Re: Re: Re: Re:
Scritto da: Arvedui 23/07/2007 1.16
Si magari ![[SM=x751605]](http://img294.imageshack.us/img294/3637/mfrlol9fr.gif)
Wikipedia non è una fonte attendibile, perchè tralascia di parlare dell'effettiva capacità di estrazione dell'uranio (i
giacimenti "facili" sono quasi tutti finiti) ma soprattutto perchè non parla del picco dell'uranio.
il metodo classico di estrazione dell'uranio prevede che la pechblenda venga triturata e mescolata con acido solforico e nitrico. L'uranio si scioglie e forma il solfato di uranile, mentre il radio e gli altri metalli del minerale vengono precipitati come solfati. Aggiungendo idrossido di sodio, si precipita il diuranato di sodio (Na2U2O7 · 6H2O), noto anche come ossido giallo di uranio (yellow cake). Per ottenere l'uranio dalla carnotite, il minerale viene finemente polverizzato e mescolato con soda e potassa calde, che sciolgono l'uranio, il radio e il vanadio. Dopo aver eliminato le sabbie inutili, il composto viene trattato con acido solforico e cloruro di bario. Una soluzione caustica e alcalina aggiunta al liquido precipita l'uranio e il radio in forma concentrata.
puoi cercare tu stesso... non è preso da wiki
e poi trovi qua un altro articolo interessante:
www.uic.com.au/uran.htm
www.uic.com.au/faq.htm
How much nuclear power is used around the world?
16 percent of world electricity is generated from nuclear power, using uranium as the fuel in about 440 nuclear power reactors.
How much is used in Australia?
None. We only have a small research reactor which produces medical isotopes.
Why is it used?
Because in many places it produces electricity cheaper than alternatives, and does so cleanly - without toxic or carbon dioxide emissions. The electricity produced is continuous, reliable and on a relatively large scale, thus meeting the main kind of demand.
Today the environmental virtues of nuclear power are increasingly attractive also - it produces virtually no emissions.
Why is it often not used?
In some places it would be more expensive than coal-fired or other plants - it largely depends on the cost of coal and/or gas where you want to generate the power.
Why do some people object to it?
The reasons are complex and based more in values and outlook than rational discourse, but in every country there are those who object to certain technologies. Particular arguments supporting these sentiments include safety, wastes and possible weapons proliferation.
What are the alternatives?
For large-scale, continuous reliable supply of electricity the only alternatives are normally coal and gas. Coal is plentiful and cheap but gives rise to about one kilogram of carbon dioxide per kilowatt-hour. Gas is a very valuable and versatile fuel and chemical feedstock, which is reflected in its high price.
Renewables such as wind power though clean, are not an alternative because they cannot provide continuous reliable supply, let alone at low cost.
is it economic?
Generally it is, and France has become the world's largest net exporter of power for this reason (80% of its electricity is nuclear). However, building nuclear plants in a country like Australia would result in slightly more expensive power because good-quality coal is so plentiful and cheap. But if carbon dioxide emissions were costed in, nuclear would be competitive.
Is it safe?
By any reckoning, it is the safest way of producing electricity, and in the western world it always has been. Some 12,500 reactor-years of operational experience for civil nuclear power is a substantial base for confidence in this. Nuclear power plants re designed so that the effects of any major problem or accident are contained within the structure.
What about the wastes?
Virtually all the wastes are contained and managed, not released to the environment like most fossil fuel wastes. Some of the wastes are hot and very radioactive, but these are small in quantity and easily managed. They have never posed a significant hazard to anyone and are unlikely to do so. Long-term disposal of such wastes will be in deep geological repositories.
Some hazardous chemicals such as arsenic remain toxic forever - radioactive waste diminishes naturally with time. The means to isolate it from humans and the environment while it decays are simple and well-proven over more than 50 years. In fact the level of radioactivity in spent fuel drops to one thousandth of its original level in 40-50 years.
The cost of waste management and disposal is incorporated in the cost of the electricity produced.
Where does most uranium come from?
About 60 percent of the annual demand comes from mines - one third of this from Canada and nearly one quarter from Australia. Uranium is mined in about 20 countries. A lot comes from Russian weapons stockpiles - recycled warheads, and in fact one tenth of all US electricity is from that source.
Of course uranium occurs naturally throughout the world's crust - it is 500 times more abundant than gold and as common as tin.
How much is needed for a power station?
A tonne of uranium fuel will keep a large power station* going for two weeks. This fuel would come from about 9 tonnes of mined uranium oxide concentrate. To get the same amount of power from coal you would need about 160,000 tonnes of it (or some 250,000 cubic metres of gas).
* 1000 MWe
But aren't world uranium resources too limited to sustain a big expansion of nuclear power?
No, while known and quantified resources are only about 50 times annual use, there is every indication that ongoing mineral exploration activities will steadily increase known resources, as they have in the past with all metal minerals.
Do uranium mines leave a damaged environment?
No, or not necessarily. Any mine is likely to have an impact on the immediate area of its operation, but environmental controls ensure that this does not extend to the surrounding environment. Also all reputable mining companies now rehabilitate the site on conclusion of mining. Uranium mines are no exception. Most major uranium mines in Australia and Canada have (or operate under) ISO 14001 certification which sets and requires a very high international standard environmentally.
What effect does nuclear power have on the environment?
Virtually none, since all wastes are contained and managed. The main environmental effect is positive - where nuclear power is used instead of fossil fuels it means that carbon dioxide emissions are avoided. Today well over two billion tonnes of such emission are avoided each year because of nuclear power - most important in relation to climate change concerns.
What about radiation?
Radiation is naturally part of our environment - we are all exposed to it all the time. Nuclear power does not cause any harmful increase in our exposure to it. Radiation is scientifically understood, easily detected and precisely measured - radioactive materials are used in hundreds of ways to improve the quality of life for everyone.
Do nuclear plants use a lot of water?
If they have to employ evaporative cooling towers, nuclear power plants use the same amount of water as any others with the same size and thermal efficiency. In practice, nuclear plants are often sited on the coast or othe large bodies of water so that they are cooled by pumping a large volume of water through them, and hence use up no fresh water. (Coal-fired plants are usually located on coalfields, otherwise a lot of coal has to be moved to them. Hence they normally employ evaporative cooling.)
But doesn't the full nuclear fuel cycle require a lot of energy input, and hence give rise to a lot of carbon dioxide emissions?
Certainly there is quite a lot of energy input needed at various stages, but overall it is less than two percent of the energy output from the nuclear plant involved. In some circumstances using obsolete technology it could conceivably reach 5% of output. Carbon dioxide emissions are correspondingly low - less than 5% of those from coal-fired power generation.
Does nuclear power give rise to nuclear weapons?
No. Hiroshima and Nagasaki, 60 years ago, are the only occasions on which atom bombs have been used in war and these preceded nuclear power for electricity. Civil nuclear power plants have never caused weapons proliferation.
In fact the safeguards regime under the Nuclear Non-Proliferation Treaty represents one of the great success stories of the UN, even if we now wish it had been even more ambitious. In the 1960s it was widely assumed at there would be 30-35 nuclear weapons states by the turn of the century. In fact there were eight - a tremendous testimony to the effectiveness of the NPT and its linked incentives both against weapons and for civil nuclear power.
SI AL NUCLEARE!!!!!!
![[SM=x751620]](https://digilander.libero.it/le.faccine/faccinea/bandiere/italy_2.gif)
![[SM=x751630]](https://digilander.libero.it/le.faccine/faccinea/bandiere/usa_2.gif)