Effect of temperature gradients on void formation in modified 316 stainless steel cladding

Focusing on the effect of temperature gradients across the cladding wall on void formation, observation of void distribution was carried out by means of electron microscopic techniques in the direction of the wall thickness i n the irradiated fuel claddings made of P, Ti-modified 316 steel. A deforma tion analysis was also conducted including irradiation creep and swelling d eformation, using a finite element method. At the beginning of swelling a s econdary stress occurred at the cladding surface due to non-uniform swellin g arising from the temperature gradient. Swelling appears to accelerate by this secondary stress, and the swelling developed a non-monotonic distribut ion, namely the swelling in mid-wall region was lower than that in the surf ace regions. This non-monotonic swelling distribution disappears with incre asing fluence, however. In the deformation analysis, it became clear that s welling is not continuously accelerated by the secondary stress, because ir radiation creep deformation relaxes the stress. (C) 2000 Elsevier Science B .V. All rights reserved.