The Manhattan Project (1986) Marshall Brickman

A teen and his girlfriend make an atomic bomb with plutonium stolen from a scientist dating his mother. 

The Manhattan Project is an American film, released in 1986. Named after the World War II-era program, the plot revolves around a gifted high school student who decides to construct a nuclear bomb for a national science fair. The film's underlying theme involves the Cold War of the 1980s when government secrecy and mutually assured destruction were key political and military issues. Produced with a budget of only $500,000, the film grossed $3,900,000 at the box office. It was directed by Marshall Brickman, based upon his screenplay co-written with Thomas Baum, and starred John Lithgow, Christopher Collet, John Mahoney, Jill Eikenberry and Cynthia Nixon. This was the first production from the shortlived Gladden Entertainment Corporation.