UNCERTAINTIES IN FAST BREEDER REACTOR FUEL PIN CLADDING STRESS AND STRAIN CALCULATIONS

摘要

Two LMFBR material response phenomena, irradiation creep and swelling, make the prediction of cladding stress and strain uncertain. Temperature gradients through the cladding wall result in high predicted swelling gradients because of the extreme sensitivity of swelling to temperature. If the phenomenological material model for irradiation swelling does not assume a stress effect, then large stresses are calculated due to the large swelling gradients. Detailed analyses have been performed on selected fuel pins where the loading on the cladding has been restricted to fission gas pressure, temperature gradients, and swelling gradients. Various combinations of phenomenological material models for irradiation creep and swelling were used. Large variations in calculated cladding stresses and strains result from the above combination of material models. Resolution of the correct material model for irradiation creep and swelling could be achieved if the residual stress distribution and swelling distribution through the cladding thickness were known. Experimental investigations are underway to develop a procedure for measuring the residual stress and swelling distribution through the cladding wall. (ERA citation 04:003214)