Cameco Corporation --- Uranium - Fuel - Electricity - Mining - Milling

Uranium is extracted from the ground, processed in a mill and becomes uranium concentrates in the form of triuranium octoxide (U₃O₈) also known as yellowcake.
The U₃O₈ is then chemically refined and converted to uranium hexafluoride (UF₆).
The UF₆ is then enriched to increase the percentage of the isotope of uranium (U-235).
The enriched UF₆ is converted into UO₂ and pressed into fuel pellets, which are inserted into thin metal tubes for assembly into fuel bundles.
The enriched uranium in fuel bundles is then ready for use in a nuclear reactor.

Enrichment

Most commercial reactors require uranium fuel to have a U-235 content of 3 - 5%.
Naturally occurring uranium is mostly made up of two different types of uranium atoms or isotopes, approximately 99.3% U-238 and 0.7% U-235.
Uranium enrichment is required to increase the U-235 concentration from 0.7% to 3 - 5%.
The enrichment process involves separation of the lighter U-235 atoms from the heavier and more predominant U-238 atoms in order to concentrate the U-235 portion.
There are two commercial enrichment methods: gaseous diffusion and centrifuge.

Gaseous Diffusion

In the gaseous diffusion process, U-235 and U-238 atoms are separated by feeding UF₆ in gaseous form through a series of porous walls or membranes that allow more U-235 to pass through.
To understand how this method of enrichment works, think of UF₆ as equal sized sand particles of two different weights suspended in air. All the sand grains are blown through thousands of sieves, one after another. Because the lighter U-235 particles travel faster than the heavier U-238 particles, more of them penetrate each sieve. As more sieves are passed, the concentration of U-235 increases.
The process continues until the concentration of U-235 is increased to 3 - 5%.
The slower U-238 particles left behind are collected as byproduct and referred to as "depleted tails" or "tails," in other words uranium with a reduced concentration of U-235.
The high amount of energy required to force the UF₆ through the porous membranes makes the gaseous diffusion process very expensive.

Centrifuge

In this type of enrichment process, the gaseous UF₆ is introduced into a centrifuge (a cylindrical container that spins the UF₆ at high speeds).
The rapid spinning flings the heavier U-238 atoms contained in the UF₆ to the outside of the centrifuge, leaving UF₆ in the centre enriched with a higher proportion of U-235 atoms.
The enrichment level achieved by a single centrifuge is insufficient to obtain the desired concentration of U-235. It is therefore necessary to connect a number of centrifuges together in an arrangement known as a cascade.
The U-235 concentration is gradually increased to 3 - 5% as it passes through the successive stages of the centrifuge cascades.
Enrichment using centrifuge technology requires very little energy, giving this method a significant cost advantage. Centrifuge technology requires only about 2% of the energy needed for gaseous diffusion technology.

Separative Work Units

Enrichment service is sold in separative work units (SWU).
A SWU is a unit that expresses the energy required to separate U-235 and U-238.

Enrichment Process

How uranium is enriched depends on:
- the amount of uranium feed (UF₆) at the beginning of the process
- the amount of SWU used
- and the concentration of U-235 atoms left over (tails assay) at the end of the process.
A reactor operator knows the amount and concentration of uranium fuel required by each reactor. By varying the level of tails assay, a reactor operator can find the most economical combination of UF₆ feed and SWU required for enrichment. To illustrate, consider the following example:
- Let's assume you are in the freshly squeezed orange juice business. By deciding first how much juice you are prepared to leave behind in the pulp, you can then decide the optimum balance between the number of oranges you require and the effort required to squeeze them.
- If oranges are cheap and the cost of squeezing is high you are less concerned with how many oranges you use, but you want to make your orange juice with the least amount of squeezing. If oranges are relatively expensive and the squeezing process is cheap, you will minimize costs by squeezing fewer oranges more times to get the same amount of juice.
- Now think of the oranges as uranium and the effort to squeeze them as SWU. If the price of uranium is relatively low, then you will use more uranium and less SWU to enrich the UF₆. If the price of uranium is high and SWU is relatively cheaper, you will use more SWU and less uranium.
Enrichment is measured both as the percentage of U-235 in the product and in the depletion. So the percentage of U-235 left behind in the tails assay is critical to the calculation of enrichment. The reactor operator always starts with the tails assay to find the best combination of UF₆ feed and SWU. The following table shows two examples of how a given quantity of enrichment could be contracted. The shaded part of the table shows the relative amounts of electricity required to produce that quantity of enrichment which points to one of the key advantages of centrifuge enrichment.

1 kg of UF₆ enriched to 3% U-235 could be produced by either of the following combinations:
			Gaseous Diffusion	Centrifuge
Tails Assay	Separative Work Units	Natural UF₆ Feed	Approximate Kilowatt Hours Required to achieve contracted enrichment
0.25%	3.8 SWU	6.0 kg	9,500	190
0.30%	3.4 SWU	6.6 kg	8,500	170

It takes about 100,000 SWU (100 t SWU) of enriched uranium to fuel a typical 1,000-megawatt commercial nuclear reactor for a year. A 1,000-megawatt plant can supply the electricity needs for a city of 600,000 people.
SWU spot prices are published weekly on the Uranium Exchange web site (www.uxc.com), however, utility contracts with a new US enrichment plant would be primarily based on long-term prices.

World Enrichment Market

The annual world market demand for enrichment is about 35 million SWU according to the World Nuclear Association.
Enrichment services are supplied by a number of sources as outlined in the table below. Actual annual production figures are not published for competitive reasons.

Supplier	Method	Approximate Annual Supply (000s SWU)	Market Share
USEC (US)	Gaseous Diffusion	4,500 – 5,500	13 - 16%
Eurodif (France)	Gaseous Diffusion	7,000 - 8,000	20 - 23%
Urenco (Europe)	Centrifuge	5,000	14%
Tenex (Russia)	Centrifuge	8,000 - 9,000	23 - 26%
Other	Centrifuge	1,500	4%
Highly Enriched Uranium (Russia)	n/a	5,500	15%
Highly Enriched Uranium (US)	n/a	500	1%
Total		35,000	100%

United States Enrichment Market

The United States is the world's largest market for enrichment services with annual demand of approximately 11 million SWU.
Domestic production currently supplies less than half of the US market and the only operating US enrichment facility is a higher cost gaseous diffusion plant.
US utilities need a secure supply of enrichment services as an integral part of their fuel supply and they prefer a competitive domestic enrichment market to provide it.

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