JPH08292284A - Pressure pipe type heavy water reactor facility - Google Patents

Abstract

PURPOSE: To provide a facility for ending an accident even if an imaginary severe accident with extremely small probability where no safety system operates and fuel melts in a pressure pipe type heavy water reactor. CONSTITUTION: Water is poured into a calandria tank 4 using a water-pouring pump 3 which is independent of a safety facility which a prior art pressure type heavy water furnace has and a water-pouring source 2 located outside a storage container, thus cooling a molten fuel remaining in a pressure pipe assembly 7 and a fuel discharged into the calandria tank 4 by pouring water and ending and cooling the molten fuel by the calandria tank 4 which is a reactor core boundary.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to equipment.

[0002]

2. Description of the Related Art In a nuclear reactor, when an accident occurs in which the coolant for nuclear fuel is lost, the emergency core cooling system cools the fuel in the core, and then the decay heat generated from the fuel by the residual heat removal system. End the accident by removing the. In the pressure tube type heavy water reactor, as shown in FIG. 6, the rapid injection system 32 that uses water in the pressure accumulator 31 as an emergency core cooling system, and the water in the condensate storage tank 33 to the steam drum 9 by the high pressure water injection pump 34. High pressure injection system for water injection 3
5, a low-pressure injection system 37 that injects water into the water drum 10 by the low-pressure water injection pump 36, a residual heat removal system 40 that cools decay heat by the circulation pump 38 and the heat exchanger 39, and the same purpose is achieved by water supply by the isolated water supply pump 41. A separate water supply system 42 is provided (the safety equipment is connected to all the drums, but only one system is shown in FIG. 6). In addition, the steam / high-temperature water discharged into the containment vessel 1 at the time of the accident is cooled by using the steam release pool 15 and the containment vessel spray system 43, and a steam release pool cooling pump 44 is provided to cool the water in the steam release pool 15. There is a cooler 45. The above safety equipment is installed in multiple layers, and in the event of an accident, these safety systems will operate and the fuel will not be damaged or melted. However, assuming a severe accident of a hypothetical reactor in which all of these safety systems do not operate and the core fuel is melted at a probability that is extremely low, due to the structure of the pressure pipe assembly shown in FIG.
Since the thickness of the pressure pipe 46 and the calandria pipe 47 is much smaller than the longitudinal dimension of the lower shield plug 48, when the nuclear fuel 49 is melted, the pressure pipe 46 and the calandria pipe 47 come into contact with the molten fuel, and Expected to be broken and released into Calandria tank 4. Although the calandria tank 4 is usually filled with heavy water, in such an accident, the heavy water in the tank is reduced by heating from the fuel and the pump stop of the heavy water circulation system, etc., and the molten fuel is sufficiently cooled by the heavy water. Otherwise, the calandria tank 4 may be eroded and its soundness may be threatened, and the molten fuel may flow out into the containment vessel.

As a conventional method for coping with a severe accident in which the fuel is melted due to the heating of the reactor core, water is poured into the melted fuel in the containment vessel as a conventional technique. These are for light water reactors that have pressure vessels.
There are 1-245191 and JP-A-2-222872. These are effective for the fuel discharged outside the pressure vessel in a reactor where the core boundary is equal to the pressure boundary such as a light water reactor, but the core boundary such as the pressure tube type heavy water reactor has a different form from the pressure boundary. It is not an optimized alternative cooling method for the furnace.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to prevent a safety accident in a pressure tube type heavy water reactor when a severe accident occurs in which fuel in a hypothetical reactor which is extremely low in probability is melted. Even, it is to provide a means for cooling the generated molten fuel in the calandria tank and terminating it inside the calandria tank, which is the core boundary.

[0005]

In order to achieve the above object, the pressure pipe type heavy water reactor equipment of the present invention is equipped with a water injection pump independent of the water injection pump of the safety equipment, whereby the water injection outside the containment vessel is achieved. The water source will allow water to be poured into the calandria tank.

In addition to this structure, the steam drum, the water drum, and the spray header of the containment vessel spray water can be poured from the above-mentioned water injection source, and the steam generated in the calandria tank is introduced into the water pool in the containment vessel to condense. The configuration has the function that can Furthermore, in addition to this configuration, the facility for pouring water into the calandria tank will be provided in conjunction with the decrease in the amount of water in the calandria tank.

A control rod guide tube may be used as a water injection path to the calandria tank.

Further, it may be so constructed that boric acid can be mixed into the water injection.

[0009]

According to the present invention, even when a severe accident of a hypothetical reactor in which the safety system does not operate at all in the pressure tube type heavy water reactor and the probability is extremely low, a water injection pump independent of the safety system is installed. By using this, water can be injected into the calandria tank from outside the containment vessel, so that the molten fuel in the calandria tank, which is the core boundary, can be cooled. In addition, by pouring water into the steam drum and water drum, the steam generated in the pressure pipe assembly can be condensed, and further the steam generated in the calandria tank can be condensed by being guided to the water pool in the containment vessel. , The steam generated by cooling the molten fuel can be condensed, and the steam generated from the water pool can also be condensed by pouring water into the containment vessel, so it is possible to prevent the pressure inside the containment vessel from rising. it can.

Further, by using the control rod guide tube as the water injection path to the calandria tank, it is possible to inject water to the calandria tank without attaching new piping to the existing pressure tube type heavy water reactor.

Further, by mixing boric acid in the water injection, it is possible to suppress the nuclear reaction of the molten fuel and suppress the heat output of the fuel.

[0012]

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

FIG. 1 shows an embodiment of the present invention. In the pressure pipe type heavy water reactor shown in the figure, a water injection source 2 outside the containment vessel 1 and a water injection pump 3 independent of the safety equipment of the prior art are connected to a calandria tank 4 via a valve 5 by a water injection pipe 6. . From the existing nuclear reactor equipment, the water injection source 2 can apply water from the pure water storage tank or the filtered water tank. Similarly, a fire extinguishing system pump can be applied as the water injection pump.

During normal operation and when the emergency core cooling system / remaining heat removal system operates even during an accident, the valve 5 is closed and it is not necessary to inject water from the water injection source 2. However, assuming a severe accident in which all safety systems do not operate, the nuclear fuel inside the pressure pipe assembly 7 melts and the fuel flows out to the calandria tank 4 filled with heavy water. At this time, the valve 5 is opened and water is poured into the calandria tank 4 by detecting a decrease in the water level of the steam drum due to a decrease in core cooling water. As a result, the fuel flowing out to the calandria tank 4 is cooled by directly pouring water into the calandria tank 4, and the molten fuel can end the accident without going out of the calandria tank 4.

FIG. 2 shows a second embodiment of the present invention. In this case, in addition to the first embodiment, the water injection from the water injection source 2 is supplied to the containment vessel spray header 8, the steam drum 9, and the water drum 10 through pipes 11 to 13. Further, the calandria tank 4 is connected to the vapor discharge pool 15 by a calandria tank vent pipe 14. A rupture disc 16 is provided in the middle of the calandria tank vent pipe 14 so that the heavy water in the calandria tank 4 does not mix moisture of light water from the steam discharge pool 15 at normal times. Further, the breaking valve opening pressure of the rupture disc 16 is set to a pressure slightly higher than the calandria tank internal pressure so as to open quickly due to the generation of steam in the calandria tank 4.

As a result, the steam generated inside the pressure pipe assembly 7 can be directly cooled and condensed. Further, when the water is cooled to the calandria tank, water is received from the fuel inside the calandria tank 4, so that steam is generated. As a result, the internal pressure of the calandria tank rises, the rupture disc 16 is destroyed, and the steam in the calandria tank 4 is discharged from the steam discharge pool 1.
It is led to 5 and condensed here. The pressure increase in the containment vessel 1 due to the evaporation from the vapor discharge pool 15 can be suppressed because the water is injected from the containment vessel spray header 8 to condense the vapor. As a result, the containment vessel 1 is not threatened by pressurization.

FIG. 3 shows a third embodiment of the present invention. In the pressure tube type heavy water reactor, the heavy water stored in the heavy water surge tank 17 absorbs the increase or decrease in the heavy water in the calandria tank 4 that occurs during normal operation. In the present invention, a water level gauge 18 is provided in the heavy water surge tank, and water is injected by opening the valve 5 and starting the water injection pump 3 in response to a low water level signal from the water level gauge. In the accident targeted by the present invention, the temperature of the molten fuel is much higher than the boiling point of the heavy water in the calandria tank 4, so that when the accident occurs, the heavy water evaporates and the water level in the heavy water surge tank 17 decreases. Therefore, if this is detected by the water level meter 18 and the water injection operation is performed by the control device 19, the accident can be ended without delay.

FIG. 4 shows a fourth embodiment of the present invention. Generally, in a pressure tube type heavy water reactor, there are several hundred pressure tube assemblies,
Since the calandria tank 4 is inside the shielding structure, it is difficult to newly install a water injection pipe to the calandria tank 4 in the existing furnace. However, this type of reactor has equipment for circulating the heavy water in the calandria tank 4. Since the heavy water inside the calandria tank 4 is heated by the fuel even during normal operation, it is taken out of the calandria tank 4 by the heavy water circulation pump 20, cooled by the heavy water cooler 21, and the control rod 22 is transferred to the calandria tank 4. It is returned to the calandria tank 4 through the control rod guide tube 23 that serves as a guide to be inserted. Therefore, if the pipe 6 of the present invention is connected to the heavy water circulation system pipe 24 and the heavy water circulation system is isolated from the present invention by the valve 25, the present invention can be easily and reduced in the number of man-hours in the existing pressure tube type heavy water reactor. It can be installed at a wage. If the valve 25 is closed during normal operation, the function of the heavy water circulation system is not impaired, and when the accident targeted by the present invention occurs, the valve 25 is opened to inject water into the calandria tank through the control rod guide pipe 23. It will be possible.

FIG. 5 shows a fifth embodiment of the present invention. This is to allow the boric acid to be mixed into the water injection mechanism of the present invention from the boric acid dissolving tank 26 of the boric acid supply system, which is an existing facility in the pressure tube type heavy water reactor, by using the boric acid injection pump 27. Generally, in a pressure tube type heavy water reactor, a change in excess reactivity due to core combustion is caused by a boric acid injection pump 2 from a boric acid dissolving tank 26 for boric acid which is a liquid poison (neutron absorbing material) as a heavy water moderator.
7 is mixed in the heavy water circulation system pipe 24 to compensate. Therefore, in an accident in which the present invention is directed to this mechanism, if boric acid is mixed into the water injected into the pressure pipe assembly 7 and the calandria tank 4, the nuclear reaction of the molten fuel is suppressed and the heat of the fuel is suppressed as compared with the case where only water is used. The output can be suppressed, and the accident can be ended more quickly. This can be achieved by connecting the boric acid injection system to the pipes 12 and 13 of the present invention by pipes 28 and 29, respectively, and controlling the presence or absence of the injection of boric acid into the pipes 12 and 13 of the present invention by the valve 30. Normally, the valve 30 is closed so that the coolant of the nuclear fuel is not mixed with boric acid. When an accident targeted by the present invention occurs, the valve 30 can be opened and boric acid can be mixed into the water injection.

[0020]

EFFECTS OF THE INVENTION According to the present invention, even in a severe accident in a nuclear reactor in which fuel melting is extremely unlikely to occur, the molten fuel can be cooled and the accident can be terminated, so that the safety of the pressure tube type heavy water reactor is improved. To do.

Further, since the vapor generated by the injection of the molten fuel can be condensed and the increase in the internal pressure of the containment vessel can be suppressed, the safety margin against the accident of the containment vessel can be improved.

Further, since the decrease in the amount of heavy water in the calandria tank due to the generation of molten fuel can be detected by the decrease in the water level in the heavy water surge tank, water can be quickly injected into the melting core, etc. It can be dealt with promptly without any manual operation, and the safety of the pressure tube type heavy water reactor will be improved.

Further, when the present invention is attached to an existing pressure tube type heavy water reactor, it is not necessary to work on the calandria tank, and it is possible to attach equipment capable of improving safety with a small labor and man-hour.

Further, it is possible to suppress the nuclear reaction of the molten fuel and suppress the heat output of the fuel, as compared with the case of using mere water.
The accident can be ended more quickly, and the safety margin against the accident can be improved.

[Brief description of drawings]

FIG. 1 is a system diagram of an embodiment showing a pressure tube type heavy water reactor of the present invention.

FIG. 2 is a system diagram of a second embodiment showing a pressure tube type heavy water reactor of the present invention.

FIG. 3 is a system diagram of a third embodiment showing a pressure tube type heavy water reactor of the present invention.

FIG. 4 is a system diagram of a fourth embodiment showing a pressure tube type heavy water reactor of the present invention.

FIG. 5 is a system diagram of a fifth embodiment showing a pressure tube type heavy water reactor of the present invention.

FIG. 6 is a system diagram showing safety equipment of a conventional pressure tube type heavy water reactor.

FIG. 7 is a sectional view of one pressure tube assembly of the pressure tube type heavy water reactor.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Containment container, 2 ... Water injection source, 3 ... Water injection pump, 4 ... Calandria tank, 5 ... Valve, 6 ... Water injection piping, 7 ... Pressure pipe assembly.

Claims (5)

[Claims] 1. A nuclear fuel and a coolant are contained in a pressure pipe, and a pressure pipe assembly and a control rod, each unit of which is a calandria pipe for accommodating the pressure pipe, are arranged in a calandria tank having a heavy water moderator. However, an accident occurred in a pressure tube type heavy water reactor having safety equipment for cooling the pressure tube assembly and the control rod by injecting water into the nuclear fuel in the pressure tube and the containment vessel at the time of an accident in the reactor. When the safety equipment does not operate at all, it has a function of injecting water into the calandria tank by using a water injection pump independent of the water injection pump of the safety equipment and a water injection source outside the containment vessel. Pressure tube type heavy water reactor. 2. The steam according to claim 1, wherein water can be injected into the pressure pipe and the containment vessel by using the water injection pump and a water injection source, and steam generated inside the calandria tank is
A pressure tube-type heavy water reactor having a function of allowing condensation when the inside of the calandria tank exceeds a certain pressure by connecting the calandria tank and a water pool in the storage container. 3. The pressure tube type heavy water reactor according to claim 1 or 2, which has a facility for pouring water in association with a decrease in the amount of water in the calandria tank. 4. A pressure tube type heavy water reactor according to claim 1, wherein a control rod guide tube is used as a water injection path to the calandria tank. 5. The pressure tube type heavy water reactor according to claim 1, 2, 3 or 4, wherein boric acid can be mixed in the injected water.