They found cracks in fuel oil lines. Last time I checked, generators need fuel to operate. In fact, the article even states: > the problem grew to a point wher

They found cracks in fuel oil lines. Last time I checked, generators need fuel to operate. In fact, the article even states: > the problem grew to a point where the diesel generator system did not work during testing. You have backups because things unexpectedly fail. It's the Swiss Cheese model: more than one system can fail at the same time so you should be able to handle multiple failures at once. Especially because failures often cause other failures to happen. Fukushima also had multiple grid connections. They had 13 emergency generators which could be cross-connected between reactors. They could also bring in mobile generators. It still wasn't enough, because they shared a huge unknown common failure mode. Fukushima is exactly the reason why ignoring defects on one of your two emergency generators for twenty years is such a big deal. When the potential impact is as large as it is with nuclear power, you simply cannot afford slacking off like this.