JP2971803B2 - Method for simultaneous separation of radioactive carbon and radioactive iodine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a radioactive solution containing radioactive carbon and radioactive iodine together with other radionuclides,
For example, radioactive carbon ( ¹⁴ C) and radioactive iodine ( ¹²⁹ I) can be simultaneously and efficiently separated from other radionuclides from radioactive liquid waste generated from a reprocessing facility for spent nuclear fuel or a facility using radioisotopes. It is about the method.

[0002]

2. Description of the Related Art Radioactive wastewater generated from nuclear facilities such as spent nuclear fuel reprocessing facilities and nuclear power plants, and radioactive wastewater generated from various facilities that handle radioisotopes contain radioactive carbon and radioactive iodine. Included with other radionuclides such as products.

As a method of separating radioactive carbon and radioactive iodine from such a radioactive waste liquid, a method of separating each of them as a single component from other radionuclides by a precipitation method or a solvent extraction method has conventionally been adopted.

[0004] That is, in the method of separating radioactive carbon conventionally performed by the Power Reactor and Nuclear Fuel Development Corporation of the present applicant, barium hydroxide (B) is contained in the radioactive waste liquid.
a (OH) ₂ ) A saturated aqueous solution is added to convert ¹⁴ C present in the waste liquid as carbonate ions into barium carbonate (BaCO ₃ ).
As a precipitate. After the precipitate is washed by decantation to remove most of the other radionuclides such as ¹²⁹ I, barium carbonate is decomposed by adding nitric acid to generate CO ₂ gas. By flowing nitrogen gas into the reaction tube, was replaced with CO ₂ gas in the reaction tube, the CO ₂
The gas is absorbed by sodium hydroxide and separated from other radionuclides as sodium carbonate (Na ₂ CO ₃ ).
On the other hand, to separate radioactive iodine, sodium sulfite (Na ₂ SO ₃ ) is added to the radioactive waste liquid to convert iodate ions (IO ₃ ⁻ ) contained in the waste liquid into iodine ions (I
^-) After reduction, the further addition of hydrogen peroxide (H ₂ O ₂₎ to oxidize the iodine (I _2). I thus obtained
The aqueous phase containing _2, I ₂ was added to carbon tetrachloride (CCl ₄₎
Was extracted with carbon tetrachloride, the carbon tetrachloride phase was separated, sodium sulfite was added thereto, and I ₂ was converted to I ⁻ and back-extracted into sodium sulfite to separate radioactive iodine.

[0005]

The above-mentioned conventional method of separating both radioactive carbon and radioactive iodine nuclides from radioactive waste liquid as single components has the following disadvantages. 1) The operation of separating the sample from other radionuclides, such as pretreatment of the sample, is complicated, takes a long time, is troublesome, and burdens the operator. 2) Separate and collect both nuclides within a fixed time,
In order to perform the analysis, two glove pox are required, and at least two workers are required. 3) Harmful chemicals such as carbon tetrachloride must be used. 4) Several kinds of chemicals such as an extractant and a precipitant are required.

Accordingly, the present invention provides a method for simultaneously separating radioactive carbon and radioactive iodine from radioactive waste liquid, which solves the above-mentioned drawbacks of the conventional method and can save labor and speed up the operation. It was done for the purpose of doing.

[0007]

Means for Solving the Problems The present inventors utilize the property that radioactive carbon and radioactive iodine in radioactive waste liquid are selectively decomposed by heat in an acidic region and vaporized, thereby converting them into gas. The inventors have found that they can be separated from other radionuclides at the same time, and have completed the present invention.

That is, the simultaneous separation method of radioactive carbon and radioactive iodine according to the present invention is characterized in that radioactive wastewater containing radioactive carbon and radioactive iodine together with other radionuclides is acidified by adding nitric acid, and then heated, whereby radioactive carbon is removed. The radioactive iodine as CO ₂ is simultaneously vaporized and separated from the radioactive waste liquid as I ₂ , and the vaporized product is passed through a first-stage absorption tube containing an aqueous sodium sulfite solution to absorb I ₂ into the aqueous sodium sulfite solution and recovered as NaI. ,
The vaporized product that has passed through the first-stage absorption tube is successively passed through a second-stage absorption tube containing an aqueous sodium hydroxide solution to absorb CO ₂ into the aqueous sodium hydroxide solution and is recovered as Na ₂ CO _3. Things.

The radioactive iodine in the radioactive liquid waste may be present in the form of iodine ion (I ⁻ ) and iodate ion (IO ₃ ⁻ ) at a ratio of 1: 1 depending on the composition of the liquid waste. In this case, IO ₃ by addition of sodium nitrite in the radioactive liquid waste ^- the I ^- was reduced to, and acidified by adding nitric acid to the radioactive liquid waste is vaporized is oxidized to I _2.

The vaporization reaction of radioactive iodine ( ¹²⁹ I) is as follows. _{^{2IO 3 - (129 I) +}} 2H + + 5HNO 2 → 5HN
O ₃ + 2H ₂ O + I ₂ ( ¹²⁹ I) ↑ 2I ⁻ ( ¹²⁹ I) + 2H ⁺ + HNO ₃ → HNO ₂ + H
₂ O + I ₂ ( ¹²⁹ I) ↑ 2I ⁻ ( ¹²⁹ I) + 2H ⁺ + 2HNO ₂ → 2NO + 2
H ₂ O + I ₂ ( ¹²⁹ I) ↑

On the other hand, since radioactive carbon in radioactive waste liquid exists in the form of carbonate, it is acidified with nitric acid and vaporized as CO ₂ . The vaporization reaction of radioactive carbon ( ¹⁴ C) is as follows. Na ₂ CO ₃ ( ¹⁴ C) + 2HNO ₃ → 2NaNO ₃ +
H ₂ O + CO ₂ ( ¹⁴ C) ↑

The vaporized product of I ₂ and CO ₂ thus separated from the radioactive liquid waste is converted into sodium sulfite (Na ₂ S).
By passing the aqueous solution through a first-stage absorption tube containing an O ₃ ) aqueous solution, I ₂ in the vaporized material can be absorbed as NaI in an aqueous sodium sulfite solution and separated and recovered according to the following absorption reaction. I ₂ ( ¹²⁹ I) ↑ + Na ₂ SO ₃ + H ₂ O → 2NaI
( ¹²⁹ I) + SO ₄ ^2- + 2H ⁺

The vaporized product from which I ₂ has been separated and removed, and then the aqueous solution containing sodium hydroxide (NaOH) 2
By passing through a stage absorption tube, C
O ₂ can be separated and recovered by absorbing Na ₂ CO ₃ into an aqueous sodium hydroxide solution. CO ₂ ( ¹⁴ C) ↑ + NaOH → Na ₂ CO ₃ ( ¹⁴ C) +
H ₂ O

In the first stage, I ₂ is absorbed, and in the second stage, CO ₂ is absorbed.
Reason for absorbing, when quantifying ¹⁴ C-separated recovered, since the β-ray spectrum of the ¹²⁹ I can not be accurate quantification will overlap with the β-ray spectrum of ¹⁴ C, the absorption pipe of the first stage ¹²⁹ This is because it is necessary to completely absorb and remove I.

[0015]

FIG. 1 shows an apparatus which can be preferably used in carrying out the present invention. This device is
It comprises a reaction tube 1, a first-stage absorption tube 2, and a second-stage absorption tube 3. An injection tube having a three-way cock 4 is inserted into the reaction tube 1, and a syringe 5 for injecting nitric acid and a nitrogen gas injection tube 7 having a flow valve 6 are connected to the three-way cock. The reaction tube 1 is immersed in a beaker 8 filled with water, and the beaker can be heated to a desired temperature by a heater 9. Further, the reaction tube 1 and the first-stage absorption tube 2, and the first-stage absorption tube 2 and the second-stage absorption tube 3
Are connected by connecting pipes 10 and 11, respectively.

The operation of the present invention using this apparatus will be described below with reference to the drawings. First, a sample of the radioactive waste liquid is collected in the reaction tube 1 and an aqueous solution of sodium nitrite is added. Then, the reaction tube is set in the beaker 8 as shown in the figure. Next, an aqueous solution of sodium sulfite is collected in the first-stage absorption tube 2, and an aqueous solution of sodium hydroxide is collected in the second-stage absorption tube 3. The syringe 5 from which nitric acid has been collected is set in the three-way cock 4 of the reaction tube 1, and nitrogen gas flows into the reaction tube 1 from the nitrogen gas injection tube 7. In this state, nitric acid is dropped from the syringe 5 to selectively decompose and vaporize radioactive iodine and radioactive carbon in the sample. Since this reaction occurs violently at the initial stage of nitric acid addition and foams, nitric acid is gradually added dropwise while observing the reaction. After the nitric acid dripping is completed, the heater 9 is turned on and about 90
Heat to 30 ° C. for 30 minutes. By replacing the generated vapor with nitrogen gas, the gas is introduced from the reaction tube 1 to the first-stage absorption tube 2 via the connection tube 10 and further to the second-stage absorption tube 3 via the connection tube 11. The radioactive iodine in the vapor is absorbed by the aqueous sodium sulfite solution in the first absorption pipe 2 and separated and recovered. Next, the vapor from which the radioactive iodine has been separated and removed is further introduced into the second-stage absorption tube 3, where the radioactive carbon is absorbed into the aqueous sodium hydroxide solution and separated and recovered.

The separation and recovery of radioactive iodine can be calculated by measuring the iodine ion concentration in the aqueous sodium sulfite solution in the first-stage absorption tube 2 and the iodine ion concentration in the initial sample with an ion chromatograph. Similarly, the separation and recovery rate of the radioactive carbon can be calculated by measuring the carbonate ion concentration in the aqueous sodium hydroxide solution of the second-stage absorption tube 3 and the carbonate ion concentration in the initial sample using an ion chromatograph. The concentration of ¹²⁹ I radioactivity (Bq / ml) in the separated and recovered aqueous sodium sulfite solution can be measured using a γ-nuclide analyzer, while the concentration of ¹⁴ C radioactivity in the separated and recovered aqueous sodium hydroxide solution can be measured. The concentration can be measured using a liquid scintillation counter.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Using the separation and recovery apparatus shown in FIG. 1, ^{129 in} radioactive concentrated waste liquid generated from a spent nuclear fuel reprocessing facility was used.
I and ¹⁴ C were separated and recovered. The reaction tube 1 has a diameter of 16.5.
The absorption pipes 2 and 3 are made of glass having a diameter of 10 mm and a length of 100 mm.
1 was manufactured from a Teflon (registered trademark) tube having a diameter of 0.8 mm.

1 ml of the waste liquid sample was collected in a reaction tube 1 and further added to the reaction tube 1 with an aqueous solution of sodium nitrite (50 g /
l) After adding 0.1 ml, the mixture was set in a beaker 8. Further, 6.0 ml of an aqueous sodium sulfite solution (0.5 M) was collected in the first-stage absorption tube 2, and 6.0 ml of an aqueous sodium hydroxide solution (2 N) was collected in the second-stage absorption tube 3, and each was set in an apparatus. A nitrogen gas was flowed from the nitrogen gas injection pipe 7. Next, 2 ml of nitric acid was collected in the syringe 5 and set in the three-way cock 4. After the nitric acid was slowly dropped into the reaction tube 1, the mixture was heated to 90 ° C. for 30 minutes with the heater 9 to obtain ¹²⁹ I and ¹⁴ C is converted to I ₂ gas and CO
_It was vaporized as _two gases. By replacing this vapor with nitrogen gas, the vapor is introduced into the first-stage absorption tube 2 and further into the second-stage absorption tube 3, and the first-stage absorption tube 2 absorbs I ₂ gas in an aqueous sodium sulfite solution. by absorbing the second stage absorber tube 3, CO ₂ gas in an aqueous solution of sodium hydroxide, ^{1 29} I and ¹⁴ C were separated and collected, respectively.

[0020] The approximately 2ml of aqueous sodium sulfite in the first stage in the absorption tube 2 at collected by γ nuclide analyzer sample bottle ¹²⁹
I radioactivity was measured. Using the remaining aqueous sodium sulfite solution, the iodine ion concentration was measured by an ion chromatograph, and the ¹²⁹ I separation and recovery rate was calculated from the ratio to the iodine ion concentration in the sample initially.

On the other hand, about 2 ml of the aqueous sodium hydroxide solution in the second-stage absorption tube 3 was collected in a sample bottle, and ¹⁴ C radioactivity was measured by a liquid scintillation counter. Using the remaining sodium hydroxide aqueous solution, the carbonate ion concentration was measured by an ion chromatograph, and the ¹⁴ C separation and recovery rate was calculated from the ratio to the carbonate ion concentration in the sample initially.

As the radioactive concentrated waste liquid as a sample, a medium-level radioactive concentrated waste liquid (MAW) and a low-level radioactive concentrated waste liquid (LAW) are used. The average was determined. Table 1 shows the results.

[0023]

The fluctuation rate (%) in Table 1 is obtained by dividing the standard deviation (1σ) by the average radioactivity concentration based on the average radioactivity concentration and the standard deviation obtained in five tests. And expressed as a percentage, and represents a relative error (%) with respect to the measured radioactivity concentration.

[0025]

As can be understood from the above description, according to the present invention, radioactive wastewater containing various radionuclides such as fission products can be easily removed from radioactive wastewater containing radioactive nuclides such as radiocarbon and radioactive iodine.
The components can be vaporized and separated at the same time without interference from other radionuclides, and the components can be efficiently separated and recovered by absorbing the vaporized product in a separate absorbing solution.

When the vapor of radioactive carbon and radioactive iodine is absorbed by the absorbing solution, the radioactive iodine vapor is absorbed and separated by the first-stage absorption tube, whereby the radiocarbon vaporized product is separated by the second-stage absorption tube. When measuring the beta ray (156 Kev) of the radioactive carbon of the absorbed sodium hydroxide aqueous solution, accurate measurement can be performed without being hindered by the beta ray (154 Kev) of iodine.

As described above, the method of the present invention can be carried out efficiently with a simple operation, so that the time required for analysis is shorter than that of a conventional method in which radiocarbon and radioactive iodine are separated and recovered separately. For example, it could be reduced from 180 minutes to 45 minutes, and the operation time in the glove box could be reduced from 165 minutes to 15 minutes, for example. In addition, the conventional method requires two analysis workers and two glove boxes, but the method of the present invention can be performed with one worker and one glove box.

Further, in the conventional method, harmful and difficult-to-treat secondary waste liquid is generated by using carbon tetrachloride as an extraction solvent. However, such a secondary waste liquid is generated in the method of the present invention. There is no. Further, since the method of the present invention can be carried out using a separation and recovery device having a simple instrument configuration, it can be applied to remote operations other than the glove box.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing an example of an apparatus that can be preferably used to carry out the method of the present invention.

[Explanation of symbols]

 1: Reaction tube 2: First stage absorption tube 3: Second stage absorption tube 4: Three-way cock 5: Syringe

Continuation of the front page (51) Int.Cl. ⁶ identification code FI C02F 1/72 C02F 1/72 Z G21F 9/08 511 G21F 9/08 511B (56) References JP-A-49-89099 (JP, A) (58) Field surveyed (Int.Cl. ⁶ , DB name) G21F 9/06 G21F 9/08

Claims (2)

(57) [Claims] 1. A radioactive solution containing radioactive carbon and radioactive iodine together with other radionuclides is acidified by adding nitric acid, and then heated, whereby radioactive carbon is converted into CO ₂ and radioactive iodine is converted into I ₂ from the radioactive solution. vaporized simultaneously separated, the vapor product and through a first-stage absorption tube containing the aqueous sodium sulfite solution to absorb the I ₂ in aqueous solution of sodium sulfite was recovered as NaI, continuing care product that has passed through the first-stage absorption tube A simultaneous separation method for radioactive carbon and radioactive iodine, wherein CO ₂ is absorbed in an aqueous sodium hydroxide solution and recovered as Na ₂ CO ₃ through a second-stage absorption tube containing an aqueous sodium hydroxide solution. 2. A IO by adding sodium nitrite to the radioactive solution ₃ ^- radioiodine I included as ^- after reduction in, characterized in that the acidified by adding nitric acid to the radioactive solution according Item 6. The method for simultaneous separation of radioactive carbon and radioactive iodine according to Item 1.