What do universities usually do with a student's graded final exams? Personally I do not recall ever having seen any of my final exams I have taken during my undergrad (except in my nightmares). Midterms, quizzes and homeworks are usually returned to the students before the final exam, but I am really curious as to what happens to the final exams after they have been graded. 

Are the exams hauled off to a secret storage facility for keepsake? Are they photocopied and kept as a student's permanent confidential academic record (unbeknownst to the student)? Are the exams hastily moved to a recycling facility and turned into fodder for new exams? 

If I were to request a copy of my final exam from undergrad (say after one year), what are the chances that the school will still have a copy?

Can someone (administrator/professors) shed a light on the secret life of a final exam?
Speaking as a professor, I typically hold on to them for a year or so just in case any student wishes to see them. That said, I can remember this happening only once in about 5000 students taught.  

When I was in college, we had the option of providing self-addressed stamped envelopes in which our final exams could be returned to us. Over half of the students availed themselves of this option.

I do not believe that my university has any formal policy, though they could have one that I am unaware of. It would seem foolish for a professor to get rid of the exams before the students have had an opportunity to see their grades and respond if something seems out of line.