JPS6125094A - Control rod for nuclear 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 a control rod for a nuclear reactor in which the ease of inserting a neutron absorber into a curved control rod guide tube in a fast breeder reactor is improved.

[Technical Background of the Invention] Among nuclear reactors, especially fast breeder reactors, reactor startup and
The control rod that performs shutdown and output adjustment is a control rod that incorporates a plurality of absorption pins containing neutron absorbing material in a cluster shape in a control rod guide tube arranged between the fuel assemblies of the reactor core.
The drive mechanism is operated from the top of the reactor, and insertion or extraction is performed via the drive shaft.

In a practical-scale fast breeder reactor, the length of the control rod is approximately 4 to 5 inches.
Although the length of the guide tube is 1.5 mm, the gap between the guide tube and the control rod is limited to be relatively narrow for economical arrangement and to prevent output fluctuations.

Therefore, during reactor operation, thermal effects in the core,
If the guide tube is bent due to neutron irradiation, it is expected that the withdrawal and insertion operations of long control rods will be difficult due to the bend in the guide tube, which is an extremely important problem especially for ease of insertion during reactor scram. .

FIG. 2 shows an example of a control rod for a nuclear reactor that has been proposed to solve this problem. Reference numeral 1 in FIG. 2 indicates a control rod guide tube, into which a large number of absorption pins as absorbers are bundled and inserted as a collection.

That is, the absorption pin assemblies 3a, 3b, and 3c that house the neutron absorbing material and are composed of upper, middle, and lower parts are respectively composed of upper lattice plates 2a, 2b, and 2c, and lower lattice plates 4a, 4b,
4a to form a cluster, and are connected to each other by universal joints 5a and 5b. These absorption pin aggregates 3a, 3b, 3c are connected to the connecting rod 1.
0 to the handling head 11, and is connected to a drive shaft 13 that is directly connected to a drive mechanism, and is pulled and inserted upward and downward into the guide tube 1. A guide tube handling head 12 is provided at the upper end of the guide tube 1 for loading and extracting the guide tube 1 into the reactor core, and a coolant outflow hole 14 is provided at the upper side of the guide tube. There is.

Furthermore, a dash ram 6 is provided at the bottom of the lattice plate 4C, and the dash ram 6 decelerates the control rod using fluid pressure by pushing it into a dash pot 7 provided at the bottom of the guide tube 1 at the final stage of falling during a scram. It is designed to stop smoothly. An entrance nozzle 8 is connected to the lower part of the guide tube 1, and is installed in a core support plate 9 provided at the lower part of the reactor core to fix the guide tube 1.

According to this control rod for a nuclear reactor, the absorption pin assembly in the guide tube 1 is divided into three equal parts and each is connected by universal joints 5a and 5b. Even if the absorption pin assemblies 3a, 3b, 3c are bent beyond the gap between the outer diameter and the inner diameter of the guide tube 1, the reactor
It can be inserted without any problem during scrum.

[Problems in the Background Art] However, in conventional control rods for nuclear reactors, the absorber is divided into three parts, and a universal joint is interposed in the intermediate connecting part, so the volume of the absorber is reduced and moreover, the absorber is divided into three parts. It becomes continuous. Therefore, it is not preferable from the viewpoint of the control rod's neutron absorption ability.

In addition, regarding deceleration after scram, a dash ram is provided at the bottom of the absorber, and the lower end of the absorber receives acceleration, so a large force is applied to the pin connection of the universal shimmed part that connects the absorbers. Since it is a segmented structure, it is expected that a force in the right angle direction will be generated and the collision force with the guide tube will be large.

[Object of the Invention] The present invention has been made to solve the above-mentioned drawbacks of the conventional example, and its object is to provide a control rod for a nuclear reactor that achieves the following two objects.

First point: By attaching the absorption pin to the upper and lower lattice plates as an integral structure, and making the support provided in the center a segmented structure, insertability when the guide tube is bent is ensured.

A second guide pipe dashpot is installed at the top of the guide pipe, and the control rod handling head is used as a dash ram.
The upper part of the absorber performs deceleration during scram.

[Summary of the Invention] 4. The present invention provides an entrance nozzle which is provided with a coolant outflow hole on the upper side surface and has a dashpot formed at the upper end, has a handling head at the upper part of the dashpot, and allows the coolant to flow into the lower end. and a cluster-shaped neutron absorption pin assembly inserted into the guide tube, the neutron absorption pin assembly having a control rod handling head whose upper end is fitted into the dashpot. The absorption pins are connected to a rod, and the cladding tubes of the absorption pins are flexible, and both upper and lower ends of the absorption pins are fixed to a pair of upper and lower lattice plates, and a plurality of universal joints are provided in the center along the axial direction. This is a control rod for a nuclear reactor, characterized in that it consists of a plurality of short rods connected through a rod and a bendable strut inserted therein.

According to the present invention, the absorption pin assembly as a neutron absorber is easily bent by a weak force, and even if the guide tube is bent, the control rod can be inserted into the reactor core without a large increase in load. It is possible to prevent the assembly from buckling.

[Embodiment of the Invention] Hereinafter, an embodiment of a control rod for a nuclear reactor according to the present invention will be described with reference to FIG. In FIG. 1, the same parts as those in FIG. 2 are indicated by the same reference numerals, and the explanation of the overlapping parts will be omitted.

In FIG. 1, the upper end of the control rod guide tube 1 has a thick wall portion 1.
5, and a dashpot 16 is provided in the center of this thick portion 15. This dashpot 16
A control rod handling head 11 connected to the upper end of the connecting rod 10 is inserted therein. An upper grid plate 18 is connected to the lower end of the connecting rod 10 via an arm 17. A plurality of elongated neutron absorption pins 19 are connected to the upper grid plate 18 in a cluster shape, for example, by screws, thereby forming an absorption pin assembly.

The lower ends of these absorption pins 19 are loosely inserted into and integrated with the lower lattice plate 20.

Further, in the center of the pair of upper and lower lattice paths 18 and the lower lattice plate 20, a column 22 which is divided into three parts and connected by a universal joint 21 is fixed so as to pass through the center of a large number of absorption pins 19. ing. The absorption pin 19 has a relatively thin and flexible cladding tube filled with a neutron absorbing material such as B4C powder, and both upper and lower ends of the cladding tube are sealed with end plugs. The support column 22 is made up of a plurality of short rods connected to the universal joint 21 so as to be bendable. Further, a buffer member 23 is connected to the bottom surface of the lower lattice plate 20. The entrance nozzle 8 connected to the lower part of the guide tube 1 is provided with a coolant inflow hole 24 .

The coolant inside the reactor (not shown) is at the entrance nozzle 8.
The water flows in through the inflow hole 24 and flows around the absorption pin 19 in the guide tube 1, and flows out through the outflow hole 14 provided above the guide tube 1.

Therefore, the integrated absorption pin 19 is connected to the upper grid plate 1.
8 and the lower lattice plate 20, they are assembled into a cluster and act as a neutron absorber.

The upper and lower lattice plates 18.20 are the pillars 2 provided in the center.
It is fixed by 3. Note that the absorption pins 19 and the lattice plates 18 and 20 are connected only by the upper lattice plate 18, and the lower lattice plate 20 is not fixed in the upper and lower directions, but is designed to absorb the difference in thermal expansion.

The support column 22 is divided into three short rods, which are connected to each other by a universal joint 21 and have buckling properties.

In addition, a dashpot 16 is provided at the upper part of the guide tube 1 using the lower structure of the handling head 12, and by inserting the control rod handling head 11 into this dashpot which also serves as a dashram, the coolant fluid is Generates pressure and gently decelerates after scram.

[Effects of the Invention] According to the present invention, the flexibility of the absorption pin assembly is improved by attaching the plurality of absorption pins 19 to the lattice plates 18 and 20 connected by the flexible supports 22 connected by the universal joints 20. becomes larger, and scram insertion is ensured even if the guide tube is bent during reactor operation.

In addition, a dashpot 16 for decelerating after scram is provided at the top of the guide tube 1, and the control rod handling head 11
By also serving as a dashpot, a decelerating force is applied above the absorber, and the force acting on the pin connection part of the universal joint 21 provided on the support column 22 is reduced, preventing collision between the absorber pin 19 and the guide tube 1. The force also becomes smaller.

[Brief explanation of drawings]

FIG. 1 is a schematic sectional view showing an embodiment of a nuclear reactor control rod according to the present invention, and FIG. 2 is a schematic sectional view showing a conventional nuclear reactor control rod. 1......Guide tube 11...Control rod handling head 16...Dashpot 18.
・・・・・・・・・Upper lattice plate 19・・・・・・・
......Absorption pin 20...Lower lattice plate 21...Universal joint 22...・・Staff representative patent attorney Kensuke Nori Chika (and 1 other person) Figure 1 Figure 2

Claims (1)

[Claims] (1) A guide pipe having a coolant outflow hole on the upper side, a dashpot formed on the upper end, a handling head on the upper part of the dashpot, and an entrance nozzle through which the coolant flows in the lower end connected. , a cluster-shaped neutron absorption pin assembly inserted into the guide tube, and the neutron absorption pin assembly is connected from an upper end to a connecting rod having a control rod handling head fitted into the dashpot, and the plurality of The cladding tube of the absorption pin is flexible, and both upper and lower ends of the absorption pin are fixed to a pair of upper and lower lattice plates, and a plurality of short rods are connected to the center along the axial direction via a plurality of universal joints. A control rod for a nuclear reactor, characterized in that it consists of a strut inserted that is connected and bendable.