Zirconium is employed as the 'inert' component in several different inert matrix fuel concepts currently under development (cermet, oxide solution, etc.). Relative to the situation in standard light water reactors, this implies a very significant increase in the zirconium inventory, with a correspondingly enhanced importance of the nuclear data for zirconium in calculating safety related parameters. The present paper discusses new numerical results for various reactivity effects. On the basis of the current findings, it is recommended that a high priority be assigned to both the reduction of uncertainties in the epithermal data for zirconium and to the improvement of methods for resonance self-shielding of these data.