In the present study, we have for the first time reported the occupancy of deuterium in a new interstitial site of ZrCoD3 which explain the hydrogen induced disproportionation behavior of ZrCo alloy. We have also reported the effect of Ni substitution on interstitial site occupancy of deuterium in ZrCo1-xNixD3, which in turn explains the improved durability of these Ni substituted deuterides against disproportionation. The crystal structure of the ZrCo1-xNix (x = 0.0, 0.1, 0.2, 0.3) deuterides was investigated by X-ray powder diffraction and neutron diffraction methods. The XRD data reveals a single phase formation for all deuterides with varying Ni content (x). The neutron diffraction study shows that deuterium occupies a new site 8e in addition to 4c(2) and 8f(1). Additionally, the Zr-D distance in 8e site is shorter than that in ZrD2. Therefore, increase in 8e site occupancy will in turn decreases the durability against disproportionation and vice-versa. Furthermore, the neutron diffraction reveals that occupancy of new Se site decreases and its Zr-D distance increases with increase in Ni content, which explicate the higher durability against disproportionation for Ni rich compound. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.