This is like the story about Krypton, where Jo-Rel actually released the pressure in the core and stopped Krypton's explosion. Later some messing around with the Phantom Zone by the reactionary Science Council caused the core to explode !
im·preg·na·ble/imˈpregˌnəbəl/Adjective 1. (of a fortified position) Unable to be captured or broken into: "an impregnable wall of solid sandstone"; "impregnable to takeovers". 2. Unable to be defeated or destroyed; unassailable.