Joe Otterson TV ReporterElla Purnell has been cast in a lead role of the upcoming “Fallout” TV series at Amazon, Variety has learned.Like the video games on which it is based, the “Fallout” series is set in a world where the future envisioned by Americans in the late 1940s explodes upon itself through a nuclear war in 2077.Purnell joins previously announced cast member Walton Goggins in the series. As with Goggins, Amazon had no comment on the character Purnell would be playing.