Internal vessel for nuclear reactor, and reactor comprising a plurality of internal vessels

Abstract

The invention relates to a vessel (10) for a nuclear reactor, comprising a jacket (H) made of material transparent to neutrons, having an inlet port (12) for a heat-transfer fluid and an outlet port (13) for the heat-transfer fluid, and a central body (15) made of moderator material, comprising at least one first channel (16.2) for the passage of the heat-transfer fluid. The invention also relates to an assembly for the manufacture of a reactor comprising a vessel of this kind, and to the reactor obtained by assembling this assembly.

Description

[0001] Inner vessel for nuclear reactor and reactor comprising several inner vessels

[0002] The present invention relates to the field of nuclear energy production and in particular to reactors implementing a high temperature cycle (or HTR from the English “High Temperature Reactor”).

[0003] BACKGROUND OF THE INVENTION

[0004] A nuclear reactor contains nuclear fuel whose fission produces heat. Here we use "nuclear fuel" in its common sense, namely to designate a material whose fission following a nuclear reaction produces heat. Many types of nuclear reactors are known, including HTR reactors, which include PBMR (Pebble Bed Modular Reactor), GT-MHR (Gas Turbine Modular Helium Cooled Reactor) or VHTR (Very High Temperature Reactor). HTR reactors are generally graphite moderator reactors whose fuel is in the form of TRISO-type particles.

[0005] The heat produced is then converted into electricity via turbines.

[0006] Nuclear power generation facilities (excluding those installed on vehicles) are generally high-power installations, ranging from a few MW to a few GW, connected to a large-scale electricity transmission network supplying thousands of consumer units (homes, industrial facilities, administrations, etc.). Consideration has recently been given to reducing the size of nuclear reactors to place them as close as possible to consumers. However, this is only possible by increasing the operational safety of the reactors and simplifying their maintenance.

[0007] SUBJECT OF THE INVENTION

[0008] The invention aims in particular to meet at least in part the above needs.

[0009] SUMMARY OF THE INVENTION

[0010] To this end, according to the invention, there is provided a vessel for a nuclear reactor comprising a first cylindrical casing made of a material transparent to neutrons having an inlet port for a heat transfer fluid and an outlet port for the heat transfer fluid, and a central body made of a moderating material comprising, along a central axis of the casing, at least a first channel for the passage of the heat transfer fluid and second channels forming housings each containing nuclear fuel.

[0011] Thus, the tank forms a small unitary assembly which can easily be assembled with other tanks to form a reactor of a size exactly adapted to the needs to be covered.

[0012] According to particular characteristics of the invention, used individually or in whole or in part in combination:

[0013] - the inlet port and the outlet port are adjacent to a first end of the casing and the inlet port is connected to a peripheral circulation space left between the central body and the casing, the first channel having a first end connected to the outlet port and a second end connected to the peripheral space in the vicinity of a second end of the casing, this second end of the casing preferably being closed by a plug;

[0014] - the nuclear fuel is in the form of cores individually surrounded by at least one confinement layer to form balls which are arranged in the first channels;

[0015] - the balls are arranged in the first channels in a stationary solid matrix.

[0016] According to a first embodiment of this tank, the first casing is surmounted by a sheath receiving a control rod sliding between a first extreme position in which the control rod extends mainly in a third channel of the central body and a second extreme position in which the control rod extends mainly in the sheath, the control rod comprising a neutron absorber.

[0017] According to particular characteristics of this first embodiment, used individually or in whole or in part in combination: ;

[0018] - the control bar is connected to an actuator arranged to move the control bar between its two extreme positions;

[0019] - the actuator comprises an electric motor connected by a cable to the control bar so as to bring the control bar to its first extreme position by unwinding the cable with the aid of gravity and to its second extreme position by winding the cable against gravity; - the actuator comprises an electrically powered clutch in an activated state allowing the winding of the cable in such a way that, in the absence of electrical power, the clutch is inactivated and releases the unwinding of the cable;

[0020] - the control bar comprises a free end provided with a shock absorber;

[0021] - the actuator comprises a cable unwinding speed limiter, the limiter being arranged to be active in the absence of electrical power to the actuator;

[0022] - the tank comprises a mechanical means for locking the control bar in its first extreme position, the mechanical locking means being arranged to maintain the control bar in its first extreme position in the absence of any power supply.

[0023] According to a second embodiment of the tank, the tank is without a control bar.

[0024] The invention also relates to an assembly for forming a nuclear reactor. This assembly comprises tanks having all or part of the above characteristics to form internal tanks of the reactor and an external tank containing a base made of moderating material defining a plurality of first housings arranged to each receive one of the internal tanks of the reactor once the latter is assembled.

[0025] According to a particular embodiment, this assembly comprises control devices integral with the internal tanks or separate from the internal tanks.

[0026] In this second case, the control devices each comprise a sheath receiving, sliding between a first extreme position and a second extreme position, a control bar comprising a neutron absorber; and the base comprises second housings for each receiving at least in part one of the control devices in such a way that the bar extends at least in major part out of the second channel in its first extreme position and into the second channel in its second extreme position.

[0027] Preferably, the control bar is connected to an actuator arranged to move the control bar between its two extreme positions.

[0028] The actuator can be of the same type as previously mentioned, i.e. cable-driven, or of another type, for example worm-driven.

[0029] According to particular characteristics of the control devices, used individually or in whole or in part in combination: ;

[0030] - the actuator comprises an electrically powered clutch in an activated state allowing the control bar to be driven by a motor of the actuator, such that, in the absence of electrical power, the clutch is inactivated and releases movement of the control bar relative to the motor;

[0031] - the screw and the control bar are connected to each other by an electromagnet which releases the bar in the event of loss of electrical power to the electromagnet;

[0032] - the control bar comprises a free end provided with a shock absorber;

[0033] - the actuator comprises a speed limiter for movement of the control bar, the limiter being arranged to be active in the absence of electrical power to the actuator;

[0034] - the sheath comprises a mechanical means for locking the control bar in its first extreme position, the mechanical locking means being arranged to maintain the control bar in its first extreme position in the absence of any power supply.

[0035] The invention finally relates to a nuclear reactor preferably formed by the assembly of the above assembly, comprising an anti-seismic base supporting the external tank and delimiting a maintenance chamber into which the inlet and outlet ports of each internal tank open, which are connected to a primary circuit for transporting heat transfer fluid.

[0036] Other characteristics and advantages of the invention will emerge from reading the following description of particular and non-limiting embodiments of the invention.

[0037] BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Reference will be made to the attached drawings, including:

[0039] [Fig. 1] Figure 1 is a schematic view of a heating installation comprising a reactor according to the invention;

[0040] [Fig. 2] Figure 2 is a schematic view, in vertical section, of a reactor according to a first embodiment usable in this installation;

[0041] [Fig. 3] Figure 3 is a schematic view, in horizontal section, of this reactor; [Fig. 4] Figure 4 is a view similar to Figure 2 of the base of this reactor;

[0042] [Fig. 5] Figure 5 is a schematic view, in vertical section, of one of the internal vessels of the reactor according to the first embodiment, in a production configuration;

[0043] [Fig. 6] Figure 6 is a schematic view, in horizontal section, of one of the internal vessels of this reactor;

[0044] [Fig. 7] Figure 7 is a schematic view, in vertical section, of one of the internal vessels of the reactor according to the first embodiment, in a transport configuration between the manufacturing plant and the reactor installation site;

[0045] [Fig. 8] Figure 8 is a schematic view, in vertical section, of one of the internal vessels of the reactor according to the first embodiment, in a transport and storage configuration after dismantling of the reactor;

[0046] [Fig. 9] Figure 9 is a schematic perspective view of the contents of an external tank of a reactor according to a second embodiment usable in this installation;

[0047] [Fig. 10] Figure 10 is a schematic view, from above, of the contents of this external tank;

[0048] [Fig. 11] Figure 11 is a schematic view, in vertical section, of one of the internal tanks of the reactor according to the second embodiment;

[0049] [Fig. 12] Figure 12 is a schematic detail view, in vertical section, of the lower end of this internal tank; [Fig. 13] Figure 13 is a schematic view, in vertical section, of a reactor control device according to the second embodiment.

[0050] DETAILED DESCRIPTION OF THE INVENTION

[0051] With reference to the figures, the invention is described here in application to a heating installation 100 for supplying heat to an industrial site I.

[0052] The heating installation 100 comprises a concrete enclosure 110 having a containment chamber 111 enclosing a nuclear reactor generally designated 1.

[0053] Two different embodiments of the reactor are described below.

[0054] A reactor according to a first embodiment will now be described with particular reference to Figures 1 to 8.

[0055] The nuclear reactor 1 comprises an anti-seismic base 120 and an external vessel 2 which rests on the anti-seismic base 120 and which contains a base 3. The anti-seismic base 120 is also arranged to be heat-insulated.

[0056] The external tank 2 is made of steel having an inner surface coated with a barrier layer 4 of neutron absorbing material, here based on boron, in contact with the periphery of the base 3.

[0057] The base 3 is made of a moderating material, in this case graphite. It is recalled that a moderating material slows down the neutrons involved in the chain reaction without absorbing them. The base 3 is crossed by cylindrical housings 5, parallel to each other and delimited by a wall covered with a sheet 6 of material transparent to neutrons. The material transparent to neutrons is here a zirconium alloy preferably comprising more than 95% by mass of zirconium and more preferably more than 98% by mass of zirconium, such as one of those designated ZIRCALOY and more particularly ZIRCALOY 4. The alloys that can be used include alloys resulting from recrystallization, for example produced under the brand name ZIRLO by the company WESTINGHOUSE and M5 by the company FRAMATOME. The housings 5 ​​extend vertically and each receive an internal tank generally designated 10.

[0058] The inner vessel 10 comprises a casing 11 of neutron-transparent material having an inlet port 12 for a heat transfer fluid and an outlet port 13 for the heat transfer fluid. The casing 11 is entirely received in the housing 5. The inlet port 12 and the outlet port 13 are coaxial with each other, the inlet port 12 extending around the outlet port 13 at a lower end of the casing 11. The inlet port 12 and the outlet port 13 comprise conduits which project from the lower end of the outer vessel 2 when the inner vessel 10 is in position in the housing 5.

[0059] The casing 11 has a tubular shape of circular cross-section and contains a tubular-shaped reinforcing frame 14 having a hexagonal cross-section whose edges are in contact with the inner surface of the casing 11. The reinforcing frame 14 stiffens the casing 11. It is understood that a peripheral fluid circulation space 14' is formed between the inner surface of the casing 11 and each facing wall of the reinforcing frame 14: these spaces allow the passage of heat transfer fluid from the inlet port 12 to the upper end of the casing 11. The casing 11 and the reinforcing frame 14 are made of a material transparent to neutrons. The neutron-transparent material is here a zirconium alloy preferably comprising more than 95% by mass of zirconium and, more preferably, more than 98% by mass of zirconium, such as one of those designated ZIRCALOY and more particularly ZIRCALOY 4.The alloys that can be used include alloys resulting from recrystallization, for example those produced under the ZIRLO brand by the WESTINGHOUSE company and M5 by the ORANO company (formerly AREVA).

[0060] In the casing 11 and more precisely in the reinforcement frame 14 is housed a central body 15 made of moderating material, here graphite. The central body 15 has a lower end resting on an internal support of the casing 11 and an upper end cooperating here with a hook connected to the internal casing 11 to hold the central body 15 in position.

[0061] The central body 15 comprises a central channel 16.1 and channels 16.2, 16.3 distributed around the central channel 16.1. The channels 16.1, 16.2, 16.3 are parallel to the central axis of the casing 11.

[0062] The channels 16.2 open at their two ends to form channels for the passage of heat transfer fluid. The channels 16.2 allow the passage of heat transfer fluid from the upper end of the casing 11 to the outlet port 13.

[0063] The channels 16.3 are closed at their two ends and form housings each containing nuclear fuel 17. The nuclear fuel is in the form of cores of combustible material individually surrounded by at least one confinement layer to form balls. More precisely, the combustible material is here in the form of uranium oxide cores individually coated by three isotropic coating layers, namely an inner layer of porous carbon, an intermediate layer of ceramic (generally a silicon carbide), and an outer layer of pyrolytic carbon. The combustible material is thus in the form of balls called TRISO (from the English "Tristructural Isotropy"). The balls are dispersed in a graphite matrix to form cylindrical pellets which are stacked on top of each other in the channels 16.3.

[0064] The graphite of the lower part of the central body 15 forms a vertical reflector and said lower part of the central body 15 rests on an insulating block 18, here made of carbon, to prevent the neutrons from moving towards the lower end of the casing 11 and the inlet and outlet ports 12, 13.

[0065] In the insulating block 18 is provided a mixing chamber 19 to which are connected on the one hand all the channels 16.2 and on the other hand the outlet port 13. It is understood that the insulating block 18 closes the channels 16.1 and 16.3.

[0066] The upper part of the envelope 11 is covered internally with a conventional type of thermal insulation such as rock wool.

[0067] On the upper part of the casing 11 is welded a sheath generally designated 20 of a control device which surmounts the casing 11 and extends projecting from the external tank 2. Alternatively, the sheath 20 could be attached in a removable manner to the casing 11. The sheath 20 delimits a central housing which extends coaxially to the central channel 16.1 and which communicates with the internal space of the casing 11 by an outlet opposite the central channel 16.1. The sheath 20 receives a control rod 21 sliding between a first extreme position in which the control rod 21 extends mainly in the central channel 16.1 of the central body 15 and a second extreme position in which the control rod 21 extends mainly in the sheath 20. The control rod 21 comprises a neutron absorber (also referred to as a neutron-absorbing material, capable of absorbing neutrons without transmutation or induced radioactivity).The material in question is in the form of a pencil and is for example a silver-indium-cadmium alloy, boron, hafnium, dysprosium titanate. It is understood that when the control rod 21 is in its first extreme position, it blocks the chain reaction while when it is in its second extreme position it does not hinder the chain reaction in any way.

[0068] The control bar 21 comprises a free end (the lower end) provided with a shock absorber 22 for abutting against the bottom of the central channel 16.1 when the control bar 21 is in its first extreme position.

[0069] The control bar 21 has an upper end connected to an actuator 23 carried by the sheath 20 and arranged to move the control bar 21 between its two extreme positions. The actuator 23 comprises an electric motor having an output shaft driving a cable winding drum 24 having a free end connected to the upper end of the control bar 21 so as to bring the control bar 21 to its first extreme position by paying out the cable with the aid of gravity, and to its second extreme position by winding the cable against gravity.

[0070] The actuator 23 further comprises an electrically powered clutch 25 in an activated state allowing the cable to be wound in such a way that, in the absence of electrical power, the clutch 25 is inactivated and releases the cable payout. The clutch here is an electromagnetic clutch. The actuator 23 comprises a limiter 26 for the payout speed of the cable 24, the limiter 26 being arranged to be active in the absence of electrical power to the actuator 23. The limiter 26 is for example a friction brake acting on the drum. It is understood that in the event of a power cut, the clutch 25 allows the cable to pay out so that the control bar 21 descends under the effect of gravity into its first extreme position and neutralizes the chain reaction.The speed of descent of the control rod 21 is controlled by the limiter 26 in such a way that the shock absorber 22 can dissipate the kinetic energy of the control rod 21 arriving in its first extreme position in abutment against the bottom of the central channel 16.1 without damaging the installation. It is understood that in the event of a power cut, the control rod 21 descends under its own weight towards its first extreme position and neutralizes the chain reaction. In the event of a problem, it is therefore sufficient to cut the power supply to neutralize the chain reaction, which is very safe. Each internal vessel 10 of the reactor 1 of the invention thus benefits from passive safety preventing the reactor from running away, particularly in the event of a power cut. The actuator 23, the clutch 25 and the limiter 26 are housed in an upper compartment 20' welded to the upper end of the sheath 20.

[0071] Each internal tank 10 further comprises a mechanical means for locking the control rod in its first extreme position, the mechanical locking means being arranged to maintain the control rod 21 in its first extreme position in the absence of any power supply. The mechanical locking means here is a locking rod 31 placed for transport in the outlet port and a drilling made in the bottom of the central channel 16.1 to hook the free end of the control rod 21.

[0072] In this case, an upper valve 27 and two lower valves 28.12 (to close the inlet port 12) and 28.13 (to close the outlet port 13) are provided here. The valves 27, 28.12, 28.13 make it possible to isolate the internal tank 10 from the outside.

[0073] The actuators 23 are connected to a central control unit 29 also connected to a battery of sensors (temperature and pressure in the internal tanks 10 in particular) making it possible to control the installation by remote operation automatically. The central control unit 29 comprises, in a manner known per se, one or more processors connected to one or more memories containing programs executable by the processor(s) to control the installation and in particular the actuators 23. These programs advantageously comprise an artificial intelligence program. The programs and the actuators 23 are arranged to be able to bring each control rod 21 into any intermediate position between the two extreme positions, to slow down the chain reaction without interrupting it completely, depending on the information provided by the sensors and any instructions provided by an operator.

[0074] The central control unit 29 is here arranged in a control chamber 112 inside the concrete enclosure 110 and is connected via a computer network to a computer server enabling communication with the central control unit 29 to collect operating parameter values ​​of the installation so as to monitor the installation and set setpoint values ​​to influence the operation of the installation.

[0075] The anti-seismic base 120 supporting the external tank 2 delimits a maintenance chamber 130 into which the inlet and outlet ports 12, 13 of the internal tanks 10 open. The external tank 2 here has a bottom covered with a radiation protection layer 30 preventing the passage of neutrons towards the maintenance chamber 130. The radiation protection layer 30 comprises for example a layer of lead, steel or tungsten depending on the maximum temperature reached at this location.

[0076] A primary heat transfer fluid circuit 140 is connected to the inlet and outlet ports 12, 13 of each internal tank 10. The heat transfer fluid is here helium. The primary heat transfer fluid circuit 140 comprises a plurality of pump / heat exchanger assemblies 141 for circulating the helium in the primary circuit 140 and a treatment system 142 for removing the impurities contained in the helium. These impurities may include radioactive elements, but also traces of oxygen and water which risk oxidizing the graphite. The pump / heat exchanger assemblies 141 and the treatment system 142 are here arranged in a technical chamber 113 of the enclosure 110, next to the confinement chamber 111 and the control chamber 112.

[0077] The heat exchangers of the pump / heat exchanger assemblies 141 are connected to a secondary circuit 150 which is connected to a heat-consuming installation of the industrial site I. The secondary circuit 150 comprises in particular one or more pumps for circulating in the secondary circuit 150 a heat transfer fluid, such as carbon dioxide or steam, between the exchangers and the heat-consuming installation of the industrial site I.

[0078] For example, reactor 1 is sized to provide 10 MW of heat to heat the heat transfer fluid of the secondary circuit 150 to a temperature of 600°C.

[0079] It is understood that the internal tanks 10 are manufactured and assembled individually in the factory. They are transported in the configuration of Figure 7, with:

[0080] - the control bar 21 in its first extreme position and the locking rod 31 in position;

[0081] - plugs 32.12, 32.13 respectively closing the inlet port 12 and the outlet port 13 (either in place of the lower valves 28.12, 28.13, or upstream and downstream of these respectively);

[0082] - the upper valve 27 closed.

[0083] This creates a manufacturing assembly for a reactor 1 comprising: the internal tanks 10 pre-assembled with the control device; the external tank 2 and the block 3.

[0084] The masonry parts will be cast directly on site or prefabricated and the assembly of the core of reactor 1 will be carried out on site from the above assembly and will be followed by the connection of reactor 1 to the primary circuit 140. The transport of the internal vessels 10 between the manufacturing plant and the reactor installation site will of course be carried out using protective packaging adapted according to the means of transport used and the regulations in force.

[0085] For the dismantling of the installation, when the fuel has been exhausted:

[0086] - the control bar 21 is brought into its first extreme position and the locking rod 31 is engaged in the free end of the control bar;

[0087] - the plugs 32.12, 32.13 are put in place to close the inlet port 12 and the outlet port 13 respectively (either in place of the lower valves 28.12, 28.13, or upstream and downstream of these respectively);

[0088] - the sheath 20 is separated from the internal casing 11 and a plug 33 is placed in the upper opening of the casing 11.

[0089] Envelope 11, and its contents, can then be placed in a radioactive waste storage container that complies with current regulations.

[0090] Alternatively, two series of internal tanks could be provided, namely:

[0091] - a first series of internal tanks identical to the internal tanks 10 described above which would be arranged in the housings 5 ​​grouped around the center of the base 3;

[0092] - a second series of internal tanks which would include a central body 15 but no nuclear fuel or control rod and which would be arranged in the housings 5 ​​extending to the periphery of the base 3 in the vicinity of the external tank 2 to surround the internal tanks of the first series.

[0093] It is understood that the internal tanks of the second series, devoid of nuclear fuel, do not emit neutrons towards the external tank 2 but that the central body 15 of the tanks of the second series will nevertheless slow down the neutrons emitted in the internal tanks of the first series and heat up to participate in the heating of the heat transfer fluid.

[0094] A reactor according to a second embodiment will now be described with reference to Figures 9 to 13. Elements identical or analogous to those previously described will bear numerical references identical to the latter.

[0095] Nuclear reactor 1 comprises, as previously:

[0096] - an anti-seismic base,

[0097] - an external tank which rests on the anti-seismic base and which contains a base 3.

[0098] These elements are generally identical to those of the first embodiment except with regard to the housing provided in the base 3.

[0099] The base 3 is crossed by first housings 5.1, cylindrical and vertical, each receiving an internal tank generally designated 10 as in the first embodiment and by second housings 5.2, cylindrical and vertical, each receiving at least part of a control device 200.

[0100] The internal tank 10 of the second embodiment is generally identical to that of the first embodiment except that it is devoid of a control device since the control devices are mounted directly on the base 3.

[0101] The inner vessel 10 comprises a casing 11 of neutron-transparent material having an inlet port 12 for a heat transfer fluid and an outlet port 13 for the heat transfer fluid. The casing 11 is entirely received in the first housing 5.1. The inlet port 12 and the outlet port 13 are coaxial with each other, the inlet port 12 extending around the outlet port 13 at a lower end of the casing 11. The inlet port 12 and the outlet port 13 comprise conduits 12.1, 13.1 which project from the lower end of the outer vessel 2 when the inner vessel 10 is in position in the housing 5.1.

[0102] The casing 11 has a tubular cylindrical shape of circular section and contains, as previously, a reinforcing frame 14 delimiting, with the internal surface of the casing 11, spaces 14' for peripheral circulation of fluid. These spaces allow the passage of heat transfer fluid from the inlet port 12 to the upper end of the casing 11.

[0103] In the casing 11 and more precisely in the reinforcing frame 14 is housed a central body 15 made of moderating material. The central body 15 has a lower end resting on an internal support of the casing 11 and an upper end cooperating here with a hook connected to the internal casing 11 to hold the central body 15 in position.

[0104] The central body 15 comprises channels 16.2, 16.3 distributed over the cross section of the central body 15. The channels 16.2, 16.3 are parallel to the central axis of the casing 11.

[0105] The channels 16.2 open at their two ends to form channels for the passage of heat transfer fluid. The channels 16.2 allow the passage of heat transfer fluid from the upper end of the casing 11 to the outlet port 13.

[0106] Channels 16.3 are closed at both ends by insulating blocks 18 and 18' and form housings each containing nuclear fuel.

[0107] The graphite of the lower part of the central body 15 forms a vertical reflector and said lower part of the central body 15 rests on the insulating block 18, here made of carbon, to prevent the neutrons from moving towards the lower end of the casing 11 and the inlet and outlet ports 12, 13.

[0108] Unlike channels 16.3, channels 16.2 extend into insulating blocks 18 and 18'.

[0109] In the insulating block 18 is provided a mixing chamber 19 to which are connected on the one hand all the channels 16.2 and on the other hand the outlet port 13.

[0110] The upper part of the casing 11 is internally covered with a conventional type of thermal insulation such as rock wool and is closed by a plug 11'. As previously, valves are provided to close the inlet port 12 and the outlet port 13. The valves make it possible to isolate the internal tank 10 from the outside.

[0111] Each control device 200 comprises a sheath generally designated 20 which delimits a central housing which extends coaxially with the second housing 5.2 and which has a lower part engaged at the bottom in the second housing 5.2. The sheath 20 receives a control rod 21 sliding between a first extreme position in which the control rod 21 extends for the most part in the second housing 5.2 and outside the sheath 20; and a second extreme position in which the control rod 21 extends for the most part in an upper part of the sheath 20 extending outside the second housing 5.2. The control rod 21 comprises a neutron absorber. It is understood that when the control rod 21 is in its first extreme position, it blocks the chain reaction while when it is in its second extreme position it does not hinder the chain reaction in any way.

[0112] The control bar 21 comprises a free end (the lower end) provided with a shock absorber 22 for coming into abutment against the bottom of the second housing xx when the control bar 21 is in its first extreme position.

[0113] The control bar 21 has an upper end connected to an actuator 23 carried by the sheath 20 and arranged to move the control bar 21 between its two extreme positions. The actuator 23 comprises an electric motor having an output shaft driving a worm screw 23.1 with reversible pitch on which is engaged a nut secured to the control bar 21 so as to bring the control bar 21 to its first extreme position by unscrewing with the aid of gravity, and to its second extreme position by screwing against gravity.

[0114] The actuator 23 further comprises an electromagnet 25 electrically powered in an activated state allowing the axial connection of the motor shaft to the worm screw and the rotational drive of the worm screw in such a way that, in the absence of electrical power supply, the electromagnet 25 is inactivated and releases the worm screw and therefore releases the descent of the worm screw, the nut and the control bar 21 under the effect of gravity. The actuator 23 comprises a limiter 26 for the descent speed of the worm screw, the limiter being arranged to be active in the absence of electrical power supply to the actuator 23. The limiter 26 is for example a friction brake. It is understood that in the event of a power cut, the electromagnet 25 allows the worm screw and the control bar 21 to descend under the effect of gravity into its first extreme position and neutralizes the chain reaction.The speed of descent of the control rod 21 is controlled by the limiter in such a way that the shock absorber 22 can dissipate the kinetic energy of the control rod 21 arriving in its first extreme position in abutment against the bottom of the second housing 5.2 without damaging the installation. It is therefore understood that in the event of a power cut, the control rod 21 descends under its own weight towards its first extreme position and neutralizes the chain reaction. In the event of a problem, it is therefore sufficient to cut the power supply to neutralize the chain reaction, which is very safe. The reactor 1 of the invention thus benefits from passive safety preventing the reactor from running away, particularly in the event of a power cut. The actuator 23, the electromagnet 25 and the limiter 26 are housed in an upper compartment 20' welded to the upper end of the sheath 20.

[0115] The actuators 23 are, as previously, connected to a central control unit which is arranged in the control chamber inside the concrete enclosure and is connected via a computer network to a computer server allowing communication with the central control unit to collect operating parameter values ​​of the installation so as to monitor the installation and set setpoints to influence the operation of the installation. The inlet and outlet ports 12, 13 of the internal tanks 10 open as previously into the maintenance chamber and are connected to the primary heat transfer fluid circuit. The external tank 2 has, as previously, a bottom covered with a radiation protection layer preventing the passage of neutrons towards the maintenance chamber.The radiation protection layer includes, for example, a layer of lead, steel or tungsten depending on the maximum temperature reached at that location.

[0116] We thus constitute a manufacturing assembly for a reactor 1 comprising:

[0117] - the pre-assembled internal tanks 10;

[0118] - the control devices 200;

[0119] - external tank 2 and block 3.

[0120] The assembly, operation and dismantling of reactor 1 are carried out as previously.

[0121] It is understood that in the nuclear reactor described here, whatever the embodiment, the nuclear fuel is immobile in the channels 16.3. The balls can be simply stacked on top of each other or embedded in a matrix.

[0122] Of course, the invention is not limited to the embodiments described but encompasses any variant falling within the scope of the invention as defined by the claims.

[0123] In particular, the installation may have a different structure than that described.

[0124] The central body of moderating material can be in a single part or in several parts assembled together.

[0125] The nuclear fuel may comprise a material other than that described, for example, a uranium carbide, or a plutonium or thorium oxide or carbide. The nuclear fuel may be a fissile or fertile material. The balls may be dispersed in a silicon carbide matrix.

[0126] Alternatively, the nuclear fuel can be used in a form other than balls, for example in the form of conventional pellets.

[0127] The heat transfer fluid of the primary circuit can be a gas other than pure helium and for example supercritical carbon dioxide.

[0128] The moderator material can be other than graphite and for example beryllium oxide or lithium fluoride.

[0129] The absorbent material may be different from that mentioned and may include, for example, cobalt, gadolinium, samarium, erbium, europium or an alloy comprising one or more of the absorbent materials mentioned, such as, for example, boron carbide.

[0130] The control rod may consist of a set of hinged absorbent pieces. This hinged assembly ensures that the rod will be able to find its way into the hole in the body's central housing even if the body becomes misaligned.

[0131] The actuator of the control device of the first embodiment can be used in the second embodiment and vice versa. The element connecting the motor to the control bar can be other than a worm or a cable, and for example a pinion / rack assembly. The electromagnet of the second embodiment can be replaced by an electrically powered clutch in an activated state allowing the rotational drive of the worm in such a way that, in the absence of electrical power, the clutch is inactivated and releases the rotation of the worm and therefore the descent of the nut and the control bar 21 under the effect of gravity.

[0132] The reinforcing frame may have any prismatic or non-prismatic shape; it may also be omitted if the wall of the envelope 11 has sufficient thickness to withstand the stresses exerted on the envelope 11.

[0133] It is recalled that a cylinder can have any section whose outline is a curve and for example a circular, oval, polygonal or other section... symmetrical or not. The valves can be replaced by plugs.

[0134] The reactor may comprise one or more internal vessels, devoid of nuclear fuel, comprising a central body of moderating material whose role is to regulate the temperature of the reactor. The internal vessels are preferably designed to be easily transported or stored in the existing fuel packagings used for pressurized water reactors.

[0135] The reactor according to the invention can just as easily be manufactured in whole or in part on site, without using an assembly such as those mentioned in the description.

[0136] The invention is described here in an application for producing heat for industrial purposes. It can obviously be used for producing heat for residential purposes.

[0137] The invention can also be used to produce electricity either as a primary source or as a supplement to heat production. It is then sufficient to add a turbine.

[0138] One or more overpressure release valves may be provided on the concrete enclosure, in particular for chamber 111.

[0139] The invention is further usable for providing heat to a process for manufacturing hydrogen by implementing an iodine-sulfur cycle.

[0140] The primary and secondary circuits can be arranged differently, as can the input and output ports, which can be located at two opposite points on the enclosure.

[0141] The primary heat transfer fluid circuit 140 can be connected to a single heat exchanger 141 to which a secondary circuit 150 for transporting heat transfer fluid from a heat consuming installation is connected.

Claims

DEMANDS 1. A reactor vessel (10) for a nuclear reactor, comprising a cylindrical shell (11) of neutron-transparent material having an inlet port (12) of a heat transfer fluid and an outlet port (13) of the heat transfer fluid, and a central body (15) of moderator material comprising, along a central axis of the shell (11), at least one first channel (16.2) for the passage of the heat transfer fluid and second channels (16.3) forming compartments which each contain nuclear fuel.

2. Tank (10) according to claim 1, in which the inlet port (12) and the outlet port (13) are adjacent to a first end of the casing and the inlet port is connected to a peripheral circulation space (14') being left between the central body (15) and the casing (11), the first channel having a first end connected to the outlet port and a second end connected to the peripheral space in the vicinity of a second end of the casing, this second end of the casing being closed.

3. Tank according to claim 2, in which the second end of the casing is sealed by a plug.

4. Vessel according to any one of the preceding claims, wherein the nuclear fuel is in the form of nuclei individually surrounded by at least one containment layer to form beads arranged in the second channels.

5. Tank (10) according to any one of the preceding claims, wherein the casing (11) has an upper end provided with a sleeve (20) receiving a control bar (21) that slides between a first position extreme in which the control bar (21) extends mostly into a housing (16.1) in the central body (15) and a second extreme position in which the control rod (21) extends mostly into the sheath (20), the control rod (21) comprising a neutron absorber.

6. Tank (10) according to claim 5, in which the control bar (21) is connected to an actuator (23) arranged to move the control bar (21) between its two extreme positions.

7. Tank (10) according to claim 6, in which the actuator (23) comprises an electric motor connected by a cable (24) to the control bar (21) so as to bring the control bar (21) to its first extreme position by unwinding the cable (24) with the aid of gravity and to its second extreme position by winding the cable (24) against gravity.

8. Tank (10) according to claim 7, in which the actuator (23) includes an electrically powered clutch (25) in an activation state allowing the winding of the cable (24) such that, in the absence of electrical power, the clutch (25) is deactivated and releases the unwinding of the cable (24).

9. Tank (10) according to claim 8, in which the control bar (21) includes a free end provided with a shock absorber (22) and / or the actuator (23) includes a cable (24) unwinding speed limiter (26), the limiter (26) being arranged to be active in the absence of power supply to the actuator (23).

10. Tank (10) according to any one of claims 6 to 9, comprising a mechanical means for locking the bar control bar (21) in its first extreme position, the mechanical locking means being arranged to maintain the control bar (21) in its first extreme position in the absence of any power supply.

11. Tank (10) according to any one of the preceding claims, wherein the neutron-transparent material is a zirconium alloy.

12. Tank (10) according to any one of the preceding claims, in which the ends of the second channels are sealed by blocks of moderator material.

13. Assembly for the manufacture of a nuclear reactor, comprising vessels according to any one of the preceding claims for forming internal vessels of the reactor and an external vessel (2) containing a base (3) of moderator material defining a plurality of first housings (5) arranged to receive each one of the internal vessels of the reactor once the latter is assembled.

14. Assembly according to claim 13, comprising control devices each comprising a sleeve (20) receiving, by sliding between a first extreme position and a second extreme position, a control bar (21) comprising a neutron absorber, the base comprising second housings each for receiving at least part of one of the control devices such that the bar extends at least for the most part out of the second channel in its first extreme position and into the second channel in its second extreme position.

15. Assembly according to claim 14, wherein the control bar (21) is connected to an actuator (23) arranged to move the control bar (21) between its two extreme positions.

16. Assembly according to claim 15, wherein the actuator (23) comprises an electric motor connected to the control bar (21) so as to bring the control bar (21) to its first extreme position by deflection of the cable (24) with the aid of gravity and to its second extreme position against gravity.

17. Assembly according to claim 16, wherein the electric motor is connected to the control bar (21) by a worm gear or a cable.

18. Assembly according to claim 16 or 17, wherein the actuator (23) comprises an electrically powered clutch (25) in an activated state allowing connection to the control bar such that, in the absence of power supply, the clutch (25) is deactivated and releases the movement of the control bar.

19. Assembly according to claim 18, wherein the control bar (21) comprises a free end provided with a shock absorber (22) and / or the actuator (23) comprises a speed limiter (26) for the movement of the control bar (21), the limiter (26) being arranged to be active in the absence of power supply to the actuator (23).

20. Assembly according to any one of claims 15 to 19, comprising a mechanical means for locking the control bar (21) in its first extreme position, the mechanical locking means being arranged to maintain the control bar (21) in its first extreme position in the absence of any power supply.

21. Together according to any one of claims 13 to 20, in which the first dwellings (5) of the base (3) are delimited by a wall covered with a sheet (6) of neutron-transparent material.

22. An assembly according to any one of claims 13 to 21, wherein the outer tank (2) has an inner wall coated with a neutron-absorbing layer (4).

23. Reactor comprising an anti-seismic base (120) delimiting a maintenance chamber (130) into which a primary circuit (140) for transporting heat transfer fluid opens, an external tank (2) resting on the anti-seismic base and containing a base (3) made of moderating material having first housings, internal tanks (10) according to any one of claims 1 to 12 which are housed in the first housings and which have inlet and outlet ports which open into the maintenance chamber and are connected to the primary circuit.

24. Reactor according to claim 23, in which the outer vessel (2) has a bottom covered with a radiation protection layer (30) preventing the passage of neutrons to the maintenance chamber (130).

25. Reactor according to claim 23 or 24, in which the primary circuit (140) of heat transfer fluid is connected to a heat exchanger (141) to which is connected a secondary circuit (150) for transporting heat transfer fluid from a heat-consuming installation.

26. Reactor according to any one of claims 23 to 25, wherein the base (3) includes second housings (5.2) and control devices (200) are received in the second housings.

Images