Neutronics Design Flexibilities of the BigT Gadolinium Absorbers

A new BA design named 'Burnable absorber-Integrated Guide Thimble' (BigT) was recently proposed for PWR. The BigT offers flexibility in BA self-shielding adjustment per design specifications. It is upon this assertion that this paper was prepared; i.e. this research aims to demonstrate the neutronics design flexibilities of BigT gadolinium absorbers. Specifically, three studies were completed to investigate sensitivities of the BigT gadolinium absorbers: (1) at a constant BA mass, (2) with a similar initial reactivity hold-down, and (3) for an optimal burnup reactivity swing. The paper clearly demonstrates neutronics flexibilities of the BigT gadolinium absorbers. Ascertained design variables are: (1) gadolinium effective shape, (2) BigT loading per lattice, and (3) BigT location in the lattice. Hybrid combination of the BigT designs may also alter the lattice depletion pattern, as well as density of gadolinium installed in the BigT absorbers. It is concluded that self-shielding of Gd can easily be adjusted in the BigT applications