  Massive material injection has been proposed as a way to mitigate the
formation of a beam of relativistic runaway electrons that may result from a
disruption in tokamak plasmas. In this paper we analyse runaway generation
observed in eleven ASDEX Upgrade discharges where disruption was triggered
using massive gas injection. We present numerical simulations in scenarios
characteristic of on-axis plasma conditions, constrained by experimental
observations, using a description of the runaway dynamics with self-consistent
electric field and temperature evolution in two-dimensional momentum space and
zero-dimensional real space. We describe the evolution of the electron
distribution function during the disruption, and show that the runaway seed
generation is dominated by hot-tail in all of the simulated discharges. We
reproduce the observed dependence of the current dissipation rate on the amount
of injected argon during the runaway plateau phase. Our simulations also
indicate that above a threshold amount of injected argon, the current density
after the current quench depends strongly on the argon densities. This trend is
not observed in the experiments, which suggests that effects not captured by 0D
kinetic modeling -- such as runaway seed transport -- are also important.
