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An extensive description of mechanical response of breeder reactor core components to transient loading is required for design and safety analysis. This description is needed for strain rates from 10−5 to 101/s, test temperatures from 232°C to over 1000°C, and neutron (n) fluences from 0 to 1.3 × 1023 n/cm2 (E > 0.1 MeV).2 An equation-of-state approach, proposed by Hart, is applied to existing tensile and burst data to develop an improved method of predicting mechanical behavior over this range of temperature and strain rates.
Parameters for the Hart deformation model, derived by Huang and Li from stress relaxation data at T ≤ 500°C, must be modified for the description of flow at higher temperatures. It was necessary to fit unirradiated tensile data, by Steichen and Paxton, to develop a more suitable flow law. Thermal recovery is explicitly treated in this correlation. Using the resulting deformation equation, the Hart structure parameter is obtained as a function of irradiation temperature and fluence. With the derived structure parameter and flow law, tensile flow properties could be satisfactorily predicted for available data. The conclusion from this fit is that the form of the flow law is essentially unchanged by irradiation. The data show that the irradiation-induced reduction of ductility can be described simply in terms of the structure parameter in the transgranular failure range. Thus, it is concluded that ductility loss in this range is due simply to exhaustion of work-hardening.
The deformation model is applied to more complex loading paths with continuous temperature variation. The effect of varied heating rate can be calculated with fair agreement with existing data for both unirradiated and irradiated 316 stainless steel. Use of this method appears to be very promising in breeder reactor design analysis.
constitutive equations, neutron irradiation effects, tensile strength, ductility, transient flow strength
Manager, Mechanical Properties, Westinghouse Hanford, Richland, Wash.