<p>Licensees of UK nuclear sites are required by ONR to demonstrate that they have resilience against a range of external threat scenarios. These scenarios are updated regularly considering developments in technology and other areas. The airspace over UK nuclear licensed sites is restricted by the Air Navigation (Restriction of Flying) (Nuclear Installations) Regulations 2007. These impose restricted airspace of a radius between 0.5 and 2 nautical miles and to a height of between 1000 and 2400 feet above mean sea level around the centre of those nuclear licensed sites listed in Schedule 2 of the Regulations. Airspace usage in the UK is regulated by the Civil Aviation Authority (CAA).</p>