Wide-range online measurement method for total alpha and total beta in water

Abstract

The application discloses a wide-range online measurement method for total alpha and total beta in water. The method is characterized by the following steps: through rapid measurement of gamma counting rate, the activity concentration of total alpha and total beta in water is estimated; water samples are divided into three radiation levels, i.e. high, medium and low; different sample processing methods, such as dilution, direct taking and concentration enrichment, are combined; the advantages of high alpha and beta detection efficiency and simple sample preparation of liquid scintillation measurement are utilized; the sample processing procedure is simplified; the sample measurement time is shortened; the measurement of water samples can be rapidly realized; and the pollution of the measurement system under the condition of high radioactivity of total alpha and total beta is reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of radiation detection technology, and in particular to a wide-range online measurement method for total alpha and total beta in water. BACKGROUND

[0002] In order to ensure the safety of the environment radiation around the nuclear facilities and nuclear activities, it is necessary to detect the total alpha and total beta radioactivity of the process wastewater generated in the production process of the nuclear facilities. The process wastewater is generally discharged by tank, and before discharge, manual sampling is required according to the national standard method (GB11217-1989), and then analysis is carried out in the laboratory according to the standard method (EJ / T900-94). The standard measurement method adopts the thick sample method, and the measurement instrument mainly uses plastic scintillator counter or flow gas proportional counter. Under normal conditions, the total alpha and total beta radioactivity level in the process wastewater is very low, which is similar to or even lower than that of the environmental water sample. Once an abnormal condition occurs, the total alpha and total beta radioactivity level in the water will be several orders of magnitude higher than that under normal conditions.

[0003] The current laboratory analysis after on-site sampling faces the following difficulties: 1) In order to avoid unnecessary exposure, personnel need to carry out under protective conditions, the process is complex and time-consuming; 2) The measurement instrument mainly uses plastic scintillator counter or flow gas proportional counter, which has low detection efficiency, and it takes a long time to measure the water sample with low total alpha and total beta radioactivity level, which is difficult to meet the time requirement of the tank discharge of the process wastewater; 3) The thick sample preparation process is complicated and difficult to operate, and the measurement result is seriously dependent on the technical level of the operator; 4) The manual analysis in the laboratory consumes a lot of manpower and the sample analysis capacity is limited; 5) The total alpha and total beta radiation level in water has a large range and a difference of several orders of magnitude, and the amount of solid residue differs significantly, sometimes requiring multiple sample preparation and measurement to obtain satisfactory results. Therefore, it is necessary to propose a wide-range online measurement method for total alpha and total beta in water suitable for the scene. SUMMARY

[0004] In order to solve the technical problems of complex process, long time consumption and large manpower consumption in the detection of total alpha and total beta radioactivity of the process wastewater generated in the production process of the nuclear facilities, the present application proposes a wide-range online measurement method for total alpha and total beta in water.

[0005] The present application proposes a wide-range online measurement method for total alpha and total beta in water, comprising the following steps:

[0006] After taking a certain volume of water sample, γ count rate measurement is carried out;

[0007] The total alpha and total beta radioactivity concentration level is estimated according to the fitting function between the γ count rate and the total alpha and total beta radioactivity concentration;

[0008] Different methods are taken to treat the water sample according to the total alpha and total beta radioactivity concentration level;

[0009] The treated water sample is made into a sample to be measured, and the activity concentration of total alpha and total beta in the water is obtained by liquid scintillation measurement.

[0010] In some embodiments, the fitting function between the total alpha and total beta radioactivity concentration and the gamma count rate related to the process condition is established according to the experimental measurement data under different process conditions.

[0011] In some embodiments, when the total alpha and total beta radioactivity concentration level is a low radiation level, the water sample is concentrated and enriched; when the total alpha and total beta radioactivity concentration level is a medium radiation level, direct sampling measurement is taken; when the total alpha and total beta radioactivity concentration level is a high radiation level, the water sample is diluted with deionized water.

[0012] In some embodiments, the low radiation level is that the total alpha and total beta radioactivity concentration is less than 10 times the minimum detectable activity MDA of the water sample with a volume of V measured by a liquid scintillation spectrometer for t hours; the high radiation level is that the total alpha and total beta radioactivity concentration is more than 10,000 times the minimum detectable activity MDA of the water sample with a volume of V measured by a liquid scintillation spectrometer for t hours; and the medium radiation level is between the low radiation level and the high radiation level.

[0013] In some embodiments, the minimum detectable activity MDA of the water sample with a volume of V measured by a liquid scintillation spectrometer for t hours is estimated as:

[0014]

[0015] The total alpha and total beta radioactivity concentration of the water sample is:

[0016] Wherein, the unit of MDA is Bq / ml, the unit of C α,β is Bq / ml, V is the sample volume participating in the liquid scintillation measurement; ε is the liquid scintillation measurement alpha or beta detection efficiency, which can be measured by a standard substance; t is the measurement time, in hours; k is the water sample enrichment or dilution coefficient; η is the enrichment sample preparation process loss correction coefficient, which is measured by a radioactive standard substance, and the direct measurement correction coefficient of the water sample at the medium radiation level and the high radiation level is 1; n α,β is the liquid scintillation spectrometer water sample measurement alpha or beta count rate, in cps, n αb,βb is the liquid scintillation spectrometer blank sample measurement alpha or beta background count rate, in cps.

[0017] In some embodiments, the volume V is 5-10 ml to ensure that the sample to be measured does not separate after the scintillation solution is added; and the time t is determined according to the time allowed for measurement.

[0018] In some embodiments, the water sample is filtered and the pH value is adjusted before the gamma counting rate measurement is performed.

[0019] In some embodiments, the pH value is adjusted to 1.7±0.2 to weaken the influence of water quality on the quenching level of the sample to be measured, and to achieve the stability of the quenching level.

[0020] In some embodiments, the certified radioactive standard solution is used to configure a spiked sample with a known activity that is the same as the measurement system and the quenching level of the measurement sample, to determine the detection efficiency and the alpha and beta discrimination error rates, and to achieve the correction of the detection efficiency and the alpha / beta discrimination error of the measurement result.

[0021] Compared with the prior art, the present application has the following beneficial effects:

[0022] The wide-range online measurement method for total alpha and total beta in water provided by the present application estimates the activity concentration of total alpha and total beta in water by quickly measuring the gamma count, divides the water sample into three levels of high, medium and low radioactivity, uses different sample processing methods such as dilution, direct taking and concentration enrichment, uses liquid scintillation measurement with the advantages of high alpha and beta detection efficiency and simple sample preparation, simplifies the sample processing process, shortens the sample measurement time, and can quickly measure the water sample while reducing the pollution of the measurement system under the condition of high radioactivity of total alpha and total beta.

[0023] The wide-range online measurement method for total alpha and total beta in water provided by the present application strictly controls the pH of the directly measured sample and the diluted measurement sample, and uses 0.05M nitric acid solution to clean the measurement sample after enrichment, which weakens the influence of the production process on the quenching level of the sample to be measured, and achieves the stability of the quenching level. The certified radioactive standard solution is used to configure a spiked sample with a known activity that is the same as the measurement system and the quenching level of the measurement sample, to determine the detection efficiency and the alpha and beta discrimination error rates, and to achieve the correction of the detection efficiency and the alpha / beta discrimination error of the measurement result.

[0024] The wide-range online measurement method for total alpha and total beta in water provided by the present application can avoid the radiation exposure of manual sampling, shorten the sampling time and measurement time, reduce the labor, and improve the analysis capacity compared with the method of on-site sampling and laboratory analysis. BRIEF DESCRIPTION OF DRAWINGS

[0025] The above and / or additional aspects and advantages of the present application will become apparent and more readily appreciated from the following description, taken in conjunction with the following drawings, in which:

[0026] Figure 1The technical roadmap of the wide-range online measurement method of total alpha and total beta in water is provided. DETAILED DESCRIPTION

[0027] Embodiments of the present application are described in detail below with reference to examples shown in the accompanying drawings, in which the same or similar numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below by reference to the accompanying drawings are exemplary and are intended to explain the present application, and cannot be understood as a limitation of the present application.

[0028] A wide-range online measurement method of total alpha and total beta in water according to an embodiment of the present application is described below with reference to the accompanying drawings.

[0029] The wide-range online measurement method of total alpha and total beta in water of the present application comprises the following steps:

[0030] After a certain volume of water sample is taken, gamma count rate measurement is performed;

[0031] The total alpha and total beta radioactivity concentration level is determined according to the fitting function between the gamma count rate and the total alpha and total beta radioactivity concentration.

[0032] The water sample is treated by different methods according to the total alpha and total beta radioactivity concentration level.

[0033] The treated water sample is made into a sample to be measured, and the activity concentration of total alpha and total beta of the water sample is obtained by liquid scintillation measurement.

[0034] Alpha and beta decay are generally accompanied by gamma decay. In the production process of nuclear facilities, under normal and abnormal conditions, there is a certain correspondence between the total alpha and total beta radioactivity level and the gamma count rate, and the total alpha and total beta radioactivity concentration level can be determined by the gamma count rate.

[0035] In practical application, the total alpha and total beta radioactivity concentration level is estimated according to the fitting function. The fitting function is a functional relationship between the total alpha and total beta radioactivity concentration and the gamma count rate established according to experimental measurement data. By extracting characteristic parameters such as pH value and hardness under different process conditions, the fitting function between the total alpha and total beta radioactivity concentration and the gamma count rate is established according to the experimental measurement data. The total alpha and total beta radioactivity concentration level is determined according to the fitting function by rapidly measuring the gamma count rate.

[0036] The water sample is treated by different methods according to the total alpha and total beta radioactivity concentration level. Specifically, when the total alpha and total beta radioactivity concentration level is a low radiation level, the water sample is concentrated and enriched; when the total alpha and total beta radioactivity concentration level is a medium radiation level, the sample is directly measured; and when the total alpha and total beta radioactivity concentration level is a high radiation level, the water sample is diluted by adding water.

[0037] The following is illustrated by a specific experimental example.

[0038] The water sample is pretreated to remove large particle residues and the pH value is adjusted to 1.7±0.2. First, the γ counting rate is measured. When the total α and β radioactivity concentration estimated from the measured γ counting rate is lower than 10 times the minimum detectable activity (MDA) of 8 ml of the water sample measured directly for 1 hour, it is a low radiation level, and the water sample needs to be enriched and then measured. When the total α and β radioactivity concentration estimated from the measured γ counting rate is higher than 10,000 times the minimum detectable activity (MDA) of 8 ml of the water sample measured directly for 1 hour, it is a high radiation level, and the water sample needs to be diluted 10 times by adding deionized water and then measured after adjusting the pH value to 1.7±0.2. The water sample between the low and high radiation levels is a medium radiation level, and it is directly sampled and measured.

[0039] The treated water sample is prepared into a sample to be measured, and the activity concentration of total α and total β in the water is obtained by liquid scintillation measurement. Specifically, a certain volume V of water sample is sampled on-line from the tank discharge process wastewater, and the γ counting rate is quickly measured by a γ detector. The total α and β radioactivity concentration level is determined according to the fitting function, and then different sample processing methods are adopted according to the total α and β radioactivity concentration level. The treated water sample is then prepared into a sample to be measured by liquid scintillation measurement, and the activity concentration of total α and total β in the water is obtained by liquid scintillation measurement.

[0040] The minimum detectable activity (MDA) of 8 ml of the water sample measured directly by the liquid scintillation spectrometer for 1 hour is estimated as follows:

[0041]

[0042] The total α and β radioactivity concentration of the water sample is:

[0043] Wherein, the unit of MDA is Bq / ml, the unit of C α,β is Bq / ml; ε is the liquid scintillation measurement α or β detection efficiency, which can be measured by standard material; k is the enrichment or dilution coefficient of the water sample; η is the enrichment sample preparation process loss correction coefficient, which is measured by radioactive standard material, and the correction coefficient is 1 for the direct measurement of the medium and high radiation level water samples; n α,β is the α or β counting rate of the liquid scintillation spectrometer water sample measurement, with the unit of cps, n αb,βb is the α or β background counting rate of the liquid scintillation spectrometer blank sample measurement, with the unit of cps.

[0044] Under low radiation level condition, a certain volume V1 of water sample is evaporated in an evaporator by heating to evaporate water, and then 12 ml of 0.05M nitric acid solution is used to clean the evaporator to obtain a concentrated sample. 8 ml of the concentrated sample is taken and added to a scintillation vial, and then 12 ml of scintillation solution is added. After mixing, the sample is prepared for measurement. The volume V1 should ensure that the activity concentration of the concentrated sample obtained after heat concentration is higher than 10 times MDA, but generally should not be greater than 1000 ml.

[0045] The low-background liquid scintillation spectrometer with α and β discrimination function is used for measurement, and α and β count rates n α,β are obtained respectively. After deducting the instrument background n αb,βb , the total α and total β radioactivity concentrations in water can be calculated.

[0046] The total α and total β radioactivity concentrations in water samples with medium radiation level are:

[0047] The total α and total β radioactivity concentrations in water samples with low radiation level are:

[0048] The total α and total β radioactivity concentrations in water samples with high radiation level are:

[0049] Wherein, ε is the liquid scintillation measurement α or β detection efficiency, which can be measured by standard material; η is the enrichment sample preparation process loss correction coefficient, which is measured by radioactive standard material; the direct measurement correction coefficient of medium radiation level and high radiation level water sample is 1; n α,β is the α or β count rate, and n αb,βb is the α or β count rate of the instrument background.

[0050] The total α and total β in water are measured by liquid scintillation, which has a detection efficiency of about 7% higher than that of proportional counter, semiconductor detector and ZnS scintillation screen by more than ten times. Liquid scintillation measurement has a detection efficiency of nearly 100% for α and more than 90% for β. Liquid scintillation measurement can distinguish α and β according to the principle that the slow component of β pulse decays faster than that of α pulse, so as to realize simultaneous measurement of α and β, and obtain the activity concentration of total α and total β in water sample in one measurement.

[0051] In addition, the detection efficiency and α / β discrimination error will change with the change of quenching level, and the quenching level of water sample will change with different process conditions. Therefore, the detection efficiency and α / β discrimination error rate need to be corrected for quenching level. Among them, the α discrimination error rate refers to the percentage of counts caused by α decay being judged as β decay, and the β discrimination error rate refers to the percentage of counts caused by β decay being judged as α decay.

[0052] In order to solve the problem that the detection efficiency and the alpha / beta error rate change with the quenching level and affect the accuracy of the measurement result, a certain amount of strong quenching agent is added to the sample to be measured, the influence of the water sample on the quenching level caused by different processes is weakened, and the quenching level is stabilized. By strictly controlling the pH value of the water sample after acidification after direct measurement and measurement after dilution, and using 0.05M nitric acid solution for cleaning after evaporation, the quenching level is kept consistent during the correction and sample measurement process, the influence of the production process on the quenching level of the sample to be measured is weakened, and the quenching level is stabilized. The certified radioactive standard solution is used to configure and measure the sample measurement system and the known activity of the spiked sample with the same quenching level as the sample measurement system, so as to determine the detection efficiency and the alpha and beta discrimination error rate, and correct the detection efficiency and the alpha / beta discrimination error of the measurement result.

[0053] Compared with on-site sampling and laboratory analysis, the method can avoid unnecessary radiation exposure of manual sampling, shorten sampling and measurement time, reduce manpower, and improve analysis capacity.

[0054] In the description of the specification, the description of the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the application. In the specification, the illustrative description of the above terms can be directed to different embodiments or examples. Moreover, the described specific features, structures, materials or characteristics can be combined in any suitable manner in any one or more embodiments or examples. In addition, the skilled in the art can combine and combine the different embodiments or examples described in the specification and the features of the different embodiments or examples without contradiction.

[0055] In addition, the terms "first", "second" are only for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of indicated technical features. Therefore, the features defined with "first", "second" can explicitly or implicitly include at least one feature. In the description of the application, the meaning of "a plurality of" is at least two, for example, two, three, etc., unless otherwise specifically limited.

[0056] Although the embodiments of the application have been shown and described, those skilled in the art can understand that various changes, modifications, replacements and variations can be made to these embodiments without departing from the principles and purposes of the application, and the scope of the application is defined by the claims and their equivalents.

Claims

1. A wide-range online measurement method for total α and total β in water, characterized in that, Includes the following steps: A certain volume of water sample was taken and the gamma count rate was measured. The total α and total β radioactivity concentration levels are estimated based on the fitting function between the γ count rate and the total α and total β radioactivity concentrations. The fitting function between the total α and total β radioactivity concentrations and the γ count rate, which are related to the process conditions, is established based on experimental measurement data under different process conditions. The water sample was treated using different methods based on the total α and total β radioactivity concentration levels. The processed water sample was prepared into a test sample, and the total α and total β radioactivity concentrations of the water sample were obtained by liquid scintillation measurement and analysis. When the total α and total β radioactivity concentration is at a low radiation level, the water sample is concentrated and enriched; when the total α and total β radioactivity concentration is at a medium radiation level, direct sampling and measurement are performed; when the total α and total β radioactivity concentration is at a high radiation level, the water sample is diluted with deionized water. The low radiation level is defined as a total α and total β radioactivity concentration less than 10 times the minimum detectable activity (MDA) of a water sample with a volume of V measured directly over t hours using a liquid scintillation spectrometer; the high radiation level is defined as a total α and total β radioactivity concentration greater than 10,000 times the minimum detectable activity (MDA) of a water sample with a volume of V measured directly over t hours using a liquid scintillation spectrometer; the medium radiation level is between the low and high radiation levels. The minimum detectable activity (MDA) of a water sample with a volume of V measured directly over t hours using a liquid scintillation spectrometer is estimated as follows: ； The total α and total β radioactivity concentrations of the water sample are: ; Among them, the MDA unit is , The unit is V is the sample volume involved in the liquid scintillation measurement; The α or β detection efficiency for liquid scintillation measurement can be obtained through standard material measurement; t is the measurement time in hours; k is the enrichment or dilution coefficient of the water sample. The correction factor for loss during the enrichment sample preparation process is obtained by measurement using radioactive standard materials. The direct measurement correction factor for the medium radiation level and the high radiation level water samples is 1. This refers to the α or β count rate during water sample measurement using a liquid scintillation spectrometer, expressed in cps. The α or β background count rate is measured in cps when the blank sample is measured by the liquid scintillation spectrometer. Before the γ count rate measurement, the water sample is filtered and the pH value is adjusted to 1.7±0.2 to reduce the influence of water quality on the quenching level of the sample to be tested and to achieve the stability of the quenching level.

2. The method as described in claim 1, characterized in that, The volume V is 5-10 ml to ensure that the sample to be tested does not separate into layers after the scintillation fluid is added; the time t is determined according to the allowable measurement time.

3. The method as described in claim 1, characterized in that, The measurement system and spiked sample with known activity and the same quenching level as the measured sample are prepared using certified radioactive standard solutions. The detection efficiency and α and β discrimination error rates are determined to correct the detection efficiency and α / β discrimination error of the measurement results.

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