David Lochbaum, director of the Union of Concerned Scientists’ Nuclear Safety Project, is slated to speak at 7 p.m. Wednesday in Plymouth South Middle School, in an event sponsored by the citizens’ group Freeze Pilgrim Plymouth. Lochbaum supports a May 12 ballot question calling for a freeze on Entergy Corp.’s application for a 20-year license renewal for Pilgrim Nuclear Power Station. The scientist’s presentation will focus on the specific design risks posed by all Mark I reactors, including Pilgrim, and the fixes needed to decrease the risk of a Fukushima-type accident in Plymouth. After Lochbaum’s presentation, the audience will be invited to ask questions.