Through the enrichment process, the concentration of which isotope is increased in natural uranium?

Enrichment raises the proportion of uranium-235, the isotope that sustains fission.

Uranium-234 is present only in traces and is not the target of enrichment.

Uranium-238 is the abundant isotope whose share is deliberately reduced by enrichment.

Uranium-239 is not a natural uranium isotope of interest here.

Natural uranium holds only about 0.7 percent uranium-235.

Reactor fuel is typically enriched to three to five percent uranium-235.