First, were you actually issued a "final" clearance or merely approved for an "interim"?
I know that 20 years ago when I joined the Navy, we were all given interim clearances while we were in the pipeline. I didn't receive my actual security clearance until I had reported to my first ship, almost 2 years after enlisting.
Even if you were issued a final clearance, the DOE would most likely re-perform the background investigation, so nothing would happen right away.
Caveat, this is based on 20 year old data and some conjecture, so take it with a grain of salt. Graphic is the SME and may be able to shed some more light on this matter.