Complex sentence: Both, as well as a third, underground, mine are now operated by French company Areva NC, a holding of the Areva group, a state owned operation of the French "Commissariat à l'énergie atomique" (CEA or COMINAK).
Split into simpler sentences: Both, as well as a third underground mine, are now operated by French company Areva NC, a holding of the Areva group. Areva state owned operation of the French "Commissariat à l'énergie atomique" (CEA or COMINAK).