Natural uranium (NU, U_nat) refers to uranium with the same isotopic ratio as found in nature. It contains 0.711% uranium-235, 99.284% uranium-238, and a trace of uranium-234 by weight (0.0055%). In terms of the amount of radioactivity, approximately 2.2 omes from uranium-235, 48.6% uranium-238, and 49.2% uranium-234.