Technically Justin, you will not have a clearance of any kind the moment you leave the Navy. You will be "debriefed" and stripped of your clearance. (No, you will not be stripped of your briefs.)
This is true of all government security clearances. Once you no longer have the need for one to do your job, you lose it. There is more to being "cleared" than just having a clean background investigation report. Even a squeaky clean, highly-trustworthy individual must have the "need to know" classified information in order to be cleared to access it.
For all the civilians reading this, it means that someone with a Top Secret clearance who serves aboard a submarine has no clearance to see Top Secret information about aircraft radar or troop movements or land based nuclear weapons. Even submariners don't get to see stuff about submarines if they get transferred to recruiting duty.
For you, it means that your clearance evaporates when you get transferred off your ship or discharged. But that's okay because you won't need it any more anyway.
In the civilian DOE world, an "active" clearance simply means that you held one recently enough that no reinvestigation (or a very limited one) needs to be conducted prior to reauthorizing your clearance.
In civilian nuclear power plants, you don't get a "clearance" because there is no classified information that you will have access to. (There is a thing called Safeguards Information, but you will not have any need to access it.) So, instead of a clearance, you will get "Unescorted Access". This means that the holder of the license (the electric company who owns or operates the nuke plant) has ensured that you meet the requirements set forth in the CFR and granted you permission to enter their site without an escort. If you work at ten different power plants next year (assuming that none of them are owned by the same licensee) you will have to go through this ten times. The good news is that they don't all have to investigate you back to the womb. Basically, they only have to make sure that you were a trustworthy soul since your last job at a nuke. Then, every five years, they do a more in-depth investigation of you. The more often you work at nukes, the shorter the paperwork gets. The process is the same as the one for getting a government security clearance except that they make you take the MMPI and maybe talk to a shrink.
Civilian nukes are not concerned with you keeping your mouth shut about what you see or hear at the plant. Except for that Safeguards Info (that you will NEVER SEE) you can yak your fool head off about anything. They are actually more concerned that you are not going to try to sabotage the plant or steal the nuclear fuel (Yeah, I know how impossible that is, but they still don't want you to try it.) or flip out and start throwing switches all willy-nilly (what a goofy expression) because your cat told you to.
