Natural uranium is composed mainly of two kinds of atoms - isotopes. The heavier isotope U-238 can not be split to release energy, so it is not suitable for electric power generation or for nuclear weapons. Natural uranium must be "enriched" to have a larger proportion of the lighter isotope U-235, which can be split to release energy in a chain reaction. This talk covers:
|The enrichment process takes natural uranium,
which contains 0.7%
U-235. One output stream is Low Enriched Uranium for power reactors with
4% U-235. The other (much larger) output is mostly U-238, and is called
"depleted uranium" (DU), because it has been depleted of most of
its U-235. DU is about half as radioactive as natural uranium but is
otherwise the same. DU is a "waste" product of enrichment. Its
uses are the subject of some controversy.
Countries that enrich uranium for the nuclear power industry or for nuclear weapons use either Centrifuge technology or gas diffusion technology - both very large industrial establishments. Laser Isotope Separation (LIS) is described below.
|The same basic enrichment
technology can be used to enrich the 4% U-235 uranium
further, up to 90%
U-235, which is required for nuclear weapons. More depleted uranium
is produced in the process.
The drivers of the enrichment process are commercial interests of the nuclear power industry, for 4% U-235; and military wants for the highly enriched uranium 90% U-235.
The international regulatory, verification and control regime centres around the nuclear Non-Proliferation Treaty (NPT). This was designed so that the enrichment to 90% U-235 ("weapons grade" uranium) is restricted to the original "nuclear powers" signatories. Control must also be applied at the low enrichment end (for the 4% U-235 nuclear power fuel) because the same general technology is used for every enrichment stage.
(Separation of Isotopes by Laser
a high technology Australian company listed on the Stock Exchange.
Silex is located at Lucas Heights, the site of Australia's research nuclear reactor.
Silex is regulated (as are all companies) by the Australian Securities and Investment Commission (ASIC), and also by the Australian Radiation Protection And Nuclear Safety Authority (ARPANSA).
Silex is doing innovative research on Laser Isotope Separation (LIS) to
obtain single isotopes of several elements:
Carbon and oxygen have a range of commercial and scientific uses.
Silicon makes better computer chips if it is a single isotope, rather than the three kinds of atoms in natural silicon.
Uranium is the main focus of Silex, to separate out the useful U-235 from the bulk of U-238, for use in nuclear power reactors.
The main principles of LIS
|Atoms of elements absorb light at a number of particular
colours. Here a graph is plotted of light absorption by uranium U-238 as it depends on colour
(wavelength). Here the wavelength scale is greatly stretched, so it covers
only a small range of wavelengths - to us they would appear all the same colour. The U-238 absorbs light a bit on either side of its best wavelength.
On the same scale, the useful isotope U-235 has a slightly different optimal wavelength to absorb light. Its absorption graph is drawn much lower because it is only 0.7% of the natural uranium. Although it has a slightly different optimal wavelength, it overlaps the U-238 graph.
|Lasers produce light of one colour - one wavelength. On this
expanded scale the laser light also appears spread out, tailing off on
each side of its peak brightness.
A laser can be tuned so that its light spectrum covers the absorption range of the wanted U-235.
When this laser light is shone onto the U-235, it absorbs the light, becoming chemically reactive. It can then be separated out chemically.
Unfortunately, the U-238 absorption spectrum overlaps with that of U-235, so some U-238 also gets out in the chemical separation. This means that the process may have to be repeated to produce sufficient enrichment of the U-235.
The details of the Silex process are confidential commercial information. The above describes the general principles, which are public knowledge. Silex says that they are not using atoms of uranium in their process but are using uranium compounds. They say that this works better than the atomic process (called AVLIS) which has been tried, but given up, by other countries.
Silex reported to its shareholders and the Stock Exchange on 25 February 2005 that the results of its experiments, and its system and economic modeling "are very encouraging, supporting the attractive economics of earlier estimates" for commercial enrichment of uranium for power generation. To confirm this, Silex is considering setting up a pilot plant, probably in the US in order to fulfill nuclear regulatory requirements. Australian and US government approval and inter-governmental agreements will be necessary to do this.
If the Silex LIS process works to produce nuclear power reactor uranium (4% U-235), it will have implications for nuclear weapons proliferation.
If it is known that LIS works to enrich uranium, it will not be long before other people can work out how it works. They will be able to implement the process from widely available technology and in a small industrial facility. A US Department of Energy report in 2001 identified this possibility as a nuclear proliferation risk ("Nuclear Proliferation Using Laser Isotope Separation - Verification Options" by SA Erickson).
A PowerPoint slide presentation (~500 kB) of the above talk is available from
the Author: Ian
Newman, University of Tasmania GPO Box 252-21, Hobart 7001, Australia. [ Download
a 4-page Word document ]
© Copyright 2005 Ian Newman.