Chemistry: electrical and wave energy – Processes and products – Processes of treating materials by wave energy
Patent
1997-07-22
1999-09-07
Phasge, Arun S.
Chemistry: electrical and wave energy
Processes and products
Processes of treating materials by wave energy
2041572, 20415722, 250281, B01D 500
Patent
active
059482141
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the separation of isotopes, particularly to producing an atomic vapour from which the isotopes are separated.
2. Description of the Related Art
The process known as atomic vapour laser isotope separation (AVLIS) has been widely reported. It is described for example in J Applied Physics B (Springer-Verlag) 46, pages 253 to 260 (1988). An atomic vapour stream comprising different constituent isotopes is formed in an evacuated chamber and is irradiated by electromagnetic radiation, e.g. laser radiation, which causes at a selected frequency photoionisation of one of the constituent isotopes allowing that isotope to be separated by an electric or magnetic field.
BRIEF SUMMARY OF THE INVENTION
According to the present invention there is provided a method of isotope separation which comprises vaporising and atomising in an evacuated chamber a supply of the element whose isotopes are to be separated to form a stream of atoms of the said element in the chamber, and characterised in that the said supply which is vaporised comprises an involatile compound of the said element which is decomposed in the vaporisation process to provide the said stream of atoms.
Where the said element is combined in the said compound with one or more other elements which when liberated by decomposition can cause deleterious or harmful effects, e.g. partially destroy the vacuum or corrode parts of the chamber or recombine with the said element, a source of one or more further elements may advantageously be employed in the supply of material to be vaporised to react with the liberated element(s) to form one or more further involatile compounds. For example, where the liberated element is a non-metallic gas or vapour such as oxygen or sulphur or a halogen, the said further element may comprise a metallic element such as iron which readily forms an appropriate involatile iron oxide or sulphide or halide as appropriate.
The present invention is to be distinguished from molecular vapour laser isotope separation known in the prior art in which a molecular stream, e.g. of uranium hexafluoride, is irradiated with laser radiation to provide photoionisation to facilitate isotope separation. The compound per se is necessarily volatile and is not decomposed until it is treated by the laser radiation. In contrast, by decomposing in the vaporisation step (usually in a crucible or hearth) an involatile compound containing the element comprising the isotopes to be separated, the cost of operating an enrichment process such as the AVLIS process, for example, can beneficially be reduced since the involatile compound can be an inexpensive (or less expensive) source of the said element. For example, many heavy metal or rare earth metals exist more cheaply in the form of an oxide than in elemental form.
The element whose isotopes are to be separated by the method of the present invention may be selected for example from Ca, Zn, Sr, Cd, Ba, Hg, C, Si, Ge, Sn, Pb, or lanthanides or actinides especially Er, Ce, Yb, Sm, Gd, U or Pu.
The present invention is particularly beneficial to the isotopic separation of gadolinium. This element is used as an additive in nuclear fuel materials to form a burnable poison which deliberately reduces fuel efficiency thereby allowing greater fuel enrichment levels to be employed without loss of control of overall activity. Only certain isotopes, viz Gd 155 and Gd 157, provide the desired poison effect and it would be beneficial to have an economical process for the separation of these isotopes from unreactive isotopes of Gd. Whilst Gd metal is very expensive owing to the high cost of conversion from its source material gadolinia, the gadolinia itself provides a suitable and inexpensive supply material to separate gadolinium isotopes by use in the present invention. Cost reduction benefits are similarly offered by the separation of isotopes of other elements using starting materials comprising compounds of the element in question, e.g. urani
REFERENCES:
patent: 5110562 (1992-05-01), Sasao et al.
J. Applied Physics B (Springer-Verlag), 46, pp. 253 to 260 (1988), J.A. Paisner. No month available.
British Nuclear Fuels plc
Phasge Arun S,.
Wong Edna
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