Trivia: Director Christopher Nolan usually prefers using practical effects when possible. For the scene where the nuclear bomb is tested, a more manageably-sized explosion was created by a pyrotechnics team. The explosion was actually fairly close to the actors, but was filmed at specific camera angles to make it seem further away and thus bigger (a technique called "forced perspective"). Super-slow-motion was also utilized, as it subconsciously creates the illusion of a larger scale.
TedStixon
25th Jul 2023