Exelon Senior Engineer interview questions

On site due to minimal travel. HR rep and senior supervisor present. Small room with table. Pretty standard environment/process. I was asked about my resume and specific work and education and if I would be comfortable working at a nuclear power plant. They were looking to hire a bunch of new people so with my background it was more or less a sure thing.

Got a call from a recruiter regarding a sr. engineer position. Was quite surprised to be honest, as I was still in school doing my Masters. Nevertheless, wanted to give it a shot. First round was with the team manager, it was a mix of technical and behavioral questions. Got through. Was called for onsite about 3 weeks later. Had a 5 hour interview session with 4 senior engineers. Only one among them was behavioral, the others were purely technical. Was quite expected, since the position was at the senior level. Answered about 50-60% of them; rest were too specific to the nature of the job. Since I was still in school, I was at a loss. Dint hear back for close to two months. Then got a mail saying; they were not interested in hiring me.