Preparation method of low-background low-tritium water

Abstract

The invention belongs to the technical field of analysis and detection, and particularly relates to a preparation method of low-background low-tritium water. The preparation method of the low-background low-tritium water provided by the invention comprises the following steps: electrolyzing a water source by using an SPE electrolysis system to obtain hydrogen with low tritium content; mixing the low-tritium-content hydrogen and the low-tritium-content oxygen, combusting, and condensing to obtain low-tritium-content condensed water; distilling the condensed water with low tritium content to obtain distilled water with low tritium content; the distilled water with the low tritium content is repeatedly subjected to the steps of electrolysis, combustion, condensation and distillation, and the low-background low-tritium water is obtained. According to the principle that hydrogen isotope electrolysis difficulty programs are different in the water electrolysis process, hydrogen with the lower tritium content generated by water electrolysis is collected and mixed with oxygen to be ignited to generate water vapor, liquid water is obtained through condensation and collection, impurities are removed through distillation, and water with the tritium content as low as possible is obtained. The low-tritium water prepared according to the method provided by the invention has an extremely low background level.

Description

Technical Field

[0001] The present invention belongs to the technical field of analytical detection, and particularly relates to a method for preparing low-background low-tritium water. Background Art

[0002] The background radiation level refers to the amount of naturally occurring radioactive radiation. Radiation is everywhere; there is radiation exposure in food, houses, the sky, the earth, mountains, waters, plants, and even within the human body. The irradiation of these natural rays is natural background radiation.

[0003] The stock of tritium in nature is extremely scarce. Nowadays, the tritium that people come into contact with and use mainly comes from artificial nuclear reactions. Artificially produced tritium is mainly used in thermonuclear weapons, labeled compounds in scientific research, and may also become a raw material for thermonuclear fusion reactions. With the continuous development of nuclear energy, the resulting environmental problems have further attracted people's attention. Nuclear contaminated water and nuclear wastewater both contain radioactive substances to varying degrees, and tritium is one of them. Inevitably, during the direct or indirect production and use of tritium, it will be discharged into the environment. In the environment, tritiated water (HTO) is the main form. Tritium in environmental air water vapor can invade the human body through respiration and skin, and will also enter the water cycle and food chain through rainwater and its molecular exchange, thus entering the human body to participate in metabolism, which will cause internal irradiation hazards to human tissues and organs. Therefore, monitoring, managing, and controlling tritium in environmental air water vapor is an essential measure.

[0004] In addition, tritium has suitable nuclear physical properties and has advantages such as low toxicity, high specific activity, and good autoradiography. Tritium and its labeled compounds play an important role in the military, industry, hydrology, geology, and various scientific research fields. Tritium is a low-energy pure β radioactive nuclide with a half-life of 12.33 a, the maximum energy of its rays is 18.6 keV, and the average energy is 5.7 keV. Liquid scintillation counting is one of the main methods for detecting tritium radioactivity at present. Limited by the detection principle of this method, to ensure the consistent sample quenching degree and the influence of the environmental background radiation level on the detection accuracy, water with as low a tritium content as possible needs to be used as the background sample. Similarly, for the measurement of low-activity tritium samples or the detection of tritium radioactivity close to the detection lower limit of the detector, the influence of tritium in the background sample on the detection accuracy will become an important factor that cannot be ignored.

[0005] At present, people need to obtain the required low-tritium water from deep groundwater or ancient glaciers that hardly participate in the surface water cycle. This collection method is difficult and costly, and it also has a certain impact on the environment. The obtained water samples usually contain rich mineral impurities and cannot be used directly. During the impurity removal process, it is very difficult to avoid contact with water containing a higher tritium content in the environment and being contaminated by it. With the development of the nuclear industry and the increasing demand for the use of tritium in related industries, finding a low-cost, high-efficiency and easy-to-operate method for preparing low-background low-tritium water has become an urgent technical problem in this field. Summary of the Invention

[0006] In view of this, the present invention provides a method for preparing low-background low-tritium water. According to the method provided by the present invention, water with a lower tritium content can be prepared. The preparation method provided by the present invention is simple and easy to operate, and has high efficiency and low cost.

[0007] In order to solve the above technical problems, the present invention provides a method for preparing low-background low-tritium water, including the following steps:

[0008] Electrolyze the water source using an SPE electrolysis system to obtain hydrogen with a low tritium content;

[0009] Mix the hydrogen with a low tritium content and oxygen for combustion and then condense to obtain condensed water with a low tritium content;

[0010] Distill the condensed water with a low tritium content to obtain distilled water with a low tritium content;

[0011] Repeat the steps of electrolysis, combustion, condensation and distillation for the distilled water with a low tritium content in sequence to obtain the low-background low-tritium water.

[0012] Preferably, the conductivity of the water source ≤ 5 μS / cm;

[0013] The water source includes distilled water, tap water or commercially available mineral water.

[0014] Preferably, the current of the electrolysis is 38 - 42 A, and the temperature of the electrolysis is 13 - 17 °C.

[0015] Preferably, the purity of the oxygen is greater than or equal to 99.99%;

[0016] The molar ratio of the hydrogen to the oxygen is 1:1.0 - 1.3.

[0017] Preferably, the combustion is carried out in a combustion tube; the temperature of the combustion tube is 500 - 540 °C

[0018] During the combustion process, the volume flow rate of the oxygen is 28 - 32 L / h, and the volume flow rate of the hydrogen during the combustion process is 23 - 27 L / h.

[0019] Preferably, the electrolysis, combustion, and condensation are carried out continuously in a closed system, and the distillation is carried out in a separate density system;

[0020] The temperature of the condensation is 0 - 4°C.

[0021] Preferably, based on the volume of the water source, the water vapor collected by the condensation is part of the water vapor generated by combustion, and the part of the water vapor is the water vapor generated by the combustion of hydrogen and oxygen generated by electrolyzing part of the water source. The volume ratio of the part of the water source to the water source is less than or equal to 0.5.

[0022] Preferably, the condensation is two-stage condensation.

[0023] Preferably, the temperature of the distillation is 100 - 200°C;

[0024] The conductivity of the distilled water with low tritium content is less than or equal to 5 μS / cm.

[0025] Preferably, the number of repetitions of electrolysis, combustion, condensation, and distillation is more than 2 times.

[0026] The present invention provides a method for preparing low-background low-tritium water, including the following steps: electrolyzing a water source using an SPE electrolysis system to obtain hydrogen with low tritium content; mixing the hydrogen with low tritium content and oxygen for combustion and then condensing to obtain condensed water with low tritium content; distilling the condensed water with low tritium content to obtain distilled water with low tritium content; and sequentially repeating the steps of electrolysis, combustion, condensation, and distillation for the distilled water with low tritium content to obtain the low-background low-tritium water. The present invention utilizes the principle that in the process of electrolyzing water, the ease of electrolysis of hydrogen isotopes is different, collects hydrogen with less tritium content generated by electrolyzing water, mixes it with oxygen and ignites it to generate water vapor, then collects the liquid water through condensation, and finally removes impurities through distillation, thereby obtaining water with as low tritium content as possible. The low-tritium water prepared according to the method provided by the present invention has an extremely low background level and extremely high purity. Compared with the conventional methods for obtaining low-tritium water, this method has high efficiency, is simple and fast to operate, has good safety, and causes less harm to the environment.

[0027] Produced according to the method provided by the present invention, each set of devices can obtain 200 - 400 mL of low-background low-tritium water by using 1000 mL of raw materials. At the same time, the content of impurity ions in the prepared low-background low-tritium water is extremely low, and the conductivity maintains at the level of 5 - 7 μS / cm, with higher purity. The water source used in the preparation method provided by the present invention is extremely easy to obtain, the production cost is low, and large-scale production can be achieved. Description of the Drawings

[0028] Figure 1 It is a schematic structural diagram of a combustion tube used in the combustion process. Detailed implementation mode

[0029] The present invention provides a method for preparing low-background low-tritium water, comprising the following steps:

[0030] Electrolyze the water source using an SPE electrolysis system to obtain hydrogen with a low tritium content;

[0031] Mix the hydrogen with a low tritium content and oxygen, burn them, and then condense to obtain condensed water with a low tritium content;

[0032] Distill the condensed water with a low tritium content to obtain distilled water with a low tritium content;

[0033] Repeat the steps of electrolysis, combustion, condensation, and distillation for the distilled water with a low tritium content in sequence to obtain the low-background low-tritium water.

[0034] The present invention electrolyzes the water source using an SPE electrolysis system to obtain hydrogen with a low tritium content. As a specific implementation mode of the present invention, the conductivity of the water source can be ≤5 μS / cm; the water source can include distilled water, tap water, or commercially available mineral water. When the conductivity of the water source is greater than 5 μS / cm, the conductivity can be reduced to ≤5 μS / cm by distillation; the current for electrolysis can be 38 - 42 A, specifically 40 A; the temperature for electrolysis can be 13 - 17 °C, specifically 15 °C.

[0035] The present invention utilizes the isotope effect of hydrogen elements during electrolysis to enable more difficult-to-electrolyze tritiated water to remain in the liquid phase in the form of water, while the more easily electrolyzed hydrogenated water is electrolyzed into hydrogen and separated in the gaseous form. This tritium-depleted hydrogen is then subjected to high-temperature oxidation (combustion) again to be converted into water and collected to obtain condensed water with a low tritium content. The present invention adopts an SPE electrolysis system, which helps to construct a closed environment and is conducive to continuous operation of subsequent combustion, condensation, and distillation in a closed system; at the same time, due to the SPE electrolysis principle and the structure of the electrolytic cell, this method is simple to operate and convenient for controlling experimental variables and maintenance.

[0036] After obtaining hydrogen with a low tritium content, the present invention mixes the hydrogen with a low tritium content and oxygen for combustion and then condensation to obtain condensed water with a low tritium content. As a specific embodiment of the present invention, the purity of the oxygen can be greater than or equal to 99.99%; the oxygen includes oxygen generated by electrolyzing water and additionally supplemented oxygen; the molar ratio of the hydrogen to the oxygen can be 1:1.0 to 1.3, specifically 1:1.0, 1:1.1, 1:1.2 or 1:1.3. In the present invention, the oxygen includes oxygen generated by electrolyzing water. The molar ratio of hydrogen to oxygen generated by electrolyzing water in the present invention is 2:1. During the combustion process, high-purity oxygen needs to be additionally supplemented to ensure an excess of oxygen, balance the pressures of hydrogen and oxygen in the closed system, and obtain a higher combustion efficiency while making the combustion stable. Therefore, the molar ratio of hydrogen to oxygen during the combustion process is approximately 1:1.

[0037] As a specific embodiment of the present invention, the combustion can be diffusion combustion; the combustion can be carried out in Figure 1 a combustion tube with the shown structure. The material of the combustion tube can be quartz glass; where 1 is the oxygen inlet, 2 is the hydrogen inlet, 3 is the water vapor outlet, and 4 is a high-temperature resistant column; the high-temperature resistant column is located directly below the water vapor outlet. The size of the high-temperature resistant column is smaller than the diameter of the combustion tube. There can be a gap of 3 to 6 mm between the high-temperature resistant column and the combustion tube; the high-temperature resistant column can be a high-temperature resistant alumina column; the high-temperature resistant column does not participate in the oxidation reaction. When the temperature reaches the ignition temperature after the two gases (oxygen and hydrogen) are mixed, the mixed gas will stably burn in the narrow space between the tube and the column, efficiently generate water vapor and discharge it from the water vapor outlet 3. At the same time, it can avoid incomplete combustion caused by too large a change in the concentration of the two gases and deflagration phenomena caused by temperature accumulation at high concentrations. Placing a high-temperature resistant column directly below the water vapor outlet 3 can maintain a stable combustion state.

[0038] In the present invention, since the molar ratio of hydrogen to oxygen generated during the electrolysis of water is 2:1, and the electrolysis, combustion, and condensation system is a sealed system that is not connected to the atmosphere, this will cause the two gases (hydrogen and oxygen) to be introduced from both ends of the combustion tube and cannot form a relatively stable combustion interface due to different generated volumes. The following technical solutions are adopted to maintain the relative stability of the combustion interface: the additionally supplied oxygen first passes through a pressure reducing valve and a flow meter to adjust the pressure to be less than or equal to 0.05 MPa and then is introduced into the oxygen inlet 1 of the combustion tube. At the same time, the oxygen outlet pipeline of the electrolytic cell is connected to the pipeline between the flow meter and the combustion tube to balance the pressure difference generated by the different volumes of hydrogen and oxygen in the closed system. At the same time, a high-temperature resistant alumina column 4 is placed below the water vapor outlet of the combustion tube to make the hydrogen-oxygen mixed gas stably burn in this narrow space to ensure the continuous and normal progress of the electrolysis and combustion processes.

[0039] As a specific embodiment of the present invention, the volume flow rate of oxygen during the combustion process can be 28 - 32 L / h, specifically 30 L / h; the volume flow rate of hydrogen during the combustion process can be 23 - 27 L / h, specifically 25 L / h; the present invention ensures an excess of oxygen to meet the amount of oxygen required for the complete oxidation of the hydrogen generated by electrolysis into water.

[0040] As a specific embodiment of the present invention, the temperature of the combustion tube can be 500 - 540 °C, specifically 520 ± 15 °C. The present invention can control the temperature of the combustion tube by resistance wire heating. First, the temperature of the combustion tube is controlled below 450 °C (to ensure that the mixed gas is not ignited), then hydrogen and oxygen are introduced (to form a stable contact interface at the tube plug before combustion), and after maintaining for 3 - 5 minutes, the temperature is slowly increased (5 °C / min) until the mixed gas is ignited (generally ignited at about 520 °C), and this temperature is maintained until the combustion ends.

[0041] As a specific embodiment of the present invention, the electrolysis, combustion, condensation, and distillation can be carried out in a closed system, where the electrolysis, combustion, and condensation are carried out continuously in the closed system, and the distillation is carried out in a separate density system. The present invention can avoid the influence of the external environment by carrying out electrolysis, combustion, condensation, and distillation in a closed system; when using the SPE system for electrolysis, the electrolyzer can electrolyze a certain volume of distilled water under conditions isolated from the environment, and then the hydrogen with a lower tritium content generated by electrolysis is introduced into the combustion tube through a pipeline (silicone hose) for combustion, and the sample does not exchange substances with the substances in the environment during the process; at the same time, the electrolyzer of the SPE is closed, with only two sample inlets and an exhaust port, and the electrolysis process can be made unaffected by the substances in the environment through pipeline connection.

[0042] As a specific embodiment of the present invention, the temperature of the condensation can be 0 - 4 °C, specifically 0 °C, 1 °C, 2 °C, 3 °C, or 4 °C; the condensation can be two-stage condensation. The present invention can improve the collection efficiency through two-stage condensation at a lower temperature.

[0043] As a specific embodiment of the present invention, based on the volume of the water source, the water vapor collected by condensation is part of the water vapor generated by combustion, and the part of the water vapor is the water vapor generated by the combustion of hydrogen and oxygen generated by electrolyzing part of the water source. The volume ratio of the part of the water source to the water source is less than or equal to 0.5. As the volume of the remaining water source for electrolysis decreases, the separation effect of tritium during the electrolysis process gradually decreases, and the separation effect significantly decreases when about half of the volume of the water source to be electrolyzed remains (the tritium activity in the collected sample significantly increases). Therefore, only the water vapor generated by electrolyzing the first half of the volume of the sample to be electrolyzed is collected, and the remaining half of the non-electrolyzed sample is discarded.

[0044] After obtaining the condensate with a low tritium content, the present invention distills the condensate with a low tritium content to obtain distilled water with a low tritium content. As a specific embodiment of the present invention, the temperature of the distillation can be 100 to 200 °C, specifically 100 °C, 120 °C, 150 °C, 180 °C or 200 °C; the distillation can be atmospheric distillation. The present invention can reduce the conductivity of the low-background low-tritium water through distillation. The conductivity of the condensate collected after electrolysis, combustion and condensation will increase. The conductivity increases by 5 to 15 μS / cm relative to the distilled water that has not been electrolyzed (the conductivity of the distilled water is 0 to 5 μS / cm). The reason for the analysis is that some impurity ions contained in the operation process and experimental equipment (materials such as hoses, quartz tubes, and alumina tube plugs) due to purity or preparation process inevitably dissolve into the sample, resulting in an increase in conductivity.

[0045] As a specific embodiment of the present invention, the conductivity of the distilled water with a low tritium content can be less than or equal to 5 μS / cm.

[0046] After obtaining the distilled water with a low tritium content, the present invention sequentially repeats the steps of electrolysis, combustion, condensation and distillation on the distilled water with a low tritium content to obtain the low-background low-tritium water. As a specific embodiment of the present invention, the number of repetitions of repeating electrolysis, combustion, condensation and distillation can be more than 2 times, specifically 2 times or 3 times.

[0047] The electrolytic cell of the present invention based on SPE electrolyzes a certain volume of water source (distilled water) in a closed system not affected by the environment to generate hydrogen with as low a tritium content as possible. Then, the generated hydrogen is introduced through the hydrogen inlet 2 of the combustion tube, and excessive oxygen is introduced through the oxygen inlet 1 of the combustion tube. First, the temperature of the combustion tube is controlled below 450 °C (to ensure that the mixed gas is not ignited), and then hydrogen and oxygen are introduced (to form a stable contact interface at the tube plug before combustion). After maintaining for 3 - 5 minutes, the temperature is slowly increased (5 °C / min) until the mixed gas is ignited (generally ignited at about 520 °C), and this temperature is maintained until the combustion ends. A high-temperature alumina cylinder is placed in the combustion tube, and this operation plays an important role in maintaining stable gas combustion and improving production efficiency. The purpose of inletting gas from both ends is to enable stable combustion on the contact surface of hydrogen and oxygen during the process of diffusing from both ends of the tubular closed combustion container to the middle. This combustion method can make hydrogen more fully oxidized, thereby further improving the production efficiency of water vapor. At the same time, this combustion method is very stable, avoiding the problem of deflagration of hydrogen and oxygen mixture at high temperatures, and further ensuring the safety of equipment and personnel. The water vapor generated by combustion is discharged through the water vapor outlet 3. The first half or less of the volume of the water sample collected before condensation, which is generated by electrolysis and combustion of the water sample, is finally distilled to remove impurity ions to obtain pure water with as low a tritium content as possible. The collected water sample needs to go through the cycles of the four steps of electrolysis, combustion, condensation, and distillation multiple times to finally obtain the low-background low-tritium water.

[0048] To further illustrate the present invention, the technical solutions provided by the present invention will be described in detail below in conjunction with embodiments, but they cannot be understood as limiting the protection scope of the present invention.

[0049] Example 1

[0050] In this example, considering the influence of the detection lower limit of the liquid scintillation counter, a tritium standard solution with an activity of 40 Bq / L and a volume of 500 mL is used as the original sample (water source) to prepare low-background low-tritium water.

[0051] The liquid inlet of the electrolytic cell is connected to the liquid storage tank through a pipeline. The hydrogen outlet of the SPE electrolysis system is connected to the hydrogen inlet of the quartz tube through a pipeline. The water vapor outlet of the quartz tube is connected to the condenser through a pipeline. The outlet of the condenser and the container for distillation are placed in a closed space.

[0052] The original sample is placed in the SPE electrolysis system and electrolyzed under the conditions of a current of 40 A and a temperature of about 15 °C. The low-tritium-content hydrogen obtained by electrolysis is introduced into the quartz tube through the hydrogen inlet 2 of the quartz combustion tube as shown at a volume flow rate of 25 L / h. At the same time, oxygen with a purity of 99.99% is introduced at a volume flow rate of 30 L / h through the oxygen inlet 1 of the quartz combustion tube as shown. Figure 1 shown quartz combustion tube, and at the same time, oxygen with a purity of 99.99% is introduced into the quartz tube through the oxygen inlet 1 of the quartz combustion tube as shown at a volume flow rate of 30 L / h. Figure 1The oxygen inlet 1 of the shown quartz combustion tube is introduced into the quartz tube at a temperature below 450 °C. After 4 minutes of introduction, it is heated at a rate of 5 °C / min to about 520 °C for ignition; hydrogen and oxygen will stably burn on the contact surface to generate low-tritium-content water vapor, and the entire process of generating water vapor by combustion proceeds simultaneously with the electrolysis process;

[0053] The low-tritium-content water vapor generated by combustion is condensed and collected under the condensation condition of 1 °C. A sample is collected every time the volume of the electrolyzed water sample decreases by 120 mL, and a total of four samples are collected to obtain low-tritium water samples at different stages.

[0054] The four collected samples are respectively subjected to atmospheric distillation. Keep the distillation temperature at about 100 °C, discard the last 5 mL of liquid, and end the distillation when the conductivity of the final sample is less than or equal to 5 μS / cm. When the conductivity of the sample is greater than 5 μS / cm, secondary distillation is required to eliminate the influence of impurity ions, and four different-stage low-tritium water samples after electrolysis, combustion, condensation, and distillation treatment are obtained.

[0055] According to the order of sample collection, the samples are divided into four stages: one, two, three, and four. 8 mL of the samples from the four stages are respectively added with 12 mL of scintillation liquid and measured using liquid scintillation counting method, and the obtained results are listed in Table 1.

[0056] Table 1 Test results of low-tritium water samples obtained at different stages

[0057] The first stage The second stage The third stage The fourth stage DPM 6.03 6.25 7.17 7.69 Bq / L 12.56 13.02 14.94 16.02

[0058] The data in Table 1 show that the increase in the activity of the samples obtained in the first stage and the second stage is relatively small, only increasing by about 0.46 Bq / L. The activity level of the samples collected in the third stage increases significantly, indicating that the activity of the samples increases with the decrease in the remaining volume of the electrolyzed water sample. Especially when the remaining volume of the electrolyzed water sample is reduced by half or more, the activity level of the collected samples is significantly improved. In order to further reduce the activity in the collected samples, the present invention only collects the samples generated when the remaining volume of the electrolyzed water sample is greater than or equal to one-half of the initial total volume to ensure that the collected samples have a lower activity level.

[0059] Example 2

[0060] In this example, considering the influence of the detection limit of the liquid scintillation counter, 500 mL of tritium standard solution with an activity of 500 Bq / L is used as the original sample (water source), and the system connected in Example 1 is used to prepare low-background low-tritium water according to the following method:

[0061] Electrolysis is carried out according to the method of Example 1, except that 500 mL of tritium standard solution with an activity of 500 Bq / L is used as the original sample;

[0062] Carry out combustion according to the method of Example 1;

[0063] Condense and collect the water vapor generated by combustion under the condensation condition of 1 °C. Stop collecting when the total volume of the water sample to be electrolyzed is reduced by half. Carry out atmospheric distillation on the collected sample at a temperature of 100 °C to obtain the first-cycle sample. Discard the last 5 mL of the distillate. If the conductivity of the sample after distillation is less than or equal to 5 μS / cm, proceed to the next step; otherwise, repeat the distillation step until the conductivity of the sample is qualified.

[0064] Repeat electrolysis, combustion, condensation, and distillation on the first-cycle sample successively according to the above conditions to obtain the second-cycle sample. Repeat electrolysis, combustion, condensation, and distillation on the second-cycle sample again according to the above conditions to obtain the third-cycle sample. And take 8 mL from the sample obtained in each cycle and mix it with 12 mL of the scintillation solution for measurement.

[0065] Measure the activity levels of the samples with different cycle numbers for the sample to be measured by liquid scintillation counting method, and the results are listed in Table 2.

[0066] Table 2 Test results of low-tritium water samples obtained with different cycle numbers

[0067] The first cycle The second cycle The third cycle DPM 92.4 41.2 18.9 Bq / L 192.5 85.8 39.4

[0068] Explanation of the results in Table 2: Repeated steps of electrolysis, combustion, and condensation can significantly reduce the tritium activity level in the sample.

[0069] Example 3

[0070] In this example, 500 mL of distilled water with a conductivity ≤ 5 μS / cm is used as the original sample (water source) to prepare low-background low-tritium water.

[0071] Carry out electrolysis according to the method of Example 2, except that 500 mL of distilled water with a conductivity ≤ 5 μS / cm is used as the original sample;

[0072] Carry out combustion, condensation, and distillation according to the method of Example 2;

[0073] Repeat the steps of electrolysis, combustion, condensation, and distillation successively according to the method of Example 2 for 3 times to obtain about 40 mL of low-background low-tritium water sample.

[0074] Take 8 mL of the low-background low-tritium water sample and add 12 mL of the scintillation solution to prepare two parallel samples, named low-tritium water 1 and low-tritium water 2 respectively. At the same time, prepare the samples to be measured from the distilled water before electrolysis and the groundwater with a conductivity ≤ 5 μS / cm after distillation in the same way and name them distilled water and background groundwater respectively. Use a 1220 Quantulus ultra-low-background liquid scintillation spectrometer to test the tritium activity levels of the samples, and the results are listed in Table 3.

[0075] Table 3 Test Results of Water Samples from Different Sources

[0076] Sample name Distilled water Background groundwater Low-tritium water 1 Low-tritium water 2 Instrument efficiency 26.9％ 26.9％ 26.9％ 26.9％ Sampling volume (mL) 8.0 8.0 8.0 8.0 Background measurement time (min) 1000 1000 1000 1000 Sample measurement time (min) 1000 1000 1000 1000 Background counting rate (cpm) 0.68 0.68 0.68 0.68 Sample counting rate (cpm) 1.40 0.68 0.70 0.70 Sample content (Bq / L) 0.28 -0.03 0.14 0.13

[0077] The measurement results in Table 3 show that: after the treatment by the method provided by the present invention, compared with the distilled water used as the preparation raw material, the tritium content in the sample decreases from 0.28 Bq / L to 0.13 Bq / L, and the tritium activity level is reduced by more than half, and the sample counting rate is very close to the background level.

[0078] Using the method provided by the present invention, ordinary distilled water can be prepared into low-background and low-tritium water that can meet the background measurement requirements. Moreover, this method has the characteristics of good safety and high preparation efficiency. Compared with ordinary distilled water, the activity level of the sample prepared by this method is lower and the sample purity is higher, which can meet the requirements for the background water sample during the measurement of low-activity samples.

[0079] Although the above embodiments have described the present invention in detail, they are only a part of the embodiments of the present invention, rather than all embodiments. People can also obtain other embodiments based on these embodiments without creative efforts, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A preparation method of low-background low-tritium water, characterized in that, Comprising the following steps: Electrolyzing a water source using an SPE electrolysis system to obtain hydrogen with a low tritium content; Mixing the hydrogen with a low tritium content and oxygen for combustion and then condensing to obtain condensed water with a low tritium content; Distilling the condensed water with a low tritium content to obtain distilled water with a low tritium content; Sequentially repeating the steps of electrolysis, combustion, condensation, and distillation for the distilled water with a low tritium content to obtain the low-background low-tritium water.

2. The preparation method of the low-background and low-tritium water according to claim 1, wherein The conductivity of the water source is ≤5 μS / cm; The water source includes distilled water, tap water, or commercially available mineral water.

3. The preparation method of the low-background and low-tritium water according to claim 1 or 2, characterized in that, The current of the electrolysis is 38 - 42 A, and the temperature of the electrolysis is 13 - 17 °C.

4. The preparation method of the low-background and low-tritium water according to claim 1, wherein The purity of the oxygen is greater than or equal to 99.99%; The molar ratio of the hydrogen to the oxygen is 1:1.0 - 1.

3.

5. The preparation method of low-background and low-tritium water according to claim 1 or 4, characterized in that, The combustion is carried out in a combustion tube; the temperature of the combustion tube is 500 - 540 °C During the combustion process, the volume flow rate of oxygen is 28 - 32 L / h, and the volume flow rate of hydrogen is 23 - 27 L / h.

6. The preparation method of the low-background and low-tritium water according to claim 1, characterized in that, The electrolysis, combustion, and condensation are continuously carried out in a closed system, and the distillation is carried out in a separate density system; The temperature of the condensation is 0 - 4 °C.

7. The preparation method of the low-background and low-tritium water according to claim 1 or 6, wherein Based on the volume of the water source, the water vapor collected by condensation is part of the water vapor generated by combustion, and the part of the water vapor is the water vapor generated by the combustion of hydrogen and oxygen generated by electrolyzing part of the water source. The volume ratio of the part of the water source to the water source is less than or equal to 0.

5.

8. The preparation method of the low-background and low-tritium water according to claim 7, characterized in that, The condensation is two-stage condensation.

9. The preparation method of low-background and low-tritium water according to claim 1, wherein The temperature of the distillation is 100 - 200 °C; The conductivity of the distilled water with a low tritium content is less than or equal to 5 μS / cm.

10. The preparation method of the low-background and low-tritium water according to claim 1, wherein, The number of repetitions of sequentially repeating electrolysis, combustion, condensation, and distillation is more than 2 times.

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