Temp DB cannot be shrunk as long as it is in use. Sql server can use it for the internal operations or for row versioning or for storing the user objects like temp tables and variables.

Some times so many transactions will be runing on the TempDB that they are so short in duation that it is very hard to notice them. Even this will prevennt Tempdb from shrinking.

For ex: Running DBCC OPENTRAN may result in no transactions for the first time. But when run for the second time it may show you any active transaction.

In most cases restarting TempDB should fix the prolem. But this should be your last option.

Thank You,

Best Regards,

SQL Buddy