Modeling irradiation creep of graphite using rate theory

Abstract

We have examined irradiation induced creep of graphite in the framework of transition state rate theory. Experimental data for two grades of nuclear graphite (H-337 and AGOT) have been analyzed to determine the stress exponent (n) and activation energy (Q) for plastic flow under irradiation. We show that the mean activation energy (Q) lies between 0.15-0.32 eV with a mean stress-exponent of 1.0±0.2. A stress exponent of unity and the unusually low activation energies strongly indicate a diffusive defect transport mechanism for neutron doses in the range of 3 to 4×10 22 n/cm 2 .

Review: Inelastic Constitutive Modeling: Polycrystalline Materials

“…With this being a glide-based mechanism (SICG), it should have a stress dependence of two. Newer published irradiation creep results [66,[71][72][73] suggest a SIPA mechanism. Results from Kennedy in the 1960s [66] showed that changing stress during irradiation did not affect the primary creep strain, which provides additional results that disagree with the pinning-unpinning mechanism and instead support a SIPA model.…”