Method of Reprocessing Nitride Spent Nuclear Fuel in Salt Melts

Abstract

A method for reprocessing nitride spent nuclear fuel in molten salts comprises chlorinating the fuel in a melt of a mixture of alkali and/or alkaline earth metal chlorides containing cadmium dichloride. The chlorination is carried out in an apparatus for reprocessing nitride spent nuclear fuel using an inert gas atmosphere The apparatus has a heated zone containing a reactor with molten chlorides and nitride spent nuclear fuel submerged therein, and also a cold zone arranged under the reactor. In the chlorination process, the zone of the apparatus containing the reactor is heated to a temperature greater than 700 C., the nitride spent nuclear fuel is kept in the melt until fully chlorinated. The cold zone of the apparatus is used for crystallizing metallic cadmium which forms during the chlorination.

Claims

1. Method of reprocessing nitride spent nuclear fuel in salt melts, involving its chlorination in the melt of a mixture of chlorides of alkali and/or alkaline-earth metals containing cadmium dichloride, wherein the chlorination is carried out in an apparatus for reprocessing nitride spent nuclear fuel with the use of an inert gas atmosphere, characterized in that the chlorination is carried out in an apparatus having a heated zone I in which a reactor with a chloride melt 4 and an immersed therein nitride spent nuclear fuel 5 is located, as well as a cold zone II located below the reactor, wherein in the course of the chlorination zone I of the apparatus with reactor 3 is heated up to a temperature higher than 700 C., the nitride spent nuclear fuel 5 is held in the melt 4 up to a complete chlorination, while cold zone II of the apparatus is used for a crystallization of metallic cadmium formed during the chlorination.

2. The method according to claim 1, characterized in that as chlorides of alkali and/or alkaline-earth metals chlorides of lithium, potassium, sodium, cesium, calcium, magnesium, strontium, barium are used.

Description

[0022] The invention is illustrated by the drawings, in which:

[0023] FIG. 1 is a schematic diagram of an apparatus for chlorinating an nitride SNF in accordance with the claimed method.

[0024] FIG. 2 is a diagram for the thermodynamic reasons for conducting the process at a temperature above 700 C.

[0025] FIG. 3 shows typical changes in the concentrations of UCl.sub.3 and CdCl.sub.2 in the LiClKCl melt when nitride SNF (UN nitride) is immersed in it. The table shows parameters and results of the utilization of the prototype and the claimed method.

[0026] An experimental confirmation of the chlorination of nitride SNF according to the present method is carried out in a closed

[0027] apparatus with an inert atmosphere, for which moisture free argon is used. The apparatus comprises a housing 1, heaters 2, a reactor 3, a chloride melt 4, a nitride spent nuclear fuel 5, a metal collector 6, cadmium 7. The apparatus has a heated zone I and a cold zone II.

[0028] In the heated zone of the apparatus, a reactor 3 in the form of a ceramic crucible made of the oxide MgO was placed, with a previously prepared mixture of the chlorides KCl, LiCl, CdCl.sub.2. A eutectic mixture of LiClKCl was prepared by zonal recrystallization for a maximum removal of oxygen impurities and mixed with purified CdCl.sub.2 in a dry box. The zone of the apparatus with the reactor was heated to a temperature of 750 C., after which in the LiClKClCdCl.sub.2 melt a UN nitride sample was immersed as the main component of the nitride SNF, and held in the melt until the reaction was complete according to the chemical analysis.

[0029] During the experiment, samples of the melt were taken through a special lock device to analyze the content of CdCl.sub.2 and the resulting UCl.sub.3. On the basis of the obtained data, the degree of conversion of the nitride UN to UCl.sub.3 in the chlorination is calculated. The main parameters and the results of the experiments are given in the table, and the typical curves of the interdependence of the contents of CdCl.sub.2 and UCl.sub.3 in the melt of LiClKCl are shown in FIG. 3. In FIG. 3 it can be seen that in the course of the chlorination the concentration of CdCl.sub.2 in the LiClKCl melt is reduced, while the concentration of UCl.sub.3 increases. This demonstrates the direct progress of reactions (1), (2) and (3). At the experimental temperature of 500 C. the metallic cadmium formed according to reactions (1) and (2) was concentrated at the bottom of the reactor, while at 750 C. cadmium was collected in a special metal collector (see FIG. 2). It can be seen from the table that at a temperature of 700 C. and above the degree of conversion of the nitride SNF (UN nitride) is 100%, while at a lower temperature the conversion is only 20 to 60%.

[0030] For an industrial use, the apparatus must be designed so that the cold zone is under the reactor in which the chlorination is carried out. In a particular case, a metal collector in the form of a crucible is placed in this zone for crystallization of the metal cadmium formed during chlorination, which the vapors of cadmium are condensed. As a result, the reactor of the apparatus produces a LiClKCl melt containing actinide chlorides, as well as separately collected cadmium.

[0031] After the completion of the chlorination, the LiClCl melt containing the actinide chlorides as well as cadmium is recovered from the apparatus and sent to the step of the electrowinning of actinides. In a particular embodiment, the electrowinning of actinides can be carried out directly in a reactor in which the chlorination is carried out.

[0032] Mixtures of chlorides of alkali and/or alkaline-earth metals (chlorides of lithium, potassium, sodium, cesium, calcium, magnesium, strontium, barium), which do not interact with nitride SNF, may be used to optimize technological parameters of the method as a chloride melt containing cadmium chloride.

[0033] Thus, the claimed method of reprocessing nitride spent nuclear fuel makes it possible to increase the degree of conversion of nitride SNF in a chloride melt to 100%, which reduces or completely eliminates the necessity of additional stages of repeated filtration and reprocessing of SNF.