Question

Calculate the atomic density of uranium-235 in atoms/cm3 in (a) natural uranium (0.72% atomic fraction of U-235) and (b) UO2 made of 3% enriched uranium (3% weight fraction of U-235). Density of enriched UO2 is 11.0 g/cm3

Answer 1

[Additional information needed to calculate the atomic density in question (a). I have collected this information from the internet:

Density of natural uranium = 19.1 g/cm³

Atomic mass of natural uranium: 238.02891 g/mol]

a. no of moles of natural U per cm³ = (19.1/238.02891) mol/ cm³ = 0.08 mol/ cm³

no of atoms of natural U per cm³ = 0.08 mol * 6.023*10²³ atoms.mol^-1 / cm³ = 4.83*10²² atoms/ cm³

So, atomic density of uranium-235 = 0.72 % of 4.83*10²² atoms/ cm³

= 3.48*10²⁰ atoms/ cm³

b. Density of enriched UO2 is 11.0 g/cm3

Mass of uranium-235 per cm³

= 3% of 11.0 g/cm3

= 0.33 g/cm3

no of moles of U235 per cm³ = (0.33 g/cm3) / (235g/mol) = 0.0014 mol/ cm3

atomic density of uranium-235 = 0.0014 mol * 6.023*10²³ atoms.mol^-1 / cm³ = 8.45*10²⁰ atoms/ cm³