There was a recent report by the NRC about the Vermont Yankee that an supervisor was fired for being drunk:
FITNESS-FOR-DUTY REPORT INVOLVING A NON-LICENSED SUPERVISOR
A non-licensed contract employee supervisor had a confirmed positive for alcohol during a random fitness-for-duty test. The employee’s access to the plant has been terminated. ..The licensee notified the NRC Resident Inspector.
I suppose you could conclude that the system is working: bad behavior is stopped. I wonder about the morale of a company where supervisors are coming to the work place drunk. It is hard to imagine that a random test has caught all of the cases of drunkenness.