JP2776897B2 - Method and apparatus for treating radioactive ruthenium-containing waste liquid - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method and an apparatus for treating a radioactive ruthenium-containing waste liquid, and particularly to a method and an apparatus for treating a radioactive ruthenium-containing waste liquid generated from a spent nuclear fuel reprocessing step.

[Conventional technology]

Generally, in the reprocessing of spent nuclear fuel, a nitric acid solution is used in a step of dissolving the cut nuclear fuel and an extraction step of separating and purifying uranium, plutonium, and fission products, respectively. Then, the nitric acid solution (nitric acid waste liquid) used in these reprocessings is evaporated (distilled) in the acid recovery system and reused in the reprocessing step.

The nitric acid solution used in the reprocessing contains radioactive and non-radioactive ruthenium. Part of this ruthenium is oxidized during the nitric acid solution evaporation process, and volatile substances (Ru
O ₄ ) and evaporates and enters the nitric acid vapor. For this reason, it is said that it is not easy to reduce the ruthenium concentration in the recovered nitric acid, and that the ruthenium removal coefficient in the acid recovery system is reduced.

Conventionally, in order to increase the decontamination efficiency of ruthenium in a nitric acid evaporator, as described in JP-A-59-88692, when recovering nitric acid by evaporating a nitric acid solution containing ruthenium with a nitric acid evaporator, A method of adding a reducing agent such as hydrazine to the nitric acid evaporator has been considered. According to this method, when evaporating a nitric acid solution, the evaporation of ruthenium contained therein is suppressed, whereby the decontamination coefficient of ruthenium can be significantly improved. In addition to the addition of hydrazine, methods for preventing ruthenium from being oxidized and mixed into nitric acid vapor are described in JP-A-63-186193 and JP-A-61-260196. There is something.

[Problems to be solved by the invention]

The conventional method is that ruthenium is volatile in a nitric acid solution.
It is intended to suppress oxidation to O ₄ . That is, the above-described conventional method reduces ruthenium generated from the evaporator regardless of radioactivity or non-radiation. However, only the radioactive ruthenium has a problem in the waste liquid generated from the reprocessing step.

Also, Journal of Nuclear Science and Technology, 25 [7], pp.603-606 (1988
July) (Jornal of Nuclear Science and Technolog
y, 25 [7], pp. 603-606 (July 1988)), the rate of oxidation of ruthenium to RuO ₄ when evaporating a nitric acid solution containing ruthenium is determined by the concentration of ruthenium in the nitric acid solution. However, it is considered that it depends on the generation rate of active nitrate groups generated in the nitric acid solution. That is, in the above paper, the concentration of ruthenium contained in the nitric acid vapor that evaporates at a constant rate from boiling nitric acid having a concentration of 9 mol / l is determined by the nitrosyl ruthenium trinitrate complex (RuNO (NO ₃ ) ₃ ) in the evaporator. From 0.3 mol / m ³ (30 mg Ru / l)
Experimental results show that the concentration of ruthenium in the nitric acid vapor is about 0.3 mg Ru / l, even if it is changed to 30 mol / m ³ (3000 mg Ru / l). Can be calculated. In contrast to this fact, the above paper infers that the oxidation reaction rate of ruthenium depends not on the concentration of ruthenium but on the generation rate of active nitrate groups generated in nitric acid.

An object of the present invention is to reduce as much as possible the amount of radioactive ruthenium mixed into a vapor such as nitric acid from an oxidizing waste liquid such as a nitric acid waste liquid by focusing on the above two points.

Still another object of the present invention is to reduce the amount of radioactive ruthenium economically in a waste liquid treatment step in addition to the above objects.

Still another object of the present invention is to provide a method for removing radioactive ruthenium, wherein the amount of radioactive ruthenium in the waste liquid is not dependent on the concentration of ruthenium in the waste liquid before the removal treatment. It is intended to reduce the amount.

[Means for solving the problem]

In order to achieve the above object, in the present invention, the ratio of radioactive ruthenium to non-radioactive ruthenium in the nitric acid waste liquid is reduced by adding a ruthenium compound having a high ratio of non-radioactive ruthenium to the nitric acid waste liquid (the ruthenium content in the nitrate waste liquid is reduced). The specific radioactivity is reduced), and the amount of radioactive ruthenium mixed into the vapor of nitric acid is reduced by performing the evaporation treatment of the nitric acid waste liquid.

Further, in order to achieve the above and other objects, the present invention provides a method for preparing a ruthenium compound having a high content of non-radioactive ruthenium, which is already recovered in the reprocessing step, and which has been used for a long time since its removal from the nuclear reactor. By using ruthenium contained in spent fuel), the amount of radioactive ruthenium is reduced economically.

The ruthenium having a high proportion of non-radioactive ruthenium may of course be non-radioactive ruthenium having a natural isotopic composition.

In addition, as a ruthenium compound to which a large proportion of non-radioactive ruthenium is added, the effect of reducing the amount of radioactive ruthenium is sufficiently exerted if the properties of the compound are close to the radioactive ruthenium compound originally present in the waste liquid to be treated. For example, it is well known that ruthenium exists as a nitrosyl-ruthenium complex in a nitric acid solution used in the reprocessing step, but the type and number of ligands coordinated to the nitrosyl-ruthenium group are determined by the nitric acid concentration and nitrous acid concentration. When the nitric acid waste liquid containing ruthenium is subjected to evaporation treatment, the soluble nitrosyl-ruthenium complex is dissolved in the nitric acid waste liquid to be treated and maintained at the treatment temperature. It is desirable to add a concentrated solution of ruthenium that has been brought to equilibrium to the treatment solution.

It is more effective to add a ruthenium compound having a high ratio of non-radioactive ruthenium to perform the evaporation treatment after the ruthenium concentration in the waste liquid has been sufficiently reduced in advance.

Furthermore, in order to achieve the other object, according to the present invention, in the case of a removal method in which the amount of ruthenium in the waste liquid after the removal treatment of radioactive ruthenium does not depend on the ruthenium concentration in the waste liquid before the removal treatment, the removal amount is included in the waste liquid. The amount of radioactive ruthenium in the treated waste liquid by adding a ruthenium compound with a higher proportion of non-radioactive ruthenium to the waste liquid to reduce the specific activity of ruthenium in the waste liquid and removing the radioactive ruthenium Is to be reduced.

[Action]

Oxidation reaction rate of the RuO ₄ ruthenium as it evaporated nitrate solution containing ruthenium, as described in aforementioned article, rather than the concentration of ruthenium nitrate solution, the active nitrate group to produce a nitric acid solution It is thought to depend on the rate of formation. Therefore, the amount of ruthenium mixed in the nitric acid vapor (the amount of ruthenium mixed in the vapor irrespective of whether it is non-radioactive or radioactive) is approximately constant if the evaporating conditions such as the evaporating temperature are constant for wastewater of a certain composition. Become.
Therefore, if the specific activity of ruthenium in the waste liquid is reduced by adding a ruthenium compound having a high proportion of non-radioactive ruthenium to the nitric acid waste liquid, the rate of oxidation of non-radioactive ruthenium in the waste liquid to RuO ₄ increases, Since the rate at which radioactive ruthenium is oxidized to RuO ₄ decreases, the amount of radioactive ruthenium mixed into the nitric acid vapor can be reduced.

The effect of reducing the amount of radioactive ruthenium can be considered as follows. (S) Reduction rate of radioactive ruthenium concentration for the purpose (radioactive ruthenium in steam or treated waste liquid when applying the present invention relative to the concentration of radioactive ruthenium in steam or treated waste liquid when the present invention is not applied) (X) is the ratio of the amount of ruthenium added per unit volume to the amount of ruthenium per unit volume present in the waste liquid before the addition of the ruthenium compound, and the added ruthenium compound is completely non-radioactive. When a ruthenium compound is used, the effect of reducing the amount of radioactive ruthenium is given by the following equation.

The value of S is only 0.5 when the value of X is 1, but approaches 1 / X as the value of X increases. When adding ruthenium recovered in the reprocessing step with a small proportion of non-radioactive ruthenium, the relationship shown in (1) deviates from the relationship shown in (1) depending on the degree, and the concentration reduction effect that can be achieved when the value of X is increased Is less. Therefore, the required amount of the ruthenium compound to be added to the waste liquid to be treated, which has a high proportion of non-radioactive ruthenium, is the target value of the radioactive ruthenium concentration reduction effect in the treated liquid and the non-radioactive ruthenium of the added ruthenium. Is determined by the ratio of

As a ruthenium compound with a high proportion of non-radioactive ruthenium, the use of natural non-radioactive ruthenium can minimize the amount of radioactive ruthenium mixed in the vapor,
Since ruthenium is expensive, the amount of radioactive ruthenium can be reduced economically by utilizing radioactively decayed ruthenium already recovered in the reprocessing step.

Further, the present invention provides a method for reducing the concentration of ruthenium in a solution, in which the reduced form of the ruthenium compound becomes unstable and the removal of ruthenium becomes insufficient due to the potential oxidizing factor of the solution system, and the removal of ruthenium becomes insufficient. It can be applied to the case of the removal processing. That is, even in the case of the removal method in which the amount of ruthenium in the waste liquid after the removal treatment of radioactive ruthenium does not exist in the concentration of ruthenium in the waste liquid before the removal treatment, a ruthenium compound having a high ratio of non-radioactive ruthenium is similarly added to the waste liquid. By reducing the specific activity of ruthenium in the waste liquid, the amount of radioactive ruthenium in the treated waste liquid can be reduced.

〔Example〕

 Hereinafter, an embodiment of the present invention will be described.

The following table shows the types and yields of ruthenium nuclides as fission products produced by fission of ²³⁵ U by thermal neutrons.

Since the reprocessing of spent fuel takes place a few years after removal from the reactor, the radioactivity of ruthenium present during the reprocessing process is practically only at half life of ¹⁰⁶ Ru for one year. .

¹⁰⁶ Ru radioactivity present in the ruthenium is primarily burnup of the fuel (combustion history) and determined by the cooling period is typically about 10 ¹² Bq / g, day become half year.

In the reprocessing step, the ruthenium concentration in the evaporator of a solution containing nitric acid or nitrate is μg / l, except in the case of a high-level waste evaporator that receives and processes most of the fission products.
About to mg / l, ¹⁰⁶ Ru radioactivity is 10 ⁶ -10 ⁹ Bq / l
About.

The concentration of ruthenium in the vapor depends on the chemical properties of the solution and the conditions of the evaporation temperature, and the ¹⁰⁶ Ru activity concentration depends on the specific activity value. It is better to lower this radioactivity concentration as much as possible from the viewpoint of preventing radiation exposure.

FIG. 1 shows how the radioactivity in the vapor can be reduced when ruthenium with a high proportion of non-radioactive ruthenium is added to a particular evaporator. The decrease in radioactivity depends on the age of the added ruthenium after reprocessing and the amount added (ratio of the amount added to the initial concentration).

The dependency relationship is In shown, here, S: radioactive vapor in the case of applying the present invention to the concentration of radioactive ruthenium in the vapor in the case of not applying the reduction rate of radioactive ruthenium ⁽¹⁰⁶ Ru) concentration (present invention ⁽¹⁰⁶ Ru) ruthenium ⁽¹⁰⁶ Ru) concentration ratio of) n: reprocessing after age of the Ru adding X: Ru per unit volume present in the waste before the Ru addition (the Ru amount per unit volume relative to the initial concentration) Ratio.

The result of substituting ∞ into the numerical value of n in the equation (2) represents the case where non-radioactive natural ruthenium is used.

When adding ruthenium compound 100 times the initial concentration and trying to reduce the initial ¹⁰⁶ Ru activity by a factor of 100, natural ruthenium will be used if recovered ruthenium that has passed 10 years after reprocessing is used. It indicates that there is no need.

If the ruthenium recovered 7 years after reprocessing is used, the ¹⁰⁶ Ru concentration can be reduced to 1/10 by adding about 500 times the initial concentration.
0, but 8 even if the added amount of the ruthenium compound is increased.
It is shown that it does not become less than × 10 ⁻³ .

Similarly, to reduce the ¹⁰⁶ Ru concentration to about 10 ^-3 , it is necessary to add ruthenium that has passed 10 years or more after reprocessing, and at least 1000 times the initial concentration is required. .

Thus, although the decrease of ¹⁰⁶ Ru radioactivity in vapor is significant amount of such additives it is necessary ruthenium, if the actual initial concentration is approximately above [mu] g / l 1000 times Addition of about mg / l does not cause any special problem.

It is desirable that the chemical form of ruthenium to be added completely matches the chemical form of ruthenium in the solution of the evaporator, but in practice it is difficult to realize. But at least,
It is necessary that the chemical property of the ruthenium compound to be added is close to the chemical property of the ruthenium compound existing initially. Therefore, a concentrated solution is prepared by dissolving a soluble nitrosyl-ruthenium complex (for example, a trinitrate complex or a derivative thereof) in the treatment solution, and the solution is kept until the equilibrium is reached chemically and isotope-exchanged at the treatment temperature. It is desirable to add this concentrated solution as needed.

The ruthenium to be added can also be prepared as a solution in which a ruthenium compound extracted with tributylphosphoric acid from a so-called high-level waste liquid under weak acidity is back-extracted into nitric acid.

Regarding ruthenium removal and decontamination from radioactive liquid waste,
In addition to those cited as conventional methods in the present specification, JP-A-47-28400, JP-A-50-140799, JP-A-56-19499, JP-A-56-19500, JP 57
JP-50698, JP-A-60-161598, JP-A-61-4
There are those described in, for example, Japanese Patent No. 5998, which removes or reduces ruthenium contained in a liquid without evaporation.

The method of the present invention is particularly suitable for the purpose of further reducing the ruthenium radioactivity by performing the evaporation treatment after reducing the ruthenium concentration in the solution by the conventional method of removing or reducing without the above-mentioned evaporation without evaporation. It is suitable. This is because the final radioactivity can be reduced even if the absolute amount of added ternium is small.

In addition, the method of the present invention provides a chemical treatment other than evaporation treatment in which the oxidizing factor in the solution system inhibits the treatment of ruthenium so that the ruthenium radioactivity in the treated waste liquid is not sufficiently reduced as can be found in a nitric acid solution. It is also suitable to be applied in the case of the law. That is, the conventional method for removing ruthenium from the radioactive liquid waste as described above generally utilizes the oxidation-reduction reaction of ruthenium to separate and separate from the solution as a compound in a more stable reduced form, or to prevent volatilization, Alternatively, it is separated from the solution as a volatile oxidized compound. Among these methods, the more realistic method for forming a compound in a reduced form reduces the ruthenium concentration in a solution depending on a potential oxidizing factor of a solution system as observed in a nitric acid solution. It is expected that the reduced form of the ruthenium compound will become unstable and ruthenium removal will be insufficient. The present invention has an effect of improving the removal rate of radioactive ruthenium by applying when the oxidizing factor of the solution inhibits the ruthenium treatment and the ruthenium radioactivity in the treated waste liquid is not sufficiently reduced in the waste liquid evaporation treatment. However, it is also suitable to be applied to a case where the reduction of ruthenium radioactivity in the treated waste liquid in a treatment method other than the evaporation treatment due to the same reason becomes insufficient.

Next, FIG. 2 shows an embodiment of a radioactive waste liquid evaporation apparatus to which the present invention is applied.

1 is a supply liquid (nitric acid waste liquid) tank, 2 is a ruthenium solution tank, 3 is a mixing tank, 4 is a stirrer, 5 is an evaporator, 6
Is a condenser, 7 is a condensate tank, and 8 is a concentrate tank.

In one embodiment of the present invention, ruthenium is 0.1 μg / l
The aqueous nitrate solution is supplied to the supply liquid tank 1. This aqueous solution is concentrated 50-fold in the evaporator 5, and the evaporator liquid having a ruthenium concentration of 5 μg / l enters the concentrate tank 8, and the vapor exiting from the top of the evaporator is condensed and liquefied in the condenser 6 and condensed. Enter the liquid tank 7. The condensate contained 0.1 μg / l ruthenium. ¹⁰⁶ Ru activity in this case is 10 ⁵
Bq / l.

Here, according to the present invention, an aqueous solution containing ruthenium, which has passed 10 years after reprocessing, is loaded into the ruthenium solution tank 2,
The mixture is mixed in the mixing tank 3 by the stirrer 4 and supplied to the evaporator 5. Here, the ruthenium concentration in the mixture is
The concentration was 0.1 mg / l, and the concentration of ruthenium in the concentrate in the evaporator was 5 mg / l. Under these conditions, the condensate tank 7
The concentration of ruthenium in the condensate discharged to the furnace is 0.1 μg / l, its ¹⁰⁶ Ru radioactivity is reduced to 2 × 10 ² Bq / l, and the ruthenium radiation in Noh could be reduced by a factor of 500.

According to the embodiment of the present invention, what is added to the evaporation solution is the same ruthenium compound originally contained in the evaporation solution, and there is no significant chemical reaction with the solution.
It does not cause the secondary problems seen in conventional methods such as adding sodium nitrite, sucrose, formalin, etc. Therefore, there is no influence on the evaporation step itself, and it can be easily applied particularly when ruthenium having a high specific activity is contained and high decontamination efficiency is required.

The simplicity of the present method is most emphasized when ruthenium to be added has a specific radioactive natural isotope composition.
However, ruthenium compounds, which are a kind of white metal element, are expensive to apply at all times, and it is economical to use ruthenium compounds with reduced radionuclide concentrations that have undergone radioactive decay and are recovered at reprocessing plants. effective. According to the embodiment of the present invention, an optimum processing condition can be given for a given condition.

In the present invention, if a ruthenium compound having the same chemical form as ruthenium in the treatment liquid can be found, it is most suitable as a ruthenium chemical to be added, and an ideal efficiency can be obtained. However, it is actually difficult to identify the chemical form of ruthenium in the processing solution. Therefore, the use of a ruthenium compound which has reached a chemical equilibrium in the waste liquid to be treated can sufficiently achieve the object and is a practical method. Nitrosyl-ruthenium-trinitrate complex (RuNO (NO ₃ ) ₃ ) is considered the most stable in highly acidic nitric acid and is the compound most likely to be present in the nitric acid effluent of the reprocessing step. In addition, equilibrium is easily reached when the acidity condition changes. According to the embodiment of the present invention, a soluble nitrosyl ruthenium trinitrate complex is dissolved in a nitric acid waste liquid as a liquid to be treated, maintained at a processing temperature, and a concentrated ruthenium solution prepared by sufficiently reaching equilibrium is treated with a processing liquid. To achieve the purpose.

Further, when the present invention is applied constantly, it is the simplest and most economical to directly add a nitric acid solution of a ruthenium compound extracted from a waste liquid without specially preparing a ruthenium chemical.

The present invention is more effective as the ruthenium concentration in the evaporation treatment liquid is lower. Therefore, it is most effective if the concentration of ruthenium in the treatment liquid is reduced in advance by the evaporation method or another method. When combining several processing methods,
The present invention can remove radioactive ruthenium most effectively by applying to the final stage.

The present invention is based on the experimental fact that the part of ruthenium that cannot be removed by the evaporation method does not depend on the ruthenium concentration in the liquid, but on the oxidizing factor of the liquid. In the removal treatment utilizing the oxidation-reduction reaction of ruthenium, it is expected that a part of ruthenium which cannot be removed depending on the oxidizing factor of the liquid is generated as in the evaporation method. The present invention has the same effect as in the evaporation method in such a case, and can enhance the radioactive ruthenium removal effect of the treatment method.

〔The invention's effect〕

ADVANTAGE OF THE INVENTION According to this invention, the amount of radioactive ruthenium which mixes in vapors, such as nitric acid, from a nitric acid waste liquid can be reduced as much as possible.

Further, according to the present invention, the amount of radioactive ruthenium can be economically reduced in the waste liquid treatment step.

Furthermore, according to the present invention, in the method for removing radioactive ruthenium, when the amount of ruthenium in the nitrate waste liquid subjected to the removal treatment does not depend on the concentration of ruthenium in the nitrate waste liquid before the removal treatment, the removal treatment may be performed in the nitrate waste liquid. Can reduce the amount of radioactive ruthenium.

[Brief description of the drawings]

FIG. 1 is a functional diagram for explaining a general embodiment of the present invention, and is a diagram showing the influence of the age and amount of added ruthenium on the rate of decrease in the concentration of radioactive ruthenium in steam in an evaporator. . FIG. 2 is a diagram showing an example of a radioactive waste liquid evaporating equipment to which the present invention is applied. 1 ... supply liquid (nitric acid waste liquid) tank, 2 ... ruthenium solution tank, 3 ... mixing tank, 4 ... stirrer, 5 ... evaporator, 6 ...
... condenser, 7 ... condensate tank, 8 ... concentrate tank.

Claims (10)

(57) [Claims] 1. A method for treating a radioactive ruthenium-containing waste liquid for separating radioactive ruthenium from the waste liquid by evaporating a nitric acid waste liquid containing the radioactive ruthenium, wherein a ratio of non-radioactive ruthenium is contained in the waste liquid before the evaporation treatment. A method for treating a radioactive ruthenium-containing waste liquid, comprising adding a ruthenium compound in an amount larger than the ratio of non-radioactive ruthenium in the ruthenium to the waste liquid and performing the evaporation treatment. 2. A method for treating a radioactive ruthenium-containing waste liquid, which comprises evaporating a nitric acid waste liquid containing radioactive ruthenium to separate radioactive ruthenium from the nitric acid waste liquid, comprising: adding a ruthenium compound containing non-radioactive ruthenium to the nitric acid waste liquid; A method for treating a radioactive ruthenium-containing waste liquid, wherein the rate of radioactive ruthenium with respect to the total amount of ruthenium in the nitric acid waste liquid is reduced and the nitric acid waste liquid is evaporated. 3. A method for treating a radioactive ruthenium-containing waste liquid, which comprises evaporating a nitric acid waste liquid containing radioactive ruthenium to separate radioactive ruthenium from the nitric acid waste liquid, comprising the steps of: A method for treating a radioactive ruthenium-containing waste liquid, characterized in that the ratio of radioactive ruthenium which oxidizes to ruthenium tetroxide is oxidized to ruthenium tetroxide is reduced by adding a ruthenium compound containing non-radioactive ruthenium to the nitric acid waste liquid. . 4. The method for treating a radioactive ruthenium-containing waste liquid according to claim 1, wherein the ruthenium compound to be added is natural ruthenium. 5. The method for treating a radioactive ruthenium-containing waste liquid according to claim 1, wherein the form of the ruthenium compound to be added is equal to the form of the ruthenium compound in the nitric acid waste liquid. A method for treating ruthenium-containing waste liquid. 6. The method for treating a radioactive ruthenium-containing waste liquid according to any one of claims 2 to 4, wherein the ruthenium compound to be added dissolves a soluble nitrosyl-ruthenium complex in a part of the nitric acid waste liquid and evaporates. A method for treating a radioactive ruthenium-containing waste liquid, wherein the liquid is kept until the chemical equilibrium is reached at a treatment temperature condition. 7. The method for treating a radioactive ruthenium-containing waste liquid according to any one of claims 2 to 4, wherein the ruthenium compound to be added is extracted from the reprocessing waste liquid containing ruthenium with tributylphosphoric acid in a weakly acidic state, and Characterized by comprising a solution containing more of the non-radioactive ruthenium than the radioactive ruthenium back-extracted by the above method. 8. A method for treating a radioactive ruthenium-containing waste liquid for removing radioactive ruthenium from a nitric acid waste liquid containing radioactive ruthenium, wherein the amount of ruthenium in the nitric acid waste liquid subjected to the removal treatment is reduced in the nitrate waste liquid before the removal treatment. This is a removal method that does not depend on the concentration of ruthenium.The removal of radioactive ruthenium by adding a radioactive ruthenium compound by adding a ruthenium compound having a higher ratio of non-radioactive ruthenium than the ruthenium contained in the nitric acid waste liquid. A method for treating a radioactive ruthenium-containing waste liquid. 9. A radioactive ruthenium-containing waste liquid treating apparatus, comprising: an evaporator for receiving a nitric acid waste liquid containing radioactive ruthenium and evaporating the nitric acid waste liquid; and a condenser for condensing nitric acid vapor from the evaporator. An apparatus for treating a radioactive ruthenium-containing waste liquid, comprising means for supplying a ruthenium compound containing non-radioactive ruthenium, which reduces the specific activity of ruthenium in the nitric acid waste liquid in the evaporator, to the evaporator. 10. An apparatus for treating wastewater containing radioactive ruthenium, comprising: an evaporator for receiving a nitric acid waste liquid containing radioactive ruthenium and evaporating the nitric acid waste liquid; and a condenser for condensing nitric acid vapor from the evaporator. Means for extracting a ruthenium compound with tributylphosphoric acid from a reprocessing waste liquid containing weakly acidic, means for back-extracting the ruthenium compound with nitric acid from a solution containing the extracted ruthenium compound, and An apparatus for treating a radioactive ruthenium-containing waste liquid, comprising: means for supplying a ruthenium compound containing non-radioactive ruthenium that reduces the specific activity of ruthenium to the evaporator.