The TVA equivalent to an AS is 60 hours in sciences. If you have that, they will consider you even if the degree is not complete. From the list of classes that you listed, you were well on your way to a science related degree. That is a plus in your corner. The POSS test, if you for some reason didn't pass the nuclear portion this time, remember this. They grade based on the number of questions answer and the amount of those that are correct. If you don't know the answer SKIP IT! They are looking for a percentage of questions answered. If you get the majoirty of them answered and 90% of those are correct, you should be fine.
On hiring into OPS. Some people have said it took two years to get a call to interview. Some have said they interviewed 3 or 4 times before being offered a job. On one occasion I saw a person test, interview and be hired into the SGPO class in 6 weeks.
If you want to work at TVA there are a couple things you can do to help yourself. Go back to school while waiting to hear. Or, go to the Laborer's Union and join. Get your face seen around the plant, show that you want the job, you will work hard, and be relible. Get to know the people in the department you want to work in. Do not try to sell yourself off to them. If someone mentions that a job opening is coming, let a comment in there that you will be applying for it. And let it go.
These are just suggestions. I wish you the best of luck.