In addition, all nuclear reactors are surrounded by six enclosures, including a one square kilometer perimeter which is sealed off to outsiders, ensuring that no radiation escapes into surrounding areas.
六層防護設施由內而外依次是：陶瓷性燃料丸、燃料護套、反應器壓力槽、包封圍阻體、反應器廠房及廠區管制區城。這些屏障全由高密度物質構成，爐心核分裂產生的輻射線，經過這六層阻隔，散放至外界的可能微乎其微。