JPS6125109B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a liquid metal cooled fast reactor core upper structure.

The structure inside the reactor vessel of a liquid metal cooled fast reactor is schematically shown in FIG. In the figure, a furnace vessel 1 is provided with a liquid metal inlet nozzle 2 at the bottom and an outlet nozzle 3 at the center. In the lower part of the reactor vessel 1, a core fuel assembly 4, a blanket assembly 5 surrounding it, a reflector 6, a control rod 7, etc. are arranged. These assemblies and the like are supported by a reactor structure 8, and a passage for liquid metal, which is a coolant, is formed in the reactor core structure 8.

A core upper mechanism 9 is attached to the upper part of the reactor vessel 1 via a rotating plug 10 . The structure of the lower part of the core upper mechanism 9 is schematically shown in FIG. That is, in the figure, the lower part of the upper core mechanism 9 is composed of a rectifying grid 17, a control rod guide tube 16, a heat shield plate 14, an in-core instrumentation well 15, and the like. The reactor vessel 1 includes a core structure 8 and a fuel assembly 4
The plenum is divided into an upper plenum 12 and a lower plenum 13, and a dip plate 11 is disposed near the liquid metal surface (see FIG. 1).

Liquid sodium is usually used as a coolant. The coolant flows into the lower plenum 13 from the inlet nozzle 2 of the reactor vessel 1, and is distributed in flow to each fuel assembly 4 by passages provided in the core structure 8, dissipating the heat generated in each fuel assembly 4. Absorb. The liquid sodium, which has become high temperature by absorbing heat, flows out from the upper part of the fuel assembly 4, passes through the straightening grid 17, crosses other lower components of the upper core mechanism 9, and flows out radially into the upper plenum 12. It is then taken out from the upper plenum 12 through the outlet nozzle 3 into the furnace vessel 1 .

The in-core instrumentation equipment arranged in the lower part of the upper core mechanism 9 corresponding to each fuel assembly 4 monitors the flow state of the coolant in each core fuel assembly 4, abnormalities in fuel pins, and the like during operation of the fast reactor. The purpose is to measure and detect damage.

The tip of the in-core instrumentation equipment is composed of a thermometer, flowmeter sensor, FDD (fuel failure detector) sampling nozzle, etc., and the part where the sensors are inserted is the in-core instrumentation. The well 15 is arranged at the center of the cylindrical portion of the rectifying grid 17 (see FIG. 2).

In order to operate a fast reactor safely and efficiently, in-core instrumentation equipment placed corresponding to each fuel assembly 4 in the reactor core is used to monitor the operating status of each fuel assembly 4,
It is necessary to obtain accurate information on abnormalities, etc.

Rectifier grid 1 placed at the bottom of core upper mechanism 9
7 has a function of rectifying the coolant flowing out from the fuel assembly 4 (straightening function) and a function of rectifying the coolant between adjacent fuel assemblies 4 in order to maintain the above-mentioned necessary functions of the in-core instrumentation equipment. It must also have a function (separation function) to prevent mutual interference due to mixing, etc.

It is desirable for the lower end of the rectifying grid 17 to be as close to the fuel assembly 4 as possible in terms of its separation function; however, due to swelling, thermal expansion, etc.
Since the heights of the two will be uneven, it is necessary to leave an interval of about 50 mm.

FIG. 3 shows a typical example of the rectifying grid 17 in the conventional upper core mechanism 9, in which a is a plan view and b is a cross-sectional view. In the figure, slits 19A are provided at six locations at each of the upper and lower ends of a cylindrical straightening tube 19 with a hole diameter smaller than the outlet hole of the fuel assembly 4, and the holding plate 18 is inserted into the slits 19A. After a large number of rectifier cylinders 19 are connected to each other, the main parts are welded to form a rectifier grid 17.

The diameter of the straightening tubes 19 is determined from the flow condition of the coolant in the upper part of the core, taking into account the above-mentioned straightening function and separation function. 18, the structure is complicated, and due to reasons such as deformation due to thermal strain during welding and structural defects, the rectifier cylinder 1 corresponding to a large number of fuel assemblies 4 has a complicated structure.
It is extremely difficult to operate the rectifying grid 9 coaxially while maintaining positional accuracy, and the rectifying grid 17 lacks a separating function.

The present invention solves the above-mentioned drawbacks of the conventional rectifying grid, and enables accurate measurement and monitoring of the operating status of each fuel assembly in the reactor core during fast reactor operation using in-core measuring equipment. It is an object of the present invention to provide an upper core mechanism that maintains a rectifying function and a separating function for coolant in a reactor, is easy to manufacture, and is equipped with a rectifying grid having axes aligned with the corresponding fuel assemblies.

Embodiments of the present invention will be described below based on the drawings. Figures 4a to 4f show an example of a rectifying grid according to the present invention, where a and b are views showing the method of assembling the same, c is a plan view showing the configuration after assembly, and d is a sectional view. , e is a partially enlarged plan view, f
is a similarly enlarged cross-sectional view.

In the figure, the rectifying grid 17 is configured in a honeycomb shape from a plurality of cylindrical rectifying cylinders 19 and a plurality of hollow hexagonal columnar rectifying cylinder supports 20 circumscribing the outer circumference of the rectifying cylinders 19. . Rectifier cylinder support 20
As shown in figure a, hollow hexagonal columns are made separately, assembled and the main parts are welded together, or as shown in figure b, after bending a thin plate into a continuous trapezoid shape. It is constructed by assembling it into a hollow hexagonal column shape and welding the main parts. In either case, the size of each hexagonal column constituting the honeycomb is half the size of the fuel assembly 4, so as shown in Figure c, every other hollow hexagonal column of the honeycomb has a rectifying tube 19. As described above, since the outer circumference of the straightening tube 19 is inscribed in the hollow hexagonal column, the straightening tube 19 is supported by the straightening tube support 20, and its pitch is aligned with the fuel assembly 4. The pitch of the two matches, and alignment of the two can be done extremely easily.

The in-furnace instrumentation well 15 is connected from the top of each straightening tube 19.
are inserted, but since the axis of the fuel assembly 4 and the axis of the straightening tube 19 are aligned, the main flow of the coolant flowing through each fuel assembly 4 is directed to the corresponding straightening tube 1.
The main flow of the coolant flowing into the fuel assembly 9 and the adjacent fuel assembly 4 flows into the corresponding straightening tube 19, and there is no risk of the coolant from the adjacent fuel assembly 4 getting mixed in, so the in-core instrumentation The tip sensors of each instrumentation device provided in the well 15 can reliably capture information such as the operating status of the corresponding fuel assembly 4.

FIG. 5 shows a second embodiment of the present invention, in which a is an enlarged plan view and b is a sectional view thereof. In the embodiment described above, one straightening tube support 20 supported the straightening tube 19 at the center of the straightening tube 19.
In this embodiment, two rectifier tube supports 20
is supported at the upper end and lower end of the rectifying tube 19, and it is possible to support it more reliably and accurately than in the above example.

FIG. 6 shows a third embodiment of the present invention, in which a is a plan view including a cross section, and b is a plan view including a cross section. In the two embodiments described above, the lower end of the instrumentation well 15 was inserted into the rectifier tube 19, but was a free end not supported by the rectifier tube 19. The flow of coolant flowing within the straightening grid 17 is not a symmetrical flow but an asymmetrical flow due to the influence of the upper core mechanism 9.
In order to accurately know the flow state of the coolant in each fuel assembly 4, it is important that the instrumentation well 15 is arranged coaxially with the rectifier tube 19. For this reason, in this embodiment, an instrumentation well holder 22 is provided on the inner periphery of the rectifying tube 19 to accurately and reliably hold the instrumentation well 15 at the center of the rectifying tube 19.
Therefore, in this embodiment, the axes of the rectifier tube 19 and the instrumentation well 15 are precisely aligned, improving instrumentation accuracy.

Furthermore, the upper end of the instrumentation well 15 is fixed to a support plate 21 provided in the upper core mechanism 9.
The distance from the fixed part to the lower end is usually 1 m or more, and on the other hand, after the coolant passes through the rectifier grid 17, it flows along the heat shield plate 14 and across the instrumentation well 15, so in some cases, the instrumentation There is a risk that the well 15 may vibrate due to the flow of coolant, which may cause fatigue failure of the instrumentation well 15, but in this example, the lower end of the instrumentation well 15 is connected to the rectifier tube 19. This concern can be eliminated because it is reliably maintained.

As described above, the present invention provides a liquid metal cooled fast reactor upper core mechanism equipped with a rectifying grid having a reliable rectifying function and a separating function. In addition to making it possible to understand the operating status, etc., the fabrication of the upper core mechanism is relatively easy, and it greatly contributes to ensuring the safety, improving performance, and reducing costs of liquid metal cooled fast reactors.

[Brief explanation of the drawing]

Figure 1 shows the general structure inside the reactor vessel of a liquid metal cooled fast reactor, Figure 2 shows the outline of the structure of the lower part of the upper core mechanism, and Figure 3 is a representative of the rectifying grid in the conventional upper core mechanism. Illustration showing an example, Figure 4a
-f are diagrams showing a first embodiment of the rectifying grating according to the present invention, and FIGS. 5 and 6 are diagrams showing second and third embodiments of the rectifying grating according to the present invention, respectively. DESCRIPTION OF SYMBOLS 1... Reactor vessel, 4... Fuel assembly, 8... Core structure, 9... Core upper structure, 15... In-core instrumentation well, 17... Rectifier grid, 19... Rectifier tube, 2
0... Rectifier tube supporter, 21... Support plate, 22...
Well holder.

Claims (1)

[Scope of Claims] 1. A plurality of cylindrical rectifier tubes and a plurality of hollow hexagonal columnar rectifier tube supports circumscribing the outer circumference of the rectifier tubes, which are installed on the upper part of nuclear fuel assemblies arranged in the reactor core. A liquid metal cooled fast reactor upper core mechanism having a honeycomb-shaped rectifying grid consisting of a hollow hexagonal column having an outer diameter that is one-half of the outer diameter of the fuel assembly. 2. The liquid according to claim 1, wherein the honeycomb-shaped rectifying grid is arranged so that the coolant flowing out from the corresponding one fuel assembly selectively flows into one of the rectifying tubes. Metal-cooled fast reactor core upper mechanism. 3. The liquid according to claim 1 or 2, wherein an instrumentation well holder for holding a tip of an instrumentation well inserted into the rectification tube is provided on the inner periphery of the rectification tube of the honeycomb-shaped rectification grid. Metal-cooled fast reactor core upper mechanism.