Device and method for removing residual tritium from filter element of wastewater filter in concrete container of heavy water reactor temporary storage

Abstract

The invention relates to a device and a method for removing residual tritium in a filter element of a wastewater filter in a concrete container of a heavy water reactor temporary storage, the device comprises a concrete container sealing top cover, a circulating air module, a tritium water adsorption and purification module and an automatic control module, the circulating air module comprises a frequency conversion fan, a preheating furnace, an air inlet and outlet pipeline system and a pneumatic valve, the tritium water adsorption and purification module comprises a filter box, a molecular sieve adsorption tank and an activated carbon adsorption tank, the molecular sieve adsorption tank and the activated carbon adsorption tank are connected in series in multiple stages, and the automatic control module is used for controlling operation parameters of the circulating air module and opening and closing states of the pneumatic valve; the circulating air module, the tritium water adsorption and purification module and the automatic control module are integrated into an equipment main body and are connected with a concrete container sealing top cover through an air inlet and outlet pipeline system to form a sealed circulating system.

Description

Technical Field

[0001] The invention relates to the technical field of radioactive waste management, and in particular to a device and method for removing residual tritium from a filter element of a wastewater filter in a concrete container of a temporary storage for a heavy water reactor. Background Art

[0002] Nuclear power plant water filters are important equipment in the nuclear island radioactive water treatment system, used to filter suspended matter in the primary circuit and related systems, and to reduce the radioactive and chemical content in the waste liquid treatment system. The filter elements of these filters need to be replaced regularly, and the discarded filter elements need to be placed in shielded containers and transported to the waste temporary storage due to the high exposure dose rate. They are placed vertically in underground concrete containers and sealed for temporary storage.

[0003] Since the temporarily stored waste filter cartridges have a high dose rate and contain a large amount of tritiated water, personnel cannot directly contact and handle them. Any treatment method requires opening the top cover of the concrete container to remove the waste filter cartridges, which will cause tritiated water to overflow and cause radiation hazards to the environment and personnel.

[0004] At present, only Qinshan No. 3 Nuclear Power Plant has the problem of temporary storage of tritium-containing filter elements in China, and there is no treatment method or technology yet. At the same time, due to the limited number of concrete containers in the temporary storage warehouse and the increasing number of waste filter elements generated during operation, it is urgent to develop a device and method for safely removing tritium without moving the waste filter elements to relieve the pressure of the temporary storage warehouse. Summary of the invention

[0005] The invention discloses a device and method for removing residual tritium from a filter element of a wastewater filter in a concrete container of a temporary storage warehouse for a heavy water reactor, aiming to solve the technical problems existing in the prior art.

[0006] The present invention adopts the following technical solutions:

[0007] In one aspect, the present invention provides a device for removing residual tritium from a filter element of a wastewater filter in a concrete container of a temporary storage facility for a heavy water reactor, comprising:

[0008] - Sealed top cover of concrete container, used to replace the original top cover of concrete container and sealed with the concrete container;

[0009] - Circulating air module, including variable frequency fan, preheating furnace, air inlet and outlet duct system and pneumatic valve;

[0010] - Tritium water adsorption purification module, including a filter box, a multi-stage series-connected molecular sieve adsorption tank and an activated carbon adsorption tank;

[0011] -Automation control module, used to control the operating parameters of the circulating air module and the opening and closing status of the pneumatic valve;

[0012] Among them, the circulating air module, tritium water adsorption purification module and automatic control module are integrated into the main body of the equipment, which are connected to the sealed top cover of the concrete container through the inlet and outlet air duct system to form a sealed circulation system.

[0013] As a preferred technical solution, the sealing top cover of the concrete container is configured to be made of stainless steel, and its surface is treated with anti-corrosion and polishing to reduce the adhesion of tritium;

[0014] The sealing cover of the concrete container achieves a sealed connection with the concrete container by compacting the rubber gasket with its own weight. When the operating pressure of the device is 2±0.2kpa, the rate of change of tritium level near the sealing cover of the concrete container is less than 10%.

[0015] As a preferred technical solution, the variable frequency fan includes a first fan, a second fan and a third fan, wherein the first fan and the third fan are used for main line circulating wind to carry detritium, and the second fan is used for the circulation of the molecular sieve adsorption tank;

[0016] The preheating furnace is used to increase the inlet air temperature into the concrete container;

[0017] The air inlet and outlet duct system includes a detachable air inlet duct and a detachable air outlet duct connected to the sealed top cover of the concrete container, and a duct assembly for realizing internal circulation and exhaust circulation;

[0018] The circulating air module also includes a plurality of pneumatic valves, a thermometer and a hygrometer, an anemometer and a pressure sensor arranged on the air inlet and outlet duct systems, which are used to realize the switching between the sealed internal circulation and the exhaust circulation, and the real-time monitoring of the process parameters.

[0019] As a preferred technical solution, the operating gas flow rate of the inlet and outlet air duct system is 50-150m 3 / h, the air inlet and outlet duct systems maintain tightness under an operating pressure of 3kpa.

[0020] As a preferred technical solution, the filter box is used to absorb and remove dust and radionuclides in the gas;

[0021] The multi-stage series-connected molecular sieve adsorption tanks include first to fourth molecular sieve adsorption tanks connected in sequence, and the molecular sieve adsorption tanks are filled with molecular sieves for adsorbing tritium;

[0022] The activated carbon adsorption tank is arranged at the rear end of the fourth molecular sieve adsorption tank and is filled with impregnated activated carbon for further purifying the gas.

[0023] As a preferred technical solution, the multi-stage series molecular sieve adsorption tanks can realize the selective use of two or four molecular sieve adsorption tanks through the opening and closing combination of pneumatic valves;

[0024] The gas tritium absorption rate of the third molecular sieve adsorption tank is greater than 95%, and the tritium water absorption rate of the fourth molecular sieve adsorption tank is 100%.

[0025] As a preferred technical solution, the automation control module includes:

[0026] -Pneumatic valve control unit, used to control the opening and closing of the pneumatic valve to achieve the selection of the air flow path;

[0027] -Equipment operation control unit, used to control the start and speed adjustment of the variable frequency fan, as well as the start and temperature adjustment of the preheating furnace;

[0028] -Parameter display unit, used to display the gas flow rate, temperature, pressure, temperature and humidity in the air inlet and outlet duct system in real time;

[0029] -Data logging unit for automatic recording of process parameters.

[0030] On the other hand, the present invention also provides a method for removing residual tritium from a filter element of a wastewater filter in a concrete container of a temporary storage facility for a heavy water reactor using the device as described in any one of the above items, comprising the following steps:

[0031] Remove the original top cover of the concrete container, and install the sealed top cover of the concrete container onto the concrete container by compacting the rubber gasket with its own weight;

[0032] Start the device to establish internal circulation and adjust the frequency conversion fan to make the gas flow rate of the inlet and outlet air duct system 50-150m 3 / h, and monitor the rate of change of tritium level near the sealed top cover of the concrete container;

[0033] The waste filter element in the concrete container is detritiated by the circulating air module until the tritium level before the first molecular sieve adsorption tank drops to the same level as the tritium level after the fourth molecular sieve adsorption tank, and both are background levels.

[0034] As a preferred technical solution, after completing the residual tritium removal step, the waste filter element is left to stand for 10-15 days;

[0035] The residual tritium removal step was repeated until the tritium level at the bottom of the concrete container did not increase after 15 days of standing, and the tritium level increase rate was less than 10% compared to the last residual tritium removal.

[0036] As a preferred technical solution, in the residual tritium removal step, when the humidity at the air outlet of the fourth molecular sieve adsorption tank is greater than 1RH, the molecular sieves in all the molecular sieve adsorption tanks are replaced.

[0037] The technical solution adopted by the present invention can achieve the following beneficial effects:

[0038] The present invention mainly provides a device and method for removing residual tritium from a wastewater filter element in a concrete container of a heavy water reactor temporary storage warehouse. The aforementioned device adopts a modular design, including a sealed top cover of the concrete container, a circulating air module, a tritium water adsorption purification module and an automatic control module, wherein the sealed top cover of the concrete container can replace the original concrete container top cover to achieve a sealing function, and can also achieve tritium removal by connecting with the device body, without moving the waste filter element, thereby avoiding tritium water overflow and radiation hazards.

[0039] The tritium water adsorption purification module of the present invention adopts a purification structure of "filter box + multi-stage series molecular sieve adsorption tank + activated carbon adsorption tank". Through the opening and closing combination of pneumatic valves, the selective use of two or four molecular sieve adsorption tanks can be achieved, and a high tritium removal efficiency is achieved.

[0040] Furthermore, the present invention realizes pneumatic valve control, equipment operation control, parameter display and data recording through an automated control module. Combined with a specific gas flow rate and multiple detritiation treatments, the tritium content of the waste filter element can be significantly reduced, providing basic conditions for subsequent treatment while reducing the radiation dose of the staff.

[0041] Relying on the device provided by the present invention, the embodiment of the present invention adopts a treatment method of first removing tritium, then standing and then removing tritium. Through repeated treatment until the tritium level at the bottom of the concrete container has no significant increase, and the growth rate of the tritium level after the last detritium removal is less than 10%, it can ensure that the tritium in the waste filter element is fully removed without moving. At the same time, by monitoring the humidity of the air outlet of the fourth molecular sieve adsorption tank and replacing the molecular sieve in time, the continuity and stability of the detritium effect are guaranteed, and the safe treatment of the waste filter element is achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments, which constitute a part of the present invention. The exemplary embodiments of the present invention and their descriptions explain the present invention and do not constitute improper limitations on the present invention. In the drawings:

[0043] Figure 1 A cross-sectional view of a sealed top cover of a concrete structure container in a preferred embodiment of the present invention;

[0044] Figure 2 This is a schematic diagram of the front structure of the device body in a preferred embodiment of the present invention;

[0045] Figure 3 A schematic diagram of the back structure of the device body in a preferred embodiment of the present invention;

[0046] Figure 4 It is a flow chart of a method for removing residual tritium from a wastewater filter element in a concrete container of a heavy water reactor temporary storage facility in a preferred embodiment of the present invention;

[0047] Figure 5 It is a schematic structural diagram of a device for removing residual tritium from a filter element of a wastewater filter in a concrete container of a temporary storage facility for a heavy water reactor in a preferred embodiment of the present invention;

[0048] Figure 6 It is a flow chart of a method for using a device for removing residual tritium from a filter element of a wastewater filter in a concrete container of a temporary storage facility for a heavy water reactor in a preferred embodiment of the present invention;

[0049] Figure 7 This is a trend diagram of tritium level changes in a thermal detritium test of a concrete container temporarily storing eight 3526 waste filter cartridges in a preferred embodiment of the present invention.

[0050] Description of reference numerals:

[0051] Concrete container sealing cover 101, a first fan 1021, a second fan 1022, a third fan 1023, a preheating furnace 103, a filter box 104, a first molecular sieve adsorption tank 105, a second molecular sieve adsorption tank 106, a third molecular sieve adsorption tank 107, a fourth molecular sieve adsorption tank 108, an activated carbon adsorption tank 109, a display control panel 110, and a flow meter 111. DETAILED DESCRIPTION

[0052] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the specific embodiments of the present invention and the corresponding drawings. In the description of the present invention, it should be noted that the term "or" is usually used in the sense of including "and / or", unless the content clearly indicates otherwise.

[0053] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected" and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or a magnetic connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be internal communication between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances. In addition, in the description of this application, the terms "first", "second", etc. are only used to distinguish the description and cannot be understood as indicating or implying relative importance.

[0054] There are currently two main problems with the treatment of spent filters in heavy water reactors: first, the spent filters are sealed and temporarily stored in concrete containers in temporary storage. Due to their high dose rate and large amounts of tritium water, any treatment requires opening the container cover and removing the spent filters, which will cause tritium water to overflow and cause radiation hazards. Second, due to the limited number of concrete containers in the temporary storage and the increasing number of spent filters generated during operation, there is an urgent need for a technical solution that can achieve tritium removal without moving the spent filters, so as to reduce the activity level of the spent filters and create conditions for subsequent treatment.

[0055] It should be noted that the concrete container described in the embodiment of the present invention is arranged underground in the temporary storage of the heavy water reactor, and is used to temporarily store the wastewater filter cartridges (hereinafter referred to as "waste filter cartridges") generated due to regular replacement or excessive pressure difference. The waste filter cartridges are placed vertically in the concrete container, and sealed and temporarily stored by the top cover of the concrete container. Taking the type B concrete container for temporarily storing type 3526 waste filter cartridges as an example, its opening diameter is 1220mm, which can accommodate 8 waste filter cartridges, and the top of the container is sealed by a top cover with a thickness of 150mm. Since the temporarily stored waste filter cartridges have a high dose rate and contain a large amount of tritium water, in order to avoid close contact and handling by personnel, it is necessary to develop a device that can replace the original concrete container top cover and realize the detritiation function.

[0056] like Figure 1 — Figure 3 In order to solve the problems existing in the prior art, an embodiment of the present invention provides a device for removing residual tritium from a wastewater filter cartridge, which is suitable for a concrete container for a temporary storage of a heavy water reactor. Preferably, the device comprises a concrete container sealing top cover 101, a circulating air module, a tritium water adsorption purification module, and an automatic control module, wherein the circulating air module, the tritium water adsorption purification module, and the automatic control module are integrated into the main body of the device, such as Figure 2 and Figure 3 The air inlet and outlet duct system provided in the circulating air module is connected to the sealed top cover 101 of the concrete container to form a sealed circulation system.

[0057] In a preferred embodiment, the concrete container sealing cover 101 is used to replace the original concrete container cover and is sealed and connected to the concrete container.

[0058] Preferably, the concrete container sealing cover 101 is integrally made of 304L stainless steel, and its surface is anti-corrosion treated and polished to reduce the adsorption and diffusion of tritium on the surface of the cover, thereby effectively preventing secondary contamination.

[0059] Preferably, the concrete container sealed top cover 101 uses its own weight to compact the rubber gasket. The rubber gasket is made of a special rubber material that is resistant to radiation and aging, and can be provided with one or more layers. Under the self-weight of the top cover, it can be fully deformed to fill the tiny unevenness on the top of the concrete container, thereby forming a reliable seal. Practice shows that when the device is running, even if the operating pressure of the air inlet and outlet duct system reaches 2±0.2kpa, the tritium level change rate near the concrete container sealed top cover 101 can still be kept below 10%, which shows that the sealing method has good airtightness.

[0060] Preferably, the design of the concrete container sealing top cover 101 also fully considers the docking requirements with the circulating air module, and ensures the uniform distribution of airflow in the concrete container by reasonably arranging the air inlet and outlet interfaces, which is conducive to improving the detritium removal efficiency. This design not only avoids the disadvantage of opening the container to remove the waste filter element in the traditional treatment method, but also achieves the goal of in-situ detritium removal.

[0061] Preferably, the concrete container sealing cover 101 is provided with a plurality of lifting rings to ensure the safety and convenience of the lifting installation and disassembly process.

[0062] Since different concrete containers have different volume specifications, in order to enable the concrete container sealing cover 101 to match various types of concrete containers, its size specifications are no longer limited here, and those skilled in the art can make adaptive adjustments according to actual usage scenarios.

[0063] In a preferred embodiment, the circulating air module includes a variable frequency fan, a preheating furnace 103, an air inlet and outlet duct system and a pneumatic valve.

[0064] Preferably, the variable frequency fan includes a first fan 1021, a second fan 1022 and a third fan 1023, wherein the first fan 1021 and the third fan 1023 are main line fans, which are operated to generate circulating air for carrying tritium in the waste filter element in the concrete container. By adjusting the fan speed, the gas flow rate can be controlled within 50 to 150 m / s. 3 / h range; after the second fan 1022 is running, the circulation of the molecular sieve adsorption tank in the tritium water adsorption purification module can be realized.

[0065] Preferably, the preheating furnace 103 is used to increase the temperature of the air entering the concrete container. The detritiation efficiency can be improved through the preheating treatment.

[0066] Preferably, the air inlet and outlet duct system is made of 304L stainless steel pipes, and flange sealing connections are used at key joints to ensure sealing under an operating pressure of 3kpa. The system includes two main parts: one is a detachable air inlet and outlet duct connected to the concrete container sealing top cover 101, which adopts a quick connector design for easy installation and disassembly; the other is a duct assembly for switching between internal circulation and exhaust circulation.

[0067] To achieve precise control and real-time monitoring, preferably, pneumatic valves, thermometers and hygrometers, anemometers, flowmeters 111, and pressure sensors and other instruments are installed at key locations of the air inlet and outlet duct systems; among them, the pneumatic valves are mainly used to switch between the internal circulation mode and the exhaust circulation mode; the thermometers and hygrometers are used to monitor the temperature and humidity changes of the gas; the anemometers are used to monitor the gas flow rate to ensure that the flow rate is maintained within the set range; the flowmeters 111 are used to detect the gas flow rate; and the pressure sensors are used to monitor the system operating pressure to ensure the safe operation of the system. These monitoring data will be transmitted to the automation control module for the adjustment of process parameters and process control.

[0068] Optionally, the circulating air module is provided with 15 pneumatic valves, 2 thermometers and hygrometers, 1 anemometer and at least 1 pressure sensor. It should be noted that the specific number of instruments and meters can be adaptively adjusted as needed, and the number set above is only an example.

[0069] In a preferred embodiment, the tritium water adsorption purification module is configured as a three-stage purification structure, which includes a filter box 104, a multi-stage molecular sieve adsorption tank and an activated carbon adsorption tank 109 arranged in sequence. After the tritium-containing gas passing through the waste filter element undergoes three-stage purification, the tritium can be removed and the gas can be purified and discharged.

[0070] Preferably, the filter box 104 is used to adsorb and remove dust and radionuclides in the gas; the gas carried out by the waste filter element in the concrete container is first filtered through the filter box 104, and multiple layers of filter media can be arranged in the filter box 104, including a coarse filter layer and a high-efficiency filter layer, which are used to remove dust particles and radionuclides in the gas to prevent these impurities from affecting the subsequent adsorption effect.

[0071] Preferably, the molecular sieve adsorption tank adopts a multi-stage series structure, including a first molecular sieve adsorption tank 105, a second molecular sieve adsorption tank 106, a third molecular sieve adsorption tank 107 and a fourth molecular sieve adsorption tank 108 connected in sequence. The molecular sieve adsorption tank is filled with molecular sieves for adsorbing tritium. The first two stages of molecular sieves are mainly used for preliminary adsorption and reducing tritium concentration. The gas tritium absorption rate of the third molecular sieve adsorption tank 107 is greater than 95%, and the tritium water adsorption rate of the fourth molecular sieve adsorption tank 108 is 100%, so as to completely adsorb the remaining tritium and ensure that the tritium content in the outlet gas is reduced to the background level.

[0072] It should be noted that the number of molecular sieve adsorption tanks in series can be increased or decreased as needed and is not necessarily limited to four.

[0073] Preferably, in order to realize process monitoring, sampling interfaces with valves are provided before and after the tank body of each molecular sieve adsorption tank, and the tritium level of the airflow at different positions can be measured in real time by connecting a tritium meter, and gas sampling and analysis can also be performed to timely grasp the treatment effect.

[0074] Preferably, the activated carbon adsorption tank 109 is disposed at the rear end of the fourth molecular sieve adsorption tank 108 and is filled with impregnated activated carbon for further purifying the gas to ensure the cleanliness of the exhaust gas.

[0075] Preferably, the multi-stage molecular sieve adsorption tanks can realize the selective use of two or four molecular sieve adsorption tanks through the opening and closing combination of the pneumatic valve. For example, when the tritium concentration is low, only two adsorption tanks can be used for treatment, which can meet the treatment requirements and reduce the system resistance; when treating high-concentration tritium, all four adsorption tanks are activated to ensure the treatment effect.

[0076] In a preferred embodiment, the automation control module is used to control the operating parameters of the circulating air module and the opening and closing state of the pneumatic valve. Specifically, the automation control module uses a programmable controller (PLC) as the core, is configured with a display control panel 110, and realizes the coordinated work of four main functional units. Preferably, the automation control module includes a pneumatic valve control unit, an equipment operation control unit, a parameter display unit, and a data recording unit.

[0077] Preferably, the pneumatic valve control unit can achieve precise control of the opening and closing status of all pneumatic valves in the system through program settings. According to different working conditions, the unit can automatically switch the pneumatic valve combination according to the preset program, realize the conversion between the internal circulation mode and the exhaust circulation mode, and the selective use of the molecular sieve adsorption tank.

[0078] Preferably, the equipment operation control unit is responsible for the operation control of the variable frequency fan and the preheating furnace 103; for the variable frequency fan, the unit can automatically adjust the fan speed according to the process requirements to maintain the gas flow rate at 50-150m 3 / h within the optimal range; for the preheating furnace 103, the temperature is accurately adjusted through the corresponding control algorithm to ensure that the temperature of the gas entering the concrete container meets the process requirements.

[0079] Preferably, the parameter display unit is configured as a display control panel 110, which displays key process parameters in the air inlet and outlet duct system in real time. The operator can check the data such as gas flow rate, temperature, pressure, temperature and humidity at any time to understand the system operation status.

[0080] Preferably, the data recording unit is used to automatically record process parameters, including operating time, gas flow, temperature, pressure, etc. These historical data can be used for operation analysis and optimization, and can also serve as an important basis for quality traceability.

[0081] Through the organic combination of the above functional units, the automatic control and real-time data recording of the device are realized, making the operation of the equipment more convenient, which not only improves the industrial safety level, but more importantly, effectively reduces the radiation dose of the staff by reducing the operation and stay time of the personnel, thereby improving the radiation safety and environmental safety level.

[0082] In the above-mentioned invention embodiment, the device for removing residual tritium from the wastewater filter element can achieve at least two important functions: first, the concrete container sealing top cover 101 has good sealing performance after replacing the original container top cover; second, by utilizing the synergistic effect of functional components such as the circulating air module, the tritium water adsorption purification module and the automatic control module, the tritium removal treatment can be performed while the waste filter element remains in place. This treatment method not only ensures the sealing of the temporary storage process, but also effectively removes the free tritium water in the waste filter element and the tritium adsorbed by the waste filter element. Compared with the method of hanging the waste filter element at the nuclear power site and letting it stand and drain naturally to remove free tritium and long-term temporary storage in a concrete container, this device can completely remove free tritium water and significantly remove tritium water adsorbed by the waste filter element at the same time, and removes more tritium. After treatment, the tritium level of the waste filter element is significantly reduced, and the reduction rate of the tritium level of the waste filter element is greater than 95%, creating favorable conditions for subsequent treatment.

[0083] Based on the device for removing residual tritium from a wastewater filter cartridge provided in the above embodiment, in one embodiment of the present invention, a method for removing residual tritium from a wastewater filter cartridge in a concrete container of a heavy water reactor temporary storage warehouse is further provided, such as Figure 4 Preferably, the method comprises at least the following steps:

[0084] Step S210: remove the original top cover of the concrete container, and install the sealing top of the concrete container onto the concrete container by compacting the rubber gasket with its own weight.

[0085] Preferably, radiation level monitoring and protection preparation are required before removing the original concrete container top cover. When installing the concrete container sealing top cover 101, it should be ensured that the rubber gasket is evenly laid on the top sealing surface of the container, and slowly put into place through the lifting equipment so that the weight of the top cover acts evenly on the rubber gasket.

[0086] Step S220: Start the device to establish internal circulation and adjust the variable frequency fan to make the gas flow rate of the inlet and outlet air duct system 50-150m 3 / h, and monitor the rate of change of tritium levels near the sealed top cover of the concrete container.

[0087] Preferably, before starting the device, the system air tightness is first checked; after starting, it is operated at a lower flow rate, and after the system is stable, the flow rate is gradually adjusted to the flow range required by the process. At the same time, the tritium level is continuously monitored through a sampling point set near the sealing top cover 101 of the concrete container to confirm the sealing performance.

[0088] Step S230: detritiate the waste filter element in the concrete container through the circulating air module until the tritium level before the first molecular sieve adsorption tank drops to the same level as the tritium level after the fourth molecular sieve adsorption tank, and both are at the background level.

[0089] Preferably, during the detritiation process, the tritium level needs to be measured regularly through the sampling interfaces before and after each molecular sieve adsorption tank. When the tritium level before the first molecular sieve adsorption tank 105 is measured repeatedly and is equivalent to the background level after the fourth molecular sieve adsorption tank 108, it can be determined that the detritiation treatment is completed.

[0090] In a preferred embodiment, after completing a residual tritium removal step, the waste filter element is allowed to stand for 10-15 days to fully remove the tritium adsorbed in the deep layer of the waste filter element; the residual tritium removal step is repeated until the tritium level at the bottom of the concrete container does not increase after 15 days of standing, and the tritium level growth rate is less than 10% compared with the last residual tritium removal.

[0091] In a preferred embodiment, in the residual tritium removal step, when the humidity at the air outlet of the fourth molecular sieve adsorption tank 108 is greater than 1RH, the molecular sieves in all molecular sieve adsorption tanks are replaced. Radiation protection should be done during the replacement process, and the replaced waste molecular sieves need to be classified, collected and treated as radioactive waste.

[0092] The residual tritium removal method provided by the present invention has the following significant advantages:

[0093] First, compared with the existing method that requires the waste filter element to be removed from the container for treatment, this method uses in-situ treatment to remove tritium while keeping the waste filter element sealed and temporarily stored. A closed loop is established in the concrete container through a circulating air system, combined with tritium water adsorption and purification treatment, which can effectively remove free tritium water and tritium adsorbed by the waste filter element, avoiding environmental pollution and personnel radiation hazards that may be caused during the transfer of the waste filter element.

[0094] Secondly, this method adopts the treatment mode of "circulation treatment-stationary-recirculation". Through the combination of circulating wind carrier and multi-stage molecular sieve adsorption, it can achieve efficient removal of free tritium water; the stationary process allows the tritium adsorbed in the deep layer of the waste filter to fully diffuse and precipitate; repeated circulation treatment ensures the detritium effect. Practice has proved that this method can significantly reduce the tritium content in the waste filter, and the detritium rate exceeds 95%.

[0095] Finally, this method uses fully automated control and online monitoring, and can achieve purification and safe discharge of the treated gas through the ventilation system, avoiding secondary pollution to the environment and personnel. This not only reduces the tritium content of the waste filter element, but also provides favorable conditions for the subsequent treatment of the waste filter element.

[0096] refer to Figure 5 and Figure 6 In a specific embodiment of the present invention, a device for removing residual tritium from a wastewater filter element in a concrete container of a heavy water reactor temporary storage facility and a method for using the device are provided.

[0097] The tritium water adsorption purification module is provided with a filter box, four molecular sieve adsorption tanks and an activated carbon adsorption tank. The molecular sieve tanks are connected in series in four stages and the molecular sieves are redundantly loaded (the molecular sieve tritium absorption ratio is calculated as 0.2). It should be noted that the number of series connections can be increased or decreased according to the tritium content of the waste filter element. The device provided in this embodiment can realize the combined use of two molecular sieve adsorption tanks or four molecular sieve adsorption tanks through the opening and closing combination of the BV-11 and BV-12 valves. The tritium absorption rate of the gas passing through the third molecular sieve tank is greater than 95% (the tritium meter is stable at the background level, and the variation range is less than 5%), and the adsorption rate of tritium water through the fourth molecular sieve adsorption tank reaches 100% (the tritium meter is stable at the background level); after passing through the activated carbon adsorption tank, the gas is free of aerosols and other radioactive nuclides, and the tritium level is maintained at the background level.

[0098] When the device in this embodiment is used to remove residual tritium from the filter element, the following steps are included:

[0099] Step S301, the filter box is loaded with adsorption filter material, the molecular sieve adsorption tank is loaded with molecular sieve, and the activated carbon adsorption tank is loaded with impregnated activated carbon. After the filling is completed, each tank is closed and connected to the main pipeline;

[0100] Step S302, open the top cover of the concrete container of the waste filter element to be processed, arrange the rubber sealing gasket ring at the contact point between the concrete container and the original top cover, and slowly and vertically place the concrete container sealing top cover of the device into the concrete container by the overhead crane, so that the concrete container sealing top cover can seal the concrete container by compacting the rubber gasket ring by its own weight;

[0101] Step S303, the device starts to establish an internal circulation: open valves BV-1, BV-2, BV-3, BV-4, BV-5, BV-6, BV-8, BV-9, BV-12, BV-14, and BV-15; then set the fan power, turn on the power of the variable frequency fans VFD-1 and VFD-3, and start; after running for a period of time, close valves BV-1, BV-2, and BV-15 to establish an internal circulation; close valve BV-12, open valve BV-11, and the airflow passes through two molecular sieve adsorption tanks; open valve BV-12, close valve BV-11, and the airflow passes through four molecular sieve adsorption tanks;

[0102] Step S304, device operation detection: after the internal circulation is established, the device operates stably for not less than 2 hours, and the operation and numerical control detection of each pneumatic valve, variable frequency fan and preheating furnace are carried out, and the flow meter, pressure gauge and thermometer and hygrometer signal display detection are carried out; if the various components and equipment of the device can operate stably for not less than 2 hours, the device operation detection is completed;

[0103] Step S305, device sealing test: after the internal circulation is established, the device is continuously operated for 2 hours, and the pressure is kept stable (the pressure is not higher than 2kPa, and the pressure is kept constant under different variable frequency fan operating frequencies, i.e. different flow rates, and the pressure change rate is less than 5%), and the device sealing test is qualified;

[0104] Step S306: After the device operation test and the sealing test are qualified, the sealing top cover is connected to the device body through the inlet and outlet air ducts;

[0105] Step S307, a tritium detector is placed 1m away from the concrete container, and a tritium detector is connected before the first molecular sieve adsorption tank and after the fourth molecular sieve adsorption tank respectively;

[0106] Step S308, detritium removal from waste filter element: establish internal circulation according to step S304, adjust the speed of variable frequency fan, control the gas flow in the pipeline to 50-150m3 / h, observe the operating pressure of the device and the tritium meter reading at 1m of the concrete container in real time, the pressure change rate is less than 5%, and the tritium meter reading change rate is less than 10%;

[0107] Step S309, detritium removal endpoint judgment: when the reading of the tritium meter before the first molecular sieve adsorption tank drops to the same level as the reading of the tritium meter after the fourth molecular sieve adsorption tank and both are at the background level, detritium removal is considered to be completed;

[0108] Step S310: After the waste filter element that has been detritiated is placed in a concrete container for 10 to 15 days, the detritiation experiment is repeated, and the waste filter element is detritiated multiple times to fully remove the tritium adsorbed in the waste filter element; after 15 days of standing, if the tritium level at the bottom of the concrete container has no significant increase and the growth rate of the tritium level after the last detritiation is less than 10%, it is considered that the detritiation of the waste filter element in the concrete container is completed;

[0109] Step S311, molecular sieve replacement: during the detritium removal operation, if the humidity of the No. 1 thermohygrometer (the humidity at the air outlet of the last molecular sieve tank) is greater than 1RH, the molecular sieve in the molecular sieve tank is replaced under radiation protection measures;

[0110] Step S312: After detritium removal is completed, the sealed top cover of the concrete container is moved out of the top of the concrete container by means of an overhead crane, and the rubber sealing gasket is removed, and the original top cover of the concrete container is placed into the concrete container to seal the concrete container; and the individual disassembly of each tank of the tritium water adsorption purification module of the device and the export of the molecular sieve are completed under radiation protection measures;

[0111] Step S313: The treated filter element can be temporarily stored in a concrete container (the original concrete container top cover is sealed) or transported to a designated location for inspection and delivery. The molecular sieve in the tritium adsorption device is placed in a waste barrel and sealed for temporary storage or cement fixation.

[0112] like Figure 7 In one embodiment of the present invention, the above device was used to conduct an actual detritium experiment. A concrete container temporarily storing 8 3526 waste filter cartridges was used as the experimental object and the above device was used for treatment. During the experiment, the device was used at 100m 3 / h gas flow rate operation, after about 14 hours of detritiation treatment, the tritium level at the bottom of the concrete container dropped from 220DAC to 3DAC, and the detritiation efficiency reached 98.6%. During the entire operation process, the tritium level of the gas flow through the fourth molecular sieve adsorption tank was always equivalent to the background tritium level of the temporary storage environment, and remained in the range of 0.5-0.6DAC, indicating that the device has a good detritiation effect and stable operation performance.

[0113] The embodiments of the present invention are described above in conjunction with the accompanying drawings, but the present invention is not limited to the above-mentioned specific implementation modes, which are merely illustrative rather than restrictive. Under the guidance of the present invention, ordinary technicians in this field can also make many forms without departing from the scope of protection of the present invention and the claims, all of which are within the protection of the present invention.

Claims

1. A device for removing residual tritium from a wastewater filter element in a concrete container of a heavy water reactor temporary storage warehouse, characterized in that: include: - Sealed top cover of concrete container, used to replace the original top cover of concrete container and sealed with the concrete container; - Circulating air module, including variable frequency fan, preheating furnace, air inlet and outlet duct system and pneumatic valve; - Tritium water adsorption purification module, including a filter box, a multi-stage series-connected molecular sieve adsorption tank and an activated carbon adsorption tank; - an automation control module, used to control the operating parameters of the circulating air module and the opening and closing state of the pneumatic valve; The circulating air module, the tritium water adsorption purification module and the automatic control module are integrated into the equipment body, and are connected to the sealed top cover of the concrete container through the air inlet and outlet duct system to form a sealed circulation system.

2. The device according to claim 1, characterized in that The sealing top cover of the concrete container is made of stainless steel, and its surface is treated with anti-corrosion and polishing to reduce the adhesion of tritium; The sealed top cover of the concrete container is sealed and connected to the concrete container by compacting the rubber gasket by its own weight. Under the condition that the operating pressure of the device is 2±0.2 kpa, the tritium level change rate near the sealed top cover of the concrete container is less than 10%.

3. The device according to claim 1, characterized in that The variable frequency fan includes a first fan, a second fan and a third fan, wherein the first fan and the third fan are used for main line circulating wind to carry detritium, and the second fan is used for the circulation of the molecular sieve adsorption tank; The preheating furnace is used to increase the inlet air temperature entering the concrete container; The air inlet and outlet duct system includes a detachable air inlet duct and a detachable air outlet duct connected to the sealed top cover of the concrete container, and a duct assembly for realizing internal circulation and exhaust circulation; The circulating air module also includes a plurality of pneumatic valves, a thermometer and a hygrometer, an anemometer and a pressure sensor arranged on the air inlet and outlet duct system, which are used to realize the switching between the sealed internal circulation and the exhaust circulation, and the real-time monitoring of the process parameters.

4. The device according to claim 3, characterized in that The operating gas flow rate of the inlet and outlet air duct system is 50-150m 3 / h, the air inlet and outlet duct system maintains sealing performance under an operating pressure of 3kPa.

5. The device according to claim 1, characterized in that The filter box is used to absorb and remove dust and radionuclides in the gas; The multi-stage series-connected molecular sieve adsorption tanks include first to fourth molecular sieve adsorption tanks connected in sequence, wherein the molecular sieve adsorption tanks are filled with molecular sieves for adsorbing tritium; The activated carbon adsorption tank is arranged at the rear end of the fourth molecular sieve adsorption tank and is filled with impregnated activated carbon for further purifying the gas.

6. The device according to claim 5, characterized in that The multi-stage series-connected molecular sieve adsorption tanks can realize the selective use of two or four molecular sieve adsorption tanks through the opening and closing combination of the pneumatic valves; The gas tritium absorption rate of the third molecular sieve adsorption tank is greater than 95%, and the tritium water absorption rate of the fourth molecular sieve adsorption tank is 100%.

7. The device according to claim 1, characterized in that The automation control module comprises: - a pneumatic valve control unit, used to control the opening and closing of the pneumatic valve to achieve the selection of the air flow path; - Equipment operation control unit, used to control the start and speed adjustment of the variable frequency fan, and the start and temperature adjustment of the preheating furnace; - A parameter display unit, used to display the gas flow rate, temperature, pressure, temperature and humidity in the air inlet and outlet duct system in real time; -Data logging unit for automatic recording of process parameters.

8. A method for removing residual tritium from a wastewater filter element in a concrete container of a temporary storage facility for a heavy water reactor using the device according to any one of claims 1 to 7, characterized in that: The following steps are involved: The original top cover of the concrete container is removed, and the sealing top cover of the concrete container is installed on the concrete container by compacting the rubber gasket by its own weight; Start the device to establish internal circulation and adjust the variable frequency fan to make the gas flow rate of the inlet and outlet air duct system 50-150m 3 / h, and monitoring the rate of change of tritium level near the sealed top cover of the concrete container; The waste filter element in the concrete container is subjected to detritiation treatment by a circulating air module until the tritium level before the first molecular sieve adsorption tank is reduced to the same level as the tritium level after the fourth molecular sieve adsorption tank, and both are background levels.

9. The method according to claim 8, characterized in that After completing a residual tritium removal step, the spent filter element is left to stand for 10-15 days; The residual tritium removal step is repeated until the tritium level at the bottom of the concrete container does not increase after standing for 15 days, and the tritium level increase rate is less than 10% compared with the last residual tritium removal.

10. The method according to claim 8, characterized in that In the residual tritium removal step, when the humidity at the air outlet of the fourth molecular sieve adsorption tank is greater than 1RH, the molecular sieves in all the molecular sieve adsorption tanks are replaced.

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