They failed in much the same manner being the incompetence of their management. In Chernobyl's case, it was inadequate training of their staff for a test proce

They failed in much the same manner being the incompetence of their management. In Chernobyl's case, it was inadequate training of their staff for a test procedure (including various side effects that this test procedure might cause) and some overrides of safety systems (in gross violation of existing regulations). In Fukushima Daiichi's case, it was management ignoring the very real risk of tsunamis, even in the face of plenty of evidence that the station was vulnerable to such (a handful of other stations around the world had been damaged by tsunamis in the preceding dozen or so years, and only fared much better because of more redundancies in their emergency systems).