Theoretical density calculation for ceramic BNA pellet materials in ACR-1000 central element

The central element of the ACR-1000 bundle is loaded with burnable neutron absorber (BNA) pellets that are ZrO2-based and contain Gd and Dy. To ensure that the desired fluorite-type cubic structure is maintained, Y2O3 is added to the matrix. To calculate the theoretical density of the new material, the lattice parameter of three compositions of BNA pellets was accurately determined by X-ray diffraction. Correspondingly, the volume of the unit cells (V) was determined. Knowing that Zr, Y, Gd and Dy occupy the lattice sites and oxygen ions are at the interstitial sites in the cells, the mass inside the cells (M) was calculated, and the theoretical densities of the materials (ρ = M/V) were determined. (author)