JPS63115090A - Core reactivity inhibitor - Google Patents

Abstract

(57) [Abstract] 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 reactor core reactivity suppression device that suppresses an increase in the reactivity of a nuclear reactor during fuel loading and fuel exchange.

[Conventional technology]

There are two main types of control rods used in conventional light water reactors: cruciform control rods and cluster control rods. The cruciform control rods are used in boiling water reactors (B
WR) and early pressurized wood reactors (PWR), a control board with a cross-sectional shape is inserted into the gap between fuel assemblies to control the reactor's reaction. Control the degree.

In a nuclear reactor using this type of control rod, the fuel assembly can be moved with the control rod inserted. If the control rods are inserted, the reactivity of the reactor is kept sufficiently low, so it is unlikely that the reactor will reach criticality and go out of control during fuel loading or fuel replacement.

Cluster type control rods are a structure made up of multiple control rods with the same diameter as the fuel rods, and the control rods are inserted into the control rod guide tube provided inside the fuel assembly and pulled out to operate the reactor. The reactivity of f! If control. This cluster-type control rod is used in PWR, and has the advantage of flattening the neutron flux distribution within the reactor compared to a cross-type control rod. A cluster type control rod for a PWR has a control rod drive mechanism above the reactor core, and each control rod is moved in and out of the control rod guide tube in the fuel assembly from the top of the fuel assembly. When replacing fuel, the cluster type control rods and control rod drive mechanism are cut. The separated cluster-type control rods remain in the fuel assembly, and the fuel assembly moves with the cluster-type control rods inserted. Therefore, the reactivity of the reactor does not increase during fuel exchange.

The structure of the control rod and drive mechanism is detailed in Atomic Band Book (Ohmsha, 1976) pp. 294-298. Further, as an example of a device for suppressing core reactivity in an emergency, there is disclosed, for example, Japanese Patent Application Laid-open No. 166890/1983.

[Problem that the invention seeks to solve]

The concept of a high-conversion light water reactor has been proposed, which improves fuel economy and makes more effective use of uranium than conventional light water reactors. This is a light water reactor, but like a fast reactor, 28♂U, which cannot be used as fuel, undergoes a nuclear reaction with high-energy surplus neutrons to produce 28Lapu, which can be used as fuel.
This aims to make advantageous use of uranium. This type of reactor requires a reduced proportion of the water domain that acts as a moderator to absorb neutron energy than conventional light water reactors. For this purpose, a triangular fuel lattice is more advantageous than the conventional square lattice because it can reduce the ratio of the water area to the fuel rods.

Also, a large water area must be provided between the fuel assemblies,
Cluster-type control rods are more advantageous than cruciform control rods, which can cause large distortions in the neutron flux and thus in the 8-force distribution.

High-conversion light water reactors can be either boiling water or pressurized wood reactors. However, in the case of a boiling water reactor, bubbles are generated at the top of the fuel assembly, so in order for the control rods to work effectively, it is better to insert them from the bottom of the fuel assembly, where fewer bubbles are generated. In a boiling water high conversion reactor, a structure in which cluster-type control rods are inserted from the bottom of a fuel assembly in which fuel rods are arranged in a triangular lattice is an excellent structure from the viewpoint of core characteristics.

However, there is one problem here. When inserting a refruster type control rod, which is different from a PWR, into a fuel assembly from the bottom of the fuel assembly, each thin rod-shaped control rod cannot stand on its own and requires some kind of support structure. When the control rod is inserted into the fuel assembly, the control rod guide tube inside the fuel assembly supports the control rod, and when the control rod is pulled out from the fM fuel coalescence, the support member provided at the bottom of the core supports the control rod. but,
If the fuel assembly is removed with the control rod inserted into the fuel assembly during refueling, the diameter will be approximately 1a1. Since the rod-shaped control rod with a length of about 3 to 4 m is supported only at its lower end, it bends. This deflection may cause plastic deformation, which is problematic in terms of the integrity of the control rod. Further, in order to solve this problem, a method can be considered in which the fuel assembly is replaced after the control rod is extracted from the fuel assembly. However, in this case, the control rods are temporarily removed from the fuel assembly. Generally, nuclear reactors are designed in such a way that even if one control rod is not inserted into the core, the reactor will shut down if other control rods are inserted into the reactor core. Even if the control rods are pulled out of the fuel assembly, the reactor will not reach criticality and go out of control. However, assuming that for some reason one other control rod was not inserted into the reactor core, two control rods would not be inserted into the reactor core at the time of fuel exchange, and there would be a risk that there would not be enough room to reach criticality. . It is possible to design a reactor so that it does not reach criticality even if two control rods are not inserted into the core, but this becomes a constraint on core design and makes it difficult to design a highly economical core. There are some difficulties in doing so. Furthermore, if liquid neutron absorbing material is injected, it is difficult to recover this neutron absorbing material upon restart.

The purpose of the present invention is to suppress the increase in reactivity during fuel loading and fuel exchange in a nuclear reactor in which cluster control rods, which have excellent characteristics as a boiling water high conversion reactor, are inserted from the bottom of the reactor core, and to ensure safety. The objective is to provide a means for loading and exchanging fuel.

[Means for solving problems]

The above object is achieved by providing a core reactivity suppressing device that assists in suppressing the core reactivity of the control rods during fuel loading and fuel exchange.

The core reactivity suppression device is composed of a control element that suppresses the core reactivity, a drive mechanism that drives the control element, an attachment/detachment device for the control element and the drive mechanism, and their control devices.

[Effect]

When loading and replacing fuel in a nuclear reactor that is inserted into the core from the bottom of the fuel assembly of cluster type I control rods, a core reactivity suppressor is used to control the control rods inserted into the fuel assembly to be replaced. Insert the control element into the fuel assembly from above while pulling out. After the control element is completely inserted into the fuel assembly, the control element is disconnected from the drive. The fuel assembly is moved and the fuel is exchanged while the control element for suppressing reactivity is housed in the fuel assembly.

After the fuel assembly into which the control element has been inserted is moved to a predetermined position, the control rods are inserted into the fuel assembly by reversing the above procedure. That is, the # node element and the drive device are connected by the attachment/detachment device, and the control rod is inserted into the fuel assembly while taking out the control element.

This series of operations completes the cycle of movement of one fuel assembly.

According to the present invention, for a nuclear reactor in which control rods are inserted into a fuel assembly from the bottom of the fuel assembly, even during fuel loading and fuel exchange, the neutron absorbing material that suppresses the reactivity of the reactor core absorbs all the fuel. [Example] Examples of the present invention will be described below.

FIG. 1 shows an overview of an embodiment of the present invention &! It is a diagram.

This figure shows the inside of the atomic building 17 during fuel exchange, with the upper lids of the containment vessel 16 and pressure vessel 1o removed. Core shroud wall 15 and upper core support plate 13 in pressure vessel 1o. A plurality of fuel assemblies 1 are loaded in a core 14 surrounded by a lower core support plate 12 . 1st
In the figure, the fuel assembly group in the reactor core is represented by a single fuel assembly 1 because one diagram is complicated. A control rod drive device 40 is installed in the lower part of the pressure vessel 10, and the fuel assembly 1
The structure is such that a cluster type # control rod 42 can be inserted into and pulled out from the bottom of the fuel assembly 1.

Also, to support the cluster type control rods 42.

A control rod support member 41 is installed in the lower plenum 11 . A traveling rail 32 is provided above the reactor building 17, and a traveling trolley 30 can be moved thereon. There is a traversing truck 31 on top of the traveling truck 30;
A core reactivity suppression device 24 is installed above. By combining the traveling truck 30 and the traversing truck 31, the core reactivity suppressing device 25 can be moved directly above any fuel assembly 1. The core reactivity suppressor 25 mainly includes control elements 20. Control element guide 21. Control element drive device 2
3. Control element attachment/detachment mechanism 22. Control element guide lifting device i! j26 and their control devices. Details of each component will be described later, but an overview of the operation will be shown here. The control element 20 is driven by drive #2 of the control element drive device 23.
7, but can be attached to and detached from the drive shaft 27 as desired using a control element attachment/detachment mechanism 22. A control element guide 21 is provided so that the positional relationship between the insertion point and the control element 20 does not deviate when the control element 20 is inserted into or withdrawn from the fuel assembly l. The control element 20 housed in the control element guide 21 is moved to the vicinity of the fuel assembly 1 by the control element guide lifting device 26. Refer to FIG. 1 and the respective drawings for each component below. I will explain it as follows.

FIG. 2 shows a cross-sectional view of the fuel assembly 1 loaded in the reactor core 14 in this embodiment. The fuel assembly 1 has fuel rods 3 arranged in a triangular lattice in a hexagonal channel box 2, and has a more dense structure than a conventional square lattice fuel assembly. Furthermore, seven control rod guide tubes 4 are arranged within the fuel assembly 1. A control rod 42 can be inserted into the fuel rod guide tube 4 from the lower part of the fuel assembly 1. The control element 20 has a structure that can be inserted into the control rod guide tube 4 from above the fuel assembly 1.

FIG. 3 is a front view and an elevation view showing the structure of the control element 20 in this embodiment. The control element 20, like the control rod 42, is made of boron carbide (B 4
C) It is composed of seven poison tubes 35 filled with powder and a handle 37 that holds the poison tubes 35 together. The diameter of the poison tube 35 is approximately IG, and the control rod guide tube 4 of the fuel assembly 1
The poison tube 35 is thick enough to be inserted into the control rod guide tube 4, and the arrangement of the poison tube 35 corresponds to the arrangement of the control rod guide tube 4. Poison tube 35
The tip of the rod is tapered, so that it can be easily inserted into the control rod guide tube 4. The length of the poison pipe 35 is slightly shorter than the height of the fuel assembly 1. At the tip of the handle 37 of the control element 20, an attachment/detachment mechanism 22 is provided that allows the control element 20 and the drive shaft 27 of the control element drive device 23 to be attached and detached.

FIG. 4 is a detailed view of the attachment/detachment mechanism 22 between the control element 20 and the control element drive shaft 27 in this embodiment.

The handle 37 of the control element 20 is hollow, and a locking plug 51 is fixed therein by a spring 53 and a holding plate 52. The tip of the drive shaft 27 is a coupling spud 54 having a leaf spring structure. The control element drive mechanism is a mechanism that causes the drive shaft 27 to slide on the inner surface of the cylinder 57 using hydraulic pressure. This drive shaft 27 has a double structure with a hollow interior so that it can be attached to and detached from the control element 20, and can actuate the piston 58 with hydraulic pressure to drive the uncoupling rod 55. It has become.

To connect the control element 20 and the drive shaft, first, the uncoupling rod 55 is pushed out and the locking plug 51 is pushed. The spring 53 is then flexed, the locking plug 51 is pressed down, and the coupling spud 54 can be inserted into the hollow control element handle 37. When the uncoupling rod 55 is pulled out by hydraulically operating the piston 58, the lock plug 51 is pushed up by the force of the spring 53. As a result, the coupling spud 54
is sandwiched between the socket 50 portion and the lock plug 51, and the control element 20 and the drive shaft 27 of the control element are connected.

To release this connection, the lock plug 51 can be pushed by operating the uncoupling rod 55.

FIG. 5 is an overview diagram when the control element 20 is moved to the upper part of the fuel assembly 1. The control element guide 21 consists of a guide plate 28 and a support member 29. On the information board 28,
In order to prevent the control element 20 from shifting, the groove is cut, thereby limiting the lateral displacement of the control element 20. After the control element 20 moves directly above the fuel assembly 1, it is inserted into the control rod guide tube 4 by the control element drive device 23.

FIG. 6 shows the operating sequence of the core reactivity suppressor 25 according to the present invention during fuel exchange.

First, the core reactivity suppressor 25 is moved above the fuel assembly 1 to be replaced. At this time, all of the control rods 42 are inserted into the reactor core (FIG. 6(a)).

Next, the control element guide 21 and the control element 20 are moved to the upper part of the fuel assembly 1 using the control element guide lifting device 26 (FIG. 6(b)).

While inserting the control element 20 into the control rod guide tube in the fuel assembly 1 to be refueled, the control rod 42 is pulled out from the fuel assembly 1 (FIG. 6(C)).

After inserting the control element 20 into the fuel assembly 1.

The drive shaft 27 and the control element 20 are separated by the attachment/detachment mechanism 22, and the cart carrying the reactivity suppressor 25 is moved (sixth
Figure (d)).

Thereafter, the fuel assembly 1 containing the control element 20 is moved together with the control element 20 to a predetermined core position by the fuel exchanger.

After moving, install the control rods 4 into the fuel assembly 1 by reversing the above procedure.
Insert 2. That is, the control element 20 is connected to the attachment/detachment mechanism 22.
control rods 4 connected to the drive shaft 27 in the fuel assembly 1.
2, while pulling out the control element 20. Control element 2
When the control rod 42 is completely pulled out from the fuel assembly 1, the control rod 42 is almost completely inserted into the fuel assembly 1.

When using this reactivity suppressor, the control element 2
If the control rod 42 is pulled out without inserting the
An interlock mechanism is provided to prevent the control element 20 from being removed without being inserted into the fuel assembly.

A load meter that detects whether the core reactivity suppressor 25 suspends the control element 20, a detector that detects the planar position of the core reactivity suppressor 25, a tip position detector of the drive shaft 27 of the control element, A detector is installed at the insertion position of each control rod 42 to prevent the neutron absorbing material from being extracted from the fuel assembly 1 by mistake. In addition, the control rod drive shaft 43
A pawl mechanism is installed on the drive shaft 27 of the control element, so that the control rod 42 and the control element 20 are inserted into and withdrawn from the fuel assembly 1 in stages. The control rods 42 and the control elements 20 are moved by detecting each other's movements so that the reactivity within the fuel assembly 1 does not change suddenly.

Although not adopted in this embodiment, if an underwater television camera, a combination of a marker and light, or a positioning device using sound waves is installed at the tip of the control element guide 21, the control element 20 can be moved into the control rod guide tube. This makes positioning for insertion easier.

In addition, in this embodiment, the traveling truck 30 and the traversing truck 31,
Although the core reactivity suppressor 25 was moved.

A structure in which a turntable is installed above the core 14 and is moved using the turntable is also possible. Further, the control element driving device may be of a magnetic jack type or a motor-driven screw type.

The number of poison tubes 35 in the control element 20 is seven in this embodiment, but the number can be changed depending on the structure of the fuel assembly 1. For example, for a fuel assembly as shown in FIG. A structure combining 19 poison tubes is possible.

FIG. 8 shows another embodiment of a control element according to the invention,
Depending on the reactor, a configuration may be considered in which three control rods are operated by one drive mechanism. In this case, if you try to pull out the control rods of one fuel assembly to move its position, the control rods of the other two fuel assemblies will also be pulled out, which will greatly increase the reactivity of the reactor core. It is possible to do so. For such a nuclear reactor, as shown in FIG. A core reactivity suppression device connected to the drive shaft is used. With this device, even in a nuclear reactor where three control rods are operated by one drive unit, fuel exchange and fuel loading can be performed safely without increasing the reactivity of the reactor core.
7 It is also possible to use liquid poison as a neutron absorber. A collapsible poison tube is inserted slightly into the fuel assembly, and a pump injects liquid poison into the poison tube. Injection of liquid poison causes the poison tube to be inserted into the assembly.

After the poison tube is filled with liquid poison, the poison tube is cut away so that it can move with the fuel assembly.

When the control rod is inserted into the fuel assembly, liquid poison is extracted from the poison tube and the poison tube is withdrawn from the fuel assembly by a drive mechanism.

By using liquid poison as the neutron absorbing material for the control element, the mechanism for driving the control element can be simplified.

〔Effect of the invention〕

According to the present invention, it is possible to suppress an increase in core reactivity due to control rod withdrawal during fuel loading and fuel exchange in a nuclear reactor in which control rods are inserted into a fuel assembly from the bottom of the assembly.

[Brief explanation of the drawing]

Fig. 1 is an overview of an embodiment of the present invention, Fig. 2 is a cross-sectional view of a fuel assembly used in an embodiment of the invention, and Fig. 3 is a control element used in an embodiment of the invention. front and elevation views,
Fig. 4 is a sectional view showing the attachment/detachment mechanism of the control element and control element drive shaft used in one embodiment of the present invention, and Fig. 5 is a perspective view when the control element and control element guide are arranged above the fuel assembly. , FIG. 6 is a schematic diagram showing the operating sequence of the core reactivity suppression device, FIG. 7 is a cross-sectional view of a fuel assembly in another embodiment of the present invention, and FIG. 8 is a diagram showing still another embodiment of the present invention. FIG. 3 is a front view of a collection of control elements in an example. 1...Fuel assembly, 4...Control rod guide tube, 10...
・Pressure vessel, 14... Core, 40... Control rod drive device, 42... Control rod, 30... Traveling truck, 31...
・Traversing trolley. 32... Traveling rail, 2o... Control element, 21.
... Control element guide, 22 ... Attachment/detachment mechanism, 23...
Control element drive device, 25... Core reactivity suppression device, 2
6... Control element guide lifting device, 27... Drive shaft,
35...Bo No. 19 Kuzu 2 Fig. VJ512] Rei Soguchi *5 eyes 'T' concave

Claims (1)

[Claims] 1. In a nuclear reactor in which the reactivity of the reactor core can be controlled by inserting and withdrawing control rods into a fuel assembly, a neutron absorbing material and a drive mechanism for carrying the neutron absorbing material into and out of an arbitrary assembly;
It is equipped with a mechanism for attaching and detaching the neutron absorbing material and the drive mechanism, and the neutron absorbing material is carried into the fuel assembly following or before the operation of withdrawing the control rod inserted into the fuel assembly from the fuel assembly. A reactor core reactivity suppression device characterized by carrying out a neutron absorbing material following or after the operation of inserting a control rod.