Vent valve system for nuclear reactor containment vessel

Abstract

To provide a vent valve system for a nuclear reactor containment vessel which can operate even when all the AC power source is lost, is not affected by the midway change of the pressure in the nuclear reactor containment vessel in ventilation and in which an operation test can be performed and which can be reused.SOLUTION: A vent valve system for a nuclear reactor containment vessel comprises: a valve 10; a valve opening operation control unit 20; and a valve opening holding unit 30. The valve 10 can perform the opening / closing operation when exhausting air from a nuclear reactor containment vessel 2 to a filter vent device 3. The valve opening operation control unit 20 performs the valve opening operation on the valve 10 when the pressure in the nuclear reactor containment vessel 2 rises to the vicinity of the limit pressure. The valve opening holding unit 30 holds the valve opening state of the valve 10 until the pressure in the nuclear reactor containment vessel 2 drops to the vicinity of the outside pressure after the valve 10 is turned into the valve opening state by the valve opening operation control unit 20 and performs the valve closing operation of the valve 10 when the pressure in the nuclear reactor containment vessel 2 drops to the vicinity of the outside pressure.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a vent valve system for a nuclear reactor containment vessel, and more particularly to a vent valve system for a nuclear reactor containment vessel that is both testable and reusable. [Background technology]

[0002] Filter vent devices have been known for preventing overpressure failure of the reactor containment vessel and the release of radioactive materials outside the containment vessel. When pressure inside the containment vessel increases, the filter vent device opens a vent valve leading from the pressure suppression chamber (wetwell) to the outside to reduce pressure. To prevent the contaminated air inside the containment vessel from being released directly into the atmosphere, the filter vent device reduces the amount of radioactive material by passing the air through water or a metal filter. The water through which the contaminated air passes is generally called scrubbing water (decontaminated water), and contains added compounds such as sodium hydroxide and sodium thiosulfate. Silver zeolite is also used as the metal filter.

[0003] The reactor containment vessel and the filter vent device are isolated by a vent valve. Normally, the vent valve is opened and closed by a motor controlled by an electric signal or by manually rotating a shaft. However, in the event of a serious accident, if all AC power is lost or workers are unable to approach, the vent valve cannot be opened or closed. If the vent valve cannot be opened and venting becomes impossible, the pressure inside the reactor containment vessel will increase, and in the worst case scenario, it may become impossible to inject cooling water or the reactor containment vessel may be damaged.

[0004] Containment vessel venting devices that are configured to enable passive venting even in the event of such a serious accident are also known (for example, Patent Document 1). The device in Patent Document 1 has a rupture disk installed in the passage between the reactor containment vessel and the filter vent device. The rupture disk is ruptured when the pressure exceeds a certain level, allowing venting without the use of a vent valve. In other words, when the pressure inside the reactor containment vessel rises to a predetermined pressure, the rupture disk is passively ruptured (passive activation), depressurizing the reactor containment vessel. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Special Publication No. 2016-502113 Summary of the Invention [Problem to be solved by the invention]

[0006] However, while the filter vent device using a rupture plate as in Patent Document 1 can passively start up even if there is a total loss of AC power, once a rupture plate is ruptured it cannot be reused. Furthermore, even if an operation test is performed to determine the pressure required to rupture the rupture plate, a rupture plate once ruptured cannot be reused, so it is not possible to perform an operation test using the same rupture plate. Furthermore, there is also the problem that the rupture pressure of the rupture plate cannot be accurately set.

[0007] Furthermore, it is possible to use existing safety valves to automatically release pressure in the event of an abnormal rise in pressure inside the containment vessel. However, even if existing safety valves are used to vent an abnormal rise in pressure inside the containment vessel, the pressure inside the containment vessel may not decrease monotonically but may rise again due to the injection of water to cool the fuel rods. In such cases, if the safety valves are frequently opened and closed in response to changes in pressure inside the containment vessel, water vapor may condense on the metal filter of the filter vent device. This reduces pressure by the amount of water vapor, causing a relative increase in the hydrogen concentration and increasing the risk of a hydrogen explosion.

[0008] Therefore, there was a need to develop a vent valve system that would be operable even in the event of a total loss of AC power, would not be affected by changes in pressure inside the reactor containment vessel during venting, and would be capable of being tested and reused.

[0009] In view of the above circumstances, the present invention provides a vent valve system for a containment vessel that can operate even if all AC power sources are lost, is not affected by changes in pressure inside the containment vessel during venting, and is capable of being tested for operation and reused. [Means for solving the problem]

[0010] In order to achieve the above-mentioned object of the present invention, the vent valve system for a reactor containment vessel according to the present invention comprises a valve that can be opened and closed when venting air from the reactor containment vessel to a filtered vent device, a valve opening control unit that opens the valve when the pressure inside the reactor containment vessel rises to near the critical pressure, and a valve open holding unit that keeps the valve open after the valve is opened by the valve opening control unit until the pressure inside the reactor containment vessel drops to near the outside air pressure, and that closes the valve when the pressure inside the reactor containment vessel drops to near the outside air pressure.

[0011] Here, the valve may be any safety valve comprising a valve seat provided at an opening from the reactor containment vessel, a valve element capable of opening and closing the valve seat, a valve stem to which the valve element is connected, and a valve spring that biases the valve stem so that the valve element is pressed toward the valve seat so that the valve seat can be opened and closed by the valve element in accordance with the force relationship with the pressure inside the reactor containment vessel.

[0012] The valve opening control section may be a valve spring of the safety valve, the biasing force of which is adjusted so that the safety valve opens when the pressure inside the reactor containment vessel rises to near the critical pressure.

[0013] The valve opening operation control section may also be comprised of a safety valve adapter equipped with a pressure control rod that operates in response to the pressure inside the reactor containment vessel, and a toggle mechanism that is biased by the pressure control rod to press the valve rod toward the valve seat until the pressure inside the reactor containment vessel rises close to the critical pressure, and that releases the pressure on the valve rod when the pressure inside the reactor containment vessel rises close to the critical pressure.

[0014] The valve open holding section may also be comprised of a forced valve-opening cylinder capable of applying a load to the valve stem that counteracts the biasing force of the valve spring so as to maintain the open state of the safety valve, a full-opening sensor that detects when the safety valve is fully open, an air-operated valve that is actuated by detection by the full-opening sensor, and an air accumulator that supplies control air to the forced valve-opening cylinder so as to maintain the open state of the safety valve by actuating the air-operated valve.

[0015] The open valve holding portion may also be made of a latch structure having a locking rod and a locking hole provided in the valve rod so that the locking rod is locked when the safety valve is fully open.

[0016] The locking rods may have sufficient shear strength to be sheared by the biasing force of the valve springs of the safety valves when the pressure inside the containment vessel drops to a level close to the outside pressure.

[0017] The latch structure may also have an air cylinder consisting of a cylinder, a piston configured to be movable within the cylinder in accordance with the pressure within the reactor containment vessel, and a piston rod fixed to the piston and serving as a locking rod, and the air cylinder may be configured to apply a biasing force to the locking rod in the direction of the valve rod when the pressure within the reactor containment vessel increases, and to apply a biasing force in the direction in which the locking rod is pulled out of the locking hole when the pressure within the reactor containment vessel decreases until it becomes close to the outside air pressure.

[0018] The valve may also be formed by combining two safety valves that use valve springs with different biasing forces, and the valve opening control unit of each safety valve may open one safety valve before the other safety valve opens, and the valve opening holding unit of each safety valve may close one safety valve after the other safety valve closes.

[0019] In addition, the valve opening operation control unit and the valve opening holding unit may include a pressure transmitter that detects the pressure inside the reactor containment vessel and converts it into an electrical signal, and a controller that controls the valve based on the electrical signal from the pressure transmitter.

[0020] Further, the valve may be an air-operable valve, and the valve opening control section may be a safety valve including a valve seat provided at an opening from the containment vessel, a valve element capable of opening and closing the valve seat, a valve stem to which the valve element is connected, and a valve spring for urging the valve stem so that the valve element is pressed toward the valve seat so that the valve seat can be opened and closed by the valve element in accordance with the force relationship with the pressure inside the containment vessel, and the valve open holding section may be a forced valve-opening cylinder for urging the valve stem with a load that counteracts the urging force of the valve spring so as to hold the safety valve in an open state, a full-open sensor for detecting a fully open state of the safety valve, an air-operated valve that is actuated by detection by the full-open sensor, and an air accumulator for supplying control air to the forced valve-opening cylinder so as to hold the safety valve in an open state by operation of the air-operated valve, and the valve may be one in which control air is supplied from the air accumulator to hold the open state when the full-open sensor detects.

[0021] The valve may be an air-operable valve, the valve opening control section may comprise an on switch that operates to open the valve, and an air cylinder that comprises a cylinder, a piston configured to be movable within the cylinder in accordance with the pressure inside the reactor containment vessel, and a piston rod fixed to the piston, the air cylinder applying a biasing force to the piston rod to press the on switch when the pressure inside the reactor containment vessel rises to near the limit pressure, and the valve open holding section may have an off switch that operates to close the valve, and the air cylinder applying a biasing force to the piston rod to press the off switch when the pressure inside the reactor containment vessel drops to near the outside pressure. [Effects of the Invention]

[0022] The reactor containment vessel vent valve system of the present invention has the advantages of being operable even in the event of a total loss of AC power, being unaffected by changes in pressure inside the reactor containment vessel during venting, and being capable of undergoing operational testing and being reusable. [Brief explanation of the drawings]

[0023] [Figure 1] FIG. 1 is a schematic block diagram for explaining an outline of a vent valve system for a containment vessel according to the present invention. [Figure 2] FIG. 2 is a schematic cross-sectional side view for explaining the configuration of the valve of the vent valve system for a containment vessel of the present invention. [Figure 3] FIG. 3 is a schematic diagram for explaining an example in which a safety valve adapter is provided to the safety valve of the vent valve system for a containment vessel of the present invention. [Figure 4] FIG. 4 is a schematic diagram for explaining an example in which the valve open holding portion of the vent valve system for a containment vessel of the present invention has a latch structure. [Figure 5] FIG. 5 is a schematic diagram for explaining an example in which the valve open holding portion of the vent valve system for a containment vessel of the present invention has another latch structure. [Figure 6]FIG. 6 is a schematic diagram for explaining another example of the valve of the vent valve system for a containment vessel of the present invention. [Figure 7] FIG. 7 is a schematic graph for explaining the change over time in pressure inside the containment vessel under the control of the containment vessel vent valve system of the present invention shown in FIG. [Figure 8] FIG. 8 is a schematic diagram for explaining an example in which an air-operable valve is used as the valve of the vent valve system for a containment vessel of the present invention. [Figure 9] FIG. 9 is a schematic diagram for explaining another example in which an air-operable valve is used as the valve of the vent valve system for a containment vessel of the present invention. [Figure 10] FIG. 10 is a schematic block diagram for explaining an example of electrically controlling the vent valve system for a containment vessel of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0024] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a schematic block diagram illustrating an outline of a containment vessel vent valve system according to the present invention. As shown in the figure, the containment vessel vent valve system 1 according to the present invention is used between a containment vessel 2 and a filtered vent device 3. The containment vessel 2 may be either a boiling water reactor or a pressurized water reactor, as long as venting is required. The containment vessel 2 is divided into a dry well and a wet well, which house the reactor pressure vessel. The containment vessel vent valve system 1 according to the present invention may be connected to a piping extending from a through-hole in the wet well, for example. However, the present invention is not limited thereto, and the piping may be extended from a through-hole in the dry well as well as the wet well. Any conventional or future containment vessel 2 may be used.

[0025] The filter vent device 3 reduces the pressure inside the reactor containment vessel 2 when the pressure inside the reactor containment vessel 2 increases. At that time, the filter vent device 3 reduces radioactive materials by passing the contaminated air inside the reactor containment vessel 2 through scrubbing water, a metal filter, etc., so that the contaminated air is not released directly into the atmosphere. Any conventional or future developed filter vent device can be used for the filter vent device 3.

[0026] The reactor containment vessel vent valve system 1 of the present invention is connected between the reactor containment vessel 2 and the filtered vent device 3. The reactor containment vessel vent valve system 1 is mainly composed of a valve 10, a valve opening control unit 20, and a valve opening holding unit 30. The valve 10 is operable to open and close when venting from the reactor containment vessel 2 to the filtered vent device 3. In other words, it opens to reduce the pressure in the reactor containment vessel 2 when it becomes too high. In the prior art, this valve was configured as a break plate, but in the present invention, as will be described in detail later, a valve that can be opened and closed, i.e., that is reusable, is used.

[0027] The valve opening control unit 20 opens the valve 10 when the pressure inside the containment vessel 2 rises near the critical pressure. That is, the valve 10 is passively activated to open in response to the pressure inside the containment vessel 2. The valve opening control unit 20 may be a function of the valve 10 itself, or it may control the valve 10 so that it opens when a preset pressure is reached. Here, if the exhaust gas pressure (back pressure) of the scrubbing water from the filter vent device 3 is low, sufficient decontamination may not be achieved with the scrubbing water. Therefore, the valve opening control unit 20 may be capable of controlling the valve opening so that the back pressure, which is the pressure on the output side, is approximately 40% of the blow-off pressure, which is the pressure on the input side when the valve 10 pops. To avoid the influence of back pressure, a safety valve employing a wing-disk structure, such as that disclosed in Japanese Patent No. 1459926 by Okano Valve Manufacturing Co., Ltd., one of the applicants of the present application, may be used.

[0028] After the valve 10 is opened by the valve opening control unit 20, the valve open holding unit 30 maintains the valve 10 in an open state until the pressure inside the containment vessel 2 drops to near the outside pressure. Furthermore, the valve open holding unit 30 closes the valve 10 when the pressure inside the containment vessel 2 drops to near the outside pressure. That is, once the valve 10 is opened, the valve open holding unit 30 maintains the fully open state and closes the valve 10 after the pressure inside the containment vessel 2 drops to near the outside pressure. Note that lowering the pressure to near the outside pressure does not necessarily mean that the pressure inside the containment vessel 2 needs to be reduced to completely zero. It is sufficient that the pressure has dropped sufficiently to the point where venting is no longer necessary.

[0029] As explained above in the problem to be solved by the invention, if the vent valve is frequently and repeatedly opened and closed in response to changes in pressure inside the containment vessel, water vapor will condense frequently on the metal filter of the filter vent device, causing a relative increase in hydrogen concentration and increasing the risk of a hydrogen explosion. Therefore, in this invention, the valve 10 is kept open until the pressure inside the containment vessel 2 drops to near the outside pressure, thereby preventing the influence of such intermediate changes in pressure inside the containment vessel. Furthermore, by closing the valve when the pressure drops to near the outside pressure, it is possible to prevent backflow into the containment vessel.

[0030] The details of the valves in the reactor containment vessel vent valve system of the present invention will be specifically described below with reference to Figure 2. Figure 2 is a schematic side cross-sectional view illustrating the configuration of the valves in the reactor containment vessel vent valve system of the present invention. In the figure, parts with the same reference numerals as in Figure 1 represent the same objects. In the illustrated example, valve 10 comprises a safety valve 11. A pipe may be drawn out from a through-hole in, for example, the wet well of the reactor containment vessel 2, and the input side of the safety valve 11 may be connected to the opening of the pipe. The safety valve 11 is preferably a sealed type that does not blow contaminated air into the surrounding area when the valve is activated. In the illustrated example, a forced-open valve cylinder 31 is used as the open valve holding unit 30, which will be described later.

[0031] As shown in FIG. 2 , the safety valve 11 is mainly composed of, for example, a valve seat 12, a valve disc 13, a valve stem 14, and a valve spring 15. The valve seat 12 is provided at an opening from the reactor containment vessel 2. The valve seat 12 is, for example, ring-shaped and is opened and closed by a valve disc 13 (described later). The valve disc 13 is capable of opening and closing the valve seat 12. The valve disc 13 is, for example, disk-shaped and is configured to be lifted and blow out when a pressure equal to or greater than a predetermined pressure is applied to the input side of the safety valve 11. The valve stem 14 is connected to the valve disc 13. That is, the valve stem 14 is connected to the central axis of the disk-shaped valve disc 13. The valve spring 15 biases the valve stem 14 so that the valve disc 13 is pressed toward the valve seat 12 so that the valve disc 13 can open and close the valve seat 12 in accordance with the force relationship with the pressure inside the reactor containment vessel 2. That is, the valve opening pressure of the safety valve 11 is determined by the biasing force of the valve spring 15 .

[0032] In the reactor containment vessel vent valve system of the present invention, the valve opening control unit 20 is realized by the valve spring 15 of the safety valve 11 used as this valve 10. That is, the valve opening control unit 20 is the valve spring 15 of the safety valve 11, the biasing force of which is adjusted so that the safety valve 11 opens when the pressure inside the reactor containment vessel 2 rises close to the critical pressure. The biasing force of the valve spring 15 may be adjusted so that the safety valve 11 fully opens when the pressure inside the reactor containment vessel 2 rises close to the critical pressure. Because the opening operation of the safety valve 11 is controlled in accordance with the pressure inside the reactor containment vessel 2, it can operate even in the event of a total loss of AC power.

[0033] In this example, a forced valve-opening cylinder 31 is used as the open valve holding unit 30. That is, the safety valve 11 shown in the figure has a relief valve function due to the forced valve-opening cylinder 31. The open valve holding unit 30 is made up of the forced valve-opening cylinder 31, a full-open sensor 32, an air-operated valve 33, and an air accumulator 34.

[0034] The forced valve-opening cylinder 31 is capable of applying a load to the valve stem 14 that counteracts the biasing force of the valve spring 15 so as to maintain the open state of the safety valve 11. In other words, the safety valve 11 is provided with a relief valve function by using the forced valve-opening cylinder 31. In the illustrated example, the forced valve-opening cylinder 31 has a piston, a piston rod, and a spring, and a link is connected to the piston rod. The piston rod is connected to the application point of the link, the valve stem 14 is connected to the force point of the link, and a fulcrum outside the force point of the link is connected to the safety valve 11. The piston of the forced valve-opening cylinder 31 can be moved by control air, which makes it possible to apply a load to the valve stem 14 that counteracts the biasing force of the valve spring 15.

[0035] The full-open sensor 32 detects when the safety valve 11 is fully open. For example, the full-open sensor 32 may be provided at a position where the upper end of the valve stem 14 reaches when the safety valve 11 is fully open. The full-open sensor 32 may be a mechanical valve such as an air switching valve with a push button. In other words, it may be anything that turns on the mechanical valve when the safety valve 11 is fully open and can supply air to the air-operated valve 33 described below. The supplied air may be supplied from, for example, an air accumulator 34 described below.

[0036] The air operated valve 33 is actuated by the detection of the full open sensor 32. That is, it may be any valve that is controlled by the input of air from the full open sensor 32. Specifically, the air operated valve 33 may be, for example, a three-port air operated valve. The three-port air operated valve has the full open sensor 32 connected to its pilot section. When the full open sensor 32 detects the full open position and air is supplied from the full open sensor 32 to the pilot section, the three-port air operated valve opens.

[0037] When the air-operated valve 33 is actuated, the air accumulator 34 supplies control air to the forced valve-opening cylinder 31 to maintain the open state of the safety valve 11. That is, when the full-open sensor 32 detects the full open state and supplies air to the pilot section, and the three-port air-operated valve operates to open, air is supplied from the air accumulator 34 to the forced valve-opening cylinder 31. This causes the piston of the forced valve-opening cylinder 31 to move upward, and a load is applied to the valve stem 14 that counteracts the biasing force of the valve spring 15 to maintain the open state of the safety valve 11.

[0038] The forced-open valve cylinder 31 is entirely controlled by the pressure and air inside the containment vessel and operates without the need for an external power source, so it can operate even in the event of a total loss of AC power. Furthermore, because it is not subject to destruction like a rupture plate, it can be tested for operation and can be reused.

[0039] The full-open sensor 32 may be configured to stay on until the pressure inside the containment vessel 2 drops to near the outside air pressure. That is, the mechanical valve may be configured to stay on in accordance with the stroke of the valve stem 14 from the maximum height at which it is fully open to the minimum height. For example, the on range can be adjusted by configuring the push button of the mechanical valve from an elastic body.

[0040] Furthermore, if the full-open sensor 32 is a type that turns on only when the safety valve 11 is fully open, the pressure inside the containment vessel 2 will decrease after the safety valve 11 is fully open, and the full-open sensor 32 will turn off before the pressure inside the containment vessel 2 drops to near the outside air pressure. If this happens, the supply of air to the pilot part of the air operated valve 33 will stop, causing the air operated valve 33 to close. Therefore, if the full-open sensor 32 turns off in this way, a lock-up valve 35 or the like may be provided between the full-open sensor 32 and the pilot part of the air operated valve 33 to maintain the supply of air to the pilot part of the air operated valve 33.

[0041] Here, if the pressure at the start of blowing is low, the blowing amount also decreases, and there is a risk that sufficient decontamination will not be possible with the scrubbing water in the filter vent device 3. Therefore, as will be explained below, the valve stem 14 of the safety valve 11 may be pressed toward the valve seat until the pressure inside the reactor containment vessel 2 rises close to the critical pressure, so that the safety valve 11 does not open until the pressure approaches the critical pressure.

[0042] FIG. 3 is a schematic diagram illustrating an example in which a safety valve adapter is provided to a safety valve of a vent valve system for a containment vessel according to the present invention. FIG. 3(a) shows the state at low pressure, FIG. 3(b) shows the state immediately before blowout, and FIG. 3(c) shows the state at the time of blowout. In the figure, parts with the same reference numerals as in FIG. 2 represent the same objects. Also, for the safety valve 11, only the valve stem 14 is shown, with other parts omitted. In this example, a safety valve adapter 21 is used as the valve opening control unit 20. As shown in the figure, the safety valve adapter 21 is provided to the safety valve 11. The safety valve adapter 21 is composed of a pressure control rod 22 and a toggle mechanism 23.

[0043] The pressure control rod 22 operates in response to the pressure inside the reactor containment vessel 2. Specifically, when the pressure inside the reactor containment vessel 2 increases, the pressure control rod 22 moves in a direction to be pushed toward a toggle mechanism 23, which will be described later. Specifically, the pressure control rod 22 may be, for example, an air cylinder made up of a cylinder connected to the reactor containment vessel 2, a piston configured to be movable within the cylinder in response to the pressure inside the reactor containment vessel 2, and a piston rod fixed to the piston and serving as the pressure control rod 22. The cylinder is connected to the reactor containment vessel, and when the pressure inside the reactor containment vessel 2 increases, the piston is pushed, and the piston rod is pushed out.

[0044] The toggle mechanism 23 is configured to be biased by the pressure control rod 22 to press the valve stem 14 toward the valve seat 12 until the pressure inside the containment vessel 2 rises near the critical pressure, and to release the valve stem 14 when the pressure inside the containment vessel 2 rises near the critical pressure. The toggle mechanism 23 in the illustrated example is composed of two links connected by a joint. An additional force spring 24 is provided at the top of the link to provide additional force when pressing the valve stem 14 toward the valve seat 12. As shown in FIG. 3(a), when the pressure inside the containment vessel 2 is low, the toggle mechanism 23 is bent to the left in the drawing. Because of the low pressure, the valve stem 14 does not lift, and neither the pressure control rod 22 nor the toggle mechanism 23 is in operation. As shown in FIG. 3(b), when the pressure inside the containment vessel 2 rises, the pressure control rod 22 is pushed out and presses the toggle mechanism 23. As a result, the two links of the toggle mechanism 23 are tensioned between the load spring 24 and the valve stem 14, pressing the valve stem 14 toward the valve seat 12 and preventing it from lifting. At this time, the pressing force is at its maximum. Therefore, the safety valve 11 will not blow out before the pressure inside the containment vessel 2 rises to near the critical pressure. Then, as shown in FIG. 3(c), when the pressure inside the containment vessel 2 reaches near the critical pressure, the pressure control rod 22 is further pushed out and presses the toggle mechanism 23, causing the toggle mechanism 23 to bend to the right in the drawing. In this state, the toggle mechanism 23 is no longer pressing down on the valve stem 14, so the valve stem 14 rises and the safety valve 11 is fully open.

[0045] Even when the biasing force of the valve spring 15 is adjusted so that the safety valve 11 opens only when the pressure inside the containment vessel 2 rises close to the critical pressure, there is a risk that the valve may open before the pressure rises close to the critical pressure. In this case, the blowout amount may be insufficient, and sufficient decontamination may not be possible with the scrubbing water in the filter vent device 3. However, by using the above-described safety valve adapter 21 as the valve opening control unit 20, it is possible to configure the valve not to open until the pressure inside the containment vessel 2 rises close to the critical pressure, thereby ensuring reliable decontamination.

[0046] The safety valve adapter 21 is connected to the reactor containment vessel 2 and operates in response to the pressure inside the reactor containment vessel 2, so it can operate even in the event of a total loss of AC power. Furthermore, because it is not destroyed like a rupture plate, it can be tested for operation and can be reused.

[0047] Next, an example in which the valve open holding portion of the vent valve system for a containment vessel of the present invention is composed of a latch structure will be described. Figure 4 is a schematic diagram for explaining an example in which the valve open holding portion of the vent valve system for a containment vessel of the present invention is composed of a latch structure. Figure 4(a) shows the state at low pressure, and Figure 4(b) shows the state at full open. In the figure, parts with the same reference numerals as in Figure 2 represent the same objects. Also, for the safety valve 11, only the valve stem 14 is shown, and other parts are omitted from the illustration. In this example, a latch structure 40 is used as the valve open holding portion 30. As shown in the figure, the latch structure 40 consists of a locking rod 41 and a locking hole 42.

[0048] The locking rod 41 is engaged with a locking hole 42, which will be described later, and is biased toward the valve stem 14 by a spring or the like. The locking hole 42 is a hole provided in the valve stem 14 so that the locking rod 41 is engaged when the safety valve 11 is fully open. As shown in FIG. 4( a), in a low-pressure state, the locking rod 41 does not affect the valve stem 14, and the valve stem 14 can move up and down. On the other hand, as shown in FIG. 4( b), when the safety valve 11 is fully open and the valve stem 14 rises, the locking rod 41 is engaged with the locking hole 42. In other words, the locking hole 42 should be provided at a position where the locking rod 41 is engaged with the locking hole 42 when the valve stem 14 is raised to the top when the safety valve 11 is fully open. This makes it possible to maintain the open state of the safety valve 11.

[0049] Furthermore, if the locking rod 41 is configured to have a predetermined shear strength, it is also possible to close the safety valve 11 when the pressure inside the reactor containment vessel 2 drops to near the outside air pressure. That is, the locking rod 41 may be configured to have such shear strength that it is sheared by the biasing force of the valve spring 15 of the safety valve 11 when the pressure inside the reactor containment vessel 2 drops to near the outside air pressure. With this configuration, after the safety valve 11 is opened, the locking rod 14 is locked in the locking hole 42 to maintain the open state of the safety valve 11 until the pressure inside the reactor containment vessel 2 drops to near the outside air pressure, and when the pressure inside the reactor containment vessel 2 drops to near the outside air pressure, the locking rod 41 is sheared and the safety valve 11 closes.

[0050] Next, an example in which the valve-opening retainer of the vent valve system for a containment vessel of the present invention has another latch structure will be described. FIG. 5 is a schematic diagram illustrating an example in which the valve-opening retainer of the vent valve system for a containment vessel of the present invention has another latch structure. FIG. 5(a) shows the low-pressure state, and FIG. 5(b) shows the fully open state. In the figures, parts with the same reference numerals as in FIG. 4 represent the same components. Regarding the safety valve 11, only the valve stem 14 is shown, and other components are omitted. In this example, an air cylinder 43 is used as another latch structure for the valve-opening retainer 30. As shown in the figure, the air cylinder 43 has a cylinder 44, a piston 45, and a piston rod 46. The cylinder 44 is connected to the containment vessel 2 and is configured to press the piston 45 (described below) in response to the pressure inside the containment vessel 2. The piston 45 is configured to be movable within the cylinder 44 in response to the pressure inside the containment vessel 2. The piston rod 46 is fixed to the piston 45 and serves as a locking rod. In a low-pressure state, the piston rod 46, which is an engagement rod, does not affect the valve stem 14, allowing the valve stem 14 to move. When the pressure inside the containment vessel 2 rises, the air cylinder 43 applies a biasing force to the piston rod 46 in the direction of the valve stem 14. Thereafter, as shown in Figure 5(b), when the safety valve 11 is fully opened and the valve stem 14 rises, the piston rod 46, to which the biasing force has been applied, is engaged in the engagement hole 42. This makes it possible to maintain the safety valve 11 in an open state.

[0051] Furthermore, when the pressure inside the reactor containment vessel 2 drops to near the outside air pressure, an urging force is applied to the piston rod 46 in the direction of pulling it out of the locking hole 42. In the illustrated example, a spring 47 is provided inside the cylinder 44 to apply an urging force in the direction of pulling the piston rod 46 out of the locking hole 42. Because the pressure inside the reactor containment vessel 2 pressing the piston 45 has dropped to near the outside air pressure, the urging force of the spring 47 pulls the piston rod 46 out of the locking hole 42.

[0052] With this configuration, after the safety valve 11 is opened, the piston rod 46 is engaged in the engagement hole 42, maintaining the open state of the safety valve 11, until the pressure inside the containment vessel 2 drops to near the outside air pressure. When the pressure inside the containment vessel 2 drops to near the outside air pressure, the piston rod 46 is withdrawn, and the safety valve 11 closes. That is, the state shown in FIG. 5(b) returns to the state shown in FIG. 5(a). Therefore, the containment vessel vent valve system of the present invention can be tested and reused. Furthermore, the air cylinder 43 is controlled by the pressure and air inside the containment vessel, and operates without requiring an external power source, so it can operate even in the event of a total loss of AC power.

[0053] Next, another example of a vent valve system for a containment vessel of the present invention will be described. FIG. 6 is a schematic diagram illustrating another example of a valve in a vent valve system for a containment vessel of the present invention. In the figure, parts with the same reference numerals as in FIG. 2 represent the same components. As shown in the figure, this example uses two safety valves 11a and 11b of different sizes. That is, the valve 10 is formed by combining two safety valves 11a and 11b that use valve springs 15a and 15b with different biasing forces. As shown in the figure, the two safety valves 11a and 11b are connected in parallel. The two safety valves 11a and 11b each use forced-open cylinders 31a and 31b as the open valve holding unit 30. That is, the safety valves 11a and 11b have the same structure as that described with reference to FIG. 2. However, the present invention is not limited to this, and a latch structure 40 such as the example shown above may also be used.

[0054] Using these two safety valves 11a, 11b, the opening and closing operations of each safety valve can be performed as follows. First, the valve springs 15a, 15b used as valve opening control units are configured to open the safety valve 11b before the safety valve 11a opens. Then, the forced valve opening cylinders 31a, 31b used as valve open holding units are configured to close the safety valve 11b after the safety valve 11a closes. In other words, the blowout pressure and retraction pressure of the safety valve 11a are configured to be higher than the blowout pressure and retraction pressure of the safety valve 11b. This makes it possible to extend the open valve period of the safety valve 11b compared to the safety valve 11a.

[0055] FIG. 7 is a schematic graph illustrating the time-dependent change in pressure inside the containment vessel as controlled by the containment vessel vent valve system of the present invention shown in FIG. 6. As shown in the figure, as the pressure inside the containment vessel increases, safety valve 11b opens first. This is adjusted so that the valve opens before the pressure inside the containment vessel rises near the critical pressure. When the pressure inside the containment vessel rises near the critical pressure, safety valve 11a opens. This causes the pressure inside the containment vessel to decrease. When the pressure drops to a predetermined level, safety valve 11a closes. Even after safety valve 11a closes, safety valve 11b does not close, so the pressure continues to decrease. The forced-open cylinder 31, functioning as the open-valve holding unit 30, keeps the valve open until the pressure inside the containment vessel drops to near the outside air pressure, at which point the valve closes.

[0056] As mentioned above, all safety valves are controlled by the pressure and air inside the reactor containment vessel and do not require an external power source to operate, so they can still operate even if all AC power is lost.

[0057] Next, an example in which an air-operable valve is used as a valve in the containment vessel vent valve system of the present invention will be described. FIG. 8 is a schematic diagram illustrating an example in which an air-operable valve is used as a valve in the containment vessel vent valve system of the present invention. In the figure, parts with the same reference numerals as in FIG. 2 represent the same components. In this example, an air-operable valve is used as the valve. Specifically, a butterfly valve 50 is used. The containment vessel vent valve system of the present invention is capable of opening and closing existing butterfly valves. The butterfly valve 50 has an air-operated butterfly valve 51. Furthermore, a safety valve 11 is used as the valve opening control unit 20. And, a forced-open valve cylinder 31 is used for the safety valve 11 as the valve opening holding unit 30. That is, the safety valve 11 and the forced-open valve cylinder 31 have the same structure as those described with reference to FIG. 2. Note that the valve is not limited to the butterfly valve 50, and any air-operable valve, such as a ball valve, can be used.

[0058] When the pressure inside the reactor containment vessel 2 rises to near the critical pressure, the safety valve 11 is fully opened, and the air-operated valve 33 is actuated by detection by the full-open sensor 32, and control air from the air accumulator 34 is supplied to the forced-open valve cylinder 31, maintaining the open state of the safety valve 11. Then, the butterfly valve air-operated valve 51 is also actuated by detection by the full-open sensor 32, and control air from the air accumulator 34 is also supplied to the butterfly valve 50, maintaining the open state of the butterfly valve 50.

[0059] When the pressure inside the reactor containment vessel 2 drops to near the outside pressure, the safety valve 11 closes, and the butterfly valve air operated valve 51 closes, closing the butterfly valve 50.

[0060] The reactor containment vessel vent valve system of the present invention configured as described above can be applied to existing butterfly valves, ball valves, etc. Both use the pressure and air inside the reactor containment vessel for control, and can operate even in the event of a total loss of AC power.

[0061] Furthermore, another example in which an air-operable valve is used as the valve of the containment vessel vent valve system of the present invention will be described. FIG. 9 is a schematic diagram illustrating another example in which an air-operable valve is used as the valve of the containment vessel vent valve system of the present invention. FIG. 9(a) shows the fully open state, and FIG. 9(b) shows the low-pressure state. In the figure, parts with the same reference numerals as in FIG. 8 represent the same components. Note that only the valve opening control unit 20 and the valve open holding unit 30 are shown, and other components are omitted. In this example, the valve opening control unit 20 uses an on switch 60 and an air cylinder 61. Furthermore, the valve open holding unit 30 uses an off switch 65 and an air cylinder 61. As described above, the on switch 60 and the off switch 65 may be configured to operate using an air-operated valve, an air accumulator, or the like. While the following description specifically focuses on the use of a butterfly valve as the valve, the present invention is not limited to this. Any air-operable valve, such as a ball valve, may also be used.

[0062] The on switch 60 opens the butterfly valve 50. For example, a mechanical valve may be used as the on switch 60. The mechanical valve may be an air selector valve with a push button, or the like. When the on switch 60 is turned on, the supply of air to the pilot part of the butterfly valve air operated valve 51 of the butterfly valve 50 is maintained so that the butterfly valve 50 opens.

[0063] The air cylinder 61 includes a cylinder 62, a piston 63, and a piston rod 64. The cylinder 62 is connected to the containment vessel 2 and is configured so that the piston 63, which will be described later, is pressed in response to the pressure inside the containment vessel 2. The piston 63 is configured to be movable within the cylinder 62 in response to the pressure inside the containment vessel 2. The piston rod 64 is fixed to the piston 63. In the illustrated example, the piston rod 64 penetrates the cylinder 62 and is configured to protrude from the left and right sides of the cylinder 62 in the drawing. As the pressure inside the containment vessel 2 increases, the piston 63 moves to the left. Then, as shown in FIG. 9( a), when the pressure rises near the critical pressure, a biasing force is applied to the piston rod 64 to press the on switch 60. A spring 65 is provided in the cylinder 62 to apply a load against the pressure inside the containment vessel 2. By appropriately adjusting the spring constant, the on switch 60 can be pressed when the pressure inside the containment vessel 2 rises near the critical pressure.

[0064] The off switch 65 used as the open valve holding unit 30 closes the butterfly valve 50. A mechanical valve, for example, may be used as the off switch 65. The mechanical valve may be an air switching valve with a push button, or the like. When the off switch 65 is turned on, the supply of air to the pilot portion of the butterfly valve air operated valve 51 of the butterfly valve 50 is stopped so that the butterfly valve 50 is closed.

[0065] In operation of the open valve holding unit 30, the air cylinder 61 moves to the right as the pressure inside the containment vessel 2 decreases. Then, as shown in Figure 9(b), when the pressure drops to near the outside air pressure, it applies a biasing force to the piston rod 64 to press the off switch 65 that closes the butterfly valve 50.

[0066] Even with this configuration, the reactor containment vessel vent valve system of the present invention can be applied to existing butterfly valves, ball valves, etc. All of these are controlled using the pressure and air inside the reactor containment vessel, and can operate even if there is a total loss of AC power.

[0067] The examples described so far all use pressure and air inside the containment vessel (PCV) for control and are passively activated even in the event of a total loss of AC power. However, if a DC power source, such as a battery, is available for emergency use, a system that converts pressure into an electrical signal for control can also be used. FIG. 10 is a schematic block diagram illustrating an example of electrically controlling the PCV vent valve system of the present invention. Note that only the valve opening control unit 20 and the valve open holding unit 30 are shown, with other components omitted. As shown, the valve opening control unit 20 and the valve open holding unit 30 of the PCV vent valve system of the present invention comprise a pressure transmitter 70 and a controller 71. The pressure transmitter 70 detects the pressure inside the PCV 2 and converts it into an electrical signal. Specifically, the pressure transmitter 70 detects the pressure inside the PCV 2 and converts it into an electrical signal for control. The controller 71 then controls the valve 10 based on the electrical signal from the pressure transmitter 70. Note that the valve 10 may be any valve that can be controlled by a control signal. For example, it may be an electric valve operated by a motor and reduction gear that can be controlled by a control signal. Alternatively, an air accumulator that supplies control air to an air-operated valve may be operated by a solenoid valve that can be controlled by a control signal. Specifically, it may be configured so that an air-operated butterfly valve used as valve 10 opens and closes by controlling an air accumulator using a solenoid valve that can be controlled by a control signal from controller 71. These pressure transmitter 70 and controller 71 are driven by DC power from battery 72.

[0068] For example, the controller 71 can arbitrarily set a predetermined blow-off pressure and a receding pressure. When the controller 71 receives the output signal from the pressure transmitter 70, it outputs a control signal to appropriately control a solenoid valve, a motor, etc. so that the valve 10 opens when the set blow-off pressure is reached. The valve 10 is then maintained open until the pressure inside the containment vessel 2 drops to near the outside air pressure. Thereafter, when the pressure inside the containment vessel 2 drops to near the outside air pressure, the solenoid valve, the motor, etc. are controlled to close the valve 10.

[0069] In this way, the pressure transmitter 70 and controller 71 can be driven by the DC power supply of the battery 72, and the controllable valve 10 can be controlled by a control signal. This makes it possible to operate even if all AC power is lost, although it is necessary to secure a DC power supply.

[0070] The vent valve system for a containment vessel of the present invention is not limited to the illustrated example described above, and various modifications can be made without departing from the spirit of the present invention. For example, the illustrated examples described above can be used in various combinations. [Explanation of symbols]

[0071] 1. Vent valve system for reactor containment vessel 2. Reactor containment vessel 3. Filter vent device 10 valves 11 Safety valve 12 Valve seat 13 Valve body 14 Valve stem 20 Valve opening operation control section 21 Safety valve adapter 22 Pressure control rod 23 Toggle mechanism 24 Additional force spring 30 Open valve holding section 31 Forced opening cylinder 32 Full open sensor 33 Air operated valve 34 Air accumulator 35 Lock-up valve 40 Latch structure 41 Locking rod 42 Locking hole 43 Air Cylinder 44 cylinders 45 piston 46 Piston rod 47 Spring 50 Butterfly valve 51 Air operated valve for butterfly valve 60 On Switch 61 Air cylinder 62 cylinders 63 Piston 64 Piston rod 65 Off Switch 70 Pressure Transmitter 71 Controller 72 Battery

Claims

1. A vent valve system between a reactor containment vessel and a filtered vent device, the vent valve system for a reactor containment vessel comprising: A valve that can be opened and closed when venting from a reactor containment vessel to a filter vent device, the valve comprising: a valve seat provided at an opening from the reactor containment vessel; a valve body capable of opening and closing the valve seat; a valve stem to which the valve body is connected; a valve spring that biases the valve stem so that the valve element is pressed toward the valve seat so that the valve seat can be opened and closed by the valve element in accordance with the force relationship with the pressure inside the reactor containment vessel; a valve comprising a safety valve comprising: a valve opening control unit that opens the valve when the pressure inside the reactor containment vessel rises to near the critical pressure; a valve open holding unit that holds the valve open after the valve is opened by the valve open operation control unit until the pressure inside the reactor containment vessel drops to near the outside pressure, and closes the valve when the pressure inside the reactor containment vessel drops to near the outside pressure, the valve open holding unit comprising: a forced valve-opening cylinder capable of applying a load to a valve stem that counteracts the biasing force of a valve spring so as to maintain an open state of the safety valve; a full-open sensor that detects a fully open state of the safety valve; an air operated valve that is actuated by detection of the full open sensor; an air accumulator that supplies control air to a forced valve-opening cylinder so that the safety valve is maintained in an open state when the air-operated valve is actuated; an open valve holding portion; A vent valve system for a nuclear reactor containment vessel, comprising:

2. A vent valve system between a reactor containment vessel and a filtered vent device, the vent valve system for a reactor containment vessel comprising: A valve that can be opened and closed when venting from a reactor containment vessel to a filter vent device, the valve comprising: a valve seat provided at an opening from the reactor containment vessel; a valve body capable of opening and closing the valve seat; a valve stem to which the valve body is connected; a valve spring that biases the valve stem so that the valve element is pressed toward the valve seat so that the valve seat can be opened and closed by the valve element in accordance with the force relationship with the pressure inside the reactor containment vessel; a valve comprising a safety valve comprising: a valve opening control unit that opens the valve when the pressure inside the reactor containment vessel rises to near the critical pressure; an open valve holding unit that holds the open state of the valve after the valve is opened by the valve opening operation control unit until the pressure inside the reactor containment vessel drops to near the outside pressure, and that closes the valve when the pressure inside the reactor containment vessel drops to near the outside pressure, the open valve holding unit having a latch structure that has a locking rod and a locking hole that is provided in the valve rod so that the locking rod locks when the safety valve is fully open; A vent valve system for a nuclear reactor containment vessel, comprising:

3. 3. The vent valve system for a reactor containment vessel according to claim 2, wherein the locking rod has a shear strength such that it is sheared by the biasing force of a valve spring of the safety valve when the pressure inside the reactor containment vessel drops to a level close to the outside pressure.

4. 3. The vent valve system for a reactor containment vessel according to claim 2, wherein the latch structure has an air cylinder including a cylinder, a piston configured to be movable within the cylinder in response to the pressure within the reactor containment vessel, and a piston rod fixed to the piston and serving as a locking rod; The air cylinder applies a biasing force to the locking rod in the direction of the valve rod when the pressure inside the reactor containment vessel increases, and also applies a biasing force in the direction in which the locking rod is pulled out of the locking hole when the pressure inside the reactor containment vessel decreases to a level close to the outside pressure. A vent valve system for a nuclear reactor containment vessel, comprising:

5. A vent valve system between a reactor containment vessel and a filtered vent device, the vent valve system for a reactor containment vessel comprising: A valve that can be opened and closed when venting from a reactor containment vessel to a filter vent device, the valve comprising: a valve seat provided at an opening from the reactor containment vessel; a valve body capable of opening and closing the valve seat; a valve stem to which the valve body is connected; a valve spring that biases the valve stem so that the valve element is pressed toward the valve seat so that the valve seat can be opened and closed by the valve element in accordance with the force relationship with the pressure inside the reactor containment vessel; a valve comprising a combination of two safety valves each using a valve spring with a different biasing force; a valve opening control unit that opens the valves when the pressure inside the reactor containment vessel rises to near the critical pressure, and the valve opening control unit of each safety valve opens one safety valve before the other safety valve opens; a valve open holding unit that holds the valve open after the valve is opened by the valve open operation control unit until the pressure inside the reactor containment vessel drops to near the outside pressure, and closes the valve when the pressure inside the reactor containment vessel drops to near the outside pressure, and the valve open holding unit of each safety valve closes one safety valve after the other safety valve closes; A vent valve system for a nuclear reactor containment vessel, comprising:

6. 6. The vent valve system for a reactor containment vessel according to claim 1, wherein the valve opening control unit is a valve spring of a safety valve, the biasing force of which is adjusted so that the safety valve opens when the pressure inside the reactor containment vessel rises to near a critical pressure.

7. 7. The vent valve system for a containment vessel according to claim 1, wherein the valve opening control unit comprises: a pressure control rod that operates in response to the pressure inside the reactor containment vessel; a toggle mechanism that is biased by the pressure control rod to press the valve stem toward the valve seat until the pressure inside the reactor containment vessel rises to near the critical pressure, and that releases the pressing of the valve stem when the pressure inside the reactor containment vessel rises to near the critical pressure; 1. A vent valve system for a nuclear reactor containment vessel, comprising a safety valve adapter comprising:

8. 8. The vent valve system for a containment vessel according to claim 1, wherein the valve opening control unit and the valve opening holding unit are a pressure transmitter that detects the pressure inside the reactor containment vessel and converts it into an electrical signal; a controller that controls the valve based on an electrical signal from the pressure transmitter; A vent valve system for a nuclear reactor containment vessel, comprising:

9. A vent valve system between a reactor containment vessel and a filtered vent device, the vent valve system for a reactor containment vessel comprising: an air-operable valve that can be opened and closed when exhausting air from the reactor containment vessel to the filter vent device; a valve opening control unit that opens the valve when the pressure inside the reactor containment vessel rises to near a critical pressure, the valve opening control unit comprising a safety valve having a valve seat provided at an opening from the reactor containment vessel, a valve element that can open and close the valve seat, a valve stem to which the valve element is connected, and a valve spring that urges the valve stem so that the valve element is pressed toward the valve seat so that the valve seat can be opened and closed by the valve element depending on the force relationship with the pressure inside the reactor containment vessel; a valve open holding unit that holds the valve open after the valve is opened by the valve open operation control unit until the pressure inside the reactor containment vessel drops to near the outside air pressure, and that closes the valve when the pressure inside the reactor containment vessel drops to near the outside air pressure, the valve open holding unit comprising: a forced valve open cylinder that can apply a load to a valve stem that counteracts the biasing force of a valve spring so as to maintain the open state of the safety valve; a full open sensor that detects a fully open state of the safety valve; an air operate valve that operates in response to detection by the full open sensor; and an air accumulator that supplies control air to the forced valve open cylinder so as to maintain the open state of the safety valve by operation of the air operate valve; Equipped with When the valve is detected by the full-open sensor, control air is supplied from the air accumulator to maintain the valve open. A vent valve system for a nuclear reactor containment vessel, comprising:

10. A vent valve system between a reactor containment vessel and a filtered vent device, the vent valve system for a reactor containment vessel comprising: an air-operable valve that can be opened and closed when exhausting air from the reactor containment vessel to the filter vent device; a valve opening control unit that opens the valve when the pressure inside the reactor containment vessel rises to near the critical pressure, the valve opening control unit comprising: an on switch that opens the valve; an air cylinder comprising a cylinder, a piston configured to be movable within the cylinder in response to the pressure within the reactor containment vessel, and a piston rod fixed to the piston, the air cylinder applying a biasing force to the piston rod so as to press an ON switch when the pressure within the reactor containment vessel rises to near the critical pressure; A valve opening operation control unit comprising: a valve open holding unit that holds the valve open after the valve is opened by the valve open operation control unit until the pressure inside the reactor containment vessel drops to near the outside pressure, and closes the valve when the pressure inside the reactor containment vessel drops to near the outside pressure, the valve open holding unit having an off switch that closes the valve; Equipped with When the pressure inside the reactor containment vessel drops to a level close to the outside pressure, the air cylinder applies a biasing force to the piston rod to press the off switch. A vent valve system for a nuclear reactor containment vessel, comprising:

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