Electric heating – Metal heating – By arc
Reexamination Certificate
1999-04-19
2001-11-27
Paschall, Mark (Department: 3742)
Electric heating
Metal heating
By arc
C219S121430, C219S121360, C219S121550, C250S292000, C250S282000, C250S284000
Reexamination Certificate
active
06323455
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention concerns improvements in and relating to processing, particularly, but not exclusively to the processing of nuclear fuel materials.
2. Present State of the Art
The production of fuel grade nuclear fuel from mined uranium ore is a long and complex process. Many variations in the process are known but in general terms the process involves taking the ex-mine grade material and gradually converting and enriching it until it is in. a form and of a grade suitable for producing fuel pellets. Stages in this process are the concentration of the initial uranium oxides as uranyl nitrate hexahydrate; a de-nitration stage to convert the material into UO
3
; a reduction stage to convert the UO
3
to U
2
; a hydrofluorination stage to form UF
4
; a further fluorination stage to produce UF
6
; an enrichment procedure by physical or chemical means; and the conversion of UF
6
in its enriched form to ceramic grade UO
2
which is in a suitable form to be formed into fuel pellets.
Substantial processing plants, in terms of their size, capital investment and running costs, are necessary to perform all of these stages. Transportation between the various stages with its attendant problems are encountered. In addition, the fluorination technique in particular requires a complex and hazardous electrolysis process to produce the fluorine required.
Recycling of fuel similarly involves a series of complex chemical and physical steps to separate the various fission products from the depleted fuel and to upgrade the
235
U concentration in the material to a stage where once again it can be employed as fuel.
The complexities of these processes are also present in other processing lines in the fuel cycle, in relation to thorium, plutonium and other materials for instance.
BRIEF SUMMARY OF THE INVENTION
According to a first aspect of the invention we provide a process comprising the steps of:
a) providing a feed, the feed consisting of mixed components;
b) introducing said feed into a magnetic field;
c) converting at least a portion of said feed into an ionised form;
d) providing at least a portion of at least one component at a first energy band and/or level and providing at least a portion of at least one component at a second energy band and/or level, the second energy band and/or level being higher than the first energy band and/or level; and
e) at least partially separating said first energy band and/or level components from said second energy band and/or level components.
The ionisation may be controlled to provide at least one component in a partially ionised form and at least one different component in at least partially non-ionised form.
The non-ionised components may be separated from the ionised components. Preferably the separation occurs prior to the passage of the feed to the selective excitation stage. Preferably the ionised components for feed to the selective excitation stage are neutralised prior to introduction to the containing magnetic field of the selective excitation stage. Preferably the feed is at least partially ionised prior to the selective excitation, once within the containing magnetic field.
Further details of the process incorporating selective ionisation and a separation based thereon are set out in the second aspect of the invention and are incorporated herein.
The separation of the high energy level components from the low energy level components may be affected by contacting these components with a chemical material, the contact resulting in the higher energy level components remaining in a still ionised form and the contact with the lower energy level components resulting in an uncharged form. Preferably a separation of the components is then made based on the charge difference.
Further details of the process in which separation is based on a selective chemical quench are set out in the fifth aspect of the invention and are incorporated herein.
Preferably the feed to the process is provided in solid, most preferably powdered form, and/or in liquid form.
Preferably the feed comprises a mixture of isotopes. One or more isotopes of different elements may be present and/or one or more different isotopes of the same element may be present. Feed containing
238
U and
233
U is particularly preferred. A feed containing
238
U,
235
U,
241
Pu and
239
Pu, potentially together with other isotopes of Pu and other elements is also preferred.
Preferably one or more, and most preferably all, of the isotopes are present in molecular form in the feed. The provision of the uranium isotopes in oxide form and optionally in dioxide form is envisaged.
Preferably the materials are fed to the selective excitation stage as an at least partially ionised gas. The conversion of the feed material into an at least partially ionised gas may be affected in a single stage, for instance a plasma generator. Alternatively the feed materials may be first converted into a gas or vapour and then subsequently at least partially ionised.
Preferably the feed, which may be solid, is introduced into heating means, the heat input resulting in vaporisation and/or evaporation and/or the provision of the solid as a gas. A furnace may be employed for this purpose. The heat input may be provided by means of radiation and/or microwave heating.
A waste stream, for instance consisting of non-volatile or less volatile material, may be extracted from the heating means.
Preferably the feed in vapour form passes in a counter current manner to the feed in solid form in the heating means.
Preferably the feed is introduced into a magnetic field prior to ionisation. The magnetic field may be configured so as to confine the ionised part of the feed after ionisation. Preferably the feed is introduced to the magnetic field as a non-ionised vapour or gas.
The feed in gas form may be converted to an at least partially ionised state by ionising means. Electron cyclotron resonance offers a particularly suitable means for ionising or part ionising the feed.
Selected components of the feed may be substantially completely ionised and/or selected components of the feed may remain substantially un-ionised.
In one embodiment it is preferred that substantially all the components containing a given element are ionised. For instance both the
238
U and
235
U components of the feed may be converted to ionised form.
Preferably one or more components of the feed are converted to ionised form, in a molecular state. The conversion of the metal oxide to metal oxide ions, such as UO
2
, to UO
2
+
, is particularly preferred in this regard. Details and options for the selective excitation of the feed, whether as elemental or molecular ions, are provided elsewhere in the application.
The higher energy level components may be collected by collecting means presented to the process flow. Preferably the lower energy level components pass the collector means to separate, subsequent collector means.
Preferably the collector means for the high energy level components comprises a collector grid. The grid may comprise a series of plates. Preferably the plates are arranged substantially parallel to the direction of feed flow.
Preferably the collector means are electrically earthed or provided with an electrical potential.
The electrical potential preferably acts to neutralise the high energy level components from their ionised to an un-ionised state.
The collector means may be provided at a temperature of below 1000K. In this way cooling ot the high energy level components from a gaseous to a liquid, or more preferably, solid state is provided.
Preferably the collector means can periodically be removed from the feed flow, particularly to a remote location. Preferably the product is removed from the collector grid at this remote location. Preferably an alternative portion on the collecting grid is presented to the feed flow, when an alternative portion of the collector means is having the product recovered from it.
Preferably the low energy level components impact on their collector means.
Bailey Geoffrey Horrocks
Whitehead Colin
Witts David John
British Nuclear Fuels PLC
Paschall Mark
Workman & Nydegger & Seeley
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