Controlled irradiation hardening of tungsten by cyclic recrystallization

Abstract

The economical lifetime of the divertor is a key concern for realizing nuclear fusion reactors that may solve the world's energy problem. A main risk is thermo-mechanical failure of the plasma-facing tungsten monoblocks, as a consequence of irradiation hardening induced by neutron displacement cascades. Lifetime extensions that could be carried out without prolonged maintenance periods are desired. In this work, the effects of potential treatments for extending the lifetime of an operational reactor are explored. The proposed treatments make use of cyclic recrystallization processes that can occur in neutron-irradiated tungsten. Evolution of the microstructure under non-isothermal conditions is investigated, employing a multi-scale model that includes a physically-based mean-field recrystallization model and a cluster dynamics model for neutron irradiation effects. The model takes into account microstructural properties such as grain size and displacement-induced defect concentrations. The evolution of a hardness indicator under neutron irradiation was studied. The results reveal that, for the given microstructure and under the assumed model behaviour, periodical extra heating can have a significant positive influence on controlling the irradiation hardening. For example, at 800°C, if extra annealing at 1200°C was applied after every 100 hrs for the duration of 1 hr, then the hardness indicator reduces from maximum 140 to below 70. * Correspondence to J.A.W. van Dommelen. Electronic mail: j.a.w.v.dommelen@tue.nl arXiv:1901.05859v1 [cond-mat.mtrl-sci]

Structural, mechanical, electronic, and thermodynamic properties of pure tungsten metal under different pressures: A first‐principles study

“…As a result, the precipitate of W has attracted great interest of many researchers. [ 5–16 ] Recently, Wirtz et al [ 5 ] experimentally investigated the effect of material properties, and W behavior showed that different production processes had certain effects on the anisotropic microstructure and the related material properties of W in the initial state while improving the recrystallization behavior, but thermal shock performance had little impact. Mannheim et al [ 6 ] used a multiscale model to study the long‐term microstructure evolution of W under cascade damage conditions and the distribution of W in nuclear fusion reactor steering gear at different irradiation temperatures.…”

“…Mannheim et al [ 6 ] used a multiscale model to study the long‐term microstructure evolution of W under cascade damage conditions and the distribution of W in nuclear fusion reactor steering gear at different irradiation temperatures. In addition, Mannheim et al [ 7 ] experimentally controlled the irradiation hardening of W by cyclic recrystallization. The results show that periodic additional heating has a significant positive effect on controlling radiation hardening under the given microstructure and assumed model behavior.…”

Microstructural evolution and regeneration in neutron-irradiated tungsten monoblocks

“…At the mesoscopic level, the local changes in grain size r g,k and defect concentrations C k and dislocation densities ρ k for a set of k representative grains in each material point l at the macroscopic level is modelled, using a mean-field recrystallization model ( Bernard et al, 2011;Mannheim et al, 2019b ). These changes are the consequence of grain growth and nucleation.…”

“…For each part, the physical mechanisms of the model are set out. The cluster dynamics model and the recrystallization model have been extensively described in Mannheim et al (2018Mannheim et al ( , 2019aMannheim et al ( , 2019b and are therefore only discussed briefly. Computational details can be found in Appendix A and Appendix B .…”

“…The results in Mannheim et al (2018) also showed the strong temperature dependence of the competition between the occuring damage and recovery mechanisms. The modelling framework was used to explore the effects of intermittent heat treatments in the temperature range of 80 0-10 0 0 • C, as a means to systematically reduce the severe irradiation hardening ( Mannheim, Dommelen, & Geers, 2019b ).…”