Each unit has two redundant safety trains, i.e. duplicate of everything they need to either shut the plant down safely and/or maintain core temperature. Each safety train has one generator, which by design, is all they need to maintain that unit. Running both trains at the outset of an emergency is likely standard EOP. Loss of one genset does not mean they have inadequate generating capacity. Additionally, they most likey can cross-tie emergency electrical busses across both units, resulting in the availability of 3 gensets, where only two are needed by design for both units. Essentially, they are still up one genset, instead of down one as you imply. 22 years in Nuclear Generation.
How big are those generators? I have heard the press talk about them, both in this case and earlier in the year when one was surrounded by the flooded Mississippi river.
Thanks for the replies, particularly in light of your experience in the field.
Many interesting design issues in the back-up power systems area, especially in light of Fukushima. It was interesting that they fired-up a fifth generator to replace the one that went down. I’m still curious about whether the load requires two spinning per reactor, or whether they just need one and spin the other for back-up. In my ignorance spinning for back-up seems odd in light of low latency for them to come on line, wear and tear and fuel consumption, but I don’t know enough one way or the other.
I was wondering if the cause of the failure to the one genset was any threat to the others. Here it was a cooling system that leaked. Was that caused by the quake or some other cause common to all gensets, or was it isolated to that one? To what extent were the other gensets stressed or threatened by the quake? Obviously, they got 4 working, but was it a close call? Interesting stuff.
Thanks for keeping the lights on!