Internal vessel for nuclear reactor and reactor with multiple internal vessels

Abstract

Reactor vessel (10) comprising a shell (11) of neutron-transparent material having a coolant inlet port (12) and a coolant outlet port (13), and a central body (15) of moderator material comprising at least one first coolant channel (16.2). Reactor comprising such a vessel. FIGURE IN ABRIDGED DIAGRAM: [Fig. 1]

Description

Title of the invention: Internal vessel for a nuclear reactor and reactor comprising several internal vessels

[0001] 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”).

[0002] BACKGROUND OF THE INVENTION

[0003] 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) reactors. HTR reactors are generally graphite moderator reactors whose fuel is in the form of TRISO-type particles.

[0004] The heat produced is then converted into electricity via turbines.

[0005] Nuclear electricity production installations (excluding those installed on vehicles) are generally high-power installations, from a few MW to a few GW, connected to a large-scale electricity transmission network supplying thousands of consumer units (homes, industrial installations, administrations, etc.).

[0006] Recently, consideration has been given to reducing the size of nuclear reactors to place them closer 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. Summary of the invention

[0009] To this end, according to the invention, there is provided a vessel for a nuclear reactor comprising a first envelope 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 at least a first channel for the passage of the heat transfer fluid.

[0010] Thus, the tank forms a small unitary assembly which can easily be assembled with other tanks to form a reactor having a size exactly adapted to the needs to be covered.

[0011] According to a particular embodiment, the central body comprises second channels forming housings each containing nuclear fuel.

[0012] According to particular characteristics of this embodiment, used individually or in whole or in part in combination: - 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; - 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; - the control bar is connected to an actuator arranged to move the control bar between its two extreme positions; - 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 cable to be wound in such a way that, in the absence of electrical power, the clutch is inactivated and releases the cable to be paid out; - the control bar comprises a free end provided with a shock absorber; - the actuator comprises a cable unwinding speed limiter, the limiter being arranged to be active in the absence of electrical power to the actuator; - 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.

[0013] The invention also relates to a nuclear reactor comprising an external vessel containing a base made of moderating material defining a plurality of fourth channels each receiving an internal tank formed from a tank as defined in the preceding paragraphs.

[0014] Other characteristics and advantages of the invention will emerge from reading the following description of a particular and non-limiting embodiment of the invention. Brief description of the drawings

[0015] Reference will be made to the accompanying drawings, among which:

[0016] [Fig-1] [Fig.l] is a schematic view of a heating installation comprising a reactor according to the invention;

[0017] [Fig.2] [Fig.2] is a schematic view, in vertical section, of the reactor of this facility ;

[0018] [Fig.3] [Fig.3] is a schematic view, in horizontal section, of a reactor according to the invention;

[0019] [Fig.4] [Fig.4] is a view similar to [Fig.2] of the base of this reactor;

[0020] [Fig.5] [Fig.5] is a schematic view, in vertical section, of one of the tanks internals of the reactor of this installation, in a production configuration;

[0021] [Fig.6] [Fig.6] is a schematic view, in horizontal section, of one of the tanks internals of the reactor of this installation;

[0022] [Fig.7] [Fig.7] is a schematic view, in vertical section, of one of the tanks internals of the reactor of this facility, in a transport configuration between the manufacturing plant and the reactor installation site;

[0023] [Fig.8] [Fig.8] is a schematic view, in vertical section, of one of the internal vessels of the reactor of this installation, in a transport and storage configuration after dismantling of the reactor. DETAILED DESCRIPTION OF THE INVENTION

[0024] 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.

[0025] The heating installation 100 comprises a concrete enclosure 110 having a containment chamber 111 containing a nuclear reactor generally designated 1.

[0026] The nuclear reactor 1 rests on an anti-seismic base 120 arranged in the confinement chamber 111 and comprises an external vessel 2 containing a base 3. The anti-seismic base 120 is also arranged to be heat-insulated.

[0027] 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.

[0028] Base 3 is made of moderating material, here graphite. It should be remembered that a moderating material slows down the neutrons involved in the chain reaction without absorbing them. The base 3 is crossed by housings 5, cylindrical, 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 which can be used include alloys resulting from recrystallization for example produced under the brand 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.

[0029] The inner vessel 10 comprises a casing 11 made 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 have the form of conduits which project from the lower end of the outer vessel 2 when the inner vessel 11 is in position in the housing 5.

[0030] The casing 11 has a tubular shape of circular cross-section and contains a tubular reinforcement 14 having a hexagonal cross-section whose edges are in contact with the internal surface of the casing 11. The reinforcement 14 stiffens the casing 11. It is understood that a peripheral fluid circulation space 14' is formed between the internal surface of the casing 11 and each wall of the reinforcement 14 opposite: 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 reinforcement 14 are made of a 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 those produced under the ZIRLO brand by the WESTINGHOUSE company and M5 by the ORANO company (formerly AREVA).

[0031] 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.

[0032] 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 envelope 11.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] The upper part of the envelope 11 is covered internally with a conventional type of thermal insulation such as rock wool.

[0038] On the upper part of the casing 11 is welded a sheath generally designated 20 which surmounts the casing 11 and extends projecting from the external tank 2. The sheath 20 delimits a central housing which extends coaxially with 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 for the most part in the central channel 16.1 of the central body 15 and a second extreme position in which the control rod 21 extends for the most part in the sheath 20. The control rod 21 comprises a neutron absorber (also referred to as 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.

[0039] 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.

[0040] 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.

[0041] The actuator 23 further comprises a clutch 25 electrically powered 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 is here 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. .

[0042] Each internal tank 10 further 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 21 in its first extreme position in the absence of any power supply. The mechanical locking means is here a locking rod 31 put in place for transport in the outlet port and a hole made in the bottom of the central channel 16.1 to hook the free end of the control rod 21.

[0043] 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.

[0044] 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.

[0045] 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 values ​​of operating parameters of the installation so as to monitor the installation and set setpoint values ​​to influence the operation of the installation.

[0046] The anti-seismic base 120 supporting the external tank 2 delimits a chamber of maintenance 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.

[0047] 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 room 112.

[0048] 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.

[0049] By way of example, the reactor 1 is for example sized to provide 10 MW of heat to heat the heat transfer fluid of the secondary circuit 150 to a temperature of 600°C.

[0050] It is understood that the internal tanks 10 are manufactured and assembled individually in the factory. They are transported in the configuration of FIGS. 7, with: - the control bar 21 in its first extreme position and the locking rod 31 in position; - 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); - the upper valve 27 closed.

[0051] The assembly of the core of reactor 1 will be carried out on site and will be followed by its connection to the primary circuit 140. The transport of the internal tanks 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.

[0052] For the dismantling of the installation, when the fuel has been exhausted: - the control rod 21 is brought into its first extreme position and the locking rod 31 is engaged in the free end of the control rod; - 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); - the sheath 20 is separated from the internal casing 11 and a plug 33 is placed in the upper opening of the casing 11.

[0053] The envelope 11, and its contents, can then be placed in a radioactive waste storage container in accordance with the regulations in force.

[0054] Alternatively, two series of internal tanks could be provided, namely: - 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; - 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.

[0055] 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.

[0056] Of course, the invention is not limited to the embodiment described but encompasses any variant falling within the scope of the invention as defined by the claims.

[0057] In particular, the installation may have a structure different from that described.

[0058] The central body made of moderating material can be in a single part or in several parts assembled together.

[0059] 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.

[0060] The beads may be dispersed in a silicon carbide matrix.

[0061] Alternatively, the nuclear fuel may be used in a form other than balls, for example in the form of conventional pellets.

[0062] The heat transfer fluid of the primary circuit may be a gas other than pure helium and for example supercritical carbon dioxide.

[0063] The moderating material may be other than graphite and for example beryllium oxide or lithium fluoride.

[0064] The absorbent material may be different from that mentioned and comprise 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.

[0065] The control bar may comprise a set of absorbent pieces hinged together. This hinged assembly ensures that the bar will be able to make its way into the hole in the central housing of the body even if the latter becomes misaligned.

[0066] The reinforcing frame may have any prismatic or non-prismatic shape; it may also be omitted if the wall of the envelope 11 has a sufficient thickness to withstand the stresses exerted on the envelope 11.

[0067] The valves can be replaced by plugs.

[0068] The reactor may comprise one or more internal vessels, devoid of nuclear fuel, comprising a central body made of moderating material whose role is to regulate the temperature of the reactor.

[0069] The inner vessels are preferably designed to be easily transported or stored in existing fuel packaging used for pressurized water reactors.

[0070] 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.

[0071] The invention can also be used to produce electricity either as a primary source or as a supplement to heat production. In this case, it is sufficient to add a turbine.

[0072] One or more overpressure release valves may be provided on the concrete enclosure, in particular for chamber 111.

[0073] The invention can further be used to supply heat to a process for producing hydrogen by implementing an iodine-sulfur cycle.

[0074] The primary and secondary circuits can be arranged differently, as can the input and output ports which can be located at two opposite points of the enclosure.

[0075] 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

Claims

1. Vessel (10) for a nuclear reactor comprising a casing (11) made of a 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 a moderating material comprising at least a first channel (16.2) for the passage of the heat transfer fluid and second channels (16.3) closed at their two ends forming housings each containing nuclear fuel.

2. A vessel (10) according to claim 1, wherein the nuclear fuel is in the form of cores individually surrounded by at least one confinement layer to form balls disposed in the second channels.

3. Tank (10) according to claim 1 or 2, in which the casing (11) is surmounted by a sheath (20) receiving a control rod (21) sliding between a first extreme position in which the control rod (21) extends mainly in a housing (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) comprising a neutron absorber.

4. Tank (10) according to claim 3, in which the control bar (21) is connected to an actuator (23) arranged to move the control bar (21) between its two extreme positions.

5. Tank (10) according to claim 4, 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) towards its first extreme position by unwinding the cable (24) with the aid of gravity and towards its second extreme position by winding the cable (24) against gravity.

6. A tank (10) according to claim 5, wherein the actuator (23) comprises a clutch (25) electrically powered in an activated state allowing the cable (24) to be wound in such a way that, in the absence of electrical power, the clutch (25) is inactivated and releases the cable (24) to be paid out.

7. Tank (10) according to claim 6, in which the control bar (21) comprises a free end provided with a shock absorber (22) and / or the actuator (23) comprises a de- emptying of the cable (24), the limiter (26) being arranged to be active in the absence of electrical power to the actuator (23).

8. Tank (10) according to any one of claims 3 to 7, comprising 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.

9.

10. A vessel according to claim 1, a nuclear fuel vacuum. A vessel (10) according to any preceding claim, wherein the neutron-transparent material is a zirconium alloy.

11. Tank (10) according to any one of the preceding claims, in which the inlet port (12) and the outlet port (13) are coaxial with each other, a peripheral circulation space (14') being left between the central body (15) and the casing (11).

12. Nuclear reactor comprising an external vessel (2) containing a base (3) made of moderating material defining a plurality of housings (5) each receiving an internal vessel formed from a vessel (10) according to any one of claims 1 to 8.

13. Reactor according to claim 12, in which the housings (5) of the base (3) are delimited by a wall covered with a sheet (6) of material transparent to neutrons.

14. A reactor according to claim 12 or 13, wherein the outer vessel (2) has an inner wall covered with a neutron absorption layer (4).

15. Reactor according to any one of claims 12 to 14, comprising an anti-seismic base (120) supporting the external tank (2) and delimiting a maintenance chamber (130) into which the inlet and outlet ports (12, 13) of each internal tank (10) open, which are connected to a primary circuit (140) for transporting heat transfer fluid.

16. Reactor according to claim 15, in which the external vessel (2) has a bottom covered with a radiation protection layer (30) preventing the passage of neutrons towards the maintenance chamber (130).

17. Reactor according to claim 15 or 16, 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.

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