More than 99% of the natural uranium in the world is in this form.
世界上99%以上的天然铀都是这种形态。
Crash Course 综合篇
By far the most common naturally occurring form of uranium is the isotope uranium-238. More than 99% of the natural uranium in the world is in this form.
到目前为止，最常见的天然铀形式是同位素铀 238。世界上99%以上的天然铀都是这种形态。
英语百科
Natural uranium
Natural uranium (NU, Unat) 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% comes from uranium-235, 48.6% uranium-238, and 49.2% uranium-234.