Use of zirconium-based moderators to enhance feedback coefficients in a mox-fueled sodium-cooled fast reactor

This work shows the effect of the use of moderating layers on the sodium void effect in sodium-cooled, mixed oxide-fueled fast breeder reactors. The moderating layers consist of either zirconium boride ZrB² or zirconium hydride ZrH². The two investigated ZrH² layers (0.1 and 0.2 mm thick) cause a strong reduction of the sodium void effect. Additionally, these layers significantly improve the fuel temperature effect and the coolant effect of the system. All changes caused by the insertion of the ZrH² layers result in a significantly increased stability of the fast reactor system against transients. The moderating layers have only a small influence on the breeding effect and on the production of minor actinides. The effect in the infinite system can be fully combined with the traditional methods of increasing the neutron leakage.