Nuclear reactor shutdown system and method

Abstract

To provide a nuclear reactor shutdown system and nuclear reactor shutdown method for emergency shutdown, which are applicable to small reactors while maintaining safety and speed.SOLUTION: A nuclear reactor shutdown system is provided, comprising: a storage container disposed above reactor core fuels stored in a reactor vessel in a sealed condition, configured to accommodate multiple neutron absorbers, and provided with an opening configured to allow the neutron absorbers to pass at the bottom; a shielded passage extending vertically through between the reactor core fuels such that an upper end thereof is in communication with the opening and a lower end is closed; and a communication unit disposed to plug the opening so as to bring the storage container into communication with the shielded passage when the temperature rises to a threshold temperature or above.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a reactor shutdown system and a method for shutting down a nuclear reactor. [Background technology]

[0002] In a nuclear power generation system that uses nuclear fuel and generates power by utilizing the heat of nuclear reaction, the heat generated in the reactor is recovered in a primary cooling system in which a primary coolant circulates between the reactor and a secondary cooling system, heat is exchanged between the primary coolant and the secondary coolant, and a turbine provided in the secondary cooling system is rotated by the energy of the secondary coolant to generate power. Such nuclear power facilities are equipped with a system for stopping the nuclear reaction of the reactor in an emergency. For example, Patent Document 1 discloses a fuel assembly that contains a control element pin including a neutron absorber fixed to the upper part by a stopper that melts when the reactor power is increased. In a nuclear reactor equipped with such a fuel assembly, when the reactor power is increased, the stopper melts and the neutron absorber falls between the fuel parts to stop the reactor. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 62-47585 Summary of the Invention [Problem to be solved by the invention]

[0004] In recent years, facilities using relatively small nuclear reactors have been considered as power generation facilities using nuclear reactors, and for example, microreactors have been proposed that do not have a primary cooling system through which primary coolant circulates, but have a heat conduction section that transfers heat inside the reactor vessel to the outside by solid thermal conduction. When using such small nuclear reactors, it may be difficult to apply conventional reactor shutdown systems as they are.

[0005] The present disclosure is devised to solve the above-mentioned problems, and aims to provide a reactor shutdown system and a reactor shutdown method for emergency shutdown that are applicable to small reactors while maintaining safety and speed. [Means for solving the problem]

[0006] In order to achieve the above-mentioned objective, a reactor shutdown system according to one embodiment of the present disclosure comprises a containment vessel arranged above core fuel stored in a sealed state in the reactor vessel, containing a plurality of neutron absorbing materials and having an opening at a bottom through which the neutron absorbing materials can pass, a shielding passage extending in a vertical direction through the core fuel, with an upper end communicating with the opening of the containment vessel and a lower end closed, and a communication portion arranged to block the opening and connecting the containment vessel and the shielding passage when the temperature reaches or exceeds a threshold temperature.

[0007] In order to achieve the above-mentioned object, a reactor shutdown method according to one embodiment of the present disclosure includes a containment vessel that is positioned above core fuel stored in a sealed state in a reactor vessel, contains a plurality of neutron absorbing materials, and has an opening at its bottom through which the neutron absorbing materials can pass; a shielded passage that extends in a vertical direction through the core fuel, with its upper end communicating with the opening of the containment vessel and its lower end being closed; and a communication part that is positioned to block the opening and connects the containment vessel to the shielded passage when a threshold temperature is reached or higher, wherein when the communication part reaches or higher than the threshold temperature, the containment vessel is connected to the shielded passage, so that the plurality of neutron absorbing materials stored in the containment vessel fall through the opening into the shielded passage. Effect of the Invention

[0008] According to the present disclosure, it is possible to obtain the effect of being applicable to small nuclear reactors while maintaining safety and speed. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic diagram showing a schematic configuration of a nuclear power generation system according to this embodiment. [Diagram 2]FIG. 2 is a schematic diagram showing a schematic configuration of a reactor shutdown system according to this embodiment. [Diagram 3] FIG. 3 is a schematic diagram showing a state in which the reactor shutdown system shown in FIG. 2 is activated. [Figure 4] FIG. 4 is a schematic diagram showing another example of a reactor shutdown system. [Diagram 5] FIG. 5 is a schematic diagram showing another example of a reactor shutdown system. [Figure 6] FIG. 6 is a schematic diagram showing another example of a reactor shutdown system.

[0010] (Embodiment) Hereinafter, the embodiments according to the present disclosure will be described in detail with reference to the drawings. Note that the present invention is not limited to these embodiments. In addition, the components in the following embodiments include those that are replaceable and easy for a person skilled in the art, those that are substantially the same, or those that are equivalent. Furthermore, the components in the following embodiments can be omitted, replaced, or modified in various ways without departing from the gist of the present disclosure. In the following embodiments, the components necessary for illustrating the embodiments will be described, and other components will be omitted, and the same components will be given the same reference numerals, and different components will be given different reference numerals.

[0011] FIG. 1 is a schematic diagram showing a schematic configuration of a nuclear power generation system according to the present embodiment. The nuclear power facility shown in FIG. 1 will be described as a nuclear power generation system that uses heat generated in a nuclear reactor to generate power, but the present disclosure is not limited thereto. The nuclear power generation system can also be applied to a facility that uses heat generated in a nuclear reactor for purposes other than power generation. The nuclear power generation system can also be used as a facility that produces radioactive materials using radiation generated in a nuclear reactor. The nuclear power generation system 10 shown in FIG. 1 includes a nuclear reactor unit 12 and a power generation unit 13. The power generation unit 13 includes a refrigerant circulation means 16, a turbine 18, a generator 20, a cooler 22, a compressor 24, and a regenerative heat exchanger 26.

[0012] The reactor unit 12 includes a reactor 30, a heat conduction section 32, and a reactor shutdown system 50. The reactor 30 includes a reactor vessel 40, a fuel core 42, and a control unit 44. The fuel core 42 is stored inside the reactor vessel 40. The fuel core 42 is stored in the reactor vessel 40 in a sealed state. The reactor vessel 40 is provided with an opening and closing section so that the fuel core 42 placed inside can be inserted and removed. The opening and closing section is, for example, a lid. The reactor vessel 40 can maintain a sealed state even when a nuclear reaction occurs inside the reactor vessel 40 and the inside becomes hot and high pressure. The reactor vessel 40 is formed of a material having a neutron radiation shielding performance, and is formed with a thickness that does not allow neutron radiation generated inside to leak to the outside. The reactor vessel 40 is formed of, for example, concrete. The reactor vessel 40 may contain a highly shielding element such as boron.

[0013] The core fuel 42 includes a plurality of fuel holding plates 43. A plurality of nuclear fuels are arranged inside the fuel holding plates 43. The fuel holding plates 43 are formed of a material that transfers heat generated by the nuclear fuel. The fuel holding plates 43 may be made of graphite, silicon carbide, or the like. The core fuel 42 generates reaction heat as the nuclear fuel undergoes a nuclear reaction.

[0014] The control unit 44 has movable shielding materials between the core fuel 42. The shielding materials are so-called control rods that have the function of blocking radiation and suppressing nuclear reactions. The reactor 30 controls the reaction of the core fuel 42 by moving the control unit 44 and adjusting the position of the shielding materials.

[0015] 1, the heat conductive portion 32 is disposed inside the reactor vessel 40 and is in contact with the fuel holding plate 43. The heat conductive portion 32 in this embodiment has a multiple plate shape and is structured to be alternately stacked with the fuel holding plate 43. The heat conductive portion 32 is a plate having an outer shape larger than the fuel holding plate 43 and protrudes into an area where the fuel holding plate 43 is not disposed. Here, the heat conductive portion 32 may be made of, for example, titanium, nickel, copper, graphite, or graphene.

[0016] In order to increase the efficiency of heat transfer to the protruding portion, the heat conductive portion 32 preferably uses graphene oriented in a direction that facilitates heat transfer along the surface of the plate. The heat conductive portion 32 transfers heat by solid thermal conduction. In other words, the heat conductive portion 32 transfers heat without using a heat medium (fluid). Specifically, the heat conductive portion 32 transfers heat generated in the core fuel 42 to the power generation unit 13 by solid thermal conduction.

[0017] In the reactor unit 12, a nuclear reaction occurs in the core fuel 42 inside the reactor 30, generating reaction heat. The generated heat is stored inside the reactor vessel 40, causing the inside to become hot. In the reactor unit 12, a part of the heat generated in the reactor 30 is transferred to the heat conduction section 32. The heat conduction section 32 heats the coolant flowing in the coolant circulation means 16 of the power generation unit 13. Here, it is preferable to use carbon dioxide (CO2) as the coolant.

[0018] The reactor shutdown system 50 is a system for emergency stopping a nuclear reaction in the core fuel 42. A detailed configuration of the reactor shutdown system 50 according to the embodiment will be described later.

[0019] The coolant circulation means 16 has a circulation path 34 that circulates outside the reactor vessel 40 and a heat exchanger 36 that circulates inside the reactor vessel 40. In the coolant circulation means 16, the circulation path 34 and the heat exchanger 36 form a closed loop, and the coolant is circulated. The circulation path 34 is a path that circulates the coolant outside the reactor vessel 40, and is connected to the turbine 18, the cooler 22, the compressor 24, and the regenerative heat exchanger 26. The heat exchanger 36 is inserted into the reactor vessel 40 and disposed inside. Both ends of the heat exchanger 36 are exposed to the outside of the reactor vessel 40 and connected to the circulation path 34. The heat exchanger 36 is a pipe through which the coolant flows, and is in contact with an area of ​​the heat conduction part 32 that is not in contact with the core fuel 42. In other words, the heat exchanger 36 is in contact with a part of the heat conduction part 32 that protrudes beyond the core fuel 42. The heat exchange section 36 exchanges heat with the heat conduction section 32 and heats the refrigerant.

[0020] The refrigerant flowing through the refrigerant circulation means 16 is supplied to the heat exchange section 36. The nuclear power generation system 10 exchanges heat between the heat conduction section 32 and the refrigerant supplied from the refrigerant circulation means 16. The heat exchanger of this embodiment is composed of the heat conduction section 32 and the heat exchange section 36 of the refrigerant circulation means 16. The heat exchanger recovers heat from the heat conduction section 32 by the refrigerant flowing through the refrigerant circulation means 16. That is, the refrigerant is heated in the heat conduction section 32. The heat medium heated in the heat exchange section 36 flows through the turbine 18, the cooler 22, the compressor 24, and the regenerative heat exchanger 26 in this order. The refrigerant that has passed through the regenerative heat exchanger 26 is supplied to the heat exchange section 36 again. In this manner, the refrigerant is circulated through the refrigerant circulation means 16.

[0021] The refrigerant that has passed through the heat conductive portion 32 flows into the turbine 18. The turbine 18 is rotated by the energy of the heated refrigerant. In other words, the turbine 18 converts the energy of the refrigerant into rotational energy and absorbs energy from the refrigerant. The generator 20 is connected to the turbine 18 and rotates integrally with the turbine 18. The generator 20 generates electricity by rotating together with the turbine 18.

[0022] The cooler 22 cools the refrigerant that has passed through the turbine 18. The cooler 22 is a chiller or a condenser in the case of temporarily liquefying the refrigerant. The compressor 24 is a pump that pressurizes the refrigerant. The regenerative heat exchanger 26 exchanges heat between the refrigerant that has passed through the turbine 18 and the refrigerant that has passed through the compressor 24. The regenerative heat exchanger 26 heats the refrigerant that has passed through the compressor 24 with the refrigerant that has passed through the turbine 18. In other words, the regenerative heat exchanger 26 exchanges heat between the refrigerant before being cooled by the cooler 22 and the refrigerant after being cooled by the cooler 22, and recovers the heat that is discarded by the cooler 22 with the refrigerant before being supplied to the reactor unit 12.

[0023] In the nuclear power generation system 10, the heat generated by the reaction of the nuclear fuel in the reactor unit 12 is transferred to the refrigerant in the heat exchange unit 36 ​​by the heat transfer unit 32, and the refrigerant flowing through the refrigerant circulation means 16 is heated by the heat transfer unit 32. In other words, the refrigerant absorbs the heat transferred by the heat transfer unit 32. As a result, the heat generated in the reactor unit 12 is transferred by the heat transfer unit 32 through solid thermal conduction and is recovered by the refrigerant. After being compressed by the compressor 24, the refrigerant is heated while passing through the heat transfer unit 32, and the compressed energy is used to rotate the turbine 18. The refrigerant is then cooled to a reference state by the cooler 22 and supplied to the compressor 24 again.

[0024] As described above, the nuclear power generation system 10 transfers heat from the nuclear reactor 30 to the coolant that serves as the medium for rotating the turbine 18 by using the heat transfer section 32 that transfers heat by solid thermal conduction.

[0025] The nuclear power generation system 10 uses carbon dioxide as a refrigerant, thereby making it possible to suppress contamination of the refrigerant even when the refrigerant is circulated inside the nuclear reactor 30. This makes it possible to reduce the risk of contamination of the medium rotating the turbine 18. In addition, by providing the heat conductive section 32 that transfers heat by solid thermal conduction, the heat conductive section 2 can block neutron radiation.

[0026] Moreover, the reactor vessel 40 is preferably formed of a material having a lower thermal conductivity than the thermal conductive portion 32. This makes it possible to prevent the heat in the reactor 30 from being discharged to the outside from portions other than the thermal conductive portion 32, which is a path for discharging the heat to the outside.

[0027] Fig. 2 is a schematic diagram showing the outline of the reactor shutdown system according to this embodiment. Fig. 3 is a schematic diagram showing the reactor shutdown system shown in Fig. 2 in an activated state. The reactor shutdown system 50 includes a neutron absorbing material 60, a containment vessel 52, a shielding passage 54, and a communication section 56.

[0028] The neutron absorber 60 is a substance that absorbs neutrons and contains, for example, boron (B), cadmium (Cd), xenon (Xe), hafnium (Hf), etc. In the embodiment, the neutron absorber 60 is a plurality of solid spheres, but the shape of each is not particularly limited as long as it can be moved in small pieces, and may include, for example, an ellipsoid or a rod. In addition, it is not limited to a solid, and may include a gel, liquid, or gas, but is preferably a solid sphere. As shown in FIG. 3, the neutron absorber 60 can be introduced into the core to reduce the neutrons absorbed by the nuclear fuel, suppress the nuclear reaction, or shut down the nuclear reactor 30.

[0029] The storage vessel 52 is disposed above the core fuel 42. The storage vessel 52 stores a plurality of neutron absorbers 60. The storage vessel 52 has an opening 52a at the bottom. The opening 52a has a diameter at least larger than that of the neutron absorbers 60, and allows the neutron absorbers 60 to pass through. The opening 52a in the embodiment is located at the center of the storage vessel 52 in the horizontal direction. The storage vessel 52 in the embodiment has a tapered inclined inner wall 52b that gradually becomes narrower toward the opening 52a.

[0030] The shielding passage 54 is a passage extending vertically through the core fuel 42. The upper end of the shielding passage 54 communicates with an opening 52a at the bottom of the containment vessel 52. The lower end of the shielding passage 54 is closed. As shown in Fig. 3, the shielding passage 54 is capable of containing the neutron absorbing material 60 that has fallen through the opening 52a of the containment vessel 52. The shielding passage 54 in the embodiment is formed to extend vertically in the center of the core.

[0031] The communication part 56 is arranged to close the opening 52a at the bottom of the containment vessel 52, as shown in Fig. 2. When the temperature is lower than a predetermined threshold temperature, the communication part 56 maintains the opening 52a sealed, as shown in Fig. 2. When the temperature reaches or exceeds the threshold temperature, the communication part 56 opens the opening 52a, as shown in Fig. 3. The communication part 56 is formed, for example, from a material that melts or changes in quality at or above the threshold temperature. The communication part 56 is formed from a material whose melting point is equal to or higher than the temperature during rated operation of the reactor vessel 40. The communication part 56 is formed, for example, from a metal such as brass.

[0032] The communicating part 56 may be, for example, in a plate shape that melts at or above the threshold temperature, develops a hole, or changes in quality, and separates from the opening 52a. The communicating part 56 may include, for example, an outer peripheral part that is fixed along the periphery of the opening 52a, and a plate-shaped inner peripheral part that melts at or above the threshold temperature, develops a hole, or changes in quality, and separates from the outer peripheral part. The communicating part 56 may be, for example, at least the outer peripheral part that changes at or above the threshold temperature, and separates from the opening 52a. The communicating part 56 may include, for example, a valve body that opens at or above the threshold temperature.

[0033] In the reactor shutdown system 50, the temperature of the communication part 56 is maintained lower than the threshold temperature during rated operation of the reactor 30. In this state, the communication part 56 closes the opening 52a of the containment vessel 52, so that the neutron absorbing material 60 is maintained in the inside of the containment vessel 52.

[0034] When an abnormality occurs in the reactor 30, the temperature inside the reactor vessel 40 rises, and the temperature of the communication part 56 reaches or exceeds a threshold temperature, the reactor shutdown system 50 causes the communication part 56 to open the opening 52a of the containment vessel 52, as shown in Fig. 3. When the opening 52a is released, the neutron absorber 60 in the containment vessel 52 that has been held by the communication part 56 falls into the shielded passage 54 through the opening 52a.

[0035] The neutron absorbing material 60 that falls inside the shielding passage 54, i.e., that reaches the inside of the reactor core, absorbs neutrons from the reactor core and suppresses the nuclear reaction of the core fuel 42. The shielding passage 54 is filled with neutron absorbing materials 60 one after another, and the nuclear reaction of the core fuel 42 is stopped as the multiple neutron absorbing materials 60 absorb the neutrons from the reactor core.

[0036] In the reactor shutdown system 50 of the embodiment, the containment vessel 52 has an inclined inner wall 52b toward the opening 52a, and the neutron absorber 60 is a solid sphere, so that the neutron absorber 60 can roll along the inclined inner wall 52b. This makes it possible to prevent the neutron absorber 60 from clogging the opening 52a when the multiple neutron absorbers 60 drop one after another from the opening 52a.

[0037] Fig. 4 is a schematic diagram showing another example of a reactor shutdown system. A reactor shutdown system 50a shown in Fig. 4 differs from the reactor shutdown system 50 shown in Fig. 2 and Fig. 3 in that it includes a plurality of sets (three sets in the example shown in Fig. 4) of a containment vessel 52, a shielded passage 54, and a communication part 56. Each of the containment vessels 52, the shielded passage 54, and the communication part 56 has the same configuration as each part of the reactor shutdown system 50, and therefore detailed description thereof will be omitted.

[0038] The respective containment vessels 52 are arranged side by side in the horizontal direction above the core fuel 42. Each containment vessel 52 contains neutron absorbing material 60. The respective shielding passages 54 are arranged side by side in the horizontal direction so as to pass between the core fuel 42. At the boundary between the opening 52a of each containment vessel 52 and the upper end of the shielding passage 54, one communication part 56 is arranged.

[0039] The reactor shutdown system 50a maintains the temperature of each communication part 56 lower than the threshold temperature during rated operation of the reactor 30 (see FIG. 1). In this state, each communication part 56 closes the opening 52a of each containment vessel 52, so that the neutron absorbing material 60 is maintained in the inside of each containment vessel 52.

[0040] When an abnormality occurs in the reactor 30 (see FIG. 1), the temperature inside the reactor vessel 40 (see FIG. 1) rises, and the temperature of any of the communication parts 56 reaches or exceeds a threshold temperature, the communication part 56 whose temperature has reached or exceeded the threshold temperature opens the opening 52a of the corresponding containment vessel 52. When the opening 52a is released, the neutron absorbing material 60 in the containment vessel 52 that was held by the communication part 56 falls through the opening 52a into the shielded passage 54.

[0041] When each of the multiple communication parts 56 reaches or exceeds a threshold temperature, it opens the opening 52a of the corresponding containment vessel 52. When the corresponding opening 52a is released and the neutron absorbing material 60 falls into the shielding passage 54, i.e., reaches the inside of the core, it absorbs neutrons from the core and suppresses the nuclear reaction of the core fuel 42. Each shielding passage 54 is filled with neutron absorbing material 60 one after another, and the nuclear reaction of the core fuel 42 is stopped by the multiple neutron absorbing materials 60 absorbing the neutrons from the core.

[0042] In this manner, in the reactor shutdown system 50a, by opening the opening 52a of the corresponding containment vessel 52 through at least any of the communication parts 56, the neutron absorber 60 contained in at least any of the containment vessels 52 falls into the corresponding shielding passage 54. That is, even if any of the communication parts 56 malfunctions and does not open the opening 52a, or if the neutron absorber 60 becomes clogged in the opening 52a, the reactor shutdown system 50a can introduce the neutron absorber 60 between the core fuel 42 from another containment vessel 52.

[0043] 4 includes three sets of containment vessels 52, shielding passages 54, and communication parts 56, but may include two sets, four sets, or more. The shapes and sizes of the containment vessels 52, shielding passages 54, and communication parts 56 do not all need to be the same. For example, the shielding passage 54 located in the horizontal center of the core fuel 42 may be made wider than the surrounding shielding passages 54.

[0044] Fig. 5 is a schematic diagram showing another example of a reactor shutdown system. A reactor shutdown system 50b shown in Fig. 5 differs from the reactor shutdown system 50 shown in Fig. 2 and Fig. 3 in that a containment vessel 53 is provided instead of the containment vessel 52, a shielded passage 54 includes a plurality of shielded passages 54a, 54b, and 54b (three in the example shown in Fig. 5), and a plurality of communication parts 56 are provided (three in the example shown in Fig. 5).

[0045] 2 and 3, detailed description of the similar configuration will be omitted. The storage vessel 53 has a plurality of openings 53a (three in the example shown in FIG. 5) at the bottom. Each opening 53a has a diameter at least larger than the neutron absorber 60, and the neutron absorber 60 can pass through it. One opening 53a is located at the center of the storage vessel 53 in the horizontal direction, and the other two openings 53a are located near the outer periphery of the storage vessel 52. The storage vessel 53 has a tapered inclined inner wall 53b that gradually becomes narrower toward each opening 53a.

[0046] The shielded passage 54 includes a shielded passage 54a and a shielded passage 54b. The shielded passage 54a is a passage that extends vertically through the center of the core fuel 42. The upper end of the shielded passage 54a is connected to an opening 53a disposed in the center of the bottom of the containment vessel 53. The lower end of the shielded passage 54a is closed. The shielded passage 54a can contain the neutron absorber 60 that has fallen through the opening 53a disposed in the center of the containment vessel 53.

[0047] The shielded passage 54b is a passage that extends vertically through a portion of the core fuel 42 that is horizontally spaced from the center thereof. The upper end of the shielded passage 54b is connected to an opening 53a disposed near the outer periphery of the bottom of the containment vessel 53. The upper end of the shielded passage 54b is bent inwardly and upwardly. The lower end of the shielded passage 54b is closed. The shielded passage 54b is capable of containing the neutron absorber 60 that has fallen through the opening 53a disposed near the outer periphery of the containment vessel 53.

[0048] 2 and 3, the communication part 57 will be described below in terms of its different configuration from the communication part 56 shown in FIG. 2 and FIG. 3, and detailed description of the similar configuration will be omitted. The communication part 57 is arranged so as to close the opening 53a of the storage container 53. One communication part 56 is arranged in each opening 53a. When the temperature is lower than a predetermined threshold temperature, the communication part 57 keeps the corresponding opening 53a sealed. When the temperature is equal to or higher than the threshold temperature, the communication part 57 opens the corresponding opening 53a.

[0049] The reactor shutdown system 50b maintains the temperature of each communication part 57 lower than the threshold temperature during rated operation of the reactor 30 (see FIG. 1). In this state, each communication part 57 closes each opening 53a of the containment vessel 53, so that the neutron absorbing material 60 is maintained in the inside of the containment vessel 53.

[0050] When an abnormality occurs in the reactor 30 (see FIG. 1), the temperature inside the reactor vessel 40 (see FIG. 1) rises, and the temperature of any of the communication parts 57 reaches or exceeds a threshold temperature, the communication part 57 whose temperature has reached or exceeded the threshold temperature opens the corresponding opening 53a of the containment vessel 53. When any of the openings 53a is opened, the neutron absorbing material 60 in the containment vessel 52 that was held by the communication part 57 falls through the opened opening 53a into the shielded passages 54a, 54b.

[0051] When each of the multiple communication parts 57 reaches or exceeds a threshold temperature, it opens the corresponding opening 53a of the containment vessel 53. When the corresponding opening 53a is released and the neutron absorbing material 60 falls into the shielding passages 54a, 54b, i.e., reaches the inside of the core, it absorbs neutrons from the core and suppresses the nuclear reaction of the core fuel 42. Each of the shielding passages 54a, 54b is filled with neutron absorbing material 60 one after another, and the nuclear reaction of the core fuel 42 is stopped by the multiple neutron absorbing materials 60 absorbing the neutrons from the core.

[0052] In this manner, in the reactor shutdown system 50b, by at least any of the communication parts 57 opening the corresponding opening 53a, the neutron absorber 60 contained in the containment vessel 53 falls into the shielded passage 54 corresponding to the opened opening 53a. That is, even if any of the communication parts 57 malfunctions and does not open the opening 53a, or if the neutron absorber 60 gets stuck in the opening 53a, the reactor shutdown system 50b can introduce the neutron absorber 60 between the core fuel 42 from the other openings 53a.

[0053] 5 includes three sets of shielding passages 54 and communication parts 57, but may include two sets, or may include four or more sets. The shapes and sizes of the shielding passages 54 and communication parts 57 do not all need to be the same. For example, the shielding passage 54a located in the horizontal center of the core fuel 42 may be made wider than the surrounding shielding passages 54b.

[0054] Fig. 6 is a schematic diagram showing another example of a reactor shutdown system. A reactor shutdown system 50c shown in Fig. 6 further includes a heating unit 58 and a control unit 70 in addition to the components of the reactor shutdown system 50 shown in Fig. 2 and Fig. 3. The heating unit 58 and the control unit 70, which are components unique to the reactor shutdown system 50c, will be described below, and detailed descriptions of components similar to those of the reactor shutdown system 50 will be omitted.

[0055] The heating unit 58 is capable of heating the communication part 56 to a temperature equal to or higher than a threshold temperature based on a control signal received from the control part 70. The configuration and heating method of the heating unit 58 are not particularly limited, and for example, the communication part 56 may be heated by directly passing an electric current through it, or may be heated by heat radiation from a heat source that heats by passing an electric current through it.

[0056] The control unit 70 sends a control signal to the heating unit 58 to heat the communication unit 56. The control unit 70 may send a control signal to heat the communication unit 56 when a predetermined operation by an operator is received. When any abnormality is detected, the control unit 70 may send a control signal to heat the communication unit 56 based on a predetermined judgment criterion. The control unit 70 may be provided as a part of a function of a control system that controls the operation of the reactor unit 12, or may be provided as a part of a function of an auxiliary power system that cooperates with the reactor unit 12 or the nuclear power generation system 10, for example, when an abnormality occurs.

[0057] (Effects of the embodiment) The reactor shutdown systems 50, 50a, 50b, and 50c and the reactor shutdown methods according to the embodiments can be understood, for example, as follows.

[0058] The reactor shutdown system 50, 50a, 50b, 50c of the first embodiment is arranged above the core fuel 42 stored in a sealed state in the reactor vessel 40, and comprises a storage vessel 52, 53 which stores a plurality of neutron absorbers 60 and has openings 52a, 53a at the bottom through which the neutron absorbers 60 can pass, shielded passages 54, 54a, 54b which extend in the vertical direction through the core fuel 42 and have upper ends which communicate with the openings 52a, 53a of the storage vessels 52, 53 and lower ends which are closed, and communication parts 56, 57 which are arranged to block the openings 52a, 53a and which communicate between the storage vessels 52, 53 and the shielded passages 54, 54a, 54b when the temperature reaches or exceeds a threshold temperature.

[0059] The reactor shutdown system 50, 50a, 50b, 50c according to the first aspect releases the retention of the neutron absorbing material 60 when the communicating parts 56, 57 that retain the neutron absorbing material 60 reach or exceed a threshold temperature in association with a temperature rise in the reactor vessel 40 in the event of an abnormality. That is, without requiring a special control function, the neutron absorbing material 60 falls between the core fuel 42 when the communicating parts 56, 57 reach or exceed a threshold temperature, so that the nuclear reaction can be passively suppressed and the function can be stopped safely and quickly in the event of an abnormal temperature rise in the reactor vessel 40. In addition, since the neutron absorbing material 60 is not a single substance but a plurality of substances that can pass through the openings 52a, 53a, there is a degree of freedom in the overall shape when it is retained by the communicating parts 56, 57. That is, there is a degree of freedom in the shape of the container 52 that contains the neutron absorbing material 60, and the longitudinal direction (the direction in which the neutron absorbing material 60 is introduced into the core fuel 42) can be shortened, making it applicable to small nuclear reactors.

[0060] The reactor shutdown systems 50, 50a, 50b, 50c according to the second aspect are provided in a reactor unit 12 including a reactor 30 including a fuel core 42 and a reactor vessel 40, and a heat conduction part 32 arranged inside the reactor vessel 40 and transmitting heat of the fuel core 42 by solid-state heat conduction. The reactor shutdown systems 50, 50a, 50b, 50c do not require a special control function, and can realize a configuration in which the neutron absorber 60 falls between the fuel core 42 when the communication control parts 56, 57 reach or exceed a threshold temperature, and therefore can also be applied to the reactor unit 12 that transmits heat of the fuel core 42 by solid-state heat conduction.

[0061] In the reactor shutdown system 50, 50a, 50b, 50c according to the third embodiment, the communication parts 56, 57 are formed of a material that melts or changes its quality at or above a threshold temperature. Such communication parts 56, 57 melt and form holes or change their quality at or above the threshold temperature, and are separated from the outer periphery. This allows a simple configuration to be realized for opening the openings 52a, 53a of the containment vessels 52, 53 when the communication parts 56, 57 reach or exceed the threshold temperature.

[0062] In the reactor shutdown system 50, 50a, 50b, 50c according to the fourth embodiment, the containment vessel 52, 53 has a tapered inclined inner wall 52b, 53b that gradually narrows toward the opening 52a, 53a. When the opening 52a, 53a of the containment vessel 52, 53 is opened and the neutron absorber 60 falls one after another from the opening 52a, 53a, the neutron absorber 60 in the containment vessel 52, 53 slides or rolls on the inclined inner wall 52b, 53b, so that it is possible to prevent the neutron absorber 60 from remaining in the containment vessel 52, 53 or clogging the opening 52a, 53a.

[0063] In the reactor shutdown system 50, 50a, 50b, 50c according to the fifth aspect, the neutron absorber 60 is a solid sphere. This allows the neutron absorber 60 to roll on the bottom of the storage vessel 52, 53, so that when the openings 52a, 53a of the storage vessel 52, 53 are opened and the neutron absorber 60 falls from the openings 52a, 53a one after another, clogging at the openings 52a, 53a can be suppressed.

[0064] The reactor shutdown system 50a according to the sixth aspect includes a plurality of containment vessels 52, shielding passages 54, and communication parts 56. Therefore, when at least any of the communication parts 56 opens the opening 52a of the corresponding containment vessel 52, the neutron absorber 60 contained in at least any of the containment vessels 52 falls into the corresponding shielding passage 54. That is, even if any of the communication parts 56 malfunctions and does not open the opening 52a, or if the neutron absorber 60 gets stuck in the opening 52a, it is possible to introduce the neutron absorber 60 between the core fuel 42 from another containment vessel 52.

[0065] In the reactor shutdown system 50b according to the seventh aspect, the containment vessel 53 has a plurality of openings 53a, a plurality of shielding passages 54, 54a, 54b are arranged so as to communicate with the plurality of openings 53a, and a plurality of communication parts 57 are provided according to the openings 53a. Therefore, when at least one of the communication parts 57 opens the corresponding opening 53a, the neutron absorber 60 contained in the containment vessel 53 falls into the shielding passage 54, 54a, 54b corresponding to the opened opening 53a. That is, even if any of the communication parts 57 malfunctions and does not open the opening 53a, or if the neutron absorber 60 gets stuck in the opening 53a, it is possible to introduce the neutron absorber 60 between the core fuel 42 from the other openings 53a.

[0066] The reactor shutdown system 50c according to the eighth aspect further includes a heating unit 58 capable of heating the communication part 56 to a threshold temperature or higher, and a control part 70 that sends a control signal to the heating unit 58 to heat the communication part 56. That is, even in a state in which the communication part 56 has not risen to the threshold temperature during an abnormality, if a further temperature rise in the reactor vessel 40 is predicted or if another abnormality is detected, the nuclear reaction can be suppressed by an active method as well, and the system can be shut down safely and quickly.

[0067] The reactor shutdown method according to the ninth aspect includes: a containment vessel 52, 53 that is disposed above a fuel core 42 that is stored in a hermetically sealed state in a reactor vessel 40, contains a plurality of neutron absorbing materials 60, and has openings 52a, 53a at the bottom through which the neutron absorbing materials 60 can pass; shielding passages 54, 54a, 54b that extend vertically through the fuel core 42, communicate at their upper ends with the openings 52a, 53a of the containment vessels 52, 53, and are closed at their lower ends; and communication sections 56, 57 which are arranged to block the openings and which connect the storage containers 52, 53 to the shielded passages 54, 54a, 54b when the temperature reaches or exceeds a threshold temperature.When the communication sections 56, 57 reach or exceed the threshold temperature, the storage containers 52, 53 communicate with the shielded passages 54, 54a, 54b, causing the multiple neutron absorbing materials 60 contained in the storage containers 52, 53 to fall through the openings 52a, 53a into the shielded passages 54, 54a, 54b.

[0068] The reactor shutdown method according to the ninth aspect releases the retention of the neutron absorbing material 60 when the communicating parts 56, 57 that retain the neutron absorbing material 60 reach or exceed a threshold temperature due to a temperature rise in the reactor vessel 40 in the event of an abnormality. That is, without requiring a special control function, the neutron absorbing material 60 falls between the core fuel 42 when the communicating parts 56, 57 reach or exceed a threshold temperature, so that the nuclear reaction can be passively suppressed and the function can be stopped safely and quickly in the event of an abnormal temperature rise in the reactor vessel 40. In addition, since the neutron absorbing material 60 is not a single mass of material but a plurality of materials that can pass through the openings 52a, 53a, there is a degree of freedom in the overall shape in the state in which it is retained by the communicating parts 56, 57. That is, there is a degree of freedom in the shape of the container vessel 52 that retains the neutron absorbing material 60, and the container vessel 52 can be shortened in the longitudinal direction (the direction in which the neutron absorbing material 60 is introduced into the core fuel 42), so that the container vessel 52 can also be applied to a small-sized reactor.

[0069] Although the embodiments of the present disclosure have been described above, the embodiments are not limited to the contents of the description of these embodiments. [Explanation of symbols]

[0070] 10. Nuclear Power System 12 Reactor Unit 13 Power generating unit 14 Heat exchanger 16 Refrigerant circulation means 18 Turbine 20. Generator 22 Chiller 24 Pump (compressor) 26 Regenerative heat exchanger 30 nuclear reactor 32 Heat Conduction Section 34 Circulation Route 36 Heat exchange section 40 Reactor vessel 42 Core fuel 43 Fuel holding plate 44 Control Unit 50, 50a, 50b, 50c Reactor Shutdown System 52, 53 Storage container 52a, 53a opening 52b, 53b Slanted inner wall 54, 54a, 54b Shielded passage 56, 57 Communication part 58 Heating Unit 60 Neutron absorber 70 Control section

Claims

1. a containment vessel disposed above the core fuel stored in a sealed state in the reactor vessel, containing a plurality of neutron absorbing materials and having an opening at a bottom through which the neutron absorbing materials can pass; a shielding passage extending vertically through the core fuel, the upper end of which communicates with the opening of the containment vessel and the lower end of which is closed; a communication part that is arranged to close the opening and that communicates between the storage container and the shielded passage when the temperature reaches or exceeds a threshold temperature; A reactor shutdown system comprising:

2. a nuclear reactor including the fuel core and the reactor vessel; a heat conduction section disposed inside the reactor vessel and configured to transfer heat of the core fuel by solid-state heat conduction; The reactor shutdown system according to claim 1 , provided in a reactor unit comprising:

3. 3. The reactor shutdown system according to claim 1, wherein the communication portion is formed of a material that melts or changes in quality at a temperature equal to or higher than the threshold temperature.

4. 4. The reactor shutdown system according to claim 1, wherein the containment vessel has an inner wall that is tapered so as to become gradually narrower toward the opening.

5. 5. The reactor shutdown system according to claim 1, wherein the neutron absorbing material is a solid sphere.

6. The reactor shutdown system according to claim 1 , further comprising a plurality of sets of the containment vessel, the shielding passage, and the communication portion.

7. The container has a plurality of the openings, The shielding passages are arranged in a plurality of locations so as to communicate with the plurality of openings, respectively; The reactor shutdown system according to claim 1 , wherein a plurality of sets of the communication portions are provided corresponding to the openings.

8. a heating unit capable of heating the communication portion to a temperature equal to or higher than the threshold temperature; The reactor shutdown system according to claim 1 , further comprising: a control unit that sends a control signal to the heating unit to heat the communication portion.

9. a containment vessel disposed above the core fuel stored in a sealed state in the reactor vessel, containing a plurality of neutron absorbing materials and having an opening at a bottom through which the neutron absorbing materials can pass; a shielding passage extending vertically through the core fuel, the upper end of which communicates with the opening of the containment vessel and the lower end of which is closed; a communication part that is arranged to close the opening and that communicates between the storage container and the shielded passage when the temperature reaches or exceeds a threshold temperature, A method for shutting down a nuclear reactor, in which when the communication portion reaches or exceeds the threshold temperature, the containment vessel and the shielded passage become connected, causing the multiple neutron absorbing materials contained in the containment vessel to fall through the opening into the shielded passage.

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