JPH0421836B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention is directed to a control rod assembly for a fast breeder reactor. [Technical Background of the Invention] A nuclear reactor control device for a fast breeder reactor is composed of a control rod assembly loaded in a reactor core and a control rod drive mechanism. The control rod assembly is composed of a lower guide tube, an entrance nozzle provided at the lower end of the lower guide tube, and a control rod housed in the lower guide tube so as to be vertically movable. The control rods are driven up and down by the control rod drive mechanism to be pulled out and inserted into the reactor core, thereby controlling the nuclear reactor. During a scram, the control rods are separated from the drive system of the control rod drive mechanism and fall into the reactor core by gravity, forming a scram. Incidentally, it is preferable that this scram time be as short as possible, and for this reason, a mechanism is provided to accelerate the fall of the control rod during the scram. As such a mechanism, the control rod assembly has a double structure consisting of a wrapper tube and a guide tube provided inside the control rod assembly, and the coolant introduced from the entrance nozzle is passed through the flow path between the wrapper tube and the guide tube. In some cases, the pressure of this coolant is introduced into the upper part of the guide tube through the neutron absorber, and the pressure of this coolant is applied to the upper surface of the neutron absorption section at the bottom of the control rod, and the pressure of this coolant accelerates the control rod. The coolant introduced into the upper part of the guide tube passes between the inner surface of the guide tube and the outer peripheral surface of the neutron absorption part, flows to the lower part of the guide tube, and then flows into the neutron absorption part to cool it. The neutron absorber is configured to flow upward through a rod portion protruding from the upper end of the neutron absorbing portion. [Problems with the background art] The above-mentioned device is configured to reduce the gap between the guide tube and the neutron absorbing section and give a large pressure drop to the coolant flowing through this gap in order to reduce the pressure in the lower part of the guide tube. Ru. In addition, in order to prevent the coolant introduced into the upper part of the guide tube from escaping upwards, an upper seal mechanism is provided to limit the flow rate of the coolant flowing between the outer circumference of the rod part of the control rod and the inner circumference of the guide tube. The gap between this upper seal mechanism and the outer peripheral surface of the rod portion is set to be a small gap. by the way,
When the control rod falls, the coolant in the lower part of the guide tube passes through the neutron absorption section and the rod section and escapes upward, but since a plurality of neutron absorption rods are housed in the neutron absorption section, the coolant does not flow upward. Road resistance is large.
For this reason, when the control rod falls during a scram, a high pressure is generated in the lower part of the guide tube, reducing the acceleration of the control rod and potentially impairing insertability. Furthermore, small gaps are formed between the control rod and the guide tube at two locations: the outer periphery of the neutron absorbing portion, the inner periphery of the guide tube, and the outer periphery of the rod portion and the upper seal mechanism. Therefore, if the straightness of the guide tube or the like is lost due to an earthquake or the like, there is a possibility that the control rod and the guide tube will interfere and the insertability of the control rod will be impaired. [Object of the Invention] The present invention was made based on the above circumstances, and its purpose is to ensure sufficient insertion of the control rod in a device that accelerates a control rod by the pressure of a coolant. The objective is to obtain a control rod assembly that can be used. [Summary of the Invention] The present invention provides a wrapper tube that is vertically provided in a reactor core and has an entrance nozzle at its lower end, and a flexible tube that is inserted into the tube from above and has a large-diameter neutron absorption section at its lower end. a control rod, a flow path formed between the control rod and the wrapper tube and guiding the coolant flowing into the entrance nozzle above the neutron absorption section, and the flow path provided above the wrapper tube. an upper seal mechanism that applies the pressure of the coolant flowing out from the neutron absorbing section to the upper surface of the neutron absorbing section; and an upper seal mechanism that is provided in the lower part of the lapper tube and is always open to remove the coolant that stays on the lower surface side of the neutron absorbing section from outside during scram. It is equipped with a coolant escape passage for letting the coolant escape. Therefore, when a control rod is inserted during a scram, the coolant in the lower part of the guide tube is released from the relief mechanism, so the pressure in the lower part of the guide does not increase and the control rod insertability is not impaired. Further, since the rod portion is bendable, there is no interference between the control rod and the guide tube even if the straightness of the guide tube is impaired, and sufficient insertability of the control rod can be ensured. [Embodiments of the Invention] Examples of the present invention will be described below. FIG. 1 shows a first embodiment of the present invention. In the figure, numeral 1 is a lapper tube, which has a regular hexagonal cross section. An entrance nozzle 2 is provided at the lower end of this wrapper tube 1, and this entrance nozzle 2 is inserted into a connecting pipe 4 provided on a core support plate 3.
This wrapper tube 1 is held in a predetermined position. A cylindrical guide tube 5 is provided within the wrapper tube 1, and a flow path 6 is formed between the outer circumferential surface of the guide tube 5 and the inner circumferential surface of the wrapper tube 1. The coolant introduced from the entrance nozzle 2 flows upward in the flow path 6 and flows into the upper part of the guide tube 5 through a through hole 7 formed at the upper end of the guide tube 5. ing. A control rod 8 is housed in the guide tube 5 so as to be movable up and down. This control rod 8 includes a neutron absorbing section 9, a hollow rod section 10 protruding from the upper end of this neutron absorbing section 9, and this rod section 1.
0 and a handling head 11 provided at the upper end of the handle. A plurality of neutron absorbing rods 12 are accommodated in the neutron absorbing section 9, and a coolant inlet 13 is formed on the lower surface of the neutron absorbing section 9. The coolant that has flowed into the upper part of the guide tube 5 passes between the inner circumferential surface of the guide tube 5 and the outer circumferential surface of the neutron absorption section 9 and flows to the lower part of the guide tube 5. The coolant flows from the lower part through the coolant inlet 13 into the neutron absorbing section 9, cools the neutron absorbing rods 12, and then passes through the hollow rod section 10 and flows upward from the outlet 14 at the upper end of this rod section 10. It is configured so that it flows out. The gap between the outer circumferential surface of the neutron absorbing section 9 and the inner circumferential surface of the guide tube 5 is formed relatively narrow, and a labyrinth section 15 is formed on the outer circumferential surface of the neutron absorbing section 9. It is configured to create a large pressure drop in the coolant flowing through the gap. Therefore, the upper part of the guide tube 5 has a high pressure and the lower part has a low pressure, and this pressure difference constantly applies a downward biasing force to the control rod 8 .
The control rod 8 is configured to be accelerated by this biasing force during scram insertion. Further, an annular upper sealing mechanism 1 is provided on the inner surface of the upper end of the guide tube 5.
6 is provided protrudingly, and a relatively narrow gap is set between the inner circumferential surface of the upper seal mechanism 16 and the outer circumferential surface of the rod portion 10, and a labyrinth portion 17 is formed on the inner circumferential surface. There is. Therefore, this sealing mechanism 16 and the rod portion 1 are removed from the upper part of the guide tube 5.
The flow rate of the coolant escaping upward through the gap between the guide tube 5 and the guide tube 5 is limited to a very small flow rate, so that the high pressure within the guide tube 5 can be maintained. Further, a dart ram 18 is provided protruding from the lower end of the neutron absorbing section 9, and a dart pot 19 is formed on the inner upper surface of the entrance nozzle 2. When the control rod 8 is lowered, the dart ram 18 enters the dart pot 19 and is configured to reduce the impact when the control rod 8 bottoms out. A relief mechanism, such as a relief passage 20, is formed in the entrance nozzle 2 in order to release the coolant in the inner lower part of the guide tube 5 to the outside. are communicating. Further, the rod portion 10 is provided with bending mechanisms 21 and 22, for example, at its base end and intermediate portion. These bending mechanisms 21 and 22 have, for example, spherical seating surfaces and are formed to be bendable in all directions. Therefore, the rod portion 10 can be bent in all directions by these bending mechanisms 21 and 22. Next, the operation of the first embodiment will be explained. The control rod 8 has a gripper 2 of a control rod drive mechanism attached to a handling head 11 at the tip of the rod portion 10.
3 is connected, and insertion and withdrawal are performed by this control rod drive mechanism. During scram, the control rods 8 are separated from the drive system of the control rod drive mechanism and inserted into the reactor core by gravity, and at this time, they are accelerated by the pressure difference between the upper and lower sides of the guide tube 5, and are inserted in a short time. be done. At this time, the coolant in the lower part of the guide tube 5 passes through the neutron absorbing section 9 and escapes from the escape passage 20 as well. Therefore, the pressure in the lower part of the guide tube 5 does not increase, the acceleration due to the pressure difference is not reduced, and the insertability is improved. Furthermore, even if the straightness of the guide tube 5 is lost due to an earthquake or the like, the control rod 8 will not interfere with the guide tube 5 because the rod portion 10 is bendable. , insertability can be maintained reliably. Note that the present invention is not limited to the above-described first embodiment. For example, FIG. 3 shows a second embodiment of the invention. In this second embodiment, a pressing member 30 is provided at the upper part of the guide tube 5, and this pressing member 30 is connected to a spring 3.
1 to bias it downward. In this second embodiment, when the control rod 8 is in the withdrawn state, the upper end of the pressing member 30 comes into contact with the neutron absorption part 9 and is pushed up with the spring 31 compressed. As mentioned above, in addition to the pressure difference between the upper and lower sides of the guide tube 5, the biasing force of the spring 31 also accelerates the control rod 8 , thereby further shortening the insertion time. Furthermore, the present invention is not limited to the second embodiment described above. For example, it is not necessarily necessary to provide a bending mechanism in the rod part; for example, the rod part itself may be made bendable by lowering its rigidity. [Effects of the Invention] As described above, the present invention has a wrapper tube provided vertically in the core and having an entrance nozzle at the lower end, and a large-diameter neutron absorption section inserted into the wrapper tube from above and at the lower end. a bendable control rod; a flow path formed between the control rod and the wrapper tube to guide the coolant flowing into the entrance nozzle above the neutron absorption section; An upper seal mechanism that applies the pressure of the coolant flowing out of the flow path to the upper surface of the neutron absorbing section, and a scram mechanism that is provided in the lower part of the lapper tube and is permanently open, and that scrams the coolant that stays on the lower surface side of the neutron absorbing section. It is equipped with a coolant escape passage for allowing the coolant to escape to the outside. Therefore, when a control rod is inserted during a scram, the coolant in the lower part of the guide tube is released from the relief mechanism, so the pressure in the lower part of the guide tube does not increase and the insertability of the control rod is not impaired. In addition, since the rod part is bendable, there is no interference between the control rod and the guide tube even if the straightness of the guide tube is lost, and the control rod can be inserted easily, which is very effective. It is.

[Brief explanation of drawings]

1 and 2 show a first embodiment of the present invention, FIG. 1 is a longitudinal sectional view, and FIG. 2 is a -
It is a sectional view along a line. Further, FIG. 3 is a longitudinal sectional view of the second embodiment. 1... Ratsupa tube, 2... Entrance nozzle,
5... Guide tube, 6... Channel, 8 ... Control rod, 9...
...Neutron absorption part, 10...Rod part, 11...Handling head, 16...Upper seal mechanism, 2
0...Escape passage (escape mechanism), 21, 22...Bending mechanism.

Claims (1)

[Claims] 1. A wrapper tube installed vertically in the reactor core and having an entrance nozzle at its lower end; a bendable control rod inserted into the wrapper tube from above and having a large-diameter neutron absorption section at its lower end; A flow path is formed between the Ratsupa tube and guides the coolant that has flowed into the entrance nozzle above the neutron absorption section, and a flow path is provided at the upper part of the Ratsupa tube that controls the pressure of the coolant flowing out from the flow path. an upper sealing mechanism that acts on the upper surface of the absorption section; and a coolant escape passage that is provided in a lower part of the rapture tube and is always open to allow the coolant that accumulates on the lower surface side of the neutron absorption section to escape to the outside during scram. A control rod assembly characterized by comprising: