Models of radiation damage for assessing controlled thermonuclear reactor design limitations with refractory metal first walls

Abstract

The results of a modeling study of the swelling, creep and embrittlement of niobium used as the first wall of a controlled thermonuclear reactor are presented. The temperature dependence was surveyed from 400°C to 900°C. A swelling peak was observed at 650°C after 14 dpa, with an upper temperature limit for swelling of 850°C. A comparison with published experimental results was made. The time dependence was essentially linear after an incubation period. An increase of helium production rate and interstitial impurities resulted in higher initial void nucleation, but a reduced overall swelling. Variation in the shear modulus and in the energy of activation for self-diffusion produced relative maxima in swelling-versus-time responses. An increase in the interstitial misfit strain parameter produced an expected increase in swelling. Embrittlement results, modeled as an increase in ultimate tensile strength, showed less embrittlement for higher irradiation temperatures, particularly in excess of 850°C. No limitations on first wall lifetime resulted from radiation enhanced creep. A calculation was made of surface loss due to sputtering and blistering using experimental data chosen from the literature. The first wall surface loss was found to be acceptable provided an efficient divertor was provided to decrease the charged particle flux to the first wall. After taking the published experimental results into consideration with the modeling results, it was concluded that a first wall constructed of Nb-1% Zr and operated at 900°C might be a viable 2 choice for operation at 1 MW/m² or less. A contribution of this work is to provide a unique combination of damage mechanisms in a consistent mathematical form for use in computer modeling radiation damage in the CTR environment. A user's guide and a code listing of CTRSCIM are provided.