The Determination of Bias Factor Stress Dependence from Experimental Data on Irradiation Creep and Stress-Affected Swelling in Austenitic Stainless Steels

摘要

The measured irradiation creep strain s in structural materials is usually fitted with the equation: ε/σ = B_odpa+DS, where σ is the applied stress, S the void swelling, and B_o and D are the material parameters. The stress dependence of swelling is sometimes described using the equation S = S_o(1+M_(σhyd)), where S_o is the stress-free swelling and σ_(hyd) is the hydrostatic stress component. On the basis of the SIPA mechanism of irradiation creep it is shown in this paper that the parameter D depends on stress as follows: D = D_o/(1+M_(σhyd)), where D_o is a constant and the parameter B_o depends on dose. Knowing the constant M, one can determine the constant D_o from experimental data on dose dependence of creep tube diametral strain at several hoop stress levels. This permits the determination of the stress dependence of the bias factor. Such a determination was made in this paper for the austenitic stainless steel 316, for which a complete set of data became available recently. One of the important results of the present paper is the conclusion that to a reasonable approximation the irradiation creep rate ε~(ic) can be determined from data on the stress-free swelling rate and stress-affected swelling.