Online analysis method of primary loop boric acid

Abstract

The invention provides an online analysis method of primary loop boric acid, and belongs to the technical field of boric acid detection. The method comprises the following steps: firstly, diluting a water sample with demineralized water, dropwise adding a methyl red indicator, and carrying out acid solution titration; when acid solution titration reaches a first end point, mannitol and phenolphthalein indicators are added for alkaline solution titration, and when acid solution titration reaches a second end point, a C alkaline solution and a V alkaline solution are recorded; and finally, calculating the concentration of boric acid according to the sampling amount V0 of the water sample, the C alkali solution and the V alkali solution. The two indicators are respectively used in the two continuous titration processes, the indicator added for the first time can indicate the arrival of the first titration end point, and the indicator added for the second time does not interfere with the arrival of the second titration end point indicated by the indicator for the second time. According to the method, for judging the titration end point of methyl red, the design of double light source detection is adopted, and the titration end point of which the pH value is equal to 5.2 + / -0.2 is determined by calculating the absorbance value of the double light sources.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of borate detection, and particularly relates to an online analysis method of borate in a primary loop. BACKGROUND

[0002] The borate is used as a neutron absorber in a primary loop of a nuclear power plant, and the content of the borate is adjusted to control power. The borate online monitor (referred to as a boron meter) is an important means for monitoring the reactivity of the reactor of the nuclear power plant, and plays a vital role in nuclear safety. Therefore, the accuracy and stability of the operation data of the boron meter play a very important role in the safe and economic operation of the nuclear power. Therefore, the boron meter is increasingly concerned in the operation of the nuclear power.

[0003] Common methods for analyzing borate include inductively coupled plasma mass spectrometry, curcumin spectrophotometry, azomethine-H acid method, mannitol method and neutron method. The methods for online analysis of borate in the primary loop of the nuclear power plant include the neutron method and the mannitol method. The neutron method has the advantages that the detection device can be directly installed on the container or the flow pipeline, the liquid to be measured in the primary loop does not need to be taken out, the generation of radioactive waste liquid is avoided, the measurement data is rapid, and the measurement period is short. The disadvantage is that the stability of the analysis data is poor. The mannitol method can measure high-concentration borate, is simple to operate, requires less medicine, and has good data stability. The pH electrode is often used as an indication of the titration end point. The electrode is interfered by impurities in the sample water during use, which reduces the measurement performance and causes the measurement result to drift. The measurement electrode also has an aging phenomenon during use. Therefore, in order to maintain the good working state of the electrode, the electrode needs to be regularly maintained and calibrated, and the electrolyte in the reference electrode needs to be regularly replaced, which increases the workload during use. Therefore, it is of great significance to study an online analysis method of borate in the primary loop. SUMMARY

[0004] The present application aims to provide an online analysis method of borate in a primary loop, so as to solve the problems of unstable data and low accuracy in the borate detection in the prior art.

[0005] In order to achieve the above-mentioned application purposes, the present application provides the following technical solutions: The present application provides an online analysis method of borate in a primary loop, comprising the following steps: Step one: dilute the water sample with desalted water, and add methyl red indicator and then perform acid solution titration; Step two: add mannitol and phenolphthalein indicator after the acid solution titration reaches the first end point, perform alkali solution titration, reach the second end point, and record C 碱溶液 and V 碱溶液 ; Step three: according to the sampling amount V0, C 碱溶液 and V 碱溶液Calculate the concentration of boric acid.

[0006] Preferably, in step one, the concentration of the methyl red indicator is 0.002~0.006%, and the amount used is 0.4~0.6 mL.

[0007] Preferably, in step one, the acid solution is a hydrochloric acid solution, a sulfuric acid solution, or a nitric acid solution; the concentration of the acid solution is 0.001~0.05 mol / L.

[0008] Preferably, in step two, the method for determining when the acid solution titration reaches the first endpoint is to measure the absorbance of the solution. The first endpoint of the titration is reached when the absorbance at 450 nm is equal to the absorbance at 550 nm or when the absorbance at 550 nm is greater than the absorbance at 450 nm by 0.030.

[0009] Preferably, in step two, the concentration of mannitol is 5-15%, and the amount used is 4-6 mL.

[0010] Preferably, in step two, the concentration of the phenolphthalein indicator is 0.03~0.05%, and the dosage is 0.5~1.5mL.

[0011] Preferably, in step two, the alkaline solution is a sodium hydroxide solution or a potassium hydroxide solution; the concentration of the alkaline solution is 0.005~0.2 mol / L.

[0012] Preferably, in step two, the method for determining whether the alkaline solution titration has reached the second endpoint is to measure the absorbance of the solution. When the absorbance at 550 nm increases by 0.02 to 0.160, the second endpoint is reached.

[0013] The beneficial effects of this invention are: The online analysis method for boric acid in the first loop of the present invention differs from the conventional boric acid analysis method which uses a pH electrode as the titration endpoint indicator. The present invention uses two indicators in two consecutive titration processes, and the indicator added in the first titration can indicate the arrival of the first titration endpoint without interfering with the indicator in the second titration indicating the arrival of the second titration endpoint.

[0014] This invention employs a dual-light source detection design to determine the titration endpoint of methyl red. The pH value of the titration endpoint is determined by calculating the absorbance values ​​of the two light sources, with a final value of 5.2 ± 0.2. Previously, methyl red was only applicable to indicating a color change range of 4.2–6.2; now, it can be used to determine a pH of 5.2 ± 0.2. With a fixed indicator concentration, the pH value of the solution can be calculated from the absorbance of the indicator's color change at a specific wavelength, essentially using the indicator as a pH meter. Attached Figure Description

[0015] Figure 1A schematic diagram of the apparatus used in the online boric acid analysis method with a primary loop. Figure 2 This is a flowchart of the online analysis method for primary loop boric acid according to the present invention; Figure 3 The scan curves are for solutions containing methyl red indicator at different pH values; Figure 4 Scan curves of solutions containing only phenolphthalein indicator at different pH values; Figure 5 The scan curves are for solutions containing methyl red and phenolphthalein indicators at different pH values. Detailed Implementation

[0016] This invention provides an online analysis method for primary loop boric acid, comprising the following steps: Step 1: Dilute the water sample with deionized water, add methyl red indicator, and then perform acid titration; Step 2: After the acid solution titration reaches the first endpoint, add mannitol and phenolphthalein indicator, and perform alkaline solution titration until the second endpoint is reached. Record the value of C. 碱溶液 and V 碱溶液 ; Step 3: Based on the water sample volume V0 and C 碱溶液 and V 碱溶液 Calculate the concentration of boric acid.

[0017] In this invention, in step one, the concentration of the methyl red indicator is 0.002~0.006%, preferably 0.003~0.005%, more preferably 0.004%, and the amount used is 0.4~0.6mL, preferably 0.5mL.

[0018] In this invention, in step one, the acid solution is a hydrochloric acid solution, a sulfuric acid solution, or a nitric acid solution, preferably a hydrochloric acid solution; the concentration of the acid solution is 0.001~0.05 mol / L.

[0019] In this invention, in step two, the method for determining when the acid solution titration reaches the first endpoint is to measure the absorbance of the solution. When the absorbance at 450 nm is equal to the absorbance at 550 nm, or when the absorbance at 550 nm is greater than the absorbance at 450 nm by 0.030, the first endpoint of the titration is reached.

[0020] In this invention, in step two, the concentration of mannitol is 5-15%, preferably 8-12%, more preferably 10%, and the amount used is 4-6 mL, preferably 5 mL.

[0021] In this invention, in step two, the concentration of the phenolphthalein indicator is 0.03~0.05%, preferably 0.04%, and the amount used is 0.5~1.5mL, preferably 1.0mL.

[0022] In this invention, in step two, the alkaline solution is a sodium hydroxide solution or a potassium hydroxide solution, preferably a sodium hydroxide solution; the concentration of the alkaline solution is 0.005~0.2 mol / L.

[0023] In this invention, in step two, the method for determining whether the alkaline solution titration has reached the second endpoint is to measure the absorbance of the solution. When the absorbance at 550 nm increases by 0.02 to 0.160, the second endpoint is reached.

[0024] The first endpoint is due to the acidity of boric acid. During operation, the primary circuit requires a slightly alkaline solution (generally around pH 7.2) to improve the corrosion resistance of structural materials. This necessitates the addition of a certain amount of LiOH. Some boric acid reacts with LiOH to form borate, reducing the amount of boric acid. If this boric acid concentration is not considered during titration, the measured boric acid concentration will be lower than the actual amount. Therefore, when using titration, the sample's pH value needs to be measured beforehand. An acidic solution is added to adjust the pH to 5.2 ± 0.2, followed by alkaline titration to the equivalence point. Boric acid is a weak acid; mannitol is added to combine it into a hydroxyl complex with a higher degree of dissociation than boric acid. The hydrogen ions precipitated from the borate-hydroxyl complex can be directly titrated with an alkaline solution. An alkaline solution (generally sodium hydroxide solution) is added to adjust the pH to 9.0 ± 0.2. The concentration of boric acid in the sample can then be calculated based on the sample volume, the concentration of the sodium hydroxide solution, and the titration amount.

[0025] The disadvantages of the existing pH electrode are: 1. It requires periodic calibration; 2. The measurement data is greatly affected by the performance of the pH electrode; 3. The pH electrode needs to be replaced approximately once a year. This invention does not have these problems.

[0026] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0027] Example 1

[0028] Take a water sample of volume V0, dilute it with deionized water, add 0.5 mL of 0.004% methyl red indicator, and then add hydrochloric acid solution (concentration 0.02 mol / L). Measure the absorbance of the solution at 450 nm and 550 nm. Titrate until the absorbance at 450 nm is equal to that at 550 nm, reaching the first endpoint (pH value approximately 5.2 ± 0.2). Stop the titration. The scanning curves at different pH values ​​during the titration process are shown in [Figure number missing].Figure 3 As shown.

[0029] from Figure 3 It can be seen that when acid solution is added dropwise to the solution, the pH value of the solution will slowly decrease from high to low. When the pH of the solution is 5.1, the absorbance of the solution at 450 nm and the absorbance at 550 nm are basically equal, which can be used to indicate the arrival of the titration endpoint (or to indicate that pH=5.4 has been reached, it is only necessary to titrate until the absorbance of the solution at 550 nm is greater than the absorbance of the solution at 450 nm by 0.030. The device used in this invention has a 30 mm optical path, but other optical path sizes can also be used. The judgment value just needs to be changed proportionally).

[0030] from Figure 3 It can be seen that as the pH value increases, the absorption of the solution with added methyl red indicator decreases at 550 nm and increases at 450 nm (initially, the absorbance at 550 nm is greater than that at 450 nm). As the pH value increases, the absorbance at 450 nm becomes closer to that at 550 nm. When the absorbance at 450 nm equals that at 550 nm (or differs by a certain value), the pH value of the solution is 5.2 ± 0.2, which is the titration endpoint when using acid titration.

[0031] After stopping the titration, add 5 mL of 10% mannitol and 1 mL of 0.04% phenolphthalein indicator, then add sodium hydroxide solution (C). NaOH =0.05mol / L), measure the absorbance of the solution at 550nm, titrate until the absorbance increases by 0.100 (the apparatus only measures absorbance at 550nm, 450nm is off), reaching the titration endpoint (pH value is about 8.8), stop the titration, and record the titration volume V of sodium hydroxide used. NaOH . Figure 5 The scan curves are for solutions containing methyl red and phenolphthalein indicators at different pH values.

[0032] We also measured the scanning curves of solutions containing only phenolphthalein indicator at different pH values, such as... Figure 4 As shown.

[0033] from Figure 4 and Figure 5 As can be seen, the solution gradually changes from colorless to red as the pH value increases. At pH = 9.0 ± 0.2, a noticeable increase in absorbance at 550 nm is observed. Furthermore, comparison shows that the addition of methyl red does not affect the absorbance at 550 nm; therefore, the titration endpoint can be determined by measuring the change in absorbance at 550 nm.

[0034] Figure 4 The color change is as follows: as the titration proceeds, the pH value increases, and the solution changes from colorless to pink.

[0035] Figure 5 The color change is as follows: as the titration proceeds, the pH value increases, and the solution changes from yellow to orange (due to the addition of methyl red indicator in the previous titration step).

[0036] Finally, based on the water sample volume V0 and the sodium hydroxide concentration (C) NaOH ) and titration volume (V) NaOH The concentration of boric acid in the solution to be tested is calculated.

[0037] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. An online analysis method for primary-loop boric acid, characterized in that, Includes the following steps: Step 1: Dilute the water sample with deionized water, add methyl red indicator, and then perform acid titration. Step 2: After the acid solution titration reaches the first endpoint, add mannitol and phenolphthalein indicator, and perform alkaline solution titration until the second endpoint is reached. Record the value of C. 碱溶液 and V 碱溶液 ; Step 3: Based on the water sample volume V0 and C 碱溶液 and V 碱溶液 Calculate the concentration of boric acid.

2. The online analysis method for primary loop boric acid according to claim 1, characterized in that, In step one, the concentration of the methyl red indicator is 0.002~0.006%, and the amount used is 0.4~0.6 mL.

3. The online analysis method for primary-loop boric acid according to claim 1 or 2, characterized in that, In step one, the acid solution is a hydrochloric acid solution, a sulfuric acid solution, or a nitric acid solution; the concentration of the acid solution is 0.001~0.05 mol / L.

4. The online analysis method for primary loop boric acid according to claim 3, characterized in that, In step two, the method for determining when the acid solution titration reaches the first endpoint is to measure the absorbance of the solution. The first endpoint of the titration is reached when the absorbance at 450 nm is equal to the absorbance at 550 nm or when the absorbance at 550 nm is greater than the absorbance at 450 nm by 0.

030.

5. The online analysis method for primary-loop boric acid according to claim 2 or 4, characterized in that, In step two, the concentration of mannitol is 5-15%, and the amount used is 4-6 mL.

6. The online analysis method for primary loop boric acid according to claim 5, characterized in that, In step two, the concentration of the phenolphthalein indicator is 0.03~0.05%, and the amount used is 0.5~1.5mL.

7. The online analysis method for primary-loop boric acid according to claim 4 or 6, characterized in that, In step two, the alkaline solution is a sodium hydroxide solution or a potassium hydroxide solution; the concentration of the alkaline solution is 0.005~0.2 mol / L.

8. The online analysis method for primary loop boric acid according to claim 7, characterized in that, In step two, the method for determining whether the alkaline solution titration has reached the second endpoint is to measure the absorbance of the solution. When the absorbance at 550 nm increases by 0.02 to 0.160, the second endpoint is reached.

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