In 1956 Kenneth Jay, sort of the inhouse historian of the United Kingdom Atomic Energy Authority, wrote a compact book about Calder Hall, the pride and joy of Christopher Hinton, the top engineer. Hinton often preached how safe British reactors were and this paragraph from Jay could have come straight from Hinton’s mouth. It was part propaganda (Hinton used to say the same things about the earlier, more primitive Windscale reactors, one of which was to catch fire a year later) but is mostly true. Calder Hall and its successor gas-cooled reactors had the virtue of large size, making them safe but too expensive to succeed in the global marketplace. I find that ironic, for France’s current offering, the European Pressurized Reactor, is touted as being the safest but is also criticized as too expensive.
It must be emphasized, however, that this is an exceptionally safe plant by any standards because the natural-uranium gas-cooled reactor has inherent safety characteristics which have been exploited to the full in Calder Hall designs. Because the coolant gas does not absorb neutrons, an accident resulting in a rapid loss of coolant would not cause power to rise and the reactor to overheat before the control rods could be operated. Moreover, it is a property of the reactor that the reactivity decreases as the temperature rises; this again is an inherent safety-valve, since any circumstances that caused a rise in temperature would also cause a decrease in power tending to offset the rise. In any event, with such a large core, temperature changes are slow. Finally, carbon dioxide is neither poisonous nor inflammable—on the contrary it blankets a fire.
Jay, Kenneth. 1956. Calder Hall: The Story of Britain’s First Atomic Power Station. Methuen, London, pp. 52-53