JPH03591B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to the structure of a nuclear reactor.

In pressurized water type light water reactors that are commonly used in the past, the flow direction of the coolant that has ascended axially into the reactor core is changed radially outward (laterally) in the upper plenum directly above the core, and then flows through the exit nozzle. and out of the reactor vessel.

A guide tube is installed in this upper plenum to guide the control rod assembly of the reactor core.
It surrounds and protects the control rod assembly from direct exposure to the lateral flow of coolant.

However, if the number of control rods or aggregations of control rods is very large, the number of guide tubes will be large.
Alternatively, it is necessary to increase the size of the guide tube, making it impossible to secure a flow path area toward the outlet nozzle. In order to solve this problem, it has been proposed to install a calandria section directly above the core exit that diverts the coolant toward the exit nozzle. The control rods are inserted through the fuel assembly into the fuel assembly so that the control rods are not directly exposed to the lateral flow of coolant. However, even in this case, if there are many control rods, only small-diameter protection tubes can be used, and there is still a risk of damage to the protection tubes due to fluid vibration due to radial flow, or damage to the control rods due to this. .

The present invention has been made in view of the above-mentioned problems.

That is, the present invention mainly provides a lower guide structure directly above the reactor core that individually surrounds and protects the control rod assemblies and has an assembly guide pipe that allows coolant to flow vertically upward. The gist of the invention is to provide a protection tube that individually surrounds the drive shaft of the rod assembly, and an upper guide structure that guides the coolant in the radial direction and directs it to the coolant outlet nozzle. Regardless of the increase, it is possible to suppress the increase in the number of protection tubes receiving the lateral flow of coolant, to ensure a sufficient coolant flow path, and to significantly improve the strength and soundness of the protection tubes.

Hereinafter, the present invention will be explained based on illustrated embodiments.

In FIG. 1, a reactor vessel 1 is provided with a coolant inlet nozzle 3 and an outlet nozzle 5 at its upper part, which communicate with a primary cooling pipe (not shown).

The container 1 is supported by a building at the lower part of the nozzles 3 and 5, and the upper part is closed with a removable upper lid body 7. The core shaft 9 suspended and supported inside the vessel 1 defines an annular flow path 11 through which the coolant descends between it and the vessel 1, has a lower core support plate 13 at the lower part, and a lower plenum 15 at the lower part. Form.

A large number of fuel assemblies 1 are mounted on the core support plate 13.
7 are installed to form the reactor core 19. The fuel assembly 17 is a bundle of a large number of fuel rods and control rod guide tubes arranged in parallel by a support grid. The core support plate 13 includes a number of through holes (not shown) through which the coolant passes, and the coolant flows in from the inlet nozzle 3 as shown by the arrow, flows down the annular passage 11, and reaches the lower plenum 15. . Thereafter, it passes through the core support plate 13 and enters the core 19.

An inner cylinder 21 supported above inside the core shell 9
constitutes a guide structure as described below.

The guide structure is recognized as a lower part and an upper part.
An upper core plate 23 located directly above the reactor core 19 to position the fuel assembly 17, an intermediate support plate 25, a lower solid portion 27 of the inner cylinder 21, and an assembly guide tube 29 that individually surrounds the control rod assembly to be described later. constitutes the lower guide structure.

FIG. 2 shows an example of a control rod assembly 30, in which the upper ends of a plurality of control rods 31 containing a neutron absorbing material are configured as one assembly via a spider 33 and a drive shaft 35.

Returning again to FIG. 1, the protective tubes 41 that individually surround the drive shafts 35 cooperate with the intermediate support plate 25, the upper part 43 of the inner cylinder having a number of flow holes, and the upper support plate 45 to form an upper guide structure. forming the body.

There are a large number of control rod assemblies 30, which are individually connected to drive devices 47 and 49 provided at the upper part of the upper lid body 7. The control rods 31 of the control rod assembly 30 are inserted into the control rod guide tubes of the fuel assembly 17, and are connected to the drive device 4.
7 and 49 in a predetermined pattern to control the reactivity of the reactor core 19 during operation of the reactor.

As described above, the coolant that has entered the core 19 flows outside the fuel rods, absorbs the heat of reaction, increases its temperature, flows into the guide tube 29, and flows upward. It then passes over the intermediate support plate 25 into the upper plenum 51 where it changes direction and flows radially outward (laterally) and exits the outlet nozzle 5 through a hole in the upper part 43 of the inner cylinder 21.

According to this embodiment, the coolant flows along the axial direction around the control rod 31, which is thin, that is, has low rigidity, so that no fluid vibration occurs and wear due to vibration is prevented.

In addition, since the coolant flows from the upper guide structure to the outlet nozzle 5 located at approximately the same height, the flow is smooth and there is little pressure loss, and even if the primary cooling system piping etc. is damaged due to some reason. Even if this occurs, the coolant circulates naturally within the vessel 1, and cooling of the core 19 can be ensured.

Furthermore, in the upper plenum 51 where the ascending coolant flows sideways, the protective tubes 41 surround the drive shafts 35, which are much smaller than the control rods 31.
Despite having a large diameter and high strength and rigidity, the coolant flow path is large and allows the coolant to flow smoothly.

Furthermore, because of this, the fluid force acting on the protection tube 41 is also small, so the excitation force is also small and the integrity is high.

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional view showing an embodiment of the present invention, and FIG. 2 is a side view showing one component of the embodiment. 1... Reactor vessel, 9... Reactor core, 17...
Fuel assembly, 19...core.

Claims (1)

[Claims] 1. A reactor core consisting of a plurality of fuel assemblies, a reactor core that encloses and supports the core in its lower part, and a reactor vessel that suspends and supports the core and forms a coolant descending annular space between the core and the core. , an upper lid body that closes the upper part of the vessel, a lower guide structure located directly above the core, an upper guide structure located above the lower guide structure, and an upper part of the vessel corresponding to the upper guide structure. In a nuclear reactor having a coolant nozzle provided on the side, the lower guide structure includes a control rod assembly guide tube that individually surrounds the control rod assemblies and allows the coolant to flow vertically upward; The upper guide structure has an inner cylinder surrounding an upper core plate and the group of guide tubes, and the upper guide structure supports a plurality of protection tubes individually surrounding the drive shaft of the control rod assembly and upper and lower ends of the protection tubes. A nuclear reactor having an upper support plate and an intermediate support plate defining an upper plenum in which coolant is laterally diverted.