Rapid analysis method for radioactive activity concentration of iodine-129 in solid

Abstract

The invention belongs to the field of radionuclide determination and radioactive solid waste treatment, and particularly relates to a rapid analysis method for the radioactive activity concentration of iodine-129 in a solid. The method comprises the following steps: oxidizing a radioactive solid sample at high temperature, adsorbing iodide ions through an anion exchange resin chromatographic column under an acidic condition, desorbing by using a NaClO solution, and measuring the radioactive activity concentration of iodine-129 in a desorption solution. The detection limit of the analysis method can reach 1.16 * 10 < 2 > Bq / kg and is far lower than the waste acceptance standard (1.00 * 10 < 6 > Bq / kg) of the northwest low-medium radioactive solid waste disposal site, the precision is superior to 20%, the recovery rate of iodine-129 can reach 76.8%-86.9%, and the method has wide application prospects in monitoring of medium-low radioactive solid wastes.

Description

Technical Field

[0001] This invention belongs to the field of radionuclide determination and radioactive solid waste management, and in particular relates to a rapid analytical method for the concentration of iodine-129 radioactivity in solids, specifically the analysis of the concentration of iodine-129 radioactivity in low-to-medium level radioactive solid waste. Background Technology

[0002] Iodine, a widely distributed element in nature, is volatile, highly water-soluble, and readily accumulates in the thyroid glands of humans and animals. Iodine-129I, the only long-lived radioactive isotope of iodine, has a half-life exceeding 15 million years and is primarily generated in nuclear reactors and nuclear weapons tests. Currently, over 90% of the solid waste generated by nuclear power plants during normal operation in my country is low-level radioactive solid waste. After on-site storage at the nuclear power plant, this waste is sent to centralized disposal sites (such as the Northwest Low- and Intermediate Radioactive Solid Waste Disposal Site) for permanent disposal. According to the "Northwest Low- and Intermediate Radioactive Solid Waste Disposal Site Operation Permit," the activity concentration levels of long-lived radionuclides such as 129I in the stored waste must be monitored during the treatment and disposal of low- and intermediate-level radioactive solid waste. However, there are currently no directly applicable national or industry standards in China for the analysis of 129I in low- and intermediate-level radioactive solid waste.

[0003] In view of this, the present invention is proposed. Summary of the Invention

[0004] The purpose of this invention is to provide a rapid method for measuring the radioactivity concentration of iodine-129 in solids, especially a method applicable to the analysis of the radioactivity concentration of iodine-129 in low- to medium-level radioactive solid waste.

[0005] This invention provides a method for analyzing the radioactivity concentration of iodine-129 in a solid, characterized by comprising the following steps: Take a solid sample, add iodine carrier solution and mix well, oxidize at high temperature and absorb with NaOH-Na2SO3 solution to obtain the collection solution; Under conditions of pH 1.0-2.0, the collected solution was passed through an anion exchange resin chromatography column to adsorb iodide ions, and then desorbed with NaClO solution to obtain the desorbed solution. The radioactivity concentration of iodine-129 in the desorption solution was determined.

[0006] In some embodiments of the present invention, the solid is radioactive solid waste or radioactively contaminated solid. Preferably, the radioactivity level of the solid is low or moderate.

[0007] In some embodiments of the invention, the solid sample is stored for more than one month to avoid the effects of iodine-131.

[0008] In some embodiments of the present invention, the amount of the solid sample is 5.0 to 10.0 g.

[0009] In some embodiments of the present invention, the iodine carrier solution is a stable iodine solution, such as a KI (iodine-127) solution. Preferably, the concentration of the KI solution is 0.5-3 mg / mL, more preferably 1-2 mg / mL. Preferably, the amount of the iodine carrier solution added is 0.5-5 ml, more preferably 1-2 ml.

[0010] In some embodiments of the present invention, the high-temperature oxidation is oxidation at 700-1000°C, for example, oxidation at 700°C, 750°C, 800°C, 850°C, 900°C, 950°C, or 1000°C. Preferably, the high-temperature oxidation is oxidation at 850-950°C. In some embodiments of the present invention, the high-temperature oxidation is high-temperature oxidation combustion decomposition performed in an oxidation furnace.

[0011] In some embodiments of the present invention, the high-temperature oxidation time is 1-3 hours. Preferably, the high-temperature oxidation time is 1-2 hours.

[0012] In some embodiments of the present invention, when the temperature reaches the target temperature, for example 700-1000°C, the atmosphere for the high-temperature oxidation previously described is N2 and O2, and after the target temperature is reached, the atmosphere is replaced with O2.

[0013] In some embodiments of the present invention, the NaOH concentration in the NaOH-Na2SO3 solution is 0.2-0.5 mol / L, and the Na2SO3 concentration is 0.1-0.5 mol / L. Preferably, the NaOH concentration in the NaOH-Na2SO3 solution is 0.2-0.4 mol / L, and the Na2SO3 concentration is 0.2-0.4 mol / L.

[0014] In some embodiments of the present invention, the concentration of the NaClO solution is 2-5%, preferably 3-4%. The NaClO solution can adsorb I... - Oxidized to IO3 - Elution is used to separate and enrich iodine.

[0015] In some embodiments of the present invention, the chromatography column is washed with HNO3-NaNO3 solution before desorption with the NaClO solution.

[0016] In some embodiments of the present invention, the concentration of HNO3 in the HNO3-NaNO3 solution is 0.05-0.3 mol / L, and the concentration of NaNO3 is 1.0-3.0 mol / L. Preferably, the concentration of HNO3 in the HNO3-NaNO3 solution is 0.1-0.2 mol / L, and the concentration of NaNO3 is 1.5-2.5 mol / L.

[0017] In some embodiments of the invention, the determination is to measure the β count rate using a liquid scintillation counter and calculate the radioactivity concentration of the iodine-129.

[0018] In some embodiments of the present invention, the radioactivity concentration of iodine-129 is calculated using the following formula:

[0019] in: c represents the radioactivity concentration of iodine-129, in becquerels per milliliter (Bq / kg). n i The count rate of the sample is expressed in counts per minute (cpm). n0 is the blank sample count rate, in units of counts per minute (cpm). 60 is the unit conversion factor; η represents the detection efficiency of iodine-129, expressed as a percentage (%). Y represents the recovery rate of iodine-129, expressed as a percentage. V i The sampling volume is measured using a liquid scintillation counter, in milliliters (mL). m is the weight of the solid sample, in grams (g). V is the final volume of the absorbent, expressed in milliliters (mL). 1000 is the conversion factor.

[0020] Compared with the prior art, the present invention has at least the following advantages: The iodine-129 analysis method of this invention eliminates the need for extraction, back-extraction, precipitation, and filtration, making it simple and easy to implement. It allows for the rapid and convenient quantitative determination of the radioactivity concentration of iodine-129 in batches of solid samples, especially in solid waste samples with intermediate and low levels of radioactivity. The detection limit of this analytical method can reach 1.16 × 10⁻⁶. 2 Bq / kg, far below the waste acceptance standard of the Northwest Low-to-Medium Radioactive Solid Waste Disposal Site (1.00×10⁻⁶). 6(Bq / kg). The analytical method of this invention has a precision better than 20%, and the recovery rate of iodine-129 can reach between 76.8% and 86.9%. The analytical method of this invention has broad application prospects in the monitoring of low- and medium-level radioactive solid waste. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the specific embodiments of this disclosure or the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this disclosure. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0022] Figure 1 This is a flowchart illustrating the method for analyzing the radioactivity concentration of iodine-129 in solids according to some embodiments of the present invention. Detailed Implementation

[0023] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0024] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. As used herein, the singular form includes the plural form unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used herein, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof. Unless otherwise stated, all parts, percentages, and ratios used herein are based on mass meters.

[0025] Furthermore, it should be understood that the one or more method steps mentioned in this invention do not preclude the existence of other method steps before or after the combined steps, or the insertion of other method steps between these explicitly mentioned steps, unless otherwise stated; moreover, unless otherwise stated, the numbering of each method step is merely a convenient tool for identifying each method step, and not for limiting the order of the method steps or limiting the scope of the invention. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered as within the scope of the invention.

[0026] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] Unless otherwise stated, all reagents used in the examples are commercially available or synthesized using conventional methods and are ready for use without further processing, as are the instruments used in the examples.

[0028] Example 1 1. Separation of iodine from the sample 1.1 Take radioactive sand samples to be sent for storage after one month of storage at room temperature, weigh 5.0013 g and 5.0002 g of the samples as parallel samples, place them in the sample boat, add 1 mL of 1 mg / mL iodine carrier (KI) solution to each sample boat, mix well, and place them in the combustion tube of the oxidation furnace. 1.2 Add 50.0 mL of absorption solution (NaOH-Na2SO3 mixed solution, 0.3 mol / L NaOH-0.3 mol / L Na2SO3) to the absorption bottle and test for leaks. Connect the absorption bottle to the outlet of the combustion tube of the oxidizer. 1.3 Connect the combustion tube inlet of the oxidation furnace to the combustion gas, adjust the gas flow rate to the set value, and check the airtightness of the entire pipeline, especially the connection between the absorption bottle and the combustion tube. Set the temperature of the oxidation zone of the oxidation furnace to 900 ℃. Turn on the oxidation furnace to perform high-temperature oxidation combustion decomposition of the sample and separate the iodine. Before the oxidation combustion temperature reaches 900 ℃, a mixture of N2 and O2 gas is introduced, and then O2 is used for combustion for 1 h; the absorption liquid captures the iodine separated by high-temperature oxidation to form a collection liquid; 1.4 Adjust the pH of the collection solution to 1.0–2.0 with nitric acid, and pass it completely through a container filled with NO3 at a flow rate of 1 mL / min. - For the type-3 resin chromatography column, discard the eluent. After loading the column, wash the column with 50 mL of a mixed solution of HNO3-NaNO3 (0.1 mol / L HNO3-2.0 mol / L NaNO3), and discard the washings. 1.5 Desorb iodine with 20 mL of 3% NaClO solution at a flow rate of no more than 1 mL / min, discard the first 3 mL of eluent, collect all subsequent eluent and dilute to a 25 mL volumetric flask; 1.6 Non-radioactive sand was used as a blank sample for the blank test.

[0029] 1.7 Accurately transfer 5.0 mL of the diluted desorption solution into a scintillation bottle, add 15 mL of scintillation solution, and mix well. Measure and record the β count rate using a liquid scintillation counter.

[0030] 2. 129 Measurement of I detection efficiency 2.1 Accurately transfer a certain volume (V) S )of 129 I. Add 3% NaClO solution to 5 mL of radioactive standard solution in a scintillation bottle, then add 15 mL of scintillation fluid and shake well.

[0031] 2.2 Measure the scintillation bottle using a liquid scintillation counter and record the β count rate (n). s ), calculated according to formula (1) 129 The detection efficiency (η) of I.

[0032] 3. 129 Determination of I recovery rate Weigh 5.0007 g of uncontaminated sand and add 35 Bq. 129 I. Apply standard solution to the sample surface. Follow steps 1.1–1.7 and record the β count rate (n). 129 The recovery rate (Y) of I is calculated according to formula (2).

[0033] 4. Result Calculation 4.1 Calculate according to formula (1) 129 I's detection efficiency: (1) In the formula: or —— 129 The detection efficiency of I is expressed as a percentage (%). n s —— 129 The count rate of the radioactive standard solution is expressed in counts per minute (cpm). n 0 — Blank sample count rate, in counts per minute (cpm); 60 – Conversion factor from CPM to CPS; V s —— 129 I. The volume of the radioactive standard solution sample is in milliliters (mL). c s —— 129 I. Activity concentration of radioactive standard solution, expressed in becquerels per milliliter (Bq / mL).

[0034] After testing and calculation, 129 The detection efficiency of I is 98.3%.

[0035] 4.2 Calculate the radioactive solid waste content using formula (2) 129 Recovery rate of I: (2) In the formula: Y —— 129 The recovery rate of I is expressed as a percentage; n --(join in 129 The count rate of the blank sample of the standard solution (I), in counts per minute (cpm). V i —Sampling volume during liquid scintillation counter measurement, in milliliters (mL); V —The final volume of the absorption solution, in milliliters (mL).

[0036] After testing and calculation, 129 The recovery rate of I was 77.8%.

[0037] 4.3 Calculate the radioactive solid waste content using formula (3) 129 I. Radioactivity concentration: (3) In the formula: c --sample 129 I. Radioactivity concentration, expressed in becquerels per milliliter (Bq / kg). n i — The sample count rate, measured in counts per minute (cpm); n 0 — Blank sample count rate, in counts per minute (cpm); m —The weight of the solid sample is expressed in grams (g). 1000 — Conversion factor from Bq / g to Bq / kg.

[0038] After measurement and calculation, the radioactivity concentration of iodine-129 in the sample was 7.62 × 10⁻⁶. 3 Bq / kg and 6.71×10 3 Bq / kg, with an average value of 7.17 × 10 3 The Bq / kg was reported, and the relative standard deviation between the two results was 8.98%.

[0039] Example 2 1. Separation of iodine from the sample 1.1 Take radioactive concrete samples to be sent for storage after one month of storage at room temperature, weigh 5.0037g and 5.0059g of the samples as parallel samples, place them in the sample boat, add 1 mL of 1 mg / mL iodine carrier (KI) solution to each sample boat, mix well, and place them in the combustion tube of the oxidizer. 1.2 Add 50.0 mL of absorption solution (NaOH-Na2SO3 mixed solution, 0.3 mol / L NaOH-0.3 mol / L Na2SO3) to the absorption bottle and test for leaks. Connect the absorption bottle to the outlet of the combustion tube of the oxidizer. 1.3 Connect the combustion tube inlet of the oxidation furnace to the combustion gas, adjust the gas flow rate to the set value, and check the airtightness of the entire pipeline, especially the connection between the absorption bottle and the combustion tube. Set the temperature of the oxidation zone of the oxidation furnace to 900 ℃. Turn on the oxidation furnace to perform high-temperature oxidation combustion decomposition of the sample and separate the iodine. Before the oxidation combustion temperature reaches 900 ℃, a mixture of N2 and O2 gas is introduced, and then O2 is used for combustion for 1 h; the absorption liquid captures the iodine separated by high-temperature oxidation to form a collection liquid; 1.4 Adjust the pH of the collection solution to 1.0–2.0 with nitric acid, and pass it completely through a container filled with NO3 at a flow rate of 1 mL / min. - For the type-3 resin chromatography column, discard the eluent. After loading the column, wash the column with 50 mL of a mixed solution of HNO3-NaNO3 (0.1 mol / L HNO3-2.0 mol / L NaNO3), and discard the washings. 1.5 Desorb iodine with 20 mL of 3% NaClO solution at a flow rate of no more than 1 mL / min, discard the first 3 mL of eluent, collect all subsequent eluent and dilute to a 25 mL volumetric flask; 1.6 Non-radioactive concrete was used as a blank sample for the blank test.

[0040] 1.7 Accurately transfer 5.0 mL of the diluted desorption solution into a scintillation bottle, add 15 mL of scintillation solution, and mix well. Measure and record the β count rate using a liquid scintillation counter.

[0041] 2. 129 Measurement of I detection efficiency 2.1 Accurately transfer a certain volume (V) S )of 129 I. Add 3% NaClO solution to 5 mL of radioactive standard solution in a scintillation bottle, then add 15 mL of scintillation fluid and shake well.

[0042] 2.2 Measure the scintillation bottle using a liquid scintillation counter and record the β count rate (n).s ), calculated according to formula (4) 129 The detection efficiency (η) of I.

[0043] 3. 129 Determination of I recovery rate Accurately weigh 5.0007 g of uncontaminated concrete sample and add 35 Bq. 129 I. Apply standard solution to the sample surface. Follow steps 1.1–1.7 and record the β count rate (n). 129 The recovery rate (Y) of I is calculated according to formula (5).

[0044] 4. Result Calculation 4.1 Calculate according to formula (4) 129 I's detection efficiency: (4) In the formula: or —— 129 The detection efficiency of I is expressed as a percentage (%). n s —— 129 The count rate of the radioactive standard solution is expressed in counts per minute (cpm). n 0 — Blank sample count rate, in counts per minute (cpm); 60 – Conversion factor from CPM to CPS; V s —— 129 I. The volume of the radioactive standard solution sample is in milliliters (mL). c s —— 129 I. Activity concentration of radioactive standard solution, expressed in becquerels per milliliter (Bq / mL).

[0045] After testing and calculation, 129 The detection efficiency of I is 98.3%.

[0046] 4.2 Calculate the radioactive solid waste content using formula (5) 129 Recovery rate of I: (5) In the formula: Y —— 129 The recovery rate of I is expressed as a percentage; n --(join in 129The count rate of the blank sample of the standard solution (I), in counts per minute (cpm). V i —Sampling volume during liquid scintillation counter measurement, in milliliters (mL); V —The final volume of the absorption solution, in milliliters (mL).

[0047] After testing and calculation, 129 The recovery rate of I was 79.6%.

[0048] 4.3 Calculation of the lower detection limit The measurement results showed that the β count rates of the samples were 44 cpm and 49 cpm, respectively, which were close to the count rate of the blank sample (41 cpm). The results were reported as the lower limit of detection. The lower limit of detection was calculated according to formula (6).

[0049] (6) In the formula: LLD—— Detection limit, Bq / kg.

[0050] N b —— Blank sample count rate, in counts per minute (cpm). t b —— The measurement time for blank samples is in seconds (s). V b —The sampling volume when measuring blank samples using a liquid scintillation counter, in milliliters (mL); m — the weight of the solid sample, in grams (g).

[0051] After measurement and calculation, the radioactivity concentration of iodine-129 in the sample was ≤1.16×10⁻⁶. 2 Bq / kg.

[0052] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for the analysis of the iodine-129 radioactivity concentration in a solid, characterized in that, The method comprises the following steps: a solid sample is taken, an iodine carrier solution is added and mixed uniformly, high-temperature oxidation is carried out, and a NaOH-Na2SO3 solution is used for absorption to obtain a trapping solution; under the condition that the pH is 1.0-2.0, the trapping solution is subjected to anion exchange resin chromatography column adsorption of iodine ions, and then a NaClO solution is used for desorption to obtain a desorption solution; the radioactivity concentration of iodine-129 in the desorption solution is determined.

2. The analysis method according to claim 1, characterized in that, The high-temperature oxidation is carried out at 700-1000℃.

3. The analysis method according to claim 2, characterized in that, The high-temperature oxidation is carried out for 1-3h.

4. The analysis method according to claim 2, characterized in that, Before the temperature reaches 700-1000℃, the atmosphere for the high-temperature oxidation is N2 and O2, and after the temperature reaches 700-1000℃, the atmosphere is changed to O2.

5. The analysis method according to claim 1, characterized in that, The concentration of NaOH in the NaOH-Na2SO3 solution is 0.2-0.5 mol / L, and the concentration of Na2SO3 is 0.1-0.5 mol / L.

6. The analysis method of claim 1, wherein, The concentration of the NaClO solution is 2-5%.

7. The analysis method of claim 1, wherein, Before desorption with the NaClO solution, the chromatography column is washed with an HNO3-NaNO3 solution.

8. The analysis method according to claim 7, characterized in that, The concentration of HNO3 in the HNO3-NaNO3 solution is 0.05-0.3 mol / L, and the concentration of NaNO3 is 1.0-3.0 mol / L.

9. The analysis method of claim 1, wherein, The determination is carried out by using a liquid scintillation counter to measure the beta count rate and calculate the radioactivity concentration of iodine-129.

10. The analysis method according to claim 9, characterized in that, The radioactivity concentration of iodine-129 is calculated by the following formula: wherein: c is the radioactivity concentration of iodine-129; n i is the count rate of the sample; n0 is the count rate of a blank sample; 60 is a unit conversion coefficient; η is the detection efficiency of iodine-129; Y is the recovery rate of iodine-129; V i The sample volume for liquid scintillation counter measurements; m is the sample weight of the solid sample; V is the constant volume of the absorption solution; 1000 is a unit conversion coefficient.

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