Question

The concentration of the lighter isotope of uranium, uranium-235, is very low in nature relative to the abundance of the heavier uranium-238. In most modern reactors, the abundance of uranium-235 in the fuel needs to be enriched by a factor of __________.

Option 1: 2
Option 2: 5
Option 3: 10
Option 4: 20

Answer 1

In most modern reactors, the abundance of uranium-235 must be enriched to a concentration of 3 to 5% to be viable for use as a fuel. This enrichment process can be quite complex due to the chemical similarity and small mass difference between uranium-235 and uranium-238.

Step-by-step explanation:

The concentration of the lighter isotope of uranium, uranium-235, is very low in nature, comprising less than 1% of natural uranium which is mostly uranium-238. To be used in most modern reactors, the abundance of uranium-235 in the fuel needs to be enriched by a factor of 3 to 5% to become viable for sustaining a nuclear fission reaction. Enriching uranium to the required levels is a challenging and sophisticated process as the isotopes are chemically identical and differ very slightly in mass, which makes mechanical separation difficult. Centrifugation and gaseous diffusion are common methods for enrichment, where uranium hexafluoride gas is used due to the difference in the molecular velocities of isotopes based on their masses.