JPS62212592A - Control rod - 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 [Field of Industrial Application] The present invention relates to a control rod, and particularly to a control rod with a long life.

[Conventional technology]

The conventional long-life type control rod is 1, for example, JP-A-53-746.
As shown in Publication No. 97, there are known control rods in which a long-life neutron absorption rod with a long nuclear and mechanical life is placed at the upper end, where the amount of neutron irradiation is high, or at the tip of the blade. . These control rods contain hafnium (Hf) or europium (Eu) at the upper end of the blade and at the wing tip.
) and other long-life neutron absorbers are arranged, and the other parts are equipped with poison tubes filled with boron carbide (84G) powder in elongated stainless steel cladding tubes.

[Problem that the invention seeks to solve]

In the above conventional technology, the long-life neutron absorber is used only in a part of the control rod, and there is a problem that the life is shorter than that of a control rod that uses only the long-life neutron absorber as the neutron absorber. be. ``In order to solve this problem, it may be possible to replace all the neutron absorbing materials in the control rods with long-life neutron absorbing materials such as hafnium. However, long-life neutron absorbers are heavier than the conventionally used 84C, and when a control rod is constructed using only long-life neutron absorbers as the neutron absorber, the weight of the control rod increases significantly. However, it was found that there was a possibility that the control rod operation by the control rod drive device would be hindered.

For this reason, the inventors attempted to reduce the weight of the control rod by thinning a part of the Hf rod placed inside the blade and thinning the sheath surrounding the long-life neutron absorber. Due to the low rigidity of the sheath, the shape of the sheath is unstable, and the ability to hold the absorbing liquid chain type neutron absorber in place is impaired, creating a new problem that may impede reactivity control. I found it.

An object of the present invention is to provide a control rod that has a long life, good operability, and can perform good reactivity control.

[Means for solving problems]

The above object can be achieved by sinking the means for preventing outward deformation of the sheath housing the absorbing liquid chain type neutron absorbing material. Here, the absorption liquid chain type neutron absorbing material refers to a neutron absorbing material in which the neutron absorption effect decays slowly because the nuclide generated by the neutron absorption reaction or its decay nuclide contains a nuclide that further absorbs neutrons. . Specific substances for the absorbing liquid chain type neutron absorbing material include Hf, E
u, O,, Ta, D'/zog and Ag-In
-Cd etc.

[Effect]

Since the thickness of the sheath surrounding the absorbing liquid chain type neutron absorbing material is reduced, the weight of the control rod can be reduced and good operability of the control rod can be obtained. Further, since a means for preventing outward deformation of the sheath is provided, the function of the sheath to hold the neutron absorbing material is not impaired. Furthermore, since the absorbing liquid chain type neutron absorbing material is used, the mechanical and nuclear life of the control rods is extended.

〔Example〕

The present invention was made based on the following studies by the inventors. In other words, if all conventional neutron absorption rods filled with B and C were replaced with neutron absorption rods made of absorbing nuclear chain type absorbers with the same diameter, the weight of the conventional control rods would increase significantly, making it difficult to control the rods. It was found that there is a possibility that the shaking of the rod may be hindered. Therefore, in order to extend the service life using absorbing nuclear chain-type absorbers, the inventors have developed a method to locally implement absorbing nuclear chains in order to obtain a predetermined reactivity control ability and improve the operability of control rods. It has been realized that it is possible to reduce the amount of type absorbent material and to reduce the thickness of the sheath surrounding the absorbing core chain type absorbent material.

Furthermore, as a result of a detailed study of this structure, we found that the thinner part of the absorbing core chain type absorber in the direction perpendicular to the side surface of the blade
It was discovered that there is a possibility that the control rods may move horizontally while they are installed in the reactor. In other words, the thin part of the absorbing nuclear chain type absorber tends to shift horizontally within the blade due to earthquakes, cooling water flow vibrations, etc., and the control rod is inserted to a predetermined depth to obtain a predetermined reactivity. If the P4 thin part of the absorbing liquid chain type neutron absorbing material shifts during the control rod service, the distance between the fuel assembly and the absorbing nuclear chain type absorbing material will change. Core reactivity changes locally. This is not desirable from the viewpoint of core reactivity control. They also discovered that if the sheath is thin, the shape of the sheath becomes unstable due to its low rigidity, which may impair its ability to hold the neutron absorbing material in a predetermined position. To prevent sheath deformation,
It is conceivable to fix it to the structure in the blade by spot welding, etc., but since the absorbing liquid chain type neutron absorbing material is made of a different material from the sheath, welding is not possible, and since the materials are different,
It is necessary to have a structure that can absorb the difference in thermal expansion during use.

The present invention has been made to solve the new problems discovered by the inventors.

Examples of this invention will be described below.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A control rod according to a preferred embodiment of the present invention, which is inserted into the core of a boiling water reactor, will be described with reference to FIGS. 1 to 3.

The control rod 1 has an external shape shown in FIG. That is, the control rod 1 has a cross-shaped cross section and has four blades 2 extending in all directions from the axis. A speed limiter 9 is provided below the blade 2. Handle 1
0 is attached to the upper end of the blade 2.

The shape of the blade 2 of the control rod 1 is shown in FIGS. 2 and 3. Each blade 2 is made of SUS placed at the axis of the control rod 1.
It consists of a U-shaped sheath (made of SUS) 5 whose both ends are attached to tie rods 8 made of steel, and neutron absorption rods 3 and 4 provided in the sheath 5. The holding part 6 is attached to the upper end of the tie rod 8, and the holding part 7 is attached to the lower end of the tie rod 8 by welding. The upper end of the U-shaped sheath 5 surrounds the holding part 6 and is attached to the holding part 6 by spot welding.

The lower end of the sheath 5 surrounds a holding part 7, and the neutron absorption rod 3 or 4 attached to the holding part 7 by spot welding is disposed within the sheath 5 as shown in FIG. It is placed and held between SUS holding parts 6 and 7 attached to the. The neutron absorption rods 3 and 4 have a sheath 5. The sheath 5, which is not joined to the holding parts 6 and 7,
It is simply placed in a space surrounded by the holding parts 6 and 7.

The sheath 5 is provided with a large number of holes, and when the control rod 1 is installed in the reactor, cooling water in the reactor flows into the sheath 5 through these holes.

A velocity limiter 9 is attached to the lower surface of the holding portion 7. The handle 10 is attached to the upper surface of the holding part 6. The function of the holding section 7 may be provided at the upper end of the velocity limiter 9 without using the holding section 7. The neutron absorption rod 3 is a round rod made of Hf and has a uniform cross-sectional area in the axial direction. The diameter of the neutron absorption rod 3 is 4.8 mm, and it is installed in a conventional control rod used in a boiling water reactor.
It is approximately equal to the diameter of a neutron absorption rod filled with 4C. The neutron absorption rod 4 is a round rod made of Hf, and the cross-sectional area is different from the lower end to a position of 1/2 of the total length of the neutron absorption rod 4 and from this 1/2 position to the upper end. In other words, the diameter of the neutron absorption rod 4 is 3 from the lower end to 1/2 of the total length.
．． 4mm, and 4.8m from 1/2 of the total length to the top end
It is m. One neutron absorption rod 3 is disposed at the tip of the blade 2, and twenty neutron absorption rods 4 are disposed within the blade 2 closer to the control rod axis than the neutron absorption rod 3. The axial length of the neutron absorption rods 3 and 4 is equal to the effective fuel length of the fuel assembly.

The sheath 5 has a projection 18 that projects inward.

The protrusions 18 are provided on both sides of the sheath 5 at the lower part of the blade 2 where the narrow diameter portion of the neutron absorption rod 4 exists. A pair of opposing protrusions 18 sandwich a narrow diameter portion of the neutron absorption rod 4. Means for preventing deformation of the sheath 5 will be explained using FIG. 4 or FIG. 5. Like the sheath 5, the pads 11 are made of SUS and are provided at several locations in the axial direction between two adjacent neutron absorption rods 4. The width of the pad 11 is the same as the inner width of the sheath 5. As shown in Figure 4, the neutron absorption rod 4
For the upper 1/2 part where the diameter is large and there is no gap between adjacent neutron absorbing rods 4, a notch is provided in the axial direction of the two adjacent neutron absorbing rods 4. He is holding 11 pieces of gold. The axial length of the notch 12 is larger than the axial length of the pad 11.

Further, as shown in FIG. 5, the diameter of the neutron absorption rods 4 is small in the lower 1/2 portion, and there is a gap between two adjacent rods, so the pad 11 is held in this portion. The sheath 5 is spot welded to the pads 11 at several locations in the axial direction.

In this embodiment, as described above, the neutron absorption rod 4 with a smaller diameter at the bottom is arranged in most of the blade 2, and the thickness of the sheath 5 is made thinner, so the weight of the control rod 1 is B
The weight is approximately the same as a control rod made of a neutron absorption rod filled with 4C. Therefore, the control rod of this embodiment can be easily operated by a control rod drive device that operates a conventional control rod. That is, good operability of the control rod 1 can be obtained. Further, the width of the blade 2 of the control rod 1 is the same as the width of a conventional control rod. Therefore, there is no need to make changes such as increasing the size of the fuel support fittings installed on the control rod guide tube and the core support plate provided below the core in the reactor pressure vessel.

The neutron absorption rods 3 and 4 use Hf as a neutron absorption material. Hf, which is an absorbing nuclear chain type neutron absorbing material, does not generate gas even if it absorbs neutrons. Therefore, control rod 1
The neutron absorbing rods 3 and 4 have an increased mechanical life. In addition, since the neutron absorption rods 3 and 4 use I-IF, which is an absorption nuclear chain type neutron absorption material, new neutron absorption material is generated by absorbing neutrons, and the nuclear lifetime is also increased.

In this embodiment, the cross-sectional area of the neutron-absorbing rods 3 at the blade tips is uniform in the axial direction, so that the neutron-absorbing rods 4 on the tie rod 8 side have a large cross-sectional area in the upper half of the total length and a larger cross-sectional area in the lower half. /
2 is considered small.

During operation or reactor shutdown, the neutron imbortance is larger in the radial direction of the control rod as it approaches the tip of the blade, and in the axial direction it is larger at the upper end and decreases toward the lower end. By arranging a large number of type neutron absorbing materials, the neutron absorbing ability (controlling ability) can be maximized even if the same amount of neutron absorbing materials are used in total.

Since the thin part of the neutron absorption rod 4 is held by the protrusion 18 that protrudes inward from the side surface of the sheath 5, the neutron absorption rod 4 is held within the sheath 5 in a direction perpendicular to the side surface of the sheath 5, that is, the side surface of the blade 2. Movement can be restrained. For this reason, while the control rods 1 are inserted into the reactor, the neutron absorption rods 4 are exposed to the sheath 5 due to earthquakes, cooling water flow vibrations, etc.
This eliminates the possibility of movement within the reactor and interfering with reactivity control. In particular, even when the control rod 1 is inserted into the reactor core, it is possible to suppress local fluctuations in reactivity control caused by the large movement of the neutron absorption rod 4 in a direction perpendicular to the side surface of the sheath 5. Further, since the sheath 5 is spot-welded to the pad 11 at several locations in the axial direction, the function of holding the neutron absorption rod will not be impaired even if the thickness is reduced. sheath 5
Since the pad 11 and the pad 11 are made of the same material (made of SUS), welding is possible, and since the pad 11 is not fixed to the Hf@ neutron absorption rod, the difference in temperature between the sheath and the neutron absorption rod during use It can also absorb differences in thermal expansion.

In this embodiment, the pads 11 are arranged in one row in the axial direction along two adjacent neutron rods, but the pads 11 are arranged at necessary positions in the blade, and the sheath 5 and pads are placed at the required positions in the blade. 11 may be spot welded.

In the above-mentioned embodiment, instead of Hf, Eua○1, Ta, which is another absorbing nuclear chain type neutron absorbing material.

D! Similar effects can be obtained using goz or Ag-InCd. However, when Eu, O, and Dy20 are used, it is necessary to fill them into a sealed cladding tube.

An example of a core of a boiling water reactor to which the control rod 1 of the above embodiment is applied will be described below.

As the core of the boiling water reactor,
The reactor core shown in Figure 3 of the publication is being considered. The core structure shown in FIG. 3 of the above publication has the configuration described in column 4, lines 5 to 6, line 11 from the bottom of the publication. The reactor core structure shown in Figure 3 of the above publication consists of power adjustment control rods that are inserted into the reactor core during reactor operation to adjust the reactor output, and power adjustment control rods that are completely pulled out from the reactor core during reactor operation. It has a reactor shutdown control rod that is quickly and completely inserted into the reactor core during shutdown. The power adjustment control rods are also fully inserted into the reactor core when the reactor is shut down. The power adjustment control rods and the reactor shutdown control rods are arranged alternately as shown in Figure 3 of the above publication.
They are arranged in a checkerboard pattern.

The power adjustment control rods are inserted into the reactor core most of the time during reactor operation, and are continuously irradiated with neutrons.

Therefore, it is desirable to use the control rod 1 of the embodiment shown in FIG. 1 described above as a control rod for output adjustment. Reactor shutdown control rods are completely withdrawn from the reactor core during reactor operation, so they absorb only a small proportion of neutrons. The controls shown in column 2 and lines 3 to 9 are used. This control rod has a large number of neutron absorbing rods filled with B4C arranged in a cross-shaped blade, and does not have an absorbing nuclear chain neutron absorbing material. The axial length of the neutron absorption rod filled with B4C is substantially the same as the effective fuel length of the fuel assembly.The structure of the control rod drive device that operates both control rods is the same.

In the case of a boiling water reactor, the control rod drive device is installed at the bottom of the reactor vessel containing the reactor core. These control rods are inserted into the core from below.

The neutron absorption rods 3 and 4 of the control rod 1 are round rods, but may be square rods or even plate-shaped. However,
If it is made into a plate shape, it will be difficult to insert the control rod into the reactor core during an earthquake.

It is also possible to use the control rod 1 as a control rod for reactor shutdown.

A control rod 13 according to another embodiment of the present invention is shown in FIG. 6. In the control rod 13, the stopper 11 of the control rod 1 is replaced with a ring 14, and the other structure is the same as that of the control rod 1. be. The ring 14 is wound around a notch 15 provided in two adjacent neutron absorption rods 4. The axial length of the notch 15 is longer than the length of the ring 14, and the ring 14 and the neutron absorption rod 4 are not fixed. The sheath 5 is fixed to the ring 14 by spot welding.

FIG. 8 also shows another embodiment of the invention. The control rod 16 of this embodiment has an angular absorbing nuclear chain type neutron absorbing rod 17 in the radial center of each blade. Elongated holes 18 are provided at several locations in the axial direction of the square neutron absorption rod 17, and the SUS
A metal fitting 19 made of aluminum is installed. The sheath 5 is fixed to the metal fitting 19 by spot welding.

FIG. 10 also shows another embodiment of the present invention. The control rod 20 of this embodiment has an angular absorbing nuclear chain type neutron absorption rod 21 in the radial center of each blade. A hole is provided in the square absorbing nuclear chain type neutron absorbing rod 21, and a rivet 22 is inserted through the hole to prevent the sheath 5 from deforming.

Another embodiment of the invention is shown in FIG. Deformation of the sheath 5 is prevented by providing cuts at several locations in the axial direction of the sheath 5 and locking the sections 24 at these sections to the neutron absorption rod 4.

Control rod 13.16.20 of the embodiment of the present invention described above
．． 23 can obtain the same effect as the control rod 1.

〔Effect of the invention〕

According to the present invention, the mechanical and nuclear lifespan is extended, and the weight is reduced, so the operability of the control rod is improved, and the movement of the blade side surface of the neutron absorption rod in the right angle direction is suppressed, so that local It is possible to prevent fluctuations in core reactivity. Additionally, deformation of the sheath can be prevented and the neutron rod is held in place.

[Brief explanation of drawings]

FIG. 1 is an external perspective view of a control rod according to a preferred embodiment of the present invention, FIG. 2 is a vertical sectional view of the blade of the control rod shown in FIG.
Figure 3 is a 1-1 sectional view of Figure 2, and Figure 4 is a -■- of Figure 2.
■A sectional view, FIG. 5 is a sectional view taken along ■--■ of FIG. FIG. 7, FIG. 9, FIG. 11, or FIG. 13 is a sectional view taken along line I-1 of FIG. 6, FIG. 10, or FIG. 12, respectively. 1.13.16.20.23, ... control rod, 2
...Blade, 3.4...Neutron absorption rod, 5...Sheath, 8...Tie rod, 18...Protrusion. 11...Batch, 12...Notch,
14...Ring, 15...Notch,
17.21...Neutron agent Patent attorney Katsuma Ogawa ' Bird 1e111 Live 4 Figure also 5 Rofuku6121 1.8r23 High 10 tffi

Claims (1)

[Scope of Claims] 1. A blade comprising an absorbing nuclear chain type neutron absorbing material and a sheath surrounding the absorbing nuclear chain type neutron absorbing material, and means for preventing outward deformation of the sheath in the blade. A control rod characterized by being provided with. 2. The absorbing nuclear chain type neutron absorbing material contains Hf, Ta, A
g-In-Cd rod, or Eu_2O_3, Dy_2
The control rod according to claim 1, wherein the control rod is a rod whose tube is filled with O_3. 3. The means for preventing outward deformation of the sheath is constituted by spot welding the sheath to a stopper half-held between the two absorbing nuclear chain type neutron absorbing rods in the blade. A control rod according to scope 1 or 2. 4. A claim in which the means for preventing outward deformation of the sheath is constructed by spot welding the sheath to metal fittings wound around the two absorption chain type neutron absorption rods in the blade. The control rod according to item 1 or 2. 5. The means for preventing outward deformation of the sheath is constructed by spot welding the sheath to a stopper provided through an absorbing nuclear chain type neutron absorbing rectangular rod in the blade. A control rod according to scope 1 or 2. 6. The control rod according to claim 1 or 2, wherein the means for preventing outward deformation of the sheath is a rivet that penetrates an absorption angle chain type neutron absorption square rod in the blade. 7. The means for preventing outward deformation of the sheath is constructed by cutting out a part of the sheath, bending it inward, and stopping it on an absorbing nuclear chain type neutron rod. Control rod according to item 2.