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

Abstract

The measured irradiation creep strain ε in structural materials is usually fitted with the equation: E/σ B0dpa+DS, where σ is the applied stress, S the void swelling, and B0 and D are the material parameters. The stress dependence of swelling is sometimes described using the equation S = S0(l+Mσhyd), where S0 is the stress-free swelling and σhyd 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(1+Mσhyd), where D0 is a constant and the parameter B0 depends on dose. Knowing the constant M, one can determine the constant D0 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 εic can be determined from data on the stress-free swelling rate and stress-affected swelling.