And this again is the fissile isotope.

这也是易裂变同位素。

youdao

Their work there was aimed at separating the light, fissile isotope of uranium (useful for making bombs and reactors), from its more abundant, but less useful, heavy cousin.

ECONOMIST: Diamonds

What they failed to appreciate, and what the company failed to tell them, was that a fast-breeder uses fuel that has a 19% concentration of the fissile isotope of uranium, 235U. Ordinary nuclear reactors use fuel containing around 3% of the fissile isotope.

ECONOMIST: All over in a flash