Answer: thermonuclear

AnswerCrossword Clue
thermonuclearof, relating to, or employing transformations in the nuclei of atoms of low atomic weight (as hydrogen) that require a very high temperature for their inception (as in the hydrogen bomb or in the sun)
thermonuclearOf, relating to, or involving weapons in which explosive force is produced by thermonuclear reactions
thermonuclearRelating to or using nuclear reactions that occur only at very high temperatures