JPH0548436B2 - - Google Patents

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 is fastened to the tube plate 10, so that
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 isolates the coolant flowing out from the fuel assembly from the coolant flowing out from other adjacent fuel assemblies. 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 also prevents measurement sensors such as a thermometer from measuring 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. is inserted into the sampling tube 11.

[Problems with Background Art] In the conventional upper core mechanism configured as described above, as the number of fuel assemblies configuring the core increases, the structure of the tube plate 10 and the instrumentation well guide tube 9 becomes complicated. In addition to being difficult to manufacture, the weight of the tube sheet 10 increases, so the control rod guide tube 7 is not suitable for earthquakes, etc.
The amount of displacement at the lower end of the rod exceeded the allowable amount of displacement, and there was a risk that the insertion of the control rod would be reduced.

[Object of the Invention] The present invention has been made in view of the above-mentioned conventional problems, and it provides a 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, which is simple and lightweight, is easy to manufacture, and can reduce the amount of displacement of the lower end of a control rod guide tube to ensure control rod insertability during earthquakes, etc. The purpose is to

[Summary of the Invention] The upper core mechanism of the fast breeder reactor of the present invention has a cylindrical structure that penetrates a rotating plug that closes the upper opening of the reactor vessel and is suspended above the fuel assemblies that constitute the reactor core. In an upper core mechanism in which a control rod guide tube that accommodates a control rod drive mechanism and a core outlet device that measures the temperature, etc. of the coolant flowing out from the fuel assembly are housed in the shell, from the lower part of the shell. A grid-like member is suspended directly above the reactor core, and instrumentation well insertion holes are formed in this grid-like member so as to be located at the center of the fuel assembly. is characterized in that it is supported in a state where it penetrates and projects downward from the grid-like member.

[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 designated by the same reference numerals.

FIG. 1 shows a longitudinal sectional view of the upper core mechanism of the present invention. In the figure, the upper core 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.

Figures 2 and 3 show the lower part of the upper core mechanism 3,
This figure shows the details of the vicinity of the upper end of the reactor core 4. The lattice member 21 is constructed by assembling narrow plates in a lattice shape so as not to block the flow furnace of coolant flowing out from each fuel assembly 30. , 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 is passed through and fixed to each of these instrumentation well insertion holes 22 .

In the upper core mechanism of the 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 from the grid member 21. Since it protrudes downward and is placed directly above the coolant outlet 31 of the fuel assembly 30, it is possible to maintain the temperature of the coolant without mixing with the coolant flowing out from other adjacent fuel assemblies. Can be measured accurately.

Moreover, the tip of the instrumentation well 8 is connected to the grid member 21.
Since the instrumentation well is supported by penetrating the instrumentation well insertion hole 22 provided in the Since the natural frequency is about 4:1 between supported and free tips, the instrumentation well does not experience fluid oscillations due to coolant exiting the fuel assembly. In the unlikely event that fluid vibrations may occur due to coolant flowing out of the fuel assembly,
This can be easily addressed by slightly changing the outer diameter or wall thickness of the instrumentation well to increase its rigidity.

Further, floating of the fuel assemblies is suppressed by the grid member disposed 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 support plate 6, a plurality of control rod guide tubes 7, and the support pipes 20. Moreover, the load on the control rod guide tubes is reduced by omitting the instrumentation well guide tube 9 and the sampling tube 11, so that the load is extremely reduced.

[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. Vertical sectional view illustrating the upper mechanism, No. 5
This figure is an enlarged vertical 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... Core, 5... Shell, 6... Support plate, 7... Control rod guide tube, 8... Instrumentation well,
9...Instrumentation well guide tube, 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.

Claims (1)

[Claims] 1. A control rod guide tube 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 core outlet equipment for measuring the temperature of coolant flowing out from the fuel assembly, a lattice member is suspended directly above the core from the lower part of the shell, and a lattice member is suspended from the lower part of the shell, and instrumentation well insertion holes are formed to be located at the center of the fuel assembly, and the lower ends of the core outlet equipment pass through these instrumentation well insertion holes and are supported in a state protruding downward from the grid member. The upper core mechanism of a fast breeder reactor is characterized by: