JPS6039994B2 - control rod - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a control rod that is composed of a guide tube and a neutron absorption rod that moves up and down within the guide tube.

As shown in Fig. 1, the control rods used in conventional fast breeder reactors consist of a guide tube 2 installed on a core support plate 1, a protection tube 3 that moves up and down within the guide tube 2, and a protective tube 3 that moves up and down within the guide tube 2. It consists of a neutron absorption register 4 housed within a protection tube 3.

The guide tube 2 has a coolant intake port 5 at its lower part, from which the coolant flows into the guide tube 2. The protection tube 3 containing the neutron absorption rod 4 has an inlet 6 for introducing the coolant on the lower surface, and
Each has a coolant outlet 7 on the top surface. Between the guide tube 3 and the protective tube 4, there are manufacturing and skirting tolerances, heat during use,
The protective tube 3 inside the guide tube 2 takes into account deformation due to irradiation, deformation due to external force from the surroundings, deformation and displacement due to earthquake force, etc.
A gap is provided that is large enough to allow unobstructed movement.

By the way, the coolant for cooling the neutron absorber 4 built into the protection tube 3 flows into the interior from the coolant intake port 5 on the lower surface of the guide tube 2, as indicated by the arrow in the figure, and then At the lower end position of the protection tube 3, the flow is divided into a flow into the protection tube and a bypass flow flowing through the gap between the protection tube and the guide tube.

The effective flow of coolant entering the protection tube 3 normally passes between a plurality of neutron absorption rods 4 and flows out to the upper part of the guide tube 2 through an outlet 7 on the top surface.

Here, it merges with the bypass flow and flows out from the upper end of the guide tube 2. However, in recent years, as fast reactors have become larger, the following problems have arisen. 'i} Due to the tendency of maximizing the neutron absorption rate 4 and increasing the filling rate, the pressure loss of the protection tube 3 increases, the effective flow rate of coolant decreases, and the bypass flow outside the protection tube 3 increases.

This bypass flow is a kind of waste flow, and its increase lowers the reactor outlet coolant temperature, which in turn lowers the plant temperature efficiency. 'ii' With the increase in the bypass flow, fluid vibrations in the protection tube 3 are likely to occur, which in turn has an adverse effect on the output fluctuations of the reactor.

The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to obtain a control rod that can secure an effective coolant and suppress vibrations of the protection tube despite the increase in the length of the neutron absorption beam.

An embodiment of the present invention will be described below with reference to the drawings.

It should be noted that parts having the same functional structure as the conventional one are given the same reference numerals, and the details will be omitted. As shown in FIG. 2, the control rod of the present invention includes a guide tube 2 installed on a core support plate 1, a protection tube 3 provided so as to be movable up and down inside this guide tube 2, and a control rod inside this protection tube 3. It is composed of a plurality of neutron absorption rods 4 provided in the neutron absorber.

An entrance nozzle 8 is attached to the lower part of the guide tube 2, which is inserted into the core support plate 1 and takes in coolant.

A handling head 9 for gripping and lifting the guide tube 2 is formed at the upper end. Further, a dashpot 11 is provided at the upper part of the lower zero-cent transformer nozzle 8 inside the guide tube 2, which cooperates with a dash ram 10 formed at the lower end of the protection tube 3. At least one through hole 12 is provided at the connection between the dashpot 1 and the entrance nozzle 8 to allow the flow of the coolant. 4
A dash ram 10 that cooperates with the dash pot is formed at the lower end of the container.

Further, a connecting tool 13 for moving the protective tube 3 up and down within the guide tube 2 is attached to the upper surface. This coupling turtle 3 is removably engaged with a control lever drive mechanism (not shown). The neutron absorber 4 housed in the protective tube 3 has a carbonized columnar (B4C) pellet 1 which is a neutron absorber in its lower half.
4 is filled.

Above is an empty gas plenum 15.
Therefore, the heat generating part of the neutron absorber 4 is mainly located in the beret 1.
It is 4. Several coolant inlets 6 are provided on the lower surface of the protection tube 3.

The coolant that has entered the protective tube 3 flows out into the guide tube 2 through coolant outlets 17 formed at equal intervals on the side surface of the protective tube 3. The coolant outlet 17 is provided at a location somewhat higher than the top surface of the pellet 14 of the neutron absorption rod 4. Next, the operation will be explained.

The protection tube 3 housed in the guide tube 2 moves up and down within the guide tube 2 to adjust the amount of neutron absorption in the furnace, thereby adjusting the heat output. The coolant also flows into the guide tube 2 through the entrance nozzle 8. Most of the coolant flowing into the guide tube 2 enters the protection tube 3 through the coolant inlet 6. The coolant flowing into the protection tube 3 cools the neutron absorption rod 4 and is ejected from the coolant outlet 17 into the annular space between the protection tube 3 and the guide tube 2. Due to this ejection, the jet flow of the coolant acts so that the protective tube 3 is located at the center of the guide tube 2 (a sea bream effect). Further, this jet stream acts as a barrier (barrier effect) to the bypass flow, and prevents an increase in the bypass flow. The coolant jetted into the annular space merges with the bypass flow and flows out from the upper end of the guide tube 2.

Incidentally, if the pressure loss exceeds the allowable value by doing as shown in this embodiment, this can be avoided by providing several holes in the guide tube 2 above the outlet 17 of the protection tube 3.

Since the control shaft of the present invention is configured as described above, the bypass flow rate flowing through the annular space between the protection tube and the guide tube is reduced, so that the protection tube can be quietly held in the guide tube.

By reducing the bypass flow rate, the coolant temperature can be increased and the plant temperature efficiency can be increased. Furthermore, since the protective tube can be held quietly, fluctuations in the output of the reactor can be reduced.
For example, in a reactor-class fast reactor control rod, the effective flow rate of coolant sodium in the protection tube is approximately 3.7 kg, and the diameter is 9.
．． When 6 side holes are provided on the 5th side, a jet reaction force of approximately 1 kg acts on the protective tube horizontally toward the center, and sufficient alignment and barrier effects can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a schematic sectional view of a conventional control rod, FIG. 2 is a schematic sectional view showing an embodiment of the control rod of the present invention, and FIG. 3 is a cross-sectional view of FIG. FIG. 2...Guide tube 3...Protection tube 4...
...Neutron absorption, 6...Coolant inlet, 7
・・・・・・Coolant outlet. Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] 1. A guide tube supported by a core support plate and capable of introducing coolant, a protection tube that moves up and down within this guide tube, a neutron absorption rod housed in this protection tube, and a neutron absorption rod provided on the lower surface of the protection tube. A control rod consisting of a coolant inlet and several coolant outlets equally spaced on the side of the protection tube.