Hi,
Hope this query helps. Kindly run this statement in your "reportserver" Database and "reportservertempdb" should be your reportserver temp DB.
select usr.username , reportpath, expiration
from Users usr,
reportservertempdb..SessionData ses
where usr.UserID = ses.ownerid
order by 1
Note: if i close the report from browser the session closes 5 minutes closely after the expiration time in my server.