Paper 10: Mechanical Design and Development of Fuel Elements for Gas-Cooled Reactors

Abstract

The fuel elements in the uranium-magnox carbon-dioxide-cooled reactors, which are currently operating and under erection in the United Kingdom and other countries, are required to maintain their physical shape and dimensions virtually unchanged during a lifetime which may be as long as five years. During its life in the reactor, the fuel element is subject to forces arising from various causes, e.g. its own weight, because of swelling of the fuel by irradiation, the flow of cooling gas over the element, thermal stresses resulting from charging, load changes and reactor shut-downs and changes in the dimensions of the graphite core which may lead to jamming of the element in the core channel during discharge. Because of the need to economize in neutron-absorbing material the uranium fuel rod itself becomes the major structural member in the element. The effects of these forces on this and the other component parts of the fuel element are examined, out-of-pile testing is described and the changes in design resulting from this prototype testing are indicated. In a short theoretical section, means of predicting fuel-element deformation in the light of creep data are given and probable limits of accuracy noted.