Click on the alphabetic index to display terms beginning with the corresponding letter or search for a term below.


Ground rock remaining after particular ore minerals (e.g. uranium oxides) are extracted.


Depleted uranium (cf. enriched uranium), with about 0.2 to 0.3% U-235.

Thermal reactor

A reactor in which the fission chain reaction is sustained primarily by slow neutrons, and hence requiring a moderator.


Changing atoms of one element into those of another by neutron bombardment, causing neutron capture and/or fission. In an ordinary reactor neutron capture is the main event, in a fast reactor fission is more common and therefore it is best for dealing with actinides. Fission product transmutation is by neutron capture.

Transuranic element

A very heavy element formed artificially by neutron capture and possibly subsequent beta decay(s). Has a higher atomic number than uranium (92). All are radioactive. Neptunium, plutonium, americium and curium are the best-known.

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