An apparatus and method for isotopic analysis of a uranium hexafluoride gas sample and measurement of its impurity content

Abstract

The present application relates to the technical field of reflection time-of-flight mass spectrometer measurement, in particular to a device for isotope analysis and impurity content measurement of uranium hexafluoride gas sample, which comprises a sample injector, an ionization area, a reflection mass analyzer, a microchannel plate detector, a preamplifier, a data acquisition card, a computer terminal and a tail gas treatment arranged in sequence, and can not only determine the trace impurity components in the uranium hexafluoride gas, but also quickly measure the abundance of uranium isotopes. The device has the characteristics of compact structure, high integration, safe and simple operation, and convenient carrying; modularization and localization are realized, and the device is easy to maintain; when the device is retired or the components are updated, the replacement and modification of the module are relatively simple; the device can quickly and accurately measure the isotope analysis and impurity content of the uranium hexafluoride gas sample.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of mass spectrometry equipment, and more particularly relates to a device and method for isotope analysis and impurity content measurement of a uranium hexafluoride gas sample. BACKGROUND

[0002] In the process of enriching uranium-235 using the separation diffusion method or the centrifugal separation method, the only stable gaseous compound of uranium, uranium hexafluoride (UF6), must be used. Therefore, UF6 is an important material form in the processes of uranium conversion, uranium enrichment, and nuclear fuel element manufacturing in the nuclear fuel cycle. At the same time, in the production and conversion processes, UF6 gas inevitably mixes with air and other impurity components, such as more than thirty metal and non-metallic nuclides of aluminum, calcium, thorium, plutonium, and the like, some of which are radioactive nuclides. A uranium enrichment plant is an important processing workshop in the nuclear fuel cycle, and the control of its operation, the analysis of its products, and the calculation of nuclear materials all require accurate results for the abundance of U, which requires the establishment of an accurate and consistent measurement system for value transfer. Rapid and accurate measurement of the content of air impurities and HF gas at each production link of UF6 is an important link in the safety work of the nuclear fuel production cycle, and is of great significance to nuclear safety issues such as uranium leakage monitoring and nuclear safeguards supervision. 235 U. Rapid and accurate measurement of the content of air impurities and HF gas at each production link of UF6 is an important link in the safety work of the nuclear fuel production cycle, and is of great significance to nuclear safety issues such as uranium leakage monitoring and nuclear safeguards supervision.

[0003] Mass spectrometry, as a high-precision analysis and testing method, is a method in which a sample is ionized to lose electrons to form ions in a vacuum environment, the ions are separated in space or time by electric field, magnetic field, or electromagnetic field according to the difference in mass-to-charge ratio, and finally the relative abundance of the ions with respect to m / q is represented in the form of a spectrum. According to the principle of the mass analyzer, it can be divided into: single-focusing analyzer, double-focusing analyzer, quadrupole rod analyzer, ion trap analyzer, chromatograph, Fourier transform ion cyclotron resonance analyzer, and time-of-flight analyzer. For the mass spectrometry of the magnetic deflection gas mass spectrometer in the Lanzhou Uranium Plant, the sampling system first removes HF by low-temperature freezing, and then the UF6 gas is sent to the ion source of the mass spectrometer. In the ion source, the neutral molecules to be tested are bombarded by 70 eV electrons to form monovalent ions, which then enter the magnetic deflection mass analyzer. By controlling the strength of the deflection magnetic field, 235 U + and 238 U +After the ions pass through the two slits, they are extracted into the Faraday cup. The ion current is directly received by the metal electrode of the Faraday cup, and the ion current size is recorded. Since UF6 gas is prone to hydration reaction to generate HF, which in turn causes corrosion of the gas mass spectrometer. When in use, the HF needs to be removed, and online monitoring cannot be achieved. Meanwhile, the magnetic spectrometer has the problem of narrow measurement range, and can only be used for isotope analysis. If spectrum scanning analysis is performed, there is the limitation of long time. The magnetic spectrometer is a major precision instrument and equipment, and is very expensive, with a price of more than ten million yuan per device. The structure is complex, and the operation and maintenance are difficult, which requires special technical personnel for daily maintenance, operation and running. Moreover, many key technologies are monopolized by foreign countries, and domestic production is not yet available.

[0004] Based on the above, the present application provides a device and a measuring method for analyzing a uranium hexafluoride gas sample. The measuring device is based on the principle of a reflection type time-of-flight mass spectrometer, and a set of instruments and analysis methods suitable for analyzing uranium hexafluoride gas are improved. The measuring method has the characteristics of rapidity and accuracy, and the advantage is more obvious for gaseous radionuclide content measurement. The present application can not only determine the trace impurity content in the uranium hexafluoride gas, but also rapidly measure the abundance of uranium isotopes. SUMMARY

[0005] The present application aims to determine the trace impurity content in the uranium hexafluoride sample gas and to realize online determination of the abundance of uranium isotopes. The present application provides a device for isotope analysis and impurity content measurement of a uranium hexafluoride gas sample, which comprises a sample inlet device, an ionization zone, a reflection type mass analyzer, a microchannel plate detector, a preamplifier, a data acquisition card, a computer terminal and a tail gas treatment device arranged in sequence.

[0006] The sample inlet device is a direct capillary inlet device or a mixed carrier gas inlet pool capillary inlet device. The capillary has a length of 40-100 cm and an inner diameter of 10-50 microns. The direct capillary inlet device is used for directly flowing the measured environment or the production line port into the measured gas. The mixed carrier gas inlet pool capillary inlet device is used for flowing the measured gas into the capillary after mixing and pressure boosting. The flow meter is used for controlling the sample inlet, which ensures the high vacuum environment required by the analysis system and ensures the sample concentration in the action area. The sample inlet device comprises a pre-sample inlet zone and a free flight zone. The ionization zone is a target zone of a double-layer cavity ion source, which can realize three functions of as high sample concentration as possible, as high sample ionization rate as possible and as many ions generated by sample ionization as possible, reduces the longitudinal spatial dispersion of the ion beam, improves the mass resolution, and achieves a mass resolution of more than 1000.

[0007] Preferably, the vacuum degree of the pre-sample inlet zone in the sample inlet device is less than 1x10 -3Pa, the vacuum degree of the free flight region is less than 2*10 -4 Pa.

[0008] Preferably, the ionization of the ionization region comprises ultraviolet Kr lamp ionization and laser ionization, the molecules after ultraviolet Kr lamp ionization are generally in the state of monovalent ions, and the molecules after laser ionization are generally fragment ions and are in the state of monovalent or more than monovalent. After being accelerated by extraction, the ions pass through the repelling electric field of the reflection mass analyzer and are reflected by the reflector, and finally the ions hit the microchannel plate detector to form an electrical signal output.

[0009] Preferably, the double-layer cavity ion source accelerates and extracts ions through four-stage pole pieces, the pole piece aperture is 1mm-3mm, the pole piece spacing is 5mm-15mm, and the voltage is 0-100V, and the appropriate pole piece aperture, spacing and voltage size realize high-efficiency extraction of ions, and the aperture, spacing and voltage size are adjusted according to ion beam currents of different mass numbers.

[0010] Preferably, the device further comprises a cascade molecular pump and a mechanical pump.

[0011] Preferably, the microchannel plate detector has a special material coating, and the working vacuum of the microchannel plate detector is less than 2*10 -4 Pa, and the special material coating is an ALD-deposited aluminum oxide coating.

[0012] Preferably, the tail gas treatment part of the device is divided into adsorption and collection, the adsorption is performed by a chemical trap, and the collection is performed by reacting water with residual toxic substances that are easily soluble in water.

[0013] Another object of the present application is to provide a method for using the device for isotope analysis and impurity content measurement of a uranium hexafluoride gas sample, and the method specifically comprises the following steps:

[0014] S1: preparing a sample to be measured

[0015] S2: starting the instrument

[0016] The vacuum of the device is extracted to less than 5*10 -5 Pa in the front-stage sampling region, the vacuum of the free flight region is extracted to less than 1*10 -4 Pa, and the power supply module of the reflection mass analyzer and the ionization light source of the double-layer cavity ion source are started;

[0017] S3: calibration of the measurement system

[0018] The ion flight time is proportional to the square root of the mass-to-charge ratio, and the flight time of ionization of a gas sample with a known mass-to-charge ratio is used as a standard to calibrate the mass spectrum.

[0019] S4: introducing a uranium hexafluoride sample

[0020] The sampling container is connected to the capillary sample injector, and the sampling container and gas circuit are heated; the amount of the uranium hexafluoride sample from the capillary sample injector into the target area of the double-layer cavity ion source is controlled by the mass flow meter, and the vacuum degree of the front-stage sampling area is ensured to be less than 1*10 -3 Pa, and the vacuum degree of the free flight area is less than 2*10 -4 Pa.

[0021] S5: collecting

[0022] The sample molecules are ionized by the light source, the ions hit the microchannel plate detector to form an electric signal and output, and the electric signal is collected by the preamplifier, the data acquisition card and the computer terminal to form a mass spectrum.

[0023] S6: data analysis

[0024] For the target substance with a concentration of more than ppm in the sample, the online rapid analysis can be realized in less than 1 min, and for the target substance with a concentration of less than ppm to ppb, the cumulative analysis can be realized in less than 5 min.

[0025] Preferably, the sample in S1 is directly connected to the sampling area to be measured if it is a production line or an environment to be measured; and the sampling container is prepared if necessary, and the sampling container needs to be passivated.

[0026] Preferably, the passivation of the sampling container is using gaseous uranium hexafluoride.

[0027] The present application has the following beneficial effects:

[0028] The application discloses a device for isotope analysis and impurity content measurement of a uranium hexafluoride gas sample, which comprises a sampling injector, an ionization area, a reflection type mass analyzer, a microchannel plate detector, a preamplifier, a data acquisition card, a computer terminal and tail gas treatment which are sequentially arranged, and can realize determination of trace impurity components in the uranium hexafluoride gas and rapid measurement of the abundance of uranium isotopes. BRIEF DESCRIPTION OF DRAWINGS

[0029] The application will be described in further detail below with reference to the drawings.

[0030] Figure 1 is a structural flow diagram of a device for isotope analysis and impurity content measurement of a uranium hexafluoride gas sample according to an embodiment of the application.

[0031] In the figure: the sample to be measured under different environments is fed through a capillary; the ultraviolet Kr lamp light and the laser light source are ionization light sources; the double-layer ion source includes an ionization target chamber and an acceleration extraction electrode; the reflective mass analyzer transports ions to a special plating microchannel plate; the ion response signal is processed by a preamplifier, a data acquisition card and a computer terminal, and a mass spectrum is output; the vacuum acquisition system sends waste gas in the device to a tail gas adsorption and collection station for treatment.

[0032] Figure 2 is a mass spectrum of a uranium hexafluoride gas sample measured according to an embodiment of the application DETAILED DESCRIPTION

[0033] In order to make the technical means, creative features, purposes and effects of the application easy to understand, the application will be further described below in combination with specific embodiments.

[0034] Embodiment one: a device for isotope analysis and impurity content measurement of a uranium hexafluoride gas sample

[0035] The application provides a device for isotope analysis and impurity content measurement of a uranium hexafluoride gas sample, which comprises, in sequence, a sample feeder, an ionization zone, a reflective mass analyzer, a microchannel plate detector, a preamplifier, a data acquisition card, a computer terminal and a tail gas treatment station; the sample feeder is a direct capillary feeder or a mixed carrier gas sampling pool capillary feeder, the capillary has a length of 40-100 cm and an inner diameter of 10-50 microns, and the direct capillary feeder is used for directly flowing the sample to be measured from an environment or a production line port; the mixed carrier gas sampling pool capillary feeder is used for mixing and pressurizing the sample to be measured and then flowing the sample into the capillary, so that the high vacuum environment required by the analysis system is ensured, and the sample concentration in the action area is ensured. The sample feeder comprises a pre-stage sampling zone and a free flight zone; the ionization zone is a target zone of a double-layer cavity ion source, which can realize three functions of as high sample concentration as possible, as high sample ionization rate as possible and as many ions generated by sample ionization as possible, reduces the longitudinal spatial dispersion of the ion beam, improves the mass resolution, and achieves a mass resolution of more than 1000. The vacuum degree of the pre-stage sampling zone in the sample feeder is less than 1x10 -3 Pa, and the vacuum degree of the free flight zone is less than 2x10 -4Pa. The ionization zone includes ultraviolet Kr lamp ionization and laser ionization. The molecules ionized by the ultraviolet Kr lamp are generally in the state of monovalent ions, and the molecules ionized by the laser are generally fragment ions and in the state of monovalent or more than monovalent. The ions are accelerated out of the device, pass through the repelling electric field of the reflection mass analyzer, are reflected by the reflector, and finally hit the microchannel plate detector to form an electrical signal output. The double-layer cavity ion source accelerates and leads out the ions through four-stage pole pieces with a hole diameter of 1 mm to 3 mm, a spacing of 5 mm to 15 mm, and a voltage of 0 to 100 V. The appropriate hole diameter, spacing, and voltage size realize the efficient leading out of the ions, and the hole diameter, spacing, and voltage size are adjusted according to the ion beam of different mass numbers. The device also includes a cascaded molecular pump and a mechanical pump, and the microchannel plate detector has a special material coating layer. The working vacuum of the microchannel plate detector is less than 2 x 10 -4 Pa. The special material coating layer is an ALD-deposited aluminum oxide coating layer. The tail gas treatment part of the device is divided into adsorption and collection. The adsorption is performed by a chemical trap, and the collection is performed by reacting water with residual toxic substances that are easily soluble in water.

[0036] Example Two, Method for Analyzing Uranium Hexafluoride Gas Sample

[0037] Referring to Figure 1

[0038] S1: Preparing the sample to be tested

[0039] Manufacturing a sampling container, passivating the sampling container using gaseous uranium hexafluoride, and then sampling, using a high-vacuum sealing valve and a double-cuff connector to seal the connection;

[0040] S2: Starting the instrument

[0041] Pumping the vacuum of the device to less than 5 x 10 -5 Pa in the front-stage sampling area, pumping the vacuum of the free-flight area to less than 1 x 10 -4 Pa, and starting the power supply module of the reflection mass analyzer and the ionization light source of the double-layer cavity ion source;

[0042] S3: Calibrating the measurement system

[0043] Using the relationship that the time of flight of ions is proportional to the square root of the mass-to-charge ratio, using a gas sample with a known mass-to-charge ratio to perform ionization and using the time of flight as a standard to calibrate, converting the time of flight of ions into mass-to-charge ratio, and completing the calibration of the mass spectrum;

[0044] S4: Introducing the uranium hexafluoride sample

[0045] ​The sampling container is connected to the capillary injector, and the sampler and gas path are heated. The amount of uranium hexafluoride sample entering the target region of the double-layer cavity ion source from one end of the capillary injector is controlled by a mass flow meter, ensuring that the vacuum degree in the pre-injection zone is less than 1 × 10⁻⁶. -3 Pa, the vacuum level in the free flight zone is less than 2 × 10⁻⁶. -4 Pa;

[0046] S5: Data Collection

[0047] Sample molecules are ionized by a light source, and the ions strike a microchannel plate detector to generate an electrical signal, which is then output. The electrical signal is collected by a preamplifier, a data acquisition card, and a computer terminal to form a mass spectrum.

[0048] S6: Data Analysis

[0049] For target analyte concentrations above ppm in samples, rapid online analysis in less than 1 minute can be achieved; for target analyte concentrations below ppm down to ppb, cumulative analysis in less than 5 minutes can be achieved.

[0050] Mass spectrometry results as follows Figure 2 As shown. The four peaks in the mass spectrum represent the peaks generated by sample UF6 in sequence. 235 UF4 + , 238 UF4 + , 235 UF5 + and 238 UF5 + The mass spectrum shows that the UF6 sample was ionized to produce uranium fluoride ion mass spectrum peaks, indicating that... 235 U and 238 The abundance of U can be determined very well.

[0051] In summary, the measuring equipment involved in this invention features a compact structure, high integration, safe and simple operation, and ease of portability and handling. Its modular design and complete domestic production facilitate maintenance and repair, making module replacement and modification convenient during equipment decommissioning or upgrades. The measurement method of this invention is rapid and accurate, with particularly significant advantages for measuring the content of gaseous radioactive nuclides. This invention can not only determine the trace (parts per million) impurity content in uranium hexafluoride gas, but also achieve online determination of the abundance of gaseous nuclides containing heavy isotopes such as uranium hexafluoride.

[0052] Finally, it should be noted that the above only describes the preferred embodiments of the present application and is not intended to limit the present application. Although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art will appreciate that the technical solutions described in the foregoing embodiments can be modified or some technical features thereof can be replaced by equivalent ones. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. An apparatus for isotope analysis and impurity content measurement of uranium hexafluoride gas samples, characterized in that, The device includes, in sequence, a sample injector, an ionization zone, a reflective mass analyzer, a microchannel plate detector, a preamplifier, a data acquisition card, a computer terminal, and an exhaust gas treatment unit. The injector is either a direct capillary injector or a mixed carrier gas injection cell capillary injector. The mixed carrier gas injection cell capillary injector mixes and pressurizes the gas to be tested before it flows into the capillary. The injection is controlled by a flow meter. The injector includes a pre-injection zone and a free-flight zone. The ionization zone is the target zone of a double-layer cavity ion source. The vacuum level in the pre-injection zone of the aforementioned injector is less than 1×10⁻⁶. -3 Pa, the vacuum level in the free flight zone is less than 2 × 10⁻⁶. -4 Pa; The capillary length of the injector is 40~100 cm and the inner diameter is 10~50 micrometers; The ionization process includes ultraviolet Kr lamp ionization and laser ionization; The dual-layer cavity ion source accelerates and extracts ions through four-stage electrodes with an aperture of 1mm~3mm, a spacing of 5mm~15mm, and a voltage of 0~100V. The device also includes cascaded molecular pumps and mechanical pumps; The microchannel plate detector has a special material coating, and its operating vacuum is less than 2 × 10⁻⁶. -4 Pa, the special material coating mentioned is an ALD deposited alumina coating; The exhaust gas treatment section of the device is divided into adsorption and collection. Adsorption is carried out by a chemical trap, and collection is carried out by reacting water with residual, water-soluble toxic substances.

2. A method for using an apparatus for isotopic analysis and impurity content measurement of uranium hexafluoride gas samples, characterized in that, The method specifically includes the following steps: S1: Prepare the sample to be tested S2: Instrument turned on The vacuum level of the device is evacuated to less than 5 × 10⁻⁶ in the pre-sample injection zone. -5 Pa, the vacuum level in the free flight zone is pumped down to less than 1 × 10⁻⁶ Pa. -4 Pa, turn on the power supply module of the reflective mass analyzer and the ionization source of the dual-layer cavity ion source; S3: Calibration of the measurement system By utilizing the square root relationship that the flight time of ions is proportional to the mass-to-charge ratio, the flight time of ionization of a gas sample with a known mass-to-charge ratio is used as a standard for calibration. The ion flight time is converted into the mass-to-charge ratio, and the mass spectrum is calibrated. S4: Introducing a sample of uranium hexafluoride. The sampling container is connected to the capillary injector, and the injector and gas path are heated. The amount of uranium hexafluoride sample entering the target region of the double-layer cavity ion source from one end of the capillary injector is controlled by a mass flow meter to ensure that the vacuum degree in the pre-injection zone is less than 1 × 10⁻⁶. -3 Pa, the vacuum level in the free flight zone is less than 2 × 10⁻⁶. -4 Pa; S5: Data Collection Sample molecules are ionized by a light source, and the ions strike a microchannel plate detector to generate an electrical signal, which is then output. The electrical signal is collected by a preamplifier, a data acquisition card, and a computer terminal to form a mass spectrum. S6: Data Analysis For target analyte concentrations above ppm in samples, rapid online analysis in less than 1 minute can be achieved; for target analyte concentrations below ppm down to ppb, cumulative analysis in less than 5 minutes can be achieved.

3. The method of using the device as described in claim 2, characterized in that, If the sample described in S1 is a factory production line or the environment to be tested, the sampler is directly connected to the sample area to be tested; if the sample described in S1 requires a sampling container, the sampling container needs to be passivated.

4. The method of using the device as described in claim 3, characterized in that, The sampling container is passivated using gaseous uranium hexafluoride.

Images