The first script for the film was written in the mid-1970s. Michael Douglas initially wanted to produce this film immediately after One Flew Over the Cuckoo's Nest (1975). Jack Lemmon agreed to play his role as early as 1976. Douglas was enormously grateful to Lemmon, as he remained ready to start work at very short notice for over a year before production started, in the process passing up other work. To return the favor, Douglas amended the shooting schedule to allow Lemmon to attend rehearsals for the Broadway play Tribute (1980), the film version of which would later star Lemmon.
When the film was first released on 16 March 1979, nuclear power executives soon lambasted the picture as being "sheer fiction" and a "character assassination of an entire industry". Then twelve days after its launch, the Three Mile Island nuclear accident occurred near Harrisburg, Pennsylvania.
Because the Three Mile Island accident, which resulted in the release of radioactive steam, occurred just weeks after release of this movie, many people associate the movie with Three Mile Island. However, the potentially far more dangerous "Incident at Browns Ferry" (Alabama) happened in 1975, four years earlier, and was caused by a number of construction flaws, operational issues, and safety failures. Brown's Ferry Alabama is more properly the "true" basis of this story. No similar situation happened in California.
All of the music in the film, including the title song "Somewhere In Between" by Stephen Bishop is diegetic, meaning it comes from normal sources of music within the film: car radios, barroom jukeboxes, television commercials, etc. There is no traditional "soundtrack" of music that the audience can hear but the characters cannot.
Producer Michael Douglas creatively demanded a harsh realism for the film by not having any music score on the soundtrack except for the Stephen Bishop's theme song "Somewhere in Between".