Fast reactor and failed fuel detection device for fast reactor

Abstract

To provide a fast reactor which includes an instrument for measuring neutron and enables facilitation of inspection and replacement of the instrument even when the instrument is failed.SOLUTION: This fast reactor S100 comprises: a reactor core 20 which houses a nuclear fuel; a main container 10; a roof slab structure 11; and a neutron detection unit 40 which measures a neutron flux of a neutron originated from a failed fuel of the reactor core 20. The neutron detection unit 40 has: a neutron guide tube 41 which extends in a height direction of the main container 10 in such a manner that the lower end side of the tube 41 is positioned within the main container 10, and the top end side penetrates through the roof slab structure 11; a moderator 43 which is arranged within the neutron guide tube 41, and decelerates a speed of the neutron; a neutron detector 44 which measures the neutron flux of the decelerated neutron; and an absorbent material 42 which is arranged below the moderator 43 within the neutron guide tube 41, absorbs a thermal neutron, and causes a delayed neutron to transmit the absorbent material 42.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a fast reactor and a failed fuel detection system for a fast reactor. [Background technology]

[0002] In the unlikely event that the fuel in the core is damaged during reactor operation, it is necessary to immediately detect the damage and prevent the damage from spreading and other malfunctions from progressing, so that the safety and availability of the reactor are not significantly reduced. For this reason, in conventional liquid metal-cooled fast reactors, the DN (Delayed Neutron) method is used to detect fuel damage and the scale of the damage. This DN method uses a detector to detect delayed neutrons emitted from delayed neutron (DN) precursor nuclei that migrate into the sodium coolant when the fuel is damaged.

[0003] When using the DN method in a loop-type reactor, the coolant that directly touches the core is discharged outside the reactor vessel through the main cooling pipes, so the neutron detection point can be set up outside the reactor vessel where temperatures are low. On the other hand, in a tank-type reactor, the primary coolant does not flow out of the main vessel, so if a neutron detector is to be installed outside the main vessel to avoid the high temperatures inside the main vessel, it is necessary to draw the sodium coolant out of the main vessel for sampling. When sampling in this way, there is the problem that it takes time to measure, making it difficult to perform efficient measurements.

[0004] On the other hand, even for a tank-type reactor, a technique has been proposed for measuring neutron flux without sampling outside the main vessel (for example, Patent Document 1). In this configuration, a hollow cylinder that allows neutrons to pass through is provided inside the main vessel, and neutrons that pass through this hollow cylinder and are guided to the outside of the main vessel are detected by a detector arranged outside the main vessel. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 4-248497 Summary of the Invention [Problem to be solved by the invention]

[0006] In Patent Document 1, the hollow cylinder is disposed in sodium, which is a coolant. During operation of a fast reactor, liquid sodium becomes hot, so it is difficult to inspect the hollow cylinder in such hot sodium, and it is also difficult to replace the hollow cylinder.

[0007] Therefore, the present invention has been made in consideration of these points, and has an object to provide a fast reactor and a damaged fuel detection device for a fast reactor that allows easy inspection and replacement of equipment for measuring neutrons even if the equipment is damaged. [Means for solving the problem]

[0008] A fast reactor according to one embodiment of the present invention comprises a core for accommodating nuclear fuel, a main vessel formed in a cylindrical shape with a bottom and an open top, for accommodating the core together with a coolant, a roof slab structure disposed on top of the main vessel for closing the main vessel, and a neutron detection unit for measuring neutron flux of neutrons originating from damaged fuel in the core, wherein the neutron detection unit comprises a neutron guide tube having a lower end located within the main vessel and an upper end extending in the height direction of the main vessel so as to penetrate the roof slab structure, the neutron guide section for guiding the neutrons from within the main vessel to above the main vessel, a moderator disposed within the neutron guide tube for slowing down the speed of the neutrons guided through the neutron guide tube, a neutron detector disposed within the neutron guide tube for measuring the neutron flux of the slowed down neutrons, and an absorber disposed below the moderator in the neutron guide tube for absorbing thermal neutrons and allowing delayed neutrons to pass through.

[0009] The absorber, the moderator, and the neutron detector may be provided in a region of the neutron guide tube that is located inside the roof slab structure.

[0010] The roof slab structure may have a heat shielding layer formed on the underside of the roof slab structure, a radiation shielding layer formed on the upper side of the roof slab structure, and a cooling gas space formed between the heat shielding layer and the radiation shielding layer and filled with a cooling gas, and the neutron detector may be located within the cooling gas space.

[0011] The interior of the main vessel may be divided into an upper plenum and a lower plenum, and further comprises an intermediate heat exchanger having an inlet window that takes in the coolant that has passed through the core in the upper plenum, and the neutron guide tube may be arranged along the intermediate heat exchanger, and the lower end of the neutron guide tube may be located below the top of the inlet window.

[0012] When the fast reactor is viewed from above, the core is located in the center of the main vessel, the intermediate heat exchanger is provided at a position away from the center by a predetermined distance in the radial direction of the main vessel, and the neutron guide tube is provided radially inward of the main vessel with respect to the intermediate heat exchanger.

[0013] The roof slab structure may include a roof slab member covering the upper part of the main vessel, and a rotating plug arranged in a central region of the roof slab structure for moving a fuel exchange machine for exchanging the nuclear fuel, and the neutron guide tube may be arranged in the roof slab member radially outward from the rotating plug.

[0014] The neutron detection unit may further include a shielding plug that is disposed above the neutron detector in the neutron guide tube and is a member that blocks heat and radiation from inside the main vessel.

[0015] A broken fuel detection device for a fast reactor according to one aspect of the present invention is a broken fuel detection device for measuring the neutron flux of neutrons originating from broken fuel in a fast reactor comprising a core for accommodating nuclear fuel, a main vessel formed in a cylindrical shape with an open top and a bottom and accommodating the core together with a coolant, and a roof slab structure disposed on top of the main vessel and closing the main vessel, the broken fuel detection device being attached to the roof slab structure such that its lower end side is located within the main vessel and its upper end side penetrates the roof slab structure. The neutron guide tube includes a neutron guide section extending in the height direction of the main vessel as shown in FIG. 1 and guiding the neutrons from inside the main vessel to above the main vessel; a moderator disposed within the neutron guide tube for slowing down the speed of the neutrons guided through the neutron guide tube; a neutron detector disposed within the neutron guide tube for measuring the neutron flux of the slowed down neutrons; and an absorber disposed below the moderator within the neutron guide tube for absorbing thermal neutrons and allowing delayed neutrons to pass through. Effect of the Invention

[0016] According to the present invention, it is possible to provide a fast reactor and a damaged fuel detection device for a fast reactor, in which the equipment for measuring neutrons can be easily inspected and replaced even if the equipment is damaged. [Brief description of the drawings]

[0017] [Figure 1] FIG. 1 is a cross-sectional view showing the configuration of a fast reactor. [Diagram 2] FIG. 1 is a schematic diagram showing an example of a fast reactor viewed from above. [Diagram 3] 1 is a table showing examples of specific values ​​of delayed neutron flux and counter count rate with and without a neutron guide tube. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] A fast reactor according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view showing the configuration of a fast reactor. FIG. 2 is a schematic diagram showing an example of a fast reactor viewed from above. Arrows in FIG. 1 indicate the flow of sodium, which is a coolant. In the following, terms indicating directions such as "up" and "down" are used according to the orientation of objects depicted in the drawings, but these terms are not intended to limit the present invention. The "vertical direction" corresponds to the height direction of the main vessel.

[0019] The fast reactor S100 is, for example, a tank-type fast reactor, which uses, for example, uranium or plutonium as fuel to control and sustain a nuclear fission chain reaction to extract energy. The fast reactor S100 includes, as its main components, a main vessel 10, a roof slab structure 11, a core 20, a core upper structure 30, a neutron detection unit 40, an intermediate heat exchanger 50, a circulation pump 60, and a direct core cooling system heat exchanger 70 (FIG. 2).

[0020] One of the features of the fast reactor S100 of this embodiment is that the neutron detection unit 40 for measuring the neutron flux has a neutron guide tube 41 fixed to the roof slab structure 11, and an absorber 42, a moderator 43, a neutron detector 44, and the like are provided inside the neutron guide tube 41. In this manner, the entire neutron guide tube 41 is not provided in the sodium coolant, but is provided on the roof slab structure 11, so that an operator can access the neutron guide tube 41 from above the roof slab structure 11. Therefore, even if the equipment for measuring neutrons is damaged, it is easy to inspect or replace the equipment.

[0021] [Configuration of each part] The fast reactor S100 is characterized by the neutron detection unit 40 and its surrounding structure. Before describing these in detail, the overall structure of the fast reactor S100 will be described.

[0022] The main vessel 10 is a cylindrical type with a bottom that is open at the top, and has a diameter of, for example, about 15 m to 20 m. The main vessel 10 accommodates a reactor core 20 together with sodium, which is a primary system coolant. A reactor core upper structure 30, an intermediate heat exchanger 50, a circulation pump 60, and a direct core cooling system heat exchanger 70 (FIG. 2) are provided inside the main vessel 10. The upper end of the main vessel 10 is closed by a roof slab structure 11. A partition plate 15 is provided inside the main vessel 10.

[0023] The partition plate 15 is, for example, a circular ring-shaped member, and is provided so as to divide the inside of the main vessel 10 into an upper plenum and a lower plenum. The upper plenum and the lower plenum communicate with each other via the core barrel 10a and the intermediate heat exchanger 50.

[0024] The core 20 is a portion that contains nuclear fuel, and includes fuel assemblies, shielding assemblies, and control rods (none of which are shown). The core 20 is contained inside a core barrel 10a provided in the main vessel 10. Although not shown, the core 20 is located in the center of the main vessel 10 when viewed from above. The core barrel 10a is open to both the upper plenum and the lower plenum, and is configured to allow coolant to pass through.

[0025] The core upper structure 30 has a cylindrical shape and is disposed above the core 20. Inside the core upper structure 30, a control rod drive mechanism (not shown) and various measuring instruments (not shown) such as thermometers and fuel damage detectors are disposed.

[0026] (Roof slab structure 11) The roof slab structure 11 is a lid that is placed on the top of the main vessel 10 and closes the main vessel 10. Regarding the cross-sectional structure of the roof slab structure 11, as shown in Fig. 1, the roof slab structure 11 has a heat shielding layer 11a, a radiation shielding layer 11b, and a cooling gas space 11c.

[0027] The heat shielding layer 11a is formed on the lower surface side of the roof slab structure 11 and is a layer that blocks heat from inside the main vessel 10. The radiation shielding layer 11b is formed on the upper surface side of the roof slab structure 11 and is a layer that blocks radiation.

[0028] The cooling gas space 11c is a space formed between the thermal shielding layer 11a and the radiation shielding layer 11b. The cooling gas space 11c is filled with a cooling gas supplied from a gas supply source (not shown). The temperature of the cooling gas space 11c during operation of the fast reactor S100 is, for example, 100°C or less, specifically, 70°C or less.

[0029] (The structure of the roof slab structure 11 as viewed from above) Next, the structure of the roof slab structure 11 viewed from the top side will be described. As shown in Fig. 2, the roof slab structure 11 includes a roof slab member 12 and a rotating plug 13. The roof slab member 12 is a structure that covers the upper part of the main vessel 10, and specifically, covers the upper part of the main vessel 10 in the area around the rotating plug 13.

[0030] The rotating plug 13 is disposed in a central region of the roof slab structure 11, inside the roof slab member 12. The rotating plug 13 has a large rotating plug 13-1 and a small rotating plug 13-2.

[0031] Both the large rotating plug 13-1 and the small rotating plug 13-2 are rotatable around a vertical axis. The small rotating plug 13-2 supports the refueling machine 14. The refueling machine 14 is a mechanism for replacing nuclear fuel in the reactor core 20. The large rotating plug 13-1 and the small rotating plug 13-2 are eccentrically disposed relative to each other. The large rotating plug 13-1 and the small rotating plug 13-2 each rotate to position the refueling machine 14 at a predetermined position on the reactor core 20. During refueling, the refueling machine 14 moves to a predetermined position and replaces the fuel at that position.

[0032] Referring again to Fig. 1, the intermediate heat exchanger 50 is a heat exchanger that cools the primary system coolant, whose temperature has been raised by the heat from the reactor core 20, by exchanging heat between the primary system coolant and a secondary system coolant (not shown) inside the intermediate heat exchanger 50. The intermediate heat exchanger 50 is formed in a cylindrical shape. The intermediate heat exchanger 50 is disposed in the vertical direction so as to penetrate the roof slab structure 11 and the partition plate 15.

[0033] The intermediate heat exchanger 50 has an inlet window 51 located in the upper plenum and an outlet window 52 located in the lower plenum. The inlet window 51 is an opening through which the high-temperature coolant in the upper plenum flows in. The outlet window 52 is an opening through which the coolant that has passed through the interior of the intermediate heat exchanger 50 flows out to the lower plenum.

[0034] The circulation pump 60 is a pump for circulating the coolant. Like the intermediate heat exchanger 50, the circulation pump 60 also extends vertically so as to penetrate the roof slab structure 11 and the partition plate 15. The circulation pump 60 pumps the coolant to the diagrid 16 through a pipe 61 located in the lower plenum.

[0035] The coolant pumped to the diagrid 16 by the circulation pump 60 flows upward through the core components such as fuel assemblies, shielding assemblies, and control rods (none of which are shown) supported in the core tank 10a. The coolant, which has been heated in the core 20 and has a temperature of, for example, about 500°C to 550°C, then flows into the upper plenum. The coolant that has flowed into the upper plenum flows into the intermediate heat exchanger 50 through the inlet window 51 of the intermediate heat exchanger 50. The coolant is then cooled to, for example, about 400°C inside the intermediate heat exchanger 50. The cooled coolant flows downward inside the intermediate heat exchanger 50 and flows out through the outlet window 52.

[0036] The coolant that flows out of the outlet window 52 and into the lower plenum is sucked in by the circulation pump 60. The sucked in coolant is pumped back to the diagrid 16 by the action of the circulation pump 60. In this way, the coolant cools the core 20 while circulating inside the main vessel 10.

[0037] 2 shows a specific example of the arrangement of the intermediate heat exchanger 50, the circulation pump 60, and the direct core cooling system heat exchanger 70, but the number and arrangement positions of these components may be appropriately changed depending on the specifications of the fast reactor S100, etc. The direct core cooling system heat exchanger 70 is a conventionally known one, so a detailed description thereof will be omitted.

[0038] (Neutron Detection Unit 40) The neutron detection unit 40 is an example of a damaged fuel detection device, and is a unit that measures the neutron flux of neutrons. The neutron detection unit 40 has a neutron guide tube 41, an absorber 42, a moderator 43, a neutron detector 44, and a shielding plug 45. The absorber 42, the moderator 43, the neutron detector 44, and the shielding plug 45 are disposed inside the neutron guide tube 41.

[0039] The number of neutron detection units 40 is arbitrary, but in this embodiment, four neutron detection units 40 are arranged adjacent to the intermediate heat exchangers 50 as shown in Fig. 2. Since the configuration of each neutron detection unit 40 is the same, one neutron detection unit 40 will be described below.

[0040] The neutron guide tube 41 is, for example, a cylindrical member made of metal. The cross-sectional shape of the neutron guide tube 41 may be any shape, such as a circle, a square, or a polygon, but is a circle in this embodiment. The diameter of the tube may be any shape, but is, for example, 10 cm to 20 cm. The neutron guide tube 41 is provided so that its upper end side is located inside the roof slab structure 11 and its lower end side is located inside the main vessel. The upper end of the neutron guide tube 41 is, for example, an opening exposed on the upper surface of the roof slab structure 11, and is provided so that an operator can access the inside of the tube from this opening. A shielding plug 45 is attached to the upper end of the neutron guide tube 41 as a lid. The neutron guide tube 41 extends along the intermediate heat exchanger 50. The neutron guide tube 41 may be provided so as to be in contact with the intermediate heat exchanger 50, or may be disposed slightly away from the intermediate heat exchanger 50.

[0041] The neutron guide tube 41 is inserted into the roof slab structure 11 from above the roof slab structure 11 and is supported by the roof slab structure 11. As an example, the neutron guide tube 41 is removable from the roof slab structure 11. The neutron guide tube 41 is removed from the roof slab structure 11 as necessary, for example, when the neutron guide tube 41 is damaged or when equipment or the like arranged inside breaks down.

[0042] The lower end side of the neutron guide tube 41 is immersed in the coolant of the main vessel 10. Specifically, the lower end of the neutron guide tube 41 is located below the uppermost part of the entrance window 51 of the intermediate heat exchanger 50. The lower end of the neutron guide tube 41 is closed, but neutrons enter the inside of the neutron guide tube 41 from this lower end and the peripheral wall part of the tube. The lower end of the neutron guide tube 41 may be located below the lowermost part of the entrance window 51.

[0043] In this embodiment, as described above, the coolant that has passed through the core 20 is drawn into the intermediate heat exchanger 50 through the inlet window 51. That is, the vicinity of the inlet window 51 is a region through which a large amount of the coolant that has passed through the core 20 flows. Therefore, by positioning the lower end of the neutron guide tube 41 in the region near the inlet window 51, in this embodiment, it becomes possible to efficiently detect neutrons from the coolant.

[0044] The neutron guide tube 41 guides neutrons from inside the main vessel 10 to the upper side of the main vessel 10. The neutron guide tube 41 is filled with an inert gas such as argon gas so that neutrons can pass through without being significantly attenuated. Specifically, the inert gas is filled in the neutron guide portion 41a, which is the region below the absorber 42.

[0045] The absorber 42 is disposed below the moderator 43 inside the roof slab structure 11. The absorber 42 is an absorber that absorbs thermal neutrons (mainly neutrons from the core 20) among neutrons that pass through the neutron guide portion 41a and move toward the roof slab structure 11 side, and transmits delayed neutrons. The absorber 42 is, for example, boron carbide. Delayed neutrons (neutrons originating from damaged fuel) emitted from delayed neutron precursor nuclei that have migrated to the sodium coolant are fast and have a large medium energy range, so they transmit through the absorber 42. On the other hand, the background neutrons from the core 20 are mainly thermal neutrons, and are attenuated in the absorber 42.

[0046] The moderator 43 is provided at a position above the absorber 42 inside the roof slab structure 11. The moderator 43 slows down the speed of the neutrons guided through the neutron guide tube 41. The moderator 43 is, for example, polyethylene. In this embodiment, as described above, the thermal neutrons from the core 20 are attenuated by the absorber 42, while the delayed neutrons that pass through the absorber 42 pass through the moderator 43 since the neutrons are mainly high speed and medium speed neutrons. The delayed neutrons that pass through the moderator 43 are slowed down by the moderator 43 and become thermalized thermal neutrons, which can be detected by the neutron detector 44. Since the moderator 43 is arranged in the cooling gas space 11c, a non-heat-resistant one can be used.

[0047] The neutron detector 44 is a detector that measures the neutron flux of neutrons. The neutron detector 44 is, for example, a "BF3 proportional counter." The neutron detector 44 measures the neutron flux of neutrons that have passed through the moderator 43 and been slowed down. The neutron detector 44 outputs a detection value, which is the detection result, to a control device (not shown), and the detection value is displayed, for example, on a display unit of the control device. The neutron detector 44 is disposed inside the roof slab structure 11, specifically, inside the cooling gas space 11c of the roof slab structure 11. Since the neutron detector 44 is disposed in the cooling gas space 11c in this manner, a non-heat-resistant grade detector can be used as the neutron detector 44 in this embodiment.

[0048] The shielding plug 45 is disposed above the moderator 43 and the neutron detector 44 in the neutron guide tube 41. The shielding plug 45 is a member that blocks heat and radiation from the core 20. The position of the shielding plug 45 is not particularly limited, but in this embodiment, the shielding plug 45 is provided as a lid in a region of the neutron guide tube 41 that is located inside the roof slab structure 11.

[0049] (Configuration seen from the top) As shown in Fig. 2, the intermediate heat exchanger 50 is provided at a position radially away from the center of the main vessel 10 by a predetermined distance. The neutron detection unit 40 is provided radially inward of the intermediate heat exchanger 50. As can be seen from Fig. 1, inside the main vessel 10, the coolant flows from the center of the main vessel 10 in which the core 20 is disposed to the radially outward. The neutron guide tube 41 of the neutron detection unit 40 may be provided radially outward of the intermediate heat exchanger 50, but in the case of the configuration in which the neutron guide tube 41 is disposed closer to the core 20 than the intermediate heat exchanger 50 as in this embodiment, the neutron flux is detected in an area where more coolant flows, so that the neutron flux can be detected effectively.

[0050] The neutron detection unit 40 is provided on the roof slab member 12. When the neutron detection unit 40 is provided on a member that does not rotate or move in this manner, it becomes easier to route the wiring connected to the neutron detection unit 40.

[0051] (Neutron flux detection) In the fast reactor S100 configured as described above, when fuel is damaged, delayed neutrons are emitted from the delayed neutron precursor nuclei that have migrated from the damaged fuel to the sodium coolant. In the configuration of this embodiment, the delayed neutrons move toward the roof slab structure 11 through the neutron guide tube 41. The delayed neutrons pass through the absorbing material 42 but are slowed down by the moderator 43, and can be detected by the neutron detector 44. In this way, in this embodiment, the neutron flux can be measured by the neutron detection unit 40 provided as a single tube.

[0052] (Delayed neutron flux and counter count rate with and without neutron guide tube) Hereinafter, a simulation result comparing the configuration of this embodiment with a configuration without a neutron guide tube will be described. Fig. 3 is a table showing examples of specific values ​​of delayed neutron flux and counter count rate with and without a neutron guide tube.

[0053] "IHX inlet window" refers to the inlet window 51 of the intermediate heat exchanger 50 (IHX). "Inside the main vessel plug" corresponds to the roof slab structure 11, and is, for example, a position 350 cm above the inlet window 51. "With neutron guide tube" refers to a configuration in which the neutron detection unit 40 is provided as in this embodiment. The neutron detector 44 is a non-heat-resistant neutron detector (BF3 proportional counter 40 cps / (n / cm 2 / s)).

[0054] As shown in the table in Figure 3, when the neutron guide tube is used, the total neutron flux at the IHX entrance window is approximately 780 n / (cm 2 ·s) and in the main vessel plug it is approximately 5 n / (cm 2 Half of the total neutrons, including fast neutrons, medium neutrons, and thermal neutrons, can be converted to thermal neutrons, resulting in a counting rate of approximately 100 cps.

[0055] "Without neutron guide tube" is a configuration in which the neutron detection unit 40 is not provided. In this configuration, a heat-resistant detector (fission counter 0.3 cps / (n / cm)) is provided together with a heat-resistant moderator near the IHX entrance window. 2 The thermal neutron flux obtained in a configuration without the neutron detection unit 40 is approximately 23 n / (cm 2 ·s) and the counting rate is approximately 7 cps.

[0056] 3, according to the configuration of this embodiment, the count value obtained by the detector is increased compared to a configuration without the neutron detection unit 40. This increase in the count value reduces statistical errors, improving the accuracy of the neutron flux measurement values.

[0057] (Effects of the S100 fast reactor) In the fast reactor S100 configured as described above, the neutron guide tube 41 of the neutron detection unit 40 is not provided in the sodium coolant but is provided so as to penetrate the roof slab structure 11, so that workers can access the neutron guide tube 41 from above the roof slab structure 11. Therefore, even if the equipment for measuring neutrons is damaged, it is easy to inspect or replace the equipment.

[0058] In particular, even in a configuration in which the neutron detector 44 is disposed within the neutron guide tube 41 as in this embodiment, the neutron flux of delayed neutrons originating from damaged fuel can be measured well because the absorber 42 and the moderator 43 are provided.

[0059] In this embodiment, the absorber 42, the moderator 43, and the neutron detector 44 are provided in a region of the neutron guide tube 41 that is located inside the roof slab structure 11. With this configuration, the neutron detector 44 and the like are disposed in the roof slab structure 11, which has a lower temperature than the inside of the main vessel 10, so there is no need to use a special detector with excellent heat resistance.

[0060] Although an example of the present invention has been described with reference to Figures 1 and 2, the present invention is not limited to the above specific configuration. For example, the neutron detection unit 40 may be provided in the rotating plug 13. Alternatively, one or more first neutron detection units may be provided in the roof slab member 12, and one or more second neutron detection units may be provided in the rotating plug 13.

[0061] This specification also discloses a damaged fuel detection device for a fast reactor, and the damaged fuel detection device corresponds to the neutron detection unit 40. The damaged fuel detection device for a fast reactor of one embodiment of the present invention is for measuring the neutron flux of neutrons originating from damaged fuel in a fast reactor S100 including a core 20 that contains nuclear fuel, a main vessel 10 formed in a cylindrical shape with a bottom and an open top that contains the core 20 together with a coolant, and a roof slab structure 11 that is disposed on top of the main vessel 10 and closes the main vessel 10. The broken fuel detection device, when attached to the roof slab structure 11, has a neutron guide tube 41 with its lower end located within the main vessel 10, extending in the height direction of the main vessel 10 so that its upper end penetrates the roof slab structure 11, and having a neutron guide section 41a formed therein for guiding neutrons from within the main vessel 10 to above the main vessel 10, a moderator 43 disposed within the neutron guide tube 41 for slowing down the speed of the neutrons guided through the neutron guide tube 41, a neutron detector 44 disposed within the neutron guide tube 41 for measuring the neutron flux of the slowed down neutrons, and an absorber 42 disposed below the moderator 43 within the neutron guide tube 41 for absorbing thermal neutrons and allowing delayed neutrons to pass through.

[0062] Although the present invention has been described above using the embodiments, the technical scope of the present invention is not limited to the scope described in the above embodiments, and various modifications and changes are possible within the scope of the gist of the present invention. For example, all or part of the device can be configured by distributing or integrating functionally or physically in any unit. In addition, new embodiments resulting from any combination of multiple embodiments are also included in the embodiments of the present invention. The effect of the new embodiment resulting from the combination combines the effect of the original embodiment. [Explanation of symbols]

[0063] 10 Main vessel 10a Core tank 11 Roof slab structure 11a Heat shield layer 11b Radiation shielding layer 11c Cooling gas space 12 Roof slab members 13 Rotating plug 14 Fuel exchange machine 15 Partition 16 Diagrid 20 Core 30 Core Superstructure 40 Neutron detection unit (damaged fuel detection device) 41 Neutron Guide Tube 41a Neutron guide section 42 Absorbent material 43 Moderator 44 Neutron Detector 45 Shielded plug 50 Intermediate heat exchanger 51 Entrance window 52 Exit Window 60 Circulation Pump 61 Piping 70 Direct core cooling system heat exchanger S100 fast reactor

Claims

1. a reactor core containing nuclear fuel; a main vessel formed in a cylindrical shape with an open top and a closed bottom, which contains the reactor core together with a coolant; a roof slab structure disposed on top of the main vessel and closing the main vessel; a neutron detection unit for measuring the neutron flux of neutrons originating from the damaged fuel of the reactor core; Equipped with The neutron detection unit includes: a neutron guide tube having a lower end side located within the main vessel, extending in the height direction of the main vessel so as to penetrate the roof slab structure and an upper end side thereof, and having a neutron guide portion formed therein for guiding the neutrons from within the main vessel to above the main vessel; A moderator disposed within the neutron guide tube for slowing down the velocity of the neutrons guided through the neutron guide tube; a neutron detector disposed within the neutron guide tube for measuring a neutron flux of the decelerated neutrons; an absorber disposed below the moderator in the neutron guide tube, the absorber absorbing thermal neutrons and transmitting delayed neutrons; A fast reactor.

2. The absorber, the moderator, and the neutron detector are provided in a region of the neutron guide tube located inside the roof slab structure.

2. The fast reactor of claim 1.

3. The roof slab structure comprises: A heat shielding layer formed on the underside of the roof slab structure; a radiation shielding layer formed on the upper surface side of the roof slab structure; a cooling gas space formed between the thermal shielding layer and the radiation shielding layer and filled with a cooling gas; having the neutron detector is located within the cooling gas space; 3. A fast reactor according to claim 1 or 2.

4. The interior of the main vessel is divided into an upper plenum and a lower plenum, an intermediate heat exchanger having an inlet window at the upper plenum for receiving the coolant that has passed through the reactor core; the neutron guide tube is disposed along the intermediate heat exchanger, and a lower end of the neutron guide tube is located below a top of the inlet window.

3. A fast reactor according to claim 1 or 2.

5. When the fast reactor is viewed from the top side, The core is located in the center of the main vessel, the intermediate heat exchanger is provided at a position spaced a predetermined distance from the center in a radial direction of the main vessel, The neutron guide tube is provided radially inward of the main vessel relative to the intermediate heat exchanger.

5. The fast reactor of claim 4.

6. The roof slab structure comprises: A roof slab member covering an upper portion of the main vessel; a rotating plug disposed in a central region of the roof slab structure for moving a refueling machine for exchanging the nuclear fuel; having The neutron guide tube is disposed in the roof slab member radially outward of the rotating plug.

3. A fast reactor according to claim 1 or 2.

7. The neutron detection unit includes: The neutron guide tube further includes a shielding plug disposed above the neutron detector and configured to shield heat and radiation from inside the main vessel.

3. A fast reactor according to claim 1 or 2.

8. A fast reactor includes a core that contains nuclear fuel, a main vessel that is formed in a cylindrical shape with a bottom and an open top and that contains the core together with a coolant, and a roof slab structure that is disposed on top of the main vessel and closes the main vessel. The damaged fuel detection device measures the neutron flux of neutrons originating from damaged fuel in the core, a neutron guide tube having a lower end located within the main vessel, an upper end penetrating the roof slab structure, and extending in the height direction of the main vessel, the neutron guide portion being formed therein, the neutron guide portion guiding the neutrons from within the main vessel to above the main vessel when the neutron guide tube is attached to the roof slab structure; A moderator disposed within the neutron guide tube for slowing down the velocity of the neutrons guided through the neutron guide tube; a neutron detector disposed within the neutron guide tube for measuring a neutron flux of the decelerated neutrons; an absorber disposed below the moderator in the neutron guide tube, the absorber absorbing thermal neutrons and transmitting delayed neutrons; A fast reactor damaged fuel detection device having the same.

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