Axial and radial shield optimization for CFBRs with ferro-boron

A series of Commercial Fast Breeder Reactors (CFBRs) are planned to be constructed in India. Ferro-boron is proposed as neutron shield in CFBR cores. This work presents the optimization studies carried out towards reducing volume and weight of shields with ferro-boron, keeping in view the requirements of maintaining secondary sodium activity below permissible limits and improving neutron monitoring efficiency at the above core location. Three shield configurations have been considered, all with reduced radial ferro-boron shields as compared to Prototype Fast Breeder Reactor (PFBR). They differ in their axial shield configuration. The studies have shown that the best configuration is with axial stainless shields above core-1 and boron carbide (B4C) shielding over blankets. This configuration preserves the secondary sodium activity and also gives rise to 50% increase in neutron detection efficiency at the above core location. The material cost reduces nearly 5 times and the advantage of weight reduction is considerable.