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. 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.
When you talk of “retrievable” uranium, it means that it is possible to extract the mineral from a reservoir and make it available for a fuel element, at a specific price that is expressed in dollars. Analysing the world map of reservoirs and knowing their nature it is possible to assess the exploitable quantity of uranium by forming cost ranges: up to 40 $, between 40 $ and 80 $ and between 80 $ and 130 $.
The cycle of nuclear fuel
Nuclear fuel is subject to a cycle throughout its life. Obvious preliminaries are all the mining operations, which are followed by a long and complex series of various purification processes, with the primary aim of eliminating the elements that absorb neutrons.
A look at the future
The current fuel cycle exploits, with current reactors, just a small part of the energy that can be extracted from uranium found in mines and leaves a legacy of waste that has to be confined for long periods of time.
Radioactivity is the phenomenon in which some unstable nuclei transform into others with the emission of particles. Radioactivity is as old as the Universe and is present everywhere: in the stars, in the Earth and in our own bodies. In fact, man has been exposed to radiation since when he appeared on Earth. Radioactivity was discovered at the end of the 19th Century thanks to the work of Henry Becquerel and Pierre and Marie Curie who in 1903 received the Nobel Prize in Physics for their important contribution to scientific knowledge. They discovered that certain minerals possessed the property of spontaneously emitting radiation: these minerals, such as uranium, radium and polonium, for example, were called “active” and the phenomenon regarding the emission of radiation was called “radioactivity”.
Atoms and matter
All matter that surrounds us is made up of atoms. Every atom consists of protons and neutrons, which together form the nucleus, surrounded by a cloud of negatively-charged electrons. Within the atom, the nucleus is made up of positively charged protons and by neutrons that lack electric charge and are therefore neutral.
How is radioactivity measured?
Radioactivity is measured in disintegrations per second and its unit of measure is the Becquerel (Bq), in honour of the physicist Henry Becquerel who discovered the spontaneous emission of radiation from uranium in 1896. As mentioned above, the radiation produced by the disintegration of radioisotopes interacts with matter, transferring energy.
Exposure to radiation
Since his appearance on Earth, man has been exposed to natural radiation to which he has adapted perfectly. The dose of natural radiation to which each living organism is exposed every year is about 2.4 mSv.
Once the harmful health effects of exposure to ionising radiation were ascertained, it became essential to formulate adequate protection measures.