Energy

The element and its properties

Uranium was discovered in 1789 by M. H. Klaproth while analysing the mineral petchblenda (believed to be an oxide mix of iron, zinc and tungsten) to which he gave the name Uranium to celebrate the discovery of the new planet in the solar system, discovered in those years. In 1789 Zirconium was discovered as well, an element of fundamental importance for nuclear reactor technology.
Uranium, in standard conditions, is a hard radioactive metal, silver-white in colour, malleable and ductile. It is quite common in nature but it is difficult to find it in high concentrations and on average it is present in the terrestrial crust in a proportion of about 3 grams of uranium per ton of crust (also called part per million, ppm): since the terrestrial crust is estimated to be 3X10¹⁹ tons, about 10¹³ tons of uranium are available (10000 billion tons), a greater quantity than silver, gold or molybdenum.
Uranium is constituted by various isotopes (atoms of the same chemical element, with the same atomic number but different mass number) present in different percentages in the terrestrial crust:

• 238U 99.2745%
• 235U 0.72%
• 234U 0.0055%

In nature about 200 minerals exist containing uranium, rarely found in isolation and more commonly present in various types of rocks, among which in particular granites (acid rocks) and siliceous rocks; smaller concentrations are present in basaltic and sedimentary rocks.
Uses of uranium
Uranium, before nuclear energy was discovered, was used primarily to stain glass. Today uranium is used primarily as a fuel in nuclear plants where the fissile material is constituted by isotope 235U.
An endless reservoir?
After having individuated an uranium presence in the terrestrial crust, it is necessary to evaluate a reservoir, that is individuate how many tons of uranium it contains. The reservoir has to be considered exploitable, otherwise we could say that the crust is an “enormous reservoir” since it contains 3 grams/ton of uranium, but we do not have a technology that allows its low cost extraction. 
An uranium reservoir is defined as exploitable once an economic limit has been defined, that is a threshold that allows a classification: reservoir evaluation is a problem of international norm.