uranium 238

noun

Chemistry.

1. the radioactive uranium isotope having a mass number 238, comprising 99.28 percent of natural uranium: used chiefly in nuclear reactors as a source of the fissionable isotope plutonium 239.

Word History and Origins

Origin of uranium 238¹

First recorded in 1940–45

Example Sentences

While uranium 235 fissions easily, nuclear fuel is not pure—it is made mostly of uranium 238, which does not fission.

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Depleted uranium, primarily uranium 238, is what’s left over after the lighter isotope uranium-235 has been removed from natural uranium.

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Seaborg’s approach had only produced plutonium 239, which decays very slowly back to uranium 238.

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Ordinary low-enriched uranium fuel contains primarily uranium 238, the most common natural isotope of the element, along with about 5 percent uranium 235, a rarer isotope that splits, or fissions, more readily.

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The uranium 238 then captures the neutron and is transformed into a new element, plutonium 239, which is also fuel.

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