It is necessary to enrich the fuel by increasing the percentage concentration of uranium-235.

必须提高铀235浓度的百分比，使燃料浓集。

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There are different kinds, or isotopes, of uranium, and the type used in nuclear power plants is called uranium-235, because these atoms are easiest to split in two.

铀有许多不同的种类，或称同位素，而在核电站中所使用的是铀235这一类，因为这些的原子最容易一分为二。

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It is made up of old fuel rods that have become sufficiently depleted of uranium-235, the isotope that drives a reactor’s main chain reaction, to be no longer useful.

乏燃料由完全耗尽铀-235的旧燃料棒组成，核反应堆的链式反应就是由铀-235激发的。

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Gas centrifuges are used to increase the proportion of fissile uranium-235 atoms within uranium.

BBC: Iran installing new Natanz centrifuges, says IAEA

In one significant respect U-233 is better than uranium-235 and plutonium-239, because of its higher neutron yield per neutron absorbed.

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Each fission reaction splits the nucleus of an atom of uranium-235 or plutonium-239 into two smaller atoms and releases a great deal of energy.

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