Interesting, thanks for the explanation.
Most of what I know about nuclear power plants was information presented in a class on the aftermath of nuclear power plant accidents. Some of those accidents were very impressive! But that taught me little about how power plants operate when everything goes well.
After reading a little bit more about the nuke plant that went down, it’s a Westinghouse Pressurized Water Reactor (PWR) design. I have experience with PWRs when I was in the navy. The plant I work in now works the same way as a PWR plant, just with a different heat source. (We use natural gas or #6 fuel oil for the heat source).
Also, it appears the unit in Texas tripped due to low steam generator (boiler) water level after two of the feedwater pumps tripped.
I have never worked at a Westinghouse PWR plant, but my plant’s steam turbine cycle is likely very similar. Our feedwater pumps do not use cooling water directly as the only components which require cooling are the bearings and mechanical seals. The bearings on these giant feedwater pumps use forced oil circulation and the mechanical seals use feedwater from a different part of the cycle. The forced oil circulating system would be cooled by a large cooling water system however. I doubt the feedwater pumps would be located in an area susceptible to freeze damage. (They aren’t at my plant as they’re on the turbine deck.)
Another poster mentioned an issue with a pressure transmitter. Again, using my plant as an example and not an actual Westinghouse PWR plant, we do have redundant differential pressure transmitters to measure the level of the tank supplying the feedwater to the feedwater pumps, which is called the deaerator storage tank. It’s mounted high up in the plant to provide suction head to the feedwater pumps. If the DST level drops too low, it is an automatic feedwater pump trip to protect the pumps from cavitating and destroying the impellor. (My guys are actually going to test this trip circuit at my plant tomorrow on an offline unit; just put it on the daily schedule. We have to test trip circuits annually.)
It’s drafty up there in our plant, but since our deaerator storage tank at the higher elevations of our boiler house, it too isn’t susceptible to freezing when a unit is running. I don’t know if the Westinghouse plant uses elevation for suction head or feedwater booster pumps, but if their DST level instrumentation froze, it’s possible that the feedwater pumps would trip, and then their steam generator would be starved for feedwater, creating a reactor scram/unit trip.
Or the feedwater pumps could have tripped for a completely different reason unrelated to weather, like an electrical fault, but at my plant, the only thing that would trip two feed water pumps at the same time is the DST low level trip.