JPH058996B2 - - Google Patents

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a pressure tube nuclear reactor.

[Conventional technology]

The basic structure of a pressure tube nuclear reactor will be explained using Figures 10, 11, and 12, taking as an example the application for permission to install a new converter reactor "Fugen" built by the Power Reactor and Nuclear Fuel Development Corporation.

A pressure tube type nuclear reactor includes a plurality of pressure tubes 21 that house a reactor core 4 and are inserted into a pressure tube guide tube 32;
A moderator tank 1 that accommodates a moderator 5 surrounding a pressure pipe guide tube, and a plurality of control rod guide tubes that are provided in the moderator tank 1 and accommodate control rods that control the output of the reactor. It consists of 10. After passing through the nuclear reactor, the plurality of pressure pipes 21 are connected to a pressure pipe manifold (not shown).

The heat generated in the reactor core is cooled by the reactor coolant circulating in the pressure pipes, and the heated reactor coolant is led to the pressure pipe collecting pipe and becomes steam. However, a part of the heat generated in the reactor core is transferred from the pressure pipe to the moderator 5 by thermal radiation via the pressure pipe guide pipe 32, and the temperature of the moderator increases. If the temperature of the moderator rises too much and boils, voids (bubbles)
It is undesirable for the temperature of the moderator to rise excessively because this will cause negative reactivity in the reactor and make reactor control unstable.

Therefore, in order to lower the temperature of the moderator, a moderator cooling device consisting of a moderator circulation pump 2, a moderator circulation pipe 33, a heat exchanger 3, and a moderator distribution pipe 9 is provided. The moderator 5 in the moderator tank 1 is sent to the heat exchanger 3 by the moderator circulation pump 2, and after being cooled by the secondary coolant circulated by the auxiliary equipment cooling system pump 8,
It returns to the moderator tank through the moderator distribution pipe 9 and the control rod guide pipe 10.

In addition, in order to shield heat radiation from the pressure tube 21 via the pressure tube guide tube 32, the distance between the outer wall of the pressure tube 21 and the inner wall of the pressure tube guide tube 32 is made sufficiently large, and carbon dioxide gas is It's flowing. In the case of "Fugen", this spacing is 16 mm.

In this way, the moderator 5 and the reactor coolant flowing in the pressure pipe 21 are thermally separated as much as possible by design, and the moderator cooling device has no connection with the cooling of the reactor coolant. does not have.

Cooling of nuclear reactor equipment using natural circulation is described in ``Fast Breeder Reactor'' (authored by Hiroshi Yasunari, published by the same publication in 1981). This will be explained with reference to FIG. The reactor core 16 is installed in a reactor vessel 14 filled with a primary coolant 20, and this primary coolant is circulated by a reactor primary cooling system to cool the heat generated in the reactor core. As one of the devices for cooling the primary coolant heated in the reactor core when a failure occurs in the reactor primary system cooling system,
an intermediate exchanger 15 that is provided in the reactor vessel and exchanges heat between the primary coolant 20 and the secondary coolant; an air cooler 17 that is connected to the intermediate heat exchanger and cools the secondary coolant; A reactor coolant emergency cooling system is provided, which is comprised of a secondary circulation pump 19 that is located between the intermediate heat exchanger 15 and the air cooler 17 and circulates secondary coolant. This device is designed to cool the primary coolant by circulating the secondary coolant with the secondary circulation pump and cooling the secondary coolant with the air cooler 17. Even in the event of a failure, cooling is possible through natural circulation of secondary coolant. However, this is for cooling the primary coolant that directly cools the core, and is not intended for the moderator.

[Problem that the invention seeks to solve]

In a pressure tube reactor, if the reactor core temperature rises abnormally due to insufficient supply of reactor coolant to the pressure tubes, emergency cooling water is injected into the pressure tube collecting pipe, and the cooling water is supplied to each pressure tube. In addition to cooling the core by reaching the core through tubes, there are various emergency core cooling systems, but all of them require some kind of power. Therefore, if the power is interrupted or a machine driven by the power fails, the core will not be cooled sufficiently, which may lead to damage to the pressure pipes or melting of the core due to overheating.

Furthermore, in a nuclear reactor having a cooling device for a coolant that is also a moderator, it is known to provide a cooling device that uses natural circulation in addition to a cooling device that uses forced circulation. However, in this conventional technology, in order to prevent the thermal efficiency from decreasing due to cooling through the natural circulation of the coolant during normal operation, the natural circulation cooling system is replaced with a forced circulation cooling system via an isolation valve, etc. During normal operation, the isolation valve, etc. is closed, and only in the event of an abnormality, the isolation valve, etc. is opened to operate the cooling device using natural circulation. Therefore, it was necessary to consider the possibility of failure of these isolation valves, etc.

The purpose of the present invention is to use a moderator, which is present in large quantities around the reactor core, as a cooling medium in a pressure tube nuclear reactor.
without using any equipment driven by power,
An object of the present invention is to provide a nuclear reactor having a device for removing heat from a reactor core.

[Means for solving problems]

The purpose is to provide a pressure pipe that accommodates a reactor core and through which coolant circulates, a pressure pipe guide pipe through which this pressure pipe is inserted, a moderator tank that contains a moderator that surrounds the pressure pipe, and a moderator tank that contains a moderator that surrounds the pressure pipe. a control rod guide tube that is provided in a fuel tank and accommodates a control rod that controls the output of the reactor; a moderator pump that is connected to the moderator tank and circulates the moderator in the moderator tank; A pressure tube nuclear reactor comprising a heat exchanger for cooling the moderator circulated by the moderator circulation pump, and a surge tank connected to the upper part of the moderator tank and provided at a position higher than the reactor core. , an air cooler is provided, the upper part of which is connected to the surge tank, the lower part of which is connected to the moderator tank, and which is built into the cooling tower and is provided at a position higher than the reactor core and lower than the surge tank to cool the moderator with air. , the moderator does not flow from the surge tank to the air cooler during normal operation through the highest part of the piping connecting the upper part of the surge tank and the air cooler;
The moderator is placed at a height where the moderator flows from the surge tank to the air cooler when the moderator boils, and is inserted into the inner wall of the pressure pipe guide tube vertically penetrating the moderator tank and into the pressure pipe guide tube. The distance between the pressure pipe and the outer wall of the pressure pipe is smaller than the rupture strain caused by thermal expansion due to overheating of the pressure pipe, and larger than the minimum space required for thermal shielding between the pressure pipe and the pressure pipe guide pipe during normal operation. This is achieved by

[Effect]

The operation of the present invention will be explained with reference to FIGS. 5, 6, 7, and 14.

The moderator 5 heated in the moderator tank 1 becomes less dense and rises in the pipe 6, passes through the surge tank 28, and reaches the air cooler 30 in the cooling tower 7. Next, the moderator is cooled by the air cooler 30, becomes denser, moves down in the pipe 29, and flows back into the moderator tank 1.

FIG. 6 shows the effect when the distance between the pressure pipe 21 and the pressure pipe guide pipe 32 is reduced, and FIG. 14 shows the thermal deformation start curve of the pressure pipe and the pressure pipe breaking strain curve.
A pressure tube always has a certain stress σ _c under normal operating conditions, and under this condition, if the pressure tube temperature exceeds the pressure tube thermal deformation start temperature T _c , the pressure tube will break at a breaking strain ε _c do. The stress σ _c applied to the pressure pipe can be expressed as follows.

σ _c = P・d _i /2t ...(1) σ _c ... Stress applied to the pressure pipe P ... Internal pressure applied to the pressure pipe t ... Wall thickness of the pressure pipe d _i ... Inner diameter of the pressure pipe Inner diameter of the pressure pipe guide tube 32 Let D _i be the pressure pipe 21
When the outer diameter of the pressure pipe is d ₀ , if D _i ≧d ₀ (1+ε _c ) (2), the pressure pipe guide pipe does not take any part in the deformation that leads to the breakage of the pressure pipe. Now, if we define the relationship between D _i and d _p as D _i <d ₀ (1+ε _c )...(3), even if the pressure pipe begins to deform due to abnormal temperature rise, the amount of strain will be small. The pressure tube 21 comes into contact with the inner surface of the pressure tube guide tube 32 before reaching the breaking strain εc, and the pressure tube guide tube effectively acts to prevent damage to the pressure tube. Furthermore, direct contact between the outer wall of the pressure tube and the inner wall of the pressure tube guide tube improves thermal conductivity from the pressure tube to the moderator in the moderator tank through the pressure tube guide tube, and the moderator of the core heat This will encourage people to move to. FIG. 7 is a diagram showing a temperature change curve 26 of the pressure pipe and a temperature change curve 27 of the pressure pipe guide pipe when the pressure pipe and the pressure pipe guide pipe contact _each other. This shows the state in which the tubes are in contact, and it is clear that the temperature of the pressure tube drops after contact, clearly demonstrating the improvement in thermal conductivity and the cooling effect of the moderator.

〔Example〕

An embodiment of the present invention will be explained with reference to FIGS. 1 to 4 and FIG. 6.

FIG. 1 shows a pressure tube nuclear reactor according to the invention. Pressure pipe 21 that accommodates the reactor core 4 and through which coolant circulates
, a moderator tank 1 that accommodates a moderator 5 surrounding the pressure pipe 21, and a control rod guide tube 10 that is provided in the moderator tank 1 and accommodates control rods that control the output of the reactor. A pressure tube type nuclear reactor is provided in a reactor containment vessel 11, and a moderator cooling device is connected to a moderator tank 1 and includes a moderator circulation pump 2 that circulates the moderator; 2, a heat exchanger 3 whose other end is connected to a moderator distribution pipe 9 and which cools the moderator with a secondary coolant circulated by an auxiliary cooling system pump 8 provided outside the reactor containment vessel; and further has one end connected to the heat exchanger 3.
, a moderator distribution pipe 9 whose other end is connected to a plurality of control rod guide tubes 10, a surge tank 28 provided at a position higher than the reactor core, and a moderator connecting the moderator tank 1 and the surge tank 28. riser pipe 6;
A cooling tower 7 provided outside the containment vessel, an air cooler 30 built into the cooling tower 7 and provided at a higher position than the reactor core, and a moderator connecting the air cooler 30 and the moderator distribution pipe 9. It has a natural circulation cooling device 35 consisting of a return pipe 29.

In this embodiment, under normal operating conditions, the liquid level of the moderator is adjusted to the moderator rising pipe 6 and the moderator return pipe 29 (in Figs. 2 and 3, the moderator distribution pipe 9 and the control rod guide tube 10 are omitted).
The cooled moderator then flows back to the moderator tank 1 via the moderator distribution pipe 9 and the control rod guide pipe 10. The increase in volume of the moderator due to temperature rise is accommodated in the space of the piping or surge tank, so that excessive pressure is not generated in the tank or piping containing the moderator.

Under normal operating conditions, the heat generated by the reactor core 4 is cooled by the paper reactor coolant circulating inside the pressure tube 21, but some of the heat is radiated from the outer wall of the pressure tube to the wall of the pressure tube guide tube. It is transmitted to the moderator in the moderator tank. As a result, the temperature of the moderator increases, so the moderator 5 is circulated by the moderator circulation pump 2 and cooled to a desired temperature by the heat exchanger 3. In this state, as shown in FIG.
9, there is no moderator flow through the air cooler 30, and no moderator cooling by natural circulation occurs.

For some reason, the temperature of the pressure pipe 21 rises abnormally, the amount of heat transferred to the moderator 5 through the pressure pipe guide pipe 32 increases, and at the same time, the moderator circulation pump 2 or the auxiliary equipment cooling system pump 8 stops. Then, the moderator 5 boils and voids (bubbles) 31 are generated in the moderator.
The moderator liquid level rises and the moderator passes through the surge tank 28 and reaches the air cooler 30 as shown in FIG. Accordingly, the moderator 5 is cooled by the air cooler 30 and flows back to the moderator tank 1 via the moderator return pipe 29, the moderator distribution pipe 9, and the control rod guide pipe 10. At the time of moderator boiling, the density of the moderator is as follows.

=α・σ _g +(1-α)σ _e ...(4) ... Density of moderator when moderator boils α ... Void ratio σ _g ... Gas phase density of moderator when moderator boils σ _e ... Deceleration Liquid phase density of the moderator when the material boils The natural circulation force is caused by the difference in the density of the moderator before and after cooling, so it can be expressed by the following equation.

ΔP=(-σ ₁ )H...(5) = {α・σ _g +(1-α)σ _e −σ ₁ }H...(6) ΔP...Natural circulation force σ ₁ ...After moderator cooling Density of moderator H...Difference in height between moderator tank and air cooler (specific height) From now on, the relationship between H and α is: H=ΔP/σ−σ ₁ =ΔP/α(σ _g −σ _e )− (σ ₁ −σ _e ) ...(7), and the difference in height between the moderator tank and the air cooler is H
If is constant, the natural circulation force increases as the void fraction increases, that is, as the boiling of the moderator becomes more intense. Figure 9 is a graphical representation of the seventh equation, and for a certain natural circulation force,
It is shown that if the void ratio, that is, the boiling state in which natural circulation is to be performed, is determined, the height H at which the cooling tower 7 should be placed can be determined.

In natural circulation cooling of the reactor primary coolant in a fast breeder reactor, when the coolant boils and creates voids, positive reactivity of the reactor occurs and the power increases,
However, in the case of a pressure tube reactor,
When the moderator boils and voids are formed, the natural circulation force increases as mentioned above, and as shown in Figure 9, it causes negative reactivity of the reactor, which decreases the reactor's output. This is advantageous for cooling the core.

When setting the specific height H of the cooling tower 7, there is no need to consider the boiling state of the reactor primary coolant of a fast breeder reactor, as the density differs greatly depending on the temperature. In the case of , there is little difference in density due to temperature, and it is possible to set the specific height H of the cooling tower to a feasible value only by taking boiling into consideration.

The cooling capacity of the moderator cooling system through forced circulation is the capacity that can cool the amount of heat generated in the reactor core transferred to the moderator and the amount of heat generated by the moderator due to gamma rays generated in the core during normal operation. It is determined. The natural circulation cooling system of this embodiment is designed to remove the decay heat generated in the reactor core after an abnormal event occurs and the reactor is shut down, so the required cooling capacity is It is determined by the previous moderator temperature, moderator inventory, decay heat generated in the core, and coolant inventory. In general, the amount of heat removed is sufficient to be several percent of the thermal output generated in the core during normal operation.

Figure 4 shows the heat pipe 12 in the moderator tank 1.
It is a figure showing an example provided with. Since the basic structure is the same as that of the conventional technique, a detailed explanation will be omitted, but the same reference numerals are given to the parts corresponding to those shown in the conventional technique of FIG. In addition to the moderator cooling device according to the prior art, a heat pipe 12 as a natural circulation cooling device has an evaporating end inside the moderator tank 1 and a condensing end provided with a cooler 13 outside the moderator tank 1. It is attached to the moderator tank 1. The heat of the moderator 5 in the moderator tank 1 evaporates the internal fluid of the heat pipe at the evaporation end of the heat pipe 12, and the evaporated internal fluid rises in the heat pipe to the condensation end. The heat is removed by the provided cooler 13 and condenses, becoming a liquid again and moving inside the heat pipe to the evaporation end. This action continues, and the moderator 5
cooling is performed. In this way, by using the heat pipe, it is possible to cool the moderator 5 in the moderator tank 1 without having to circulate it using dynamic equipment, reducing the operating time of the moderator circulation pump. In addition, it is possible to cool the moderator containing radioactive substances by natural circulation without taking it out of the reactor containment vessel, which is advantageous in terms of radiation control.

FIG. 6 shows an embodiment in which the distance between the pressure pipe 21 and the pressure pipe guide pipe 32 is limited. The basic structure of the nuclear reactor is composed of conventional technology and a moderator natural circulation cooling device, and since examples have been described, detailed explanation will be omitted. The distance between the pressure pipe 21 and the pressure pipe guide pipe 32 is determined by the above-mentioned D _i <d ₀ (1+ε _c ) ...(8) D _i ... Pressure pipe outer diameter d ₀ ... Pressure pipe outer diameter ε _c ... Pressure pipe The size shall be such that it satisfies the breaking strain and functions as a heat shield during normal operation. In the case of "Fugen", 6 to 10 mm is appropriate. Even if the temperature of the pressure tube 21 increases sharply and deforms due to heat or internal pressure, the ratio of the outer diameter of the pressure tube 21 to the inner diameter of the pressure tube guide tube 32 is determined by the equation (8) above, so rupture will not occur. Before the strain ε _c is reached, the outer diameter of the pressure pipe 21 comes into contact with the inner wall of the pressure pipe guide pipe 32, improving heat transfer from the pressure pipe 21 to the moderator 5 through the pressure pipe guide pipe 32, resulting in deceleration. The core can be efficiently cooled by the material, and the pressure pipe guide tube 32 acts as a reinforcing material to prevent the pressure pipe 21 from deforming.

〔Effect of the invention〕

According to the present invention, even if an accident occurs in a pressure tube reactor in which the reactor coolant cooling system, which consists of dynamic equipment, cannot be used, it is possible to delay the temperature rise in the reactor core, giving time for other countermeasures to be taken. In addition, it is possible to increase the margin and improve the reliability when evaluating the moderator cooling device based on probability theory. Furthermore, during normal operation, the moderator is not cooled by natural circulation, and no heat is wasted.

Furthermore, by limiting the distance between the pressure tube housing the core and the pressure tube guide tube, the temperature rise of the core in the event of an accident can be delayed and more time can be taken to take measures against the accident.

[Brief explanation of the drawing]

Fig. 1 is a system diagram showing an embodiment of the present invention, Fig. 2 is a diagram showing the operating state of the embodiment of the present invention during normal operation, Fig. 3 is a diagram showing the operating state at the time of an accident, and Fig. 4 is a system diagram showing another embodiment of the present invention, FIG. 5 is a diagram showing the operation of the present invention, FIG. 6 is a diagram showing another embodiment of the present invention, and FIG. 7 is a diagram showing pressure pipes and pressure pipes. Figure 8 shows the relationship between the void ratio α of the moderator and the specific height H of the air cooler. Figure 9 shows the relationship between the void ratio α of the moderator and the core. A diagram showing the relationship with reactivity, Figure 10 is a system diagram showing a conventional pressure tube reactor, Figure 11 is a diagram showing the pressure tube, pressure tube guide pipe, and moderator tank, and Figure 12 is a diagram showing the pressure tube. Figure 1 showing the interconnection of the pressure pipe guide pipe and the pressure pipe guide pipe.
Figure 3 shows an emergency cooling system for the reactor primary coolant of a fast breeder reactor, and Figure 14 shows the pressure tube thermal deformation onset curve and pressure tube rupture strain curve. DESCRIPTION OF SYMBOLS 1... Moderator tank, 2... Moderator circulation pump, 3... Heat exchanger, 4... Core, 5... Moderator, 6... Moderator riser pipe, 7... Cooling tower, 10...
... Control rod guide tube, 12 ... Natural circulation cooling device (heat pipe), 13 ... Cooler, 21 ... Pressure pipe,
28... Surge tank, 29... Moderator return pipe,
30...Air cooler, 32...Pressure pipe guide pipe, 3
5...Natural circulation cooling device.

Claims (1)

[Scope of Claims] 1. A pressure pipe that accommodates a reactor core and through which coolant circulates, a pressure pipe guide pipe through which this pressure pipe is inserted, and a moderator tank that contains a moderator that surrounds the pressure pipe. a control rod guide tube provided in the moderator tank and accommodating a control rod that controls the output of the nuclear reactor;
A pressure moderator comprising a moderator circulation pump connected to the moderator tank and circulating the moderator in the moderator tank, and a heat exchanger cooling the moderator circulated by the moderator circulation pump. In a tubular nuclear reactor, there is a surge tank connected to the top of the moderator tank and installed at a position higher than the reactor core, and a surge tank that is connected to the surge tank at the top and to the moderator tank at the bottom, built in the cooling tower, and installed at a position higher than the reactor core. and an air cooler installed at a position higher than the core and lower than the surge tank to cool the moderator with air, and the highest part of the piping connecting the upper part of the surge tank and the air cooler during normal operation. The pressure pipe type is characterized in that the moderator does not flow from the surge tank to the air cooler, and is arranged at a height where the moderator flows from the surge tank to the air cooler when the moderator boils. Reactor. 2. The distance between the inner wall of the pressure tube guide tube and the outer wall of the pressure tube inserted into the pressure tube guide tube must be smaller than the rupture strain due to thermal expansion due to overheating of the pressure tube, and the distance between the pressure tube and the pressure tube during normal operation is 2. The pressure tube nuclear reactor according to claim 1, wherein the distance between the tube guide tubes is larger than the minimum distance required for heat shielding. 3. A pressure pipe that accommodates the core and through which coolant circulates, a pressure pipe guide pipe through which this pressure pipe is inserted, a moderator tank that contains a moderator that surrounds the pressure pipe, and a moderator tank that contains a moderator that surrounds the pressure pipe. a control rod guide tube that is installed in the reactor and accommodates control rods that control the output of the reactor;
A pressure moderator comprising a moderator circulation pump that is connected to the moderator tank and circulates the moderator in the moderator tank, and a heat exchanger that cools the moderator circulated by the moderator circulation pump. A pressure tube nuclear reactor characterized in that a heat pipe is provided with an evaporator placed inside a moderator tank and a condensing end provided with a cooler outside the moderator tank. 4. The distance between the inner wall of the pressure tube guide tube and the outer wall of the pressure tube inserted into the pressure tube guide tube must be smaller than the rupture strain due to thermal expansion due to overheating of the pressure tube, and the distance between the pressure tube and the pressure tube during normal operation is 4. The pressure tube nuclear reactor according to claim 3, wherein the distance between the tube guide tubes is larger than the minimum distance required for heat shielding.