JPS612092A - Upper mechanism of core for fast breeder reactor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an upper core mechanism of a fast breeder reactor that uses a liquid metal such as liquid sodium as a coolant.

[Technical Background of the Invention] Generally, in fast breeder reactors that use liquid sodium as a coolant, core exit instrumentation such as a thermometer is installed at the exit of each fuel assembly for operation monitoring and abnormality diagnosis. A structure is adopted in which the core is supported by the upper core mechanism.

In the conventional fast breeder reactor, as shown in FIG. 4, the upper opening of the reactor vessel 1 is closed with a rotating plug 2, and the core upper mechanism 3 attached to this rotating plug passes through the rotating plug. Its lower end is suspended above the reactor core 4 installed in the reactor vessel 1 .

The upper core mechanism 3 is provided with a plurality of support plates 6 inside a cylindrical shell 5, and a plurality of control rod guide tubes 7 that accommodate control rod drive mechanisms (not shown) that hold and drive control rods. A plurality of instrumentation well guide tubes 9 are installed in which a large number of thin tube-shaped instrumentation wells 8 containing thermometers and the like are converged.

Further, in the lower part of the upper core mechanism 3, as shown in an enlarged view in FIG. 5, a tube plate 10 is installed which fastens and holds the vicinity of the lower end of each control rod guide tube 7. Each control rod guide tube 7 has a tube plate 10
By being fastened to the core 4, the bending rigidity is increased, and the relative displacement of the housed control rod drive mechanism with respect to the reactor core 4 during an earthquake or the like is maintained within the allowable displacement amount.

Further, the tube sheet 10 is disposed directly above each fuel assembly (not shown) constituting the reactor core 4, and separates the coolant flowing out from the fuel assembly from the coolant flowing out from the adjacent fuel assembly. It holds a cylindrical sampling tube 11 which is guided upward. Projections 12 are attached to the lower ends of these sampling tubes 11 to limit the floating of the fuel assembly within a certain range even if the fuel assembly should float.

The sampling pipe 11 prevents fatigue damage to the instrumentation well 8 caused by fluid vibration caused by coolant flowing out from the fuel assembly, and prevents measurement of measurement sensors such as thermometers due to fluctuations in the instrumentation well 8. In order to prevent a decrease in accuracy, the instrumentation well 8 is housed in an instrumentation well guide tube 9 that hangs down from the support plate 6 at the lower end of the body 5, and the tip of the instrumentation well 8 that has passed through the guide tube 9 is inside the sampling tube 11. is inserted into.

[Problems with the background art] In the conventional core upper mechanism configured as described above,
As the number of fuel assemblies composing the reactor core increases, the tube plate 1
0 and the instrumentation well guide tube 9 become complicated and difficult to manufacture, and the tube plate 10. '7) Due to the increased weight, the amount of displacement of the lower end of the control rod guide tube 7 during an earthquake or the like exceeds the allowable amount of displacement, which may reduce the insertion of the control rod.

[Object of the Invention] The present invention has been made in view of the above-mentioned problems, and it is possible to improve the structure for core exit instrumentation even in a nuclear reactor with a large number of fuel assemblies targeted for core exit instrumentation. To provide an upper core mechanism for a fast breeder reactor that is simple and lightweight, easy to manufacture, and that can reduce the amount of displacement at the lower end of a control rod guide tube to ensure control rod insertability during earthquakes, etc. With the goal.

[Summary of the Invention] The upper core mechanism of the fast breeder reactor of the present invention penetrates a rotating plug that closes the upper opening of the reactor vessel, and the reactor core structure (
A control rod guide tube that houses a control rod drive mechanism in a cylindrical shell vertically installed above the fuel assembly, and a core outlet device that measures the temperature of the coolant flowing out from the fuel assembly. In the upper core mechanism for storing and deploying the fuel assemblies, a lattice-like member is suspended from the lower part of the reactor directly above the core, and an instrumentation well insertion hole is formed in this lattice-like member so as to be located at the center of the fuel assembly. The instrumentation well insertion hole is disposed through the lower end of the core outlet equipment.

[Embodiments of the Invention] Examples of the present invention will be described below with reference to FIGS. 1, 2, and 3.

In these figures, the same members as in FIGS. 4 and 5 are given the same reference numerals.

FIG. 1 shows a longitudinal sectional view of the upper core mechanism of the present invention. In the figure, the core upper mechanism 3 has a cylindrical shell 5, and a plurality of support plates 6 are provided inside the shell. These support plates contain a plurality of control rod guide tubes 7 that house control rod drive mechanisms, and a plurality of instrumentation wells 8 that house thermometers and the like that perform core exit instrumentation. A well guide tube 9 is attached. Further, a lattice-like member 21 is suspended from the lower end of the body 5 via a plurality of support pipes 20 disposed around the circumference thereof.

2 and 3 show details of the lower part of the upper core mechanism 3 and the vicinity of the upper end of the core 4, and the lattice member 21 does not block the flow path of the coolant flowing out from each fuel assembly 30. It is constructed by assembling thin cloth temporary pieces in a lattice shape, and an instrumentation well insertion hole 22 is transparently provided directly above the center of the coolant outlet 31 of each fuel assembly 30.

The vicinity of the tip of the instrumentation well 8 passes through and is fixed in each of these instrumentation well insertion holes 22 .

In the upper core mechanism of the IC present invention configured as described above, the tip of the instrumentation well 8 housing a thermometer etc. for measuring the temperature of the coolant flowing out from each fuel assembly 30 is connected to the fuel assembly 30. Since it is disposed directly above the coolant outlet 31 of the fuel assembly, the temperature of the coolant can be measured without mixing with the coolant flowing out from other adjacent fuel assemblies.

Moreover, since the tip of the instrumentation well 8 is supported by penetrating the instrumentation well insertion hole 22 provided in the grid-like member 21, the instrumentation well guide tube of the conventional core upper mechanism is removed. When compared with the instrumentation well in , i.e. when the tip of the instrumentation well is supported and free,
Since the natural frequency is approximately 4=1, the instrumentation well will not experience fluid vibrations due to the coolant flowing out of the fuel assembly. In the unlikely event that coolant leaks from the fuel assembly,
If there is a possibility of fluid vibration occurring, this can be easily dealt with by slightly changing the outer diameter or wall thickness of the instrumentation well to increase its rigidity.

The lifting of the fuel assemblies is suppressed by a grid-like member placed directly above them.

Furthermore, the amount of displacement of the lower end of the control rod guide tube 7 during an earthquake or the like is restrained by the lattice member 21 supported at multiple points by the tube plate 21, a plurality of control rod guide tubes 7, and the support pipes 20; Well guide tube 9 and sampling tube 11
By omitting this, the load on the control rod guide tube is reduced, so it becomes extremely small.

[Effects of the Invention] As is clear from the above description, according to the present invention, even in large nuclear reactors with a large number of fuel assemblies targeted for core exit instrumentation, the structure and composition of the core exit instrumentation equipment can be improved. Because it can be simplified and lightweight, it is easy to manufacture, and the displacement of the lower end of the control rod guide tube during earthquakes can be reduced, ensuring ease of control rod insertion and improving the safety of the reactor. I can do it.

[Brief explanation of the drawing]

FIG. 1 is a vertical cross-sectional view of the upper core mechanism showing an embodiment of the present invention, FIGS. 2 and 3 are a plan view and a vertical cross-sectional view of the vicinity of the lattice member in the present invention, respectively, and FIG. 4 is a conventional core structure. FIG. 5 is a vertical cross-sectional view illustrating the upper mechanism, and FIG. 5 is an enlarged vertical cross-sectional view showing the vicinity of the instrumentation well guide tube in FIG. 2. 1...Reactor vessel 2...Rotating plug 3...Core upper mechanism 4...Reactor core 5......Body 6...Support plate 7...Control rod guide tube 8...Instrumentation well 9...Instrumentation well guide pipe 10...
...Tube plate 11...Sampling tube 12...
...Protrusion 20 ... Support pipe 21 ... Grid member 22 ... Instrumentation well insertion hole 30 ...・
...Fuel assembly 31...Coolant outlet plan Fig. 1 Fig. 2 Fig. 3 Fig. 4 Fig. 5

Claims (2)

[Claims] (1) A control rod guide that houses a control rod drive mechanism in a cylindrical shell that penetrates a rotating plug that closes the upper opening of the reactor vessel and is vertically installed above the fuel assemblies that make up the reactor core. In the upper core mechanism that houses and deploys tubes and core exit equipment for measuring the temperature of the coolant flowing out from the fuel assembly, a lattice-like member is suspended from the lower part of the shell directly above the core, and the lattice-like member is The member has an instrumentation well insertion hole formed in the center of the fuel assembly, and these instrumentation well insertion holes are provided so as to penetrate through the lower end of the core outlet equipment. Upper core mechanism of the reactor. (2) The upper core mechanism of a fast breeder reactor according to claim 1, wherein the lattice-like member is suspended from the shell by a control rod guide tube and a support pipe.