JPH05297173A - Pressure tube type reactor - Google Patents

Abstract

PURPOSE:To improve self-control property and operating performance in a pressure tube type reactor by properly setting the ratio of moderator volume to fuel volume in the reactor, and making an output coefficient and a coolant void coefficient to a more negative value without increasing the diameter and thickness of a pressure tube. CONSTITUTION:A pressure tube reactor has a moderator sealed tube 4 enclosing a calandria tube 2 and having a moderator 3 interposed with the calandria tube 2, and a calandria tank 9 having a calandria tank upper header 6 in the upper part and a calandria tank lower header 8 in the lower part. The moderator 3 is stored in the calandria tank upper header 6 and the calandria tank lower header 8, respectively, and the calandria tank upper header 6 is allowed to communicate with calandria tank lower header 8 through the moderator sealed tube 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pressure tube type nuclear reactor.

[0002]

2. Description of the Related Art In a conventional pressure tube type nuclear reactor, as disclosed in, for example, Japanese Patent Application Laid-Open No. 55-49190, the pressure tubes are basically arranged to have a constant square lattice spacing. ing.

In order to improve the controllability of the core,
On the basis of arranging the pressure tubes at a constant square lattice spacing, the square lattice spacing is reduced in a place where the control rod guide tube and the neutron instrumentation pipe are not arranged (see Japanese Patent Laid-Open No. 58-34386). And heavy water pipes are alternately arranged (see Japanese Patent Laid-Open No. 61-26891), gas is injected into the heavy water moderator (see Japanese Patent Laid-Open No. 58-132692), and the water level of the heavy water moderator is set. Related techniques such as a method and structure for arbitrarily controlling (see Japanese Patent Laid-Open No. 56-12590) are disclosed.

[0004]

The core constituent dimensions of a conventional pressure tube reactor are severely restricted by two requirements, that is, material strength and nuclear characteristics. A conventional pressure tube reactor will be described with reference to FIGS.

FIG. 8 is a schematic cross-sectional view of a conventional core portion, FIG. 9 is an explanatory view of a moderator region in a unit cell, and FIG. 10 is a quarter.
FIG. 11 is a cross-sectional view of a unit cell, and FIG. 11 is an explanatory view showing the performance of a pressure tube reactor, 1 is a pressure tube, 2 is a calandria tube,
9 is a calandria tank, 10 is a control rod guide tube, 11 is a neutron instrumentation tube, and 13 is a fuel pellet.

In the calandria tank 9, the calandria tubes 2 are arranged at a constant square lattice interval, and between the tubes in the calandria tube 2, a control rod guide tube 10 or a neutron instrumentation tube 11 is appropriately arranged. ing. Further, the calandria tank 9 generally holds heavy water as a moderator at atmospheric pressure.

In the case where the pressure pipes 1 are arranged in a square lattice spacing, the cross-sectional area M ₂ of the moderator allocated to each pressure pipe 1 is represented by the shaded area in FIG. It can be calculated by the following formula.

[0008]

[Equation 1] M ₂ = l ² −0.25πC ² …………………………………… (1) where 1 is the pressure tube lattice spacing and C is the calandria tube outer diameter. is there.

On the other hand, the total cross-sectional area F ₂ of the fuel to be inserted per one pressure tube 1 is calculated from the area of the fuel pellet 13 shown in the sectional view (1/4) of the pressure tube 1 (FIG. 10). Calculated by the formula.

[0010]

F ₂ = 0.25πnd ² ………………………………………………………………………………………………………… (2) where n is the number of fuel rods per pressure tube, and d is the fuel pellet. Is the diameter. Both the moderator and the fuel are considered to have the same cross-sectional area and the same height in the vertical direction.

Therefore, the ratio (M / F) of the moderator volume M and the fuel volume F is obtained by the following equation.

[0012]

Equation 3] _{M / F = M 2 / F} 2 = 4 (l 2 -0.25πC 2) / (πnd 2) ... (3) As is clear from equation (3), moderator volume and the fuel volume The ratio of P depends on the pressure tube lattice spacing l.

On the other hand, since the pressure inside the pressure pipe 1 becomes high, the thickness of the pressure pipe 1 can be reduced by reducing the inner diameter of the pressure pipe 1, and the amount of material necessary for forming the pressure pipe 1, the material strength and the It is advantageous in terms of neutron economy.

However, in this case, the volume of fuel contained in the pressure pipe 1 becomes small. Therefore, in order to keep the ratio of the moderator volume to the fuel volume constant in this state, it is necessary to reduce the pressure tube lattice spacing 1 as is clear from the equation (1).

However, the smaller the pressure tube lattice spacing l is,
Manufacturing of pressure tube reactor becomes difficult.

Therefore, in order to improve the manufacturability of the pressure tube reactor, when the pressure tube lattice spacing 1 is widened and the moderator volume is kept constant in this state, the calandria is calculated from the relation of the formula (1). The outer diameter of the pipe must be widened.

However, as is apparent from FIG. 10, the outer radius C / 2 of the calandria tube is 1/2 of the pressure tube lattice spacing l.
It cannot be larger. Therefore, the moderator volume increases from the relationship of the equation (1).

That is, when the fuel volume is kept constant, the ratio of the moderator volume to the fuel volume increases, and in a pressure tube reactor using heavy water as the moderator, as shown in FIG. Since the coolant void reactivity shifts in the positive direction, the self-controllability of the furnace tends to deteriorate.

Therefore, it is necessary to keep the ratio of the moderator volume to the fuel volume constant, but this requires increasing the fuel volume. Therefore, the inner diameter of the pressure tube for containing the fuel, that is, the volume of the high pressure portion increases, and the thickness of the pressure tube also increases, which is disadvantageous from the viewpoint of the strength of the pressure tube, the neutron economy, and the amount of required material.

Further, conventionally, there have been problems that the performance evaluation of the controllability of the core in the pressure tube reactor is complicated, and the reactor system is enlarged.

An object of the present invention is, in a pressure tube reactor, appropriately setting the ratio of moderator volume to fuel volume to increase the output coefficient and the coolant without increasing the diameter and thickness of the pressure tube. It is to improve the self-controllability and operating performance of the furnace by making the void coefficient and the like more negative values.

[0022]

The above object can be achieved as follows.

(1) In a pressure tube type nuclear reactor having a core comprising a pressure pipe for containing nuclear fuel and a coolant, a calandria pipe containing the pressure pipe, and a calandria tank containing the calandria pipe, a calandria pipe is provided. And a moderator material enclosing tube in which the moderator material is interposed between the calandria tube and the calandria tube, and the core is formed by arranging two or more units of the minimum unit of the calandria tube, the moderator and the moderator material enclosing tube. To do.

(2) In (1), the calandria tank has a calandria tank upper header on the upper side and a calandria tank lower header on the lower side, and the calandria tank upper header and the calandria tank lower header are provided. Stores a moderator, and the calandria tank upper header and the calandria tank lower header communicate with each other through a moderator sealing tube.

(3) In (1), a liquid having a property of absorbing neutrons is formed by a gas filling portion of the calandria tank inside the calandria tank and outside the moderator sealing tube. A gravity drop mechanism for injecting into the gas filling portion of the calandria tank.

(4) In (1), the control rod guide tube of the control rod to be inserted into the core is provided with a mechanism for circulating the moderator.

(5) In (1), a poison tube is used for at least a part of the control rods inserted into the core.

(6) In (1) to (3), the moderator enclosure tube is made of zircaloy or zirconium-niobium alloy.

[0029]

According to the present invention, in a pressure tube type reactor, two or more moderator embedding tubes, which include a calandria tube and a moderator is interposed between the calandria tube, are arranged to form a reactor core. There is a calandria tank upper header at the upper part of the calandria tank, and a calandria tank lower header at the lower part, and a moderator is stored in each of the calandria tank upper header and the calandria tank lower header. The upper header of the calandria tank and the lower header of the calandria tank communicate with each other through a moderator sealing pipe.

Therefore, from the above configuration, the ratio of the moderator volume to the fuel volume is a function of the inner diameter of the moderator encapsulation tube, the outer diameter of the calandria tube, and the fuel pellet diameter. The ratio does not affect the pressure tube grid spacing.

Therefore, the pressure tube lattice spacing can be increased without increasing the size of the pressure tube, the manufacturability of the furnace can be improved, and the coolant void coefficient can be set on the more negative side. Controllability and safety are improved.

Further, inside the calandria tank, a void held outside the moderator sealing tube is formed by the calandria tank gas sealing portion, and is injected into the calandria tank gas sealing portion to absorb neutrons. It has a gravity drop mechanism for liquids with properties.

Therefore, when it is necessary to stop the reactor urgently, it is possible to stop the reactor by injecting a liquid having a property of absorbing neutrons into the gas filling portion of the calandria tank.

Further, since the control rod guide tube of the control rod to be inserted into the core is provided with a mechanism for circulating the moderator, the control rod is cooled by the moderator and does not cause a temperature rise due to neutron absorption. , Control rod reactivity can be maintained.

Further, since the poison tube is used for at least a part of the control rods to be inserted into the core, both the control rod drive mechanism and the mechanical drive parts in the reactor can be reduced in number.

Further, since the moderator-filled tube is made of zircaloy or zirconium-niobium alloy, neutron absorption by the moderator-filled tube in the reactor is reduced, and the neutron economy of the core can be improved.

[0037]

Embodiments of the present invention will be described below with reference to FIGS.

FIG. 1 is a schematic vertical sectional view of the core portion of the first embodiment, FIG. 2 is a schematic horizontal sectional view of the core portion of the first embodiment, and FIG. 3 is a moderator region in the unit lattice of the first embodiment. FIG. 4, FIG. 4 is a cross-sectional view of the 1/4 unit lattice of the first embodiment, FIG. 5 is an illustration of the moderator circulation system of the second embodiment, and FIG. 6 is an emergency reactor shutdown of the third embodiment. FIG. 7 is an explanatory view of the system, FIG. 7 is an explanatory view of the control rod of the fourth embodiment, 3 is a moderator, 4 is a moderator enclosing pipe, 5
Is a moderator supply pipe, 6 is a header of a calandria tank,
Reference numeral 7 is a moderator discharge pipe, 8 is a calandria tank lower header, 12 is a calandria tank gas sealing portion, 14 is a heavy water dump tank, 15 is a heavy water circulation pump, 16 is a heavy water cooler, 17 is a poison melting tank, and 18 is Poison removal tower, 1
Reference numeral 9 is a heavy water purification tower, 20 is a tank, 21 is a valve, 22 is a check valve, 23 is a pump, 24 is a moderator supply port, 25 is a control rod, and others are the same as the above-mentioned symbols.

The first embodiment of the present invention will be described with reference to FIGS.

In FIG. 1, the pressure tube 1 is housed in a calandria tube 2, and the pressure tube 1 contains a fuel assembly and a coolant. The calandria tube 2 has a function of insulating the moderator under low temperature and atmospheric pressure conditions from the high temperature pressure tube 1.

In this embodiment, there is a moderator material enclosing tube 4 containing the calandria tube 2, and the moderator material 3 is interposed between the calandria tube 2 and the moderator material enclosing tube 4.

The moderator 3 is connected to the calandria tank upper header 6 through a moderator supply pipe 5 and to the calandria tank lower header 8 through a moderator discharge pipe 7, respectively.

Further, the moderator sealing pipe 4 is provided with the calandria tank upper header 6 or the calandria tank lower header 8.
Through, it is connected to another moderator material enclosing pipe.

In the calandria tank 9, the calandria tank gas sealing portion 12 which is held outside the moderator sealing tube 4 is filled with a nuclear inert gas at atmospheric pressure. In this embodiment, carbon dioxide is used as this gas.

As shown in FIG. 2, in the calandria tank 9, the moderator material enclosing tubes 4 are arranged at a constant square lattice interval, and the control rod guide tubes are arranged between the moderator material enclosing tubes 4. 10
And a neutron instrumentation tube 11 are arranged.

Next, a method of properly setting the ratio of the moderator volume to the fuel volume in this embodiment will be described with reference to FIGS. 3 and 4.

The cross-sectional area of the moderator, which is assigned to one of the pressure tubes having a structure in which the moderator embedding tubes 4 are arranged on a square lattice, is represented by the shaded area M ₁ in FIG. 3, and the area M ₁ is It is calculated by the following formula.

[0048]

[Formula 4] M ₁ = 0.25π (m ² −C ² ) ……………………………… (4) Where, m is the inner diameter of the moderator enclosure tube and C is the outside of the calandria tube. Diameter (both mentioned above).

Meanwhile, cross-sectional area of the fuel to be inserted into one per pressure tube 1 is represented by the total area F ₁ of the fuel pellets 13 in the pressure tube 1 shown in FIG. 4, the total area F ₁ by the following equation Required by.

[0050]

[Formula 5] F ₁ = 0.25πnd ² ………………………………………… (5) where n is the number of fuel rods per pressure tube, and d is fuel. The diameter of the pellet (both mentioned above).

Both the moderator and the fuel are considered to have the same cross-sectional area and the same height in the vertical direction.

Therefore, the ratio (M / F) of the moderator volume to the fuel volume can be obtained by the following equation.

[0053]

[Equation 6] M / F = M ₁ / F ₁ = (m ² −C ² ) / (nd ² ) ……………… (6) As is clear from the equation (6), the moderator volume is And the fuel volume can be determined independently of the pressure tube lattice spacing l.

Therefore, the ratio of the moderator volume to the fuel volume is appropriately set, and the coolant void reactivity is maintained at a value on the more negative side so that the self-controllability is good, and the pressure tube lattice spacing 1 is set to the core. It can be arbitrarily determined only from the viewpoint of manufacturability.

Further, as can be seen from the equation (6), the inner diameter and the thickness of the pressure tube and the inner diameter and the thickness of the calandria tube can be determined regardless of the ratio of the moderator volume to the fuel volume.

Therefore, in order to improve the manufacturability of the core, it is not necessary to increase the size of the pressure tube 1 and the calandria tube 2 even if the pressure tube lattice spacing 1 is widened.

Further, the core can be constructed without increasing the high pressure part, and the degree of freedom in designing the related equipment of the core is increased.

FIG. 5 is an explanatory diagram of the moderator circulation system of the second embodiment.

Heavy water is used as the moderator, and the heavy water discharged from the calandria tank lower header 8 is once stored in the heavy water dump tank 14.

Thereafter, the heavy water is sent to the heavy water cooler 16 by the heavy water circulation pump 15, and when the heavy water is in the moderator enclosure tube 4, the heavy water cooler 16 removes the heat generated by neutron irradiation and gamma ray absorption. Then, the heavy water is sent to the header 6 of the calandria tank.

Further, in order to control the gradual reactivity associated with the combustion of fuel, heavy water is mixed with poison, and the poison is supplied from the poison dissolving tank 17.

Poisons and other impurities in the heavy water are removed by the poison removing tower 18 and the heavy water purifying tower 19.

As described above, by providing the calandria tank upper header 6 and the calandria tank lower header 8 in the calandria tank 9, the moderator can be supplied into each moderator enclosure pipe 4, and the number of pressure pipes 1 can be increased. It is not necessary to provide the moderator piping for supplying the moderator mode enclosing tube 4 to the outside of the core.

As the moderator system, the conventional mode can be used as it is. When the moderator enclosing pipe 4 is used, the moderator circulation system can be made complicated.

FIG. 6 shows the case of the third embodiment. In this embodiment, a portion of the calandria tank 9 in which a nuclearly inert gas is sealed, that is, a calandria tank gas sealing portion 12 is present.

That is, the tank 20 for storing a liquid having a property of absorbing neutrons is provided above the calandria tank 9. In this example, boric acid water was used.

When it is necessary to stop the furnace urgently, the valve 21 is opened and the calandria tank gas sealing portion 12 is opened.
The sealed gas is released, the check valve 22 is opened, and boric acid water is injected into the gas sealed portion 12 of the calandria tank by the gravity drop method to stop the reactor.

That is, the reactor can be stopped without using a control rod and a drive unit such as a poison high-speed injection pump, and the system of the emergency reactor shutdown system is simplified. When the nuclear reactor is restarted, the boric acid water is collected in the tank 20 using the pump 23.

FIG. 7 shows the case of the fourth embodiment. In this embodiment, the control rod guide pipe 10 connects the calandria tank upper header 6 and the calandria tank lower header 8 so that the moderator passes through the moderator supply port 24 and inside the control rod guide pipe 10. To do.

Since the control rod 25 is cooled by the moderator, the temperature does not rise due to neutron absorption,
Control rod reactivity can be maintained.

As a fifth embodiment, some of the many control rods to be inserted into the core are replaced with poison tubes. The neutron flux density is controlled by containing boric acid, which is a solution of neutron absorbing material, in the poison tube and changing the concentration of boric acid.

That is, a poison tube is used to reduce both the number of control rod drive mechanisms and mechanical drive parts in the furnace.

Further, as a sixth embodiment, zircaloy or zirconium-niobium alloy is used as the material of the moderator enclosing tube. As a result, neutron absorption by the moderator encapsulation tube in the reactor is reduced and the neutron economy of the core is improved, as compared with the case where carbon steel such as stainless steel is used as the moderator encapsulation tube material.

[0074]

According to the present invention, in the pressure tube type nuclear reactor, the pressure tube lattice spacing can be expanded without increasing the size of the pressure tube and the manufacturability of the furnace is improved.

Further, it is possible to set the coolant void coefficient on the more negative side, and the self-controllability and safety in the furnace are improved.

Further, the moderator circulation system is simplified, and the safety system in the furnace is simplified and reliability is improved.

Further, the reliability of the control system and the economical efficiency of fuel in the furnace are improved.

Furthermore, the furnace system is simplified and the mechanical failure of the furnace is reduced.

[Brief description of drawings]

FIG. 1 is a schematic vertical sectional view of a first embodiment of the present invention.

FIG. 2 is a schematic cross-sectional view of the core portion of the first embodiment of the present invention.

FIG. 3 is an explanatory diagram of a moderator area within a unit lattice according to the first embodiment of this invention.

FIG. 4 is a cross-sectional view of the 1/4 unit cell of the first embodiment of the present invention.

FIG. 5 is an explanatory diagram of a moderator circulation system according to a second embodiment of the present invention.

FIG. 6 is an explanatory diagram of an emergency reactor shutdown system according to a third embodiment of the present invention.

FIG. 7 is an explanatory diagram of a control rod according to a fourth embodiment of the present invention.

FIG. 8 is a schematic cross-sectional view of a core portion of a conventional example.

FIG. 9 is an explanatory diagram of a moderator region in a unit cell of a conventional example.

FIG. 10 is a cross-sectional view of a 1/4 unit cell of a conventional example.

FIG. 11 is an explanatory diagram showing the performance of a pressure tube reactor.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Pressure pipe, 2 ... Calandria pipe, 3 ... Moderator, 4 ... Moderator encapsulation pipe, 6 ... Calandria tank upper header, 8 ...
Calandria tank lower header, 9 ... Calandria tank, 10 ... Control rod guide tube, 17 ... Poison melting tank, 18
... poison removal tower, 25 ... control rod.

Claims (6)

[Claims] 1. A pressure tube-type nuclear reactor comprising a pressure pipe for containing nuclear fuel and a coolant, a calandria pipe containing the pressure pipe, and a calandria tank containing the calandria pipe, and forming a core, wherein: There is a moderator material enclosing tube that includes a calandria tube and a moderator material is interposed between the calandria tube and the calandria tube, the moderator, and a combination of the minimum units of the moderator material enclosing tube is 2 units or more. A pressure tube type nuclear reactor characterized in that the cores are arranged in an array. 2. The calandria tank has a calandria tank upper header at an upper portion and a calandria tank lower header at a lower portion, and the calandria tank upper header and the calandria tank lower header are respectively provided. The pressure tube reactor according to claim 1, wherein a moderator is stored, and the calandria tank upper header and the calandria tank lower header are communicated with each other through the moderator sealing tube. 3. A liquid having a property of absorbing neutrons, which is formed in the calandria tank gas sealing portion inside the calandria tank and is formed outside the moderator sealing pipe, The pressure tube reactor according to claim 1 or 2, further comprising a gravity dropping mechanism for injecting the gas into the doria tank. 4. The pressure tube reactor according to claim 1, further comprising a mechanism for circulating a moderator through a control rod guide tube of a control rod inserted into the core. 5. The pressure tube reactor according to claim 1, wherein a poison tube is used for at least a part of the control rods inserted into the core. 6. The pressure tube reactor according to claim 1, 2 or 3, wherein the moderator-encapsulating tube is made of zircaloy or zirconium-niobium alloy.