[en] The early development of the uranium/Magnox fuel elements, and the present state of knowledge and understanding of the behaviour of the elements in the Central Electricity Generating Board's reactors, are reviewed and summarized. Irradiation growth plays an important part in the dimensional changes that occur in the bar but its effects are kept within acceptable limits by controlling the grain size and texture of the bar and by appropriate design of the element. The increase in volume (swelling) due to fission products does not present any significant problems until, at an irradiation level that depends on the composition and method of manufacture of the bar, an annulus of gross porosity (enhanced swelling) is formed in those regions operating at about 430⁰C. The average irradiation level at which channels are currently discharged, i.e. about 4000 MWd/t is chosen to avoid the formation of such porous uranium. Elements of recent manufacture in which the swelling resistance of the fuel has been optimized should not be subject to this limitation until substantially higher irradiation are achieved. Factors affecting the ductility of the can wall and deformation of the fins are discussed. The numbers and types of failure that have been experienced during the past decade are recorded and attention is drawn to the present very low incidence of failure. (author)