What is Uranium and How does it work? – part two

Published October 12th, 2000 - 02:00 GMT

By underground or open-cut methods, depending on its depth. After mining, the ore is crushed and ground up. Then it is treated with acid to dissolve the uranium, which is then recovered from solution. Uranium may also be mined by in situ leaching (ISL), where it is dissolved from the orebody in situ and pumped to the surface.  

 

The end product of the mining and milling stages, or ISL, is uranium oxide concentrate (U3O8). This is the form in which uranium is exported from Australia and other countries with no developed secondary processing.  

 

Before it can be used in a reactor for electricity generation, however, it must undergo a series of processes to produce a useable fuel.  

 

For most of the world's reactors, the next step in making a useable fuel is to convert the uranium oxide into a gas, uranium hexafluoride (UF6), which enables it to be enriched. Enrichment increases the proportion of the uranium-235 isotope from its natural level of 0.7 percent to 3 - 4 percent.  

 

This enables greater technical efficiency in reactor design and operation, particularly in larger reactors, and allows the use of ordinary water as a moderator.  

 

After enrichment, the UF6 gas is converted to uranium dioxide (UO2) which is formed into fuel pellets. These fuel pellets are placed inside thin metal tubes which are assembled in bundles to become the fuel elements for the core of the reactor.  

 

For reactors which use natural uranium as their fuel (and hence which require graphite or heavy water as a moderator) the U3O8 concentrate simply needs to be refined and converted directly to uranium dioxide.  

 

Spent reactor fuel is removed, stored, and then either reprocessed or disposed of underground (see Nuclear Fuel Cycle or Radioactive Waste Management in this series).  

 

Who uses nuclear energy?  

Over 16 percent of the world's electricity is generated from uranium in nuclear reactors. This amounts to about 2300 billion kWh, as much as from all sources worldwide in 1960.  

 

This comes from over 430 nuclear reactors with a total output capacity of more than 350 000 MWe operating in 32 countries. A further thirty reactors are under construction, and another 70 are on the drawing board.  

 

The combined capacity of all these reactors is over 430,000 MWe - nearly twelve times Australia's total electricity generating capacity.  

 

Belgium, Bulgaria, Finland, France, Germany, Hungary, Japan, South Korea, Lithuania, Slovakia, Slovenia, Spain, Sweden, Switzerland and Ukraine all get 30 percent or more of their electricity from nuclear reactors.  

 

The USA has over 100 reactors operating, with capacity of almost three times Australia's total, and supplying 20 percent of its electricity. The UK gets about a quarter of its electricity from uranium.  

 

Who has and who mines uranium?  

Uranium is widespread in many rocks, and even in seawater. However, like other metals, it is seldom sufficiently concentrated to be economically recoverable. Where it is, we speak of an ore-body. In defining what is ore, assumptions are made about the cost of mining and the market price of the metal. Uranium reserves are therefore calculated as tones recoverable up to a certain cost. 

 

Australia's reasonably assured resources of uranium are 894,000 tones U3O8 recoverable at up to US$80/kg U (A$ 90 000/tone U3O8, which is about three times the market 'spot' price). Australia's reserves are about 25 percent of the world's total.  

 

Although it has more than any other country, Australia is not the only one with major deposits. Others include Canada, USA, South Africa, Namibia, Brazil and Kazakhstan. China may also have substantial deposits of uranium. Many more countries have smaller deposits which could be mined.  

 

Despite being so well-endowed with uranium reserves, political factors mean that Canada is well in front of Australia as the main supplier of uranium to world markets.  

 

Uranium is sold only to countries which are signatories of the Nuclear Non-Proliferation Treaty, and which allow international inspection to verify that it is used only for peaceful purposes.  

 

Customer countries for Australia's uranium countries must also have a bilateral safeguards agreement with Australia. Exports in 1998-99 amounted to about 6000 tonnes of U3O8 valued at nearly $300 million. This was about 16 percent of world mine production of uranium.  

 

What are the other uses of nuclear energy?  

Many people, when talking about nuclear energy, have only nuclear reactors (or perhaps nuclear weapons) in mind. Few people realise the extent to which the use of radioisotopes has changed our lives over the last few decades.  

 

Using relatively small special purpose nuclear reactors it has become possible to make a wide range of radioactive materials (radioisotopes) at low cost. 

 

For this reason the use of artificially produced radioisotopes has become widespread since the early 1950s, and there are now some 270 "research" reactors in 59 countries producing them.  

 

Radioisotopes: 

In our daily life we need food, water and good health. Today, radioactive isotopes play an important part in the technologies that provide us with all three. They are produced by bombarding small amounts of particular elements with neutrons.  

 

In medicine, radioisotopes are widely used for diagnosis and research. Radioactive chemical tracers emit gamma radiation which provides diagnostic information about a person's anatomy and the functioning of specific organs. 

 

Radiotherapy also employs radioisotopes in the treatment of some illnesses, such as cancer. More powerful gamma sources are used to sterilise syringes, bandages and other medical equipment. About one in two Australians is likely to experience the benefits of nuclear medicine in their lifetime, and gamma sterilisation of equipment is almost universal.  

 

In the preservation of food, radioisotopes are used to inhibit the sprouting of root crops after harvesting, to kill parasites and pests, and to control the ripening of stored fruit and vegetables.  

 

Irradiated foodstuffs are accepted by world and national health authorities for human consumption in an increasing number of countries. They include potatoes, onions, dried and fresh fruits, grain and grain products, poultry and some fish. Some prepacked foods can also be irradiated.  

 

In the growing crops and breeding livestock, radioisotopes also play an important role. They are used to produce high yielding, disease and weather resistant varieties of crops, to study how fertilizers and insecticides work, and to improve the productivity and health of domestic animals.  

 

Industrially, and in mining, they are used to examine welds, to detect leaks, to study the rate of wear of metals, and for on-stream analysis of a wide range of minerals and fuels.  

 

There are many other uses. A radioisotope derived from the plutonium formed in nuclear reactors is used in most household smoke detectors.  

 

Radioisotopes are used by police to fight crime, in detecting and analyzing pollutants in the environment, to study the movement of surface water and to measure water runoffs from rain and snow, as well as the flow rates of streams and rivers.  

 

Other reactors: 

There are also other uses for reactors. Over 400 small nuclear reactors power some 250 ships, mostly submarines, but ranging from icebreakers to aircraft carriers. These can stay at sea for long periods without having to make re-fuelling stops. The world's first nuclear powered container ship was built in Russia.  

 

The heat produced by nuclear reactors can also be used directly rather than for generating electricity. In Sweden and Russia, for example, it is used to heat buildings and to provide heat for a variety of industrial processes such as water desalination.  

 

Military weapons: 

Both uranium and plutonium were used to make bombs before they became important for making electricity and radioisotopes. But the type of uranium and plutonium for bombs is different from that in a nuclear power plant. Bomb-grade uranium is highly-enriched (>90 percent U-235, instead of about 3.5 percent); bomb-grade plutonium is fairly pure (>90 percent) Pu-239 and is made in special reactors.  

 

Today a lot of military uranium is becoming available for electricity production. The military uranium is diluted about 25:1 with depleted uranium (mostly U-238) from the enrichment process before being used.  

Source: Uranium Information Centre 

 

 

© 2000 Mena Report (www.menareport.com)

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