Nuclear reactor vessel comprising a fuel assembly and a heat pipe

Abstract

Nuclear reactor vessel (1), the vessel comprising a coolant (3) and a fuel assembly (5) placed in the coolant, the assembly comprising a plurality of needles (7) containing fuel pellets and extending in a vertical direction (Z), characterized in that the vessel comprises a heat pipe (9) extending in the vertical direction from a first end (10) of the heat pipe to a second end (12) of the heat pipe, the vessel being configured, when the fuel assembly is disposed of in the vessel: to immerse the first end in the coolant such that the first end is located above a head (14) of the plurality of needles, to place the second end above a surface (16) of the coolant, the vessel comprising a temperature sensor (18) for the second end of the heat pipe. Figure to be published for the abstract: Figure 1

Description

Title of the invention: Nuclear reactor vessel comprising a fuel assembly and a heat pipe

[0001] The invention relates to temperature monitoring in a nuclear reactor vessel and in particular to temperature monitoring of a heat transfer fluid at the outlet of the fuel assemblies. STATE OF THE ART

[0002] The core of a nuclear reactor employs an array composed of a large number of needles / pencils (in the remainder of this text we will use only the term needles for ease of reading) containing the nuclear fuel. Each needle comprises a metallic tube or cladding that contains a stack of pellets, generally cylindrical, of fuel made of a suitable fissile material such as uranium oxide or a mixture of uranium oxide and plutonium. The upper and lower ends of the tube are free of fuel pellets and constitute a plenum for a gas or other fluid under high pressure that fills the top of the needle, as well as a clearance space around the fuel pellets to allow for expansion or swelling due to irradiation. The fuel needles are supported in parallel groups in fuel assemblies.The nuclear reactor, for its part, is composed of a large number of these fuel assemblies arranged in a suitable configuration at the reactor core.

[0003] To monitor the proper functioning of a nuclear reactor, detect a potential accident / incident, or track its power increase / reduction during startup or shutdown phases, it is common practice to place temperature indicator devices, such as thermocouples, inside the reactor (see French patent application FR2338551). Indeed, a temperature rise beyond a certain limit could, for example, compromise the integrity of the fuel rods. To prevent this, a safety device must be able to intervene to limit the reactor's operating power, or even shut it down.

[0004] For this safety purpose, thermocouples are passed through conduits that guide them through internal components of the reactor to a position located above the core. A multitude of thermocouples thus placed at preselected locations above the core or above fuel assemblies makes it possible to provide a core temperature profile.

[0005] The measurement of this temperature profile is transmitted electrically by an electrical cable which runs continuously from the thermocouples located above the assemblies to the outside of the reactor vessel.

[0006] This continuity of material poses difficulties, particularly when it is necessary to open the reactor vessel to replace the fuel assemblies. It is common practice to shut down the reactor regularly to renew the fuel assemblies. All thermocouple cables must then be disconnected during a time-consuming and potentially dangerous operation. This is especially true for certain lead-cooled fast reactors (LFRs), which, unlike some light water reactors (LWRs), do not have an upper structure in which the thermocouple cables are bundled together to simplify their connection and disconnection.

[0007] There is a need for a simpler method of measuring the temperature of fuel assemblies than in the prior art, particularly with regard to reactor maintenance and fuel assembly replacement. EXPOS

[0008] One aim of the present presentation is to propose a simpler method of measuring the temperature of fuel assemblies than in the prior art, particularly with regard to reactor maintenance and fuel assembly renewal.

[0009] The goal is achieved by means of a nuclear reactor vessel, the vessel comprising a coolant and a fuel assembly placed in the coolant, the assembly comprising a plurality of needles containing fuel pellets and extending in a vertical direction, the vessel comprising a heat pipe extending in the vertical direction from a first end of the heat pipe to a second end of the heat pipe,

[0010] The tank being configured, when the fuel assembly is placed in the tank: - to immerse the first end in the heat transfer fluid so that the first end is located above one end of the plurality of needles, - to place the second end above a surface of the heat transfer fluid,

[0011] the tank comprising a temperature sensor for the second end of the heat pipe.

[0012] Such a tank is advantageously and optionally supplemented by the following various features taken alone or in combination:

[0013] - the sensor is separated by at least one centimeter from the second end of the heat pipe;

[0014] - the sensor is an optical sensor, the sensor being configured for example to measure the emissivity of the second end;

[0015] - the sensor includes a light collector located inside the tank, a transducer located outside the tank and an optical link, such as an optical fiber, between the collector and the transducer;

[0016] - the sensor includes a transducer located inside the tank;

[0017] - the heat pipe is thermally insulated along the vertical direction between the first end and the second end, the heat pipe comprising an inner jacket and an outer jacket separated from the inner jacket by a housing containing a partial void or a thermally insulating material;

[0018] - the heat pipe comprises a fluid inside the inner jacket, the fluid including, for example, sodium or ammonia;

[0019] - the assembly is a first assembly and the heat pipe is a first heat pipe, the tank comprising several assemblies including the first assembly and several heat pipes including the first heat pipe, each assembly being associated with a heat pipe, the tank comprising means for producing a two-dimensional image in which the second ends of the heat pipes appear; and

[0020] - the sensor is a first sensor, the tank comprising several sensors including the first sensor, the tank including connections to allow communication from each sensor through the tank, the connections passing through the tank via the same passage provided in the tank.

[0021] The exposition also relates to a method for measuring the temperature of a fuel assembly in a heat transfer fluid contained in a nuclear reactor vessel, the assembly comprising a plurality of needles containing fuel pellets and extending in a vertical direction, the method comprising, in the presence of a heat pipe, the following steps:

[0022] - the placement of the heat pipe so as to have a first end of the heat pipe in the heat transfer fluid above a head of the plurality of needles and a second end of the heat pipe above a surface of the heat transfer fluid, the heat pipe extending from the first end to the second end in the vertical direction, and

[0023] - the acquisition by a sensor of a temperature measurement of the second end.

[0024] Such a method is advantageously and optionally complemented by the following features: the assembly is a first assembly and the heat pipe is a first heat pipe, the tank comprising several assemblies including the first assembly and several heat pipes including the first heat pipe, each assembly being associated with a heat pipe, the acquisition step comprising the acquisition of a two-dimensional image in which the second ends of the heat pipes appear, the method further comprising the identification in the two-dimensional image of the second end of each heat pipe on the basis of positions in the two-dimensional image. DESCRIPTION OF THE FIGURES

[0025] Other features and advantages will become apparent from the following description, which is purely illustrative and not limiting, and should be read in conjunction with the accompanying drawings on which:

[0026] - Fig. 1 and Fig. 2 are schematic representations of a reactor vessel nuclear;

[0027] - Figures 3 and 4 are schematic representations of a heat pipe of a tank;

[0028] - [Fig.5] and [Fig.6] are schematic representations of a heat pipe arranged close to a support rod;

[0029] - [Fig. 7] is a schematic representation of a combustible assembly and

[0030] - [Fig. 8] is a schematic representation of a method for measuring temperature of a fuel assembly in a nuclear reactor vessel. DETAILED DESCRIPTION OF THE INVENTION Nuclear reactor vessel

[0031] In relation to figures 1 and 2, a main reactor vessel 1 comprises a vessel body 2 which is configured to receive a heat transfer fluid which may be a molten metal 3. The vessel 1 comprises a top closure slab 4 which hermetically seals the vessel body 2.

[0032] The closing plate 4 comprises a fixed part 4a and a movable part 4b. The fixed part 4a surrounds the movable part 4b. The movable part 4a defines a central opening into which the movable part 4b fits when the tank 1 is closed. The movable part 4b can be detached from the fixed part 4a to open the closing plate 4.

[0033] The tank 1 further comprises one or more fuel assemblies. With reference to Figures 1 and 2, the illustrated tank 1 comprises eight fuel assemblies, referenced 5a, 5b, 5c, 5d, 5e, 5f and 5g.

[0034] Each fuel assembly comprises a plurality of needles 7 containing pellets of nuclear fuel such as uranium, plutonium, or "mixed oxide" type fuel, also known as MOX, which comprises plutonium and depleted uranium. The plurality of needles 7 is also referred to as a needle bundle.

[0035] The plurality of needles 7 is housed in a main section 46 of the fuel assembly. The main section 46 extends from a base 48 of the main section to an upper support 50. The support rod 6 is fixed to the upper support 50.

[0036] Each fuel assembly extends in the vertical direction. The assembly has a principal direction of extension that is vertical, meaning that the vertical dimension of the assembly is significantly greater than its horizontal dimensions. When the vessel comprises a plurality of fuel assemblies, the assemblies are arranged parallel to each other and at the same height.

[0037] The assembly is immersed inside the heat transfer fluid 3, for example of molten metal. The needle bundle is located inside the heat transfer fluid 3 and oriented vertically from bottom to top from a foot 13 of the plurality of needles to a head 14 of the plurality of needles.

[0038] The heat transfer fluid is set in motion within the tank, and in particular, during a portion of this motion, the heat transfer fluid passes through the fuel assemblies from bottom to top. This portion of the motion corresponds to a heating of the heat transfer fluid. The heat generated by a fuel assembly is transferred to the heat transfer fluid as it moves up the assembly. The temperature of the heat transfer fluid thus increases progressively from the bottom to the top of the fuel assembly.

[0039] The fuel assembly includes a support rod 6 that extends vertically above the head 14 of the needle bundle. The support rod 6 allows the fuel assembly 5 to be moved vertically. The upper part of the support rod 6 is attached to a ballast 44. The ballast 44 forms part of the fuel assembly. The ballast 44 secures the fuel assembly to a retaining block 11 included in the vessel 1.

[0040] The tank 1 includes a heat pipe 9 which extends vertically above the head 14 of the needle bundle. The heat pipe has an elongated shape in the vertical direction. It includes a first end 10 located at the bottom and a second end 12 located at the top.

[0041] The heat pipe (also known by the English name "heat pipe") is a heat conductor which is generally intended to transport heat, for example, on the basis of the principle of heat transfer by phase transition of a fluid.

[0042] In a first example and with reference to [Fig. 3], the heat pipe extends along a principal axis of extension A. This means that the dimension of the heat pipe along axis A is significantly larger than the dimensions orthogonal to axis A. A radial direction and a circumferential direction can be defined from axis A. When the heat pipe is placed within the tank, axis A corresponds to the vertical direction. The heat pipe may, in particular, have a cylindrical shape with a circular cross-section along axis A.

[0043] In a second example and with reference to [Fig. 4], the heat pipe comprises three distinct portions along a vertical direction Z. The heat pipe 9 comprises: - an upper portion 37 which includes the first end 10, - a lower portion 38 which includes the second end 12, and - a central portion 35 which is located between the upper portion 37 and the lower portion 38.

[0044] The heat pipe is intended to be installed in the tank so that the upper portion is located vertically above the central portion 35 and the lower portion 38.

[0045] Each of the three portions extends along a principal axis of extension: the upper portion 37 along axis B, the middle portion 35 along axis C, and the lower portion 38 along axis D. For each portion, this means that the dimension of the portion along its principal axis of extension is significantly larger than the dimensions orthogonal to that axis. Each portion may, in particular, have a cylindrical shape with a circular cross-section along its principal axis. Axes B, C, and D are parallel but not coincident. Axes B, C, and D may lie in the same plane, as illustrated in [Fig. 4]. The heat pipe is intended to be installed in the tank so that each of these axes is vertical.

[0046] The heat pipe also includes transition portions 40 and 42. The first transition portion 40 is located between the upper portion 37 and the central portion 35. The second transition portion 42 is located between the central portion 35 and the lower portion 38.

[0047] The shape of the heat pipe 9 in this second example allows the first end 10, the second end 12 and the central portion 35 to be placed in different horizontal positions.

[0048] In particular, it is possible to position the central portion 35 close to, or even against, a support rod 6. This allows, in particular, for improved mechanical stability of the heat pipe within the tank. The heat pipe is surrounded by the heat transfer fluid, which is set in motion within the tank, and in particular, the heat transfer fluid flows through the fuel assemblies from bottom to top. The movement of the heat transfer fluid exerts mechanical stress on the heat pipe, which can thus be deformed or set into oscillation. The heat pipe, whose central portion 35 is positioned close to, or even against, a support rod 6, is subjected to less mechanical stress from the movement of the heat transfer fluid, so that the heat pipe is more resistant to the movements of the heat transfer fluid. The mechanical stability of the heat pipe is thus improved.

[0049] With reference to [Fig. 5], the heat pipe 9a conforms to the second example as previously presented. The central portion 35 of the heat pipe is placed against the support rod 6. The support rod extends vertically in a centered manner around the axis E which is directed vertically. The upper part 37 of the heat pipe passes through the ballast 44. The upper part 37 in particular protrudes above the ballast 44 so that the second end 12 is opposite the slab 4.

[0050] Each support rod 6 can be surrounded by a plurality of heat pipes 9 distributed angularly and regularly around the support rod 6. For example, a support rod 6 can be surrounded by three heat pipes 9 separated two by two at an angle of 120 degrees.

[0051] Figure 6 is a top view of the ballast 44, representing a horizontal projection of the ballast 44. The support rod 6 protrudes above the ballast 44. Three heat pipes 9a, 9b, and 9c surround the support rod 6. The upper portions of each of these heat pipes protrude above the ballast 44. The heat pipes are evenly distributed around the axis E, on which the support rod 6 is centered. In the horizontal projection, two heat pipes are separated at an angle 46 centered on the axis E. In this example, the angle 46 is 120 degrees. Using three heat pipes ensures a more reliable temperature measurement. If one of them fails, the other two remain operational.

[0052] Fig. 7 represents a fuel assembly 5 comprising the ballast 44. Fig. 7 illustrates the heat pipes 9a and 9b, the needle bundle support rod 6, the upper support 50, the fuel needles 7 comprising the needle head 14 and the section base 48.

[0053] The heat pipe may have two sheaths: an outer sheath 26 and an inner sheath 28. The sheaths 26 and 28 are centered on axis A. The outer sheath 26 radially surrounds the inner sheath 28. In other words, the inner sheath 28 surrounds axis A, and the outer sheath surrounds both axis A and the inner sheath 28. The inner sheath 28 is located radially between axis A and the outer sheath 26. These sheaths are, for example, cylindrical walls with a circular cross-section. The heat pipe 9 defines a cavity 30 between these sheaths. The cavity 30 may contain a partial void or a thermally insulating material. Such an interior of the cavity allows the interior of the inner sheath 28 to be thermally insulated from the exterior of the heat pipe 9 along the entire radial axis A. This insulation helps to improve the equivalence between the temperature of the first end 10 and the temperature of the second end 12.In particular, it limits disturbances in heat transmission along the heat pipe 9.

[0054] The heat pipe 9 may include within the inner jacket 28 a fluid 32. This fluid may in particular be sodium or ammonia.

[0055] The heat pipe includes, for example, a plug 34 at the first end 10 and a plug 36 at the second end 12. The plugs 34 and 36 allow the connection to be closed the housing and the interior of the inner casing 28 are sealed airtight. The plugs 34 and 36 can advantageously be heat-conducting.

[0056] The heat pipe 9 is arranged in the tank 1 such that the first end 10 is inside the heat transfer fluid 3, and more precisely above the head 14 of the needle assembly. Advantageously, the plug 34 is very close to the head 14 of the needle assembly, or it is located at a distance of 10 centimeters or less from the head 14. The position of the first end 10 corresponds to an area where the heat transfer fluid reaches its maximum temperature, that is, at the end of the portion of the heat transfer fluid's movement that passes through the needle assembly from bottom to top. The vertical position of the plug 34 is advantageously lower than the vertical position of the head 14: in other words, the plug 34 is located vertically below the head 14.Furthermore, when multiple fuel assemblies are present, each comprising a heat pipe, the distance between a plug of the first heat pipe and a head of the first assembly is much smaller than the distance between the plugs of the first heat pipe and a second heat pipe of a second fuel assembly. In this way, the influence of the second heat transfer fluid on the temperature of the first heat transfer fluid is minimized.

[0057] The first end 10 can advantageously be placed inside the main section 46.

[0058] The heat pipe 9 is arranged in the tank 1 such that its second end 12 is above a surface 16 of the molten metal heat transfer fluid 3. Advantageously, the second end 12 can be positioned opposite the upper closing plate 4 of the tank 1. In other words, the heat pipe 9 is long enough that its second end 12 is visible from the lower face 8 of the plate 4. There is therefore optical access from the lower face 8 to the second end 12 of the heat pipe 9.

[0059] The tank 1 includes a temperature sensor 18 which is configured to measure the temperature of the second end 12.

[0060] The presence of a heat pipe whose first end 10 is close to the head 14 of the needle bundle allows the second end 12 to be used as a reference temperature for the head of the needle bundle, i.e., as a reference temperature for the fuel assembly. Indeed, the first end 10 is close to the fuel assembly, so the temperature of the assembly is close to the temperature of the first end 10. Moreover, the heat pipe is configured to promote heat transfer and be thermally homogeneous. The temperature of the second end 12 is thus close to the temperature of the first end 10. Since the second end 12 is above the heat transfer fluid 3, it is no longer necessary to place the temperature sensor in contact with or in the immediate vicinity of the assembly, i.e., inside the heat transfer fluid itself. It becomes possible to use a sensor that measures the temperature of the second end to measure the temperature of the assembly. The heat pipe thus enables new, simpler ways to measure the temperature of a fuel assembly than in the prior art.

[0061] The temperature sensor 18 can, for example, be a temperature probe such as a thermocouple or a platinum resistance probe. The heat-sensitive part of the sensor is then placed in contact with the second end 12. Other types of sensors requiring contact with the second end 12 can be used.

[0062] The sensor includes a transducer 22 configured to convert the temperature value of the second end (or the value of a reference quantity for the temperature of the second end) into an intermediate measurement signal of another type, for example, an electrical signal. The sensor may include a processing unit 23 for determining a temperature value from the measurement signal value. This processing unit may, in particular, use a calibration of the intermediate signal based on the temperature of the second end.

[0063] When the transducer produces an electrical signal, it may contain an electronic component. Furthermore, when the transducer is located inside the tank 1, this electronic component may be hardened. In other words, this electronic component is made resistant to malfunctions and degradation caused by radiation and subatomic particles propagating within the tank.

[0064] Advantageously, a "non-contact" or "remote" temperature sensor can be chosen, meaning that the sensor is separated by at least one centimeter from the second end of the heat pipe.

[0065] Since the sensor is separated by at least one centimeter from the second end of the heat pipe, there is no continuity of material between the fuel assembly and the sensor. This makes it possible, for example, to leave the sensors connected when opening the tank. Measuring the temperature of a fuel assembly becomes even simpler.

[0066] When the temperature sensor is a remote sensor, it may, in particular, be an optical sensor. Specifically, it may use a sensor that measures the emissivity of the second end 12, or a pyrometer sensitive to infrared radiation, or a sensor configured to measure infrared luminosity. The sensor may further include a laser source configured to produce a laser beam that is directed onto the second end 12. The sensor can then operate based on the reflection of the laser beam onto the second end 12. When the sensor is optical, it may alternatively include a calibrated part that has the property of deforming as a function of temperature. This temperature-sensitive part can be attached to the second end 12 so as to be in contact Thermal sensor with cap 36. In this alternative, the sensor may include a camera configured to acquire an image of the heat-sensitive part. This image constitutes an intermediate measurement signal. The sensor may further include an image processing unit to determine a dimension value of the part and, based on this value, produce a temperature measurement of the fuel assembly.

[0067] In the case of an optical sensor, the sensor input 18, configured to receive the radiation emitted by the second end 12, is placed opposite this second end 12. To minimize measurement uncertainties, the distance between the sensor input 18 can be chosen to be less than or equal to 100 centimeters and more advantageously less than or equal to 20 centimeters.

[0068] It is possible, according to a preferred mode, to use an optical sensor 18 which comprises different parts. The sensor may include a light collector 20, a transducer 22 and an optical link 24, such as an optical fiber, between the collector and the transducer.

[0069] The light collector 20 is configured to collect radiation, in particular infrared, emitted by the second end 12. The collector 20 can, for example, be an optical lens, advantageously optimized for infrared wavelengths.

[0070] Preferably, the collector 20 is fixed to the closing slab 4 of the tank 3, and in particular to the lower face 8 of the slab 4.

[0071] In relation to [Fig. 1], the collector 20 is fixed to the movable part 4b of the closing slab 4.

[0072] In relation to [Fig.2], the collector 20 is fixed to the stationary part 4b of the closing slab 4. In this case, the collector 20 remains stationary during an opening or closing of the slab 4.

[0073] The transducer 22 is configured to convert an optical signal into a signal of another type, for example an electrical signal. The transducer can be, for example, a pyrometer, a thermopile, a photodiode, a photoresistor, or a thermal camera.

[0074] A pyrometer can be configured to acquire the heat emitted by a material, this heat being emitted in the form of infrared radiation. This radiation is specific to each material and is a function of its emissivity. It varies with the material's temperature. By comparing this variation to a reference black body, it is possible to deduce the material's temperature from the pyrometer measurement, even in demanding environments with high sensitivity.

[0075] The optical link 24 allows the optical signal produced by the collector to be transmitted to the transducer. The optical link can use hardened optical fibers for nuclear medium or laser fibers going directly to point at the second end 12 of the heat pipe.

[0076] In this preferred mode, the light collector can be located inside the tank, the transducer can be located outside the tank, and the optical link can pass through the tank and in particular the tank closure slab.

[0077] Placing the transducer outside the tank notably prevents it from being exposed to gamma radiation and neutron fluxes propagating within it. This allows the transducer to operate more optimally and increases its lifespan.

[0078] However, it is possible to use an optical sensor whose transducer is located inside the tank. Such a sensor can be connected externally to transmit the temperature measurement or an intermediate measurement signal via a link to enable communication through the tank. The sensor may include a processing unit located outside the tank 1.

[0079] As previously stated, the tank 1 may comprise a plurality of assemblies. In this case, the tank 1 may comprise, for each assembly, an associated heat pipe. The heat pipe associated with the assembly comprises a lower end located in the heat transfer fluid, for example, molten metal, near the head of the needle bundle of the assembly. The heat pipe comprises an upper end located above the surface of the heat transfer fluid.

[0080] In this case, where the vessel includes a heat pipe for each assembly, the vessel 1 may include, for each heat pipe, a sensor configured to measure the temperature of the second end of the heat pipe. The vessel then includes links to allow communication from each sensor through the vessel. These links may be optical fibers to carry an optical signal, or channels configured to carry an intermediate measurement signal or, alternatively, the final measurement signals. The various links may advantageously pass through the vessel via a single opening provided within the vessel. This minimizes penetrations into the upper closure slab and limits the spatial footprint of the slab penetration required for transmitting the temperature monitoring of the fuel assemblies.

[0081] It should be noted that when the transducer is located inside the tank and its operation is based on the measurement of infrared radiation, a single transducer is capable of processing the optical measurement signals from several heat pipes. In this way, only one electrical cable connected on one side to the transducer and on the other to the outside of the tank 1 is necessary to transmit the temperature information from several heat pipes. The number of connections passing through the tank can thus be limited.

[0082] When the tank 1 comprises a plurality of assemblies and a heat pipe for each assembly, the tank 1 may advantageously comprise means for producing a two-dimensional image in which all or part of the second ends of the heat pipes appear.

[0083] The means may include, in particular, second-end imaging optics. The image may be formed on a photosensitive pixel array located in the tank. Alternatively, the image may be formed on a microlens array, each configured to inject the light it receives into an optical fiber. Each optical fiber thus carries the light emitted by a portion of the field imaged by the lens. The optical fibers are connected to one or more transducers to transmit the light signal. The transducer(s) are configured to reconstruct the two-dimensional image. The transducer(s) may be located outside the tank 1.

[0084] The sensor includes a processing unit 23 configured to identify the location of the second ends of the heat pipes within the two-dimensional image. This identification can be based on a predetermined imaged field, in which case the positions of the second ends are known before image acquisition. This identification can be achieved using an optical signature of the emission from the second ends. A characteristic of this emission (shape of the second end emitting the radiation, wavelength, intensity) allows the position of the second ends to be detected in the image. Once the position of a second end is determined, the measured radiation associated with this position can provide information about the temperature of the second end.

[0085] Method for measuring the temperature of a fuel assembly

[0086] A nuclear reactor vessel such as has been presented so far makes it possible to implement a method for measuring the temperature of a fuel assembly in a heat transfer fluid, for example molten metal, contained in a nuclear reactor vessel

[0087] We will present a method of implementing this process, in relation to [Fig.8].

[0088] During a first step El, the heat pipe 9 is placed so that its first end 10 is in the heat transfer fluid 3 above a head 14 of the needle bundle, its second end 12 above a surface 16 of the heat transfer fluid 3, the heat pipe 9 extending from the first end 10 to the second end 12 in the vertical direction.

[0089] During a second step E2, a temperature measurement of the second end 12 is acquired by the sensor.

[0090] In the case where the tank comprises a plurality of assemblies and for each assembly an associated heat pipe, the acquisition step E2 may include Advantageously, the acquisition of a two-dimensional image of the second ends of the heat pipes or a portion of the heat pipes. In this case, the method further includes an E3 step of identifying the second end of each heat pipe in the two-dimensional image based on positions in the two-dimensional image.

Claims

Demands

1. Nuclear reactor vessel (1), the vessel comprising a heat transfer fluid (3) and a fuel assembly (5) placed in the heat transfer fluid, the assembly comprising a plurality of needles (7) containing fuel pellets and extending in a vertical direction (Z), characterized in that the vessel comprises a heat pipe (9) extending in the vertical direction from a first end (10) of the heat pipe to a second end (12) of the heat pipe, the vessel being configured, when the fuel assembly is disposed in the vessel: - to immerse the first end in the heat transfer fluid so that the first end is located above a head (14) of the plurality of needles, - to place the second end above a surface (16) of the heat transfer fluid, the vessel comprising a temperature sensor (18) of the second end of the heat pipe.

2. Tank according to claim 1 in which the sensor is separated by at least one centimeter from the second end of the heat pipe.

3. Tank according to any one of claims 1 and 2 in which the sensor is an optical sensor, the sensor being configured for example to measure an emissivity of the second end.

4. Tank according to claim 3, wherein the sensor comprises a light collector (20) located inside the tank, a transducer (22) located outside the tank and an optical link (24), such as an optical fiber, between the collector and the transducer.

5. The tank of any one of claims 1 to 3, wherein the sensor comprises a transducer located inside the tank.

6. Tank according to any one of claims 1 to 5, wherein the heat pipe is thermally insulated along the vertical direction between the first end and the second end, the heat pipe comprising an inner jacket (28) and an outer jacket (26) separated from the inner jacket by a housing (30) containing a partial void or a thermally insulating material.

7. Tank according to claim 6, in which the heat pipe comprises a fluid (32) inside the inner jacket, the fluid comprising for example sodium or ammonia.

8. Tank according to any one of claims 1 to 7 wherein the assembly is a first assembly and the heat pipe is a first heat pipe, the tank comprising several assemblies including the first assembly and several heat pipes including the first heat pipe, each assembly being associated with a heat pipe, the tank comprising means for producing a two-dimensional image in which the second ends of the heat pipes appear.

9. Tank according to any one of claims 1 to 8 wherein the sensor is a first sensor, the tank comprising several sensors including the first sensor, the tank comprising links to allow communication from each sensor through the tank, the links passing through the tank by the same passage provided in the tank.

10. Method for measuring the temperature of a fuel assembly (5) in a heat transfer fluid (3) contained in a nuclear reactor vessel (1), the assembly comprising a plurality of needles (7) containing fuel pellets and extending in a vertical direction (Z), the method comprising, in the presence of a heat pipe (9), the following steps: - (E1) placing the heat pipe so as to have a first end (10) of the heat pipe in the heat transfer fluid above a head (14) of the plurality of needles and a second end (12) of the heat pipe above a surface (16) of the heat transfer fluid, the heat pipe extending from the first end to the second end in the vertical direction, and - (E2) acquiring by a sensor (18) a temperature measurement of the second end.

11. A method according to claim 10, wherein the assembly is a first assembly and the heat pipe is a first heat pipe, the tank comprising several assemblies including the first assembly and several heat pipes including the first heat pipe, each assembly being associated with a heat pipe, the acquisition step comprising the acquisition of a two-dimensional image in which the second ends of the heat pipes appear, the method further comprising identification in the two-dimensional image from the second end of each heat pipe based on positions in the two-dimensional image.

Images