CN106910536B - Reactivity control system and nuclear reactor - Google Patents

Abstract

Embodiment of the invention discloses that a kind of reactivity control system for nuclear reactor and the nuclear reactor with reactivity control system.Reactivity control system includes：Multiple laterals, at least part of each in multiple laterals are suitable for being arranged in the reactor core of nuclear reactor；Various control particle；Multiple control particle input units, the multiple control particle input unit are respectively used to inputting various control particle into the upper end of lateral；And particle output channel, it is connect with the lower end of lateral, for exporting control particle from lateral.Reactivity control system according to an embodiment of the invention and nuclear reactor structure are simple.

Description

Reactivity Control Systems and Nuclear Reactors

technical field

Embodiments of the present invention relate to a reactivity control system for a nuclear reactor and the nuclear reactor.

Background technique

The commonly used reactor reactivity control method is to control neutron reactivity by inserting control rods into the reactor core and moving them up and down. The principle is to absorb neutrons in the reactor through the absorber in the control rods and adjust the Neutron balance, so as to achieve the purpose of reactivity control and shutdown. Reactor control rods are usually made of solid metals such as B ₄ C or silver-indium-cadmium.

Contents of the invention

An object of embodiments of the present invention is to provide a reactivity control system and a nuclear reactor whereby, for example, the structure of the reactivity control system and the nuclear reactor can be simplified.

According to an embodiment of the present invention, there is provided a reactivity control system for a nuclear reactor, the reactivity control system comprising: a plurality of branch conduits, at least a portion of each of the plurality of branch conduits being adapted to be disposed in a stack of a nuclear reactor In the core; a variety of control particles; a plurality of control particle input devices, the plurality of control particle input devices are respectively used to input various control particles into the upper end of the branch pipeline; and a particle output pipeline, connected with the lower end of the branch pipeline, for It is used to output control particles from the branch pipeline.

According to an embodiment of the present invention, the particle sizes of the plurality of control particles are different from each other.

According to an embodiment of the present invention, the reactivity control system further includes: a sorting device, which is used to sort the particles output from the particle output pipeline, and supply the sorted particles to a plurality of control particle input devices The corresponding control particle input device in .

According to an embodiment of the present invention, the reactivity control system further includes: a lifting device for lifting the particles output from the particle output pipeline and supplying them to the sorting device.

According to an embodiment of the invention, the plurality of control particles includes reactivity enhancing particles and reactivity reducing particles.

According to an embodiment of the invention, the plurality of control particles also includes particles that maintain reactivity.

According to an embodiment of the present invention, each branch pipe includes a main body and various holes formed in the main body with different cross-sectional areas to provide different reactivity when at least one of the various control particles is filled; or each A branch pipeline includes multiple sub-pipes, each of which has a variety of holes with different cross-sectional areas, so as to provide different reactivity when at least one of the various control particles is filled.

According to an embodiment of the invention, the plurality of holes includes circular holes of various diameters.

According to an embodiment of the present invention, the round holes with various diameters include round holes with four kinds of diameters, and the ratio of the cross-sectional areas of the round holes with four kinds of diameters is: 1:12:6:3.

According to an embodiment of the present invention, the reactivity control system further includes: a plurality of particle storage tubes arranged at the upper end of each branch pipeline for respectively storing various control particles transported by a plurality of control particle input devices; A variety of control particles stored in a particle storage tube are introduced into the introduction tubes of the branch pipelines.

According to an embodiment of the present invention, the reactivity control system further includes: a valve disposed at the lower ends of the plurality of particle storage tubes for opening and closing openings at the lower ends of the plurality of particle storage tubes.

According to an embodiment of the present invention, the reactivity control system further includes: a valve disposed at the lower end of the plurality of branch pipes for opening and closing openings at the lower ends of the plurality of branch pipes.

According to an embodiment of the present invention, the reactivity control system further includes: a controller, the controller controls the opening and closing of the valve, so that at least one of the plurality of branch pipelines is injected with at least two kinds of control particles. Particles, while forming sections of different control particles in the vertical direction.

According to an embodiment of the present invention, a nuclear reactor is provided, and the nuclear reactor includes: a core; and the above-mentioned reactivity control system, wherein at least a part of the branch pipe is arranged in the core.

According to the embodiments of the present invention, for example, the structure of the reactivity control system and the nuclear reactor can be simplified.

Description of drawings

The accompanying drawings are used to provide a further understanding of the present invention, and constitute a part of the description, and are used together with the embodiments of the present invention to explain the present invention, and do not constitute a limitation to the present invention. In the attached picture:

FIG. 1 is a schematic perspective view of a nuclear reactor with a reactivity control system according to an embodiment of the present invention;

Figure 2 is a schematic diagram of a nuclear reactor with a reactivity control system according to an embodiment of the present invention;

3 is a schematic diagram of branch ducts in the core of a nuclear reactor with a reactivity control system according to an embodiment of the present invention; and

FIG. 4 is a schematic diagram of a branch pipeline of a reactivity control system according to an embodiment of the present invention.

Detailed ways

The specific implementation manners of the present invention will be described below in conjunction with the accompanying drawings.

Embodiments of the present invention will be described below in conjunction with the accompanying drawings. It should be understood that the embodiments described here are only used to illustrate and explain the present invention, and are not intended to limit the present invention.

Fig. 1 is the three-dimensional schematic view of the nuclear reactor with reactivity control system according to the embodiment of the present invention; Fig. 2 is the schematic diagram of the nuclear reactor with reactivity control system according to the embodiment of the present invention; Fig. 3 is the nuclear reactor with reactivity control system according to the embodiment of the present invention 4 is a schematic diagram of a branch pipe of a reactivity control system according to an embodiment of the present invention. Referring to FIGS. 1 to 4 , a nuclear reactor according to an embodiment of the present invention includes: a core 17 ; and a reactivity control system. At least a portion of a branch conduit of the reactivity control system is disposed in the core.

As shown in FIGS. 1 to 4, a reactivity control system 100 for a nuclear reactor according to an embodiment of the present invention includes: a plurality of branch pipes 15, and at least a part of each of the plurality of branch pipes 15 is suitable for being arranged in a nuclear reactor. In the core 17; a variety of control particles; a plurality of control particle input devices, the plurality of control particle input devices are respectively used to input a variety of control particles into the upper end of the branch pipeline 15; and the particle output pipeline 5, and the branch pipeline 15 The lower end is connected for outputting the control particles from the branch pipeline 15. The particle sizes of the various control particles may be different from each other. In addition, the plurality of control particles may also have different specific gravity, different added material, different shape, or different in other respects, so as to be able to be sorted by the sorting device. The plurality of control particles can include particles that increase reactivity and particles that decrease reactivity, or the plurality of control particles can include particles that increase reactivity, particles that decrease reactivity, and particles that maintain reactivity.

As shown in Figures 1 and 2, according to an embodiment of the present invention, the reactivity control system 100 further includes a sorting device 7, which is used to sort the particles output from the particle output pipeline 5, and The sorted particles are supplied to corresponding control particle input devices among the plurality of control particle input devices.

As shown in FIG. 1 and FIG. 2 , according to an embodiment of the present invention, the reactivity control system 100 further includes a lifting device 6 for lifting the particles output from the particle output pipeline 5 and supplying the sorting device 7 .

As shown in FIGS. 3 and 4 , each branch pipe 15 includes a main body 151 and a variety of holes formed in the main body 151 with different cross-sectional areas, so as to provide different effects when filling at least one of a variety of control particles. Reactivity; or each branch pipe 15 includes multiple sub-pipes, each of which has a variety of holes with different cross-sectional areas, so as to provide different reactivity when at least one of the various control particles is filled. The variety of holes may include circular holes of various diameters. For example, the round holes with various diameters include round holes with four kinds of diameters, and the ratio of the cross-sectional areas of the round holes with four kinds of diameters is: 1:12:6:3. The various holes may be generally parallel and extend generally vertically.

As shown in Figures 1 and 2, according to an embodiment of the present invention, the reactivity control system 100 further includes: arranged at the upper end of each branch pipe 15, for storing the various control particles transported by a plurality of control particle input devices respectively A plurality of particle storage tubes 11 , 12 , 13 ; and an introduction tube 14 for introducing various control particles stored in the plurality of particle storage tubes 11 , 12 , 13 into a branch pipeline 15 . The particle storage pipes 11 , 12 , 13 and the introduction pipe 14 may be considered as part of the branch pipe 15 or may not be considered as part of the branch pipe 15 .

As shown in Figures 1 and 2, according to an embodiment of the present invention, the reactivity control system 100 further includes: disposed at the lower ends of the plurality of particle storage tubes 11, 12, 13, for opening and closing the plurality of particle storage tubes 11 , The valve of the opening of the lower end of 12,13. As shown in FIG. 1 and FIG. 2 , according to the embodiment of the present invention, valves for opening and closing openings at the lower ends of the plurality of branch pipes 15 are provided at the lower ends of the plurality of branch pipes 15 .

As shown in Figures 1 and 2, according to an embodiment of the present invention, the reactivity control system 100 further includes: a controller that controls the opening and closing of the valves so that at least one of the plurality of branch pipelines 15 Injecting at least two kinds of control particles among the plurality of control particles to form sections of different control particles in the vertical direction.

The reactivity control system 100 can be installed in any type of reactor system, and a plurality of branch pipes 15 can be symmetrically distributed around the central axis of the reactor core 17 . The number of branch pipes 15 can be specifically set according to the actual reactor conditions, and can be made of the same structural material as the core 17 . At least a part of the branch duct 15 may extend vertically.

According to an example of the present invention, as shown in FIGS. 1 to 4 , the reactivity control system 100 includes: a branch pipe 15 disposed in a core 17 of a nuclear reactor for controlling neutron reactivity in the reactor. A variety of control particles are reactivity enhancing material, neutron absorbing material and reactivity maintaining material respectively, and the input pipelines for these three kinds of control particles include annular main pipeline 1, 2, 3 and branch pipeline 15 respectively, each control The input pipelines of particles all include a main pipeline 1, 2, 3 and a plurality of branch pipelines connected thereto, and each branch pipeline includes vertical sections as particle storage pipes 11, 12, 13 and converging sections as introduction pipes 14 . The main pipelines 1 , 2 , 3 and the branch pipelines are all located above the branch pipeline 15 , and are respectively used to feed the reactivity enhancing material, neutron absorbing material and reactivity maintaining material into the branch pipeline 15 . The lower end of the branch pipe 15 is connected to the particle output pipe 5, the particle output pipe 5 has a certain inclination angle, and is used for outputting the control particles or their mixtures input by a plurality of control particle input devices from the branch pipe 15. The reactivity control system 100 also includes a reactivity monitoring device, which is arranged on the upper, middle and lower parts of the branch pipeline 15 for real-time monitoring of the reactivity of neutrons inside the core, and transmits the monitoring information to the control system. Particulate control devices such as electric valves. The particle control device is respectively located at the lower end of the particle storage pipes 11, 12, 13 (vertical sections) at the branch pipes of the control particle input pipe, at the upper end entrance of the branch pipe 15, and at the interface between the lower end of the branch pipe 15 and the particle output pipe 5, They are respectively used to adjust the input, output, flow rate and flow rate of the control particles at the corresponding positions. For example, through the controller to control electric valves and so on. The reactivity control system 100 also includes a control particle lifting device 6, which is located downstream of the particle output pipeline 5, and is used to lift the output control particles to the control particle sorting device 7 above the core. The control granule sorting device 7 is located downstream of the control granule lifting device 6 and upstream of the control granule input pipeline, and is used to sort the lifted mixed control granules, re-divide them into three kinds of control granules, and inject the corresponding three kinds of control granules in the input pipeline.

According to an embodiment of the present invention, as shown in Figures 3 and 4, the branch pipes 15 are arranged around the centerline of the nuclear reactor core 17, and each branch pipe 15 includes a hexagonal prism main body 151 and four types of pipes formed inside the main body 151. The cylindrical hole of size, the top of each branch pipe 15 is all connected with the converging section 14 in the control particle branch pipe, and the bottom is connected with the particle output pipe 5.

According to an embodiment of the present invention, the main body 151 of the branch pipe 15 can be selected from high temperature resistant, radiation resistant ceramic materials, such as carbide, nitride or oxide ceramics (for example, zirconia, aluminum oxide, nitride carbide, Silicon carbide, etc., and high-temperature-resistant materials made of mixtures of these materials), or metal alloys (Hastelloy) etc. are made into a hexagonal main body 151, and four kinds of diameters in different numbers are arranged on the main body 151, respectively D1, D2, D3 , The cylindrical hole of D4 is used as the flow channel of the control particles. The four cross-sectional areas corresponding to the four diameter holes are respectively S1, S2, S3 and S4, and the relationship between them is as follows: S1=12*S2=6*S3=3*S4.

According to another embodiment of the present invention, the branch pipe 15 can also be designed as a form without a main body, directly arranged and fixed by pipes with different numbers and four diameters according to certain design requirements, and the periphery is wrapped with a hexagonal shell. The upper end and the lower end of the pipeline 15 are provided with perforated end caps, and the perforated positions of the end caps correspond to the positions of the corresponding pipelines. The shell wall thickness and end cap can be set to 3.5-5mm respectively, and the material can be selected from high temperature resistant, radiation resistant ceramic materials, such as carbide, nitride or oxide ceramics (such as zirconia, alumina, nitride Picks, silicon carbide, etc., and high temperature resistant materials composed of mixtures of these materials), or metal alloys (Hastelloy), etc.

According to the embodiment of the present invention, the three kinds of control particles are all spherical or quasi-spherical, but have different diameters. Wherein, the reaction enhancing material may be neutron multiplying materials such as beryllium carbide and beryllium oxide, the neutron absorbing material may be neutron absorbing materials such as boron carbide, and the maintaining material may be alumina, magnesium oxide and other materials.

According to an embodiment of the present invention, the particle output pipeline 5 includes a plurality of branch pipelines and an annular main pipeline, the upper port of each branch pipeline is connected with the lower outlet of the branch pipeline 15, and the lower port is connected with the annular main pipeline of the particle output pipeline 5. connect.

According to an embodiment of the present invention, the annular main pipe of the particle output pipe 5 is inclined at 0° to 90° relative to the horizontal plane, for example, the inclination of the annular main pipe of the particle output pipe 5 relative to the horizontal plane enables the particles to move by gravity.

According to an embodiment of the present invention, a control particle collection device 16 is connected to the lowermost end of the annular main pipe of the particle output pipeline 5, and the elevator in the control particle lifting device 6 lifts the control particles collected in the control particle collection device 16 to The control particle sorting device 7 above the reactor core 17 .

According to an embodiment of the present invention, the control particle sorting device 7 re-sorts the mixed control particles into three different control particles according to the particle diameter or particle size, and injects them into corresponding input pipes respectively. or input device.

According to an embodiment of the present invention, the reactivity control system for a nuclear reactor further includes: an annular main pipeline 3 arranged in the reactivity enhancing material input pipeline 1, the neutron absorbing material input pipeline 2, and the reactivity maintaining material input pipeline The particle conveying device inside is used to convey the sorted control granular materials to the corresponding branch pipelines 15 respectively. The particle conveying device can be an endless roller conveyor with an opening at the entrance of the corresponding branch pipeline 15, and a converging baffle is provided in front or behind each opening, so that the particles move toward the center of the roller table while rolling. Convergence, particle conveying device can also choose other conveyors.

The reactivity control system for a nuclear reactor according to an embodiment of the present invention also includes: a valve, which can connect and disconnect the input pipeline, the communication between the output pipeline and the branch pipeline 15, and can be adjusted by controlling the size of the valve Control the input, output flow and velocity of particles.

According to the embodiment of the present invention, the reinforcing material can enhance the reactivity of the reactor, and can be used to compensate for the loss of reactivity during the start-up phase of the reactor or at the end of the fuel life; the absorbing material can reduce the reactivity of the reactor, and can be used to reduce the reactivity or emergency shut down; Sustaining materials maintain the existing reactivity of the reactor, neither increase nor decrease the reactivity of the reactor.

The reactivity control system for a nuclear reactor according to the embodiment of the present invention can effectively improve the neutron absorption efficiency and the neutron absorption accuracy of control particles.

Fig. 1 and Fig. 2 have shown the nuclear reactor reactivity control system of the embodiment of the present invention, Fig. 3 has shown the cross-section of the reactivity control system core 17 and branch pipe 15 according to the embodiment of the present invention, Fig. 4 has shown The cross section of the branch pipe 15 in the reactivity control system according to the embodiment of the present invention is shown.

A nuclear reactor according to an embodiment of the present invention includes: a core 17 ; and a reactivity control system 100 . The branch pipe 15 of the reactivity control system 100 is arranged in the core 17 . As shown in Figures 1 to 4, the nuclear reactor reactivity control system 100 of the embodiment of the present invention includes: a reactivity enhancing material input main pipeline 1, a neutron absorbing material input main pipeline 2, a reactivity maintaining material input main pipeline 3, branches Pipeline 15, particle output pipeline 5, control particle lifting device 6, control particle sorting device 7, reactivity monitoring device for real-time detection of neutron reaction in the core, and control particle for adjusting material flow rate and flow rate Valves and other components in the control device.

As shown in Figure 3, the control system can be installed in any type of reactor system, such as critical reactors, subcritical reactors. The branch pipes 15 are distributed symmetrically with respect to the axis center of the reactor core 17 . The number of branch pipelines 15 can be specifically set according to actual reactor conditions. The branch pipe 15 can be a hexagonal prism structure as shown in Figure 4, or other prism structures, such as a quadrangular prism, a pentagonal prism, etc., and the branch pipe 15 is provided with four cylindrical diameters of D1, D2, D3, and D4. The cross-sectional area of various channels has the following relationship: S1=12*S2=6*S3=3*S4, and the reactor control particles flow through the designated channels according to the actual situation.

As shown in Figure 1 and Figure 2, the three kinds of control particles sorted from the control particle sorting device 7 are respectively injected into the main pipeline 1 of the reactive reinforcing material and the main pipeline of the neutron absorbing material through the pipelines 8, 9 and 10. 2. The reactivity maintaining material is input into the main pipeline 3 . The control particles are conveyed to the particle storage pipes 11, 12, 13 (eg vertical sections) at the corresponding branch pipes 15 by the particle conveying device in the pipeline, and filled up. The particle storage tubes 11 , 12 , 13 (vertical sections) at each branch pipeline 15 place contain a quantity of control particles that is greater than the total amount of control particles that can be accommodated in all the holes of the branch pipeline 15 connected thereto. At the beginning, the valves at the lower ends of the particle storage pipes 11, 12, and 13 (vertical sections) at each branch pipeline 15, the valves above the cylindrical holes of the branch pipeline 15, and the valves at the interface between the particle output pipeline 5 and the branch pipeline 15 are all closed state.

When a specific situation occurs, the reactivity control can be carried out according to the following control methods: (1) When it is detected that the neutron reactivity of a certain position in the reactor is lower than the set threshold value, then through the calculation of the controller in the control particle control device, Open the valve at the lower end of the particle storage pipe 11 (vertical section) at the branch pipe 15 near the corresponding position and the predetermined hole valve of the branch pipe 15, so that the reinforced granular material flows into the corresponding hole of the branch pipe 15 through the introduction pipe 14 (branch converging pipe) (2) When the neutron reactivity of a certain position in the reactor is detected to be higher than the set threshold, the valve at the lower end of the particle storage pipe 12 (vertical section) at the branch pipe near the corresponding position and the valve at the lower end of the branch pipe 15 are opened. , so that the neutron-absorbing particles flow into the channel of the branch pipe 15 through the introduction pipe 14 (branch convergence pipe); The neutron reactivity of a position is lower than the set threshold, then first open the valve at the lower end of the particle storage pipe 12 (vertical section) at the branch pipe near the corresponding position and the designated hole valve of the branch pipe 15, so that the neutron absorbing particles pass through The introduction pipe 14 (branch converging pipe) flows into the channel of the branch pipe 15, and after injecting a preset amount of neutron-absorbing particles, close the valve at the lower end of the particle storage pipe 12 (vertical section) at the branch pipe, and open the valve at the branch pipe 15. The valve at the lower end of the particle storage pipe 11 (vertical section) makes the reactivity enhanced particles flow into the pores of the branch pipe 15 through the branch converging pipe 14, and vice versa; When the regions with low sub-reactivity are separated by a certain distance, reactivity maintenance control particles can be added in the middle, and the addition method is the same as above. If all the reactivity-enhancing particles are injected into the branch pipe 15, it is used to start the reactor; if all the neutron-absorbing particles are injected, it is used for emergency shutdown. Injection of controlled particles is driven entirely by gravity.

Considering the fineness of the control and the ease of operation, the branch pipeline 15 is provided with cylindrical channels with four diameters D1, D2, D3, and D4, and the cross-sectional areas of the various channels have the following relationship: S1=12*S2 =6*S3=3*S4, the numbers of four diameters of cylindrical channels are 1, 12, 6, 6 respectively, the reactivity of a single S2 circular hole filled with neutron absorbing material is a basic unit μ, the whole The total reactivity value of the branch conduit 15 is 60 μ. According to the calculation results, the combination of different numbers and diameters of pores can be selected to achieve a reactivity control value of -60μ~60μ. If the calculation results show that selecting a channel with a large diameter or selecting multiple channels with a small diameter can meet the control requirements, the channel with a large diameter is preferred for filling. Multiple branch pipes 15 are placed in the reactor to control neutrons in different regions respectively. The neutron-absorbing material is used in the negative reactivity control channel, and the neutron multiplication material or moderator material is used in the positive reactivity control channel. In the power distribution control, different neutron control particles can be injected into a channel in sections. Or branch pipes 15 in different regions inject different neutron control particles. The power distribution control is mainly used to solve the phenomenon of uneven neutron flux density in the core, so as to make the power density uniform.

After the reactivity of the reactor is adjusted to the specified standard, open the valve below the branch pipeline 15, and the control particles will be introduced into the particle output pipeline 5 through the branch pipeline 15, and the particle output pipeline 5 with an inclined angle can guide the control particles into the control particle collection device In 16, wait for the control particle lifting device 6 to lift it to the control particle sorting device 7, and the control particle lifting device 6 can be a bucket elevator, a screw elevator, etc. The control granules lifted to the control granule sorting device 7 can be sorted by size to separate the three different control granules and inject reinforcement materials into the main pipeline 1 and absorbent materials into the main pipeline 1 through pipelines 8, 9 and 10 respectively. The pipeline 2 and the maintenance material are input into the main pipeline 3 for the next round of circulation. The replacement of control particles does not affect the normal operation of the reactor. The dose of each control particle injected into the branch pipeline 15 needs to be calculated according to actual needs. The valve can use a rotary valve (for example, an electric rotary valve), which can adjust the opening diameter.

The particle conveying device in the main pipe 1 for reinforcement material input, the main pipe 2 for absorption material input, and the main pipe 3 for maintenance material can be a bucket conveyor.

The reactivity control system according to the embodiment of the present invention can improve the control efficiency and accuracy of control range of neutrons by control particles.

The above embodiments are only used to illustrate the present invention, but not to limit the present invention. Those of ordinary skill in the relevant technical field can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, all Equivalent technical solutions also belong to the category of the present invention, and the scope of patent protection of the present invention should be defined by the claims.

Claims (14)

1. A reactivity control system for a nuclear reactor comprising: a plurality of branch conduits, at least a portion of each of the plurality of branch conduits adapted to be disposed in a core of a nuclear reactor; A variety of control particles; a plurality of control particle input devices, the plurality of control particle input devices are respectively used to input various control particles into the upper end of the branch pipeline to inject at least one of the various control particles into the branch pipeline by gravity; and The particle output pipeline is connected with the lower end of the branch pipeline, and is used for outputting control particles from the branch pipeline. 2. The reactivity control system for a nuclear reactor according to claim 1, wherein The particle diameters of the plurality of control particles are different from each other. 3. The reactivity control system for a nuclear reactor according to claim 1, further comprising: A sorting device, the sorting device is used for sorting the particles output from the particle output pipeline, and supplying the sorted particles to corresponding control particle input devices among the plurality of control particle input devices. 4. The reactivity control system for a nuclear reactor according to claim 3, further comprising: The lifting device is used to lift the particles output from the particle output pipeline and supply them to the sorting device. 5. The reactivity control system for a nuclear reactor according to claim 1, wherein: Various control particles include reactivity-enhancing particles and reactivity-decreasing particles. 6. The reactivity control system for a nuclear reactor according to claim 1, wherein: Various control particles also include particles that maintain reactivity. 7. A reactivity control system for a nuclear reactor according to claim 5 or 6, wherein: Each branch conduit includes a main body and a plurality of holes formed in the main body with different cross-sectional areas to provide different reactivity when filled with at least one of the plurality of control particles; or Each branch pipe includes multiple sub-pipes, each of which has a variety of holes with different cross-sectional areas, so as to provide different reactivity when at least one of the various control particles is filled. 8. The reactivity control system for a nuclear reactor according to claim 7, wherein: The variety of holes includes circular holes of various diameters. 9. The reactivity control system for a nuclear reactor according to claim 8, wherein: The round holes with various diameters include four kinds of diameters, and the ratio of the cross-sectional areas of the four kinds of diameters is: 1:12:6:3. 10. The reactivity control system for a nuclear reactor according to claim 1, further comprising: A plurality of particle storage tubes arranged at the upper end of each branch pipeline for respectively storing a plurality of control particles delivered by a plurality of control particle input devices; and An introduction tube for introducing various control granules stored in a plurality of granule storage tubes into the branch pipeline. 11. The reactivity control system for a nuclear reactor according to claim 10, further comprising: A valve for opening and closing openings at the lower ends of the plurality of particle storage tubes is provided at the lower ends of the plurality of particle storage tubes. 12. The reactivity control system for a nuclear reactor according to claim 11, further comprising: The valves arranged at the lower ends of the multiple branch pipes are used to open and close the openings at the lower ends of the multiple branch pipes. 13. A reactivity control system for a nuclear reactor according to claim 11 or 12, further comprising: a controller, the controller controls the opening and closing of the valve, so that at least one of the plurality of branch pipes is injected with at least two kinds of control particles among the plurality of control particles, and a zone of different control particles is formed in the vertical direction part. 14. A nuclear reactor comprising: core; and The reactivity control system of claim 1, wherein at least a portion of said branch conduit is disposed in said core.