KR20190105445A - Method for reducing rare earth element content in uranium, transuranium and rare earth element solid - Google Patents

Abstract

The present invention relates to a method for reducing rare earth element content in uranium, transuranium and rare earth element solids, comprising the steps of: (a) filling molten salts into a reactor; and (b) inserting uranium, transuranium and rare earth element solids into the molten salts, injecting chloride into the molten salts to oxidize the rare earth elements, and reacting the same.

Description

METHODS FOR REDUCING RARE EARTH ELEMENT CONTENT IN URANIUM, TRANSURANIUM AND RARE EARTH ELEMENT SOLID}

The present invention relates to a method for reducing the rare earth element content in uranium, superuranium and rare earth element solids.

Pyroprocessing, one of the spent fuel treatment processes, uses an electrochemical reaction in a high temperature molten salt electrolyzer. In the electrolytic refining process, U is recovered using a solid cathode, and in the electrolytic refining process, a liquid cadmium cathode is used. Recover the TRU element, including The electrolytic smelting process is a U / TRU recovery process.The difference in reduction potential for the electrodeposition of metal chlorides in the liquid cadmium cathode is small, and RE (rare earth element) is also electrodeposited as an impurity together with U / TRU. It is recovered. It is known that recovered U / TRU / RE ingots can be fed to high-speed fuel and burned to significantly reduce the level of high-level waste in spent fuel. However, if the RE content in the U / TRU / RE ingot supplied to the fuel of the high speed reactor is high, there is a possibility that the integrity of the metal fuel rods may be inferior. Therefore, the RE content in the recovered U / TRU / RE ingot is kept below a certain concentration. Must be maintained. Due to the electrode characteristics of the liquid cadmium cathode of the U / TRU recovery process, when the concentration of TRU in the hot molten salt is relatively lower than RE, the excess RE can be recovered together with the U / TRU, which can be used as a fuel for high-speed reactors. It is recycled into the system (used as a cathode material in the electrolytic refining process or as a reactant in the UCl ₃ manufacturing process) after ingoting through a distillation process. When the RE is recycled into the system, the concentration of RE in the molten salt of the electrolyzer increases, increasing the load on the U / TRU recovery process for the fuel supply of the fast reactor.

In the process of developing global pyroprocessing technology to date, research has been conducted to recover U / TRU / RE ingots while keeping the RE content as low as possible in the U / TRU recovery process. In other words, although solid Al electrodes, liquid metal electrodes other than cadmium, and multi-stage extraction processes have been studied, U // due to obstacles such as differences in thermodynamic equilibrium values, overpotential characteristics of electrodes or high temperature multistage process equipment operation, etc. RE content in TRU / RE ingots remains an unavoidable phenomenon.

Therefore, the development of a process that can reduce the RE content in the recovered U / TRU / RE ingot to supply directly to the fuel of the fast reactor or reduce the load of the U / TRU recovery process by reducing the RE content even when recycled to the system. It is an urgent situation.

Domestic Patent Publication No. 10-1345987 (2013.12.20)

The present invention (a) filling the molten salt in the reactor; And (b) charging uranium, superuranium and rare earth element solids into the molten salt, injecting chloride into the molten salt to oxidize the rare earth elements and reacting them with uranium, superuranium and rare earths. It is intended to provide a method for reducing the rare earth element content in an elemental solid.

However, the technical problem to be achieved by the present invention is not limited to the above-mentioned problem, another task that is not mentioned will be clearly understood by those skilled in the art from the following description.

In one embodiment of the invention, (a) filling the molten salt in the reactor; And (b) charging uranium, superuranium and rare earth element solids into the molten salt, injecting chloride into the molten salt to oxidize the rare earth elements and reacting them with uranium, superuranium and rare earths. A method of reducing the rare earth element content in an elemental solid is provided.

The method for reducing the rare earth element content in uranium, superuranium and rare earth element solids according to the present invention comprises the steps of: charging molten salt in a reactor; And charging uranium, superuranium, and rare earth element solids into the molten salt, injecting chloride into the molten salt to oxidize the rare earth element, and then reacting them. Adopted in consideration of chloride generation free energy (ΔGf °), by rarely oxidizing the rare earth elements in the uranium, ultra uranium and rare earth element solids, it is possible to reduce the rare earth element content.

Thus, the uranium, ultrauranium and rare earth element solids having reduced content of rare earth elements may be used for the production of sodium-cooled fast reactor (SFR) nuclear fuel, and recycled to the anode material of the electrolytic refining process or the reaction of the UCl ₃ manufacturing process. It can also be used as a material to reduce the load on the electrosmelting process.

1 is a view schematically showing a method of reducing the rare earth element content in uranium, ultra uranium and rare earth element solids according to an embodiment of the present invention.
FIG. 2 is a schematic illustration of an apparatus used to reduce the rare earth element content in uranium, ultrauranium and rare earth element solids in accordance with one embodiment of the present invention.

The inventors of the present invention are studying a method for reducing the rare earth element content that acts as an impurity in uranium, superuranium and rare earth element solids, and by using chloride as a rare earth element oxidant for selectively oxidizing the rare earth element, It was confirmed that the rare earth element content in the ultra uranium and rare earth element solids can be effectively reduced, and completed the present invention.

Hereinafter, the present invention will be described in detail.

Rare Earth Element Content in Uranium, Superuranium and Rare Earth Element Solids Reduction  Way

The present invention (a) filling the molten salt in the reactor; And (b) charging uranium, superuranium and rare earth element solids into the molten salt, injecting chloride into the molten salt to oxidize the rare earth elements and reacting them with uranium, superuranium and rare earths. A method of reducing the rare earth element content in an elemental solid is provided.

Optionally, the method of reducing the rare earth element content in uranium, superuranium and rare earth element solids according to the present invention comprises: (c) recovering uranium, superuranium and rare earth element solids with reduced rare earth element contents from the reactor through the reaction; It may include a step. Specifically, the recovery may be carried out by removing the molten salt through distillation, and more specifically, the recovery may be carried out from the reactor to the uranium, superuranium and rare earth element solids with reduced rare earth element content through the reaction or After unexported, it can be carried out by distillation to remove the molten salt.

As used herein, the term "super uranium (TRU)" refers to an element having an atomic number greater than that of uranium (U), and includes neptunium (Np), plutonium (Pu), americium (Am), and curium (Cm). It includes.

As used herein, the term "rare earth element (RE)" refers to 15 lanthanum elements of atomic number 57 to 71, scandium (Sc) of atomic number 21 and yttrium (Y) of 39, that is, a total of 17 elements are generic.

As used herein, the term "uranium, ultrauranium and rare earth element solids" is a solid comprising uranium, ultrauranium and rare earth elements, and may further include other unavoidable impurities. The uranium, ultra uranium and rare earth element solids can be recovered from the electrosmelting process (U / TRU recovery process of pyroprocessing), where it can be used in the manufacture of sodium cooled fast reactor (SFR) fuel by reducing the rare earth element content. have.

1 is a view schematically showing a method of reducing the rare earth element content in uranium, ultra uranium and rare earth element solids according to an embodiment of the present invention.

As shown in FIG. 1, the method for reducing the rare earth element content in uranium, ultra uranium, and rare earth element solids according to an embodiment of the present invention includes filling molten salt in a reactor (S1); Charging uranium, ultrauranium and rare earth element solids into the molten salt (S2); Injecting a chloride for oxidizing the rare earth element into the molten salt (S3); And reacting them (S4).

Optionally, the method for reducing the rare earth element content in uranium, superuranium and rare earth element solids according to one embodiment of the present invention is carried out from the reactor to remove uranium, superuranium and rare earth element solids having a reduced rare earth element content through the reaction. Or after the non-export, it may further include a step (S5) to remove the molten salt by distillation.

First, the method for reducing the rare earth element content in uranium, superuranium and rare earth element solids according to the present invention includes the step of filling molten salt in the reactor [step (a)].

Specifically, the reactor is a container for filling molten salt, it is not necessary to use a large-capacity electrolyzer (a large capacity (eg, more than 30kg) reactor) used in pyroprocessing into the reactor, the capacity of the reactor Is enough to process the uranium, ultrauranium, and rare earth element solids described later (a small capacity (eg, 30 kg or less capacity) reactor).

In addition, as the molten salt, salts used in uranium and ultra uranium recovery processes may be used, and specifically, it is preferable to use LiCl-KCl eutectic salts, but is not limited thereto. This has the advantage of preventing contamination of the process salts by other elements. For the reaction described later, the molten salt is preferably maintained at a temperature of 400 ° C to 700 ° C, more preferably at a temperature of 500 ° C to 700 ° C, but is not limited thereto.

Next, a method of reducing the rare earth element content in uranium, ultrauranium and rare earth element solids according to the present invention is to charge uranium, superuranium and rare earth element solids in the molten salt, and to oxidize the rare earth elements in the molten salt. Chloride, followed by reacting them [step (b)].

Specifically, the uranium, ultrauranium and rare earth element solids are charged in the molten salt, characterized in that to perform an oxidation reaction to reduce the content of excessive rare earth elements in the uranium, superuranium and rare earth element solids. The uranium, ultra uranium and rare earth element solids are charged into a molten salt in a mesh basket to improve mass transfer performance of the reactants.

Therefore, the products of uranium, ultrauranium, and rare earth elements recovered in the U / TRU recovery process of pyroprocessing may be in the form of agglomerates (ingots) or in powder form depending on the performance of the distillation process. Despite this type difference, the reaction and recovery in the molten salt are not affected.

In addition, the chloride is for oxidizing the rare earth element, compared with the chloride of the rare earth element to be reduced, the absolute value of the chloride generation free energy (ΔGf °) may be small, the chloride is uranium chloride; Or a rare earth element chloride including yttrium chloride or gadolinium chloride, but is not limited thereto. At this time, in the case of yttrium chloride or gadolinium chloride, the absolute value of chloride generation free energy (ΔGf °) in the rare earth element chloride belongs to the smaller one.

At this time, the chloride of the rare earth element to be reduced may be at least one selected from the group consisting of neodymium chloride, cerium chloride, praseodymium chloride and lanthanum chloride.

Table 1 shows the chloride production free energy (ΔGf °) of uranium chloride, superuranium chloride and rare earth element chloride at about 500 ° C.

Chloride class ΔGf ° (kJ / mol) Uranium Chloride UCl ₃ -232.35 Superuranium Chloride NpCl ₃ -242.91 PuCl ₃ -261.41 CmCl ₃ -264.99 AmCl ₃ -266.38 Rare Earth Element Chloride YCl ₃ -272.50 GdCl ₃ -273.02 NdCl ₃ -281.45 CeCl ₃ -287.37 PrCl ₃ -288.89 LaCl ₃ -293.62

As shown in Table 1, the absolute value of ΔGf ° of the uranium chloride was found to be the smallest, followed by the ultrauranium chloride and the rare earth element chloride. At this time, in the case of yttrium chloride or gadolinium chloride, it is confirmed that the absolute value of ΔGf ° belongs to the smaller one in the rare earth element chloride. Therefore, a chloride having a smaller absolute value of ΔGf ° can be used as the rare earth element oxidant as compared with the chloride of the rare earth element to be reduced. For example, when uranium chloride is used as the rare earth element oxidant, the reaction scheme is as follows:

RE + UCl ₃ → RECl ₃ + U.

On the other hand, Table 2 shows the free energy (G) and equilibrium constant (K) during the reaction of ultrauranium and uranium chloride or the reaction of rare earth element solids and uranium chloride at about 500 ° C. based on the HSC Chemistry code.

Scheme ΔG (kcal) K With ultrauranium
Reaction of Uranium Chloride Np + UCl ₃ → NpCl ₃ + U -7.502 1.32E + 02 Pu + UCl ₃ → PuCl ₃ + U -22.439 2.21E + 06 Cm + UCl ₃ → CmCl ₃ + U -17.502 8.87E + 04 Am + UCl ₃ → AmCl ₃ + U -24.254 7.19E + 06 Reaction of Rare Earth Elements with Uranium Chloride Y + UCl ₃ → YCl ₃ + U -29.483 2.16E + 08 Gd + UCl ₃ → GdCl ₃ + U -29.010 1.59E + 08 Nd + UCl ₃ → NdCl ₃ + U -37.977 5.45E + 10 Ce + UCl ₃ → CeCl ₃ + U -40.555 2.92E + 11 Pr + UCl ₃ → PrCl ₃ + U -41.162 4.33E + 11 La + UCl ₃ → LaCl ₃ + U -44.708 4.36E + 12

As shown in Table 2, when the reaction between the uranium and rare earth elements and the uranium chloride, ΔG has a negative value, it is confirmed that all the oxidation reaction of the ultra uranium and rare earth elements is well performed. However, the equilibrium constant (K) of the rare earth element and the uranium chloride reaction is about 10 ² to 10 ¹⁰ higher than the equilibrium constant (K) of the reaction of the uranium chloride with the uranium chloride. It is confirmed that it works well. Therefore, when uranium chloride is used as a rare earth element oxidizing agent, the rare earth element content can be selectively oxidized at a high reaction rate compared to uranium and super uranium in the uranium, super uranium and rare earth element solids, thereby reducing the rare earth element content. It can be seen as having.

In addition, Table 3 of the uranium and the rare earth element chloride (GdCl ₃₎ reaction hours, transuranic and rare earth element chloride upon reaction or a rare earth element and the rotating earth element chloride (GdCl ₃₎ of from about 500 ℃ based on HSC Chemistry code In the reaction, the free energy (ΔG) and equilibrium constant (K) are shown.

Scheme ΔG (kcal) K With uranium
Reaction of GdCl ₃ U + GdCl ₃ → UCl ₃ + Gd 29.010 6.30E-09 With ultrauranium
Reaction of GdCl ₃ Pu + GdCl ₃ → PuCl ₃ + Gd 6.571 1.39E-02 Rare earth elements
Reaction of GdCl ₃ Nd + GdCl ₃ → NdCl ₃ + Gd -8.967 3.43E + 02 La + GdCl ₃ → LaCl ₃ + Gd -15.699 2.74E + 04

As shown in Table 3, in the reaction of uranium and ultrauranium with a rare earth element chloride (GdCl ₃ ), ΔG has a positive value, and it is confirmed that the oxidation reaction of uranium and superuranium is not well achieved. When the rare earth element and the rare earth element chloride (GdCl ₃ ) are reacted, ΔG has a negative value, and it is confirmed that the rare earth element is oxidized. Therefore, when a rare earth element chloride having a small absolute value of chloride generation free energy (ΔGf °) is used as a rare earth element oxidant, the uranium and super uranium in the uranium, super uranium and rare earth element solids are not oxidized, By selectively oxidizing, it can be seen to have the advantage of reducing the rare earth element content.

In this case, the chloride may be injected at one time or in divided portions. Specifically, in the case where the chloride is divided and injected, compared with the case in which the chloride is injected at the same time, by relatively suppressing the reaction with ultra uranium, it can have the advantage of improving the selective reaction with rare earth elements have.

In addition, since the reaction is a very fast reaction rate using molten salt as a medium, stirring is not particularly necessary in a small capacity reactor (eg, 30 kg or less), but in a large capacity reactor (eg, more than 30 kg), the reactant is not required. It can be carried out by further operating a stirrer to increase the reaction rate by improving the mass transfer performance of. Specifically, the stirrer is preferably operated at a speed in a range in which no loss occurs due to separation of the molten salt filled in the reactor, but is not limited thereto.

Meanwhile, in order to improve the mass transfer performance of the reactants, instead of further operation of the stirrer, uranium, ultrauranium and rare earth elemental solids may be placed in a mesh basket in the molten salt, and then charged into the molten salt. .

Optionally, the method of reducing the rare earth element content in uranium, superuranium and rare earth element solids according to the present invention is to recover the uranium, super uranium and rare earth element solids having reduced rare earth element contents through the reaction from the reactor [( c) step] may be further included.

Specifically, the recovery may be carried out by removing the molten salt through distillation, and more specifically, the recovery may be carried out from the reactor to the uranium, superuranium and rare earth element solids with reduced rare earth element content through the reaction or After unexported, it can be carried out by distillation to remove the molten salt.

First, when the rare earth element content of uranium, ultra uranium and rare earth element solids are removed from the reactor through the reaction, the distillation may be performed to remove residual molten salts carried out together with the uranium, super uranium and rare earth element solids. It is for. On the other hand, when the uranium, ultra uranium and rare earth element solids of which the rare earth element content is reduced through the reaction are not carried out (when a small capacity (eg, 30 kg or less) of the reactor is used, in the form of powder in the reactor) When precipitated], the distillation may be for removing the entire remaining molten salt in the reactor.

The distillation may be carried out at a temperature higher than the melting point of the uranium, ultra uranium and rare earth element solids under reduced pressure, preferably at a temperature of 600 ° C. to 1200 ° C. under a pressure condition of 1 Torr or less, but is not limited thereto. Do not.

Finally, the content of rare earth elements in the uranium, ultra uranium and rare earth element solids in which the rare earth element content is reduced may be 10 wt% or less, and preferably 5 wt% or less, but is not limited thereto.

As described above, the method of reducing the rare earth element content in uranium, superuranium and rare earth element solids according to the present invention comprises the steps of: charging molten salt in a reactor; And charging uranium, superuranium, and rare earth element solids into the molten salt, injecting chloride into the molten salt to oxidize the rare earth element, and then reacting them. Adopted in consideration of chloride generation free energy (ΔGf °), by rarely oxidizing the rare earth elements in the uranium, ultra uranium and rare earth element solids, it is possible to reduce the rare earth element content.

Thus, the uranium, ultrauranium and rare earth element solids having reduced content of rare earth elements may be used for the production of sodium-cooled fast reactor (SFR) nuclear fuel, and recycled to the anode material of the electrolytic refining process or the reaction of the UCl ₃ manufacturing process. It can also be used as a material to reduce the load on the electrosmelting process.

Hereinafter, preferred examples are provided to aid in understanding the present invention. However, the following examples are merely provided to more easily understand the present invention, and the contents of the present invention are not limited by the following examples.

[ Example ]

Example  One

The apparatus shown in FIG. 2 was used to reduce the RE content in the ingot form U (substituted for U and TRU) / RE (specifically Ce and Nd) solids. Specifically, after filling the solid-state LiCl-KCl molten salt in the reactor of the STS material and heated the reactor to 500 ℃ by an external heater (not shown). Ingot-shaped U / RE solids were placed in a mesh-shaped basket made of STS, and then charged into a molten salt. Thereafter, UCl ₃ was injected at a time as a RE oxidant in accordance with the target RE equivalent equivalent to the molten salt, and then reacted. Then, after removing the U / RE solids with a reduced RE content through the reaction from the reactor, it was distilled at 800 ℃ or more under reduced pressure to remove the molten salt, it was prepared in ingot form again. At this time, it was confirmed that at least about 90% by weight of RE in the RE content in the initial U / RE solids was removed. On the other hand, the molten salt in which RECl ₃ accumulated in the reactor was removed through the salt waste treatment process to remove LiCl-KCl eutectic salt and recover RECl ₃ to solidify.

Example  2

RE as an oxidant, instead of UCl ₃ was carried out in the same manner as in Example 1, except that the GdCl _3. As a result, it was found that most of the Ce content in the initial U / RE solids was removed and Nd remained below about 10% by weight.

The foregoing description of the present invention is intended for illustration, and it will be understood by those skilled in the art that the present invention may be easily modified in other specific forms without changing the technical spirit or essential features of the present invention. will be. Therefore, it should be understood that the embodiments described above are exemplary in all respects and not restrictive.

Claims (9)

(a) filling the reactor with molten salt; And
(b) charging uranium, superuranium and rare earth element solids into the molten salt, injecting chloride into the molten salt to oxidize the rare earth elements, and then reacting them.
A method for reducing the rare earth element content in uranium, superuranium and rare earth element solids.
The method of claim 1,
In (b) the molten salt is maintained at a temperature of 400 ℃ to 700 ℃
A method for reducing the rare earth element content in uranium, superuranium and rare earth element solids.
The method of claim 1,
In (b), the uranium, superuranium and rare earth element solids are in the form of ingots or powders.
A method for reducing the rare earth element content in uranium, superuranium and rare earth element solids.
The method of claim 1,
In (b), the chloride has a smaller absolute value of the chloride free energy (ΔGf °) than the chloride of the rare earth element to be reduced.
A method for reducing the rare earth element content in uranium, superuranium and rare earth element solids.
The method of claim 4, wherein
The chloride of the rare earth element to be reduced is at least one selected from the group consisting of neodymium chloride, cerium chloride, praseodymium chloride and lanthanum chloride.
A method for reducing the rare earth element content in uranium, superuranium and rare earth element solids.
The method of claim 1,
The chloride in (b) is uranium chloride; Or a rare earth element chloride comprising yttrium chloride or gadolinium chloride
A method for reducing the rare earth element content in uranium, superuranium and rare earth element solids.
The method of claim 1,
The reaction in (b) is carried out by further operating the stirrer to increase the reaction rate
A method for reducing the rare earth element content in uranium, superuranium and rare earth element solids.
The method of claim 1,
(c) recovering uranium, ultrauranium and rare earth element solids having a reduced rare earth element content through the reaction from the reactor;
A method for reducing the rare earth element content in uranium, superuranium and rare earth element solids.
The method of claim 8,
The recovery is carried out by removing the molten salt through distillation
A method for reducing the rare earth element content in uranium, superuranium and rare earth element solids.

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