JPS6189583A - Control rod for nuclear reactor and exchange method thereof - 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 application of the invention] The present invention relates to a control rod in a nuclear reactor and a method for replacing the same.

[Background of the invention]

Figure 4 shows an outline of a conventional control rod.

Boro/Carby) (B4C) Stainless steel poison tubes 1 filled with powder are arranged in a cross shape, the periphery is covered with a sheath 2, and an upper handle 3 is attached to the top.
I) control rod part 'F! which is also attached at the coupling part 4! By moving the JJ mechanism up and down, the reactivity and power distribution of the reactor are controlled.

This coupling portion 4 is released by pulling up the lifting handle 5.

Furthermore, did you install velocity limiter 6? I]lJ#
Reduces the speed when the bar falls.

In such control rods, boron (BIG) is a neutron absorber and absorbs neutrons through the following reaction.

B” +n −+)Ie’ +L i” ・−−
-------- (1) When a control rod is pushed into a nuclear reactor to control reactivity and power distribution during operation of a nuclear reactor, each time a neutron is absorbed by the reaction in equation (1), a boron atom is 1
Eleven directions disappear. Therefore, the irradiation time in the reactor is long, and the boron in the atoms and control rods is reduced, which shows the relationship between the neutron absorption IJ degradation rate.

In FIG. 5, the irradiation time when the neutron absorption capacity degradation rate of the control rod reaches the limit value is the control rod life.

Also, according to equation (1), when boron absorbs neutrons, H
generate e.

Since He is a gas, the irradiation progresses and He enters the poison tube.
It becomes hard.

Figure 6 shows the relationship between irradiation time and poison tube internal pressure.

In FIG. 6, the irradiation time when the poison pipe internal pressure reaches its limit is the life of the control rod.

Conventionally, control rods whose neutron absorption capacity deterioration rate or poison pipe pressure approached the limit values and were likely to exceed these limits in the next cycle were replaced with new blades during regular inspections. Ta.

Figure 7 shows an example of a core layout diagram seen in a horizontal cross section of the reactor core.

In the figure, 7 is the control rod, 8 to 10 are the neutron instrumentation system, and 8 is the L
PRM, 9 indicates IRM, and 10 indicates S-M.

Among these, the control rods inserted into the effective fuel length of the reactor core during operation are part of the reactor core, so the frequency of use varies greatly depending on the position of the control rod, and the control rods in frequently used positions have a longer irradiation time. Many of these control rods reach the end of their lifespan quickly, so they often have to be replaced with new control rods. However, since the blade and velocity limiter division operation section is located in the velocity limiter section at the bottom of the control rod, the division operation was performed after the four fuel assemblies adjacent to the control rod were removed from the reactor. In addition, even if the fuel assembly can be divided without taking it out, there is a spacer that prevents the main bodies of the fuel assembly from coming into direct contact with each other, and a spacer that prevents the assemblies from coming into direct contact with each other during fuel loading and normal operation. The structure was such that blades up to i loaded with fuel assemblies could not be replaced because they would interfere with the channel fasteners.

Figure 8 shows an enlarged horizontal cross-sectional view of the core.

Numeral 11 is a spacer for preventing direct contact between the fuel assembly bodies, and 12 is a channel fastener for preventing the assembly bodies from coming into contact with each other during fuel loading and normal operation.

Reference numeral 13 indicates the blade portion of the control rod. When the control rod is pulled out to the upper part of the core to replace the control rod blade with fuel loaded in the reactor core, this blade 13
are the spacer 11 and channel fastener 12 of the fuel assembly.
The structure is such that it cannot be pulled out.

Figure 9 shows a vertical cross section of the core. 7 is a control rod; 14 is a fuel length boat in which a fuel assembly 15 supports the fuel assembly 15 at the bottom; 16 is a control rod drive mechanism, which is connected to the control rod 7 through a coupling portion 4; As a result of the above, it was impossible to replace the control rod blades while the fuel assemblies were still loaded.

Therefore, in the past, the push rod was replaced by the following method.

■ Pull out the control rod from the control rod drive device to the fully withdrawn position.

■ Remove the four fuel assemblies around the control shaft from the reactor core.

■ Release the coupling between the velocity limiter section and the blade.

■ Remove the control rod blade from the reactor core.

■ Transfer the control rod blades taken out from the reactor core to the spent fuel pool.

■ Attach the new control rod to the reactor core.

■ Install the blade guide.

■ Load fuel.

In the conventional method as described above, it takes about four hours to replace one control rod, and the number of replacements per day is two.

[Purpose of the invention]

An object of the present invention is to provide a new nuclear reactor control rod that significantly reduces control rod replacement time.

[Summary of the invention]

If control rods that have reached the end of their service life can be replaced with new blades while still being loaded with fuel, it will significantly reduce the time required to replace the control rods and reduce radiation exposure.

Therefore, we created a structure in which the control rod can be uncoupled from the blade and the perocity limiter by operating the control rod drive mechanism, and furthermore, by partially modifying the fuel assembly and control rod drive mechanism, it is possible to keep the fuel loaded. The structure is such that the control rod blades can be replaced.

[Embodiments of the invention]

The present invention will be explained in detail below.

In order to make it possible to quickly replace control rods that have been used during operation and have reached the end of their service life, this structure allows operation from the rod drive mechanism on the uncoupling side of the control rod blade and velocity limiter section. And so.

FIG. 1 shows how a control rod according to the present invention is attached to a nuclear reactor. According to the present invention, it is possible to disconnect the control rod drive mechanism and the velocity limiter section from the lower part of the control rod drive mechanism using the pull-up handle 5 from the upper part of the reactor, and to disconnect the control rod drive mechanism from the lower part of the control rod drive mechanism. The control rod blade 13 and the velocity limiter section 6 can be disconnected from the bottom of the rod section yJtJ mechanism.

Each control rod drive mechanism 16 and velocity limiter 6
The operation for disconnecting the velocity limiter section 6 and the blade section 13 is performed by moving the lock plug 21 inside the velocity limiter, since the piston tube 20 of the control rod drive mechanism is pushed up from inside the reactor pedestal as in the conventional type. FIG. 2 shows an enlarged view of the control rod drive mechanism and the velocity limiter section 6 in a connected state, with a larger space.

FIG. 3 shows the AAlfi plane of FIG. 2.

As shown in Fig. 3, the part of the control rod that connects to the velocity limiter 6 of the drive mechanism has a structure in which slits are cut radially, and the upper part has an 8-shaped protrusion. Control rod part for connection! When the upper part of the di structure is pressed against the velocity limiter, the upper part of the control rod drive mechanism contracts radially and is inserted into the velocity limiter.
At the position of the spherical tank in the velocity limiter, it is seated on the return lever of the upper part of the control rod drive mechanism. In this state, the opening (plug 21), which is pressed downward by the spring 22, descends to complete the connection.

FIG. 4 shows an enlarged view of the state shown in FIG. 81 in which the connection can be disconnected, and FIG. 5 shows an enlarged view of the state in which the connection can be disconnected.

When the piston tube 20 of the control rod = Ijlh mechanism is pushed upward, the uncoupling bale 18 overcomes the spring force of the spring and pushes up the lock plug 21, making the upper part of the control rod drive mechanism retractable, and in that state the control is performed. Pulling the rod upward will release the connection.

FIG. 6 shows a state in which the control rod blade section 13 and the velocity limiter section 6 can be disconnected from each other.

Figure 7 shows the control rod blade section and velocity limiter section 13.
An enlarged view of the connection between the control rod drive mechanism and the control rod velocity limiter in a state in which the connection between the control rod drive mechanism and the control rod velocity limiter can be released.

In addition to the state shown in Figures 4 and 5, the piston tube 2
0 is pushed up, the protrusion of the connection release bale 18 plays the role of the lock plug 21 in the normal connection state, so the control rod section WIhVA structure and the control rod velocity limiter section 6 cannot be connected. However, in this state, the upper lifting handle 23 that moves with the locking plug 21 also moves upward, and the rod 24 at the top of the upper lifting handle 23 pushes up the upper locking plug 24 to release the coupling between the blade section 13 and the velocity limiter section 6. becomes possible. In this state, when the handle on the control rod is pulled upward, the connection between the blade 13 and the velocity limiter section 6 is released, and the control rod blade can be replaced while the fuel remains loaded.

(1) The control rod is withdrawn to the fully withdrawn position by the control rod drive mechanism.

(2) Insert the piston tube of the control rod drive mechanism and set the coupling between the blade section and the velocity limiter section so that it can be released.

(3) Pull up the control rod blade.

(4) Move the control rod blade to the spent fuel pool.

(5) Place the new blade into the furnace and connect it to the velocity limiter section.

(6) Test the operation of the control rod drive mechanism.

〔Effect of the invention〕

According to the above method, the time required to replace each control rod is approximately one hour, which is approximately 1/8 of the conventional process.The required personnel and time for replacement can be greatly reduced, making the reactor more economical. Contribute to improvement.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing how control rods according to the present invention are installed in a nuclear reactor;
Fig. 2 is an enlarged view of the connection between the control rod @ mechanism and the velocity limiter in Fig. 1, Fig. 3 is an explanatory view of section AA in Fig. 2,
FIG. 4 is a state diagram in which the control rod drive mechanism and velocity limiter according to the present invention can be disconnected from each other, FIG. 5 is an enlarged view of the connection between the control rod drive mechanism and velocity limiter section in FIG. Figure 7 is a state diagram in which the control rod blade section and velocity limiter section can be disconnected according to the present invention.
The figure is an enlarged view of the connection between the control rod drive mechanism and the velocity limiter part in Figure 6, Figure 8 is a fl+ view of the conventional control rod, Figure 9 is an explanatory diagram of the relationship between irradiation time and neutron absorption deterioration rate, Figure 1O is an explanatory diagram of the relationship between irradiation time and the rise in pressure inside the poison tube.
11 is an enlarged horizontal cross-sectional view of a general nuclear reactor, FIG. 12 is an enlarged horizontal cross-sectional view of the core of FIG. 11, and FIG. 13 is a vertical cross-sectional view of the core of FIG. 12. 1...Abun-Parod, 2...Sheath, 3...
Upper lift handle, 4... Coupling part, 5... Pulling knob, 6... Velocity limiter, 7...
Control rod, 8... LP M19... IM, 10...
・SR, M, 11... Space? , 12... Fastener, 13... V-do, 14... Fuel assembly, 15...
...Fuel length boat, 16...Control rod drive mechanism, 17.
・・Velocity limiter and blade coupling part,
18... Connecting operation rod, 19... Control rod drive Mh mechanism automatic exchange device, 20... Piston tube, 21...
Lock plug, 22...Spring, 23...Upper lifting handle, 24...Rod, 25...1st 20th 30th 2nd Figure S Figure 8 Bird? Mouth to mouth irradiation time

Claims (1)

[Claims] 1. In a control rod that can be separated into a blade filled with a neutron absorbing material and a velocity limiter section that reduces the speed of falling, the splitting operation is performed from the control rod drive mechanism side. A nuclear reactor control rod characterized by having a structure that allows it to be divided into two parts. 2. Insert the piston tube in stages to disconnect the control rod drive mechanism automatic exchange device, disconnect the control rod drive mechanism and velocity limiter in the first stage insertion state, and then disconnect the control rod drive mechanism and velocity limiter in the second stage. A reactor control rod replacement method characterized by disconnecting a control rod blade and a velocity limiter part using a disconnection salve provided at the top of a pulling handle in an inserted state.