CLEVELAND (AP) -- Federal regulators say they're stepping up oversight at an Ohio nuclear reactor where an incident in April exposed workers to increased radiation levels.

The Nuclear Regulatory Commission said Friday that an inspection of the Perry Nuclear Power plant near Cleveland found low to moderate safety concerns.

Four workers at the plant on Lake Erie were exposed to higher radiation levels than normal on April 22 while they were attempting to remove a monitor for measuring nuclear reactions. NRC officials say in a statement that the plant wasn't prepared for the possibility of overexposure.

The agency plans further inspections, and the plant must develop corrective and preventive measures.

The plant has said the highest radiation exposure to any of the workers was the equivalent of two or three chest X-rays.