JPS6235289A - Supporter for control rod of 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] [Industrial Application] Control rods of conventional nuclear reactors, such as pressurized wood reactors, contain neutron absorbing materials of various absorption capacities for shutdown and power level control. However, first, plutonium was grown,
Some contain materials that do not absorb neutrons, which are later combusted as fuel elements.

[Prior Art] Generally, the upper end of such a control rod is attached to an assembly called a spider. This spider supports a plurality of control rods so that they can be simultaneously inserted into and withdrawn from the reaction region of the reactor core. The control rods enter the fuel assembly simple in the core region.

An assembly of spiders and multiple control rods is called a control rod cluster or water exclusion rod cluster, depending on the function of the control rods.

During operation of a nuclear reactor, control rods are withdrawn from the reaction region of the reactor core by raising the assembly into the upper internals of the reactor pressure vessel. The eight shifts of the assembly are guided by a guide tube with a plurality of guide members or cards in contact with the control rod in a plurality of areas. The number of guide members provided for each control rod is determined by the desire to minimize this number to reduce drag and the need to reduce the distance between guide members to suppress the amplitude of vibrational force induced by the flow. It was chosen as a product of compromise between the two.

Drag can be suppressed through hydraulic balancing and through design approaches that reduce drag friction.

Problems to be Solved by the Invention The drag forces thus cause wear on the surface of each rod sliding along the guide member.

Further, each rod is held in a raised position within the guide tube;
Flow-induced vibrations cause movement relative to the guide member, and this movement is believed to be a further cause of wear.

Such wear can affect the life of the control rods.

The rate of this wear is determined in part by the materials from which the control rods and guide members are made. The latter guide member is usually made of stainless steel, but it is recommended that the control rod, which is a neutron absorbing material, be covered with stainless steel, and the water exclusion rod be covered with a material that does not absorb neutrons, such as a zirconium alloy. Common.

In this way, wear of the neutron-absorbing control rods occurs primarily during insertion and withdrawal. In the case of water displacement rods, this movement is limited, but the lower hardness of the material makes them susceptible to wear due to flow-induced vibrations while in the raised position.

When the outer wall of a control rod wears down to a certain depth, it must be replaced with a new one. Therefore, if such wear can be delayed, the life of the spider and control rod assembly can be extended.

A primary object of the present invention is to provide a nuclear reactor control rod drive system with a drive shaft system that substantially increases the wear resistance and thereby extends the life of the drive shaft.

[Means for Solving the Problems] In order to achieve the above-mentioned object, according to the present invention, a first end position is completely inserted into the core of a nuclear reactor, and a second end position is withdrawn from the core. A plurality of control rods arranged so as to be able to move eight times vertically between A control rod support apparatus comprising guide means for contacting and wearing out the control rods, wherein the control rods are periodically rotated so that the contact position on the outer surfaces of these control rods with which the guide means is in contact changes. A control rod support apparatus is provided that includes an operatively coupled displacement means.

[Function] In the reactor control rod support device, each control rod is The area of the outer surface of the guide member contacts and wears. A displacement device coupled to the control rod and periodically rotating it is provided so that the contact position changes.

[Example] The spider 2 of the control rod/spider assembly shown in FIG. 1 supports several control rods 4 for controlling a nuclear reactor so as to move vertically as necessary. Each control rod is supported by the spider 2 via a respective support unit 6. One embodiment of this unit 6 is shown in FIG.

The support unit 6 consists of a housing 8 and a housing cap 10, which components together define a cylindrical chamber 12.

Each control rod 4 is connected to an extension member 16. A support rod 20 is screwed into this extension member 16. This support rod 20 passes through the unit 6 and its chamber 12,
It can be moved axially with respect to the unit 6.

A ring 22 is fixed to the support rod 20, and this ring 22
A compression spring 24 is interposed between the chamber 12 and the bottom wall of the chamber 12. In this way, the support rod 20 is supported by the unit 6 via the spring 24.

Returning to FIG. 1, each control rod 4 is pulled up into the upper core structure of the reactor vessel in order to extract the control rod 4 from the core reaction area of the reactor. is guided by a guide member, for example, a plurality of cards 30. These cards 30 are spaced apart from each other around the associated rod 4.

When the control rod 4 moves up and down, the associated guide member card 30
A drag force is generated by contact with the This drag, of course, causes an amount of wear on the outer surface of the control rod 4.

When the assembly 2.4 reaches its upper end position, each support bar 20
The upper end of the guide tube abuts against a stop member 34 installed on the guide tube. The position of this stop member 34 is such that when the assembly 2.4 is in its upper end position, each ring 22 is pushed down in the chamber 12 from the position shown in FIG. 2, compressing the spring 24 almost completely. It is determined that

According to the invention, the support rod 20. The above-described downward movement of the extension member 16 and associated control rod 4 and ring 22 causes them to rotate relative to the housing 8. This rotational movement changes the contact position of each control rod 4 with respect to the associated guide member or card.

One suitable mechanism for producing such desired rotation is shown in exploded view in FIG. This mechanism consists of a boss 36 provided on the outer surface of the support rod 20, and a set of upper bosses 38, 40, 42 provided on the wall of the chamber 12 so as to extend in the circumferential direction.
... and one set of lower bosses 44, 46, etc.

The bosses 36 have cam surfaces 50 each operatively associated with a guide surface 52.54 formed on the lower boss 44.46. In addition, the boss 36 has an upper camming surface 58 that is operatively associated with a guide surface 60.62 formed on the upper boss 40.42, respectively.

The support rod 20 together with the extension member 16 and associated control rod 4
Whenever the assembly 2.4 is raised to a parking position and then lowered again into the reactor core, it rotates. When the assembly reaches its upper end position, the upper end of each support bar 20 abuts the associated stop member 34. Spider 2 and housing 8 are then raised a short distance relative to support rod 20. As a result, the cam surface 50 of the boss 36 slides along the guide surface 52, causing the support rod 20 to rotate a certain amount. Thus, Boss 36
are lined up in the gap between the lower bosses 44 and 46.

Next, when the spider 2 is lowered again, each support rod 20
Initially, it remains in contact with the associated stop member 34. As a result, each housing 8 lowers relative to its associated support bar 20 as the spring 24 stretches. During this time, the cam surface 58 slides upward along the guide surface 60 of the upper boss 40, causing the support rod 20 to rotate a certain amount further and
are located in the gap between the upper bosses 40 and 42.

According to one embodiment of the invention, the total rotational momentum imparted to the support rod 20 by sliding along the guide surface 52.60 is 45°.
It will be about. In this case, when the assembly descends and enters the core, each control rod 4 will assume a position shifted by 45 degrees from its previous position. As a result, each guide member or card 3
0 will come into contact with the new surface area of the associated control rod 4 at a position offset by an angle consisting of the previously contacted surface area.

FIG. 4 illustrates another control rod support unit 64. FIG. This support unit 64 comprises an upper end plug 66 which is fixed to the spider 2 and has an axial passage for the support rod 20. A housing 68 is screwed into the bottom of the end plug 66. This housing 68 is secured thereto using a locking pin 69. According to this embodiment, since a large space can be formed inside the housing, a large spring 24 can be disposed, and the inner wall of the housing 68 can be
．． 40 etc. can be easily formed.

FIG. 5 shows the second part of the mechanism for rotating each rod according to the invention.
An example is shown below. This embodiment includes a housing 68 of the same shape as shown in FIG. However, an advantage of the structure shown in FIG. 5 is that there is no need to form bosses 38 or the like inside housing 68. That is,
In this embodiment, the power control rod or water displacement rod is supported by a support rod 70 which is supported within the housing 68 by a compression spring 24. A drive rod 72 extending downwardly through the housing 68 also extends upwardly through a top plug connected to the housing 68 . This upper end stopper is shown in FIG. 4 but not in FIG. The upper end of drive rod 72 is arranged to engage stop member 34 shown in FIG. Drive rod 72
The lower end of carries a rotation generating member 74 . The rotation generating member 74 is formed with two independent male threads 75 that engage with a helical groove 76 formed on the inner wall of the housing 68 and are angularly shifted from each other. The lower end of the rotation generating member 74 is
It has an annular sawtooth structure with alternating gentle slopes and vertical surfaces.

A disk 78 is fixed to the upper end of the support rod 70. The upper end of this disk 78 is provided with a serration structure that mates with the serration structure on the lower end of member 74 . disc 7
The lower end of disk 78 is similarly provided with an annular sawtooth structure having alternating slopes and vertical surfaces, but this slope is inclined in the opposite direction to the gentle slope at the upper end of disk 78 .

In normal operating conditions, when the spider 2 is removed from its withdrawn position, the spring 24 is in tension, pressing the disk 78 against the member 74. As a result, this member 74 and the drive rod 72 are equally supported by the spring 24. When the spider 2 rises and reaches its extraction position, the drive rod 72
The upper end of the contact member 34 hits the stop member 34. When the housing 68 moves further upward with the spider 2, the male screw 75
The member 74 rotates while being guided by the spiral groove 76. As a result, member 74 is driven downwardly with respect to housing 68.

The engagement of the serrations on the lower end of member 74 and the upper end of disk 78 causes disk 78, support rod 70, and the control rod supported thereto to move downwardly relative to housing 68 with equal rotation. This rotational movement is not prevented by the spring 24. 5, the upper end 24 of this spring slides along the slope of the lower end of the disk 78. The lower end of spring 24 seats in a hole formed in the bottom of the chamber defined by housing 68. As a result, the spring 24 itself does not rotate.

However, the spring 24 is compressed axially as a result of the downward movement of the disk 78 with respect to the housing 68.

According to an exemplary embodiment of the invention, the dimensions of the drive rod 72, external threads 75 and helical groove 76 are such that the mechanism for rotating the support rod when the spider moves to its fully withdrawn position is 9.
It is set to rotate from 0° to 180°.

Then, as the spider moves downward from the withdrawn position,
Spring 24 pushes disk 78 up against housing 68. As a result, an upward force is applied to the member 74, causing it to move upwardly with respect to the housing 68, while the male thread 75 moves B along the helical groove 76, causing the member 74 to rotate. However, during this movement, spring 2
The upper end of 4 comes into abutment with one of the vertical surfaces of the sawtooth structure at the lower end of disk 78. At this time, disk 7
8 and its support rod 70 will no longer rotate and member 7
The slope of the sawtooth structure at the lower end of disk 78 is forced to slide along the sawtooth structure at the upper end of disk 78 . At the end of this return movement, member 74 and disk 78 resume the position shown in FIG. 5, but disk 78, support rod 70, and the control rod supported thereon have rotated a net 90 degrees during that period. . Although FIG. 5 shows a sawtooth structure with four teeth each, a different number of teeth could be provided if desired, and the slope of the external thread 75 and the helical groove 76 could be changed during each withdrawal motion of the spider. It can also be varied to provide different amounts of rotation.

In the normal operating position of FIG. 5, with the spider assembly removed from its extracted position, each vertical plane of the sawtooth structure at the bottom of member 74 is circumferentially disposed from the associated vertical plane of the sawtooth structure at the top of disk 78. Please note that they are separated. This spacing allows member 74 to come to a resting position when pushed up relative to housing 68 by the action of spring 24. That is, in this position, the vertical plane of the associated sawtooth structure of member 74 is properly positioned relative to the vertical plane of the sawtooth structure on the top of disk 78, so that disk 78 and the components secured thereto are properly positioned relative to the vertical plane of the sawtooth structure on top of disk 78 for the next 90°. Gives rotation.

An important advantage of such a construction is that there is little need for machining the interior of the housing 68. In fact, the machining required involves drilling a small diameter hole in the bottom of the chamber that housing 68 defines;
All that is required is to machine a helical groove 76 near the top of the opening. Machining such grooves at these locations is a relatively simple matter.

6 and 7 are detailed plan views showing portions of two types of guide members that may be used primarily as guide means for control rod movement within the upper core structure of a nuclear reactor pressure vessel; FIGS. It is. Such a guide member is fixed to the pressure vessel such that the control rod 4 moves through the guide member in a vertical direction.

FIG. 6 shows a portion of one guide card 30 that can be used to guide each rod of a control rod cluster. The complete card 30 is in the shape of a cross and its arms are illustrated. This card 30 has a central slot 8 through which Spider 2's arm passes.
4 and a plate member 82 with a precise opening 86 formed therein. Since each aperture 86 guides a respective control rod, the total number of apertures 86 in card 30 is equal to the number of control rods carried by spider 2 of FIG. The plate member 82 is made of a suitable metal and has a suitable wall thickness, for example, 3.7 mm.
It has a thickness of cm.

Since the aperture 86 has a slightly larger diameter than each wire 4 that it guides, generally speaking each wire 4 will be seated at a particular location on the circumference of the associated aperture 86, where wear will occur.

As each line 4 rotates, the surface portion of the rod that corresponds to the above-mentioned specific portion of the aperture 86 changes.

Typically, a number of cards or plates 82 are provided, such as five cards, which are spaced vertically along the top of the interior of the pressure vessel.

FIG. 7 illustrates similar portions of a suitable guide member for guiding each line of the water displacement rod assembly. In this case, the guide area is defined by upper and lower end plates 88 in which slots 90 are formed.

Between these end plates 88, a plurality of C hard tubes 92 and a plurality of half tube assemblies 94 extend in the vertical direction. Multi-tube 92
and assembly 94 guide each water displacement rod. As shown,
Each assembly 94 consists of two tube sections, each extending less than half the diameter of the associated rod.

Again, the inner diameter of tube 92 and assembly 94 is slightly smaller than the diameter of rod 4, so that each wire is supported in a particular part of the tube or half-tube assembly with which it is associated.

[Effects of the Invention] In the case of water displacement rods, the aforementioned rotation updates the position at which the guide member or card bears on the surface of the rod, thereby changing the position at which wear occurs. The new contact surface of each wire 20 has already been pre-oxidized to form a hard zirconium layer which acts to inhibit wear.

The angle of each rotation step, for example 45@, can be chosen to take advantage of the longitudinal stretching of the zirconium alloy by the fast neutrons while the rod is in the core. As a result, even after the rod has rotated 360 degrees, the new wear position does not correspond to the position before the full 360 degree rotation. Furthermore, the resulting helical wear section has a less significant effect on the longitudinal strength of the control rod.

For control rod clusters, choose the rotation step angle and
Not only can the contact surfaces be renewed, but the wear lines can be located symmetrically. As a result, the influence of the line on control rod warpage will be reduced.

[Brief explanation of drawings]

FIG. 1 is an elevational view, partially in section, of a rod/spider assembly incorporating rod displacement means according to an embodiment of the present invention. FIG. 2 is a detailed sectional view showing a main part of the embodiment of FIG. 1. FIG. 3 is a detailed developed view of the cam structure used in the embodiment of FIG. 2. FIG. 4 is a diagram similar to FIG. 2 showing a second embodiment of the invention. FIG. 5 is a detailed sectional view showing a third embodiment of the invention. FIG. 6 is a detailed plan view of an example of a guide member that can be used with the device according to the invention. FIG. 7 is a diagram similar to FIG. 6 showing another example of the guide member. 2... Spider 4... Control rod 6... Support unit 30... Guide member 36... Boss 38. 42... Upper boss 44. 46... Lower boss 50.58... Cloud cam surface 52.54.60.62... Guide surface slot

Claims (1)

[Claims] 1. A plurality of nuclear reactor cores arranged so as to be movable in the longitudinal direction between a first end position in which they are completely inserted into the core of the nuclear reactor and a second end position in which they are withdrawn from the reactor core. a control rod support apparatus comprising control rods and guide means for wearing the control rods by sliding contact with at least discrete areas of the outer surface of each control rod when the control rods are in the vicinity of a second end position; Control rods characterized in that they include displacement means operatively coupled to the control rods for periodically rotating the control rods such that the contact position on the outer surfaces of these control rods with which the guide means contact changes. Support device. 2. The device according to claim 1, wherein the support means for supporting the control rod is limited relative to the support means in the longitudinal direction when the control rod is moved to the second end position. an apparatus for supporting a control rod for movement by a limited amount, the displacement means rotating the control rod in response to the limited amount of movement; 3. The device according to claim 2, wherein the displacement means includes a cam mechanism for coupling each control rod to the support means and periodically rotating each control rod with respect to the support means. A device characterized by: 4. The apparatus of claim 3, wherein for each of the control rods the displacement means is structurally separate from the control rod and provides support when the control rod is moved to the second end position. a first member mounted on the support means for rotation and vertical movement relative to the means; a second member carried by the control rod;
in response to the rotation of the first member when the first member moves to the end position.
and a drive member arranged to rotate in the direction of. 5. The device according to claim 4, wherein for each control rod, the displacement means is interposed between the control rod and the support means to push the control rod with respect to the support means. comprising a compression spring for permitting vertical movement of the control rod relative to the support means when the control rod is near the second end position. 6. The device according to claim 5, characterized in that the compression spring is associated with the drive member and prevents rotation of the drive member in a direction opposite to the first direction. Device.