JPH0523396B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a control rod assembly for controlling the core power of a nuclear reactor using liquid metal cooling, and in particular to a control rod assembly that eliminates the problem of thermal stress occurring in the upper part of the reactor core. Concerning aggregates.

[Technical background of the invention and its problems]

The control rod assembly has a control rod body containing a neutron absorber that can be moved up and down in a guide tube, and controls the core output by inserting and removing the neutron absorber into the core region. The above neutron absorber is
Since heat is generated by absorbing neutrons in the reactor core, the inside of the guide tube is structured so that liquid metal coolant can flow between the inside and outside of the control rod body, between the neutron absorbers, etc.

By the way, since the amount of neutrons absorbed by a neutron absorber differs depending on the amount inserted into the core region,
The amount of heat generated also varies greatly depending on the amount of insertion of the control rod body into the core region. In other words, if we focus on the control rods of a nuclear reactor during normal power operation,
As the amount of insertion of the control rod body into the core region increases, the amount of heat generated by the neutron absorber increases, and as the amount of insertion decreases, the amount of heat generated by the neutron absorber decreases. On the other hand, since the coolant flow rate is set based on the maximum heat generation of the neutron absorber,
If the amount of control rod bodies inserted into the core region is small, most of the coolant will not contribute to heat removal, and the coolant outlet temperature of the control rod assembly will not rise much. As a result, the outlet temperature of the control rod assembly becomes, for example, about 200° C. lower than the outlet temperature of the adjacent fuel rod assembly, resulting in a large temperature difference. Moreover, the striped temperature waves caused by the coolants from the control rod assemblies and fuel assemblies, which have such a temperature difference, hit the rectifier, etc. at the lower end of the upper core mechanism installed in the upper part of the reactor core, so the rectifier This caused large thermal stress in equipment, etc., resulting in localized thermal fatigue.

[Purpose of the invention]

The present invention has been made in consideration of these circumstances, and its purpose is to connect the outlet of the control rod body to the outlet of the adjacent fuel assembly, regardless of whether the control rod body is inserted into or removed from the guide tube. It is an object of the present invention to provide a control rod assembly that can reduce the maximum temperature difference between the reactor cores, prevent the generation of thermal stress in the upper core mechanism, and eliminate thermal fatigue caused by this.

[Summary of the invention]

The present invention provides a guide tube that is provided in the core of a liquid metal cooled nuclear reactor and has a guide tube handling head at its upper end, and a guide tube that is provided in the guide tube so as to be movable up and down and that is inserted through the center hole of the guide tube handling head. A control rod body having a control rod handling rod on the upper part connected to a control rod drive mechanism, and a control rod body provided on the control rod so as to be movable in the vertical direction when the control rod body is pulled up by the control rod drive mechanism. a coolant flow restrictor that comes into contact with the lower surface of the guide tube handling head to control the flow rate of coolant flowing through the guide tube; The present invention is characterized in that it includes a stopper that limits movement, and an elastic body that is provided on the control rod handling rod and presses the coolant flow restrictor against the stopper.

[Embodiments of the invention]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A control rod assembly according to an embodiment of the present invention will be described below with reference to the drawings.

Figures 1 and 2 are diagrams showing the schematic configuration of the control rod assembly, and Figure 1 shows the fully inserted state of the control rods.
Further, FIG. 2 shows the control rod in a fully withdrawn state.

That is, numeral 1 in the figure is a guide tube in which the control rod main body 2 is accommodated so as to be movable up and down. This guide tube 1
has an entrance nozzle 3 at its lower end and a guide tube handling head 4 at its upper end. The entrance nozzle 3 is attached to a core support plate 5 fixed to the reactor. The guide tube handling head 4 is supported by a mechanism (not shown) to attach and detach the guide tube to the nuclear reactor. At the lower end of the entrance nozzle 3,
A coolant inflow hole 6 is formed inside the guide tube 1 for introducing a coolant such as liquid sodium. A coolant discharge hole 7 is provided at the upper end of the guide tube 1 for discharging the coolant introduced into the guide tube 1 . A fixing plate 8 is integrally provided inside the guide tube 1 at a position slightly below the coolant discharge hole 7 so as to divide the inside of the guide tube 1 into upper and lower halves. A center hole 9 for the coolant to flow is provided in the center of the fixed plate 8.

The control rod body 2 includes a plurality of neutron absorbers 11
, lattice plates 13 and 14 that support the upper and lower ends of these neutron absorbers 11 and have a plurality of coolant flow holes 12, and a protection tube 15 that accommodates them.
A control rod handling rod 16 provided at the upper end of this protection tube 15 for pulling out the control rod body.
It is made up of. The protective tube 15 has a ram part 18 having a plurality of coolant inflow holes 17 at its lower end, and a plurality of coolant discharge holes 19 at its upper end. The outer diameter of the protective tube 15 is set smaller than the inner diameter of the guide tube 1, so that a coolant flow path 21 is formed in the gap between the two. Further, a coolant flow path 22 is also formed in the gap between the neutron absorbers 11 .

The control rod handling head 16 passes through the center holes 9, 7 of the guide tube handling head 4 and is connected to a control rod drive mechanism (not shown), and is pulled up to the upper part of the guide tube 1 by this control rod drive mechanism.
At an intermediate position of the handling rod 16 and below the fixed plate 8, a coolant flow restrictor 23 is provided.
is installed. This coolant flow restrictor 23
The control rod is composed of a notched disc body 25 movably mounted on the control rod handling rod 16, and a coil spring 26 mounted between the notched disc body 25 and the upper end of the protection tube 15. ing. As shown in FIG. 3, the notched disc body 25 has two
It has two notches 27. and,
This notched disk body 25 is designed to prevent the control rod handling rod 16 from floating upward due to the fluid force of the coolant flowing through the inside of the guide tube 1.
By the stopper 28 provided in the middle part of
Its upper position is regulated.

Next, the operation of the control rod assembly according to this embodiment configured as described above will be explained.

Now, when the control rod body 2 is in the full insertion position shown in FIG. 1, the coolant introduced into the guide tube 1 from the coolant inflow hole 6 of the entrance nozzle 3 flows as shown by the arrow in the figure. It reaches the center hole 9 of the fixed plate 8 via the coolant flow path 21 or the coolant flow path 22,
The coolant passes through the center hole 9 and is discharged from the coolant discharge hole 7. At this time, the flow rate of the coolant flowing through the inside of the guide tube 1 is a value set in consideration of the case where the neutron absorber 11 generates the most heat.

Next, when the control rod body 2 is gradually pulled up,
Eventually, the upper end of the notched disk 25 comes into contact with the lower end of the fixed plate 8. Furthermore, when the control rod main body 2 is pulled up, the distance between the notched disc body 25 and the protective tube 15 is narrowed, and the coil spring 26 is contracted. In this way, when the notched disc body 25 and the fixing plate 8 come into contact with each other, the coolant flowing from below the fixing plate 8 to the information flows through the notched part 27 provided in the notched disc body 25.
This results in a large amount of coolant passing through the pipe, greatly limiting the flow rate of the coolant. As a result, the coolant temperature near the coolant discharge hole 7 increases.

FIG. 4 is a diagram showing changes in the exit temperature A of the control rod assembly and the exit temperature B of the fuel rod assembly depending on the position of the control rod body 2. That is, the outlet temperature B of the fuel assembly is lowest when the control rod body 2 is in the fully inserted position because the reactivity is low, and highest when it is in the fully withdrawn position because the reactivity is high; It is changing linearly. On the other hand, in a conventional control rod assembly, the flow rate of the coolant flowing through the inside of the guide tube 1 is uniquely determined, so when the control rod body 2 is in the fully inserted position, the control rod The outlet temperature A′ of the assembly was highest and lowest at the fully withdrawn position, and varied linearly between them.
For this reason, there was a large difference in the outlet temperature between the two during full drawing. However, according to this embodiment,
At an intermediate position between the fully inserted position and the fully withdrawn position of the control rod body 2, for example, at point C, the notched disc body 25
acts to limit the flow rate of the coolant, so
The exit temperature of the control rod assembly will rise rapidly at point C. As a result, as shown in the same figure, the conventional maximum temperature difference T is changed to the maximum temperature difference T', and the temperature difference △
It becomes possible to decrease by T.

In the above embodiment, the notched disc body 25 is used as the coolant flow restricting body 23 , but for example, a disc body having a plurality of coolant flow holes or a disc body having a plurality of coolant flow holes, or when it comes into contact with the fixing plate 8, the fixing plate 8 A disc body or the like having a protrusion on its upper end so as to form a small gap with the plate 8 may be used. In short, the flow rate of the coolant passing through the center hole 9 of the fixed plate 8 may be restricted using a hydrodynamic resistor.

〔Effect of the invention〕

As explained above, according to the present invention, the flow rate of the coolant flowing through the guide tube is reduced on the way from the fully inserted position to the fully withdrawn position, so that the amount of heat generated by the neutron absorber is reduced. At a withdrawal stroke position with a small amount, the coolant outlet temperature of the control rod assembly can be increased. For this reason, the maximum temperature difference between the exit temperature of the control rod assembly and the exit temperature of the fuel rod assembly can be reduced compared to the conventional method, which ultimately alleviates thermal stress and thermal fatigue of the reactor structure. This can contribute to improving the reliability of nuclear reactors.

In addition, since the present invention only adds an extremely simple configuration, the structure does not become complicated, and the ease of inserting control rods, which is one of the important functions of a control rod assembly, is not impaired. Not at all. Furthermore, according to the present invention, when the control rod handling rod is separated from the control rod drive mechanism with the control rod body pulled up, the control rod body is rapidly inserted into the reactor core by the elastic force of the elastic body. The furnace can be brought to an emergency stop in a short time.

[Brief explanation of the drawing]

Fig. 1 is a vertical cross-sectional view of a control rod assembly in a fully inserted state according to an embodiment of the present invention, Fig. 2 is a longitudinal cross-sectional view of the control rod assembly in a fully withdrawn state, and Fig. 3 is a cutout of the control rod assembly. FIG. 4 is a perspective view showing the disc body, and a characteristic diagram showing the control rod outlet temperature with respect to the control rod stroke of the control rod assembly in comparison with a conventional example. 1... Guide tube, 2... Control rod body, 3... Entrance nozzle, 4... Guide tube handling head, 6... Coolant inflow hole, 7... Coolant discharge hole,
8... Fixed plate, 9... Center hole, 11... Neutron absorber, 15... Protection tube, 16... Control rod handling rod, 23 ... Coolant flow rate restrictor, 25...
...Notched disc body, 26... Coil spring, 27...
Notch part, 28...stopper.

Claims (1)

[Claims] 1. A guide tube provided in the core of a liquid metal cooled nuclear reactor and having a guide tube handling head at its upper end, and a control rod that is provided within the guide tube so as to be able to rise and fall and is inserted through the center hole of the guide tube handling head to drive the control rod. a control rod body having a control rod handling rod on the upper part connected to the mechanism, and a guide provided on the control rod handling rod so as to be movable in the vertical direction when the control rod body is pulled up by the control rod drive mechanism. A coolant flow restrictor that comes into contact with the lower surface of the tube handling head to limit the flow of coolant flowing through the guide tube, and a coolant flow restrictor that is provided on the control rod handling rod to prevent upward movement of the coolant flow restrictor. A control rod assembly comprising: a restricting stopper; and an elastic body provided on the control rod handling rod and pressing the coolant flow rate restrictor against the stopper.