Chemical control method for deoxidizing primary loop during overhaul start-up period of nuclear power plant

Abstract

The invention relates to the technical field of pressurized water reactor nuclear power plant chemistry, in particular to a chemical control method for deoxygenization of a primary loop in the overhaul starting period of a nuclear power plant, and the method comprises the following steps: 1, confirming that the primary loop meets the hydrazine filling condition; 2, adding a hydrazine solution into a primary loop reactor coolant for the first time; 3, the temperature of the main system is increased, after full reaction, whether the dissolved oxygen content of a main system loop and the liquid phase of the voltage stabilizer is qualified or not is checked, if not, the step 4 is executed, and hydrazine is added; 4, adding the hydrazine solution into the primary loop reactor coolant again; 5, after full reaction, checking whether the liquid-phase dissolved oxygen content of the main system loop and the voltage stabilizer is qualified or not again, and if not, repeating the step 4 until the liquid-phase dissolved oxygen content is qualified; and step 6, sweeping and blowing the main system and putting the main system into operation of the desalting bed. According to the method, the chemical control method of the deoxidizing platform is optimized, and the deoxidizing effect is effectively improved; according to the method, a control formula of the hydrazine adding amount is provided, and the hydrazine adding frequency is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of chemical technology for pressurized water reactor nuclear power plants, and particularly to a chemical control method for deaeration of the primary loop during the startup of a nuclear power plant overhaul. Background Art

[0002] During the overhaul of a nuclear power plant unit, since the main system is open to the outside world, the reactor coolant contains a high level of dissolved oxygen after sufficient contact with air. Dissolved oxygen will greatly corrode equipment in a high-temperature environment and shorten the service life of the equipment. Therefore, during the reactor startup phase, deaeration of the primary loop reactor coolant is required. Hydrazine (chemical formula: N2H4) has strong reducibility and reacts with oxygen in water to form water and nitrogen without increasing the salt content in water, and is used for chemical deaeration of the primary loop in pressurized water reactor nuclear power plants. Therefore, during the overhaul of a nuclear power plant, after the reactor coolant is heated to a certain stage, a certain amount of hydrazine is added, and the reaction between hydrazine and oxygen is utilized to achieve the purpose of deaeration of the primary loop.

[0003] During the up-chemical deaeration platform stage of a nuclear power plant overhaul, if the amount of hydrazine added is too small, it needs to be added multiple times, and after each addition, it is necessary to wait until the oxygen concentration in the main system is stable before deciding the amount of hydrazine to be added; if too much is added, the oxygen concentration in the main system can quickly reach the qualified level, but the decomposition of hydrazine into ammonia (chemical formula: NH3) will occur due to the rise in the temperature of the reactor coolant, resulting in a large amount of ammonia and hydrazine residues in the main system. The operating personnel need to continuously carry out vapor purging of the pressurizer and nitrogen purging of the volume control tank (equipment number: RCV002BA) to sweep the ammonia and hydrazine into the ventilation system of the nuclear auxiliary building to reduce the concentrations of ammonia and hydrazine until the sum of the ammonia and hydrazine concentrations is less than or equal to 1.0 mg / kg as specified, and only then is it allowed to put into operation the purification demineralizer bed of the chemical and volume control system (system abbreviation: RCV). Therefore, adding too much or too little hydrazine greatly affects the progress of the overhaul. In the prior art, since the reaction between hydrazine and oxygen is very complex, the reaction rate depends on temperature, pH value, hydrazine concentration, catalyst, reaction time, etc. At the same time, there must be certain differences in the temperature control rate, purging control, chemical measurement, etc. for each deaeration. Therefore, it is very difficult to succeed in deaeration once only by formula calculation, and there is no truly suitable hydrazine addition scheme. Summary of the Invention

[0004] The present invention provides a chemical control method for deaeration of the primary loop during the startup of a nuclear power plant overhaul, which is used to solve the problems in the prior art that it is difficult to control the dosage of hydrazine added in the primary loop deaeration scheme during the startup of a nuclear power plant overhaul, the number of hydrazine additions is too many, and the subsequent cleaning of ammonia and hydrazine residues takes a long time and has high labor costs.

[0005] The technical solution of the present invention is as follows:

[0006] The present invention provides a chemical control method for deaeration of the primary circuit during the startup of a nuclear power plant overhaul, and the method includes:

[0007] Step 1: Confirm that the primary circuit meets the conditions for adding hydrazine.

[0008] Step 2: Add hydrazine solution to the primary circuit reactor coolant for the first time, and the calculation method for the volume of the first addition of hydrazine solution is as shown in formula (1);

[0009] V1 = 1.9×M (1)

[0010] Wherein, V1 is the volume of hydrazine with a concentration of 50% to be added; M is the dissolved oxygen concentration of the main system before addition.

[0011] Step 3: Raise the temperature of the main system. After sufficient reaction, check whether the dissolved oxygen content in the liquid phase of the main system loop and the pressurizer is qualified for deaeration. If it is unqualified, perform Step 4 to add hydrazine.

[0012] Step 4: Add hydrazine solution to the primary circuit reactor coolant again, and the calculation method for the volume of the added hydrazine solution is as shown in formula (2);

[0013] V2 = A×Y (2)

[0014] Wherein, V2 is the volume of 50% hydrazine to be added, Y is the dissolved oxygen concentration of the main system before addition, and A is the addition coefficient; if the dissolved oxygen content in the liquid phase in Step 3 is less than 0.4 mg / kg, A = 3.2; if the dissolved oxygen content in the liquid phase in Step 3 is greater than or equal to 0.4 mg / kg, the value of A should be reduced.

[0015] Step 5: After sufficient reaction, check again whether the dissolved oxygen content in the liquid phase of the main system loop and the pressurizer is qualified for deaeration. If it is unqualified, repeat Step 4 until the dissolved oxygen content in the liquid phase is qualified.

[0016] Step 6: Blow the main system and put the demineralizer bed into operation.

[0017] In some embodiments, specifically in Step 1, confirming that the primary circuit meets the conditions for adding hydrazine means that the reactor coolant system is in a cold shutdown state, the coolant temperature is 80°C to 120°C; the volume control tank is sealed with nitrogen; the 1st and 2nd mixed bed demineralizers of the chemical and volume control system and the purification bed bypass of the mixed bed demineralizer of the boron recovery system; the pressurizer heaters and main pumps of the main system are put into operation; the pressurizer spray has been fully opened.

[0018] In some embodiments, the criterion for determining whether the dissolved oxygen content in the main system loop and the pressurizer liquid phase is qualified for deoxygenation in step two is specifically whether the dissolved oxygen content in the liquid phase is less than 100 μg / kg; if the dissolved oxygen content in the liquid phase is less than 100 μg / kg, the chemical deoxygenation is qualified, and if the dissolved oxygen content in the liquid phase is greater than or equal to 100 μg / kg, hydrazine needs to be added again.

[0019] In some embodiments, in step three, the temperature of the main system is raised to 110 degrees Celsius.

[0020] 5. A chemical control method for deoxygenation of the primary loop during the startup of a nuclear power plant overhaul according to claim 1, characterized in that in step four, if the dissolved oxygen content in the liquid phase in step three is greater than or equal to 0.4 mg / kg, the value of A is 2.5.

[0021] In some embodiments, in step five, the secondary inspection of whether the dissolved oxygen content in the main system loop and the pressurizer liquid phase is qualified for deoxygenation is specifically whether the dissolved oxygen content in the liquid phase is less than 100 μg / kg.

[0022] In some embodiments, in step six, the main system is purged and the demineralizer bed is put into operation, specifically including directly putting into operation the mixed bed demineralizer of the boron recovery system after the dissolved oxygen content in step five is qualified, and then putting into operation the mixed bed demineralizer of the chemical and volume control system after the ammonia and hydrazine concentrations meet the requirements.

[0023] In some embodiments, when the ammonia and hydrazine concentrations meet the requirements, the specific requirement is that the sum of the ammonia and hydrazine concentrations does not exceed 1.0 mg / kg.

[0024] In some embodiments, putting into operation the mixed bed demineralizer of the chemical and volume control system specifically includes putting into operation the No. 1 mixed bed demineralizer of the chemical and volume control system or the No. 2 mixed bed demineralizer of the chemical and volume control system.

[0025] Implementing the present invention has the following beneficial effects:

[0026] The advantages of the present invention compared with the prior art are as follows:

[0027] 1) The present invention proposes a chemical control method for deoxygenation of the primary loop during the startup of a nuclear power plant overhaul. This method optimizes the chemical control method of the deoxygenation platform, effectively improves the deoxygenation effect; this method proposes a control formula for the addition amount of hydrazine, reducing the number of times of adding hydrazine.

[0028] 2) The present invention proposes a chemical control method for deoxygenation of the primary loop during the startup of a nuclear power plant overhaul. This method optimizes the control strategy for putting the demineralizer bed into operation after adding hydrazine, greatly shortening the residence time of the chemical deoxygenation process, extending the service life of the RCV mixed bed resin, and having extremely high economic benefits; the present invention is simple to operate and has strong applicability, and can be widely promoted and used. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a flowchart of a chemical control method for deaeration of the primary loop during the startup of a nuclear power plant overhaul proposed in an embodiment of the present invention. Detailed implementation manners

[0030] The technical solutions of the present invention will be clearly and completely described below in conjunction with the accompanying drawings and specific implementation manners. Obviously, the described embodiments are some but not all of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0031] As Figure 1 shown, the present invention proposes a chemical control method for deaeration of the primary loop during the startup of a nuclear power plant overhaul, and the method includes:

[0032] Step 1: Determine that the primary loop meets the conditions for adding hydrazine, where the conditions include:

[0033] 1. The reactor coolant system (abbreviated as RCP in the system) is in a cold shutdown state, and the coolant temperature is 80°C to 120°C;

[0034] 2. The volume control tank RCV002BA is sealed with nitrogen;

[0035] 3. The No. 1 and No. 2 mixed bed demineralizers of the chemical and volume control system (abbreviated as RCV001 and RCV002DE) have been bypassed, and the purification bed of the mixed bed demineralizer of the boron recovery system (abbreviated as TEP006DE) has been bypassed;

[0036] 4. The main system pressurizer heater has been put into operation;

[0037] 5. The operator increases the pressurizer spray as much as possible to ensure the uniformity of the pressurizer water and the main loop water;

[0038] 6. The main pump has been put into operation.

[0039] Step 2: Add hydrazine to the primary loop reactor coolant for the first time. The added hydrazine solution is a commercially available 50% hydrazine solution. Add the 50% hydrazine solution to the chemical mixing tank REA006BA for the first time and inject it into the primary loop main system after meeting the conditions of Step 1. The calculation method for the first hydrazine addition is as shown in formula (1)

[0040] V1 = 1.9 × M (1)

[0041] where V1 is the volume of 50% hydrazine to be added, in L; M is the dissolved oxygen concentration in the main system before addition, in mg / kg.

[0042] Step 3: After the first addition of hydrazine, the temperature of the main system directly rises to nearly 110°C. After the reaction of the added hydrazine is sufficient, check the dissolved oxygen content in the liquid phase of the main system loop and the pressurizer. If the content is less than 100 μg / kg, the chemical deoxygenation is qualified. If the content is greater than or equal to 100 μg / kg, additional hydrazine needs to be added again.

[0043] Step 4: After the reaction of the added hydrazine is sufficient, according to the dissolved oxygen content in the liquid phase of the main system loop and the pressurizer in Step 3, add hydrazine again. When the decrease in oxygen content is slow and reaches a basic stability and Y exceeds 0.4 mg / kg, the calculation method for the second addition of hydrazine is as follows:

[0044] V2 = 2.5 × Y (2)

[0045] Where, V2 is the volume of hydrazine with a concentration of 50% to be added, in L; Y is the dissolved oxygen concentration of the main system before addition, in mg / kg.

[0046] When the decrease in oxygen content is slow and reaches a basic stability and is in the range of 100 μg / kg < Y < 0.4 mg / kg, the calculation method for the second addition of hydrazine is as follows:

[0047] V2 = 3.2 × Y (3)

[0048] Where, V2 is the volume of hydrazine with a concentration of 50% to be added, in L; Y is the dissolved oxygen concentration of the main system before addition, in mg / kg.

[0049] Step 5: After adding hydrazine again, check the dissolved oxygen content in the liquid phase of the main system loop and the pressurizer. If the oxygen content still does not meet the control specification of less than 100 μg / kg, repeat the addition amount in formula (2) or formula (3) to add hydrazine until it is qualified.

[0050] Step 6: Blow the main system and put the demineralizer into operation. After the oxygen content is qualified, purging and putting the demineralizer into operation are required. In the prior art, after the dissolved oxygen in the liquid phase of the main system loop and the pressurizer is qualified, detection and purging are carried out until the concentration of [NH3] + [N2H4] ≤ 1.0 mg / kg, and then the No. 1 or No. 2 mixed bed demineralizer (RCV001 or 002DE demineralizer) of the chemical and volume control system is put into operation. The demineralizers used are shown in Table 1.

[0051] Table 1 Demineralizer Information Table

[0052]

[0053] In the present invention, after the dissolved oxygen meets the requirements, the mixed bed demineralizer TEP006DE of the boron recovery system is directly put into operation, and after the concentrations of [NH3] + [N2H4] meet the requirements, the No. 1 or No. 2 mixed bed demineralizer of the chemical and volume control system (the RCV001 or 002DE demineralization bed) is put into operation. This control method can not only purify the excess ammonia and hydrazine by using the mixed bed demineralizer TEP006DE of the boron recovery system and meet the requirements quickly, but also the mixed bed demineralizer TEP006DE of the boron recovery system can continue to purify the main system without affecting any overhaul process, effectively saving the time of the critical path of the overhaul. In addition, the hydrogen-type resin used in TEP has a lower price, only about one-tenth of the lithium-type resin of RCV. By adopting this method, the service life of the RCV mixed bed resin can be greatly extended, with extremely high economic benefits.

[0054] The method proposed by the present invention is simple in operation and strong in applicability, which can effectively improve the deoxygenation effect, reduce the number of times of adding hydrazine, and greatly shorten the residence time of the chemical deoxygenation process. Table 2 below shows the deoxygenation process time-consuming of previous overhauls of a certain nuclear power plant unit.

[0055] Table 2 Deoxygenation process time-consuming of previous overhauls of a certain nuclear power plant unit

[0056]

[0057] As can be seen from the table, after adopting the hydrazine addition amount control formula of the present invention during the overhaul of code 106, the number of times of adding hydrazine is effectively reduced, and it can currently be basically stably controlled within 2 times; after adopting the method combining the hydrazine addition amount control formula of the present invention and changing the operation strategy of the demineralization bed during the overhaul of code 107, compared with the previous addition based on experience and the traditional bed operation strategy, the deoxygenation time-consuming is shortened by more than 90%, greatly shortening the time occupied by the critical path of deoxygenation.

[0058] In the prior art, the operator adds hydrazine based on experience (long time and many times). After the deoxygenation reaches the standard, it is purged until the residues of ammonia and hydrazine ≤ 1.0 mg / kg (long time, and during the purging period, since the demineralizer cannot be put into the main system, the main system cannot be purified), and finally the RCV001 / 002DE purification bed is put into operation.

[0059] The present invention uses the hydrazine dosing formula to add hydrazine for deoxygenation. After the deoxygenation reaches the standard, the purification method combining the operation of the mixed bed demineralizer TEP006DE of the boron recovery system and purging is used to remove the residues of ammonia and hydrazine until (short time, and the primary loop is purified during the removal of the residues of ammonia and hydrazine) ≤ 1.0 mg / kg, and finally the RCV001 / 002DE purification bed is put into operation. The present invention reduces the number of times of adding hydrazine, reduces the time of deoxygenation and removing the residues of ammonia and hydrazine, and reduces the labor, material and time costs, with good economic benefits.

[0060] The above embodiments only represent several implementation manners of the present invention. The description thereof is relatively specific and detailed, but it should not be construed as a limitation to the scope of the patent of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several variations and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the appended claims.

Claims

1. A chemical control method for primary circuit deoxygenation during overhaul startup of a nuclear power plant, characterized in that: The method comprises: Step 1: Confirm that the primary circuit meets the conditions for adding hydrazine; Step 2: Adding hydrazine solution to the primary reactor coolant for the first time. The volume of hydrazine solution added for the first time is calculated as shown in formula (1); V1=1.9×M (1) Wherein, V1 is the volume of hydrazine with a concentration of 50% to be added; M is the dissolved oxygen concentration of the main system before addition; Step 3: Raise the temperature of the main system, and after sufficient reaction, check whether the dissolved oxygen content of the main system loop and the stabilizer liquid phase is qualified for deoxygenation. If not, perform step 4 to add hydrazine; Step 4: Add hydrazine solution to the primary reactor coolant again. The volume of hydrazine solution added is calculated as shown in formula (2); V2=A×Y (2) Wherein, V2 is the volume to which 50% hydrazine needs to be added, Y is the dissolved oxygen concentration of the main system before addition, and A is the addition coefficient; if the dissolved oxygen content of the liquid phase in step three is less than 0.4 mg / kg, A=3.2; if the dissolved oxygen content of the liquid phase in step three is greater than or equal to 0.4 mg / kg, the value of A should be reduced; Step 5: After sufficient reaction, check again whether the main system loop and the stabilizer liquid phase dissolved oxygen content are qualified for deoxygenation. If not, repeat step 4 until the liquid phase dissolved oxygen content is qualified; Step 6: Purge the main system and put the desalting bed into operation.

2. A chemical control method for primary circuit deoxygenation during overhaul startup of a nuclear power plant according to claim 1, characterized in that: In the step 1, it is confirmed that the conditions for adding hydrazine to a loop are specifically as follows: the reactor coolant system is in a cold shutdown state, and the coolant temperature is 80°C to 120°C; the control box is sealed with nitrogen; the chemical and volume control system No. 1 and No. 2 mixed bed desalters, and the boron recovery system mixed bed desalter purification bed are bypassed; the main system stabilizer heater and main pump are put into operation; and the stabilizer sprays are all turned on.

3. A chemical control method for primary circuit deoxygenation during overhaul startup of a nuclear power plant according to claim 2, characterized in that: The standard for judging whether the liquid phase dissolved oxygen content of the main system loop and the stabilizer is qualified for deoxygenation in the step 2 is specifically whether the liquid phase dissolved oxygen content is less than 100 μg / kg; if the liquid phase dissolved oxygen content is less than 100 μg / kg, the chemical deoxygenation is qualified; if the liquid phase dissolved oxygen content is greater than or equal to 100 μg / kg, hydrazine needs to be added again.

4. According to claim 3, according to claim 1, a chemical control method for primary circuit deoxygenation during overhaul startup of a nuclear power plant, characterized in that: In step three, the temperature of the main system is increased to 110 degrees Celsius.

5. A chemical control method for primary circuit deoxygenation during overhaul startup of a nuclear power plant according to claim 1, characterized in that: In step 4, if the dissolved oxygen content in the liquid phase in step 3 is greater than or equal to 0.4 mg / kg, the value of A is 2.

5.

6. A chemical control method for primary circuit deoxygenation during overhaul startup of a nuclear power plant according to claim 1, characterized in that: In the step 5, it is checked whether the main system loop and the stabilizer liquid phase dissolved oxygen content are qualified for deoxygenation, specifically whether the liquid phase dissolved oxygen content is less than 100 μg / kg.

7. A chemical control method for primary circuit deoxygenation during overhaul startup of a nuclear power plant according to claim 1, characterized in that: In the step six, the main system is purged and the desalination bed is put into operation, which specifically includes directly putting into operation the mixed bed desalination device of the boron recovery system after the dissolved oxygen content in the step five is qualified, and then putting into operation the mixed bed desalination device of the chemical and volume control system after the concentration of ammonia and hydrazine meets the requirements.

8. A chemical control method for primary circuit deoxygenation during overhaul startup of a nuclear power plant according to claim 7, characterized in that: The concentrations of ammonia and hydrazine meet the requirements, and the specific requirement is that the sum of the concentrations of ammonia and hydrazine does not exceed 1.0 mg / kg.

9. A chemical control method for primary circuit deoxygenation during overhaul startup of a nuclear power plant according to claim 7, characterized in that: The mixed bed desalter of the chemical and volumetric control system is put into operation, specifically including the mixed bed desalter No. 1 of the chemical and volumetric control system or the mixed bed desalter No. 2 of the chemical and volumetric control system.

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