Simplify the following text for a Grade 14 native English-speaking person.
Original: On April 21 , 2010 , a dozen environmental organizations called on the United States Nuclear Regulatory Commission to investigate possible limitations in the AP1000 reactor design .
Simplified: On April 21 , 2010 , a dozen environmental groups called on the United States Nuclear Regulatory Commission to investigate possible problems in the AP1000 reactor design .