Due to its advantageous physical properties, tungsten (W) is being considered as a candidate structural material in fusion applications. In this paper, we perform stochastic cluster dynamics calculations of irradiation damage accumulation in pure W under fast neutron spectra in up to doses of 1.5 dpa in the 400∼600 • C interval. Our calculations suggest that He bubbles and dislocation loops accumulate under fusion conditions, but not under fast fission spectra. We study the temperature dependence of swelling and find that it is maximum in the 550∼590 • C temperature range, falling precipitously above 600 • C. Swelling levels are very low, never surpassing a fraction of a percentage point. We also provide hardening estimates based on the accumulation of sessile dislocation loops under fusion conditions and show that they are moderate, ranging between 70 and 137 MPa at 400 • C.
An improved version of a recently developed stochastic cluster dynamics (SCD) method (Marian and Bulatov, 2012) [6] is introduced as an alternative to rate theory (RT) methods for solving coupled ordinary differential equation (ODE) systems for irradiation damage simulations. SCD circumvents by design the curse of dimensionality of the variable space that renders traditional ODE-based RT approaches inefficient when handling complex defect population comprised of multiple (more than two) defect species. Several improvements introduced here enable efficient and accurate simulations of irradiated materials up to realistic (high) damage doses characteristic of next-generation nuclear systems. The first improvement is a procedure for efficiently updating the defect reactionnetwork and event selection in the context of a dynamically expanding reaction-network.Next is a novel implementation of the τ -leaping method that speeds up SCD simulations by advancing the state of the reaction network in large time increments when appropriate. Lastly, a volume rescaling procedure is introduced to control the computational complexity of the expanding reaction-network through occasional reductions of the defect population while maintaining accurate statistics. The enhanced SCD method is then applied to model defect cluster accumulation in iron thin films subjected to triple ion-beam (Fe 3+ , He + and H + ) irradiations, for which standard RT or spatially-resolved kinetic Monte Carlo simulations are prohibitively expensive.
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