GC: n

CT: Natural uranium contains 0.7% of the U-235 isotope. The remaining 99.3% is mostly the U-238 isotope which does not contribute directly to the fission process (though it does so indirectly by the formation of fissile isotopes of plutonium). Isotope separation is a physical process to concentrate (‘enrich’) one isotope relative to others. Most reactors are light water reactors (of two types – PWR and BWR) and require uranium to be enriched from 0.7% to 3-5% U-235 in their fuel. This is normal low-enriched uranium (LEU). There is some interest in taking enrichment levels to about 7%, and even close to 20% for certain special power reactor fuels, as high-assay LEU (HALEU).

S: WNA – https://goo.gl/WoUJtF (last access: 19 December 2016)

N: 1. – uranium (n): Rare metallic element, 1797, named 1789 in Modern Latin by its discoverer, German chemist and mineralogist Martin Heinrich Klaproth (1743-1817), for the recently found planet Uranus
– natural (adj): C. 1300, naturel, of one’s inborn character; hereditary, by birth; early 14c. as of the world of nature (especially as opposed to man), from Old French naturel of nature, conforming to nature; by birth and directly from Latin naturalis by birth, according to nature from natura “nature”.
2. Natural uranium is a metal found in nature. It contains about 0.711 percent of uranium-235, 99.283 percent of uranium-238, and a trace (0.006 percent) of uranium-234.
3. Natural uranium it is fissile; it can sustain a fission chain reaction. It is the only fissile isotope that is a primordial nuclide or found in significant quantity in nature. Being fissionable means that it starts a nuclear reaction and keeps it going. Normally, the amount of the natural uranium isotope is enriched from 0.7% of the uranium mass to about 5%.
4. The difference between lightly enriched uranium / slightly enriched uranium (LEU/SEU) and highly enriched uranium (HEU) is the percentage of fissile isotopes present.

• Highly enriched uranium has a high percentage (usually referring to 20% or above) of U-235 and/or U-233 isotopes
• Slightly/Lightly enriched uranium has a lower percentage (usually in the range of 0.7 to 20%) of U-235 and/or U-233 isotopes
• Natural uranium (unenriched) is mostly U-238 (non-fissile) with a small percentage (0.71%) of the fissile isotope U-235, there is almost no U-233 in natural uranium (NU).

S: 1. OED – https://goo.gl/ULGQ0m (last access: 19 December 2016). 2. NRC – https://goo.gl/91rwAu (last access: 21 December 2016). 3. NRC – https://goo.gl/91rwAu; Rev – https://goo.gl/xwAAJ6 (last access: 21 December 2016). 4. Red – https://goo.gl/XtOaLq (last access: 21 December 2016).

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CR: depleted uranium, enriched uranium, nuclear energy, polonium , uranium .