Method for analyzing total alpha in boric acid-containing water

Abstract

The invention belongs to the technical field of water quality radioactivity detection, and particularly relates to a method for analyzing total alpha in boric acid-containing water. Heating the surface of the sample liquid in the stainless steel sample measuring disc by using an infrared dryer to evaporate the water, adding ethanol into the sample to continue heating when the water sample begins to separate out crystals or the water sample is thick and is about to separate out crystals, repeatedly adding ethanol and heating when the water sample begins to separate out crystals or the water sample is thick and is about to separate out crystals, and measuring the alpha specific activity until the sample is completely evaporated to dryness and no crystal is generated. The mode of heating the surface of the sample is adopted, the boric acid-containing sample cannot splash in the heating treatment process, the loss of alpha radionuclide due to liquid splashing is avoided, and the measurement result is more accurate; boric acid in the sample is volatilized by ethanol treatment, so that the influence of boric acid on sample measurement is avoided, and the measurement result is more accurate.

Description

Technical Field

[0001] The invention belongs to the technical field of water quality radioactivity detection, and particularly relates to a total alpha analysis method in boric acid-containing water. Background Art

[0002] When the fuel cladding of a pressurized water reactor nuclear power plant is damaged, fuel may be released from the fuel assembly into the coolant. Among them, alpha radionuclides, mainly transuranic elements, may cause alpha contamination of the system, equipment and work site, and also increase the risk of alpha contamination of workers. When this situation is suspected, it is necessary to measure the total alpha radioactivity of the coolant to accurately grasp the status of the nuclear fuel assembly and guide the radiation protection work of alpha radionuclides.

[0003] At present, the standard analytical methods for total alpha in my country are: the standard methods for measuring total alpha radioactivity in water include the international standard ISO9696-2007 "Water quality-Measurement of total alpha in non-salt water-Thick source method" and the national recommended standard GB / T 5750.13-2023 "Standard test methods for drinking water Part 13: Radioactivity indicators" and the environmental standard HJ 898-2017 "Determination of total alpha radioactivity in water quality-Thick source method". The main steps of these methods are similar: heat the acidified water sample to evaporate to near dryness, burn the residue at high temperature and grind it into powder, put the powder into the measuring plate, and use a low background alpha measurement system to measure the alpha specific activity.

[0004] The coolant of a pressurized water reactor nuclear power plant contains high concentrations of boric acid. Using existing standard methods for sample processing will produce a large amount of boric acid crystals. The solution containing boric acid crystals is very easy to splash during the heating process. The splashing loss of α radioactive nuclides will cause inaccurate measurement results. The presence of boric acid crystals in the residue will affect sample spreading and measurement. Therefore, the existing method is not suitable for the total α measurement of boric acid samples. Summary of the invention

[0005] The object of the present invention is to provide a total alpha analysis method in boric acid-containing water to solve the problems existing in the existing total alpha standard analysis method for measuring boric acid-containing samples.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] A total α analysis method in boric acid-containing water comprises the following steps: using an infrared dryer to heat the surface of a sample liquid in a stainless steel sample measuring plate to evaporate its water content; when the water sample begins to precipitate crystals or the water sample becomes thick and is about to precipitate crystals, adding ethanol to the sample and continuing to heat it; repeatedly adding ethanol and heating the sample when the water sample begins to precipitate crystals or the water sample becomes thick and is about to precipitate crystals, until the sample is completely evaporated and no crystals are produced, and measuring the α specific activity.

[0008] Determination of instrument background: Take an unused and uncontaminated sample measuring disc, rinse it with anhydrous ethanol, dry it, and place it on a low-background α and β measuring instrument to continuously measure the total α background count rate of the instrument for more than 2 hours.

[0009] Determination of standard source: Place the sample measuring plate in the drying plate of the infrared dryer, accurately add 5Bq~10Bq of standard substance to the center of the sample measuring plate, add 3mL of anhydrous ethanol to the sample measuring plate, shake the drying plate slightly to make the standard source cover the bottom of the sample measuring plate, place the drying plate in the infrared dryer to heat, evaporate the liquid in the sample measuring plate, take out the drying plate and cool it naturally for 3 minutes, measure the total α count rate of the standard source measuring plate on the low background α, β measuring instrument, measure at least three times, each time for 60 minutes, record the average value of the standard source count rate, and record the counting time.

[0010] Preparation of samples to be tested: Place the sample measuring tray in the drying tray of the infrared dryer, accurately measure 10 mL of sample and slowly add it to the center of the sample measuring tray, gently shake the sample measuring tray to cover the bottom of the sample measuring tray with the sample, place the drying tray in the infrared dryer and heat it until crystals begin to precipitate, then take out the drying tray and cool it naturally for 5 minutes, add 3 mL of anhydrous ethanol to the sample measuring tray, gently shake the drying tray to dissolve the boric acid in the sample, and then heat it in the infrared dryer for 1 minute. Pay attention to the heating process. When crystals begin to precipitate in the sample measuring tray or the liquid area shrinks, take out the drying tray and evaporate the remaining ethanol with the residual heat of the drying tray, cool it naturally for 3 minutes, repeat the step of adding anhydrous ethanol and heating until there is no crystal visible to the naked eye, then repeat the step of adding anhydrous ethanol and heating twice to ensure that the boric acid crystals are completely volatilized.

[0011] Sample determination: After the sample to be tested is evaporated to dryness, the total α count rate is measured on a low-background α and β measuring instrument immediately. The measurement should be conducted at least three times, each time for 60 minutes. The average value of the standard source count rate and the counting time should be recorded.

[0012] Total α activity concentration: A—total α radioactivity concentration in the sample; N s —sample counting rate; N b —background count rate; E—detector efficiency; V—volume of sample evaporated in the measuring dish, detector efficiency Activity data of the α-241Am standard source measured on that day.

[0013] Result representation: When the measurement result is less than 0.1Bq / L, retain three decimal places; when the measurement result is greater than or equal to 0.1Bq / L, retain three significant figures.

[0014] The beneficial effects achieved by the present invention are:

[0015] The present invention adopts a method of heating the sample surface, so that the boric acid sample will not splash during the heating process, thereby avoiding the loss of alpha radioactive nuclides due to liquid splashing, and the measurement result is more accurate; ethanol treatment is used to volatilize the boric acid in the sample, thereby avoiding the influence of boric acid on sample measurement, and the measurement result is more accurate. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 A schematic diagram of a method for total alpha analysis in boric acid-containing water;

[0017] In the figure: 1-infrared drying machine; 2-sand tray; 3-sample measuring tray. DETAILED DESCRIPTION

[0018] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0019] A method for total α analysis in boric acid-containing water, using an infrared dryer to heat the sample liquid surface in a stainless steel sample measuring plate to evaporate its water, adding ethanol to the sample and continuing to heat it when the water sample begins to precipitate crystals or the water sample becomes viscous and is about to precipitate crystals, repeatedly adding ethanol and heating when the water sample begins to precipitate crystals or the water sample becomes viscous and is about to precipitate crystals, until the sample is completely evaporated and no crystals are produced. The α specific activity is measured using a low background α measurement system. The specific operation method is as follows:

[0020] Determination of instrument background: Take an unused and uncontaminated sample measuring disc, rinse it with anhydrous ethanol, dry it, and place it on a low-background α and β measuring instrument to continuously measure the total α background count rate of the instrument for more than 2 hours.

[0021] Determination of standard source: Place the sample measurement plate in the drying plate of the infrared dryer. Accurately add 5Bq to 10Bq of standard substance to the center of the sample measurement plate, add 3mL of anhydrous ethanol to the sample measurement plate, and gently shake the drying plate to make the standard source cover the bottom of the sample measurement plate. If the diameter of the sample measurement plate is large, the amount of anhydrous ethanol measured can be appropriately increased. Place the drying plate in the infrared dryer, turn on the instrument to heat, evaporate the liquid in the sample measurement plate, take out the drying plate and cool it naturally for 3 minutes. Measure the total α count rate of the standard source measurement plate on the low background α and β measuring instrument, measure at least three times, each time for 60 minutes, record the average value of the standard source count rate, and record the counting time.

[0022] Preparation of the sample to be tested: Place the sample measuring plate in the drying plate of the infrared dryer. Accurately measure 10mL of sample and slowly add it to the center of the sample measuring plate. Gently shake the sample measuring plate so that the sample covers the bottom of the sample measuring plate. If the diameter of the sample measuring plate is large, the amount of sample measured can be appropriately increased. Place the drying plate in the infrared dryer, turn on the instrument and heat until crystals begin to precipitate, then remove the drying plate and cool naturally for 5 minutes. Add 3mL of anhydrous ethanol to the sample measuring plate and gently shake the drying plate to dissolve the boric acid in the sample. Heat it in the infrared dryer for another 1 minute. Pay attention to the heating process. When crystals begin to precipitate in the sample measuring plate or the liquid area shrinks, remove the drying plate and evaporate the remaining ethanol with the residual heat of the drying plate. Cool naturally for 3 minutes. Repeat the step of adding anhydrous ethanol and heating until there is no visible crystallization, then repeat the addition of anhydrous ethanol and heating twice to ensure that the boric acid crystals are completely volatilized.

[0023] Sample determination: After the sample to be tested is evaporated to dryness, the total α count rate is measured on a low-background α and β measuring instrument immediately. The measurement should be conducted at least three times, each time for 60 minutes. The average value of the standard source count rate and the counting time should be recorded.

[0024] Detector efficiency: Where: Activity data Bq of α-241Am standard source measured on the day; Activity concentration of total α: Where: A—total α radioactive concentration in the sample (MBq / m 3 );N s —sample counting rate (counts / second, cps); N b —background count rate (counts / second, cps); E—detector efficiency (%); V—volume of sample evaporated in the measuring pan (cm 3 ).

[0025] Result representation: When the measurement result is less than 0.1Bq / L, retain three decimal places; when the measurement result is greater than or equal to 0.1Bq / L, retain three significant figures.

[0026] The invention uses an infrared dryer to heat the surface of the sample liquid to avoid splashing of the liquid; ethanol is added to the sample and heated to volatilize the boric acid in the sample.

Claims

1. A method for analyzing total α in boric acid-containing water, characterized in that: Use an infrared dryer to heat the surface of the sample liquid in the stainless steel sample measuring dish to evaporate its water. When the water sample begins to precipitate crystals or the water sample becomes viscous and is about to precipitate crystals, add ethanol to the sample and continue heating. Repeatedly add ethanol and heat when the water sample begins to precipitate crystals or the water sample becomes viscous and is about to precipitate crystals until the sample is completely evaporated and no crystals are produced, and measure the α specific activity.

2. The method for total α analysis in boric acid-containing water according to claim 1, characterized in that: Determination of instrument background: Take an unused and uncontaminated sample measuring disc, rinse it with anhydrous ethanol, dry it, and place it on a low-background α and β measuring instrument to continuously measure the total α background count rate of the instrument for more than 2 hours.

3. The method for total α analysis in boric acid-containing water according to claim 2, characterized in that: Determination of standard source: Place the sample measuring plate in the drying plate of the infrared dryer, accurately add 5Bq~10Bq of standard substance to the center of the sample measuring plate, add 3mL of anhydrous ethanol to the sample measuring plate, shake the drying plate slightly to make the standard source cover the bottom of the sample measuring plate, place the drying plate in the infrared dryer to heat, evaporate the liquid in the sample measuring plate, take out the drying plate and cool it naturally for 3 minutes, measure the total α count rate of the standard source measuring plate on the low background α, β measuring instrument, measure at least three times, each time for 60 minutes, record the average value of the standard source count rate, and record the counting time.

4. The method for total α analysis in boric acid-containing water according to claim 3, characterized in that: Preparation of samples to be tested: Place the sample measuring tray in the drying tray of the infrared dryer, accurately measure 10 mL of sample and slowly add it to the center of the sample measuring tray, gently shake the sample measuring tray to cover the bottom of the sample measuring tray with the sample, place the drying tray in the infrared dryer and heat it until crystals begin to precipitate, then take out the drying tray and cool it naturally for 5 minutes, add 3 mL of anhydrous ethanol to the sample measuring tray, gently shake the drying tray to dissolve the boric acid in the sample, and then heat it in the infrared dryer for 1 minute. Pay attention to the heating process. When crystals begin to precipitate in the sample measuring tray or the liquid area shrinks, take out the drying tray and evaporate the remaining ethanol with the residual heat of the drying tray, cool it naturally for 3 minutes, repeat the step of adding anhydrous ethanol and heating until there is no crystal visible to the naked eye, then repeat the step of adding anhydrous ethanol and heating twice to ensure that the boric acid crystals are completely volatilized.

5. The method for total α analysis in boric acid-containing water according to claim 4, characterized in that: Sample determination: After the sample to be tested is evaporated to dryness, the total α count rate is measured on a low-background α and β measuring instrument immediately. The measurement should be conducted at least three times, each time for 60 minutes. The average value of the standard source count rate and the counting time should be recorded.

6. The method for total alpha analysis in boric acid-containing water according to claim 5, characterized in that: Total α activity concentration: A—total α radioactivity concentration in the sample; N s —sample counting rate; N b —background count rate; E—detector efficiency; V—volume of sample evaporated in the measuring dish, detector efficiency Activity data of the α-241Am standard source measured on that day.

7. The method for total alpha analysis in boric acid-containing water according to claim 6, characterized in that: Result representation: When the measurement result is less than 0.1Bq / L, retain three decimal places; when the measurement result is greater than or equal to 0.1Bq / L, retain three significant figures.

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