  During disruptions in fusion-grade tokamaks like ITER, large electric fields
are induced following the thermal quench (TQ) period which can generate a
substantial amount of Runaway Electrons (REs) that can carry up to 10 MA
current with energies as high as several tens of MeV [1-3] in current quench
phase (CQ). These runaway electrons can cause significant damage to the
plasma-facing-components due to their localized energy deposition. To mitigate
these effects, impurity injections of high-Z atoms have been proposed [1-3]. In
this paper, we use a self-consistent 0D tokamak disruption model as implemented
in PREDICT code [6] which has been upgraded to take into account the effect of
impurity injections on RE dynamics as suggested in [4-5]. Dominant RE
generation mechanisms such as the secondary avalanche mechanism as well as
primary RE-generation mechanisms namely Dreicer, hot-tail, tritium decay and
Compton scattering (from {\gamma}-rays emitted from activated walls) have been
taken into account. In these simulations, the effect of impurities is taken
into account considering collisions of REs with free and bound electrons as
well as scattering from full and partially-shielded nuclear charge. These
corrections were also implemented in the relativistic test particle model to
simulate RE-dynamics in momentum space. We show that the presence of impurities
has a non-uniform effect on the Runaway Electron Distribution function. We also
show that the combined effect of pitch-angle scattering induced by the
collisions with impurity ions and synchrotron emission loss results in the
faster dissipation of RE-energy distribution function [7]. The variation of
different RE generation mechanisms during different phases of the disruption,
mainly before and after impurity injections is reported.
