You are an expert at summarizing long articles. Proceed to summarize the following text: 
combustion engineering -lrb- ci -rrb- of the united states will waive royalty payments when and if south korea 's electric power corp. -lrb- kepco -rrb- supplies safe nuclear reactors to north korea , yonhap news agency said saturday .
us south korean firms agree on royalty exemption on reactors for north