In theory, exit code 0 means "No errors found, or successfully repaired" - though I don't know why it has then failed to complete & light the Done button.
Exit code 8 was "A corrupt filesystem was found during a check, or repairs did not succeed." which would not really be surprising if you were trying to work on the partition you were booted from.
Disk Utility is actually running a process called fsck_hfs which has published exit codes on the OS X developer pages
fsck_hfs indicates some status by exit value. The current list of exit status results is:
0 No errors found, or successfully repaired.
3 A quick-check (the -n option) found a dirty filesystem; no repairs were made.
4 During boot, the root filesystem was found to be dirty; repairs were made, and the
filesystem was remounted. The system should be rebooted.
8 A corrupt filesystem was found during a check, or repairs did not succeed.
47 A major error was found with -E.
If you cannot normally Quit Disk Utility, force Quit it with Cmd ⌘ Opt ⌥ Esc , or persuade the Mac to restart or shut down normally, then you may have no option but to hold the power key until it shuts down.