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, MOX fuelled fast breeder reactors. The moderating layers are consisting of either zirconium boride ZrB2 or zirconium hydride ZrH2. The two investigated ZrH2 layers (0.1mm and 0.2 mm thick) cause a strong reduction of the sodium void effect. Additionally these layers improve the fuel temperature effect and the coolant effect of the system significantly. All changes caused by the insertion of the ZrH2 layers cause 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.