A licensed reactor operator at the Cook nuclear power plant in Bridgman, Michigan violated the Fitness for Duty policy. The employee was evaluated under for-cause testing and has been suspended from accessing the site.
Fitness for duty tests are administered either randomly, in a lottery-style system where “winners” get to report to the medical office for testing, or for-cause, which are administrated after supervisors note aberrant behaviors and order follow-up testing to ensure compliance. Aberrant behaviors cover a wide range of actions from staggering, making simple mistakes (such as turning the wrong switch), acting belligerent or out of character, among a multitude of overall deviations from normal behavior for the individual.
Source: NRC Event Notifications