A nuclear explosion is not always an act of war, but can sometimes be accidental.
Such an accident can unintentionally have very far-reaching effects.
To dream of a nuclear explosion can highlight our anxiety about great change in our lives. We do not yet know what effect that change may have. We do, however, know we must undertake radical change, but would prefer it to be a more gradual process.
Also consult the entries for apocalypse, atom bomb and bomb.