was said to be neutrons reacting with the water.
WSU's research reactor is very small and doesn't generate electricity. It is used to irradiate samples for various forms of research. Used a lot in biological, medical and other fields of inquiry.
Soon after we left the observation deck in the pool room, a buzzer sounded while we were heading down some stairs. As we waited at a landing, our tour guide checked his message and said that the reactor had just shut down. I think we all had little Geiger counters around our necks that they issued to tourists; like having little hardhats. None of these were reporting any radiation problem.
Apparently there was a minor glitch in the reactor's control panel. If anything is amiss, everything shuts down as a precautionary step.
Possibly the only loss was the sample that was being irradiated at that time. That experiment would just have to be redone later.
We continued our tour past a couple more labs and classrooms. Then it was back outside to a sunny day.