Nuclear power plant pipeline ice slurry decontamination system, decontamination method and decontamination effect verification method

Abstract

The invention discloses a nuclear power plant pipeline ice slurry decontamination system, a decontamination method and a decontamination effect verification method. The nuclear power plant pipeline ice slurry decontamination system comprises a main loop coolant system, an ice slurry making machine, an ice slurry storage tank, a hydrogen peroxide storage tank, a boron recovery system and a waste liquid treatment system. According to the nuclear power plant pipeline ice slurry decontamination system, system operation process water is used for preparing ice slurry, after the ice slurry is injected into an in-service pipeline, the ice slurry can be well attached to the inner wall of a complex pipeline due to the high viscosity and the semi-solid property of the ice slurry, upstream water pressure pushes an ice piston, radioactive pollutants on the inner wall of the pipeline can be effectively removed through friction scouring, and the service life of the pipeline is prolonged. The radioactive pipeline cleaning agent has a good decontamination effect on a radioactive pipeline, has no adverse effect on a pipeline base material, does not need to add other chemical reagents, is good in operation condition and high in safety coefficient, and after ice slurry is naturally melted, a boron recovery system and a radioactive waste liquid treatment system are utilized for purification treatment, so that secondary radioactive waste is not newly added at all.

Description

Technical Field

[0001] The invention relates to the technical field of nuclear power plant radioactive contamination decontamination, and in particular to a nuclear power plant pipeline ice slurry decontamination system, a decontamination method and a decontamination effect verification method. Background Art

[0002] The fission products and activated corrosion products in the main circuit of a pressurized water reactor nuclear power plant continue to accumulate as the operating time of the unit increases. These radioactive nuclides are distributed and deposited on the main circuit and nuclear auxiliary system equipment and pipelines with the flow of coolant. They are the main radiation source items that affect the collective dose of power plant overhauls. The rigid demand for radioactive decontamination before maintenance is very urgent.

[0003] Since radioactive activated corrosion products are closely bonded to the oxide film on the metal surface of the pipeline, the system structure is complex, and the pipeline layout is intricate, the radiation source control problem cannot be completely solved by increasing shielding protection. The use of physical decontamination methods such as ultrasound, high-pressure water jets, and air-water pulses may lead to problems of radioactive diffusion or environmental inaccessibility. The use of chemical decontamination technology may result in a high corrosion safety risk. Simple water flushing has basically no effect, which has always been a difficult and painful point in the decontamination of nuclear power units in service.

[0004] Ice slurry is a mixture of ice and water with an average diameter of ice crystal particles not exceeding 1mm. It is a solid-liquid two-phase flow formed by tiny ice particles and water. Commonly used freezing point depressants are alcohols such as ethanol, ethylene glycol, and propylene glycol, as well as salt substances such as sodium hydroxide and sodium chloride. The function of freezing point depressants is to lower the freezing point of water so that water cannot freeze at temperatures below 0°C. As the concentration of freezing point depressants increases, the freezing point of the solution will continue to decrease, and the water near the ice crystals will not be able to crystallize at the same temperature, so that the ice particles in the solution remain at a certain particle size and do not grow larger.

[0005] Ice slurry flushing is an emerging pipeline cleaning technology that can improve the shortcomings of traditional water flushing technology and has been successfully applied in the cleaning of municipal water supply networks. Ice slurry mixed with water forms a soft "ice piston" with good permeability. The shear force generated by the collision and friction between the ice slurry and the inner wall of the pipe can reach 2 to 4 orders of magnitude of water. Under the action of shear force, the stable structure of the sediment and attachments on the inner wall of the pipe is destroyed and peeled off, and moves forward with the ice slurry until it is discharged from the pipe.

[0006] Public reports show that nuclear power plants use liquid nitrogen to quickly freeze the main circuit coolant to -30°C to prepare pipeline ice plugging. While successfully solving the problem of the downstream burst valve being unable to be isolated during maintenance, it has no adverse effect on the tensile strength and yield strength of the 304L stainless steel base material and weld material. The ice slurry flushing temperature is controlled within -5°C. Although the ice slurry with a high ice content has a higher viscosity, the pipeline temperature is higher than the ice slurry temperature. The ice slurry will melt when flowing through the pipeline and will not adhere to the pipe wall like other high-viscosity fluids. Therefore, the impact of the ice slurry on the metal pipeline substrate can be ignored. Summary of the invention

[0007] The technical problem to be solved by the present invention is to provide a nuclear power plant pipeline ice slurry decontamination system, a decontamination method and a decontamination effect verification method.

[0008] The technical solution adopted by the present invention to solve the technical problem is: constructing a nuclear power plant pipeline ice slurry decontamination system, which includes a main circuit coolant system, an ice slurry making machine, an ice slurry storage tank, a hydrogen peroxide storage tank, a boron recovery system and a waste liquid treatment system;

[0009] The main loop coolant system is connected to the pipeline to be decontaminated through a first input pipeline, the main loop coolant system is connected to the ice slurry making machine through a second input pipeline, the outlet end of the hydrogen peroxide storage tank is connected to the first interface end of the first input pipeline, the outlet end of the ice slurry making machine is connected to the ice slurry storage tank, the ice slurry storage tank is connected to the second interface end of the first input pipeline through a third input pipeline, the outlet end of the pipeline to be decontaminated is connected to the boron recovery system, the main loop coolant system is connected to the boron recovery system through a reflux pipeline, and the waste liquid treatment system is connected to the boron recovery system.

[0010] In some embodiments, a branch pipeline is connected between the second input pipeline and the ice slurry storage tank;

[0011] The third input pipeline is provided with an ice slurry delivery pump.

[0012] In some embodiments, a circulation pump, a first control valve and a second control valve are sequentially arranged on the first input pipeline;

[0013] The circulation pump and the first control valve are located between the first interface end of the first input pipeline and the second interface end of the first input pipeline, and the second control valve is located between the second interface end of the first input pipeline and the pipeline to be decontaminated.

[0014] In some embodiments, a vacuum insulation layer is provided on the outer side of the ice slurry storage tank, a stirring motor is provided inside the ice slurry storage tank, and a guide baffle is arranged on the inner wall of the ice slurry storage tank.

[0015] In this embodiment, a decontamination method for a nuclear power plant pipeline ice slurry decontamination system is also constructed, which is based on the nuclear power plant pipeline ice slurry decontamination system and includes the following steps:

[0016] S1, injecting process water running in the pipeline into the ice slurry making machine;

[0017] S2, connecting the upstream of the pipeline to be decontaminated to the ice slurry delivery pump;

[0018] S3, turning on the stirring motor in the ice slurry storage tank to stir the ice slurry, and mixing the ice slurry and process water to a predetermined parameter;

[0019] S4, open the second control valve, start the ice slurry delivery pump, and continuously inject the ice slurry into the pipeline to be decontaminated;

[0020] S5. When the volume of the ice slurry reaches the proportion of the pipeline to be decontaminated, the ice slurry delivery pump is turned off, the circulation pump is turned on, and the flow rate is controlled to push the ice slurry to decontaminate the pipeline to be decontaminated;

[0021] S6. After the ice slurry cleaning, flush the pipeline to be cleaned with a flushing solution within a preset temperature;

[0022] S7. After the ice slurry melts naturally, the waste liquid is purified and recovered using the boron recovery system and the waste liquid treatment system.

[0023] In some embodiments, the preset temperature of the flushing solution is 40-80° C., hydrogen peroxide is added to the flushing solution, and the concentration of the hydrogen peroxide is 5-50 mg / L.

[0024] In this embodiment, a method for verifying the decontamination effect of an ice slurry decontamination system for a nuclear power plant pipeline is also constructed, which includes the following steps:

[0025] S10, washing the first sample and the second sample with boric acid solution and boric acid ice slurry respectively, to evaluate the decontamination effects of the boric acid solution and the boric acid ice slurry;

[0026] S20, washing different test samples with boric acid ice slurry at different flow rates to evaluate the decontamination effect of the boric acid ice slurry at different flow rates;

[0027] S30, conducting a simulated corrosion test of a metal substrate using boric acid ice slurry.

[0028] In some embodiments, step S10 includes:

[0029] S101, selecting a first sample and a second sample of the same specification, applying ink to the inner sides of the tube walls of the first sample and the second sample with a brush, and then placing the samples in an oven for drying to enhance the adhesion between the ink and the tube walls of the first sample and the second sample;

[0030] S102, preparing boric acid ice slurry, performing a dynamic cleaning comparison experiment through a circulating pump, and controlling the flushing flow rate to be a set flow rate;

[0031] S103, cyclically flushing the first sample with a boric acid solution, and cyclically flushing the second sample with a boric acid ice slurry, and naturally drying the first sample and the second sample after flushing;

[0032] S104, cutting open the first sample and the second sample respectively to check the internal cleanliness of the first sample and the second sample;

[0033] S105. After the ice slurry in the boric acid ice slurry is completely melted, compare the absorbance of the boric acid liquid and the boric acid ice slurry to light of a characteristic wavelength.

[0034] In some embodiments, step S20 includes:

[0035] S201, taking a plurality of test samples of the same specifications, wherein hard scale is deposited on the inner side of the tube wall of the test samples;

[0036] S202, preparing boric acid ice slurry, and performing a dynamic cleaning comparison experiment through a circulating pump, controlling the boric acid ice slurry to clean different test samples at different cleaning flow rates within the same time;

[0037] S203, cutting a plurality of the test samples to check the amount of deposited scale inside;

[0038] S204. After the boric acid ice slurry is completely melted naturally, the pH value is adjusted to completely dissolve the sediment, and the calcium ion concentration in the boric acid ice slurry is obtained to evaluate the decontamination effect of the boric acid ice slurry for cleaning at different flow rates.

[0039] In some embodiments, step S30 includes:

[0040] S301, taking a plurality of corrosion test samples, grinding the corrosion test samples, scrubbing and degreasing the samples, drying and weighing the samples, and performing a morphological microscopic analysis of the corrosion test samples using a scanning electron microscope to obtain a morphological diagram before the test;

[0041] S302, using a metal corrosion rotating coupon instrument, fixing the corrosion test sample on a rotating rod, immersing the sample in boric acid ice slurry, and adjusting the rotation speed of the metal corrosion rotating coupon instrument;

[0042] S303, placing the container containing the boric acid ice slurry in a refrigerated water bath, using ethylene glycol refrigeration liquid as a coolant, to ensure that the temperature of the boric acid ice slurry does not rise during the corrosion test;

[0043] S304, after continuous operation for a certain period of time, immersing the corrosion test sample in a hydrogen peroxide solution;

[0044] S305, washing the corrosion test sample with deionized water, weighing it after drying, and performing a morphology microscopic analysis on the corrosion test sample with a scanning electron microscope to obtain a post-test morphology diagram;

[0045] S306, comparing the morphology image before the test and the morphology image after the test to evaluate the corrosion degree of the corrosion test sample caused by the ice slurry decontamination process.

[0046] The implementation of the present invention has the following beneficial effects: The ice slurry decontamination system for nuclear power plant pipelines uses the process water of the system to prepare ice slurry. After being injected into the in-service pipeline, the high viscosity and semi-solid nature of the ice slurry enable it to fit the inner wall of the complex pipeline well. The upstream water pressure pushes the "ice piston" to effectively remove the radioactive pollutants on the inner wall of the pipeline through friction flushing. The decontamination effect verification method of the ice slurry decontamination system for nuclear power plant pipelines shows that the ice slurry flushing technology has a better decontamination effect on radioactive pipelines, has no adverse effect on the pipeline matrix material, does not need to add other chemical reagents, has good operating conditions, and has a high safety factor. After the ice slurry melts naturally, it is purified by using a boron recovery system and a radioactive waste liquid treatment system, and no secondary radioactive waste is added at all. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] In order to more clearly illustrate the technical solution of the present invention, the present invention will be further described below in conjunction with the accompanying drawings and embodiments. It should be understood that the following drawings only show certain embodiments of the present invention and should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work. In the drawings:

[0048] Figure 1 is a schematic diagram of the overall structure of an ice slurry decontamination system for nuclear power plant pipelines in some embodiments of the present invention;

[0049] Figure 2 This is the morphology of the corrosion test sample before decontamination with boric acid ice slurry at a magnification of 10,000 times;

[0050] Figure 3 This is the morphology of the corrosion test sample after decontamination with boric acid ice slurry at a magnification of 10,000 times. DETAILED DESCRIPTION

[0051] In order to have a clearer understanding of the technical features, purposes and effects of the present invention, the specific embodiments of the present invention are now described in detail with reference to the accompanying drawings. In the following description, it should be understood that the directions or positional relationships indicated by "front", "back", "up", "down", "left", "right", "longitudinal", "horizontal", "vertical", "horizontal", "top", "bottom", "inside", "outside", "head", "tail", etc. are based on the directions or positional relationships shown in the accompanying drawings, are constructed and operated in a specific direction, and are only for the convenience of describing the present technical solution, rather than indicating that the device or element referred to must have a specific direction, and therefore cannot be understood as a limitation to the present invention.

[0052] It should also be noted that, unless otherwise clearly specified and limited, the terms such as "installed", "connected", "connected", "fixed", "set" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral one; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. When an element is referred to as being "on" or "under" another element, the element can be "directly" or "indirectly" located on the other element, or one or more intermediate elements may be provided. The terms "first", "second", "third", etc. are only for the convenience of describing the present technical solution, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first", "second", "third", etc. may explicitly or implicitly include one or more of the features. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to the specific circumstances.

[0053] See also Figure 1 , is a nuclear power plant pipeline ice slurry decontamination system in some embodiments of the present invention, which includes a main loop coolant system 1, an ice slurry making machine 2, an ice slurry storage tank 3, a hydrogen peroxide storage tank 4, a boron recovery system 5 and a waste liquid treatment system 6;

[0054] The main loop coolant system 1 is connected to the pipeline to be decontaminated 8 through a first input pipeline 71, the main loop coolant system 1 is connected to the ice slurry making machine 2 through a second input pipeline 72, the outlet end of the hydrogen peroxide storage tank 4 is connected to the first interface end of the first input pipeline 71, the outlet end of the ice slurry making machine 2 is connected to the ice slurry storage tank 3, the ice slurry storage tank 3 is connected to the second interface end of the first input pipeline 71 through a third input pipeline 73, the outlet end of the pipeline to be decontaminated 8 is connected to the boron recovery system 5, the main loop coolant system 1 is connected to the boron recovery system 5 through a return pipeline 74, and the waste liquid treatment system 6 is connected to the boron recovery system 5.

[0055] The first input pipeline 71 is provided with a circulation pump 711, a first control valve 712 and a second control valve 713 in sequence; the circulation pump 711 and the first control valve 712 are located between the first interface end of the first input pipeline 71 and the second interface end of the first input pipeline 71, and the second control valve 713 is located between the second interface end of the first input pipeline 71 and the pipeline 8 to be decontaminated.

[0056] Specifically, the core principle of ice slurry cleaning technology is that the shear force generated by the collision and friction between ice slurry and the inner wall of the pipeline can reach 2 to 4 orders of magnitude of water. In addition, in the alternating hot and cold environment, the internal sediments of the main loop and nuclear auxiliary system pipelines will generate internal stress due to the different expansion coefficients of radioactive sediments and metal pipelines. Under the coupling of friction shear force and alternating stress, ice slurry cleaning technology will promote the peeling and cleaning of radioactive sediments in the pipeline. In this embodiment, the scraping method is used in the ice slurry making machine 2 to dynamically and continuously make ice slurry from the system operating process water. The scraping method uses a shell and tube condenser to make ice slurry. The refrigerant evaporates on the outside of the tube, and the scraper inside the tube rotates to scrape the ice crystals attached to the wall. The ice slurry preparation solution uses the operating water quality of the nuclear power plant, that is, a coordinated aqueous solution of boric acid and lithium hydroxide, in which the boron concentration is 10 to 2500 mg / L and the lithium concentration is 0 to 3.5 mg / L, which meets the control range of chemical reagents in the primary coolant of the pressurized water reactor. As the mass fraction of boric acid increases, the supercooling of the solution gradually decreases. The preferred boric acid solution has a boron concentration of 1000 mg / L, and the corresponding freezing temperature is minus 1.5°C. The ice crystals formed have a viscosity similar to that of plasticine, which can better improve the ice slurry friction stripping cleaning effect. The ice slurry prepared from the ice slurry making machine 2 can be injected into the pipeline to be decontaminated 8 after passing through the ice slurry storage tank 3. According to the pipeline conditions and the operating environment, the concentration of the ice slurry used and the injection volume ratio of the ice slurry are different. The commonly used ice slurry concentration is 20% to 70%, and the ratio of the injected ice slurry volume to the volume of the pipeline section to be decontaminated is 0.20 to 0.80. The selection of the optimal ice slurry parameters is related to the pipeline material, diameter, length and spatial arrangement, ensuring that it can not only efficiently remove pollutants during the decontamination process, but also will not cause blockage or damage to the pipeline. The pipeline to be decontaminated 8 may include a chemical volume control system RCV pipeline 81, a residual heat removal system RRA pipeline 82, a chemical sampling system REN pipeline 83 and a spent fuel pool cooling treatment system PTR pipeline 84.

[0057] Furthermore, after the ice slurry injection is completed, the ice slurry with high viscosity and solid-liquid two-phase flow characteristics can fit tightly to the inner wall of the complex pipeline, and the circulation pump 711 is started. The upstream water pressure pushes the ice slurry in a piston-like continuous friction to clean the entire pipeline. After the ice slurry is decontaminated, in order to improve the decontamination effect, a hot hydrogen peroxide solution is further used for flushing. The solution temperature is 40 to 80°C, and the hydrogen peroxide addition concentration is 5 to 50 mg / L. The hydrogen peroxide solution can be provided by the hydrogen peroxide storage tank 4. The radioactive pollutants deposited in the pipeline are transferred to the boron recovery system 5 and the waste liquid treatment system 6 along with the ice slurry and hot flushing liquid, and the coolant and boron are all recovered and recycled.

[0058] A branch pipeline 75 is connected between the second input pipeline 72 and the ice slurry storage tank 3, and the coolant can be input into the ice slurry storage tank 3 through the second input pipeline 72, and an ice slurry delivery pump 731 is provided on the third input pipeline 73, and the ice slurry delivery pump 731 can deliver the ice slurry in the ice slurry storage tank 3 to the pipeline to be decontaminated 8. The ice slurry delivery pump 731 can be a screw pump or a gear pump. The screw pump is selected to deliver high-flow and high-viscosity ice slurry with a stable flow, small pressure pulsation and low noise. The gear pump with a simple and compact structure is selected for delivering small and medium flow ice slurry.

[0059] A vacuum insulation layer is provided on the outside of the ice slurry storage tank 3, a stirring motor is provided inside the ice slurry storage tank 3, and a guide baffle is arranged on the inner wall of the ice slurry storage tank 3. It can be understood that the ice slurry storage tank 3 is provided with a vacuum insulation layer on the outside, a stirring motor is provided inside, and a guide baffle is arranged around the inner wall, which effectively avoids the formation of ice-water stratification and dead corner retention due to the low density of ice when the ice-water mixture is stored statically, and has a high space utilization rate.

[0060] Compared with traditional chemical decontamination, ice slurry is used for decontamination of metal pipelines in the main circuit and nuclear auxiliary system. While achieving satisfactory decontamination capacity, no other chemicals are used at all. The decontamination reagents have no adverse effects on the metal matrix material. The decontamination process is advanced, no secondary waste is generated, and there is no risk of radioactive material diffusion. The safety factor related to the decontamination operation is high, the operation is simple, and the economy is good.

[0061] In this embodiment, a decontamination method for a nuclear power plant pipeline ice slurry decontamination system is also constructed, which is based on the above-mentioned nuclear power plant pipeline ice slurry decontamination system and includes the following steps:

[0062] S1, injecting process water running in the pipeline into the ice slurry making machine 2;

[0063] S2, connecting the upstream of the pipeline to be decontaminated 8 to the ice slurry delivery pump 731;

[0064] S3, turning on the stirring motor in the ice slurry storage tank 3 to stir the ice slurry, and mixing the ice slurry and process water to a predetermined parameter;

[0065] S4, open the second control valve 713, start the ice slurry delivery pump 731, and continuously inject the ice slurry into the pipeline 8 to be decontaminated;

[0066] S5, when the volume of the ice slurry reaches the proportion of the pipeline to be decontaminated 8, the ice slurry delivery pump 731 is turned off, the circulation pump 711 is turned on, and the flow rate is controlled to push the ice slurry to decontaminate the pipeline to be decontaminated 8;

[0067] S6, after the ice slurry cleaning, flush the contamination pipe 8 with a flushing solution within a preset temperature;

[0068] S7, after the ice slurry melts naturally, the boron recovery system 5 and the waste liquid treatment system 6 are used to purify and recover the waste liquid.

[0069] Specifically, in step S1 , process water running in a pipeline, preferably new process water without radioactive contamination, is injected into the ice slurry making machine 2 , and the ice slurry made by the rotating scraper blade naturally falls into the ice slurry storage tank 3 .

[0070] In step S2, the upstream of the pipeline to be decontaminated 8 is connected to the ice slurry delivery pump 731, preferably to an easily opened position with a low environmental dose rate, to confirm that there is no risk of overflow of the radioactive coolant upstream and downstream of the pipeline to be decontaminated 8.

[0071] In step S3, the stirring motor is turned on in the ice slurry storage tank 3 to stir the ice slurry, and the ice slurry is mixed with process water to a predetermined parameter. The size of the monitored conductivity can directly reflect the ice content.

[0072] In step S4 , the second control valve 713 is opened, the ice slurry delivery pump 731 is turned on, and the ice slurry is continuously injected into the pipeline 8 to be cleaned, so as to clean the pipeline 8 to be cleaned.

[0073] In step S5, after the volume of the ice slurry reaches a certain proportion of the pipe to be decontaminated 8, the ice slurry delivery pump 731 is turned off, the circulation pump 711 is turned on, and the flow rate is controlled to push the ice slurry to decontaminate the pipe to be decontaminated 8. At this time, the ice slurry flows forward in a piston-like manner, and the ice slurry has a scraping effect on the radioactive contaminants on the wall, thereby achieving the purpose of decontamination.

[0074] In step S6, after the ice slurry cleaning, the cleaning pipe 8 is flushed with a flushing solution within a preset temperature. To improve the flushing effect, the preset temperature of the flushing solution is 40-80°C, and hydrogen peroxide is added to the flushing solution, and the concentration of hydrogen peroxide is 5-50 mg / L.

[0075] In step S7, after the ice slurry melts naturally, the waste liquid is purified and recovered by using the boron recovery system 5 and the waste liquid treatment system 6, without increasing secondary radioactive waste.

[0076] In addition, the ice slurry flowing through the pipe pushes the water flow at the front end and scrapes the wall surface, so that the accumulated debris in the pipe is pushed away and the deposited dirt is scraped off and taken away. The expansion coefficients of radioactive sediments and metal pipes in the alternating hot and cold environment are different, and the internal stress generated will promote the peeling of radioactive sediments in the pipe.

[0077] Boric acid has a low solubility in water, which is 5.74g at room temperature of 25℃ and only 2.52g at zero degrees. The ice slurry prepared with boric acid solution has a low salt content, uniform particles, and is not prone to clustering. The ice content of ice slurry is a very important parameter in ice slurry cleaning, which refers to the percentage of ice crystal particle volume to total volume in ice slurry. The higher the ice content, the better the decontamination ability of ice slurry.

[0078] Ice slurry decontamination mainly relies on the piston-like flow of ice slurry and the wall shear force. The decontamination effect of ice slurry increases with the increase of ice content or flow rate. In addition to ice content and flow rate, the size of ice particles in ice slurry and the salt concentration of ice slurry will also affect the piston-like flow and wall shear force.

[0079] In this embodiment, a decontamination effect verification method of the nuclear power plant pipeline ice slurry decontamination system is also constructed to verify the decontamination effect of the nuclear power plant pipeline ice slurry decontamination system, which includes the steps of:

[0080] S10, washing the first sample and the second sample with boric acid solution and boric acid ice slurry respectively, to evaluate the decontamination effects of the boric acid solution and the boric acid ice slurry;

[0081] S20, washing different test samples with boric acid ice slurry at different flow rates to evaluate the decontamination effect of the boric acid ice slurry at different flow rates;

[0082] S30, conducting a simulated corrosion test of a metal substrate using boric acid ice slurry.

[0083] The boric acid liquid is ordinary boric acid liquid without ice slurry, and the boric acid ice slurry liquid is boric acid liquid containing ice slurry.

[0084] Step S10 includes:

[0085] S101, selecting a first sample and a second sample of the same specification, applying ink to the inner sides of the tube walls of the first sample and the second sample with a brush, and then placing them in an oven for drying to enhance the adhesion between the ink and the tube walls of the first sample and the second sample;

[0086] S102, preparing boric acid ice slurry, performing a dynamic cleaning comparison experiment through a circulation pump 711, and controlling the flushing flow rate to be a set flow rate;

[0087] S103, cyclically flushing the first sample with a boric acid solution, and cyclically flushing the second sample with a boric acid ice slurry, and naturally drying the first sample and the second sample after flushing;

[0088] S104, cutting open the first sample and the second sample respectively to check the internal cleanliness of the first sample and the second sample;

[0089] S105. After the ice slurry in the boric acid ice slurry is completely melted, compare the absorbance of the boric acid liquid and the boric acid ice slurry to light of a characteristic wavelength.

[0090] Specifically, step S10 is used for a dynamic cleaning experiment of a seamless austenitic stainless steel pipe.

[0091] In step S101, the first sample and the second sample are both 022Cr19Ni10 seamless austenitic stainless steel tubes with a specification of Φ14mm×1mm and a length of 100mm. The inner side of the tube wall is repeatedly brushed with blue-black ink with a brush and then placed in a 105°C oven for drying for 24 hours to enhance the adhesion between the ink and the tube wall.

[0092] In step S102, a 1.14% boric acid ice slurry with an ice content of 30% is prepared, and a dynamic cleaning comparison experiment is performed through a circulation pump 711, and the flushing flow rate is controlled to be 0.5 m / s;

[0093] In step S103, the first sample is cleaned with a 1.14% boric acid solution at room temperature for 3 minutes, and the second sample is cleaned with a 1.14% boric acid ice slurry with an ice content of 30% at room temperature for 3 minutes. After the cleaning, the samples are naturally dried.

[0094] In step S104, the first sample and the second sample are cut open to check the internal cleanliness of the first sample and the second sample. In the specific test, the first sample rinsed with boric acid solution has obvious ink residue at the bottom, and the second sample rinsed with boric acid ice slurry has significantly less ink residue on the tube wall than the first sample, and the rinsing effect is significantly improved;

[0095] In step S105, after the ice slurry in the boric acid ice slurry is completely melted, the absorbance of the two cleaning liquids at wavelengths of 288nm and 610nm is compared. In the same 1.14% boric acid solution, the absorbance of the boric acid ice slurry is 6.6 times that of the boric acid solution, indicating that the cleaning ability of the ice slurry is more than 6 times stronger than that of water washing.

[0096] Step S20 includes:

[0097] S201. Take a number of test samples with the same specifications, and hard scale is deposited on the inner side of the tube wall of the test samples;

[0098] S202, preparing boric acid ice slurry, and performing a dynamic cleaning comparison experiment through a circulation pump 711, controlling the boric acid ice slurry to clean different test samples at different cleaning flow rates within the same time;

[0099] S203, cutting a plurality of test samples and checking the amount of internal deposited scale;

[0100] S204. After the boric acid ice slurry is completely melted naturally, the pH value is adjusted to completely dissolve the sediment, and the calcium ion concentration in the boric acid ice slurry is obtained to evaluate the decontamination effect of the boric acid ice slurry for cleaning at different flow rates.

[0101] Specifically, in step S20, the ice slurry is used to clean the oxide scale of the internal threaded alloy steel pipe of the water-cooled wall.

[0102] In step S201, four 12Cr1MoV internally threaded alloy structural steel pipes are taken, with a specification of Φ32mm×6.3mm. Dark brown hard scale is deposited on the inner side of the pipe wall with a thickness of 0.1-0.2mm. The main component of the scale is phosphate deposits, of which calcium, iron and phosphorus elements account for 37.28%, 17.64% and 33.35% of the weight ratio of the scale sample, and the area under the scale is flat without obvious corrosion pits.

[0103] In step S202, a 1.43% boric acid ice slurry with an ice content of 60% is prepared, and a dynamic cleaning comparison experiment is performed through a circulation pump 711, and the cleaning flow rates are controlled to be 0.5m / s, 1.0m / s, 1.5m / s, and 2.0m / s in sequence, and the cleaning time is 30min.

[0104] In step S203, a plurality of test samples are cut to check the amount of scale deposited inside. In the test results, as the flow rate increases, the amount of scale remaining on the surface of the sample is significantly reduced, and the decontamination effect is significantly improved.

[0105] In step S204, after the boric acid ice slurry is completely melted naturally, nitric acid is added to adjust the pH value to 1.8, and the phosphate deposits that have been peeled off are allowed to completely dissolve for 30 minutes, and the calcium ion concentration in the cleaning solution is sampled and analyzed for comparison. In the test results, as the cleaning flow rate increases, the calcium ion concentration in the solution increases exponentially, and the calcium ion concentrations are 344 mg / L, 578 mg / L, 689 mg / L, and 761 mg / L, respectively, indicating that increasing the ice slurry flow rate can improve the pipeline decontamination effect.

[0106] Step S30 includes:

[0107] S301, taking a corrosion test sample, grinding it, scrubbing and degreasing it, drying and weighing it, and performing a morphology microscopic analysis of the corrosion test sample using a scanning electron microscope to obtain a morphology diagram before the test;

[0108] S302, using a metal corrosion rotating coupon instrument, fixing the corrosion test sample on a rotating rod, immersing the sample in boric acid ice slurry, and adjusting the rotation speed of the metal corrosion rotating coupon instrument;

[0109] S303, placing the container containing the boric acid ice slurry in a refrigerated water bath, using ethylene glycol refrigeration liquid as a coolant, to ensure that the temperature of the boric acid ice slurry does not rise during the corrosion test;

[0110] S304, after continuous operation for a certain period of time, immersing the corrosion test sample in a hydrogen peroxide solution;

[0111] S305, washing the corrosion test sample with deionized water, weighing it after drying, and performing a morphology microscopic analysis of the corrosion test sample with a scanning electron microscope to obtain a post-test morphology diagram;

[0112] S306. Compare the morphology images before and after the test to evaluate the corrosion degree of the corrosion test sample by the ice slurry decontamination process.

[0113] Specifically, in step S30, in order to verify that the decontamination method of the present invention does not damage the metal material of the decontamination equipment, the corrosion test sample is a 304L stainless steel substrate test piece. This embodiment uses a 304L stainless steel substrate test piece for corrosion testing, and the test process uses the extreme working conditions of the decontamination method of the present invention.

[0114] In step S301, the 304L stainless steel substrate test piece is polished to 1000 mesh, scrubbed with ethanol to remove oil, dried and weighed, and the morphology is microscopically analyzed using a scanning electron microscope. Figure 2 This is the morphology image at a magnification of 10,000 times before the test.

[0115] In step S302, a metal corrosion rotating coupon tester is used to fix a 304L stainless steel substrate test piece on a polytetrafluoroethylene rotating rod and immerse it in a boric acid ice slurry with an ice content of 70% at -4.0°C, a boric acid concentration of 1.43%, an adjusted rotation speed of 150 rad / min, and a simulated linear velocity of 0.55 m / s.

[0116] In step S303, the container containing the boric acid ice slurry is placed in a refrigerated water bath, and ethylene glycol refrigeration liquid is used as a coolant to ensure that the temperature of the boric acid ice slurry does not rise during the test.

[0117] In step S304, after running continuously for 24 hours, the corrosion test sample is immersed in a hydrogen peroxide solution at a temperature of 80°C and a hydrogen peroxide concentration of 50 mg / L for 24 hours.

[0118] In step S305, the corrosion test sample is rinsed with deionized water, dried and weighed. In the specific test results, the surface of the corrosion test sample is bright, and the maximum thinning amount calculated based on the weight change is 0.016μm. Then, a scanning electron microscope is used to perform a morphological microanalysis on the corrosion test sample to obtain a post-test morphology diagram, such as Figure 3 This is a morphology image at a test magnification of 10,000 times.

[0119] In step S306, the morphology before and after the test are compared to evaluate the degree of corrosion of the corrosion test sample by the ice slurry decontamination process. In the test results, when the corrosion test sample is scrubbed with ice slurry and decontaminated with hydrogen peroxide, there are no corrosion pits on the surface of the substrate, and the wear marks are clear and not blunt. It can be concluded that the decontamination method of the present invention will not cause secondary damage to the metal surface of the decontamination equipment. The impact of the ice slurry decontamination process on the corrosion test sample is shown in the following table.

[0120] 304L base material Weight loss / mg <![CDATA[Surface area / mm 2 > Substrate thinning amount / μm First corrosion test sample 0.21 1822 0.015 Second corrosion test sample 0.22 1820 0.015 The third corrosion test sample 0.24 1840 0.016

[0121] The ice slurry decontamination system for nuclear power plant pipelines uses the process water of the system to prepare ice slurry. After being injected into the in-service pipeline, the high viscosity and semi-solid nature of the ice slurry enable it to fit well to the inner wall of the complex pipeline. The upstream water pressure pushes the "ice piston" to effectively remove radioactive pollutants from the inner wall of the pipeline through friction flushing. The decontamination effect verification method of the ice slurry decontamination system for nuclear power plant pipelines shows that the ice slurry flushing technology has a better decontamination effect on radioactive pipelines, has no adverse effect on the pipeline matrix material, does not need to add other chemical reagents, has good operating conditions, and has a high safety factor. After the ice slurry melts naturally, it is purified using the boron recovery system 5 and the radioactive waste liquid treatment system 6, and no secondary radioactive waste is added at all.

[0122] It can be understood that the above embodiments only express the preferred implementation modes of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the patent scope of the present invention. It should be pointed out that, for ordinary technicians in this field, without departing from the concept of the present invention, the above technical features can be freely combined, and several deformations and improvements can be made, which all belong to the protection scope of the present invention. Therefore, all equivalent changes and modifications made to the scope of the claims of the present invention should belong to the scope covered by the claims of the present invention.

Claims

1. A nuclear power plant pipeline ice slurry decontamination system, characterized in that: It comprises a main loop coolant system (1), an ice slurry making machine (2), an ice slurry storage tank (3), a hydrogen peroxide storage tank (4), a boron recovery system (5) and a waste liquid treatment system (6); The main loop coolant system (1) is connected to the pipeline to be decontaminated (8) via a first input pipeline (71), the main loop coolant system (1) is connected to the ice slurry making machine (2) via a second input pipeline (72), the outlet end of the hydrogen peroxide storage tank (4) is connected to the first interface end of the first input pipeline (71), the outlet end of the ice slurry making machine (2) is connected to the ice slurry storage tank (3), the ice slurry storage tank (3) is connected to the second interface end of the first input pipeline (71) via a third input pipeline (73), the outlet end of the pipeline to be decontaminated (8) is connected to the boron recovery system (5), the main loop coolant system (1) is connected to the boron recovery system (5) via a return pipeline (74), and the waste liquid treatment system (6) is connected to the boron recovery system (5).

2. The nuclear power plant pipeline ice slurry decontamination system according to claim 1, characterized in that: A branch pipeline (75) is connected between the second input pipeline (72) and the ice slurry storage tank (3); The third input pipeline (73) is provided with an ice slurry delivery pump (731).

3. The nuclear power plant pipeline ice slurry decontamination system according to claim 1, characterized in that: The first input pipeline (71) is provided with a circulation pump (711), a first control valve (712) and a second control valve (713) in sequence; The circulation pump (711) and the first control valve (712) are located between the first interface end of the first input pipeline (71) and the second interface end of the first input pipeline (71), and the second control valve (713) is located between the second interface end of the first input pipeline (71) and the pipeline to be decontaminated (8).

4. The nuclear power plant pipeline ice slurry decontamination system according to claim 1, characterized in that: A vacuum insulation layer is provided on the outer side of the ice slurry storage tank (3), a stirring motor is provided inside the ice slurry storage tank (3), and a guide baffle is arranged on the inner wall of the ice slurry storage tank (3).

5. A decontamination method for a nuclear power plant pipeline ice slurry decontamination system, which is based on the nuclear power plant pipeline ice slurry decontamination system according to any one of claims 1 to 4, characterized in that: Includes steps: S1, injecting process water running in the pipeline into the ice slurry making machine (2); S2, connecting the upstream of the pipeline to be decontaminated (8) to the ice slurry delivery pump (731); S3, turning on the stirring motor in the ice slurry storage tank (3) to stir the ice slurry, and mixing the ice slurry and process water to a predetermined parameter; S4, opening the second control valve (713), starting the ice slurry delivery pump (731), and continuously injecting the ice slurry into the pipeline to be decontaminated (8); S5, when the volume of the ice slurry reaches the proportion of the pipeline to be decontaminated (8), the ice slurry delivery pump (731) is turned off, the circulation pump (711) is turned on, and the flow rate is controlled to push the ice slurry to decontaminate the pipeline to be decontaminated (8); S6, after the ice slurry cleaning, flushing the pipeline (8) to be cleaned with a flushing solution within a preset temperature; S7. After the ice slurry melts naturally, the waste liquid is purified and recovered using the boron recovery system (5) and the waste liquid treatment system (6).

6. The decontamination method for the nuclear power plant pipeline ice slurry decontamination system according to claim 5, characterized in that: In step S6, the preset temperature of the flushing solution is 40-80°C, hydrogen peroxide is added to the flushing solution, and the concentration of the hydrogen peroxide is 5-50 mg / L.

7. A method for verifying the decontamination effect of an ice slurry decontamination system for a nuclear power plant pipeline, characterized in that: Includes steps: S10, washing the first sample and the second sample with boric acid solution and boric acid ice slurry respectively, to evaluate the decontamination effects of the boric acid solution and the boric acid ice slurry; S20, washing different test samples with boric acid ice slurry at different flow rates to evaluate the decontamination effect of the boric acid ice slurry at different flow rates; S30, conducting a simulated corrosion test of a metal substrate using boric acid ice slurry.

8. The decontamination effect verification method of the nuclear power plant pipeline ice slurry decontamination system according to claim 7, characterized in that: Step S10 includes: S101, selecting a first sample and a second sample of the same specification, applying ink to the inner sides of the tube walls of the first sample and the second sample with a brush, and then placing the samples in an oven for drying to enhance the adhesion between the ink and the tube walls of the first sample and the second sample; S102, preparing boric acid ice slurry, and performing a dynamic cleaning comparison experiment through a circulation pump (711), controlling the flushing flow rate to be a set flow rate; S103, cyclically flushing the first sample with a boric acid solution, and cyclically flushing the second sample with a boric acid ice slurry, and naturally drying the first sample and the second sample after flushing; S104, cutting open the first sample and the second sample respectively to check the internal cleanliness of the first sample and the second sample; S105. After the ice slurry in the boric acid ice slurry is completely melted, compare the absorbance of the boric acid liquid and the boric acid ice slurry to light of a characteristic wavelength.

9. The decontamination effect verification method of the nuclear power plant pipeline ice slurry decontamination system according to claim 7, characterized in that: Step S20 includes: S201, taking a plurality of test samples of the same specifications, wherein hard scale is deposited on the inner side of the tube wall of the test samples; S202, preparing boric acid ice slurry, and performing a dynamic cleaning comparison experiment through a circulation pump (711), controlling the boric acid ice slurry to clean different test samples at different cleaning flow rates within the same time; S203, cutting a plurality of the test samples to check the amount of deposited scale inside; S204. After the boric acid ice slurry is completely melted naturally, the pH value is adjusted to completely dissolve the sediment, and the calcium ion concentration in the boric acid ice slurry is obtained to evaluate the decontamination effect of the boric acid ice slurry for cleaning at different flow rates.

10. The decontamination effect verification method of the nuclear power plant pipeline ice slurry decontamination system according to claim 7, characterized in that: Step S30 includes: S301, taking a plurality of corrosion test samples, grinding the corrosion test samples, scrubbing and degreasing the samples, drying and weighing the samples, and performing a morphological microscopic analysis of the corrosion test samples using a scanning electron microscope to obtain a morphological diagram before the test; S302, using a metal corrosion rotating coupon instrument, fixing the corrosion test sample on a rotating rod, immersing the sample in boric acid ice slurry, and adjusting the rotation speed of the metal corrosion rotating coupon instrument; S303, placing the container containing the boric acid ice slurry in a refrigerated water bath, using ethylene glycol refrigeration liquid as a coolant, to ensure that the temperature of the boric acid ice slurry does not rise during the corrosion test; S304, after continuous operation for a certain period of time, immersing the corrosion test sample in a hydrogen peroxide solution; S305, washing the corrosion test sample with deionized water, weighing it after drying, and performing a morphology microscopic analysis on the corrosion test sample with a scanning electron microscope to obtain a post-test morphology diagram; S306, comparing the morphology image before the test and the morphology image after the test to evaluate the corrosion degree of the corrosion test sample caused by the ice slurry decontamination process.

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