Hi,
Thank you for contacting Microsoft Community.
BitLocker Drive Encryption help us to protect all files stored on the drive Windows is installed on (operating system drive) and on fixed data drives (such as internal hard drives). We can use BitLocker to protect all files stored on removable data drives (such as external hard drives or USB flash drives).
I suggest you to refer to the mentioned article and check if it helps:
http://windows.microsoft.com/en-US/windows-8/bitlocker-recovery-keys-faq
Note:
I highly recommend backing up all of your important files and folders onto an external storage device before attempting any type of OS repair or upgrade.
Hope this helps.
Regards,
Anusha