Radiation growth of uranium is another form of dimensional instability that occurs under irradiation without the need of any stress in a lower temperature (i. e.,

around 300 °C) regime. Since it does not require stress to occur, it is not considered radiation-induced creep. Also, since the volume of the material remains constant during radiation growth, it is not considered as irradiation swelling. Under radia­tion exposure, a single crystal of alpha-uranium expands in the [010] direction, con­tracts along the [100] direction, and remains more or less unaltered in the [001] direction. The result of this characteristic expansion/contraction is that the volume remains essentially constant. However, in order for radiation growth to take place, single crystal of uranium is not essential but polycrystalline uranium strong crystal­lographic texture can also exhibit the effect. Deformation processing and heat treat­ment is important to minimizing or eliminating the radiation growth effect by suitable texture engineering. Minimization of radiation growth can be achieved by processing the material to produce a fine-grained microstructure with randomly ori­ented grains. Also, suitable alloying additions to stabilize isotropic phases can help.

The radiation growth coefficient (Gt) is given by Percentage length increase

Percentage atom burnup

There have been a number of studies to understand radiation growth, but it remains elusive. A leading hypothesis of radiation growth by Buckley [ ] is based on differential directional rates of interstitial atoms and vacancies. The interstitials have a tendency to migrate along the [010] direction and to the vacancies in the [100] or [001] directions, leading to basically removal of mass from one side and plating them on the other side. Figure 7.8 shows the irradiation growth effect in a uranium fuel against the fuel burnup.