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WHAT IS URANIUM?

Nuclear Monitor Issue: 
#362-363
Special: Uranium Special Edition
06/12/1991
Article

(December 6, 1991) Uranium is a dark grey, radioactive, metallic element, discovered by the German chemist H.M. Klaproth in 1789.

(362-3.uranium) WISE Amsterdam - Uranium has two main uses: as an explosive component of nuclear bombs, and as fuel for nuclear reactors. Uranium is both radio-logically and chemically toxic. It poses a health hazard as a heavy metal as well as a radioisotope.

Naturally occurring uranium is a mixture of three isotopes: uranium-234 (0.01%), uranium-235 (0.71%), and uranium-238 (99.28%). Uranium is the heaviest non-human-made element. Uranium ore normally contains a few hundredths of a percent uranium, though extremely high-grade ore in Saskatchewan, Canada contains up to 60% uranium.

Uranium metal, also called depleted uranium (DU) cannot by itself cause an atomic explosion. DU is used to make armour piercing, incendiary ammunition, and to strengthen armor in military vehicles. Du is used for these purposes because it: has a high density (it is the heaviest non-humanmade substance on Earth); is relatively soft compared to other metals; and it is pyrophoric (starts on fire spontaneously) when finely divided. Ammunition is specially made to take advantage of one or more of these three attributes. DU is also attractive because it is cheaper and more accessible than alternative substances, such as tungsten. Because of its high density, bullets made out of DU are more efficient than any other material at passing through steel. DU is not only the best armor penetrator, but is required to penetrate modern armor plating.

URANIUM MINING AND THE NUCLEAR FUEL CHAIN

 

Uranium mining is referred to in industry jargon as the "front end" of the nuclear industry. This is because uranium mining is commonly regarded as the first link in the nuclear fuel chain, even though it is preceded by exploration. The nuclear fuel chain is the sequence of interdependent opera-tions involved in producing nuclear weapons, uranium ammunition, fuel for nuclear electricity generation, and radioactive isotopes for medical and industrial purposes. Civil and military aspects of the fuel chain are so inter-dependent that it is impossible to completely separate them. However, some medical and industrial radio-active isotopes can be produced by particle accelerators, which are not based on uranium fuel and not connected to nuclear power generation and nuclear weapons production.

Whether regarded primarily civil or military, the nuclear fuel chain requires conversion of uranium from one chemical form to another and transportation involving great distances. The nuclear fuel chain is more technically complex, capital intensive, time consuming, and dangerous than the production process for other forms of energy. These attributes of the nuclear fuel chain are the reason why there is no nation that operates its nuclear industry entirely within its own borders. The few nations possessing the resources (natural, financial, and human) to do so have chosen not to for many reasons, not the least being to minimize local risks such as contamination from uranium mining and weapons testing.

The most common sequence in the fuel chain for commercial electricity producing reactors begins with uranium exploration, proceeds to uranium mining and milling, conver-sion, enrichment, fuel fabrication, fission in a light-water reactor (LWR), reactor waste storage, and finally reactor decommissioning. A variation of this sequence is when natural uranium is used as fuel in heavy-water reactors, such as the Canadian made CANDU.

The primary purpose of the uranium processing stages of exploration, mining, milling, conversion, enrich-ment, and reprocessing is to extract the U235 for use in nuclear weapons and reactors. U235 is the most essential radioisotope for nuclear fission, since it is the only one of the three primary fissionable materials that occurs naturally.

 

1989 URANIUM PRODUCTION BY COMPANY
(% of total western world production and export sales from the USSR and China)
Cameco 15%
Cogema 14%
Rio-Tinto-Zinc 11%
Nuclear Fuel Corp. of South Africa 8%
Energy Resources of Australia 8%
Denison 5%
Uranerz 5%
Others 34% USA 14%
USSR, China 3%
USSR, China Olympic Dam
South America, Europe, Far East 15%

Source: "The Source," October 1990, Cameco Corp., 2121-11th St. West, Saskatoon, Saskatchewan, Canada s7M 1J3. Tel. 1-306-956-6310. Fax: 1-306-956-6318.

Greatest producer by country in 1988 was (only those over 100 tonnes included): Canada, U.S.A., South Africa, Namibia, Australia, France, Niger, Gabon, Spain, India, Portugal.

It takes roughly three years to produce the initial fuel for an LWR. With some overlap, the five major steps -- mining, conversion to UF6, enrichment, fuel fabrication, and fuel inspection and loading -- each take about a year. The long lead times and overlap of processing steps associated with fuel supply, coupled with inven-tory supplies of often three or more years, means that disruption at one step must be over five years in order to effect reactor operation.

In the exclusively military sequence, some of the uranium is enriched to a higher percentage, and spent reactor fuel is reprocessed to extract the uranium and plutonium for use in nuclear bombs. The production of nuclear weapons usually involves the same uranium mines, conversion plants, enrichment plants, reprocessing plants, and often fuel fabrication plants and nuclear reactors that are part of the fuel chain for production of commercial nuclear electricity.

EXPLORATION AND BULK SAMPLING

Exploration is often confused with bulk sampling and even full-scale mining. This short description tries to clarify the differences.

Exploration for uranium, or any mineral, may be of a form that does or does not disturb the ground. The usual exploration sequence is: aerial gamma ray surveys, ground geo-chemical analysis by means of soil and water samples, test drilling, and drilling in a grid pattern. Aerial gamma ray surveys are not ground disturbing. Regular aircraft flights may however disturb people and wildlife. If results of aerial surveys are favorable, the process continues to soil and water samples, drilling individual holes, and drilling in a grid pattern. In some cases vegetation and bee samples may be taken. Bees and their pollen are analyzed for heavy metal content because of the effective way bees "sample" an area.

When drilling intersects an ore body and underground aquifer there is risk of groundwater contamination. Pre-viously isolated ore bodies can come in contact with water allowing the spread of radium and other isotopes. In addition, finely ground material inside the drill hole dissolves and is quickly carried away along with drilling fluids and chemicals. Further, dumping of drilling fluids can contaminate surface and groundwater. It is for these reasons that uranium exploration has been strictly regulated or made illegal in some areas (for example British Columbia, Canada and Colorado, U.S.A.). Also of concern is that the arrival of people and machines into a wilderness area will drive off most large wild animals.

Uranium exploration ends once enough geological and engineering data is gathered to determine if mining of a deposit is technically and economically feasible. Modern mathematical models and standardized engineering techniques make it possible to provide the necessary technical and economic data only days after the exact dimensions of a deposit are known. The exact dimensions are determined once a deposit is drilled in a grid pattern. From that point on, any further ground disturbing activity at the site cannot be considered exploration as it is already known whether or not mining is technically and economically feasible.

The first step in mine development after exploration is taking bulk ore samples for use in fine-tuning the milling process. Small quantities of ore are milled, often in a small scale mill, to determine the types and propor-tions of chemicals to be used in full scale operation.

MINING

The most common types of uranium mines are open pit and underground. Another form of mining is solution or leach mining, which is a technique of injecting highly acidic solutions into an ore body and then extracting the uranium from the solution. Uranium is also separated from sea water. Uranium is often mined in conjunction with other minerals such as gold and phosphate.

Uranium mining cannot take place without catastrophically effecting the immediate surrounding environment. Wastes produced from uranium mining include: overburden material, ore grading too low to be milled, pit and mine shaft water, runoff from precipitation, and dust. Uranium mills are usually located close to uranium mines to minimize ore transport costs. Thus, uranium mill wastes are usually near uranium mines.

Uranium miners can die of cancer and contract serious lung diseases as a direct result of working in uranium mines. Further, in many places in the world uranium mining, like mining of many other minerals, takes place on land that was traditionally used by Indigenous people. This has often been the cause of serious conflict.

MILLING

Uranium milling is the removal of uranium from ore, accomplished by crushing the rock, grinding it down to a fine sand, and mixing it with large amounts of water and chemicals. The chemicals are either acids or bases, depending on the pH of the ore. Both of the processes are able to remove about 90% of the uranium and only a few percentages of the other radionuclei.

The final product from a uranium mill is a fine, yellow-gold powder called U3O8, though it is commonly referred to as yellowcake. It consists of between 70-90% uranium, the rest being uranium decay products and heavy metals. Yellowcake is trans-ported to a uranium conversion plant where it is converted to uranium hexafluoride (UF6) or an intermediate product depending on its intended use.

The solid, fine sand that is left over after the milling process is called uranium mill tailings. Large volumes of tailings are produced in the uranium milling process over a short period of time. Hundreds of tonnes of waste are normally produced for every tonne of yellowcake. Uranium tailings contain about 85% of the total radioactivity in the ore, including about 99% of the radium. In addition, the tailings contain almost 100% of the heavy metals in the ore.

There is usually at least twice as much liquid waste produced in the milling process as tailings. Accidental release of the liquid and solid wastes from their retention barriers is common. Liquid wastes have a greater impact on the surrounding environment than solid wastes as they can carry contamination great distances via streams, rivers and lakes. The radio-nuclei and heavy metals in the wastes can accumulate in plants and animals downstream to levels thousands of times the surrounding water concen-tration. This contamination can eventually find its way to people.

Source: Goldstick, Miles. April 1991. "The Hex Connection, Some Problems And Hazards Associated With The Transportaion Of Uranium Hexafluoride." 196 pp., see pp. 29-36.
Swedish University of Agricultural Sciences, Department of Ecology and Environmental Research, Box 7072, S-750 07 Uppsala, Sweden.
Available from WISE-Stockholm.