U-235 – Only naturally occurring isotope of uranium which is capable of fission and is present in approximately 0.71% by weight in natural uranium.

U3O8 – Triuranium Octaoxide occurs naturally as the uranium-bearing mineral pitchblende and is the primary constituent of yellowcake. It is in the form of concentrate that it is often referred to as yellowcake with the weight of 1 lb. U in U3O8 = 1.17924 lbs.

UF6 – Uranium Hexaflouride is a compound of uranium produced during the conversion process. At temperatures above 56 degrees Celsius it takes the form of a gas and therefore is suitable for use in the enrichment process of U3O8 into a fuel for nuclear reactors.

Ultramafic Rock – Dark coloured igneous rock composed of less than 45% silica is mainly composed of olivine and pyroxene. It forms an important part of the earth’s oceanic crust.

Unconformity – Discontinuity in the succession of rocks which represents a gap in time and deposition, recognizable by a surface separating younger rocks from much older rocks.

Unconstrained Inversion – Calculation of a susceptibility model that is not guided by the input or reference to known geologic or geophysical information. The results are then based simply on a best fit model of the input data.

Under-Determined – Problem is said to be under-determined when there are more unknowns than data and there are not enough equations to obtain a unique solution.

Uranium – Heaviest naturally occurring element which in itself is metallic and slightly radioactive.