Irradiation Induced Creep in Graphite at High Temperature and Dose? A Revised Model

Abstract

The application of a stress to graphite under neutron irradiation induces an inelastic strain referred to as irradiation induced creep. Existing models for the irradiation induced creep of graphite are reviewed. Previously we reported a model for irradiation induced creep at high temperatures and doses and highlighted the failure of current creep models to adequately describe experimental data. Here we report a revision to one such model originally proposed by Kelly and Burchell. The proposed revision incorporates a new term in the creep model which allows for the generation of cracks and porosity at high temperatures and neutron doses. The new term is derived from the dimensional change equations previously proposed by Simmons and Kelly, and is sensitive to the sign of the applied creep load (e.g., compressive or tensile). It is argued that the cracks and pores that are formed during high dose creep may be divided into two types, those that affect the coefficient of thermal expansion, and those that do not. The new term added to the creep model accounts for pores and cracks in the latter category. An improved prediction of the tensile creep strain in H-451 graphite neutron irradiated at 900�C and ~2x1022 n/cm2 [E>50 keV] is reported. The revised model can account for the observed differences in creep strain between compressive and tensile loading.