I was intrigued to find that as early as May 1956, the threat of an airplane crashing into a power reactor, with its load of radioactive fission products, was considered. In fact a British politician asked the United Kingdom Atomic Energy Authority about this risk. An engineer drafted a response that summed up:
In general terms, we think that any such incident is unlikely except by the remotest chance to involve a release of radioactivity in the neighbourhood. We think that at worst it might cause considerable inconvenience to the factory and to the workers.
Shirlaw, D. 1956. Shirlaw to Balfour, Apr. 24, 1956. AB 19/89, National Archives, Kew, United Kingdom.