Use of Gd as burnable absorber to enhance the operation safety of the VVER-1000 MWe core of KK project

Full text: For the VVER-1000 MWe reactor core of the Kudankulam (KK) Project, a physics design study is presented with burnable absorber of type gadolinium oxide (Gd2O3) mixed with fuel instead of the present boron type burnable absorber rods (BAR) of CrB2 material in Al matrix. The new core design would allow the use of all the rod cluster control absorbers (121 RCCAs) right from first fuel cycle. In this paper, we discuss briefly about the choice of number of Gd pins, their locations and the Gd content thereof. The results of calculations with assembly lattice cell code EXCEL using the latest 172 group WIMS/D-4 library based on ENDF/B- VI.8 data is presented. The core diffusion calculations are done by TRIVVER code in five energy groups and with 24 triangles per hexagon. An equilibrium core burnup model is incorporated in TRIVVER code for this purpose. The EXCEL-TRIVVER calculations demonstrate that it is possible to preserve or even improve the physics characteristics in comparison with the existing physics design characteristics of the VVER-1000 MWe core of KK Project