JPH0552979A - Small-sized fast breeder reactor - Google Patents

Abstract

PURPOSE:To increase the controllable combustion reactivity of a small-sized fast breeder reactor by simple constitution, to achieve the ensurance of non- criticality at the time of submersion, the extension of the reactivity life of nuclear fuel and the simplification of maintenance and to certainly perform reactor stopping operation in case of emergency to enhance reliability. CONSTITUTION:A reactor vessel 12 wherein a reactor core 14 internally loaded with nuclear fuel is packed with a cooling material 5 and at least either one of upper and lower parts is closed by a shield plug 16 and the reflection device 13 freely rising and falling so as to be capable of receiving the reactor vessel 12 and controlling the combustion reactivity of nuclear fuel are mounted. Further, the piercing pipe 20 provided so as to pierce the reactor core 14 in the vertical direction of the reactor vessel 12 and the control rod 21 capable of being inserted in and taken out from the piercing pipe 20 and controlling reactor output are provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a small-sized fast reactor, and more particularly to a small-sized fast reactor having a simple structure in which a drive unit for controlling reactor power output and refueling is eliminated from the inside of a reactor vessel.

[0002]

2. Description of the Related Art Generally, in designing a nuclear reactor, simplification of the structure is considered from the viewpoint of repair, and it is necessary not to install equipment having a drive unit such as a control rod and a fuel exchanger inside the reactor vessel. desirable.

As a small fast reactor of this type, a small fast reactor 1 having a simplified structure is known as shown in FIG. FIG. 5 is a diagram conceptually showing the small fast reactor 1 having a heat output of 125 MW.

The small fast reactor 1 comprises a reactor vessel 2 and a substantially sleeve-shaped control reflector 3 provided on the outside of the reactor vessel 2 so as to be movable up and down.

The reactor vessel 2 is composed of a tubular body having an opening at the top. A nuclear fuel is loaded inside the reactor vessel 2 to form a reactor core 4, and a coolant 5 such as liquid metal sodium is filled and the reactor core 4 is immersed therein. A shield plug 6 is detachably provided at the opening of the reactor vessel 2 to seal the inside of the reactor vessel 2.

The control reflector 3 is arranged outside the reactor vessel 2 and is driven up and down by a drive mechanism 7. The control reflector 3 controls the leakage of neutrons generated from the core 4 by moving the outer periphery of the reactor vessel 2 in the vertical direction, and controls the combustion reactivity of nuclear fuel.

Reference numerals 8, 9, and 11 represent an intermediate heat exchanger, an electromagnetic pump, and a partition, respectively.

[0008]

It is expected that the small fast reactor 1 will be used in a place where the furnace itself may be submerged or submerged. However, since the small fast reactor 1 has a simple structure, the plutonium enrichment of the nuclear fuel 4 is determined according to the reactivity control ability of the control reflector 3. Therefore, the enrichment degree of the nuclear fuel 4 is set to, for example, about 23%, and the reactivity control capability of the control reflector 3 is set to about 10% Δk to 20% Δk with respect to the nuclear fuel 4.

On the other hand, assuming that the small fast reactor 1 is submerged in water and the surroundings of the reactor vessel 2 are all filled with water, the amount of reactivity applied by water (reactivity value of water) is about 8% Δk. ..

Therefore, for example, when the reactivity control capability of the control reflector 3 is set to about 15% Δk with respect to the nuclear fuel 4, when the small fast reactor 1 is submerged in water, the subcriticality of the small fast reactor 1 is reduced. As the reflector control capability required to hold the above, subtracting about 8% Δk which is the reactivity value of water from about 15% Δk which is the reactivity control capability of the control reflector 3, The reactivity control capacity that can be used for the original operation control (combustion compensation, temperature compensation, furnace shutdown margin, etc.) is about 7% Δk.

Thus, as an abnormal event, the small fast reactor 1
If the possibility of being submerged in water cannot be ruled out, the controllable combustion reactivity of the small fast reactor 1 is the reactivity that the control reflector 3 can control and the reactivity of water around the small fast reactor 1 when submerged. And the controllable combustion reactivity becomes slight.

Therefore, considering the possibility of submersion in water, there is a problem that the reactivity life of the small fast reactor 1 cannot be extended.

The present invention has been made in consideration of the above-mentioned circumstances. It has a simple structure and increases the controllable combustion reactivity of a small fast reactor to ensure subcriticality when submerged in water and the reaction of nuclear fuel. It is an object of the present invention to provide a small-sized fast reactor which is capable of prolonging its service life and simplifying maintenance, and which can surely perform a furnace shutdown operation in an emergency to improve reliability.

[0014]

In order to solve the above-mentioned problems, a small fast reactor according to the present invention fills a core loaded with nuclear fuel with a coolant and shields at least one of the upper and lower parts. A reactor vessel closed with a plug, a reflecting device for controlling the combustion reactivity of the nuclear fuel that can be moved up and down so that the reactor vessel can be housed, and penetrates the reactor core from at least one of the vertical direction of the reactor vessel. And a control rod that is detachably inserted into and removed from the through tube to control the furnace output.

[0015]

The small fast reactor according to the present invention accommodates the reactor core loaded with the nuclear fuel inside the reactor vessel, fills it with the coolant and closes it with the shield plug, and the reflector moves up and down to accommodate the reactor vessel. To control the burning reactivity of nuclear fuel, and a through pipe is provided in the reactor vessel through at least one of the vertical direction through the core, and control rods are detachably inserted into and removed from this through pipe to output the reactor power. Since it is possible to increase the controllable combustion reactivity, it is possible to secure subcriticality when the small fast reactor is submerged in water. Further, as the controllable combustion reactivity increases, a nuclear fuel having a long reactivity life can be used as the nuclear fuel.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the small fast reactor according to the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a conceptual view showing a small fast reactor according to a first embodiment of the present invention, and FIG. 2 is a vertical sectional view showing a cross section of the small fast reactor shown in FIG. Note that the portions corresponding to those in FIG. 5 are described with the same reference numerals.

As shown in FIG. 1, the small fast reactor 10 is, for example, a small reactor having a heat output of 125 MW. Small fast reactor 10
Includes a reactor vessel 12 and a reflecting device 13 that moves up and down so as to accommodate the reactor vessel 12.

The reactor vessel 12 is composed of a bottomed cylindrical body having an opening at the top, and a cylinder 12B is formed on the upper side and a bottom 12C is formed on the lower side. A nuclear fuel is loaded inside the reactor vessel 12 to form a reactor core 14, and a coolant 5 such as liquid metal sodium is filled and the reactor core 14 is immersed therein.

The core 14 has an equivalent diameter of about 92 cm and a height of 30.
It has a size of 0 cm and the nuclear fuel is composed of metallic fuel with a plutonium enrichment of about 23%. The core 14 is supported by the core support plate 14A. The core support plate 14A is provided with a plurality of circulation holes 14B on the outer peripheral side and a plurality of core communication holes 14C on the inner peripheral side.

A shield plug 16 is removably provided at the opening of the reactor vessel 12 to seal the inside of the reactor vessel 12.

The reflection device 13 comprises a control reflector 3 and a drive mechanism 7 for driving the control reflector 3 up and down.

The control reflector 3 is formed in a substantially hollow cylindrical shape and is provided outside the reactor vessel 12. The control reflector 3 has an inner diameter larger than the outer diameter of the reactor vessel 12, and is controlled by the drive mechanism 7 so as to be vertically movable from below the reactor vessel 12 along the outer periphery of the reactor vessel 12. .. The control reflector 3 controls the combustion reactivity of the core 14 by moving up and down the outer circumference of the reactor vessel 12.

The reactor vessel 12 is provided with a ring-shaped intermediate heat exchanger 8 so that the heat of the core 14 can be taken out through the coolant 5. An annular electromagnetic pump 9 is provided below the intermediate heat exchanger 8 to guide the heat-exchanged coolant 5 to below the reactor vessel 12 and circulate the coolant 5.

Partition walls 11 are extended from the core support plate 14A on the inner peripheral sides of the intermediate heat exchanger 8 and the electromagnetic pump 9, and the cores 14 are housed inside the partition walls 11. The partition wall 11 defines the upper portion 12B of the reactor vessel 12 on a high temperature side in which the core 14 is housed and a low temperature side in which the intermediate heat exchanger 8 and the electromagnetic pump 9 are arranged.

By the way, at the axial center of the reactor vessel 12,
An inner pipe 20 as a through pipe is provided. The inner pipe 20 penetrates the core 14 from the shield plug 16 in the upper part of the reactor vessel 12, reaches the core support plate 14A, and extends in the vertical direction.
The diameter of the inner tube 20 is set to about 20 cm, for example.

A control rod 21 is attached to the inner pipe 20 of the reactor vessel 1.
It can be inserted and removed from above 2 in a removable manner. Control rod 21
Is composed of boron carbide (B ₄ C) enriched with ¹⁰ B, and the reactivity control ability is set to about 10% Δk. Control rod 21
The upper end of is connected to the control rod drive mechanism 22 via a bellows 23. The control rod drive mechanism 22 is housed in a housing 24 provided on the shielding plug 16, and drives and controls the control rod 21 so as to be vertically displaceable in the inner pipe 20. The control rod 21 is vertically displaced in the inner pipe 20 by the control rod drive mechanism 22 and is moved in and out of the core inner pipe 20A penetrating the core 14 to control the combustion reactivity of nuclear fuel in the core 14. To do.

Next, the operation of the small fast reactor 10 will be described.

In the small fast reactor 10, the drive mechanism 7 moves the control reflector 3 up and down to cover the outer periphery of the reactor vessel 12 at a desired opening degree and control the combustion reactivity of the nuclear fuel loaded in the core 14. ..

When the temperature of the coolant 5 is raised in the core 14,
It rises in the partition wall 11 and is introduced into the intermediate heat exchanger 8 for heat exchange. The heat-exchanged coolant 5 is discharged upward by the electromagnetic pump 9, introduced into the lower portion 12C of the reactor vessel 12 through the flow hole 14B, and guided to the core 14 again through the core communication hole 14C. It circulates inside 12.

By the way, when the small fast reactor 10 is submerged due to an abnormal event and the entire circumference of the reactor vessel 12 is filled with water, the reactivity application amount by water (reactivity value of water) is about. 8% Δk. Therefore, for example, the reactivity control capability of the control reflector 3 is about 15% Δk with respect to nuclear fuel.
Is set to 1, the reactivity control capability of the control reflector 3 is about 1 as the reflector control capability required to maintain the subcriticality of the small fast reactor 10 when the small fast reactor 10 is submerged in water.
By subtracting about 8% Δk, which is the reactivity value of water, from 5% Δk, the small fast reactor 10 can be used for operation control (combustion compensation, temperature compensation, reactor shutdown margin, etc.) using only the control reflector 3. The reactivity control capability is about 7% Δk.

Therefore, when such a small fast reactor 10 is submerged in water, when the control rod drive mechanism 22 puts the control rod 21 into the core inner tube 20A, the control rod 21 has a reactivity control capability of 10% Δk. Therefore, the reactivity value of water when submerged exceeds about 8% Δk. Therefore, the small fast reactor 10
When the control abilities of the control rod 21 and the control reflector 3 are combined when the water is submerged, the reactivity that can be used for operation control of the small fast reactor 10 increases to about 17% Δk, and the subcriticality of the small fast reactor 10 increases. Can be sufficiently secured. Therefore, as the controllable combustion reactivity increases, a nuclear fuel having a long reactivity life can be used.

On the other hand, when the small fast reactor 10 is used in a place where there is no risk of being submerged in water, the control rod 21 and the control reflector 3 can be used together, so that the fissile material of the nuclear fuel in the core 14 can be used. By increasing the enrichment (enrichment) and controlling the excess reactivity by the control rod 21, it is possible to compensate for the decrease in reactivity due to long-term combustion, so that the reactivity life of the nuclear fuel is greatly increased. Can be extended to. For example, in the case of a small fast reactor having a scale of 50,000 KWe, it can be extended by about 10 years when used in combination, resulting in a reactivity life of about 20 years.

Further, since the control rod 21 is inserted into the inner pipe 20 from the outside of the reactor vessel 12, the control rod system 21,
It is not necessary to open the shield plug 16 at the time of maintenance work such as maintenance, inspection and repair of 22, 23, and if nuclear fuel having a long reactivity life is loaded, maintenance inside the reactor vessel 12 becomes unnecessary for a long period of time. Become.

Next, a second embodiment of the small fast reactor according to the present invention will be described with reference to FIG. The parts corresponding to those in FIGS. 1, 2 and 5 are designated by the same reference numerals, and the description thereof will be omitted.

As shown in FIG. 3, the small fast reactor 30 comprises a reactor vessel 32 and a reflecting device 13 that moves up and down so as to accommodate the reactor vessel 32. Reactor vessel 32
Is a bottomed cylindrical body having an opening 32A at the bottom. The core 14 is supported by the core support plate 14A.

A shield plug 33 is detachably provided in the opening 32A of the reactor vessel 32 to seal the inside of the reactor vessel 32.

The reflecting device 13 comprises a control reflector 3 and a drive mechanism 7 for driving the control reflector 3 up and down.

By the way, in the axial center of the reactor vessel 32,
An inner pipe 31 as a through pipe is provided. The inner pipe 31 extends vertically from the shield plug 33 of the reactor vessel 32 through the core support plate 14A and the core 14.

The control rod 21 is attached to the inner pipe 31 of the reactor vessel 3.
It can be inserted / removed from the lower part of 2. Control rod 21
Is composed of boron carbide (B ₄ C) enriched with ¹⁰ B, and the reactivity control ability is set to about 10% Δk. Control rod 21
The lower end of is connected to the control rod drive mechanism 22 via a bellows 23. The control rod drive mechanism 22 and the bellows 23 are
It is housed in a housing 24 provided below the shielding plug 33. The control rod drive mechanism 22 drives and controls the control rod 21 so as to be vertically displaceable within the inner pipe 31. Control rod 2
1 is vertically displaced in the inner pipe 31 by the control rod drive mechanism 22 and is put in and taken out in the core inner pipe 31A penetrating the core 14 to control the combustion reactivity of the nuclear fuel in the core 14. Is becoming

Therefore, in the small fast reactor 30 according to the second embodiment, the small fast reactor 10 according to the first embodiment moves the control rod 21 in and out from above the reactor vessel 12. The control rod 21 is put in and taken out from below the reactor vessel 32.

Next, the operation of the second embodiment of the small fast reactor will be described.

In the small fast reactor 30, the drive reflector 7 moves the control reflector 3 up and down to cover the outer periphery of the reactor vessel 32 at a desired opening degree and control the burning reactivity of nuclear fuel in the core 14.

If the small fast reactor 30 is submerged due to an abnormal event and the entire circumference of the reactor vessel 32 is filled with water, the reactivity application amount by water is about 8% Δk. Therefore, for example, if the reactivity control capability of the control reflector 3 is set to about 15% Δk with respect to the nuclear fuel, the small fast reactor 30 is controlled only by the control reflector 3 when the small fast reactor 30 is submerged in water. The reactivity control capacity that can be used for operation control (combustion compensation, temperature compensation, furnace shutdown margin, etc.) is approximately 7% Δk.

Therefore, when the control rod drive mechanism 22 puts the control rod 21 into the inner pipe 31A of the reactor core when the small fast reactor 30 is submerged in water, the control rod 21 has a reactivity control capability of 10% Δk. Therefore, the reactivity value of water when submerged exceeds about 8% Δk. Therefore, the small fast reactor 30
When the control abilities of the control rod 21 and the control reflector 3 are combined during submersion in water, the reactivity that can be used to control the operation of the small fast reactor 30 increases to about 17% Δk, and the subcriticality of the small fast reactor 30 increases. Can be sufficiently secured. Therefore, as the controllable combustion reactivity increases, a nuclear fuel having a long reactivity life can be used as the nuclear fuel.

On the other hand, when the small fast reactor 30 is used in a place where it is unlikely to be submerged in water, the control rod 21 and the control reflector 3 can be used in combination, so that the degree of enrichment of the fissile material in nuclear fuel is high. By increasing the (enrichment degree) and controlling the excess reactivity by that amount with the control rod 21, it is possible to compensate for the decrease in reactivity due to long-term combustion, and thus to significantly extend the reactivity life of the nuclear fuel. You can

Further, since the control rod 21 is inserted into the inner pipe 31 from the lower portion of the reactor vessel 32, the control rod system 21,
It is not necessary to open the shield plug 33 at the time of maintenance work such as maintenance, inspection and repair of 22, 23, and the shield plug 33
Maintenance work can be performed independently from. When a nuclear fuel having a long reactivity life is loaded in the core 14,
Maintenance of the inside of the reactor vessel 32 becomes unnecessary for a long period of time.

Next, a third embodiment of the small fast reactor of the present invention will be described with reference to FIG. The parts corresponding to those in FIGS. 1 to 3 and 5 are designated by the same reference numerals, and the description thereof will be omitted.

As shown in FIG. 4, the small fast reactor 40 comprises a reactor vessel 42 and a reflecting device 13 which moves up and down so as to accommodate the reactor vessel 42. Reactor vessel 42
Is a hollow cylindrical body having openings 42A and 42B at the top and bottom, respectively. The core 14 is the core support plate 14
Supported by A.

Shield plugs 16 and 33 are detachably provided at the openings 42A and 42B of the reactor vessel 42 to seal the inside of the reactor vessel 42.

An intermediate heat exchanger 8 is provided above the inside of the reactor vessel 42, and heat of the reactor core 14 is taken out through the coolant 5. An electromagnetic pump 9 is provided below the core support plate 14A to guide the heat-exchanged coolant 5 to below the reactor vessel 12 and circulate the coolant 5.

By the way, as shown in FIG. 4, the small fast reactor 40 is provided with an inner pipe 41 as a through pipe penetrating the axial center portion of the reactor vessel 42. The inner pipe 41 is the reactor vessel 4
2 The shield plug 16 at the upper part penetrates the core 14 and the core support plate 14A, and further penetrates the shield plug 33 to extend in the vertical direction.

Control rods 21A and 21B are inserted into and removed from the inner pipe 41 from both directions above and below the reactor vessel 42. The control rods 21A and 21B are made of boron carbide (B ₄ C) enriched with ¹⁰ B, and the reactivity control ability is set to about 10% Δk. Upper and lower control rods 21A, 2
The drive side ends of 1B are connected to the control rod drive mechanisms 22A and 22B via bellows 23A and 23B, respectively. Control rod drive mechanism 22A, 22B and bellows 2
3A and 23B are housed in housings 24A and 24B, respectively. The housings 24A and 24B are provided above the shield plug 16 and below the shield plug 33, respectively.

The control rod drive mechanisms 22A and 22B drive and control the control rods 21A and 21B so as to be vertically displaceable within the inner pipe 41. The control rods 21A and 21B are displaced vertically in the inner pipe 41 by the control rod drive mechanisms 22A and 22B, and are taken in and out in the core inner pipe 41A that penetrates the core 14 to cause a combustion reaction of nuclear fuel in the core 14. Control the degree.

Therefore, in the small-sized fast reactor 40 according to the third embodiment, the small-sized fast reactors 10, 30 according to the first and second embodiments are either above or below the reactor vessels 12, 32. While the control rod 21 is taken in and out from one side, the control rod 21 is taken in and out from both upper and lower directions of the reactor vessel 42.

Next, the operation of the third embodiment of the small fast reactor will be described.

In the small fast reactor 40, the drive mechanism 7 moves the control reflector 3 up and down to cover the outer periphery of the reactor vessel 42 at a desired opening degree and control the burning reactivity of nuclear fuel in the core 14.

When the small fast reactor 40 is submerged due to an abnormal event and the entire circumference of the reactor vessel 42 is filled with water, the control reflector is provided as in the first and second embodiments. The reactivity control capacity of 3 is about 1 for the nuclear fuel of the core 14.
When 5% Δk is set, the reaction that can be used for operation control (combustion compensation, temperature compensation, furnace shutdown margin, etc.) by using only the control reflector 3 when the small fast reactor 40 is submerged in water The degree controllability is about 7% Δk.

Therefore, when such a small fast reactor 40 is submerged in water, the control rod drive mechanism 22A, 22B is used to control the control rod 21.
When A and 21B are put into the core inner tube 41A, the control rods 21A and 21B have a reactivity control ability of 10% Δk, and therefore, the reactivity value of water at the time of submersion exceeds about 8% Δk. .. Therefore, when the small fast reactor 40 is submerged in water, the control rod 21
When the control capabilities of A and 21B and the control reflector 3 are combined, the reactivity that can be used to control the operation of the small fast reactor 40 increases to about 17% Δk, and the subcriticality of the small fast reactor 40 is sufficiently secured. be able to. Therefore, as the controllable combustion reactivity increases, a nuclear fuel having a long reactivity life can be used as the nuclear fuel.

Further, when each control rod 21 is driven independently, fine power control can be performed on the core 14.

On the other hand, when the small fast reactor 40 is used in a place where there is no danger of being submerged in water, the control rods 21A and 21B and the control reflector 3 can be used together, so that the fissile material of the nuclear fuel is rich. By increasing the degree of chemical conversion (concentration) and controlling the excess reactivity by the control rods 21A and 21B,
Since the decrease in reactivity due to long-term combustion can be compensated, the reactivity life of nuclear fuel can be significantly extended.

[0062]

As described above, the small-sized fast reactor according to the present invention is a nuclear reactor in which a core filled with nuclear fuel is filled with a coolant and at least one of upper and lower parts thereof is closed with a shielding plug. A container, a reflecting device that controls the combustion reactivity of nuclear fuel by being able to move up and down so as to accommodate this reactor container, and a through pipe provided through the reactor core from at least one of the vertical direction of the reactor container, Since it has a control rod that is detachably inserted into and removed from this through-pipe and controls the furnace output, the subcriticality can be sufficiently ensured even in the unlikely event that the small fast reactor is submerged in water. As a result, the furnace shutdown operation can be performed reliably, safety can be improved, and maintenance can be simplified.

Further, when the small fast reactor is used in a place where there is no risk of being submerged in water, the controllable combustion reactivity of the small fast reactor is increased to prolong the reactivity life of nuclear fuel and improve the economic efficiency. Can be planned.

[Brief description of drawings]

FIG. 1 is a conceptual diagram showing a small fast reactor according to a first embodiment of the present invention.

FIG. 2 is a vertical cross-sectional view of FIG.

FIG. 3 is a conceptual diagram showing a small fast reactor according to a second embodiment of the present invention.

FIG. 4 is a conceptual diagram showing a small fast reactor according to a third embodiment of the present invention.

FIG. 5 is a conceptual diagram showing a conventional small fast reactor.

[Explanation of Codes] 1, 10, 30, 40 Small fast reactor 2, 12, 32, 42 Reactor vessel 4, 14 Core 5 Coolant 6, 16, 33 Shield plug 13 Reflector 20, 31, 41 Through tube 21 , 21A, 21B control rod 22, 22A, 22B control rod drive mechanism

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazumi Miyaki 1 Komukai Toshiba-cho, Kouki-ku, Kawasaki-shi, Kanagawa Stock company Toshiba Research Institute

Claims (1)

[Claims] 1. A nuclear reactor vessel in which nuclear fuel is loaded with a coolant, at least one of upper and lower parts of which is closed by a shielding plug, and a nuclear reactor which can be moved up and down so as to accommodate the nuclear reactor vessel. A reflection device for controlling the combustion reactivity of the reactor, a through pipe provided through the reactor core from at least one of the vertical direction of the reactor vessel, and a reactor output that is removably inserted into and removed from the through pipe A small fast reactor characterized by being equipped with a control rod that operates.