Grain Secondary Recrystallisation in Advanced Gas Cooled Reactor Fuel Cladding: Characterisation and Modelling

Secondary recrystallisation and resultant abnormal grain growth behaviour in a specific nano-particle pinned stainless steel alloy have been investigated under a particular combination of stress and annealing conditions. The tests were carried out as function of time and temperature in order to study the effect of specific grain size distributions and grain growth models. The models of size distribution and grain growth were first revisited and applied to estimate the incubation time for the explored temperatures. The pre-required sample history is pointed out as an important issue. The grain particle size data are obtained for samples of known prior cold work and recrystallisation conditions. Careful application of the grain growth model shows that the analysis of the mean sizes of the grains and the nano-particles should be more precise and accurate than currently measured to achieve a correct evaluation of incubation time. Recommendations on additional R&D work on the way to apply the model and to avoid secondary grain growth are consequently suggested.