Method and system for detecting a uranium hexafluoride leak

Abstract

Method and system for detecting a uranium hexafluoride leak. The detection method allows for the detection of the presence of uranium hexafluoride (UF6) in a gas stream (G). The detection method comprises humidifying the gas stream by circulating the gas stream (G) through contact with a copolymer fluoropolymer based on sulfonate tetrafluoroethylene, in particular Nafion, and then detecting the presence of hydrogen fluoride (HF) in the gas stream (G) using a sensor. Figure for the abstract: Figure 1

Description

Title of the invention: Method and system for detecting a uranium hexafluoride leak

[0001] The present invention relates to the field of uranium hexafluoride leak detection.

[0002] Uranium dioxide (UO2) is a fissile material used as nuclear fuel in nuclear power generation reactors.

[0003] It is possible to produce UO2 from uranium hexafluoride (UF6). To do this, it is possible to use a conversion unit configured to convert gaseous UF6 into uranium oxyfluoride (UO2F2) by hydrolysis in a reactor, by injecting gaseous UF6 and dry steam into the reactor to obtain UO2F2 powder, then converting the UO2F2 powder into UO2 powder by pyrohydrolysis in a furnace, by circulating the UO2F2 powder in the furnace and injecting dry steam and gaseous dihydrogen (H2) into the furnace.

[0004] Gaseous UF6 is produced for example by vaporizing UF6 in solid or liquid state contained in a reservoir disposed in an autoclave oven swept by a flow of sweeping gas, the reservoir being fluidly connected to one or more injection nozzles of gaseous UF6 into the reactor.

[0005] For safety reasons, it is desirable to detect any possible leakage of UF6 in the autoclave oven, reliably and limiting the number of false alarms, for example by detecting the presence of UF6 in the scavenging gas stream.

[0006] One of the aims of the invention is to propose a method for detecting UF6 in a gas stream that is reliable and robust.

[0007] To this end, the invention proposes a method for detecting the presence of uranium hexafluoride in a gas stream, the detection method comprising:

[0008] - humidification of the gas stream by circulation of the gas stream in contact with fluoropolymer copolymer based on sulfonate tetrafluoroethylene, in particular Nafion; then

[0009] - the detection of the presence of hydrogen fluoride in the gas stream using a sensor.

[0010] A copolymer fluoropolymer material based on sulfonated tetrafluoroethylene, in particular in Nafion, is capable of retaining moisture and easily transferring it to a gaseous stream circulating in contact with the material.

[0011] In the presence of UF6 in the gas stream, humidification of the gas stream causes a hydrolysis reaction of UF6 with water, generating hydrogen fluoride (HF) whose presence can be detected using an appropriate sensor.

[0012] The copolymer fluoropolymer material based on sulfonated tetrafluoroethylene, in particular in Nafion, is a simple, effective and reliable means of humidifying the gas stream appropriately for the detection of UF6, without having to add air to the gas stream, which would cause dilution of UF6.

[0013] The use of the copolymer fluoropolymer material based on sulfonated tetrafluoroethylene, in particular in Nafion, thus allows the precise detection of UF6 at a lower threshold.

[0014] A demisting device located upstream of the humidification device allows impurities, for example in the form of liquid droplets and / or solid particles, to be retained, which could cause false alarms by deposition and / or interaction of these with a sensor, and impair detection.

[0015] In particular embodiments, the detection method comprises one or more of the following optional features, taken individually or in all technically possible combinations:

[0016] - the circulation of the gas flow in contact with the fluoropolymer copolymer based of tetrafluoroethylene sulfonate, in particular Nafion, is carried out by circulating the gas flow through a conduit delimited at least in part by a wall made of fluoropolymer copolymer based on tetrafluoroethylene sulfonate;

[0017] - the detection method includes the defossilation of the gas flow before the humidification of the gas flow;

[0018] - the devesiculation is achieved by passing the gas flow through a porous body;

[0019] - the porous body is a foam or a mass of fibers;

[0020] - the porous body is made of metal, in particular steel, preferably steel stainless.

[0021] The invention also relates to a system for detecting uranium hexafluoride in a gas stream, the detection system comprising:

[0022] - a humidification device configured for humidifying the gas stream by circulation of the gas flow in contact with fluoropolymer copolymer based on sulfonate tetrafluoroethylene, in particular Nafion, and

[0023] - a measuring device configured to receive the gas flow after it has passed through the humidification device, the measuring device including a sensor configured to detect the presence of hydrogen fluoride in the gas stream.

[0024] In particular embodiments, the detection system comprises one or more of the following optional features, taken individually or in all technically possible combinations:

[0025] - the humidification device includes a conduit for the circulation of the flow of gas, delimited at least in part by a wall made of fluoropolymer copolymer based on sulfonate tetrafluoroethylene;

[0026] - the detection system includes a demister device fluidly connected to the humidification device and configured for the removal of droplets present in the gas stream before it passes through the humidification device;

[0027] - the devesiculating device is configured for devesiculating the gas flow by passage through a porous body, for example a foam or a mass of fibers, the porous body preferably being made of metal, in particular steel, preferably stainless steel.

[0028] The invention also relates to an installation comprising a production device configured for the production of uranium fluoride hexafluoride by vaporizing the uranium fluoride hexafluoride contained in a reservoir in an autoclave furnace and circulating a flow of scouring gas in the autoclave furnace, and a detection system as defined above arranged for detecting the presence of uranium fluoride hexafluoride in the scouring gas flow.

[0029] In one embodiment, the installation includes a conversion unit configured for the conversion of uranium hexafluoride into uranium dioxide, the conversion unit being connected to the production device for its supply of uranium hexafluoride.

[0030] The invention and its advantages will be better understood upon reading the following description, given solely by way of non-limiting example, and made with reference to the accompanying drawings, in which:

[0031] - [Fig. 1] [Fig. 1] is a schematic view of an installation comprising a system detection for the detection of UF6 in a gas flow of the installation;

[0032] - [Fig.2] [Fig.2] illustrates steps in a method for detecting UF6 in a stream of gas.

[0033] As illustrated in [Fig.1], an installation 10 includes a detection system 12 for detecting the presence of UF6 in a gas stream G to be monitored from the installation 10.

[0034] The detection system 12 includes a demister 14 configured to separate from the gas stream G organic impurities, present for example in the form of liquid droplets or solid particles (such as fumes), suspended in this gas stream G.

[0035] The devesiculating device 14 includes a gas inlet 16 for receiving the gas flow G and a gas outlet 18 for the outlet of the devesiculated gas flow G.

[0036] The vesiculating device 14 has optionally a pressure balancing device 20 configured to achieve pressure balancing between the inside and outside of the vesiculating device 14.

[0037] The devesiculating device 14 is for example configured for the passage of the gas flow G through a porous body 22. This makes it possible to cause the deposition of the droplets present in the gas flow G on the porous body 22.

[0038] The porous body 22 is for example a foam, preferably an open-cell foam, or a mass of fibers or more generally any substance having a high exchange surface.

[0039] A porous body 22 in the form of a foam or a cluster of fibers allows significant contact of the gas flow with the porous body 22, promoting the deposition of liquid droplets present in the gas flow G on the porous body 22.

[0040] The porous body 22 is, for example, made of metal, in particular steel, preferably stainless steel. The porous body 22 is, in particular, a metallic foam or a mass of metallic fibers.

[0041] The devesiculating device 14 comprises a chamber 26 inside which is disposed the porous body 22, the gas inlet 16 being arranged so that the gas flow G enters the chamber 26 and passes through the porous body 22 to go from the gas inlet 16 to the gas outlet 18.

[0042] Where appropriate, the balancing device 20 is configured to achieve pressure balancing between the inside and outside of the enclosure 26 of the devesiculator 14.

[0043] Preferably, the gas inlet 16 of the demisting device 14 is provided with an inlet valve 28.

[0044] Preferably, the pressure balancing device 20 of the devesiculating device 14 is equipped with a balancing valve 30.

[0045] The detection system 12 includes a humidification device 32 configured to humidify the gas flow G.

[0046] The devesiculating device 14 is fluidly arranged upstream of the humidification device 32 for devesiculating the gas flow G in the devesiculating device 14 before its humidification in the humidification device 32.

[0047] The humidification device 32 is configured to circulate the flow of gas G through a conduit 34 at least partly delimited by a wall 36 made of fluoropolymer copolymer based on sulfonate tetrafluoroethylene, in particular Nafion, so as to allow an exchange of moisture through the wall 36, between the outside and the inside of the conduit 34.

[0048] A wall 36 made of fluoropolymer copolymer based on sulfonate tetrafluoroethylene, in particular Nafion, is capable of retaining moisture from the outside and transferring it partly to a gas flow circulating inside the conduit 34.

[0049] Thus, the circulation of the gas flow G via the conduit 34, at least partially delimited by a wall 36 made of tetrafluoroethylene-based fluoropolymer copolymer Sulfonated, particularly in Nafion, allows the humidity to be balanced between the flow of gas G and the outside air, and thus to humidify the flow of gas G.

[0050] In the presence of UF6 in the gas stream, humidification of the gas stream causes hydrolysis of UF6 and consequently the appearance of HF.

[0051] The conduit 34 is for example rigid or flexible.

[0052] The detection system 12 includes a measuring device 40 arranged to receive the gas flow G exiting the humidification device 32, the measuring device 40 including a sensor 42 configured to detect the presence of HF in the gas flow G, and preferably to measure the HF content in the gas flow G.

[0053] The sensor 42 is configured to provide a measurement signal Mes indicating the presence of HF in the gas flow G, and, preferably, representative of the HF content of the gas flow G.

[0054] The sensor 42 is for example configured for the detection of the presence of HF by colorimetry or using a specific electrode (redox type sensor).

[0055] The detection system 12 advantageously includes an electronic data processing unit 44 comprising a measurement module 46 configured to receive the measurement signal Mes from the sensor 42 and to determine the presence of UF6 in the gas flow G as a function of the measurement signal Mes, in particular as a function of the HF content of the gas flow G indicated by the measurement signal Mes.

[0056] In examples, the measurement module 46 is a software application comprising code instructions stored in a memory 48 of the electronic data processing unit 44 and executable by a processor 50 of the electronic data processing unit 44.

[0057] In variants, the measurement module 46 is a programmable logic component, in particular an in situ programmable gate array (or FPGA for "Field Programmable Gate Array"), or a specialized integrated circuit (or ASIC for "Application Specified Integrated Circuit").

[0058] In examples, the detection system 12 includes a user terminal 52 connected to the electronic data processing unit 44 for the transmission of data relating to the measurement from the electronic data processing unit 44 to the user terminal 52 and their consultation by a human operator.

[0059] The user terminal 52 includes, for example, a human-machine interface, including in particular a display screen (not shown) and a graphical user interface. The user terminal 52 is, for example, a computer, a digital tablet, or a mobile phone.

[0060] The installation 10 illustrated in [Fig. 1] includes, for example, a conversion unit 54 configured for the conversion of UF6 in gaseous form into powdered UO2.

[0061] The conversion unit 54 is for example configured to carry out a hydrolysis of gaseous UF6 in the presence of dry steam in a reactor to obtain UO2F2 powder, then a conversion of the UO2F2 powder into UO2 powder by pyrohydrolysis of the UO2F2 powder in a furnace in the presence of dry steam and gaseous H2.

[0062] As schematically shown in [Fig.1], the conversion unit 54 receives as input gaseous uranium hexafluoride UF6, a stream of dry water vapor H2O and an incoming stream of neutral gas N2 and has separate outlets for UO2 powder, a stream of gaseous hydrogen fluoride HF and an outgoing stream of neutral gas N2.

[0063] The installation 10 includes, for example, a production device 56 configured for the production of gaseous UF6 and the supply of gaseous UF6 to the conversion unit 54.

[0064] The production device 56 includes, for example, a tank 58 containing UF6 in solid or liquid form arranged in an autoclave oven 60 configured for the circulation of a gas flow G for scavenging, the tank 58 being fluidly connected to the conversion unit 54 for supplying the conversion unit with gaseous UF6.

[0065] It is necessary to ensure that the scavenging gas flow exiting the autoclave furnace 60 does not contain UF6 from an internal UF6 leak in the autoclave furnace 60.

[0066] The detection system 12 is for example fluidically connected to the autoclave oven 60 to receive the outgoing sweep gas flow as the gas flow G to be monitored, and to detect the possible presence of UF6 in the sweep gas flow exiting the autoclave oven 60.

[0067] Steps of a method for detecting a leak of UF6 which can be implemented by a detection system 12 according to [Fig.1] are illustrated in [Fig.2].

[0068] The detection method includes a step El of devesiculating the gas flow G, carried out in the devesiculating device 14, to remove from the gas flow G droplets present in the gas flow G.

[0069] The devesiculation is carried out for example by passing the gas flow G through a porous body 22 in such a way that the gas flow G passes through the porous body 22 and droplets present in the gas flow G are deposited on the porous body 22.

[0070] The detection method includes a step E2 of humidifying the gas flow G, carried out in the humidification device 32, by circulating the gas flow G in contact with a copolymer fluoropolymer based on sulfonated tetrafluoroethylene, in particular Nafion.

[0071] The E2 step of humidifying the gas flow G is carried out after the El step of devesiculation.

[0072] The circulation of the gas flow G in contact with a wall 36 made of fluoropolymer copolymer based on sulfonate tetrafluoroethylene, in particular Nafion, is carried out for example by circulation of the gas flow G in a conduit 34 at least partly delimited by the wall 36 made of fluoropolymer copolymer based on sulfonate tetrafluoroethylene, in particular Nafion.

[0073] This makes it possible to balance the humidity between the flow of gas G circulating in the conduit 34 and the outside air, and thus to humidify the flow of gas G.

[0074] The detection method includes a step E3 of detecting the presence of HF in the humidified gas stream G, for example using a sensor 42 configured to detect the presence of HF, and, preferably, measuring the HF content of the gas stream.

[0075] The detection method includes a step E4 of determining the presence of HF in the gas flow G as a function of the measurement signal provided by the sensor 42, for example using a detection module 46 of an electronic data processing unit 44.

[0076] The detection method advantageously includes a reporting step E5 comprising sending and / or displaying a message to an operator, the message indicating the detection of HF in the gas flow G, the HF content of the gas flow G, and / or the occurrence of a UF6 leak. The message is, for example, sent by the electronic data processing unit 44. The message is, for example, sent to and / or displayed on the user terminal 52.

[0077] The detection system 12 makes it possible to easily, reliably and robustly detect the presence of UF6 in a gas stream G, in particular to detect the presence of a leak of UF6 in an autoclave oven 60 of a production device 56 for the production of gaseous UF6.

[0078] The circulation of the gas flow G via a conduit 34 at least partly delimited by a wall 36 made of fluoropolymer copolymer based on sulfonate tetrafluoroethylene, in particular Nafion, allows humidification of the gas flow G without dilution of UF6, capable of causing hydrolysis of the UF6 possibly present in the gas flow, with the appearance of HF detectable by means of an appropriate sensor 42.

[0079] The defoaming device 14 arranged upstream of the humidification device 32 allows to retain foreign bodies and / or impurities which could cause false alarms and impair detection.

Claims

Demands

1. Method for detecting the presence of uranium hexafluoride (UF6) in a gas stream (G), the detection method comprising: - humidification of the gas stream by circulating the gas stream (G) in contact with a copolymer fluoropolymer based on sulfonated tetrafluoroethylene, in particular Nafion; then - detection of the presence of hydrogen fluoride (HF) in the gas stream (G) using a sensor.

2. A detection method according to claim 1, wherein the circulation of the gas flow in contact with a copolymer fluoropolymer based on sulfonate tetrafluoroethylene, in particular Nafion, is achieved by circulating the gas flow (G) through a conduit (34) delimited at least in part by a wall (36) made of copolymer fluoropolymer based on sulfonate tetrafluoroethylene.

3. Detection method according to claim 1 or 2, comprising defoaming of the gas stream (G) before humidification of the gas stream (G).

4. Detection method according to claim 3, wherein the devesiculation is carried out by passing the gas flow (G) through a porous body (22).

5. Detection method according to claim 4, wherein the porous body (22) is a foam or a mass of fibers.

6. A detection method according to claim 4 or 5, wherein the porous body (22) is made of metal, in particular steel, preferably stainless steel.

7. Uranium hexafluoride (UF6) detection system in a gas stream (G), the detection system comprising: - a humidification device (32) configured for humidifying the gas stream (G) by circulating the gas stream (G) in contact with a copolymer fluoropolymer based on sulfonate tetrafluoroethylene, in particular Nafion, and - a measuring device (40) configured to receive the gas stream (G) after passing through the humidification device (32), the measuring device (40) comprising a sensor (42) configured to detect the presence of hydrogen fluoride (HF) in the gas stream (G).

8. Detection system according to claim 7, wherein the humidification device (32) comprises a conduit (34) for the circulation of the gas flow (G), delimited at least in part by a wall (36) made of fluoropolymer copolymer based on tetrafluoroethylene sulfonate.

9. A detection system according to claim 7 or 8, comprising a defoaming device (14) fluidly connected to the humidification device (32) and configured for the removal of droplets present in the gas stream (G) before it passes through the humidification device (32).

10. A detection system according to claim 9, wherein the defoaming device (14) is configured for defoaming the gas flow (G) by passing through a porous body (22), for example a foam or a bundle of fibers, the porous body (22) preferably being made of metal, in particular steel, preferably stainless steel.

11. Installation comprising a production device (56) configured for the production of uranium fluoride hexafluoride (UF6) by vaporizing uranium fluoride hexafluoride (UF6) contained in a tank (58) in an autoclave furnace (60) and circulating a flow of scavenging gas in the autoclave furnace (60), and a detection system according to any one of claims 7 to 10 arranged for the detection of the presence of uranium fluoride hexafluoride (UF6) in the scavenging gas flow.

12. Installation according to claim 11, comprising a conversion unit (54) configured for the conversion of uranium hexafluoride (UF6) into uranium dioxide (UO2), the conversion unit (54) being connected to the production device (56) for its supply of uranium hexafluoride (UF6).