The US Nuclear Regulatory Commission has cited Cooper Nuclear Station near Brownville for having too many plant operators fail an exam for re-qualification.
The agency said Thursday that the violation is of low to moderate importance. However, an agency spokesman says the violation has certain significance because of Cooper's ongoing problems.
The agency has given the Nebraska Public Power District plant a rating as the poorest functioning nuclear power facility in the nation.
NPPD spokeswoman Beth Boesch says 46 plant operators took a re-exam in November and December. The test is required every two years for control room operations. She says all operators passed simulation and walkthrough portions of the test, but 36-percent failed the written portion.
The agency allows a 25-percent failure rate.
Boesch says those who failed retested on the written exam, and all but two passed.