Friday, May 7, 2010

Mining Nuclear Fuel.


The fuel for nearly all current nuclear reactors ultimately derives from the world's uranium resource. Reactors using fuel sourced from thorium are also possible, and the present generation of LWRs can use uranium bred from thorium as fuel, but this technique is not in widespread use. The greater story of obtaining nuclear fuel is thus the story of uranium mining.

Current world uranium production:

In 2009, 50,572 tonnes of uranium was mined worldwide. Kazakhstan led production with 13,820 tonnes (27%), Canada produced 10,173 tonnes (20%) and Australia 7,982 tonnes (16%), although Australia has the largest commercially extractable reserves as currently defined.

Mining techniques:

There are three main techniques in use for uranium mining. These are open pit mining, underground mining, and in situ leach mining. In open pit mining, the overburden of material is blasted and excavated away to reveal the ore body, which is then blasted, excavated and removed with loaders and dumptrucks. Underground mining is carried out in the same manner as for other underground mines, with access tunnels, and drilling and blasting. In situ leach mining involves drilling boreholes down into an ore body, pumping a leaching fluid into the ore and then pumping the resulting solution to the surface to extract the uranium. The leaching fluid is sometimes a combination of hydrogen peroxide and sulphuric acid (Australia), sometimes high concentration sulphuric acid alone (Kazakhstan), or sometimes an alkaline solution (United States), depending on the nature of the ore body. The World Nuclear Association states that 7% of the world's uranium mined in 2009 was extracted as a by-product to other mining activity. That figure includes the uranium produced at Olympic Dam.

Health concerns:

The anti-nuclear movement often claims that uranium mining is a highly dangerous and environmentally hazardous practice. The examples used to support these claims generally come from the mid-20th century, such as the often quoted case of the Navajo uranium miners in the United States during the 1950s. Significant numbers of Navajo miners went on to develop small cell carcinoma in later life. This was determined to result from exposure to radon-222, a natural radioactive decay product deriving from uranium which was concentrated in poorly ventilated mine tunnels. Radon is often present in all kinds of underground mines because uranium is a common, widely distributed element in earth's crust. Underground coal mines often have elevated uranium concentrations and thus high radon levels. Proper ventilation and toxic gas removal systems are essential safety measures for all underground mining operations, not just uranium mines.

Workers in open pit mines are usually inside the sealed cabins of vehicles, and water is sprayed in the mine to settle dust particles. In situ leach mining protects workers from the risk of radon by never exposing them to it.

Uranium contamination of ground water is a possibility and needs to be managed. The health risk of ingesting uranium comes from the chemical toxicity (roughly similar to that of lead), and first manifests in mammals as kidney damage. Uranium is too weakly radioactive to present a radiotoxicity problem. Most experts consider the health impacts of uranium mining to be of the same order as mining for other heavy metals, such as gold, or lead.

It should be understood that the regulations governing the mining, refining, enrichment and milling of uranium are now so extensive and encompassing that uranium is very likely the most heavily regulated mineral in the world.

Resources and reserves:

According to the World Nuclear Association, as of 2007 the global known recoverable reserves of uranium were 5,469,000 tonnes. The largest national share of that reserve was Australia (1,243,000 tonnes, 23%), followed by Kazakhstan (817,000 t, 15%), Russia (546,000 t, 10%), South Africa (435,000 t, 8%), Canada (423,000 t, 8%), USA (342,000 t, 6%), Brazil (278,000 t, 5%), Namibia (275,000 t, 5%), Niger (274,000 t, 5%), Ukraine (200,000 t, 4%) and Jordan (112,000 t, 2%).

These reserves are presently extractable at a cost of US$130/kg or less. Uranium was extracted from phosphate deposits in the United States and Belgium prior to 1998, and could be again if the price of uranium rises enough. The uranium resource associated with the phosphate reserves is estimated to be 27 million tonnes. There are many similar low grade uranium deposits which could be tapped if the price of uranium rises much above the current level. The price of uranium is not a major factor in the price of nuclear power, and could increase many times over the current level before significantly impacting the cost of nuclear power for the end user.

Environmental footprint and comparisons with other energy sources:

What kind of environmental footprint does mining for nuclear fuel and related minerals have, and how does it compare with other electrical generation technologies? This powerpoint presentation by Dr. Per Peterson, professor and chair of nuclear engineering at Berkeley, presents figures on concrete and steel requirements for nuclear, wind, coal and combined cycle natural gas (see slide 11). Working through the numbers and adding fuel to the total, we arrive at the following figures for the mining needed to produce 1 megawatt.year of electrical energy (1MWe.y) for each technology:


676 tonnes (0.74t steel + 8.44t concrete + 666.7t U ore at 300ppm)


680 tonnes (123t steel + 557t concrete)


~5,500 tonnes (4.19t steel + 16.4t concrete + 5,500t coal)

Combined Cycle Natural Gas:

963 tonnes (0.147t steel + 2.88t concrete + 960t gas)

These numbers need some qualification for their proper significance to be appreciated. The final figures for the fossil fuel power sources only use the mass of fuel finally consumed. If the same method had been used for nuclear power, the mass of natural uranium mined as fuel would have been 0.2 tonnes, yielding a final figure for nuclear power of 9.38 tonnes, far below any of the others. Critics could justifiably point out that uranium ore is usually far more dilute than the coal or gas resources, and insisted that the mass of raw ore needed should be considered. The grade for the ore body at the Rossing mine in Namibia of 300ppm, one of the poorest ore bodies currently mined, was used to obtain the 676 tonne figure.

The figure for wind power is almost identical, but wind has severe and most likely unresolvable issues with variability and intermittency which render it all but useless for inclusion in the power grid of an industrial society.

The figure for coal power is dominated by mining for the fuel to the extent that mining for plant building materials falls into the noise. From the mining perspective, coal is the worst offender by far.

Natural gas requires much less fuel mass than coal, but suffers other problems associated with its extraction. Wide publicity has recently been given to the newly discovered shale gas reserves in the United States, which are said to represent a significant extension of global reserves. Experience is now showing that these reserves cannot be accessed without extensive damage to large areas of underground rock layers, with associated earth tremors and serious gas leaks resulting in significant environmental difficulties in the regions being exploited.

Finally, the figure for nuclear power assumes the use of light water reactor technology. This is the current standard in power reactor technology, and is likely to remain so for the next few decades, but following that it is likely that most new nuclear capacity will be breeder reactors. The figure for fuel mining for nuclear power above is based on the assumption that 200 tonnes of natural uranium is to be mined for 1 tonne of fissile fuel, but a well-designed fast breeder reactor can eventually consume all the natural uranium, so the mining requirement shrinks to 0.5% of that figure. This would bring down the fuel mining figure for nuclear power from 666.7 tonnes to 3.35 tonnes. The amount of structural steel and concrete required for a breeder reactor compared to a light water reactor may change somewhat, but even if it is ten times that of an LWR (which it won't be, and it may well be less), the total mining requirement remains far less than that of the competitors.