I was interested in this, because breakers have been a big problem at nuclear plants. Circuit breakers in a nuclear plant are mostly control switches. A small control current switches off and on a very large current (also called relays). There are also the 'house-type' that switch off when there is an excess current.
The old breakers and relays were 'mercury-wetted'. These were notorious for poofing on and off, especially if somebody looked at them funny! They are also horribly bad for earthquakes, since the mercury sloshes around, and randomly activates them. When we were re-seismically qualifying Pickering A, all of these 'bad actors' had to be replaced. Darlington also has replaced the mercury switches.
The new relays and breakers are solid state, and much more rugged. Sounds like this plant still has the old type, since who would expect an earthquake in Alabama?
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