阅读说明：本技术 核电站环境气态碳14活度浓度测定方法 (Method for measuring activity concentration of gaseous carbon 14 in nuclear power station environment ) 是由 张素杰 李华林 黄志勇 李林海 姚昕 于 2019-10-09 设计创作，主要内容包括：本发明涉及核电站化学检测与分析技术领域,公开了一种核电站环境气态碳14活度浓度测定方法,包括：采集空气样品,将空气样品中的碳元素固定为碳酸盐；通过预处理将碳酸盐转化为固体碳酸钙,并将固体碳酸钙研磨至指定目数,获得碳酸钙粉末固体；称取指定质量的碳酸钙粉末固体于样品瓶内,加入第一指定体积的除盐水和第二指定体积的闪烁液,摇匀后得到待测样品；待测样品经冷处理后,放入液闪谱仪中,避光静置；待待测样品静置第一指定时长后,测量待测样品的计数率。本发明提供的核电站环境气态碳14活度浓度测定方法,其获得的样品具有较好的稳定性,有利于提高环境气态碳14活度浓度测量的稳定性。(The invention relates to the technical field of chemical detection and analysis of nuclear power stations, and discloses an activity concentration determination method of nuclear power station environment gaseous carbon 14, which comprises the steps of collecting an air sample, fixing carbon elements in the air sample into carbonate, converting the carbonate into solid calcium carbonate through pretreatment, grinding the solid calcium carbonate to a specified mesh number to obtain calcium carbonate powder solid, weighing the calcium carbonate powder solid with specified mass in a sample bottle, adding desalted water with a specified volume of and scintillation liquid with a specified volume, shaking uniformly to obtain a sample to be determined, placing the sample to be determined into a liquid flash spectrometer after cold treatment, standing in a dark place, and measuring the count rate of the sample to be determined after the sample to be determined is kept at a position of for a specified time.)

The method for measuring the activity concentration of gaseous carbon 14 in the environment of nuclear power stations is characterized by comprising the following steps:

collecting an air sample, and fixing carbon elements in the air sample into carbonate;

converting the carbonate into solid calcium carbonate through pretreatment, and grinding the solid calcium carbonate to a specified mesh number to obtain calcium carbonate powder solid;

weighing the calcium carbonate powder solid with a specified mass in a sample bottle, adding th desalted water with a specified volume and scintillation liquid with a second specified volume, and shaking the desalted water and the scintillation liquid in the sample bottle uniformly to obtain a sample to be detected;

after cold treatment, the sample to be detected is placed into a liquid flash spectrometer and kept standing in a dark place;

and after the to-be-measured sample is kept still for th specified time, measuring the counting rate of the to-be-measured sample, wherein the total measuring times are specified times, and the time length of each measurement is second specified time length.

2. The method for measuring the activity concentration of gaseous carbon 14 in the nuclear power plant environment according to claim 1, wherein the sampling volume of the air sample is not less than a third designated volume, and the sampling flow rate is 2-10L/min.

3. The method of determining the activity concentration of gaseous carbon 14 in a nuclear power plant environment of claim 1, wherein the step of fixing the carbon element in the air sample to carbonate comprises:

oxidized carbon and/or organic carbon in the air sample is converted to carbon dioxide by means of catalytic oxidation.

4. The method for determining the activity concentration of gaseous carbon 14 in the nuclear power plant environment according to claim 1, wherein the step of fixing the carbon element in the air sample into carbonate comprises the steps of:

the air sample was passed through at least two bubblers filled with a lye at the concentration specified at .

5. The method for determining the activity concentration of gaseous carbon 14 in a nuclear power plant environment according to claim 4, wherein the step of converting the carbonate into solid calcium carbonate through pretreatment and grinding the solid calcium carbonate to a specified mesh number to obtain calcium carbonate powder solid comprises the following steps:

after the sampling of the air sample is finished, transferring the alkali liquor in the bubbler to a reaction vessel;

adjusting the pH value of the alkali liquor to a specified pH value, then adding a fourth specified volume of calcium salt solution, wherein the concentration of the calcium salt solution is a second specified concentration, and sealing the reaction container after stirring to obtain a precipitation reaction mixed liquor;

after the precipitation reaction mixed solution is kept stand for a third designated time, solid calcium carbonate is separated from the precipitation reaction mixed solution, the solid calcium carbonate is dried, and the dried solid calcium carbonate is weighed;

and grinding the solid calcium carbonate to obtain the calcium carbonate powder solid with the specified mesh number.

6. The method of determining nuclear power plant environmental gaseous carbon 14 activity concentration according to claim 1, wherein the specified mass comprises 2.0g, the th specified volume comprises 6ml, and the second specified volume comprises 36 ml.

7. The method for determining the concentration of gaseous carbon 14 activity in the nuclear power plant environment according to claim 1, wherein the sample to be tested is subjected to cold treatment and comprises:

and putting the sample to be tested into ice water for rapid cooling.

8. The method of determining the concentration of gaseous carbon 14 activity in a nuclear power plant environment of claim 1, wherein the specified time period comprises 12 hours, the specified number of times comprises 10 times, and the second specified time period comprises 200 minutes.

9. The method for determining the concentration of activity of gaseous carbon 14 in a nuclear power plant environment of claim 1, wherein the method for determining the concentration of activity of gaseous carbon 14 in a nuclear power plant environment further comprises:

measuring a background sample count rate using the liquid flash spectrometer;

measuring the counting rate of a standard sample by using the liquid flash spectrometer;

and calculating the detection efficiency of the liquid flash spectrometer according to the counting rate of the background sample and the counting rate of the standard sample.

10. The method for determining the concentration of activity of gaseous carbon 14 in a nuclear power plant environment according to claim 9, wherein the concentration of activity of carbon 14 in the air sample is calculated by the following formula:

in the formula:

c-carbon 14 activity concentration of air sample, Bq/L;

m-total weight of the solid calcium carbonate, g;

e-detection efficiency of the liquid flash spectrometer;

w-specified mass of the calcium carbonate powder solids, g;

v-volume of the air sample, L;

n_c-the count rate of the sample to be tested, cpm;

n_b-count rate of the background sample, cpm.

11. The method of determining nuclear power plant environmental gaseous carbon 14 activity concentration of claim 10, wherein the β net count rate (n) of carbon 14 of the air sample is calculated by the following formula_c-n_b) The uncertainty σ of (a) is specifically:

in the formula:

T_c-measurement time of the sample to be measured, min;

T_b-measurement time of the background sample, min.

12. The method of determining the concentration of activity of gaseous carbon 14 in the nuclear power plant environment of claim 10, wherein, when calculating the concentration of activity of carbon 14 in the air sample, the count rate of the sample to be tested is the average of all count rates remaining after times of measurement before rejection.

Technical Field

The invention relates to the field of chemical detection and analysis of nuclear power stations, in particular to a method for measuring the activity concentration of gaseous carbon 14 in nuclear power station environments.

Background

In a pressurized water reactor nuclear power plant,¹⁴c is mainly composed of fuel, core structural material and loop coolant¹⁴N、¹⁷O and¹³c is generated by activation. In order to meet the requirements of environmental monitoring, the concentration of the ambient gaseous carbon 14 of the nuclear power plant needs to be measured. However, in the prior art, the environmental gaseous carbon 14 has a problem of poor stability during sample preparation, and further influences the measurement of the activity concentration of the environmental gaseous carbon 14.

Disclosure of Invention

Aiming at the prior art, the invention provides an activity concentration measuring method of nuclear power station environment gaseous carbon 14, so as to improve the stability of samples and improve the stability of the measurement of the activity concentration of the environment gaseous carbon 14.

The invention provides a method for measuring the activity concentration of gaseous carbon 14 in nuclear power station environments, which comprises the following steps:

collecting an air sample, and fixing carbon elements in the air sample into carbonate;

converting the carbonate into solid calcium carbonate through pretreatment, and grinding the solid calcium carbonate to a specified mesh number to obtain calcium carbonate powder solid;

weighing the calcium carbonate powder solid with a specified mass in a sample bottle, adding th desalted water with a specified volume and scintillation liquid with a second specified volume, and shaking the desalted water and the scintillation liquid in the sample bottle uniformly to obtain a sample to be detected;

after cold treatment, the sample to be detected is placed into a liquid flash spectrometer and kept standing in a dark place;

and after the to-be-measured sample is kept still for th specified time, measuring the counting rate of the to-be-measured sample, wherein the total measuring times are specified times, and the time length of each measurement is second specified time length.

Optionally, the sampling volume of the air sample is not less than a third designated volume, and the sampling flow is 2-10L/min.

Optionally, before the fixing of the carbon element in the air sample into carbonate, the method includes:

oxidized carbon and/or organic carbon in the air sample is converted to carbon dioxide by means of catalytic oxidation.

Optionally, the fixing of the carbon element in the air sample into carbonate includes:

the air sample was passed through at least two bubblers filled with a lye at the concentration specified at .

Optionally, the converting the carbonate into solid calcium carbonate by pretreatment, and grinding the solid calcium carbonate to a specified mesh number to obtain calcium carbonate powder solid comprises:

after the sampling of the air sample is finished, transferring the alkali liquor in the bubbler to a reaction vessel;

adjusting the pH value of the alkali liquor to a specified pH value, then adding a fourth specified volume of calcium salt solution, wherein the concentration of the calcium salt solution is a second specified concentration, and sealing the reaction container after stirring to obtain a precipitation reaction mixed liquor;

after the precipitation reaction mixed solution is kept stand for a third designated time, solid calcium carbonate is separated from the precipitation reaction mixed solution, the solid calcium carbonate is dried, and the dried solid calcium carbonate is weighed;

and grinding the solid calcium carbonate to obtain the calcium carbonate powder solid with the specified mesh number.

Optionally, the specified mass comprises 2.0g, the th specified volume comprises 6ml, and the second specified volume comprises 36 ml.

Optionally, the sample to be tested is subjected to cold treatment, including:

and putting the sample to be tested into ice water for rapid cooling.

Optionally, the th specified duration includes 12h, the specified times includes 10 times, and the second specified duration includes 200 min.

Optionally, the method for measuring the concentration of the activity of gaseous carbon 14 in the nuclear power plant environment further includes:

measuring a background sample count rate using the liquid flash spectrometer;

measuring the counting rate of a standard sample by using the liquid flash spectrometer;

and calculating the detection efficiency of the liquid flash spectrometer according to the counting rate of the background sample and the counting rate of the standard sample.

Optionally, the carbon 14 activity concentration of the air sample is calculated by the following formula:

in the formula:

c-carbon 14 activity concentration of air sample, Bq/L;

m-total weight of the solid calcium carbonate, g;

e-detection efficiency of the liquid flash spectrometer;

w-specified mass of the calcium carbonate powder solids, g;

v-volume of the air sample, L;

n_c-the count rate of the sample to be tested, cpm;

n_b-count rate of the background sample, cpm.

Alternatively, the β net count rate (n) of the carbon 14 of the air sample is calculated by the following equation_c-n_b) The uncertainty σ of (a) is specifically:

in the formula:

T_c-measurement time of the sample to be measured, min;

T_b-measurement time of the background sample, min.

Optionally, when calculating the carbon 14 activity concentration of the air sample, the count rate of the used sample to be tested is an average value of all remaining count rates of the sample to be tested after discarding the count rates of times before the measurement.

The method for measuring the activity concentration of the gaseous carbon 14 in the environment of the nuclear power station comprises the steps of collecting an air sample, fixing carbon elements in the air sample into carbonate, converting the carbonate into solid calcium carbonate through pretreatment, grinding the solid calcium carbonate to a specified mesh number to obtain a calcium carbonate powder solid, weighing the calcium carbonate powder solid with specified mass into a sample bottle, adding specified volume desalted water and second specified volume scintillation liquid, shaking the desalted water and the scintillation liquid in the sample bottle uniformly to obtain a sample to be measured, placing the sample to be measured into a liquid scintillation spectrometer after cold treatment, standing in a dark place, and measuring the counting rate of the sample to be measured after the sample to be measured is stood for specified time, wherein the total number of times of measurement is specified times, and the time of each measurement is second specified time.

Detailed Description

In order to make the technical problems, technical solutions and advantages of the present invention more apparent, the present invention is further described in with reference to the following embodiments.

The embodiment of the invention discloses a method for measuring the concentration of gaseous carbon 14 activity in the environment of nuclear power stations, which comprises the following steps:

collecting an air sample, and fixing carbon elements in the air sample into carbonate;

converting the carbonate into solid calcium carbonate through pretreatment, and grinding the solid calcium carbonate to a specified mesh number to obtain calcium carbonate powder solid;

weighing the calcium carbonate powder solid with a specified mass in a sample bottle, adding th desalted water with a specified volume and scintillation liquid with a second specified volume, and shaking the desalted water and the scintillation liquid in the sample bottle uniformly to obtain a sample to be detected;

after cold treatment, the sample to be detected is placed into a liquid flash spectrometer and kept standing in a dark place;

and after the to-be-measured sample is kept still for th specified time, measuring the counting rate of the to-be-measured sample, wherein the total measuring times are specified times, and the time length of each measurement is second specified time length.

In this embodiment, a suitable sampling location may be selected for collecting the air sample according to a corresponding national standard method or other reference methods. The carbon element in the air sample can be fixed as carbonate by the gas absorption device. The gas absorption device may use lye as the adsorbent. The gas absorption device is used for absorbing carbon dioxide in the air sample. Before the air sample enters the gas absorption device, the air source can be purified by a filtering device such as a pneumatic water filter. Flow meters may be provided at the filtering means and the gas absorption means to measure the flow of the air sample into the gas absorption means.

After the collection of the air sample is finished, the alkali liquor in the gas absorption device can be treated to generate calcium carbonate precipitate. Drying the calcium carbonate precipitate to obtain solid calcium carbonate. And weighing to obtain the total mass of the solid calcium carbonate. And grinding the solid calcium carbonate to a specified mesh number to obtain the calcium carbonate powder solid. The specified mesh number may be 300 mesh.

For example, 2g of the calcium carbonate powder solid can be weighed in a sample bottle, 6ml of desalted water and 36ml of scintillation liquid are added, the scintillation liquid is used for scintillator mixed liquid for liquid scintillation counting measurement, the scintillator is activated by rays to emit fluorescence, and a fluorescence signal is amplified and recorded by an instrument for measurement.

And (3) carrying out cold treatment on the sample to be detected, putting the sample into a liquid flash spectrometer, and standing in a dark place. The cold treatment may refer to placing the sample to be tested in an environment of 0 ℃. The environment of 0 ℃ here may be a liquid environment at a temperature of 0 ℃, such as an ice water environment.

The count rate of the sample to be tested may be measured after the sample to be tested is left for specified time period in example, the time period comprises 12 hours the set of count rates may be measured in a multiple cycle manner for example, 10 times may be measured, each time the time period is 200 minutes.

Optionally, the sampling volume is not less than a third designated volume, and the sampling flow is 2-10L/min.

In this embodiment, the collection volume of the finally collected air sample may be determined by a corresponding gas volume measuring device. To ensure that there is a sufficient amount of test sample for subsequent measurements, the sample volume is not less than the third specified volume. For example, the third designated volume may be 3m³. Different gas absorption devices correspond to different samplesUnder the condition of , the sampling flow rate can be 2-10L/min.

Optionally, before the fixing of the carbon element in the air sample into carbonate, the method includes:

oxidized carbon and/or organic carbon in the air sample is converted to carbon dioxide by means of catalytic oxidation.

In this embodiment, a catalytic oxidation device may be disposed between the flow meter and the gas absorption device, the catalytic oxidation device converts carbon oxides and/or organic carbons in the air sample into carbon dioxide by catalytic oxidation, the catalytic oxidation device may use palladium as a catalyst, the oxidation temperature may be 400 ℃, and a buffer pipe may be disposed between the catalytic oxidation device and the gas absorption device to prevent liquid in the gas absorption device from flowing back to the catalytic oxidation device.

Optionally, the fixing of the carbon element in the air sample into carbonate includes:

the air sample was passed through at least two bubblers filled with a lye at the concentration specified at .

In this example, the carbon dioxide in the air sample can be absorbed by lye, sodium hydroxide or potassium hydroxide can be used as the lye, the designation concentration can be 0.4mol/L and the lye volume added per bubbler can be 250 ml.

Optionally, the converting the carbonate into solid calcium carbonate by pretreatment, and grinding the solid calcium carbonate to a specified mesh number to obtain calcium carbonate powder solid comprises:

after the sampling of the air sample is finished, transferring the alkali liquor in the bubbler to a reaction vessel;

adjusting the pH value of the alkali liquor to a specified pH value, then adding a fourth specified volume of calcium salt solution, wherein the concentration of the calcium salt solution is a second specified concentration, and sealing the reaction container after stirring to obtain a precipitation reaction mixed liquor;

after the precipitation reaction mixed solution is kept stand for a third designated time, solid calcium carbonate is separated from the precipitation reaction mixed solution, the solid calcium carbonate is dried, and the dried solid calcium carbonate is weighed;

and grinding the solid calcium carbonate to obtain the calcium carbonate powder solid with the specified mesh number.

In this embodiment, after the air sample is sampled, the alkali solution in the bubbler may be transferred to the reaction vessel. The reaction vessel may be a beaker. With 250g/L NaOH or NH₄Cl solution (20 g of solid powder dissolved in about 50ml of water) adjusted the pH of the lye to the indicated pH. When the pH value is adjusted, the pH regulator needs to be slowly dripped and fully stirred. The specified pH may be 11.

The calcium salt solution may be a calcium chloride solution. Weigh 15 g of CaCl₂The solid reagent was dissolved in 20ml of demineralized water and stirred until completely dissolved. And dropwise adding the calcium chloride solution into the alkali liquor with the pH value adjusted, and keeping the alkali liquor in a stirring state. Here, the fourth designated volume may refer to 15 grams of CaCl₂Volume of solid reagent dissolved in 20ml of demineralized water.

After the calcium salt solution is added, a reaction container can be sealed by a high molecular film, then the reaction container is kept stand for periods (about 4 hours), suction filtration is carried out, then desalted water is used for washing the filtered precipitated solid, the suction filtration is carried out repeatedly and is carried out for three times in total, finally times of suction filtration are carried out, alcohol is dripped along the cup wall, no powder residue is ensured on the cup wall of a suction filtration vessel, then the precipitated solid is placed into an oven and dried to constant weight at 105 ℃, solid calcium carbonate and the mass of the solid calcium carbonate are obtained, then the solid calcium carbonate is ground to the specified mesh number, and the calcium carbonate powder solid is obtained, wherein the specified mesh.

In the embodiment, the specified duration comprises 12h, the specified number of times comprises 10, and the second specified duration comprises 200 min.

Optionally, the method for measuring the concentration of the activity of gaseous carbon 14 in the nuclear power plant environment further includes:

measuring a background sample count rate using the liquid flash spectrometer;

measuring the counting rate of a standard sample by using the liquid flash spectrometer;

and calculating the detection efficiency of the liquid flash spectrometer according to the counting rate of the background sample and the counting rate of the standard sample.

In this embodiment, sodium carbonate is used as a starting material, calcium carbonate powder is prepared through the steps of precipitation, drying and the like, demineralized water and scintillation liquid are added to prepare a background sample, and the counting rate of the background sample is measured according to the method provided in the above embodiment. Carbon 14 powder with an activity of about 16Bq/g can be used as a starting material, desalted water and scintillation fluid are added to prepare a standard sample, and the counting rate of the standard sample is measured according to the method provided in the above example.

The detection efficiency of the liquid flash spectrometer is the percentage of the quotient of the difference between the counting rate of the standard sample and the counting rate of the background sample and the activity of the standard sample, and can be expressed as follows by a formula:

in the above formula, E is the detection efficiency of the liquid flash spectrometer;

n_c-the count rate of the standard sample, cpm;

n_b-count rate of background sample, cpm;

A_{sign board}Activity of standard sample, Bq or dpm. The activity is also known as decay rate, i.e., the number of decay times per minute of radiation.

Optionally, the carbon 14 activity concentration of the air sample is calculated by the following formula:

in the formula:

c-concentration of carbon activity 14 in the air sample, Bq/L, which refers to the amount of radioactivity per liter of air sample per second;

m-total weight of solid calcium carbonate, g;

e-detection efficiency of liquid flash spectrometer;

w-specified mass of calcium carbonate powder solids, g;

v-volume of air sample, L;

n_c-the count rate of the sample to be tested, cpm;

n_bcount rate of background sample, cpm.

From this, the accurate carbon 14 activity concentration of the air sample can be calculated.

Alternatively, the β net count rate (n) of the carbon 14 of the air sample is calculated by the following equation_c-n_b) The uncertainty σ of (a) is specifically:

in the formula:

T_c-measurement time of the sample to be measured, min;

T_b-measurement time of the background sample, min.

In this embodiment, the β net count rate (n) of the carbon 14 of the air sample can be calculated from the above equation_c-n_b) To assess the accuracy of the final test results cases where the β net count rate (n) of the carbon 14 was calculated_c-n_b) Can be combined with the uncertainty of the carbon source, the uncertainty of the efficiency, the uncertainty of the weighing to calculate the uncertainty of the activity concentration of the carbon 14.

Optionally, when calculating the carbon 14 activity concentration of the air sample, the count rate of the used sample to be tested is an average value of all remaining count rates of the sample to be tested after discarding the count rates of times before the measurement.

In this embodiment, the previous times of measurement data are discarded, so that the measurement result is more stable.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.