Combined method for measuring concentration of trace gas phase iodine in containment and analyzing forms of various types of iodine

Abstract

The invention belongs to the technical field of gas-phase iodine and liquid-phase iodine detection, and particularly relates to a combined method for measuring the concentration of trace gas-phase iodine in a containment and analyzing forms of various types of iodine. Comprising the following steps: preparing and selecting alkaline absorption liquid, collecting trace gas-phase iodine and liquid-phase iodine samples, establishing an iodine concentration standard curve, measuring the gas-phase iodine samples, establishing an iodine form-concentration standard curve, measuring the liquid-phase iodine samples and the like. The combined method is based on the combined method of monitoring the total concentration of gaseous iodine and chemically analyzing the form of iodine in the pit liquid pool, and can measure the trace gaseous iodine concentration in different areas at different time and monitor the form of iodine in the pit liquid pool at different moments; and dynamically carrying out migration analysis of gaseous iodine in a gas phase space in the containment and chemical evolution analysis of iodine in a water pool.

Description

Technical Field

[0001] The invention belongs to the technical field of gas-phase iodine and liquid-phase iodine detection, and in particular relates to a method for combining trace gas-phase iodine concentration measurement and multiple iodine form analysis in a containment. Background Art

[0002] During the operation of the reactor, due to the fission and subsequent decay of uranium 235 and its isotopes, a series of radioactive nuclides (Te / I / Xe / Cs / Ba) are produced in the fuel cladding. If a serious nuclear accident occurs in a nuclear power plant, a large amount of radioactive materials may be released into the environment. Among the radioactive fission products that may be released, radioactive iodine becomes one of the most important source nuclides due to its high fission yield, volatility, environmental mobility and significant radioactive hazards. A large amount of radioactive iodine isotopes ( 129 I, 131-135 I, 138-141 I), where 138-141 The half-life of I is extremely short and the harm it causes can be ignored. 129 I and 131 I has an extremely long half-life (1.57×10 7 The most harmful radioactive iodine isotopes are those with large initial stockpiles and high specific activity. Direct discharge into the air will pollute the environment and easily accumulate in the human thyroid gland, increasing the risk of thyroid cancer and seriously endangering human health. Therefore, in the context of nuclear safety, the removal of iodine has become particularly important.

[0003] Due to the great harm of iodine to the human body, it plays a key source control role in severe accident management. In the reactor containment, iodine exists in a variety of physical states (such as gas and aerosol), of which about 95% exists in the form of CsI aerosol particles, and the remaining 5% exists in the form of gas (such as I2, CH3I and HI), and most iodides are easily dissolved in water to form iodine ions. When the radiation energy of the nuclear reaction is absorbed by water molecules, radiolysis products are produced in the water pool, causing iodine ions to be converted into volatile molecular iodine I2, which re-enters the gas phase space of the containment and further diffuses into the environment. The chemical properties of iodine in water are quite complex, involving a wide variety of iodides, so it is very important to monitor the iodine concentration in the gas phase space of the containment and the pit liquid pool and to chemically analyze its morphology.

[0004] Although iodine has weak chemical activity, it is very easy to react with other elements. In addition, its complex and changeable form, instability and easy sublimation make the quantitative and qualitative analysis of iodine very limited and complicated. Currently, according to the iodine content in the sample to be tested, we can divide the iodine analysis method into constant, micro and trace iodine analysis.

[0005] In recent years, the detection methods of iodine have been significantly developed, including various types of volumetric analysis, spectral analysis and mass spectrometry. Volumetric analysis is mainly used for the determination of constant iodine, while photometry and chromatography are more mainstream analytical methods. Although photometry is simple and fast, its sensitivity will be affected by many factors, and polarography will be affected by electrode characteristics. In addition, inductively coupled plasma mass spectrometry (ICP-MS) has excellent performance in the detection of trace and ultra-trace iodine due to its high sensitivity, low detection limit, strong anti-interference and high degree of automation. In addition, the morphological analysis methods of iodine often use photometry, neutron activation method, high performance liquid chromatography-inductively coupled plasma mass spectrometry (HPLC-ICP-MS), ion chromatography combined with ICP-MS and other methods. Among them, inductively coupled emission-mass spectrometry and neutron activation method are often used to determine iodine isotopes, but the instruments are expensive and are not currently popular. The photometric method for measuring iodine is simple and rapid. I2 reacts with starch to form a blue complex with a maximum absorption value at 580nm. However, the color development of this method is unstable and there are many factors that affect the sensitivity.

[0006] At the same time, the current iodine analysis methods have many limitations. On the one hand, the iodine detection scheme commonly used in the nuclear power field has a complex operating process and may not be sensitive enough for samples with lower concentrations. Given that the concentration of gaseous iodine in the containment is usually extremely low, generally only at the ppb level, previous methods are often unable to accurately measure it. On the other hand, the chemical forms of iodine in water are diverse and prone to change, but the existing iodine form analysis in the pit liquid pool has not yet been quantified, and there is a lack of an effective quantitative detection method to conduct iodine chemical evolution analysis after the accident. In addition, the process of spraying to remove gaseous iodine in the containment is a transient process, and the content of fission product iodine is extremely low, about 1μg / g. The concentration of gaseous iodine in the gas phase space decreases rapidly with the start-up of the containment spray system, and the trace gaseous iodine concentrations in different areas and at different spraying times are different. Therefore, the sensitivity and accuracy of trace gaseous iodine measurement are extremely high; at the same time, as the alkaline spray liquid accumulates in the pit liquid pool, the pH value of the liquid phase will change, which in turn affects the chemical reaction of iodine and forms various forms of iodine (such as I2, I - 、I3 - IO3 - Therefore, there is an urgent need for a method that can not only accurately measure the trace gas-phase iodine concentration in the containment, but also quantitatively analyze the various iodine forms in the pit liquid pool, so as to better deal with the iodine pollution problem in nuclear accidents. Summary of the invention

[0007] In view of the above-mentioned deficiencies in the prior art, the present invention provides a method for combining the measurement of trace gas-phase iodine concentration in a containment vessel with the analysis of multiple iodine forms, which can dynamically perform gaseous iodine migration analysis in the gas phase space within the containment vessel and iodine chemical evolution analysis in the water pool, thereby solving the problems of low measurement accuracy and sensitivity of existing low-concentration trace gas-phase iodine and the inability to comprehensively analyze multiple iodine forms at the same time.

[0008] To achieve the above purpose, the technical solution adopted by the present invention is:

[0009] A method for combining the measurement of trace gas-phase iodine concentration in a containment vessel with the analysis of multiple iodine forms is provided, comprising the following steps:

[0010] S1: preparing and selecting alkaline absorption liquid: preparing different types of alkaline absorption liquid, and detecting the iodine content in the alkaline absorption liquid by inductively coupled plasma mass spectrometry, comparing the iodine absorption performance of each alkaline absorption liquid, and determining the absorption error;

[0011] S2: Collect trace gaseous iodine and liquid iodine samples: use a gas washing bottle filled with alkaline absorption liquid to absorb the gaseous iodine in the containment at different times and in different areas; use a liquid iodine sampling bottle to collect and store the liquid iodine in the pit water at different times;

[0012] S3: Establishing an iodine concentration standard curve: preparing iodine standard substance use solutions of different concentrations, and sequentially detecting each iodine standard substance use solution by an inductively coupled plasma mass spectrometer to obtain an iodine concentration standard curve;

[0013] S4: Measurement of gas-phase iodine samples: Use an inductively coupled mass spectrometer to measure the samples in turn, use a standard curve to quantitatively analyze the measurement results, and obtain the iodine concentration in the absorption liquid. Then, the total amount of gas-phase iodine is obtained by dividing the absorption liquid volume by the extracted gaseous iodine volume.

[0014] S5: Establish an iodine form-concentration standard curve: prepare iodine solutions and KI solutions of different concentrations with pure water, and use a spectrophotometer to detect the iodine solutions of different concentrations in turn to obtain a linear curve of the absorbance values ​​of the solutions of each concentration at 203nm, 226nm, and 288nm;

[0015] S6: Liquid iodine sample measurement: The liquid iodine samples of the pit water collected at different times were measured using an ultraviolet spectrophotometer, and the absorbance values ​​at the absorption wavelengths of 203nm, 226nm, and 288nm were recorded. According to the iodine form standard curve, I2, I - , I3 - concentration value.

[0016] The beneficial effects of the above technical solution are as follows: in step S1, the configuration and selection of alkaline absorption liquid is the key to the measurement of trace gas phase iodine concentration. By configuring different types of alkaline absorption liquids and detecting the iodine content in these absorption liquids by inductively coupled plasma mass spectrometry (ICP-MS), the optimal alkaline absorption liquid is confirmed, which can effectively prevent iodine ions (I - ) is converted into iodine (I2), thereby ensuring the accuracy of the measurement of trace gaseous iodine; in step S2, by collecting gaseous iodine in different areas and at different times in the same containment and liquid iodine in the pit water, wherein the gaseous iodine is absorbed by a gas washing bottle filled with alkaline absorption liquid, ensuring that the gaseous iodine (I2) is quickly converted into iodine ions (I - ); in step S3, by preparing iodine standard substance use solutions of different concentrations, and using ICP-MS to detect these solutions in turn, the corresponding relationship between iodine concentration and measurement signal, that is, iodine concentration standard curve, can be obtained, which can provide a reliable quantitative basis for the subsequent gas-phase iodine sample measurement; in step S4, the sample is measured by ICP-MS, and the measurement results are quantitatively analyzed by the standard curve to obtain the iodine element concentration in the absorption liquid, and then the total amount of gas-phase iodine can be calculated by combining the absorption liquid volume and the extracted gaseous iodine volume, so as to achieve accurate measurement of trace gas-phase iodine concentration in the containment; in step S5, by drawing a linear curve between absorbance value and iodine concentration, an iodine form-concentration standard curve is obtained, which can provide an analysis basis for the subsequent liquid-phase iodine sample measurement; in step S6, according to the iodine form-concentration standard curve, the measured absorbance value is substituted into the curve, and different forms of iodine (I2, I3) in the pit water can be obtained. - 、I3 - At the same time, the total iodine concentration in the pit water can be measured by inductively coupled plasma mass spectrometry, and then the iodate ion (IO3 - ) concentration, thereby achieving accurate analysis of various iodine forms in pit water.

[0017] The method for measuring trace gas phase iodine concentration uses alkaline absorption liquid to suppress the iodide ion (I - ) is converted into iodine (I2), which ensures the stability of iodine during the measurement process. It is then detected by inductively coupled plasma mass spectrometry (ICP-MS), which can accurately measure the iodine content in the absorption liquid and thus accurately calculate the concentration of gas-phase iodine. The iodine speciation analysis method can simultaneously determine the I2 in the pit water. - 、I3 - IO3 -and I2 and other forms; the combined method of trace gas-phase iodine concentration measurement and multiple iodine form analysis can monitor the gas-phase iodine concentration in different areas and at different times in the containment and the iodine form changes in the pit liquid pool in real time, which is beneficial to understand the migration law of gas-phase iodine and the iodine chemical evolution process in the pit liquid pool, and the combined method can comprehensively reflect the distribution of iodine elements in the containment, including gas-phase iodine concentration and multiple iodine forms in the pit liquid pool, which provides important reference information for nuclear safety monitoring and accident response. At the same time, after a nuclear accident occurs, the combined method can provide detailed gas-phase iodine concentration and iodine form data, which is beneficial to analyze the cause of the accident, evaluate the consequences of the accident and formulate response measures.

[0018] Furthermore, S1 specifically includes the following steps:

[0019] S11: Prepare (NH4)2CO3 with a mass percentage concentration of 1% by adding 1.00 g of 3(NH4)2CO3 solid to a 100 mL container, dissolve it in ultrapure water to a volume of 100 ml, stir evenly, filter it with a 0.45 μm microporous filter membrane, and transfer it to a brown reagent bottle for storage;

[0020] S12: Prepare 1% NH3·H2O by mass percentage: measure 100 ml of 1% ammonia solution by mass fraction and store it in a brown reagent bottle;

[0021] S13: Prepare a NaOH solution with a mass percentage concentration of 1% by adding 1.00 g of NaOH solid to a 100 mL container, dissolve it in ultrapure water to make up to 100 ml, stir evenly, filter it with a 0.45 μm microporous filter membrane, and transfer it to a brown reagent bottle for storage;

[0022] S14: Prepare C4H with a mass percentage concentration of 1% 13 NO solution: Add 4 mL of 25% solution to 96 mL of ultrapure water, stir evenly, and transfer to a brown reagent bottle for later use:

[0023] S15: 0.2 g of elemental iodine was dissolved in the above absorption liquids, and the iodine content in different absorption liquids was detected by inductively coupled plasma mass spectrometry, and the absorption performance was compared. The C4H4O3 with a mass percentage concentration of 1% was selected. 13 NO solution is used as a standard alkaline solution for collecting trace gas-phase iodine.

[0024] The beneficial effects of the above technical solution are as follows: by comparing tetramethylammonium hydroxide (C4H 13The iodine absorption performance of four different alkaline absorption liquids, namely, 1% C4H2O ... 13 NO solution is the best standard alkaline solution for collecting trace gas-phase iodine, C4H 13 The molecular structure and chemical properties of NO make it have a stronger ability to capture and stabilize iodine, which can effectively inhibit the iodine ion (I - ) is converted into elemental iodine (I2), ensuring that iodine exists in the absorption liquid in the form of stable iodide ions.

[0025] Furthermore, S3 specifically includes the following steps:

[0026] S31: Prepare a solution with a mass concentration of 10 mg / L: measure a stock solution of a standard iodine substance with a mass concentration of 1000 mg / L, place it in a 10 mL volumetric flask, and dilute it with ultrapure water to obtain an iodine intermediate solution with a mass concentration of 100 mg / L; then measure the iodine intermediate solution with a mass concentration of 100 mg / L, place it in a 10 mL volumetric flask, and dilute it with ultrapure water to obtain an iodine solution with a mass concentration of 10 mg / L;

[0027] S32: 0.00, 0.10, 0.50, 1.00, 2.00, 5.00, 8.00, and 10.00 mL of iodine solution with a mass concentration of 10 mg / L are respectively measured and put into 8 10 mL volumetric flasks, and ultrapure water is added to each volumetric flask to make up the volume, and after stirring evenly, iodine standard substance working solutions with iodine contents of 0.0, 0.1, 0.5, 1.0, 2.0, 5.0, 8.0, and 10.0 mg / L are obtained, and after stirring evenly, the solutions are transferred to brown polyethylene bottles and refrigerated for storage;

[0028] S33: using an inductively coupled plasma mass spectrometer to detect the iodine standard substance use solutions in sequence, and repeating the measurement 3 times for each solution; obtaining the calibration equation and linear correlation coefficient of the iodine element this time.

[0029] The beneficial effects of adopting the above technical solution are as follows: the iodine content can be quantitatively analyzed through the iodine concentration standard curve, that is, the measured signal value can be converted into the actual concentration value of the iodine element, thereby improving the measurement accuracy; and in the reactor containment, by regularly measuring the concentrations of gaseous iodine and liquid iodine and analyzing them with reference to the iodine concentration standard curve, abnormal changes in iodine concentration can be discovered in time, providing support for severe accident management.

[0030] Furthermore, the calculation formula for the total amount of gas phase iodine in S4 is:

[0031]

[0032] Among them, C 气体 is the concentration of total iodine in the gas phase; C 液体 is the iodine concentration in the alkaline absorption solution; V 液体 is the volume of alkaline absorption liquid; V 气体 is the volume of gaseous iodine collected.

[0033] The beneficial effect of adopting the above technical solution is: by collecting gas-phase iodine samples from different regions and at different times, the total amount of gas-phase iodine in each region can be accurately calculated using the formula, which is conducive to comprehensive and accurate measurement of trace gas-phase iodine concentration.

[0034] Furthermore, S5 specifically includes the following steps:

[0035] S51: Prepare a linear standard curve of I2 absorbance-concentration: prepare iodine (I2) solutions with mass concentrations of 5.08, 10.15, 15.23, 20.30, 25.38, 30.46, 35.53, 40.61, 45.68, and 50.76 mg / L respectively with ultrapure water, detect the iodine solutions of the above concentrations in turn with a spectrophotometer, obtain the ultraviolet absorption spectrum of the iodine (I2) solution at each concentration, take the absorbance at the absorption wavelength of 203 nm as the ordinate, and the iodine solution concentration as the abscissa, and obtain the linear curve value of I2 concentration-absorbance at 203 nm;

[0036] S52: Production I - Absorbance-concentration linear standard curve: ultrapure water was used to prepare I with concentrations of 1.27, 2.54, 3.81, 5.08, 6.35, 7.61, 8.88, 10.15, 11.42, and 12.69 mg / L, respectively. - The above concentrations of I were detected in turn by spectrophotometer. - Solution, to obtain each concentration of I - The ultraviolet absorption spectrum of the solution is based on the absorbance at the absorption wavelength of 226nm as the ordinate, I - The solution concentration is the horizontal axis, and I - Concentration - linear curve value of absorbance at 226nm;

[0037] S53: Make I3 - Absorbance-concentration linear standard curve: Prepare iodine (I2) standard solutions with concentrations of 5, 10, 50, and 100 μmol / L and dissolve them in 500 μmol / L KI solution respectively. Measure the spectra of these four mixed solutions at 288 nm. Take the absorbance at the absorption wavelength of 288 nm as the ordinate. The I3 generated after the chemical reaction - The mass concentration of the solution is plotted as the horizontal axis, and the absorbance I3 at 288nm in the spectrum of the mixed solution is obtained.- Linear curve of solution concentration.

[0038] The beneficial effects of the above technical solution are as follows: based on the Lambert-Beer law, that is, the relationship between absorbance and concentration is proportional, by measuring the absorbance of the sample at a specific wavelength and comparing it with the standard curve, the actual concentration of the iodine form in the sample can be obtained. Steps S51 to S53 establish I2, I - 、I3 - The standard curve between concentration and absorbance at a specific wavelength can realize the accurate determination of the concentration of iodine forms in unknown samples collected in the containment. This method has high accuracy and precision and can realize the accurate analysis of various iodine forms in the pit fluid in the containment, thereby understanding the iodine chemical reaction process in the pit.

[0039] Furthermore, the calculation formula for the total iodine concentration in the pit in S6 is:

[0040]

[0041] in, is the iodate ion concentration in the pit; C I is the original source concentration in the pit; is the I obtained based on the form-concentration standard curve - concentration, is the I2 concentration obtained based on the form-concentration standard curve, I3 is obtained based on the form-concentration standard curve - concentration.

[0042] The beneficial effects of adopting the above technical solution are: the formula takes into account the various forms of iodine (I - , I2, I3 - and io3 - ), which can comprehensively reflect the chemical forms of iodine in the pit and help to understand the distribution and transformation of different forms of iodine in the pit.

[0043] In summary, the combined method for measuring trace gas-phase iodine concentration in a containment vessel and analyzing multiple iodine forms provided by the present invention has the following beneficial effects:

[0044] (1) This combined method has higher testing efficiency and is suitable for batch sample testing. By introducing gaseous iodine I2 into the alkaline absorption liquid, the conversion of I2 to I2 by each alkaline solution is compared. - The effect of adding C4H 13 NO solution can successfully convert 95% of gas-phase iodine into iodide ions (I -), the iodide ion concentration measured under experimental conditions was 1.867 mg / L, while the theoretical value was 1.96 mg / L, with a measurement error of only about 4.7%. This extremely low error indicates that C4H 13 The NO solution has higher accuracy and reliability in absorbing gaseous iodine and preventing iodine from volatilizing, and the detection limit of the present invention can be as low as 0.01 μg / g, and the precision and accuracy are significantly improved. It is particularly suitable for high-sensitivity detection of trace gaseous iodine in the containment (in the range of 0.01 to 10 μg / g).

[0045] (2) The iodine forms of the pit water measured by this combined method include iodine ions I - 、Iodine trianion I3 - , iodate ion IO3 - , iodine I2 and other forms. The determined iodine forms are accurate and comprehensive, which is conducive to clarifying the iodine chemical reaction process in the pit and is of great significance for evaluating the environmental behavior and migration path of iodine after the accident. In addition, the detection method has high sensitivity, is not affected by other impurities in the water sample and factors such as chromaticity, and has better practicality.

[0046] (3) The experimental system of the combined method is based on the same containment reaction system, integrating the measurement and analysis of gas phase and liquid phase iodine, ensuring the high consistency of experimental parameters (such as temperature, pressure, humidity, etc.), thereby avoiding the experimental deviation caused by system differences, and by monitoring the dynamic migration behavior of iodine under spraying conditions (including generation, migration and removal), the behavior mechanism of volatile iodine in a complex environment is fully revealed. This method not only enhances the depth of iodine behavior research, but also provides a high-precision experimental basis for accurate evaluation of iodine behavior after accidents and severe accident management. In addition, the present invention pays more attention to the unity of experimental conditions and the dynamic nature of data, which is an important breakthrough in the field of iodine behavior research. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 is a schematic diagram of the method of the present invention;

[0048] Figure 2 It is a standard curve diagram of the concentration of the iodine standard solution in the present invention;

[0049] Figure 3 Spectra of I2 solutions at different concentrations in the present invention;

[0050] Figure 4 I - Spectrum of the solution;

[0051] Figure 5 I3 at different concentrations in the present invention - Spectrum of the solution;

[0052] Figure 6It is a linear curve graph of I2 concentration-absorbance at 203nm in the present invention;

[0053] Figure 7 In the present invention, - Linear curve of concentration-absorbance at 226nm;

[0054] Figure 8 I3 in the present invention - Linear curve of concentration-absorbance at 288nm DETAILED DESCRIPTION

[0055] The specific implementation modes of the present invention are described below so that those skilled in the art can understand the present invention. However, it should be clear that the present invention is not limited to the scope of the specific implementation modes. For those of ordinary skill in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the attached claims, these changes are obvious, and all inventions and creations utilizing the concept of the present invention are protected.

[0056] like Figure 1 As shown, the method provided by the present invention for combining the measurement of trace gas-phase iodine concentration in a containment with the analysis of multiple iodine forms comprises the following steps:

[0057] S1: preparing and selecting alkaline absorption liquid: preparing different types of alkaline absorption liquid, and detecting the iodine content in the alkaline absorption liquid by inductively coupled plasma mass spectrometry, comparing the iodine absorption performance of each alkaline absorption liquid, and determining the absorption error;

[0058] S2: Collect trace gaseous iodine and liquid iodine samples: use a gas washing bottle filled with alkaline absorption liquid to absorb the gaseous iodine in the containment at different times and in different areas; use a liquid iodine sampling bottle to collect and store the liquid iodine in the pit water at different times;

[0059] S3: Establishing an iodine concentration standard curve: preparing iodine standard substance use solutions of different concentrations, and sequentially detecting each iodine standard substance use solution by an inductively coupled plasma mass spectrometer to obtain an iodine concentration standard curve;

[0060] S4: Measurement of gas-phase iodine samples: Use an inductively coupled mass spectrometer to measure the samples in turn, use a standard curve to quantitatively analyze the measurement results, and obtain the iodine concentration in the absorption liquid. Then, the total amount of gas-phase iodine is obtained by dividing the absorption liquid volume by the extracted gaseous iodine volume.

[0061] S5: Establish an iodine form-concentration standard curve: prepare iodine solutions and KI solutions of different concentrations with pure water, and use a spectrophotometer to detect the iodine solutions of different concentrations in turn to obtain a linear curve of the absorbance values ​​of the solutions of each concentration at 203nm, 226nm, and 288nm;

[0062] S6: Liquid iodine sample measurement: The liquid iodine samples of the pit water collected at different times were measured using an ultraviolet spectrophotometer, and the absorbance values ​​at the absorption wavelengths of 203nm, 226nm, and 288nm were recorded. According to the iodine form standard curve, I2, I - , I3 - concentration value.

[0063] In step S1, configuring and selecting the alkaline absorption liquid specifically includes the following steps:

[0064] S11: Prepare (NH4)2CO3 with a mass percentage concentration of 1% by adding 1.00 g of (NH4)2CO3 solid to a 100 mL container, dissolve it in ultrapure water to a volume of 100 ml, stir evenly, filter it with a 0.45 μm microporous filter membrane, and transfer it to a brown reagent bottle for storage;

[0065] S12: Prepare 1% NH3·H2O by mass percentage: measure 100 ml of 1% ammonia solution by mass fraction and store it in a brown reagent bottle;

[0066] S13: Prepare a NaOH solution with a mass percentage concentration of 1% by adding 1.00 g of NaOH solid to a 100 mL container, dissolve it in ultrapure water to make up to 100 ml, stir evenly, filter it with a 0.45 μm microporous filter membrane, and transfer it to a brown reagent bottle for storage;

[0067] S14: Prepare C4H with a mass percentage concentration of 1% 13 NO solution: Add 4 mL of 25% solution to 96 mL of ultrapure water, stir evenly, and transfer to a brown reagent bottle for later use:

[0068] S15: 0.2 g of elemental iodine was dissolved in the above absorption liquids, and the iodine content in different absorption liquids was detected by inductively coupled plasma mass spectrometry, and the absorption performance was compared. The C4H4O3 with a mass percentage concentration of 1% was selected. 13 NO solution is used as a standard alkaline solution for collecting trace gas-phase iodine.

[0069] The iodine concentrations of different types of alkaline absorption solutions measured according to steps S11 to S15 are shown in Table 1:

[0070] Table 1 Iodine concentration measurement results of different types of alkaline absorption liquid

[0071]

[0072]

[0073] The configuration and selection of alkaline absorption liquid in S1 are the key to the measurement of trace gas-phase iodine concentration. By configuring different types of alkaline absorption liquids and detecting the iodine content in these absorption liquids by inductively coupled plasma mass spectrometry (ICP-MS), it can be seen from Table 1 that C4H 13 The iodine concentration of the NO solution was 1.867 mg / L, which was able to successfully convert 95% of the gas-phase iodine into iodide ions (I - ), the absorption error is 4.7%, which is closest to the theoretical value of 1.96 mg / L (0.2 g of elemental iodine dissolved in 100 ml of absorption solution), and its deviation is significantly lower than that of other solutions, which shows that compared with NaOH (1.352 mg / L), (NH4)2CO3 (1.571 mg / L) and NH3·H2O (1.569 mg / L), C4H 13 Due to its unique molecular structure and chemical properties, NO has a stronger ability to capture and stabilize iodine, which can effectively inhibit the iodine ion (I - ) is converted into volatile iodine (I2), thereby ensuring that iodine exists in the absorption liquid in a stable ionic form, providing a better choice for the collection and analysis of trace gas-phase iodine. The best alkaline absorption liquid is confirmed to be 1% by mass concentration of C4H 13 NO solution can effectively prevent iodide ions (I - ) is converted into elemental iodine (I2), thereby ensuring the accuracy of trace gas-phase iodine measurement.

[0074] In step S2, the gaseous iodine and the liquid iodine in the pit water in different areas and at different times in the same containment are collected, wherein the gaseous iodine is absorbed by a gas washing bottle filled with alkaline absorption liquid, ensuring that the gaseous iodine (I2) is quickly converted into iodide ions (I - ).

[0075] In step S3, establishing an iodine concentration standard curve specifically includes the following steps:

[0076] S31: Prepare a solution with a mass concentration of 10 mg / L: measure a stock solution of a standard iodine substance with a mass concentration of 1000 mg / L, place it in a 10 mL volumetric flask, and dilute it with ultrapure water to obtain an iodine intermediate solution with a mass concentration of 100 mg / L; then measure the iodine intermediate solution with a mass concentration of 100 mg / L, place it in a 10 mL volumetric flask, and dilute it with ultrapure water to obtain an iodine solution with a mass concentration of 10 mg / L;

[0077] S32: 0.00, 0.10, 0.50, 1.00, 2.00, 5.00, 8.00, and 10.00 mL of iodine solution with a mass concentration of 10 mg / L are respectively measured and put into 8 10 mL volumetric flasks, and ultrapure water is added to each volumetric flask to make up the volume, and after stirring evenly, iodine standard substance working solutions with iodine contents of 0.0, 0.1, 0.5, 1.0, 2.0, 5.0, 8.0, and 10.0 mg / L are obtained, and after stirring evenly, the solutions are transferred to brown polyethylene bottles and refrigerated for storage;

[0078] S33: The iodine standard substance solutions are detected in sequence by an inductively coupled plasma mass spectrometer, and each solution is measured three times to obtain a standard curve of the iodine standard solution concentration of the iodine element.

[0079] The standard curve of the iodine standard solution concentration of this iodine element is as follows Figure 2 As shown, by establishing an iodine concentration standard curve, the iodine content can be quantitatively analyzed, that is, the measured signal value can be converted into the true concentration value of the iodine element, thereby improving the measurement accuracy. In addition, in the reactor containment, by regularly measuring the concentrations of gaseous iodine and liquid iodine and analyzing them with reference to the iodine concentration standard curve, abnormal changes in iodine concentration can be discovered in time, providing support for severe accident management.

[0080] In step S4, the sample is measured using ICP-MS, and the measurement results are quantitatively analyzed using a standard curve to obtain the iodine concentration in the absorption liquid. The measured iodine concentration of the absorption liquid is corrected by combining the absorption error, the volume of the absorption liquid, and the volume of the extracted gaseous iodine to obtain the true gas-phase iodine concentration, which is then combined with the following formula:

[0081] The total amount of gas-phase iodine can be calculated, thereby achieving accurate measurement of the trace gas-phase iodine concentration in the containment.

[0082] In step S5, establishing an iodine form-concentration standard curve specifically includes the following steps:

[0083] S51: Prepare a linear standard curve of I2 absorbance-concentration: prepare iodine (I2) solutions with mass concentrations of 5.08, 10.15, 15.23, 20.30, 25.38, 30.46, 35.53, 40.61, 45.68, and 50.76 mg / L respectively with ultrapure water, detect the iodine solutions of the above concentrations in turn with a spectrophotometer, obtain the ultraviolet absorption spectrum of the iodine (I2) solution at each concentration, take the absorbance at the absorption wavelength of 203 nm as the ordinate, and the iodine solution concentration as the abscissa, and obtain a standard curve of I2 concentration-absorbance at 203 nm;

[0084] S52: Production I -Absorbance-concentration linear standard curve: ultrapure water was used to prepare I with mass concentrations of 1.27, 2.54, 3.81, 5.08, 6.35, 7.61, 8.88, 10.15, 11.42, and 12.69 mg / L, respectively. - The above concentrations of I were detected in turn by spectrophotometer. - Solution, to obtain each concentration of I - The ultraviolet absorption spectrum of the solution is based on the absorbance at the absorption wavelength of 226nm as the ordinate, I - The solution concentration is the horizontal axis, and I - Standard curve of concentration-absorbance at 226nm;

[0085] S53: Make I3 - Absorbance-concentration linear standard curve: Prepare iodine (I2) standard solutions with concentrations of 5, 10, 50, and 100 μmol / L and dissolve them in 500 μmol / L KI solution respectively. Measure the spectra of these four mixed solutions at 288 nm. Take the absorbance at the absorption wavelength of 288 nm as the ordinate. The I3 generated after the chemical reaction - The mass concentration of the solution is plotted as the horizontal axis, and the absorbance at 288nm in the spectrum of the mixed solution is obtained -I3 - Standard curve of solution concentrations.

[0086] The spectrum of I2 solution prepared by S51 is as follows: Figure 3 As shown in the figure, the ordinate is the absorbance value and the abscissa is the wavelength. Figure 3 As shown in the figure, the higher the I2 concentration, the larger the corresponding absorbance value at 203nm (the curve goes from bottom to top). The absorbance value is proportional to the concentration value, so by measuring the absorbance values ​​of iodine I2 solutions of different concentrations at 203nm, we can fit the following: Figure 6 The linear standard curve of I2 concentration-absorbance at 203nm is shown.

[0087] I made from S52 - The spectrum of the solution is Figure 4 As shown in the figure, the ordinate is the absorbance value and the abscissa is the wavelength. Figure 4 As shown, with I - As the concentration increases, the absorbance values ​​at 193nm and 226nm gradually increase (the curve goes from bottom to top). Since 190nm is the lower limit of the UV spectrophotometer, the absorbance value at a wavelength of 226nm is selected as the measurement value. - The optimal wavelength for concentration can therefore be measured by measuring different I - The absorbance value of the concentration solution at 226nm is fitted as follows Figure 7 I -Linear standard curve of concentration-absorbance at 226nm.

[0088] I3 made from S53 - The spectrum of the mixed solution is shown in Figure 5 As shown in the figure, the ordinate is the absorbance value and the abscissa is the wavelength. Figure 5 As shown, with I3 - As the concentration increases, the absorbance values ​​at 288nm and 353nm gradually increase. - As the concentration increases, the absorption peak at 288nm changes more significantly, so the absorbance value at a wavelength of 288nm is selected as the determination of I3 - The optimal wavelength for concentration can therefore be measured by measuring different I3 - The absorbance value of the concentration solution at 288nm is fitted as follows Figure 8 I3 shown - Linear standard curve of concentration-absorbance at 288nm.

[0089] Step S5 is based on the Lambert-Beer law, that is, the relationship between absorbance and concentration is proportional. By measuring the absorbance of the sample at a specific wavelength and comparing it with the standard curve, the actual concentration of the iodine form in the sample can be obtained. Steps S51 to S53 establish I2, I - 、I3 - The standard curve between the concentration and the absorbance of the collected pit liquid phase iodine samples at various wavelengths is then measured, combined with the following Figure 3 to Figure 8 The spectrum and standard curve shown can be used to derive the concentration of the corresponding iodine form, thereby realizing the accurate determination of the iodine form concentration in the unknown sample collected in the containment. This method has high accuracy and precision, and can realize the accurate analysis of various iodine forms in the pit fluid in the containment, thereby understanding the iodine chemical reaction process in the pit.

[0090] In step S6, according to the iodine form-concentration standard curve, the measured absorbance value is substituted into the curve to obtain the different forms of iodine (I2, I - 、I3 - At the same time, the total iodine concentration in the pit water can also be measured by inductively coupled plasma mass spectrometry, combined with the formula:

[0091]

[0092] Calculate the iodate ion (IO3 - ) concentration, thereby achieving accurate analysis of various iodine forms in pit water.

[0093] Example 1

[0094] Based on the combined method for measuring trace gas-phase iodine concentration in a containment vessel and analyzing multiple iodine forms provided by the present invention, this embodiment tests the dynamic process of 0.5 g of solid elemental iodine reacting in a containment vessel, specifically comprising the following steps:

[0095] Step 1: Initial iodine source injection: at 0.2 m 3 0.5g of solid iodine is added to a tank container of 1.56 million cubic meters in volume. The solid iodine is heated to completely evaporate into iodine vapor. At this time, the initial iodine vapor concentration in the tank is 2.5g / m 3 ;

[0096] Step 2: Spray to remove iodine vapor: Use the spray system in the tank container to spray to remove the iodine vapor in the container, and the spray time is 10 minutes;

[0097] Step 3: Prepare alkaline absorption solution: Prepare C4H 13 NO solution: add 4 mL of 25% solution to 96 mL of ultrapure water, stir well, and transfer to a brown reagent bottle for later use;

[0098] Step 4: Collect trace gas phase iodine sample: Use 25 ml of C4H 13 The NO solution scrubber absorbs the gaseous iodine in the containment;

[0099] Step 5: Collecting liquid iodine samples: using a liquid iodine sampling bottle to collect and preserve the liquid iodine in the pit water;

[0100] Step 6: Measurement of gas-phase iodine samples: The samples were measured using an inductively coupled mass spectrometer, combining the standard curve of the iodine standard solution concentration with the C4H 13 The absorption error measurement results of NO alkaline absorption liquid were quantitatively analyzed to obtain the iodine concentration in the absorption liquid of 0.10 mg / L. The gas phase iodine concentration was obtained by dividing the absorption liquid volume (25 ml) by the volume of gaseous iodine extracted (50 ml) to 0.04 g / m 3 ;

[0101] Step 7: Measurement of iodine forms in liquid iodine sample: The sample was measured using a spectrophotometer to obtain the spectra of the pit water solution at each wavelength. The absorbance at 203nm was 0.65, the absorbance at 226nm was 1.09, and the absorbance at 288nm was 0.04. Based on the above linear curves of iodine forms and absorbance at each wavelength, the I2 concentration in the pit water solution was 8.66 mg / L, I - The concentration is 10.42 mg / L, I3 - The concentration is 0.12 mg / L;

[0102] Step 8: Measurement of the total amount of iodine in the liquid iodine sample: The liquid iodine was measured using an inductively coupled mass spectrometer, and the iodine element (I) concentration in the pit water solution was found to be 48.60 mg / L. The iodate ion (IO3 - ) concentration is 20.5 mg / L.

[0103] This embodiment can be used to simulate the environment inside the containment and test the reaction dynamic process of 0.5g solid elemental iodine under specific conditions, including the production of iodine vapor, spray removal, and subsequent measurement and analysis of gas and liquid phase iodine. Step 1 simulates the initial state of the initial iodine source in the containment. By heating the solid elemental iodine, it is completely evaporated into iodine vapor, so that a certain iodine vapor concentration is formed in the tank container. According to the mass of iodine added and the volume of the container, it can be concluded that the initial iodine vapor concentration is 2.5g / m 3 ; Step 2 simulates the removal process of iodine vapor by the spray system in the containment. The spray system can absorb and remove iodine vapor by spraying alkaline solution, ensuring that iodine vapor can be fully removed; C4H 13 NO solution was selected as the standard alkaline solution because of its strong ability to capture and stabilize iodine, which can ensure its stability and effectiveness during use; Step 4 and Step 5 collected gaseous and liquid iodine samples respectively. The gaseous iodine sample was filled with a 1% mass percentage concentration of C4H 13 The washing bottle of NO solution is used to absorb the gaseous iodine remaining in the tank container, and the liquid iodine sample is collected from the pit water through the sampling bottle to analyze the liquid iodine form that may be generated during the spraying process; step 6 uses an inductive ion coupled mass spectrometer to measure the gaseous iodine sample, and compares it with the standard curve of the iodine standard solution concentration to obtain the iodine element concentration in the absorption liquid, thereby reflecting the gaseous iodine content remaining in the tank container after spraying; steps 7 and 8 use an ultraviolet spectrophotometer to measure the collected liquid iodine sample of the pit water, and record the absorbance values ​​at the absorption wavelengths of 203nm, 226nm, and 288nm, respectively, and according to the iodine form-concentration standard curve established previously, the different forms of iodine (I2, I3) in the pit water are obtained. - 、I3 - At the same time, in combination with steps 4 to 8, by using gas-phase iodine and liquid-phase iodine samples in different areas and at different times in the tank container, the distribution of gas-phase iodine in the space inside the containment and its changing trend over time can be fully understood, and the migration law of gas-phase iodine in the containment can be fully understood, which is conducive to understanding its behavioral characteristics in the containment, and by real-time monitoring of the concentration and distribution of gas-phase iodine, key data support can be provided for severe accident management; and by collecting and analyzing the liquid-phase iodine in the pit water at different times, the different forms of iodine (such as I2, I - 、I3- etc.), which helps to understand the chemical evolution of iodine in water.

[0104] In summary, the method for measuring trace gas-phase iodine concentration in containment and analyzing various iodine forms provided by the present invention is based on the same containment reaction system, which ensures the high consistency of experimental parameters (such as temperature, pressure, humidity, etc.), thereby avoiding the experimental deviation caused by system differences, and accurately monitoring the dynamic distribution of gas-phase and liquid-phase iodine, especially the migration behavior under spraying conditions, to reveal the generation, migration and removal mechanism of volatile iodine. This method not only enhances the depth of iodine behavior research, but also provides a high-precision experimental basis for evaluation and accident management.

Claims

1. A method for combining the measurement of trace gas-phase iodine concentration in a containment vessel with the analysis of multiple iodine forms, characterized in that: The following steps are involved: S1: preparing and selecting alkaline absorption liquid: preparing different types of alkaline absorption liquid, and detecting the iodine content in the alkaline absorption liquid by inductively coupled plasma mass spectrometry, comparing the iodine absorption performance of each alkaline absorption liquid, and determining the absorption error; S2: Collect trace gaseous iodine and liquid iodine samples: use a gas washing bottle filled with alkaline absorption liquid to absorb the gaseous iodine in the containment at different times and in different areas; use a liquid iodine sampling bottle to collect and store the liquid iodine in the pit water at different times; S3: Establishing an iodine concentration standard curve: preparing iodine standard substance use solutions of different concentrations, and sequentially detecting each iodine standard substance use solution by an inductively coupled plasma mass spectrometer to obtain an iodine concentration standard curve; S4: Measurement of gas-phase iodine samples: Use an inductively coupled mass spectrometer to measure the samples in turn, use a standard curve to quantitatively analyze the measurement results, and obtain the iodine concentration in the absorption liquid. Then, the total amount of gas-phase iodine is obtained by dividing the absorption liquid volume by the extracted gaseous iodine volume. S5: Establish an iodine form-concentration standard curve: prepare iodine solutions and KI solutions of different concentrations with pure water, and use a spectrophotometer to detect the iodine solutions of different concentrations in turn to obtain a linear curve of the absorbance values ​​of the solutions of each concentration at 203nm, 226nm, and 288nm; S6: Liquid iodine sample measurement: The liquid iodine samples of the pit water collected at different times were measured using an ultraviolet spectrophotometer, and the absorbance values ​​at the absorption wavelengths of 203nm, 226nm, and 288nm were recorded. According to the iodine form standard curve, I2, I - , I3 - concentration value.

2. The method for combining the measurement of trace gas-phase iodine concentration in a containment vessel with the analysis of multiple iodine forms according to claim 1, characterized in that: The S1 specifically includes the following steps: S11: Prepare (NH4)2CO3 with a mass percentage concentration of 1% by adding 1.00 g of (NH4)2CO3 solid to a 100 mL container, dissolve it in ultrapure water to a volume of 100 ml, stir evenly, filter it with a 0.45 μm microporous filter membrane, and transfer it to a brown reagent bottle for storage; S12: Prepare 1% NH3·H2O by mass percentage: measure 100 ml of 1% ammonia solution by mass fraction and store it in a brown reagent bottle; S13: Prepare a NaOH solution with a mass percentage concentration of 1% by adding 1.00 g of NaOH solid to a 100 mL container, dissolve it in ultrapure water to make up to 100 ml, stir evenly, filter it with a 0.45 μm microporous filter membrane, and transfer it to a brown reagent bottle for storage; S14: Prepare C4H with a mass percentage concentration of 1% 13 NO solution: Add 4 mL of 25% solution to 96 mL of ultrapure water, stir evenly, and transfer to a brown reagent bottle for later use: S15: 0.2 g of elemental iodine was dissolved in the above absorption liquids, and the iodine content in different absorption liquids was detected by inductively coupled plasma mass spectrometry, and the absorption performance was compared. The C4H4O3 with a mass percentage concentration of 1% was selected. 13 NO solution is used as a standard alkaline solution for collecting trace gas-phase iodine.

3. The method for combining the measurement of trace gas-phase iodine concentration in a containment vessel with the analysis of multiple iodine forms according to claim 1, characterized in that: The S3 specifically includes the following steps: S31: Prepare a solution with a mass concentration of 10 mg / L: measure a stock solution of a standard iodine substance with a mass concentration of 1000 mg / L, place it in a 10 mL volumetric flask, and dilute it with ultrapure water to obtain an iodine intermediate solution with a mass concentration of 100 mg / L; then measure the iodine intermediate solution with a mass concentration of 100 mg / L, place it in a 10 mL volumetric flask, and dilute it with ultrapure water to obtain an iodine solution with a mass concentration of 10 mg / L; S32: 0.00, 0.10, 0.50, 1.00, 2.00, 5.00, 8.00, and 10.00 mL of iodine solution with a mass concentration of 10 mg / L are respectively measured and put into 8 10 mL volumetric flasks, and ultrapure water is added to each volumetric flask to make up the volume, and after stirring evenly, iodine standard substance working solutions with iodine contents of 0.0, 0.1, 0.5, 1.0, 2.0, 5.0, 8.0, and 10.0 mg / L are obtained, and after stirring evenly, the solutions are transferred to brown polyethylene bottles and refrigerated for storage; S33: using an inductively coupled plasma mass spectrometer to detect the iodine standard substance use solutions in sequence, and repeating the measurement 3 times for each solution; obtaining the calibration equation and linear correlation coefficient of the iodine element this time.

4. The method for combining the measurement of trace gas-phase iodine concentration in a containment vessel with the analysis of multiple iodine forms according to claim 1, characterized in that: The calculation formula for the total amount of gas phase iodine in S4 is: Among them, C 气体 is the concentration of total iodine in the gas phase; C 液体 is the iodine concentration in the alkaline absorption solution; V 液体 is the volume of alkaline absorption liquid; V 气体 is the volume of gaseous iodine collected.

5. The method for combining the measurement of trace gas-phase iodine concentration in a containment vessel with the analysis of multiple iodine forms according to claim 1, characterized in that: The S5 specifically includes the following steps: S51: Prepare a linear standard curve of I2 absorbance-concentration: prepare iodine (I2) solutions with mass concentrations of 5.08, 10.15, 15.23, 20.30, 25.38, 30.46, 35.53, 40.61, 45.68, and 50.76 mg / L respectively with ultrapure water, detect the iodine solutions of the above concentrations in turn with a spectrophotometer, obtain the ultraviolet absorption spectrum of the iodine solution at each concentration, take the absorbance at the absorption wavelength of 203 nm as the ordinate, and the iodine solution concentration as the abscissa, and obtain the linear curve value of I2 concentration-absorbance at 203 nm; S52: Production I - Absorbance-concentration linear standard curve: ultrapure water was used to prepare I with concentrations of 1.27, 2.54, 3.81, 5.08, 6.35, 7.61, 8.88, 10.15, 11.42, and 12.69 mg / L, respectively. - The above concentrations of I were detected in turn by spectrophotometer. - Solution, to obtain each concentration of I - The ultraviolet absorption spectrum of the solution is based on the absorbance at the absorption wavelength of 226nm as the ordinate, I - The solution concentration is the horizontal axis, and I - Concentration - linear curve value of absorbance at 226nm; S53: Make I3 - Absorbance-concentration linear standard curve: Prepare iodine (I2) standard solutions with concentrations of 5, 10, 50, and 100 μmol / L and dissolve them in 500 μmol / L KI solution respectively. Measure the spectra of these four mixed solutions at 288 nm. Take the absorbance at the absorption wavelength of 288 nm as the ordinate and the I3 generated by the chemical reaction as the ordinate. - The concentration is plotted as the horizontal axis, and the absorbance I3 at 288nm in the spectrum of the mixed solution is obtained. - Linear curve of solution concentration.

6. The method for combining the measurement of trace gas-phase iodine concentration in a containment vessel with the analysis of multiple iodine forms according to claim 1, characterized in that: The calculation formula for the total iodine concentration in the pit in S6 is: in, is the iodate ion concentration in the pit; C I is the original source concentration in the pit; is the I obtained based on the form-concentration standard curve - concentration, is the I2 concentration obtained based on the form-concentration standard curve, I3 is obtained based on the form-concentration standard curve - concentration.

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