Method for purifying iodine in primary circuit during maintenance of nuclear power plant

Abstract

The present application relates to a kind of nuclear power plant overhaul when the purification method of iodine in primary loop, the purification method includes: using purification device to the iodine in primary loop unit of nuclear power plant overhaul is handled using hydrogen peroxide purification;The purification device includes primary loop unit and chemical volume control unit, hydrogen peroxide feeding equipment is arranged in the chemical volume control unit;Hydrogen peroxide feeding equipment is connected with the primary loop unit cooling liquid pipeline and communicates;The cooling liquid pipeline outlet of the primary loop unit and the chemical volume control unit are communicated.The specific hydrogen peroxide feeding system is configured to the primary loop cooling system of nuclear reactor, the treatment of iodine in primary loop cooling system is realized, and iodine-131 in elemental form can be oxidized to iodate ion (IO 3‑ ) after being removed by chemical volume control system desalination bed purification, while avoiding the need for lithium removal process when using lithium hydroxide to remove iodine.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of nuclear power, in particular to a method for purifying iodine in the primary loop during the maintenance of a nuclear power plant. BACKGROUND

[0002] In a nuclear power plant, the uranium-235 atomic nucleus of the pressurized water reactor nuclear fuel undergoes fission reaction to produce various radioactive fission products, one of which is iodine-131. The fuel cladding is the first safety barrier that contains radioactive fission products, and the radioactive fission products are locked inside the fuel cladding. The fuel cladding is in contact with the primary coolant. If the fuel cladding is damaged, the fission products will directly enter the primary coolant, and the iodine-131 in the primary coolant will increase significantly. According to the EPRI guide, the iodine-131 in the primary loop opening should be less than 370 Bq / g. Therefore, when the iodine-131 concentration in the primary loop increases due to fuel damage, in order to prevent the increase of personnel dose during shutdown, it is necessary to remove iodine from the primary loop.

[0003] Although the existing technology involves removing iodine in the primary loop by various means, such as CN104338510A discloses a method for removing radioactive iodine in a gas cooled reactor, which uses a silver-loaded adsorbent to remove radioactive iodine in the primary loop of a gas cooled reactor at a high temperature of 350-650℃. The silver-loaded adsorbent is prepared by using silver as the adsorption component and molecular sieve as the carrier, and is prepared by impregnation and high-temperature heat treatment. The silver-loaded adsorbent has high thermal stability and strong decontamination capacity.

[0004] CN114130355A discloses the use of activated carbon fiber in the preparation of a gas adsorption material or the manufacture of an iodine filtration device, a gas adsorption material, and an iodine filtration device. The activated carbon fiber has a porous structure, which includes micropores with a diameter not exceeding 2nm and other pore diameters, and the volume of the micropores accounts for 65%-95% of the total pore volume of the porous structure. This scheme uses activated carbon fiber with a micropore ratio of 65%-95% as raw material to prepare a gas adsorption material or manufacture an iodine filtration device. By adjusting the proportion of micropores, the absorption of water vapor by activated carbon fiber is reduced, providing more space for the absorption of gaseous iodine, and increasing the adsorption efficiency of the gas adsorption material or the iodine filtration device for gaseous iodine.

[0005] However, the existing scheme usually adds lithium hydroxide to the primary loop to maintain an alkaline environment in the primary loop, promotes the conversion of elemental iodine (I2) to ionic iodine, and then removes it by the desalination bed of the chemical and volume control system. After the outage, boronization is required, and according to the conventional method, lithium hydroxide needs to be added to the primary loop to maintain an alkaline environment. When the iodine-131 concentration is purified to the target concentration, the chemical and volume control system can be used for lithium removal and oxidation operation, resulting in a longer maintenance period. SUMMARY

[0006] In view of the problems in the prior art, the purpose of the present application is to provide a method for purifying iodine in a primary loop during maintenance of a nuclear power plant, so as to solve the problem of long maintenance period caused by low efficiency of iodine treatment during primary loop maintenance in the prior art.

[0007] To achieve the above purpose, the present application adopts the following technical solutions:

[0008] The present application provides a method for purifying iodine in a primary loop during maintenance of a nuclear power plant, wherein the device for purifying iodine in a primary loop during maintenance of a nuclear power plant comprises a primary loop unit and a chemical volume control unit, and a hydrogen peroxide feeding device is arranged in the chemical volume control unit;

[0009] The hydrogen peroxide feeding device is connected in communication with a cooling liquid pipeline of the primary loop unit;

[0010] The cooling liquid pipeline outlet of the primary loop unit is connected in communication with the chemical volume control unit.

[0011] The purification method provided by the present application realizes efficient treatment of iodine in the primary loop cooling system of a nuclear reactor by configuring a specific hydrogen peroxide feeding system for the primary loop cooling system, and the elemental iodine-131 can be oxidized into iodate ions (IO 3- ) and then removed by a desalination bed of a chemical volume control system, while avoiding the need for a lithium removal process when lithium hydroxide is used to remove iodine; further, after the oxidation operation of the primary loop of the unit is completed, stopping the main pump will reduce the pressure of the primary loop, causing the release of radioactive fission products in the damaged fuel cladding, and iodine-131 may suddenly increase, at this time, the primary loop is still in an acidic and oxidizing environment, and the elemental iodine will still be oxidized into iodate ions (IO 3- ) and then removed by the desalination bed of the chemical and volume control system, that is, the present application can also avoid the problem of secondary pollution of iodine.

[0012] In the present application, the hydrogen peroxide feeding device arranged in the chemical volume control unit is used to send hydrogen peroxide into the primary loop unit, and preferably, the feeding device is arranged at the inlet of the liquid phase in the primary loop unit.

[0013] As a preferred technical solution of the present application, the hydrogen peroxide feeding device is provided with a dissolved oxygen detection device.

[0014] In the present application, the dissolved oxygen detection device can be shared with a primary loop sampling system, or a separate one can be configured.

[0015] In the present application, the concentration of the hydrogen peroxide solution fed by the hydrogen peroxide feeding device can be controlled by manual detection, or other means for detecting the concentration in the art.

[0016] As a preferred technical solution of the present application, the chemical solvent control unit is provided with a cation exchange resin bed and a mixed resin bed.

[0017] In the present application, the resin in the cation exchange resin bed can be a gel type cation resin (H + ) (nuclear grade) and the like. For example, the resin of GRAVEX GR-2-16NG (H) AGR216NG10.

[0018] In the present application, the mixed resin bed can be a gel type mixed bed resin used in the chemical and container control system in the art 7 Li + / OH - ) (nuclear grade) and the like. For example, the resin of GRAVEX GR-4-7NG (Li / H) AGR407NG71.

[0019] As a preferred technical solution of the present application, the outlet of the cooling liquid pipeline of the primary circuit unit is in turn connected to the mixed resin bed and the cation exchange resin bed.

[0020] As a preferred technical solution of the present application, the dissolved hydrogen in the primary circuit unit is ≤50 cc / kg, for example, it can be 50 cc / kg, 48 cc / kg, 46 cc / kg, 44 cc / kg, 42 cc / kg, 40 cc / kg, 38 cc / kg, 36 cc / kg, 34 cc / kg, 32 cc / kg, 30 cc / kg, 28 cc / kg, 26 cc / kg, 24 cc / kg, 22 cc / kg, 20 cc / kg, 18 cc / kg, 16 cc / kg, 14 cc / kg, 12 cc / kg or 10 cc / kg, etc., but not limited to the listed values, other values not listed in this range are also applicable.

[0021] Preferably, the primary circuit unit is filled with liquid before the hydrogen peroxide is introduced.

[0022] In the present application, the primary circuit unit is filled with liquid, which is a certain concentration of boron-containing water. The concentration of boron in the aqueous solution can be reasonably selected according to the prior art.

[0023] Preferably, the operating speed of the coolant main pump in the primary loop unit is ≥ 50% of the maximum rotating speed of the main pump before the hydrogen peroxide is fed in, for example, it can be 50% of the maximum rotating speed of the main pump, 55% of the maximum rotating speed of the main pump, 60% of the maximum rotating speed of the main pump, 65% of the maximum rotating speed of the main pump, 70% of the maximum rotating speed of the main pump, 75% of the maximum rotating speed of the main pump, 80% of the maximum rotating speed of the main pump, 85% of the maximum rotating speed of the main pump, or 90% of the maximum rotating speed of the main pump, etc., but not limited to the listed values, and other values not listed in the range are also applicable.

[0024] Preferably, the operating temperature of the primary loop unit is 60-82℃ before the hydrogen peroxide is fed in, for example, it can be 60℃, 61℃, 62℃, 63℃, 64℃, 65℃, 66℃, 67℃, 68℃, 69℃, 70℃, 71℃, 72℃, 73℃, 74℃, 75℃, 76℃, 77℃, 78℃, 79℃, 80℃, 81℃, or 82℃, etc., but not limited to the listed values, and other values not listed in the range are also applicable.

[0025] In the present application, the temperature of the pressure stabilizer in the primary loop unit is also controlled within 60-82℃, for example, it can be 60℃, 61℃, 62℃, 63℃, 64℃, 65℃, 66℃, 67℃, 68℃, 69℃, 70℃, 71℃, 72℃, 73℃, 74℃, 75℃, 76℃, 77℃, 78℃, 79℃, 80℃, 81℃, or 82℃, etc., but not limited to the listed values, and other values not listed in the range are also applicable. Further, the basic function of the pressure stabilizer is to establish and maintain the pressure of the primary loop system to avoid volume boiling of the coolant system in the reactor. The pressure stabilizer maintains the primary loop at a constant pressure during steady-state operation of the power plant; limits the pressure change within the allowable value during transient; and prevents overpressure of the primary loop system and maintains the integrity of the primary loop during accidents.

[0026] Preferably, the hydrogen concentration in the water trap of the primary loop unit is ≤ 2% before the hydrogen peroxide is fed in, for example, it can be 2%, 1.9%, 1.8%, 1.7%, 1.6%, 1.5%, 1.4%, 1.3%, 1.2%, 1.1%, 1%, 0.9%, 0.8%, 0.7%, 0.6%, 0.5%, 0.4%, 0.3%, 0.2%, or 0.1%, etc., but not limited to the listed values, and other values not listed in the range are also applicable.

[0027] Preferably, the mixed resin bed and the cation exchange resin bed in the chemical solvent control unit operate in series before the hydrogen peroxide is fed in.

[0028] As a preferred technical solution of the present application, the concentration of hydrogen peroxide in the primary loop during the purification process is 2-10 ppm, for example, it can be 2 ppm, 2.2 ppm, 2.4 ppm, 2.6 ppm, 2.8 ppm, 3 ppm, 3.2 ppm, 3.4 ppm, 3.6 ppm, 3.8 ppm, 4 ppm, 4.2 ppm, 4.4 ppm, 4.6 ppm, 4.8 ppm, 5 ppm, 5.2 ppm, 5.4 ppm, 5.6 ppm, 5.8 ppm, 6 ppm, 6.2 ppm, 6.4 ppm, 6.6 ppm, 6.8 ppm, 7 ppm, 7.2 ppm, 7.4 ppm, 7.6 ppm, 7.8 ppm, 8 ppm, 8.2 ppm, 8.4 ppm, 8.6 ppm, 8.8 ppm, 9 ppm, 9.2 ppm, 9.4 ppm, 9.6 ppm, 9.8 ppm or 10 ppm, etc., but not limited to the listed values, other values not listed in this range are also applicable.

[0029] In the present application, the concentration of hydrogen peroxide in the liquid phase in the primary loop can be a fixed value within the range specified by the present application, or it can fluctuate within a small range within the range, such as 3-4 ppm, 5-8 ppm, 6-7 ppm, 8-10 ppm, 2-5 ppm, etc.

[0030] As a preferred technical solution of the present application, the concentration of dissolved oxygen in the liquid phase in the primary loop during the purification process is ≥2 ppm, for example, it can be 2 ppm, 3 ppm, 4 ppm, 5 ppm, 6 ppm, 7 ppm, 8 ppm, 9 ppm or 10 ppm, etc., but not limited to the listed values, other values not listed in this range are also applicable.

[0031] As a preferred technical solution of the present application, the hydrogen peroxide liquid phase containing in the primary loop unit during the purification process enters the mixed resin bed and the cation exchange resin bed in the chemical solvent control unit.

[0032] As a preferred technical solution of the present application, the liquid phase after being treated by the cation exchange resin bed returns to the primary loop unit.

[0033] As a preferred technical solution of the present application, the method for purifying iodine in the primary loop during the maintenance of a nuclear power plant comprises using a purification device to purify the iodine in the primary loop unit during the maintenance of a nuclear power plant with hydrogen peroxide.

[0034] The purification device comprises a loop unit and a chemical volume control unit, the chemical volume control unit is provided with a hydrogen peroxide feeding device; the hydrogen peroxide feeding device is communicated with a cooling liquid pipeline of the loop unit; an outlet of the cooling liquid pipeline of the loop unit is communicated with the chemical volume control unit; the hydrogen peroxide feeding device is provided with a dissolved oxygen detection device; the chemical solvent control unit is provided with a cation exchange resin bed and a mixed resin bed; the outlet of the cooling liquid pipeline of the loop unit is communicated with the mixed resin bed and the cation exchange resin bed in sequence.

[0035] Before the hydrogen peroxide is fed, the dissolved hydrogen in the loop unit is less than or equal to 50 cc / kg, the loop unit is filled with liquid, the operating speed of a coolant main pump in the loop unit is greater than or equal to 50% of the maximum rotating speed of the main pump, the working temperature of the loop unit is 60-82 DEG C, the hydrogen concentration in a drain tank of the loop unit is less than or equal to 2%, and the mixed resin bed and the cation exchange resin bed in the chemical solvent control unit are operated in series.

[0036] During the purification process, the concentration of hydrogen peroxide in the loop unit is 2-10 ppm, and the concentration of dissolved oxygen in the liquid phase is greater than or equal to 2 ppm.

[0037] During the purification process, the liquid phase containing hydrogen peroxide in the loop unit enters the mixed resin bed and the cation exchange resin bed in the chemical solvent control unit, and the liquid phase treated by the cation exchange resin bed returns to the loop unit.

[0038] In the application, the loop unit is a reactor coolant system, which is divided into a cooling system, a pressure regulating system and an overpressure protection system. The coolant system is composed of a reactor coolant pump, a reactor, a steam generator and corresponding pipelines, and can carry out the heat generated in the reactor when the nuclear power plant is normally operated, and transmit the heat to the secondary loop working medium through the steam generator to generate steam and drive the steam turbine generator to generate electricity. At the same time, the main coolant system works under high temperature and high pressure, and the equipment and pipelines constitute a pressure boundary, which is an important barrier to prevent radioactive leakage.

[0039] In the present application, the chemical volume control system is able to maintain the proper water inventory of the primary system when the reactor is heated, cooled or power is changed at a specified rate. It bears the change of water volume caused by the maximum heating rate in the process of starting from cold to hot state zero power and the maximum cooling rate in the process of stopping from hot state zero power to cold. It can also provide sufficient makeup water in the general leakage accident of the primary system. The main functions are: (1) to adjust the concentration of boron solution to control the reactivity of the reactor; (2) to purify the reactor coolant to maintain the required water quality; (3) to partially serve as a primary loop water volume control and maintain the water level of the primary loop system stabilizer; (4) when the shaft seal type primary coolant pump is used, the system also supplies water to the shaft seal; (5) according to the design requirements, the charging pump of the system can also serve as a high pressure safety injection pump to inject boron water into the primary system. However, in the recent design, the functions of the charging pump and the high pressure safety injection pump are independent of each other, and the charging pump no longer serves as the function of the high pressure safety injection pump.

[0040] Compared with the prior art, the present application has the following beneficial effects:

[0041] The purification device provided by the present application can realize the removal of iodine in the primary loop unit and the corrosion products on the inner wall of the primary loop unit by using hydrogen peroxide as a treatment reagent, thereby reducing the irradiation dose of the overhaul personnel. That is, the effect of two-step treatment (lithium hydroxide removal of iodine + oxidation of corrosion products) in the prior art is achieved by one process, which significantly shortens the overhaul time and improves the operation efficiency of the nuclear power plant. DETAILED DESCRIPTION

[0042] In order to better illustrate the present application and facilitate the understanding of the technical solutions of the present application, the typical but non-limiting embodiments of the present application are as follows:

[0043] Example 1

[0044] The present embodiment provides a method for purifying iodine in the primary loop of a nuclear power plant during maintenance, which uses a purification device to purify and treat the iodine in the primary loop unit of the nuclear power plant during maintenance by using hydrogen peroxide;

[0045] The purification device comprises a primary loop unit and a chemical volume control unit, and a hydrogen peroxide feeding device is arranged in the chemical volume control unit;

[0046] The hydrogen peroxide feeding device is connected in communication with the coolant pipeline of the primary loop unit;

[0047] The coolant pipeline outlet of the primary loop unit is connected in communication with the chemical volume control unit.

[0048] The hydrogen peroxide supply device is equipped with a dissolved oxygen detection device to detect the concentration of hydrogen peroxide and dissolved oxygen in the liquid phase within the primary loop unit, thereby ensuring that the purification process can proceed smoothly.

[0049] The chemical solvent control unit is equipped with a cation exchange resin bed and a mixed resin bed; the coolant pipeline outlet of the primary loop unit is sequentially connected to the mixed resin bed and the cation exchange resin bed.

[0050] In this embodiment, the resin in the cation exchange resin bed can be a gel-type cation exchange resin (H). + (Nuclear grade), is a hydrogen-form sulfonated copolymer of styrene and divinylbenzene, with sulfonic acid group as the functional group, and is GRAVEX's GR-2-16NG(H)AGR216NG10 resin;

[0051] In this embodiment, the mixed resin bed can be a gel-type mixed bed resin ( 7 Li + / OH - (Nuclear grade), is a sulfonic acid-based cation exchange resin and a quaternary ammonium-based anion exchange resin, specifically GRAVEX's GR-4-7NG(Li / H)AGR407NG71 resin;

[0052] The specific purification process is as follows:

[0053] Before introducing hydrogen peroxide, ensure that the dissolved hydrogen in the primary loop is ≤50cc / kg, the primary loop unit is filled with liquid, the operating speed of the main coolant pump in the primary loop unit is 50% of the maximum speed of the main pump, the operating temperature of the primary loop unit is 70℃, the hydrogen concentration in the hydrophobic tank of the primary loop unit is ≤2%, and the mixed resin bed and cation exchange resin bed in the chemical solvent control unit can be operated in series. Then, the iodine in the primary loop unit during nuclear power plant maintenance is purified by hydrogen peroxide using the iodine purification device in the primary loop during nuclear power plant maintenance.

[0054] During the purification process, ensure that the concentration of hydrogen peroxide in the liquid phase of the primary loop unit is 6 ppm and the concentration of dissolved oxygen in the liquid phase is 4 ppm.

[0055] In the purification process, the hydrogen peroxide-containing liquid phase in the primary loop unit sequentially enters the mixed resin bed and cation exchange resin bed in the chemical solvent control unit via pipelines within the primary loop. The liquid phase treated by the cation exchange resin bed is then returned to the primary loop unit for recirculation. During the purification process, the radionuclides in the primary loop coolant are simultaneously monitored until iodine-131 drops below the target value.

[0056] Through the above process, the purification device provided by the application realizes efficient treatment of iodine overflow in the primary cooling system of the nuclear reactor by configuring a specific hydrogen peroxide input system for the primary cooling system, and the elemental iodine-131 can be oxidized into iodate ions (IO 3- ) and then removed by the chemical volume control system desalination bed, while avoiding the lithium removal process required when lithium hydroxide is used to remove iodine; further, after the oxidation operation of the primary cooling system is completed, stopping the main pump will reduce the pressure of the primary cooling system, causing the release of radioactive fission products in the damaged fuel cladding, and iodine-131 may suddenly increase, at which time the primary cooling system is still in an acidic and oxidizing environment, and elemental iodine will still be oxidized into iodate ions (IO 3- ) and removed by the chemical and volume control system desalination bed, that is, the application can also avoid the secondary pollution problem of iodine.

[0057] It is declared that the detailed structural features of the application are illustrated by the above embodiments, but the application is not limited to the above detailed structural features, that is, it does not mean that the application must rely on the above detailed structural features to be implemented. It should be understood by those skilled in the art that any improvement of the application, equivalent replacement of the components selected by the application, increase of auxiliary components, selection of specific modes, etc., all fall within the protection scope and disclosure scope of the application.

[0058] The preferred embodiments of the application are described in detail above, but the application is not limited to the specific details in the above embodiments, and within the technical concept scope of the application, the technical solutions of the application can be variously modified, and these simple modifications all belong to the protection scope of the application.

[0059] In addition, it should be noted that each specific technical feature described in the above specific embodiments can be combined in any appropriate manner without contradiction, and in order to avoid unnecessary repetition, the application will not further describe various possible combination manners.

[0060] Furthermore, various different embodiments of the application can also be combined in any manner, as long as it does not deviate from the idea of the application, and it should also be considered as disclosed by the application.

Claims

1. A method for purifying iodine in the primary circuit during nuclear power plant maintenance, characterized in that, The purification method includes: using a purification device to purify the iodine in the primary loop unit during nuclear power plant maintenance with hydrogen peroxide. The purification device includes a primary loop unit and a chemical volume control unit. The chemical volume control unit is equipped with a hydrogen peroxide supply device. The hydrogen peroxide supply device is connected to the coolant pipeline of the primary loop unit. The coolant pipeline outlet of the primary loop unit is connected to the chemical volume control unit. Before hydrogen peroxide is introduced, the dissolved hydrogen in the primary loop unit is ≤50cc / kg; before hydrogen peroxide is introduced, the operating speed of the main coolant pump in the primary loop unit is ≥50% of the maximum speed of the main pump; before hydrogen peroxide is introduced, the operating temperature of the primary loop unit is 60-82℃; before hydrogen peroxide is introduced, the hydrogen concentration in the hydrophobic tank of the primary loop unit is ≤2%; during the purification process, the concentration of hydrogen peroxide in the primary loop is 2-10ppm; during the purification process, the concentration of dissolved oxygen in the liquid phase of the primary loop is ≥2ppm.

2. The method for purifying iodine in the primary loop during nuclear power plant maintenance as described in claim 1, characterized in that, The hydrogen peroxide supply device is equipped with dissolved oxygen detection equipment.

3. The method for purifying iodine in the primary loop during nuclear power plant maintenance as described in claim 1 or 2, characterized in that, The chemical volume control unit is equipped with a cation exchange resin bed and a mixed resin bed.

4. The method for purifying iodine in the primary loop during nuclear power plant maintenance as described in claim 3, characterized in that, The coolant pipeline outlet of the primary loop unit is sequentially connected to the mixed resin bed and the cation exchange resin bed.

5. The method for purifying iodine in the primary loop during nuclear power plant maintenance as described in claim 1, characterized in that, Before the hydrogen peroxide is introduced, the primary loop unit is filled with liquid.

6. The method for purifying iodine in the primary loop during nuclear power plant maintenance as described in claim 1, wherein before the hydrogen peroxide is introduced, the mixed resin bed and the cation exchange resin bed in the chemical volume control unit are operated in series.

7. The method for purifying iodine in the primary loop during nuclear power plant maintenance as described in claim 1, characterized in that, In the purification process, the hydrogen peroxide liquid phase in the primary loop unit enters the chemical volume control unit to mix with the cation exchange resin bed.

8. The method for purifying iodine in the primary loop during nuclear power plant maintenance as described in claim 7, characterized in that, The liquid phase after treatment by the cation exchange resin bed is returned to the primary loop unit.

9. The method for purifying iodine in the primary loop during nuclear power plant maintenance as described in claim 1, characterized in that, The hydrogen peroxide feeding device is equipped with dissolved oxygen detection equipment; the chemical volume control unit is equipped with a cation exchange resin bed and a mixed resin bed; the coolant pipeline outlet of the primary loop unit is connected to the mixed resin bed and the cation exchange resin bed in sequence. Before the hydrogen peroxide is introduced, the primary loop unit is filled with liquid, and the mixed resin bed and cation exchange resin bed in the chemical volume control unit are connected in series. In the purification process, the liquid phase containing hydrogen peroxide in the primary loop unit enters the chemical volume control unit to mix the resin bed and the cation exchange resin bed. The liquid phase after being treated by the cation exchange resin bed is returned to the primary loop unit.