Yes you can use those tapes , but it should come back to Sratch pool since it is expired the data so should unassigned state.
Ensure image cleaning is running every day.
You can expire the images as AJ mentioned,
or else go for Media ->right client on media -quick erase, it will erase the tape and make it useful for next backup. before you do this ensure you do not have vaild data init.
Please do NOT expire tapes that 'are almost full'.
The are 'almost full' of valid backups that are needed for restores.
Expired tapes can be reused. If 'Assign Time' field is empty, you can simply put the tapes backup in the robot. These tapes will then be available to be overwritten.
Please take care that tapes do not have a hardware expiration date.
Only images must be expired.
If you look at 'nbemmcmd -listmedia -mediaid <media-id>' output, both these fields must be empty:
If you do not have a Scratch pool, check that Unassigned tapes are in the correct backup pools.
To see what is 'available', use the available_media script.
You did not mention or select your OS.
This script is in <install-path>\veritas\netbackup\bin\goodies folder on Windows.
On Unix/Linux, in /usr/openv/netbackup/bin/goodies.
even if u wish to expire tapes manually using command bpexpdate for reuse please make sure do it for tapes whose exipration is nearest like tapes whose data expiration date is around june 25th , 26th june 2014 etc