Testing device and method for fission source item release in irradiated fuel element

Abstract

The invention provides a test device and method for fission source item release in an irradiated fuel element, and relates to the technical field of nuclear safety fission product source item tests. The test device comprises a reaction kettle, a water circulation system and a pressure stabilizing system, the water circulation system comprises a water tank, a make-up pump, a surge tank and a preheater which are sequentially connected through pipelines, the preheater is communicated with the feeding end of the reaction kettle, the surge tank is communicated with the discharging end of the reaction kettle, and a circulating pump is further arranged at the discharging end of the reaction kettle; the pressure stabilizing system comprises a gas steel cylinder and a filter which are sequentially connected through a pipeline, and the filter is respectively communicated with the pressure stabilizing tank and the reaction kettle; an ion exchange bypass and a water condensation bypass are further arranged on a connecting pipeline of the pressure stabilizing tank and the reaction kettle, an ion exchange column is arranged on the ion exchange bypass, and a condenser is arranged on the water condensation bypass. Dynamic source item tests of radionuclides can be carried out, so that nuclide release behavior researches of irradiated fuel elements in various element forms can be realized.

Description

Technical Field

[0001] The present invention relates to the technical field of nuclear safety fission product source term testing, and in particular to a testing device and method for releasing fission source terms in irradiated fuel elements. Background Art

[0002] The fuel element is the heart of a nuclear reactor. Once a fuel element is damaged, a large amount of radioactive fission products will enter the coolant, causing a significant increase in the radioactivity level of the primary water circuit, which directly threatens the operational safety and radiation protection performance of the reactor. The fuel element damage diagnosis procedure is based on the physical model of the generation, release and migration of fission products in the reactor. Combined with the radioactivity concentration information of each characteristic nuclide in the coolant, it can timely and accurately determine whether damage has occurred, and evaluate the damage ratio of the fuel cladding, the size of the rupture, and the burnup range of the damaged component. The release behavior of fission products is the core of all source term analysis research and has become one of the important factors in demonstrating the inherent safety of reactors. The study of the release behavior of nuclides in fuel elements after irradiation can provide more solid and reliable data support for the evaluation and prediction of the radiation impact of normal reactor operation and accidental release.

[0003] The new fuel elements have various structural forms, such as spherical, annular, plate-shaped, etc., and their fission product release laws are significantly different from those of traditional rod-bundle fuel elements. Existing fuel rod fission source analysis tools are no longer applicable to these new elements. For example, the spherical fuel elements of high-temperature gas-cooled reactors use a unique graphite matrix release and diffusion model, while there is a lack of corresponding laws or data references for annular and plate-shaped fuel elements. In order to fill this knowledge gap, it is necessary to conduct research on the release behavior of nuclides in new fuel elements after irradiation and to master the release behavior and laws of nuclides, which is of great significance to ensure the safe operation and evaluation of fuel elements. Summary of the invention

[0004] The purpose of the present invention is to provide a test device for the release of fission source terms in irradiated fuel elements, which can carry out dynamic source term tests of radioactive nuclides to realize the study of the nuclide release behavior of irradiated fuel elements in various element forms, solve the experimental technology gap of existing defective fuel element source term simulation and analysis tools, and lay a solid foundation for source term analysis and safety performance evaluation of irradiated fuel elements.

[0005] Another object of the present invention is to provide a test method for the release of fission source terms in fuel elements after irradiation, which can study the release behavior of nuclides in fuel elements of different forms, is easy to operate, and can quickly carry out experiments.

[0006] The present invention is achieved through the following technical solutions:

[0007] A test device for releasing fission source terms in irradiated fuel elements, comprising a reactor, a water circulation system and a pressure stabilizing system;

[0008] The water circulation system includes a water tank, a water supply pump, a pressure-sustaining tank and a preheater which are sequentially connected through pipelines. The preheater is connected to the feed end of the reactor, the pressure-sustaining tank is connected to the discharge end of the reactor, and a circulation pump is also provided at the discharge end of the reactor;

[0009] The pressure stabilizing system includes a gas cylinder and a filter which are sequentially connected through pipelines, and the filter is connected to the pressure stabilizing tank and the reactor respectively;

[0010] An ion exchange bypass and a water condensation bypass are also provided on the connecting pipeline between the pressure stabilizing tank and the reactor. An ion exchange column is provided on the ion exchange bypass, and a condenser is provided on the water condensation bypass.

[0011] The inventors have found that the existing fuel element detection usually detects whether the fuel element is damaged, specifically by judging whether the nuclides are released from the fuel element and the activity concentration information of the released nuclides, so as to judge the operation of the reactor according to the damage of the fuel element. However, for undamaged fuel elements, it is impossible to detect the release of nuclides from the fuel elements by the above method. During the operation of the reactor, when the fuel elements are damaged, it is impossible to predict the impact of accident radiation in time, and it is impossible to take effective protective measures in time, which will affect personal safety, equipment safety and environmental safety.

[0012] Therefore, the inventors adopted the above-mentioned test device, through the cooperation of the reactor, the water circulation system and the voltage stabilizing system, to artificially prepare defective elements, let the defective elements release nuclides, take samples for detection after the release, and conduct research on the nuclide release behavior of the fuel elements. By mastering the nuclide release behavior and laws, the safe operation and performance of the fuel elements can be evaluated, and at the same time, a solid and reliable experimental basis can be provided for the evaluation and prediction of the radiation impact of normal operation and accidental release of the reactor.

[0013] Among them, the test device for the release of fission source terms in irradiated fuel elements uses a single element as the test piece, rather than the entire fuel assembly, to study the release of nuclides from the fuel element to the loop device. In addition, the test device can also study the nuclide release behavior of defective or damaged fuel elements after irradiation.

[0014] The reactor is a high-temperature and high-pressure reactor. The upper side of the reactor is connected to a feed pipeline that integrates liquid feeding, pressurization, pressure replenishment and pressure measurement. The bottom is connected to a discharge pipeline. The feed pipeline is two 3 / 8 pipes, and the discharge pipeline is a 3 / 8 pipe. The feed pipeline and the discharge pipeline are connected to the water circulation system and the pressure stabilization system respectively. During the test, the reactor is arranged in a sealed shielding box room.

[0015] The water circulation system is driven by a power system, and necessary online / offline monitoring of water quality parameters can be performed outside the sealed shielding box, especially the activity concentration of characteristic γ radionuclides in the water.

[0016] After the reactor is sealed, the water in the water circulation system is pumped out from the water tank through the water supply pump, passes through the pressure regulating tank, and enters the reactor. The reactor, the pressure regulating tank, and the connecting pipes are all filled with the medium (water), and the water supply stops automatically. Before the circulating water enters the reactor, it is heated by the preheater to the specified temperature (not less than 150℃), and then enters the reactor through the insulation pipeline.

[0017] When the device is in normal heating operation cycle, the circulation pump runs, and the water in the pipeline circulates in and out of the reactor. When the water in the loop is lost due to sampling, etc., it is automatically replenished by the water in the pressure-regulating tank. When the water level in the pressure-regulating tank is low, the water replenishment pump replenishes the pressure-regulating tank.

[0018] The water containing radionuclides flowing out of the discharge pipeline at the bottom of the reactor is pumped out by a circulation pump and can be selected to flow into the ion exchange column for enrichment and treatment. The discharge pipeline is connected to a water condensation bypass to achieve rapid cooling of the circulating water. The sampled water can be directly quantitatively sampled after being cooled to a certain temperature by the condenser.

[0019] The pressure stabilizing system continuously provides stable pressure for the entire test device. The gas in the gas cylinder is filtered and reduced in pressure to the specified pressure. The stabilized gas is introduced from the top of the reactor and the pressure stabilizing tank to stabilize the gas pressure of the device.

[0020] Furthermore, a stop valve I is arranged between the water tank and the water supply pump, a one-way valve I and a solenoid valve I are arranged between the water supply pump and the pressure-stabilizing tank; a solenoid valve II is arranged at the outlet end of the pressure-stabilizing tank, a solenoid valve III is arranged between the pressure-stabilizing tank and the preheater, and a solenoid valve IV, a solenoid valve V and a one-way valve II are arranged on the connecting pipeline between the pressure-stabilizing tank and the reactor.

[0021] Furthermore, the ion exchange column is arranged in parallel with the electromagnetic valve IV, and the two ends of the ion exchange column are respectively provided with the electromagnetic valve VI and the one-way valve III.

[0022] Furthermore, the condenser is arranged in parallel with the solenoid valve V, the two ends of the condenser are respectively provided with a solenoid valve VI I and a solenoid valve VIII, and the discharge end of the condenser is provided with a stop valve II.

[0023] Furthermore, a pressure stabilizing valve is provided at the outlet of the filter, a solenoid valve IX is provided on the connecting pipeline between the filter and the pressure stabilizing tank, and a back pressure valve and a safety valve are provided on the connecting pipeline between the filter and the reactor.

[0024] Furthermore, a pressure gauge is provided at the outlet end of the gas cylinder, and a thermometer is provided on the reactor.

[0025] Furthermore, the reaction kettle comprises a kettle body and a kettle cover, the kettle cover is threadedly connected to the kettle body, a perfluoroether O-ring is arranged at the connection between the kettle cover and the kettle body, and a loading interface is arranged on the kettle cover.

[0026] Furthermore, the test device also includes a control system, which is electrically connected to the pressure gauge, the thermometer and the circulation pump.

[0027] A test method for the release of fission source terms in irradiated fuel elements comprises the following steps:

[0028] The test piece is loaded into the reactor, the reactor is filled with water, the reactor is heated and pressure-regulated, the water circulation is started, the test piece is subjected to a nuclide release test, and sampling is performed for testing.

[0029] Further, the test temperature is 100-300°C, the test pressure is 0.1-10MPa, the single test time is ≥72h, and the water flow rate during the water circulation process is 2m / s. Preferably, the test temperature is 200°C and the test pressure is 3.5MPa.

[0030] The technical solution of the present invention has at least the following advantages and beneficial effects:

[0031] 1. This device has good sealing, radioactivity and inclusiveness. The temperature, pressure, medium flow rate and other parameters in the reactor and its circulation loop can be measured, controlled and adjusted to meet the research on the release behavior of fuel element nuclides under different conditions;

[0032] 2. This device can realize the circulation of water under high temperature and high pressure, rapid heating and cooling of circulating water, quantitative sampling of circulating water, selective enrichment of nuclides in circulating water, etc. It can select direct sampling or sampling after enrichment according to the different nuclide contents, and analyze and detect the nuclides released into the water;

[0033] 3. The temperature, pressure and liquid level parameters in this device can be monitored in real time and automatically recorded through the control system, which is convenient for observing the entire state of the research system and taking different countermeasures;

[0034] 4. The software program parameters of the control system of this device are easy to set and modify, meeting the actual needs of various applications and significantly improving data processing capabilities and automation levels;

[0035] 5. When the control system of this device detects that a certain variable (temperature, pressure, flow, liquid level) exceeds the upper or lower limit of the set value, the computer operation screen will display "flashing" at the relevant part, and start the buzzer alarm, automatically record the alarm information, so that the operator can intervene effectively in time;

[0036] 6. The present invention is easy to operate, meets the experimental requirements for studying the release behavior of nuclides in fuel elements after irradiation, and solves the problem of the lack of an experimental research platform for the release behavior of nuclides in fuel elements after irradiation. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 A schematic diagram of the structure of an experimental device for releasing fission source terms in fuel elements after irradiation provided in Example 1 of the present invention.

[0038] Icons: 1-reactor, 2-water tank, 3-water make-up pump, 4-pressure stabilizing tank, 5-preheater, 6-circulation pump, 7-gas cylinder, 8-filter, 9-ion exchange column, 10-condenser, 11-stop valve I, 12-check valve I, 13-solenoid valve I, 14-solenoid valve II, 15-solenoid valve III, 16-solenoid valve IV, 17-solenoid valve V, 18-check valve II, 19-solenoid valve VI, 20-check valve I II, 21-solenoid valve VI I, 22-solenoid valve VIII, 23-stop valve II, 24-pressure stabilizing valve, 25-back pressure valve, 26-safety valve, 27-solenoid valve IX, 28-pressure gauge, 29-thermometer, 30-control system. DETAILED DESCRIPTION

[0039] The present invention is further described below in conjunction with specific embodiments, but the embodiments do not limit the present invention in any form. Unless otherwise specified, the raw materials and reagents used in the embodiments of the present invention are conventionally purchased raw materials and reagents.

[0040] Example 1

[0041] like Figure 1 As shown, this embodiment provides a test device for releasing fission source terms in fuel elements after irradiation, including a reactor 1, a water circulation system and a pressure stabilizing system;

[0042] The water circulation system includes a water tank 2, a water supply pump 3, a pressure-suppressing tank 4 and a preheater 5 which are sequentially connected through pipelines. The preheater 5 is connected to the feed end of the reactor 1, the pressure-suppressing tank 4 is connected to the discharge end of the reactor 1, and a circulation pump 6 is also provided at the discharge end of the reactor 1.

[0043] The pressure stabilizing system includes a gas cylinder 7 and a filter 8 which are sequentially connected through pipelines, and the filter 8 is connected to the pressure stabilizing tank 4 and the reactor 1 respectively;

[0044] An ion exchange bypass and a water condensation bypass are also provided on the connecting pipeline between the pressure stabilizing tank 4 and the reactor 1. An ion exchange column 9 is provided on the ion exchange bypass, and a condenser 10 is provided on the water condensation bypass.

[0045] In this embodiment, a stop valve I11 is provided between the water tank 2 and the water supply pump 3, a one-way valve I12 and a solenoid valve I13 are provided between the water supply pump 3 and the pressure-stabilizing tank 4; a solenoid valve II 14 is provided at the outlet end of the pressure-stabilizing tank 4, a solenoid valve III 15 is provided between the pressure-stabilizing tank 4 and the preheater 5, and a solenoid valve IV16, a solenoid valve V17 and a one-way valve II 18 are provided on the connecting pipeline between the pressure-stabilizing tank 4 and the reactor 1.

[0046] In this embodiment, the ion exchange column 9 is arranged in parallel with the electromagnetic valve IV16, and the two ends of the ion exchange column 9 are respectively provided with the electromagnetic valve VI 19 and the one-way valve II 20.

[0047] In this embodiment, the condenser 10 is arranged in parallel with the solenoid valve V17, and the two ends of the condenser 10 are respectively provided with a solenoid valve VI I 21 and a solenoid valve VIII 22, and the discharge end of the condenser 10 is provided with a stop valve II 23.

[0048] In this embodiment, a pressure stabilizing valve 24 is provided at the outlet of the filter 8, a solenoid valve IX27 is provided on the connecting pipeline between the filter 8 and the pressure stabilizing tank 4, and a back pressure valve 25 and a safety valve 26 are provided on the connecting pipeline between the filter 8 and the reactor 1. The gas in the gas cylinder 7 is filtered and decompressed to a specified pressure, and the back pressure valve 25 ensures overpressure stabilization, and the safety valve 26 ensures the pressure safety of the entire device.

[0049] In this embodiment, a pressure gauge 28 is provided at the outlet of the gas cylinder 7, and a thermometer 29 is provided on the reactor 1. The pressure and temperature of the device can be monitored by the pressure gauge 28 and the thermometer 29, so as to adjust the test conditions of the test piece nuclide release in time.

[0050] In this embodiment, the reactor 1 includes a reactor body and a reactor cover, the reactor cover is threadedly connected to the reactor body, a perfluoroether O-ring is provided at the connection between the reactor cover and the reactor body, and a loading interface is provided on the reactor cover. Among them, the loading interface is an electric rotation and lifting structure. During the test, the water in the reactor 1 completely immerses the test piece, and two temperature measuring points are set near the upper and lower ends of the test piece, which can monitor the temperature of the medium attached to the test piece in real time during the test to ensure that the test piece undergoes a nuclide release test.

[0051] In this embodiment, the test device further includes a control system 30, which is electrically connected to the pressure gauge 28, the thermometer 29 and the circulating pump 6. The pressure, temperature, liquid level and flow rate of the entire device are monitored and controlled by the control system 30, thereby realizing automatic monitoring, control, interlocking protection and alarm of the entire device.

[0052] Example 2

[0053] A test method for the release of fission source terms in irradiated fuel elements comprises the following steps:

[0054] S1. Load the test piece into the reactor 1, cover the reactor tightly, and test the air tightness of the system.

[0055] S2. Replenish water to reactor 1: open stop valve I11, check valve I12, solenoid valve I14, solenoid valve II 14, and solenoid valve III 15, and start the water replenishment pump 3 to replenish water to the pressure-stabilizing tank 4 and reactor 1 until the reactor 1 is full of water, then turn off the water replenishment pump 3, and close the stop valve I11, check valve I12, solenoid valve I14, solenoid valve II 14, and solenoid valve III 15.

[0056] S3, heating and pressure regulation of reactor 1: set the temperature parameter to 200℃ on the control panel, start the heating button, the system pressure and temperature are mainly achieved by heating medium (water), with pressure auxiliary regulation, the pressure is adjusted to 3.5MPa by controlling the switch size of gas cylinder 7, if the system pressure is too high, release the pressure by opening the solenoid valve IX27, and the water in the device is in a circulating state during heating.

[0057] S4. Start water circulation and conduct nuclide release test on test pieces: When system temperature and pressure reach set values, the nuclide release test of irradiated fuel elements is started, ion exchange bypass and water condensation bypass are closed, and the parameters of circulation pump 6 are adjusted to make water circulate at the set flow rate. During the circulation process, nuclide online monitoring and analysis are carried out to determine whether to test, terminate or take samples. The single high temperature and high pressure continuous circulation test time is generally not less than 72 hours, and the water flow rate during the water circulation process is 2m / s.

[0058] S5. Sampling and testing:

[0059] S51, direct sampling of circulating water, close solenoid valve V17, open solenoid valve VI I21 and solenoid valve VIII22, lead part of the circulating water to the pipeline of condenser 10, open solenoid valve V17, close solenoid valve VI I21 and solenoid valve VIII22, open the water condensation bypass, cool the circulating water in the entire loop, and after the water in the pipeline of condenser 10 is cooled to below 40°C, open stop valve II I23 to sample the circulating water;

[0060] S52, circulating water cooling, open the water condensation bypass, close the solenoid valve V17, open the solenoid valve VI I21 and the solenoid valve VIII22, and the circulating water in the entire circuit can be cooled;

[0061] S53, nuclide enrichment in circulating water, after the circulating water is cooled, close the solenoid valve 1 V16, open the solenoid valve VI 19, and use the ion exchange column 9 to adsorb and enrich the nuclides in the circulating water. After the enrichment is completed, the ion exchange column 9 can be disassembled for sampling and analysis. After a single test is completed, the resin column used for nuclide enrichment needs to be replaced.

[0062] S6. Monitoring and control:

[0063] The pressure, temperature, liquid level and flow parameter information of the device are communicated to the control system 30. The operation screens of the software include: alarm screen, process control screen, pressure screen, temperature screen, liquid level screen, interlock control screen, real-time curve screen, historical curve screen and threshold setting, etc., which can monitor and automatically record relevant data in real time. The software can be used to compile and modify multi-stage automatic heating programs, start-up programs, parking programs, emergency shutdown programs, as well as process parameters and alarm limits.

[0064] S7, interlocking protection and alarm:

[0065] The control system 30 can perform interlocking protection and alarm on the research system. 1) Low alarm: When the system detects that a certain variable (temperature, pressure, flow, liquid level) exceeds the upper or lower limit of the set value, the computer operation screen will display "yellow flashing" at the relevant part and start the buzzer alarm to warn the operator to intervene; at the same time, the system automatically records the alarm information. 2) High alarm: When a low alarm occurs, if the operator does not intervene effectively in time, a certain variable of the system (temperature, pressure, flow, liquid level) will continue to rise or fall until it exceeds the upper or lower limit of the set value. The computer operation screen will display "red flashing" at the relevant part and start the buzzer alarm again to warn the operator to intervene compulsorily; at the same time, the system automatically records the alarm information.

[0066] S8. Loop cleaning and decontamination:

[0067] After a single irradiation or after the completion of the nuclear release test of the fuel element, the circuit needs to be flushed and cleaned according to the water replenishment process. If necessary, the system can be decontaminated with a decontamination agent (sodium thiosulfate).

[0068] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A test device for releasing fission source terms in irradiated fuel elements, characterized in that: Including reactor, water circulation system and pressure stabilizing system; The water circulation system comprises a water tank, a water supply pump, a pressure-sustaining tank and a preheater which are sequentially connected through pipelines, the preheater is connected to the feed end of the reactor, the pressure-sustaining tank is connected to the discharge end of the reactor, and the discharge end of the reactor is also provided with a circulation pump; The pressure stabilizing system comprises a gas cylinder and a filter which are sequentially connected through a pipeline, and the filter is respectively connected to the pressure stabilizing tank and the reactor; An ion exchange bypass and a water condensation bypass are also provided on the connecting pipeline between the pressure stabilizing tank and the reactor. An ion exchange column is provided on the ion exchange bypass, and a condenser is provided on the water condensation bypass.

2. The test device for releasing fission source terms in irradiated fuel elements according to claim 1, characterized in that: A stop valve I is arranged between the water tank and the water supply pump, a one-way valve I and a solenoid valve I are arranged between the water supply pump and the pressure-stabilizing tank; a solenoid valve II is arranged at the outlet end of the pressure-stabilizing tank, a solenoid valve III is arranged between the pressure-stabilizing tank and the preheater, and a solenoid valve IV, a solenoid valve V and a one-way valve II are arranged on the connecting pipeline between the pressure-stabilizing tank and the reactor.

3. The test device for releasing fission source terms in irradiated fuel elements according to claim 2, characterized in that: The ion exchange column is arranged in parallel with the electromagnetic valve IV, and the two ends of the ion exchange column are respectively provided with an electromagnetic valve VI and a one-way valve III.

4. The test device for releasing fission source terms in irradiated fuel elements according to claim 2, characterized in that: The condenser is arranged in parallel with the solenoid valve V, the two ends of the condenser are respectively provided with a solenoid valve VII and a solenoid valve VIII, and the discharge end of the condenser is provided with a stop valve II.

5. The test device for releasing fission source terms in irradiated fuel elements according to any one of claims 1 to 4, characterized in that: The outlet end of the filter is provided with a pressure stabilizing valve, the connecting pipeline between the filter and the pressure stabilizing tank is provided with an electromagnetic valve IX, and the connecting pipeline between the filter and the reactor is provided with a back pressure valve and a safety valve.

6. The test device for releasing fission source terms in irradiated fuel elements according to claim 5, characterized in that: The outlet end of the gas cylinder is provided with a pressure gauge, and the reactor is provided with a thermometer.

7. The test device for releasing fission source terms in irradiated fuel elements according to claim 6, characterized in that: The reaction kettle comprises a kettle body and a kettle cover, wherein the kettle cover is threadedly connected to the kettle body, a perfluoroether O-ring is arranged at the connection between the kettle cover and the kettle body, and a loading interface is arranged on the kettle cover.

8. The test device for releasing fission source terms in irradiated fuel elements according to claim 6, characterized in that: The test device also includes a control system, which is electrically connected to the pressure gauge, the thermometer and the circulation pump.

9. A test method based on the test device for releasing fission source terms in irradiated fuel elements according to any one of claims 1 to 8, characterized in that: The following steps are involved: The test piece is loaded into the reactor, the reactor is filled with water, the reactor is heated and pressure-regulated, the water circulation is started, the test piece is subjected to a nuclide release test, and sampling is performed for testing.

10. The test method for the release of fission source terms in irradiated fuel elements according to claim 9, characterized in that: The test temperature is 100-300℃, the test pressure is 0.1-10MPa, the single test time is ≥72h, and the water flow rate during the water circulation process is 2m / s.

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