The physics of uranium nitride fuels used in CANDU-6 reactors has been assessed by means of full core Monte-Carlo simulations. It is shown that the application of Unat15N allows for increasing the average residence time of a fuel bundle from 210 to 360 days, as compared to a conventional UnatO2fuel. Whereas a 20% increase in coolant void worth is observed, the total power coefficient is reduced by half, due to a change in sign of the Doppler coefficient. Moreover, thanks to the better thermal conductivity of UN, the margin to fuel melt is raised considerably. Hence, uranium nitride could constitute a more efficient fuel for CANDU reactors, while possibly allowing to extend the grace time for actuation of shut-down during a power transient.