Question

Radioactive tailings are created in which step of the nuclear fuel production?

Answer 1

Residual material left over from ore grinding (milling) prior to extraction.
https://energy.gov/ne/nuclear-fuel-cycle

Explanation:

Uranium mill tailings are primarily the sandy process waste material from a conventional uranium mill.
https://www.nrc.gov/materials/fuel-cycle-fac/stages-fuel-cycle.html

The tailings or wastes produced by the extraction or concentration of uranium or thorium from any ore processed primarily for its source material content is byproduct material.
https://www.nrc.gov/waste/mill-tailings.html