JPH04279898A - Liquid metal cooled nuclear reactor - Google Patents

Abstract

PURPOSE:To prevent giving damage to fuel aggregate 2 due to the sliding among the fuel aggregate 2, and to reduce the liquid level of a cooling material 7. CONSTITUTION:The stand-by point of a fuel transfer pot 3 for storing fuel aggregate 2 is provided on one end part in a core tank 20, and the depth is defined so that the upper end of the fuel transfer pot 3 when the fuel transfer pot 3 is stored in the stand-by point is of the same horizontal position as the upper surface of a core supporting structure 1. As a result, the damage to a fuel coating tube is reduced, while the height of a reactor is reduced.

Description

[Detailed description of the invention]

FIELD OF THE INVENTION This invention relates to liquid metal cooled nuclear reactors.

[Prior Art] An example of a fuel exchange device for a fuel assembly used in a conventional liquid metal cooled nuclear reactor is shown in FIGS. 7 and 8.
This will be explained using FIG. Figure 7 is a schematic longitudinal sectional view showing a fuel assembly exchange device for a liquid metal cooled nuclear reactor, Figures 8 and 9.
7 are a schematic plan view and a schematic vertical cross-sectional view of the core support plate shown in FIG. 7, respectively. 7, 8 and 9, 2 is a fuel assembly, 3 is a fuel transfer pot, 4 is a fuel exchanger, 5 is a reactor vessel, 6 is a fuel inlet/outlet machine, 7 is a coolant, 10 is a shielding plug, 19 2 indicates a core support plate, and 20 indicates a core barrel. In these figures, the core support plate 19 is attached to the core barrel 20.
A fuel assembly 2 supported by the core barrel 20 is loaded, and a fuel transfer pot 3 is attached to one side of the core barrel 20, and the fuel assembly 2 is transferred between the core barrel 20 and the fuel transfer pot 3. A fuel exchange machine 4 for transporting used and new fuel assemblies, and a fuel loading/unloading machine 6 for transporting used and new fuel assemblies into and out of the reactor vessel 5 are provided. When exchanging fuel assemblies, when transporting the spent fuel assemblies 2 out of the reactor vessel 5, one of the fuel assemblies 2 is pulled out from within the core support plate 19 using the fuel exchange machine 4, and the core barrel 20 is removed. After being transferred to above the fuel transfer pot 3, it is separated from the fuel exchanger 4 and stored in the fuel transfer pot 3. The fuel assembly 2 housed in the fuel transfer pot 3 is carried out of the reactor vessel 5 along with the fuel transfer pot 3 by a fuel loading/unloading machine 6. Next, when carrying a new fuel assembly 2 into the reactor vessel 5, the fuel loading/unloading machine 6
Fuel transfer pot 3 containing a new fuel assembly 2
After transporting the entire fuel assembly 2 into the reactor vessel 5,
is pulled out from the fuel transfer pot 3 by the fuel exchanger 4 and transferred to the position in the core tank 20 where a new fuel assembly 2 is loaded, then separated from the fuel exchanger 4 and loaded into the core support plate 19. Note that the liquid level of the coolant 7 in the reactor vessel 5 is maintained at the same level as that of the fuel assembly 2 during operation in order to remove the decay heat of the fuel assembly 2 even while the fuel assembly 2 is being transported by the fuel exchanger 4. It is maintained at a level where the heat generating part is immersed. Note that Japanese Patent Laid-Open No. 1-172797 discloses a related technique in which a flow resistance element protrusion is provided on a neutron shield housing tube to regulate the flow of coolant.

[Problems to be Solved by the Invention] The above-mentioned prior art uses a fuel assembly with a storage tube removed type because when replacing the fuel assembly, the fuel assembly is moved greatly in the vertical direction on the core support plate. When doing so, there were problems in the following points. The problem will be explained using FIGS. 10 and 11. Figure 1
0 and 11 are a vertical cross-sectional view of a storage tube deleted type fuel assembly and an enlarged vertical cross-sectional view of the core fuel pin of FIG. 10, respectively.
14 is a core fuel pin, 22 is a core fuel pellet, and 23 is a core fuel cladding tube. In the case of a nuclear reactor using the storage tube deleted type fuel assembly 2 described above, when the storage tube deleted type fuel assembly 2 is inserted or removed from the core support plate 19 during fuel assembly replacement, the adjacent fuel assembly 2 There was a risk that the core fuel cladding tube 23 enclosing the core fuel pellets 22 would be damaged due to the sliding between them. It is an object of the present invention to prevent fuel damage from occurring due to sliding between fuel assemblies and to prevent fuel assemblies from collapsing when the fuel assemblies are moved in and out of the core support plate during fuel assembly replacement. The aim is to reduce the height of the reactor by requiring a lower level of coolant to remove the heat.

[Means for Solving the Problems] The above object can be achieved as follows. (1) Fuel assemblies loaded onto the core support plate provided in the reactor vessel are transported to and from the reactor vessel by a fuel exchanger via a fuel transfer pot at a standby location. In a liquid metal cooled nuclear reactor having a fuel transfer pot, a standby area for the fuel transfer pot is provided at one end of the core tank, and when the fuel transfer pot is accommodated in the standby area, the upper end of the fuel transfer pot is connected to the upper surface of the core support plate. It must have a depth that allows for the same horizontal position. (2) In (1), the upper part of the fuel transfer pot has a notch, and has a depth such that the lower end of the notch is in the same horizontal position as the upper surface of the core support when the fuel transfer pot is accommodated in the standby area. thing. (3) In (1), the distance between the top of the core and the liquid level of the coolant during reactor operation, which has a liquid level above the top of the core, is the same as that of the coolant during rated operation of the reactor and between the spent fuel assemblies. Maintain the liquid level of the coolant in the furnace so that it is approximately the same as the height of the liquid level fluctuation due to temperature differences during transportation. (4) In (3), a flow hole is provided around the core barrel between the heat generating part of the spent fuel assembly and the top of the core, and at a position below the coolant during spent fuel transportation.

According to the present invention, when replacing fuel assemblies, the fuel assemblies are not moved significantly in the vertical direction, so that almost no sliding action occurs between adjacent fuel assemblies. In addition, the liquid level of the coolant during transport of spent fuel assemblies is considerably lower than the liquid level during reactor operation due to temperature drop, but the liquid level of coolant during transport of spent fuel assemblies is lower than the liquid level at the top of the core. Since the coolant liquid level can be set to be approximately the same as the above, the coolant liquid level can be set to be low. Furthermore, a flow hole is provided around the core tank between the upper end of the heat generating part of the spent fuel assembly and the top of the core, and below the coolant liquid level during spent fuel transportation. The coolant liquid level during transportation of the finished fuel assembly is lowered until the top of the fuel assembly is sufficiently exposed, and each movement of the fuel exchanger grabbing and releasing the fuel assembly can be monitored on the ITV. It becomes easier.

[Example] Examples will be described below. Figures 1 to 6
1 shows an embodiment of the present invention, FIG. 1 is a schematic longitudinal sectional view of a liquid metal cooled nuclear reactor, FIGS. 2 and 3 are a schematic plan view and a schematic longitudinal sectional view of a core support structure, respectively, and FIG. 4 is a fuel transfer diagram. A perspective view of the pot, FIGS. 5 and 6 are a cross-sectional view showing the core arrangement, and an external view of the neutron shield, respectively. 1 to 6, 1 is a core support structure, 8 is a guide tube, 9 is an ITV, 1
1 is a core assembly without a storage tube, 12 is a blanket fuel assembly, 13 is a neutron shield, 15 is a blanket fuel pin, 16 is a storage tube for the neutron shield, 17 is a neutron shielding material, and 18 is a flow resistance element protrusion. , 21 is a flow hole, 2
Reference numeral 4 indicates a fuel assembly inlet/outlet, 32 indicates a storage pipe for a blanket fuel assembly, and the other symbols are the same as those mentioned above. In FIG. 1, in the reactor vessel 5, a standby location for the fuel transfer pot 3 according to the present invention is provided at one end of the core tank 20, and the lower end of the fuel transfer pot 3 is connected to the core support structure 1. A notch is provided so that it is at the same horizontal position as the top surface of the. Furthermore, although the fuel assembly 2 is supported by the core support structure 1, FIGS. 2 and 3 show an enlarged view of the core support structure 1, and FIG. 4 shows a cutout. The structure of the fuel transfer pot 3 is shown in a perspective view for easy understanding. Further, a hole 21 is provided around the core barrel 20 . In the fuel assembly 2, as shown in FIG.
A blanket fuel assembly 12 includes a core fuel assembly 11 without a storage tube, a blanket fuel assembly 12, and a neutron shield 13, and has a blanket fuel assembly storage tube 32 on the outer periphery of the core fuel assembly 11 without a storage tube. Further, on the outer periphery, a neutron shield 13 having a flow resistance element protrusion 18 as shown in FIG. 6 is arranged around the neutron shield housing tube 16. The vertical range in which the flow resistance element protrusion 18 is provided on the neutron shield 13 corresponds to the height from the lower end of the neutron shield 13 to the upper end of the heat generating part of the core fuel assembly 11 without a storage tube. The flow resistance element protrusion 18 allows the blanket fuel assembly storage pipe 32
A gap is provided between each adjacent pipe of the neutron shield housing pipe 16 and the flow resistance element protrusion 18 exists between the upper and lower directions, and the coolant 7 uniformly flows upward. Above the upper end, the coolant 7 can also flow in the lateral direction, making it possible to ensure a sufficient flow rate of coolant for the core fuel assembly 11 during reactor operation. As shown in FIG. 1, the core support structure 1 supports the core at the lower end of a notch provided at the entrance/exit of the fuel assembly 2 of the fuel transfer pot 3 that houses the fuel assembly 2 during fuel assembly replacement. It has a structure that allows it to be installed at the same horizontal position as the top surface of the structure 1. Furthermore, when the fuel assembly 2 stored in the fuel transfer pot 3 is carried out of the reactor vessel 5 by the fuel loading/unloading machine 6, the fuel assembly 2 is also transported in order to remove the decay heat of the fuel assembly 2 during the transport. The structure is such that there is no cutout up to that height so that the heat generating part of the fuel assembly 2 is immersed in the coolant, but a cutout is provided above it for the fuel assembly 2 to be taken in and taken out. When replacing a fuel assembly, the fuel assembly 2 closest to the fuel transfer pot 3 (2-1 in FIG. Pull it up. Thereafter, the fuel assembly 2 is transferred laterally to the fuel transfer pot 3 and separated from the fuel exchanger 4. The fuel transfer pot 3 containing the fuel assembly 2 is carried out of the reactor vessel 5 by the fuel loading/unloading machine 6, and then the empty fuel transfer pot 3 is carried into the reactor vessel 5 again. In this way, all the fuel assemblies 2 in the core support structure 1 are transferred to the reactor vessel 5 in order from the fuel assemblies located outside the core (in the order 2-2 and 2-3 in FIG. 2). After being carried out, a new fuel assembly 2 is stored in a fuel transfer pot 3, carried into a reactor vessel 5, and installed in a core support structure 1 by a fuel exchanger 4. According to this embodiment,
When moving the fuel assembly 2 in and out of the core support structure 1, it is only necessary to pull out the fuel assembly 2 by the amount necessary to separate it from the core support structure 1. The risk of damage to the core fuel cladding tube 23 can be reduced. In addition, since the amount of vertical movement of the fuel assembly 2 can be reduced, the liquid level of the coolant 7 necessary for removing decay heat from the fuel assembly 2 being transported can be kept low, so the level of the coolant 7 can be kept low. It becomes possible to reduce the height. In addition, coolant 7 due to nuclear reactor shutdown
As the temperature decreases, the liquid level of the coolant 7 contracts until the top of the fuel assembly 2 is exposed. However, in order to remove the decay heat of the fuel assembly 2, a pump (not shown) is used to cool the coolant 7 outside the core tank 20. After the coolant 7 flows into the core barrel 20 from the bottom of the core barrel 20, it overflows and flows out of the core barrel. However, in the case of this embodiment, the flow hole 21 is provided around the core barrel 20 at a height between the liquid level of the coolant 7 and the upper end of the heat generating part of the fuel assembly 2. The coolant 7 in the core barrel 20 flows out of the core barrel 20 through the flow hole 21 . Therefore, the liquid level of the coolant 7 is lowered to a level where the top of the fuel assembly 2 is sufficiently exposed, and the complicated operation of gripping and releasing the fuel assembly 2 by the fuel exchanger 4 is eliminated through the guide tube 8 of the shielding plug 10. This can be done while being monitored by ITV9. Note that even if the fuel transfer pot 3 is not provided with a notch and a standby location for the fuel transfer pot 3 is provided so that the upper end of the fuel transfer pot 3 is at the same horizontal position as the top surface of the core support structure 1, the notch is not provided. The same effect can be obtained with almost the same operation as in the case where the notch is provided, but in this case, the depth of the waiting area of the fuel transfer pot 3 is deeper than in the case where the notch is provided.

Effects of the Invention According to the present invention, when replacing a fuel assembly, there is no need to move the fuel assembly significantly in the vertical direction. When replacing the fuel cladding, the risk of damage to the fuel cladding due to sliding between the fuel assemblies can be reduced. Furthermore, the coolant liquid level when replacing the fuel assembly can be kept low, and the height of the reactor can be reduced. Furthermore, since the liquid level of the coolant during fuel assembly replacement can be lowered until the top of the fuel assembly is sufficiently exposed, the operation of grabbing and releasing the fuel assembly by the fuel exchanger can be performed while being monitored by the ITV. This improves the reliability of fuel assembly replacement.

[Brief explanation of the drawing]

FIG. 1 is a schematic vertical cross-sectional view of a liquid metal cooled nuclear reactor showing one embodiment of the present invention.

FIG. 2 is a schematic plan view of the core support structure shown in FIG. 1.

FIG. 3 is a schematic vertical cross-sectional view of the core support structure shown in FIG. 1.

FIG. 4 is a perspective view of the fuel transfer pot shown in FIG. 1;

FIG. 5 is a cross-sectional view showing the core arrangement.

FIG. 6 is an external view of a neutron shield.

FIG. 7 is a schematic vertical sectional view showing a conventional fuel assembly exchange device.

8 is a schematic plan view of the core support plate shown in FIG. 7. FIG.

9 is a schematic longitudinal sectional view of the core support plate shown in FIG. 7. FIG.

FIG. 10 is a longitudinal cross-sectional view of a storage tube deleted type fuel assembly.

FIG. 11 is an enlarged longitudinal cross-sectional view of the core fuel pin of FIG. 10;

[Explanation of symbols]

1 Core support structure 2 Fuel assembly 3 Fuel transfer pot 4 Fuel exchange machine 5 Reactor vessel 6　Fuel loading/unloading machine 7 Coolant 19 Core support plate 20 Core tank 21 Flow hole

Claims (5)

[Claims] [Claim 1] Fuel assemblies loaded on a core support plate provided in a reactor barrel are carried in and out of the reactor vessel by a fuel exchanger via a fuel transfer pot at a standby location. In a liquid metal cooled nuclear reactor having the fuel transfer pot, a standby location for the fuel transfer pot is provided at one end of the core barrel, and when the fuel transfer pot is accommodated in the standby location, the fuel transfer pot A liquid metal cooled nuclear reactor characterized in that the upper end of the reactor has a depth such that the upper end thereof is at the same horizontal position as the upper surface of the core support plate. 2. The upper part of the fuel transfer pot has a notch, and the depth is such that the lower end of the notch is at the same horizontal position as the upper surface of the core support when the fuel transfer pot is accommodated in the standby location. The liquid metal cooled nuclear reactor according to claim 1, comprising: 3. The distance between the top of the reactor core and the liquid level of a coolant during reactor operation that has a liquid level above the top of the reactor core,
A claim in which the liquid level of the coolant in the reactor is maintained so as to be approximately the same as the height of fluctuation in the liquid level due to a temperature difference between the coolant during rated operation of the reactor and during transportation of the spent fuel assembly. The liquid metal cooled nuclear reactor according to item 1. 4. The core tank at a position between the upper end of the heat generating part of the spent fuel assembly and the top of the core and below the liquid level of the coolant during transportation of the spent fuel assembly. Claim 3 comprising a flow hole around the periphery of the
The liquid metal cooled nuclear reactor described. 5. The fuel assembly loaded on the core support plate provided in the core barrel is moved in and out of the core barrel from the side. 4. The liquid metal cooled nuclear reactor according to 4.