Effect of zirconium-hydride layers on reducing coolant void reactivity of steam cooled fast breeder reactors

The introduction of zirconium-hydride (ZrH1.7) layer between the seed and blankets is very effective in reducing the coolant-void reactivity of steam-cooled FBR. The void reactivity reduction is attributed to the rapid increase of neutron absorption and to the decrease of neutron production in the blanket due to the moderation through the layer. The reason is that the neutron multiplication factor decreases, reflecting the neutron balance of the whole core. It is effective even the layer thickness is 1 or 2 cm. Compared with the conventional uniform introduction of this moderator into the seed, the fixed layer concept is more effective in reducing void reactivity and hardly deteriorate the breeding ratio. The negative void reactivity is proved for the non-flat large-sized radial heterogeneous core where the layers are placed between the seeds and blankets. The neutron absorption rate increases, the fast fission rate decreased in the central, inner and radial blankets. (author)