CN114779312A - On-line measurement method of C-14 in gaseous effluent of nuclear power plant - Google Patents

Abstract

The invention relates to an on-line measurement method for C-14 in the gaseous effluent of a nuclear power plant. By automatically sampling the gaseous effluent of the nuclear power plant, a primary filter device is used to remove oil dirt, dust and water vapor in the sampling air flow; Catalytic oxidation converts C-14 in the form of CO, CH ₄ , etc. into CO ₂ ; then the sampled gas flow enters into polymer membrane modules such as molecular sieves to further increase the concentration of CO ₂ in the sampled gas flow; through MOFs material under certain conditions, CO _2. Selective adsorption is carried out. When the adsorption reaches saturation, CO ₂ is separated under certain conditions; finally, the sampled gas flow is fed into the detector to measure the C-14 emission of beta particles, and the C-14 activity concentration in the gaseous effluent is finally completed. Measurement. The on-line measurement method of C-14 in the gaseous effluent of a nuclear power plant disclosed in the invention is safe and stable, and can realize the on-line measurement of C-14.

Description

On-line measurement method of C-14 in gaseous effluent of nuclear power plant

technical field

The invention belongs to the field of radionuclide measurement, in particular to an on-line measurement method for C-14 in gaseous effluent of a nuclear power plant.

Background technique

C-14 is a radioactive isotope of carbon. The half-life is 30 years. A certain amount of C-14 is produced during the operation of nuclear power plants and is released into the environment in the form of gaseous effluents. Due to its long half-life, C-14 has a high residence time and high isotope exchange rate in the environment, and participates in the global carbon cycle. C-14 entering the human body will cause long-term internal exposure damage to humans and is recognized as the nuclide that produces the potential maximum collective dose to the public.

As a by-product in nuclear power production, due to its various special properties, C-14 content has become an important indicator of radioactive environmental monitoring and evaluation in nuclear power plants. There are currently no regulations and standards for on-line monitoring of gaseous effluent C-14 from chimneys of nuclear power plants and other nuclear facilities in my country, and the development of on-line measurement methods and related instruments for C-14 in gaseous effluents is relatively backward.

Nuclear power plants and other nuclear facilities usually use cumulative sampling and monitoring methods for C-14 in the gaseous effluent of chimneys. The most common method is to use solution absorption methods (such as inorganic alkalis, ammonia solutions, organic amine absorbents, etc.) Samples were analyzed for laboratory measurements. C-14 cumulative sampling and laboratory analysis and measurement can only be used to estimate the average emission level and total activity of C-14 in the gaseous effluent of the chimney for a period of time. It is impossible to monitor the instantaneous emission of C-14 through online monitoring. Real-time monitoring of accidental and unplanned emissions of higher activity concentrations of C-14.

Therefore, it is necessary to study an on-line measurement method of C-14 in gaseous effluent of nuclear power plants to solve one of the problems that need to be studied and solved urgently in the field of nuclear power plant operation safety supervision.

SUMMARY OF THE INVENTION

In view of the defects existing in the prior art, the purpose of the present invention is to provide an on-line measurement method for C-14 in the gaseous effluent of a nuclear power plant, so as to realize the on-line measurement of C-14 in the gaseous effluent of the nuclear power plant.

In order to achieve the above purpose, the technical scheme adopted in the present invention is: an on-line measurement method for C-14 in the gaseous effluent of a nuclear power plant, the method comprising the steps:

S1. Continuous sampling of gaseous effluent from nuclear power plants and primary purification and impurity removal;

S2, the sample gas flow after primary purification and impurity removal is catalytically oxidized and converted into a measured gas flow containing CO ₂ gas;

S3, separating and enriching CO ₂ in the measured gas stream containing CO ₂ gas;

S4, adsorb the CO ₂ gas flow after separation and enrichment;

S5. Separating CO ₂ in the MOFs module that has reached the adsorption saturation state, and measuring the formed CO ₂ gas flow, and then calculating the content of C-14.

Further, in step S2, a solid catalyst is used to catalytically oxidize the sample gas stream to convert it into a measured gas stream containing CO ₂ gas.

Further, the solid catalyst is at least one of Pd-Al ₂ O ₃ and Pt-Al ₂ O ₃ .

Further, in step S3, a polymer membrane separation component is used to separate other gases in the sample gas stream, so as to enrich the CO ₂ gas in the sample gas stream.

Further, the polymer membrane is a molecular sieve.

Further, step S4 includes introducing the separated and enriched CO ₂ gas stream into a MOFs component having a specific adsorption function for CO ₂ , and the MOFs component can selectively adsorb CO ₂ under certain conditions.

Further, according to the inherent adsorption capacity of the MOFs component for CO ₂ , it is judged whether the MOFs component reaches the adsorption saturation state.

Further, in step S5, the _CO2 in the MOFs component is separated under certain conditions by analyzing the MOFs component.

Further, in step S5, a PIPS detector is used to measure the beta particles emitted by the decay of C-14 to measure the activity concentration of C-14.

The effect of the present invention is: adopting the on-line measurement method of C-14 in the gaseous effluent of a nuclear power plant disclosed in the present invention, using an air compressor to automatically sample the gaseous effluent of the nuclear power plant, and removing the C-14 in the sampling air flow through a primary filter device Oil pollution, dust and water vapor; the sampled air flow through the primary filter device enters the catalytic oxidation module, and the solid catalyst is used for catalytic oxidation to convert C-14 in the form of CO and CH ₄ into CO ₂ , which improves the online performance of C-14. The stability and safety of the measurement; then the sampling air flow enters the molecular sieve and other polymer membrane modules to further increase the concentration of CO ₂ in the sampling air flow; the CO ₂ is selectively adsorbed by the MOFs material under certain conditions, and when the adsorption reaches saturation, CO ₂ is separated under certain conditions; finally, the gas flow is passed into the PIPS detector measurement box to measure the beta particles emitted by the decay of C-14, and finally the measurement of the C-14 activity concentration in the gaseous effluent is completed.

Description of drawings

FIG. 1 is a method flow chart of a method for on-line measurement of C-14 in gaseous effluent of a nuclear power plant according to Embodiment 1 of the present invention.

Detailed ways

The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

Example 1

As shown in FIG. 1 , an embodiment of the present invention discloses an on-line measurement method for C-14 in gaseous effluent of a nuclear power plant, comprising the following steps:

S1. Sampling and primary purification of gaseous effluent

The gaseous effluent of the nuclear power plant is continuously sampled by equipment such as air compressors, and the intake master valve and flow measurement equipment are used to quantitatively measure the sample gas flow volume. In order to improve the detection accuracy of the C-14 detector, the sample airflow is passed through the primary filter device to remove impurities such as water vapor, oil stains, and dust.

S2. Catalytic oxidation of the sample gas stream after primary purification and impurity removal is converted into CO ₂

The radionuclide C-14 in the sample gas stream mainly exists in the form of compounds such as CO ₂ , CO and CH ₄ . The sample gas stream after primary purification and impurity removal enters the catalytic oxidation module, and through the catalytic oxidation module, other forms of compounds are converted into _CO2 for further concentration and collection. Select solid catalysts such as at least one of Pd-Al ₂ O ₃ and Pt-Al ₂ O ₃ to catalytically oxidize the sample gas stream to convert it into CO ₂ gas. Compared with the open flame combustion method, the catalytic oxidation method improves the measurement system. security and stability. The sample gas stream is then dried with a desiccant to remove the water vapor produced by the catalytic reaction. After the sample gas stream passes through the catalytic oxidation module, the _CO2 concentration is increased.

S3. Separation and enrichment of CO ₂ in the sample gas stream

After sufficient conversion by the catalytic oxidation module, C-14 in the sample gas stream mainly exists in the form of _CO2 . Then it is sent to the membrane separation and enrichment module, and other gases in the sample gas stream are separated by polymer membrane separation components such as molecular sieves, and the CO ₂ gas in it is further enriched and purified.

S4. Adsorb the CO ₂ gas stream after separation and enrichment

The CO ₂ gas stream after separation and enrichment is introduced into a MOFs (Metal organic Framework, metal organic framework material) component that has a specific adsorption function for CO _2. The MOFs component can selectively adsorb CO _{2 under certain conditions, and the CO 2 gas} flow is carried out. of other gaseous impurities are removed.

S5. Separate the CO ₂ that has reached the adsorption saturation state, and measure the formed high-concentration CO ₂ gas stream, and then obtain the content of C-14 through conversion and calculation.

When the adsorption of MOFs components reaches saturation, CO ₂ is desorbed and separated under certain conditions, and then enters the C-14 radioactivity measurement module. Different MOFs components have different desorption conditions.

C-14 is a radioactive isotope of carbon. The half-life is 30 years. The average energy of β rays emitted by decay is 49.47keV. The β-ray emitted by C-14 is usually measured by a β-ray measuring instrument to determine the activity of C-14. At present, C-14 cumulative sampling and laboratory analysis and measurement mostly use liquid scintillator detectors, which cannot be measured online, and will produce scintillation fluid waste. This method selects PIPS (Planar Implanted Passivated Silicon) detector to measure C-14 activity concentration. The C-14-loaded CO ₂ sampled airflow was introduced into the PIPS detector measurement box, and the beta particles emitted by its decay were measured, and the measured values were quantitatively analyzed through the subsequent electronics part and data processing software.

It can be seen from the above-mentioned embodiments that the on-line measurement method of C-14 in the gaseous effluent of a nuclear power plant disclosed in the present invention adopts an air compressor to automatically sample the gaseous effluent of the nuclear power plant, and removes the C-14 in the sampling air flow through a primary filter device. Oil pollution, dust and water vapor; the sampled air flow through the primary filter device enters the catalytic oxidation module, and the solid catalyst is used for catalytic oxidation to convert C-14 in the form of CO and CH ₄ into CO ₂ , which improves the online performance of C-14. The stability and safety of the measurement; then the sampling air flow enters the molecular sieve and other polymer membrane modules to further increase the concentration of CO ₂ in the sampling air flow; the CO ₂ is selectively adsorbed by the MOFs material under certain conditions, and when the adsorption reaches saturation, The CO ₂ is separated analytically under certain conditions; finally, the gas flow enters the PIPS detector measurement box to measure the beta particles emitted by the decay of C-14, and finally complete the measurement of the C-14 activity concentration in the gaseous effluent.

The method described in the present invention is not limited to the examples described in the specific implementation manner. Those skilled in the art can obtain other implementation manners according to the technical solutions of the present invention, which also belong to the technical innovation scope of the present invention.

Claims (9)

1. an on-line measurement method for C-14 in a nuclear power plant gaseous effluent, the method comprising the steps: S1. Continuous sampling of gaseous effluent from nuclear power plants and primary purification and impurity removal; S2, the sample gas flow after primary purification and impurity removal is catalytically oxidized and converted into a measured gas flow containing CO ₂ gas; S3, separating and enriching CO ₂ in the measured gas stream containing CO ₂ gas; S4, adsorb the CO ₂ gas flow after separation and enrichment; S5. Separating CO ₂ in the MOFs module that has reached the adsorption saturation state, and measuring the formed CO ₂ gas flow, and then calculating the content of C-14. 2. the method for measuring C-14 on-line in a kind of nuclear power plant gaseous effluent according to claim 1, is characterized in that: in step S2, adopting solid catalyst to carry out catalytic oxidation to described sample gas flow, to be converted into a gas comprising _CO the measured airflow. 3. The method for measuring C-14 on-line in the gaseous effluent of a nuclear power plant according to claim 2, wherein the solid catalyst is at least one of Pd-Al ₂ O ₃ and Pt-Al ₂ O ₃ kind. 4. The method for on-line measurement of C-14 in a gaseous effluent of a nuclear power plant according to claim 1, wherein in step S3, a polymer membrane separation assembly is used to separate other gases in the sample gas flow to enrich _CO2 gas in the sample gas stream. 5 . The method for online measurement of C-14 in gaseous effluent of a nuclear power plant according to claim 4 , wherein the polymer membrane is a molecular sieve. 6 . 6. The method for measuring C-14 on-line in the gaseous effluent of a nuclear power plant according to claim 1, wherein step S4 comprises introducing the _CO2 gas flow after separation and enrichment into a specific adsorption function for _CO2 The MOFs assembly, which performs selective adsorption of _CO2 under certain conditions. 7. The method for online measurement of C-14 in a gaseous effluent of a nuclear power plant according to claim 1, characterized in that: according to the inherent adsorption capacity of the MOFs assembly for _CO2 , it is judged whether the MOFs assembly has reached an adsorption saturation state . 8. The method for measuring C-14 in gaseous effluent of a nuclear power plant on-line according to claim 1, characterized in that: in step S5, the MOFs components are analyzed under certain conditions to analyze the _CO2 adsorbed therein. to separate. 9. C-14 on-line measurement method in a kind of nuclear power plant gaseous effluent according to claim 1 is characterized in that: adopt PIPS detector in step S5 to measure the beta particle of C-14 decay emission to measure C- 14 activity concentrations.

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