Opening address

1. Dynamic response has always been an important parameter as far as nuclear reactors are concerned, for safety as well as for opera tional reasons. For someone whose memories go back to the early studies that were carried out at Risley and at Harwell in the late 1940s, the extent to which prediction methods have been developed and applied to the whole plant is very striking. It may come as a surprise to some members of the audience that serious consideration was given to steam raising in so called "waste-heat" (or fire-tube) boilers coupled to developments of the Windscale reactors as early as 1948 or 1949. I do not recall that any attention was given to the dynamic behaviour of such steam plant; had it been, I would hazard a guess that the stored energy of the boilers would have been measured in hours rather than seconds of full power operation!