Observations have shown that high amounts of dust are present in galaxies even less than a billion years after the Big Bang. As this timescale is far too short for dust enrichment by evolved AGB stars,  dust grains are assumed to be produced in the ejecta of core collapse supernovae  where the dust is condensed to (sub-)micrometre sized particles. However, due to interactions with the circumstellar and interstellar medium, reverse shocks will traverse the ejecta which could potentially destroy large amounts of the newly formed dust material. Besides gas-grain interactions (inertial and thermal sputtering, subject to a separate contribution by F. Schmidt), grain-grain collisions can provide an important contribution to the dust destruction rate and need to be investigated intensively.  Grain-grain collisions  are enabled through velocity differences between grains due to the time and spatial-dependent impact of the reverse and following shock waves and the grain size-dependent gas drag. Depending on the relative velocity, grain sizes and material properties, mutual collisions can result in bouncing, fragmentation or vaporisation of one or both colliding objects and to a redistribution of the grain size distribution.  In order to determine survival rates and the resulting grain size distributions, I performed spatially highly resolved 2D hydrodynamical simulations using the publicly available code 'AstroBEAR' to simulate a shock interacting with clumpy supernova ejecta. For the analysis of the collision rate, I utilized the velocity, density and temperature field given by the hydrodynamical simulation to evaluate dust grain trajectories, distances and relative velocities of certain dust grains. I determined the probability of a collision of two dust grains in the ejecta and explore the resulting collision products, taking into account the re-distribution of dust mass into smaller grains due to shattering as well as the reduction of dust mass due to vaporisation. I have calculated the dust destruction rates as functions of shock velocities and initial conditions of the ejecta and compare the influence of grain-grain collisions to the impact of both inertial and thermal sputtering.    This work was supported by ERC Grant 694520 SNDUST.