Having the power cut in the middle of an I/O operation to a drive will not change its BitLocker protectors (e.g. password). However, this could lead to corruption on the disk that could prevent you from unlocking the drive even through you're using the correct key.
For such a scenario you can use Microsoft's Bitlocker Repair Tool. Here's a description from Microsoft's site:
This tool can be used to access encrypted data on a severely damaged hard disk if the drive was encrypted by using BitLocker Drive Encryption. Repair-bde can reconstruct critical parts of the drive and salvage recoverable data as long as a valid recovery password or recovery key is used to decrypt the data.
The Bitlocker Repair Tool is a command-line program that's included with Windows Windows 7 and Windows Server 2008 R2. It's also available for download for Windows Vista and Server 2008 SP1.
How to Repair a Corrupt BitLocker drive using The BitLocker Repair Tool (Repair-bde) Command
Note: These instructions are from Microsoft's website. The article is written for Windows 7 but applies to any version of Windows that supports the Repair-bde command.
To complete the procedure in this scenario:
Your test computer must have a BitLocker-protected drive.
You must be able to provide administrative credentials.
You must have at least one of the following:
Recovery key file location
Recovery package file location and the corresponding recovery password
Recovery package file location and the corresponding recovery key file location
You must have an empty output volume of equal or larger size than the BitLocker-protected drive (whose contents will be completely overwritten after the repair operation).
The following procedure provides the command-line syntax for using each type of recovery information with the Repair-bde tool. For this procedure, we recover access to the data stored on drive C: and write the recovered data to an output volume on Z: by using the parameters in the following table.
Recovery information Value
Recovery password 062612-026103-175593-225830-027357-086526-362263-513414
Recovery key file location F:\RecoveryKey.bek
Recovery package file location F:\ExportedKeyPackage
Replace these parameters as appropriate for your test environment.
To repair a BitLocker-protected drive by using Repair-bde
Open a Command Prompt window as an administrator.
a. To do this, click Start, type
cmd in the Search programs and files box, right-click cmd.exe, and then click Run as administrator.
b. If the User Account Control dialog box appears, confirm that the action it displays is what you want, and then click Yes.
At the command prompt, type one of the following commands, depending on which recovery information you want to use:
a. To repair using a recovery password:
repair-bde C: Z: -rp 062612-026103-175593-225830-027357-086526-362263-513414
b. To repair using a recovery key:
repair-bde C: Z: -rk F:\RecoveryKey.bek
c. To repair using a recovery package and the corresponding recovery password:
repair-bde C: Z: -kp F:\ExportedKeyPackage -rp 062612-026103-175593-225830-027357-086526-362263-513414
d. To repair using a recovery package and the corresponding recovery key:
repair-bde C: Z: -kp F:\ExportedKeyPackage -rk F:\RecoveryKey.bek
Note: If the path to the key package is not specified, Repair-bde will search the drive for a key package. However, if the hard drive has been damaged, the tool may not be able to find the package and will prompt you to provide the path. We recommend that you include the key package in the Active Directory key storage so that you can export the key package if needed.