FIELDS MARK (GB)
| FR1462256A | 1966-04-15 | |||
| GB1158287A | 1969-07-16 |
| 1. | A fluoride volatility reprocessing procedure in the reprocessing of irradiated nuclear fuel wherein the fluorination ofthe fuel is carried out by feeding the fuel to an ionised gas plasma and contacting the resultant excited fuel with a fluorinating agent whereby fluorination is effected. |
| 2. | A procedure according to Claim 1 wherein the ionised gas plasma is an ICP or a microwave plasma. |
| 3. | A procedure according to Claim 1 or Claim 2 wherein the fuel is fed to the ionised gas plasma in the form of a slurry or a powder fluidised by a gas. |
| 4. | A procedure according to any ofthe preceding claims wherein the fluorinating agent is fluorine. |
| 5. | A procedure according to any ofthe preceding claims wherein the fuel is irradiated LWR fuel. |
| 6. | A fluoride volatility reprocessing procedure in the reprocessing of irradiated nuclear fuel substantially as described herein. |
| 7. | A procedure according to Claim 1 and substantially as described with reference to the accompanying drawing. |
This invention relates to fluorination and in particular to the fluorination of irradiated fuel in nuclear fuel reprocessing.
Plant size contributes significantly to the cost of a facility for reprocessing irradiated nuclear fuel. For any process, if one or more ofthe process stages can be earned out in smaller apparatus and at increased rate, this is likely to lead to considerable cost savings, provided overall throughput is not compromised.
Fluonde volatility reprocessing involves fluorination of irradiated fuel and the subsequent separation of fission product fluorides and actinide fluoπdes from UF 6 . Fluorination is currently carried out using a fluidised bed to nullify the effect ofthe highly exothermic fluoπnation reaction. A large vessel is required and a large volume of highly contaminated fluid bed material is produced, which matenal ultimately has to be treated and disposed of. Fluoπnation of all the UO or U O g and fission products and actinides takes approximately one day per fuel assembly. Accordingly the throughput per fluid bed is limited.
According to the present invention there is provided a fluonde volatility reprocessing procedure in the reprocessing of irradiated nuclear fuel wherein fluoπnation of the fuel is earned out by feeding the fuel to an ionised gas plasma and contacting the resultant excited species with a fluoπnating agent whereby fluonnation is affected.
The ionised gas plasma provides a source of intense heat and avoids the need for a fluid bed. allowing the fluonnation reaction to be speeded up.
The ionised gas plasma may be, for instance, an inductively-coupled plasma (ICP) or a microwave plasma. In other embodiments of the present invention regions of intense heat may be created by means of a laser or by the use of infra-red light. Reference will be made hereinafter to ICPs but it should be understood that this is by way of example only.
ICPs are commonly used in analytical chemistry for the determination of concentrations of metals in solution. They provide a small and intense source of heat (temperatures up to 10,000 K are routinely achievable) and thus break down all known material to elements and ions. The plasma is created by the application of a radio frequency (rf) field, through a cooled induction coil, to an inert gas such as argon or nitrogen. The gas is ionised and the ions and electrons produced interact with the fluctuating magnetic field produced by the induction coil. Ohmic heating occurs as a consequence of resistance to movement of the ions and electrons and causes the high temperature.
Normally, in analytical applications, solutions containing the species to be analysed are sprayed into the centre ofthe plasma as an aerosol. In the case ofthe present invention, however, it has been found possible very efficiently to introduce solids in the form of a slurry into the plasma. A 100% conversion of solids to atoms and ions is readily achievable. Alternatively, a powder fluidised by an inert gas could be supplied to the plasma.
A feedstock of UO 2 and/or U 3 O 8 in slurry form when fed to an ICP results in the formation of excited U atoms (U*). These excited atoms react with a fluorinating (or chlorinating) agent to produce volatile uranium species, such as UF 6 .
In the case where the slurry is formed from irradiated LWR fuel, a variety of volatile and involatile fission product fluorides and actinide fluorides is produced, thereby enabling the separation of UF 6 from the involatile fission product fluorides.
The process ofthe present invention produces relatively little waste (no bed material waste in contrast ofthe fluidised-bed process) and the plant volume requirements are small. Furthermore, the process provides rapid chemical conversion of oxide fuel and fission products into separable species. An additional benefit is that the constituent parts of the apparatus are small in size and therefore readily disposable.
The accompanying drawing shows, diagrammatically, apparatus of use in the present invention. The apparatus includes a vessel 1 within which is located an induction coil 3 to the interior of which an inert gas such as argon is fed via tubes 5. Between tubes 5 is located a further tube 7
by which fuel slurry may be fed to a central position within the induction coil. Application of a radio frequency field to the induction coil (which is cooled) results in the formation of an ICP 9 , into which the fuel slurry is fed. This results in the formation of excited U atoms (U*) which pass through an orifice in plate 1 1 to an upper region of vessel 1 which comprises a fluorinating atmosphere. This atmosphere is typically fluorine gas but may also be provided by another fluorinating agent including a novel reagent such as XeF 2 , KrF 2 , O 2 F 2 , HF, BrF 3 or BrF 5 . The UF 6 and other volatile fission products produced by the reaction then pass into a storage tank and ultimately into the plant designed for separation ofthe fission product fluorides and the actinide fluorides.