JP2008151625A - Control rod of self-propelled type - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce construction costs and decrease power generation costs by shortening the lower parts of reactor structural materials though they are required to be about three times as long as nuclear fuel assemblies because they need a space for accommodating control rods below a core, further below which a space for a control rod drive mechanism is required. <P>SOLUTION: A control rod 400 of a self-propelled type consists of support rods 420 made of titanium alloy or stainless steel incorporating a driving part, a propelling part, a fixing part and a receiver 440 and battery-cum-control-rod-blades 410 which incorporate as a power source silver-cadmium batteries functioning also as a neutron absorber. The control rod 400 can move vertically by driving a screw 412 coupled directly to a drive motor 411 by the receiver 440 which receives signals from outside with the silver-cadmium batteries, sucking water from a tapered water inlet 419 and spouting the water from a fountain nozzle 413 and can stay in a fixed position for a long period owing to a round-bar notch 424. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a control rod for a nuclear reactor.

FIG. 1 is an overview diagram showing the structure of a boiling water reactor (BWR) (Non-Patent Document 1). Reactor power is controlled by control rods that move up and down between nuclear fuel assemblies containing nuclear fuel material. The control rod can be moved up and down by means of a control rod drive in a control rod drive mechanism housing located under the reactor pressure vessel.
Fig. 2 is a BWR core structure diagram (Non-patent Document 2). The lower end of the nuclear fuel assembly (30) containing the nuclear fuel material is supported by a detachable nuclear fuel support fitting (2) attached to the core support plate (1), and the upper end via a channel box (35). It leans against the upper grid plate (3). At the center of the four nuclear fuel assemblies (30) between the lattices of the upper lattice plate (3), there is a control rod (100) that can be operated up and down to control the nuclear reactor.
Fig. 3 shows a partial plan view of the core in which the nuclear fuel assembly (30) and control rod blades (110) are arranged. The control rod blade (110) and the support structure material (120) that supports the control rod blade (110) are portions that move up and down in the reactor core of the control rod (100) of FIG. In the nuclear reactor, the nuclear fuel assemblies (30) are arranged in a lattice pattern with the control rod side leakage water passage (51) and the leakage water passage (52) opposite to the control rod interposed therebetween. A cooling water passage (49) is provided between the nuclear fuel rods (31). A water rod (36) may be arranged instead of several nuclear fuel rods (31).
: Nuclear Safety Research Association (ed.), 1992 "Summary of light water reactor power plant". : Nuclear Safety Research Association (ed.), 1998 “Light Water Reactor Fuel Behavior”.

In recent years, there has been a demand for a reduction in power charges. Therefore, reduction of power generation cost by BWR is required.
As can be seen from FIG. 1, the lower part of the structural material in the nuclear reactor is about three times as long as the nuclear fuel assembly (30) due to the device for moving the control rod. We want to shorten this lower part to reduce construction costs and power generation costs.

By attaching a screw, a drive motor, a power source, and a control signal receiver to the control rod (100) like an underwater scooter, the control rod (100) can move by itself.
The operating status of the control rod can be grasped by the display of the in-core instrumentation system such as LPRM (Local Power Range Monitor) that monitors neutrons.

  As the design of nuclear fuel assemblies progresses, the line power density tends to be reduced. As a result, it is becoming less necessary for the control rod to be operated precisely. If the control system of the present invention is used, the control rod drive mechanism housing or the like that has been in the lower part of the reactor vessel can be removed, so that the lower part length of the structural material in the reactor can be shortened. Cost can be reduced.

  As a result, construction costs were low, and as a result, BWRs with low power generation costs could be provided.

FIG. 4 is a partial plan view of the core of a nuclear reactor in which the self-propelled control rod of the present invention is arranged. The conventional control rod wing (110) was replaced with a battery combined control rod wing (410), and the support structural member (120) was replaced with a support rod (420).
FIG. 5 is an overview of the self-propelled control rod (400) of the present invention. The self-propelled control rod (400) incorporates a titanium alloy or stainless steel support rod (420) with built-in drive unit, propulsion unit, fixed unit and receiver, and a silver-cadmium battery, which is also a neutron absorber, as a power source. Battery control rod wing (410). A self-propelled control rod (400) that drives a screw (412) directly connected to a drive motor (411) by a silver-cadmium battery as a power source, sucks water from a tapered water inlet (419), and jets water from a fountain nozzle (413). ). The round bar notch (424) is for holding the self-propelled control rod (400) in a fixed position for a long time. The self-propelled control rod (400) is moved up and down by a receiver (440) that receives an external signal.
FIG. 6 is a diagram for explaining in detail how the self-propelled control rod (400) moves up and down. When the self-propelled control rod (400) hits the stopper (431) fixed to the channel box (35) and finishes rising, the round bar notch (424) with a rounded tip is fixed to the channel box (35). The nail (432) gets caught and the self-propelled control rod (400) stays at that height. The round bar notch (424) moves the mover (422) outward by the Coulomb force due to static electricity of the fixed drive source (425) fixed in the support bar (420) or electromagnetic force by the solenoid, and the spring (423) The round bar notch (424) is seated on the fixed claw (432). When the round bar notch (424) passes through the fixed claw (432) from below when the self-propelled control rod (400) rises from below, the tip of the round bar notch (424) rubs against the fixed claw (432). As a result, the spring (423) is shrunk and the round bar notch (424) is shrunk so that it can pass through the fixed claw (432). To fully insert from the fully pulled up state, the mover (422) is supported by the spring (423) at the tip of the round bar notch by switching off the silver-cadmium battery as the power source to the fixed drive source (425). The self-propelled control rod (400) falls because it is stored in the rod (420) and leaves the fixed claw (432). Furthermore, if the screw (412) is rotated in the reverse direction to suck water from the fountain nozzle (413) and squirt water from the tapered water inlet (419) and apply a downward force, the round bar notch (424) bends the spring (423). Bend inward and forcefully fall. When the coolant is lost, the buoyancy is reduced, so that the spring (423) bends due to the weight of the self-propelled control rod (400) and the round bar notch (424) bends and falls inside. The fixed claw (432) is fixed to the channel box (35) with a low melting point metal whose melting point is slightly higher than 286 ° C or a permanent magnet whose Curie point is slightly higher than 286 ° C. The self-propelled control rod (400) drops and is fully inserted. If Teflon (registered trademark) processing is applied to the surface of the fixed claw (432) (the friction is reduced when pressure is applied), the round bar notch (424) is easily detached and the safety is further improved.
Since the linear power density of BWR nuclear fuel assemblies (30) in recent years has been reduced, it is not necessary to adjust the power distribution in the height direction as in the past. Therefore, it is sufficient that the self-propelled control rod (400) is fully inserted or lifted. In addition, since the combustion reactivity is also small, the amount of neutron absorbing material is small, so that a light control rod is sufficient.
The self-propelled control rod (400) is operated by receiving a signal from the outside by the receiver (440). The electric wires that send signals to each device are made of heat-resistant coated copper wires or conductive ceramics.
Since silver and cadmium of the silver-cadmium battery that is the power source are neutron absorbers, the silver-cadmium battery also serves as a neutron absorber.
As the power source, a fuel cell or a thermoelectric semiconductor (a small uranium 235 is laid on the high temperature side and a coolant is on the low temperature side) can be considered. A lightweight boron carbide (B4C) sintered thin plate may be considered as a neutron absorber. In addition, if the external power line is routed to the upper grid plate (3) and led to the self-propelled control rod (400) of the present invention, a long-term high-output power source can be obtained. If the screw (412) is rotated and the self-propelled control rod (400) is floated to the top, the self-propelled control rod (400) will drop and the control rod can be reliably inserted if the external power is turned off in the event of an accident.
The drive motor (411) and the screw (412) were used as the propulsion unit, but if the heat is rapidly generated by a large number of electric heating coils, the vapor generated by the water evaporation becomes jet injection and is injected from the fountain nozzle (413). . The propulsion device has no moving parts and is highly reliable.

FIG. 7 is a schematic view of the external water pressure driven self-propelled CR system (500) of the present invention. The lightweight control rod blade (510) is a neutron absorber in which a sintered thin plate of boron carbide (B4C) is coated with a titanium alloy, stainless steel, or carbon fiber. The lightweight control rod blade (510) is supported by a central cylindrical tube (520) made of titanium alloy or stainless steel. There is a CR side drainage pipe (530) in the central cylindrical pipe (520). The drain water supplied to the CR side drain pipe (530) is drained or supplied from the outside through the drain pipe (540). The drainage water pipe (540) is detachable at the pipe connection port (541). This figure is a view showing a state in which the lightweight control rod blade (510) is fully pulled out from the lower part where it has been fully inserted into the core. When water from the outside is supplied to the CR side drainage pipe (530) through the drainage pipe (540), the water is discharged from the drainage nozzle (531) to the central cylindrical pipe (520) in the direction of the arrow. . Then, the lightweight control rod blade (510) rises in the central cylindrical pipe (520) supported by the lower stopper (533) fixed to the lower part of the CR side drainage pipe (530). The upper stopper (521) fixed to the central cylindrical pipe (520) comes into contact with the lower end of the drainage water nozzle (531), and the lightweight control rod wing (510) stops rising. The bellows notch (532) between the CR side drainage pipe (530) and the central cylindrical pipe (520) comes out of the central cylindrical pipe (520) and supports the central cylindrical pipe (520) as shown in FIG. . However, since there is no flow of water, there is no arrow indicating the flow of water.
FIG. 8 is a view for explaining a state in which the light weight control rod blade (510) is fully inserted from the upper part to the lower part where it has been fully extracted from the core. The water sucked in the central cylindrical pipe (520) from the drain water nozzle (531) into the CR side drain pipe (530) in the direction of the arrow is drained to the outside through the drain pipe (540). Then, the pressure inside the bellows of the bellows notch (532) attached to the upper part of the CR side drainage pipe (530) supporting the central cylindrical pipe (520) decreases, the bellows contracts, and the notch becomes the CR side drainage pipe (530). The lightweight control rod wings (510) fall down in the central cylindrical tube (520) because they are drawn in. The lower end of the central cylindrical pipe (520) is in contact with the lower stopper (533) attached to the lower part of the CR-side drainage pipe (530), and the lightweight control rod blade (510) is dropped in the central cylindrical pipe (520). Stop. The state shown in FIG. 7 is obtained. However, since there is no flow of water, there is no arrow indicating the flow of water.
The bellows notch (532) is removed, and during normal operation, the CR side drainage pipe (530) is subjected to a slightly higher water pressure than the reactor water pressure, and most of the lightweight control rod blades (510) are placed in the core. In the event of an accident where the water pressure in the CR side drainage pipe (530) drops, the lightweight control rod blades (510) of both the central cylindrical pipe (520) are placed in the core. Fall. Safety is further enhanced.
Although water pressure is used as a driving source, the same applies to water vapor or helium gas.
FIG. 9 is an overview of the external hydraulic drive self-propelled CR system (500) as seen from above. The drainage water pipe (540) for supplying water from the outside and discharging water to the outside goes up or down the upper grid plate (3), and the CR of the external water pressure driven self-propelled CR system (500). It is connected to the side drain water pipe (530). 7 and 8 show the positional relationship between the omitted nuclear fuel assembly (30) and the channel box (35).
Can be used to inject emergency cooling water in case of loss of coolant. If boric acid water or sodium pentaborate mixed water is injected, it can also serve as a back-up control rod system.

FIG. 10 is an overview of the external hydraulically driven liquid CR system (600) of the present invention. Liquid neutron absorber (612) such as borate water or water containing sodium borate is filled in zircaloy hollow blade (613), which is a rectangular container made of a hollow zirconium alloy supported by solid central structural material (620) The reactor power is adjusted according to the liquid level. The liquid neutron absorber (612) is supplied or discharged from each blade discharge pipe (611) through the absorber pipe (610) from the outside.
On the Zircaloy hollow wing (613) is stored a solid poison sudare (650) in which several thin plates made of a solid neutron absorber such as B4C are folded. Normally, the magnet has a Curie point temperature slightly higher than 286 ° C or a low melting point metal with a melting point slightly higher than 286 ° C and is kept in a folded state. Neutrons are absorbed strongly.
Reactor power is controlled by adjusting the degree of opening of the solid poison sudare (650) by laying a float on the solid poison sudare (650) and filling the zircaloy hollow blade (613) with pure water. You can also. If water is discharged to the outside in the event of an accident, the solid poison sudare (650) will be fully opened and neutrons will be strongly absorbed and the reactor can be shut down urgently.
The absorbent material pipe (610) is connected to each blade water discharge pipe (611) of the external hydraulic pressure driving liquid CR system (600) over or under the upper lattice plate (3). The absorbent tube (610) may be brought from the vicinity of the top spray nozzle in FIG. 1 from directly above the external hydraulically driven liquid CR system (600). In that case, it is necessary to remove or shift the position of the steam dryer. The steam separator is also removed or displaced, or the absorbent tube (610) passes through the steam separator.

  In recent years, nuclear power has begun to attract attention as a measure to prevent global warming caused by carbon dioxide gas and oil prices. Since the structure is simple, it can be backfitted to the current furnace and can be realized early.

An overview of the structure of a conventional boiling water reactor (BWR) reactor. BWR core structure diagram. FIG. 3 is a partial plan view of a core in which a nuclear fuel assembly (30) and control rod blades (110) are arranged. The core plane fragmentary figure which arrange | positions the self-propelled control rod of this invention. FIG. 3 is an overview of the self-propelled control rod (400) of the present invention. The figure which showed the mechanism in which a self-propelled control rod (400) moves up and down. FIG. 3 is an overview of an external water pressure driven self-propelled CR system (500) of the present invention. The figure explaining the state which the light-weight control rod wing | blade (510) inserts from the upper part to the lower part. An overview of the external water pressure driven self-propelled CR system (500) as seen from above. 1 is an overview of an external hydraulically driven liquid CR system (600) of the present invention.

Explanation of symbols

1 is a core support plate.
2 is a nuclear fuel support bracket.
3 is the upper grid plate.
30 is a nuclear fuel assembly.
31 is a nuclear fuel rod.
35 is a channel box.
36 is a water rod.
49 is a cooling water passage.
51 is a control rod side leakage water passage.
52 is the leaking water passage opposite to the control rod.
100 is a control rod.
110 is the control rod wing.
120 is a support structure.
400 is an overview of the self-propelled control rod (400) of the present invention.
410 is a battery control rod.
Reference numeral 411 denotes a drive motor.
412 is a screw.
413 is a fountain nozzle.
419 is a tapered water inlet.
420 is a support rod.
422 is a mover.
423 is a spring.
424 is a round bar notch.
425 is a fixed drive source.
431 is a stopper.
432 is a fixed nail.
440 is a receiver.
500 is an overview of the external water pressure driven self-propelled CR system (500) of the present invention.
510 is a lightweight control rod wing.
520 is a central cylindrical tube.
521 is the upper stopper.
530 is the CR side drainage pipe.
531 is a drainage nozzle.
532 is a bellows notch.
533 is a lower stopper.
540 is a drainage pipe.
541 is a pipe connection port.
600 is an overview of the external water pressure driven liquid CR system (600) of the present invention.
610 is an absorbent tube.
611 is each wing drainage pipe.
612 is a liquid neutron absorber.
613 is a Zircaloy hollow wing.
620 is a solid central structural material.
650 is a solid poison sudare.

Claims (3)

Battery control rod with built-in drive unit, propulsion unit, fixed unit, titanium alloy or stainless steel support rod (420) and neutron absorber silver-cadmium battery as power source 410), a screw (412) that is directly connected to the drive motor (411) by a silver-cadmium battery is driven by a receiver (440) that receives a signal from the outside, and water is sucked from the tapered water intake (419) and a fountain nozzle (413) A self-propelled control rod (400) which is moved up and down by jetting water and stays in a fixed position for a long time by a round bar notch (424). The drainage water pipe (540) that reaches the core from above or below the upper grid plate (3) goes to the inside of the central cylindrical pipe (520) and becomes the CR side drainage pipe (530). Sintered boron carbide (B4C) that is supplied to the pipe (530) and discharged from the discharge nozzle (531) to the titanium alloy or stainless steel central cylindrical pipe (520) and supported by the central cylindrical pipe (520) A lightweight control rod blade (510), which is a neutron absorber coated with a titanium alloy or stainless steel or carbon fiber on a thin plate, is raised together with the central cylindrical pipe (520), and the CR side drainage pipe (530) and the central cylindrical pipe (520 An external water pressure driven self-propelled CR system (500) characterized by being held in a fixed position for a long time by an accordion notch (532) between them. A liquid neutron absorber (612) such as boric acid water or sodium pentaborate containing water is externally placed in the zircaloy hollow blade (613), which is a rectangular container made of a hollow zirconium alloy supported by the solid central structural material (620). An external water pressure driven liquid CR system (600) characterized in that the reactor power is adjusted by supplying or discharging from each blade discharge pipe (611) through the absorber pipe (610) from the outside.

Images