Reinstall windows on bitlocker protected partition


I want to do a reinstall of my windows 7 installation and I currently have bitlocker with usb key authentication(no tpm). So I'm wondering if I will run into any troubles if I just reinstall over the old windows as I would rather not have to format the drive.
What will happen. Will bitlocker automaticly be initialized in the new installation or will I have to activate it again?
Should I reformat the OSvolume and what will then happen to the hidden startup volume?
Anyone got any ideas cause I find no documentation on this at microsofts support???

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