To make fuel for electricity-generating reactors, uranium is enriched to less than 5 percent of the isotope U-235.

为将燃料做成电能反应堆，铀被浓缩至U-235同位素含量5%以下。

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The prime example is the element uranium (U), which occurs naturally as two isotopes-the lighter, fissionable U-235 and the heavier, non-fissionable U-238.

铀（U）元素就是一个很好的例子。 天然铀有两种同位素； 较轻的负235可以裂变，较重的铀238则不会裂变。

youdao

Only three fissile materials are known at present, there being U-233, U-235, and plutonium.

目前已知有三种裂变材料，它们是铀233，铀235，以及钚。

youdao

Natural uranium is only 0.7% U-235, which is what you need for your reactor.

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Reactors need u-235 in concentrations of 3% to 5%, requiring the enrichment step to make it useful.

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If yellowcake is expensive, GE can fire its lasers more often and grab as much u-235 as possible.

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