JP2012230058A - Decompression device of containment vessel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a decompression device of a containment vessel capable of venting gas in the containment vessel at any pressure level and further of safely coping with leakage of radioactive materials in a case where the leakage thereof occurs.SOLUTION: A decompression device of a containment vessel comprises: an exhaust pipe 13 that is connected to a containment vessel 2 through a first isolation valve 12 and transfers gas generated in the containment vessel 2 to an exhaust tower 15; a stand-by gas treatment system 11 connected to a middle of the exhaust pipe 13 through a second isolation valve 14; an emergency exhaust pipe 13c that branches from an upstream side of the second isolation valve 14 of the exhaust pipe 13; a plurality of stop valves 18 disposed in series on the emergency exhaust pipe 13c; a radiation monitor 19 disposed downstream of the plurality of stop valves 18 of the emergency exhaust pipe 13c; and control means 20 that fully opens the second isolation valve 14 in response to an output of the radiation monitor 19 and further starts up the stand-by gas treatment system 11.

Description

  The present invention relates to a depressurization device for a reactor containment vessel, and in particular, in a reactor containment vessel in which the pressure has increased when an emergency water injection to the reactor pressure vessel and the reactor containment vessel is urgently needed. The present invention relates to a depressurization device for a reactor containment vessel that can be decompressed to an arbitrary pressure level and can also be injected with a pump having a low discharge pressure.

  In a boiling water reactor (BWR), for example, a Mark-I type BWR, a reactor pressure vessel 1 is incorporated in a steel reactor containment vessel 2 as shown in FIG.

  The Mark-I type BWR reactor containment vessel 2 includes a reactor pressure vessel 1 and a flask-type dry well 3 surrounding a recirculation system (not shown), and a donut-type suppression chamber concentrically disposed below the flask-type dry well 3. 4, a plurality of vent pipes 5 that radially connect the dry well 3 and the suppression chamber 4, a donut-shaped vent header 6 that is connected to the tip of the vent pipe 5 in the internal space of the suppression chamber 4, and the vent header 6. It is comprised from the pressure suppression system, such as several downcomer pipes 7. FIG.

  The suppression chamber 4 is filled with pool water, and the tip portion of the downcomer pipe 7 is submerged below the surface of the water.

  The leading end of the main steam escape pipe 10 extending from the main steam relief safety valve 9 attached to the main steam system pipe 8 is also led to the surface of the suppression chamber 4.

  When the pressure in the reactor pressure vessel 1 rises excessively, the main steam relief safety valve 9 is operated to release a part of the steam from the reactor pressure vessel 1 into the pool water of the suppression chamber 4. Thus, the pressure increase in the reactor containment vessel 2 is suppressed.

  The pool water in the suppression chamber 4 is cooled and circulated by the residual heat removal system (RHR), but this residual heat removal system does not function properly. After the main steam relief valve is opened, it is closed due to equipment failure. When accidents such as failure do not occur, the pressure and temperature in the reactor containment vessel 2 rapidly increase, and finally there is a risk of exceeding the design limit of the reactor containment vessel 2.

  Even in such a case, an emergency gas processing system (SGTS) 11 is provided as a facility for safely processing a gas containing a radioactive substance released into the reactor containment vessel 2.

  The emergency gas treatment system (SGTS) 11 includes a moisture removal device, a high performance particle filter, an iodine charcoal filter, an exhaust fan, and the like (not shown). Via the 2nd isolation valve 14, it connects with the exhaust pipe 13 which joined the exhaust pipes 13a and 13b derived | led-out from the chamber 4 via the 1st isolation valves 12a and 12b, respectively.

  The high-pressure gas discharged from the reactor containment vessel 2 through the exhaust pipe 13 is reduced to a positive pressure close to normal pressure by the second isolation valve 14, and fission products and the like are generated in the emergency gas processing system (SGTS) 11. It is removed and discharged from the exhaust tower 15 at a high place.

  Further, the emergency exhaust pipe 13 c branches from the exhaust pipe 13 on the upstream side of the second isolation valve 14. A motor-operated valve (MO) 16 and a rupture disk 17 are arranged in series in the branched emergency exhaust pipe 13 c, and the downstream side of the rupture disk 17 is connected to the exhaust tower 15.

  A large amount of gas containing a radioactive substance that cannot be processed by the emergency gas processing system (SGTS) 11 is released from the reactor containment vessel 2, and the pressure and temperature of the reactor containment vessel 2 rapidly rise and the reactor containment vessel 2 may be damaged, the motor-operated valve 16 is opened by remote control, and when the gas pressure in the pipe reaches the preset burst pressure of the rupture disk 17, the rupture disk 17 bursts and the pressure is increased. The reactor containment vessel 2 is prevented from being destroyed by overpressure by abruptly releasing the gas.

  By the way, in such a pressure reduction device for a containment vessel that prevents damage to the reactor containment vessel 2 due to the rupture of the rupture disc 17, the burst set pressure of the rupture disc 17 is set to the reactor containment vessel. Since the pressure is set to be equal to or higher than the maximum operating pressure of 2, gas venting in the reactor containment vessel 2 at a pressure lower than this pressure cannot be performed.

Therefore, in the event of an urgent need for alternative water injection to the reactor core, such as during a reactor coolant loss accident (LOCA), only pumps with discharge pressures greater than the maximum operating pressure of the containment vessel should be used. There was a problem that the pump procurement range was limited.
In addition, the exhaust pipe from the reactor containment vessel is branched into two paths on the way, two stop valves that are opened and closed by remote control are arranged in series on one path, and the rupture disk and the other path are arranged on the other path. Stop valve opened and closed by remote operation is arranged in series, these two paths are merged downstream to make one, and the containment pressure reduction of the reactor containment vessel in which the orifice and wire mesh metal filter are arranged in series downstream An apparatus is known (Patent Document 1).

  In this reactor containment vessel decompression device, it is possible to remotely operate the two stop valves to release the gas in the reactor containment vessel at an arbitrary pressure level.

  However, the sealing capacity of the stop valve is not perfect compared to the rupture disk, and the wire mesh metal filter does not completely remove radioactive material, so a small amount of radioactive material leaks from the stop valve side during normal operation. there's a possibility that.

Japanese Patent Laid-Open No. 3-235093

  In the conventional decompression device that prevents the rupture disk from rupturing due to the overpressure of the reactor containment vessel, the rupture disc burst setting pressure is set to a pressure higher than the maximum use pressure of the reactor containment vessel. When urgent alternative water injection was required, only pumps with discharge pressures higher than the maximum operating pressure of the containment vessel could be used, and there was a problem that the pump procurement range was limited.

Further, in a decompression device in which an exhaust pipe is branched into two paths, a rupture disk is arranged in one path, and two stop valves are arranged in series in the other path, a small amount of radioactive material may leak from the stop valve side. there were.
The present invention has been made to solve such a conventional problem, and is capable of venting the gas in the reactor containment vessel at an arbitrary pressure level and in the case where a leak of radioactive material occurs. It is an object of the present invention to provide a reactor containment vessel decompression device that can start a gas processing system (SGTS) and perform safe processing.

In order to achieve the above object, a depressurization apparatus for a reactor containment vessel according to the present invention is an exhaust pipe that is connected to the reactor containment vessel via a first isolation valve and transfers gas generated in the reactor containment vessel to an exhaust tower. An emergency gas treatment system (SGTS) connected to the exhaust pipe through a second isolation valve, an emergency exhaust pipe branched from the upstream side of the second isolation valve of the exhaust pipe, and the emergency exhaust A plurality of stop valves arranged in series with the pipe; a radiation monitor arranged downstream of the plurality of stop valves of the emergency exhaust pipe;
And a control means for opening the second isolation valve by the output of the radiation monitor and activating the emergency gas processing system.

  The stop valve can be either an electric valve or an air operated valve. In the case of a motorized valve, it can be driven by a battery in addition to an AC power supply. In the case of an air-operated valve, if the gas pressure in the reactor containment vessel is used as the working air, all AC power is lost (SBO) However, it is possible to reduce the pressure in the reactor containment vessel.

    The reactor containment vessel side of the exhaust pipe may be composed of a branch pipe connected to the dry well of the reactor containment vessel and the suppression chamber via separate first isolation valves.

  The processing gas processed in the emergency gas processing system is transferred to an exhaust tower through an exhaust pipe and discharged at a high place.

  The reactor containment protection apparatus of the present invention can vent the containment vessel at any pressure lower than the maximum use pressure of the reactor containment vessel, and therefore, during a reactor coolant loss accident (LOCA). When the alternative water injection to the core is urgently needed, the reactor containment vessel can be vented at any pressure according to the discharge pressure of the usable pump. Can also be used for maximum effective water injection.

  In addition, when radioactive material leaks from the stop valve, the radiation monitor detects this and opens the second isolation valve and activates the emergency gas treatment system, so the pressure in the exhaust pipe (reactor containment vessel) The internal pressure) can be reduced to suppress leakage from the stop valve.

1 is a system diagram of an embodiment of a reactor containment decompression apparatus according to the present invention. The system diagram of the conventional reactor containment vessel decompression device.

  Next, an example in which the reactor containment vessel decompression apparatus of the present invention is applied to a reactor containment vessel of a boiling water reactor power plant (Mark-I type BWR) will be described with reference to FIG.

(Embodiment)
FIG. 1 is a system diagram of this embodiment.

  The reactor containment vessel of the embodiment shown in FIG. 1 has the same structure as the conventional reactor containment vessel shown in FIG. Description is omitted.

  The nuclear reactor containment vessel 2 to which this embodiment is applied is a so-called Mark-I type BWR, and includes a dry well 3, a suppression chamber 4, a vent pipe 5, a vent header 6, a downcomer pipe 7 and the like pressure suppression system. The main part consists of

    The reactor containment vessel 2 is provided with exhaust pipes 13a and 13b that pass through the dry well 3 and the suppression chamber 4 and open to the internal space, and are closed by first isolation valves 12a and 12b, respectively. . These isolation valves 12a and 12b are automatically closed by a signal such as a low reactor water level, a high dry well pressure or a high radioactivity level to prevent the radioactive material from flowing out of the reactor containment vessel 2. Yes. The first isolation valve 12b of the exhaust pipe 13b connected to the suppression chamber 4 side of the reactor containment vessel 2 is closed when the suppression chamber 4 is full, and only the exhaust pipe 13a on the dry well 3 side is opened.

The exhaust pipes 13a and 13b are joined together, and a second isolation valve 14 and an emergency gas processing system (SGTS) 11 that are opened by a signal to be described later are sequentially arranged in the joined exhaust pipe 13.
The second isolation valve 14 is a high-performance particle filter of an emergency gas treatment system (SGTS) 11, an iodine charcoal filter, and a high-pressure gas in the exhaust pipe 13 having the same pressure as that in the reactor containment vessel 2. The pressure is reduced to a pressure (positive pressure) that effectively functions.
The gas that has been processed by the emergency gas processing system (SGTS) 11 and from which radioactive substances have been removed is sent to the exhaust tower 15 and released at a high place.

An emergency exhaust pipe 13c is connected to the upstream side of the second isolation valve 14 of the exhaust pipe 13, and two stop valves 18a and 18b that are opened and closed by remote control are attached in series to the emergency exhaust pipe 13c. A radiation monitor 19 for detecting leakage of the stop valves 18a and 18b is disposed downstream thereof.
These stop valves 18a and 18b may be constituted by either an electric valve or an air operated valve. In the case of an electric valve, it can be driven by a battery (storage battery, dry cell). In the case of an air-operated valve, the gas pressure of the reactor containment vessel is used as the operating air, and the signal system can be operated by a battery power supply. Thus, even in the case of total AC power loss (SBO), it can function.
The stop valves 18a and 18b are simultaneously opened when urgent pressure reduction is required, but the opening degree of the downstream stop valve 18b is made larger than the opening degree of the upstream stop valve 18a, or the stop valve Both 18a and 18b may be half open. Further, the number of stages is not limited to two, and three or more stages may be arranged in series as necessary.

  When the radiation monitor 19 detects the leakage of radioactive material from the stop valves 18a and 18b, the control device 20 determines whether or not the radiation level is within an allowable range. A signal is sent to the valve 14 to open the second isolation valve 14 at a predetermined opening that reduces the gas pressure in the exhaust pipe 13 to a pressure level that can be processed by the emergency gas processing system (SGTS) 11. The gas processing system (SGTS) 11 is started.

  By opening the second isolation valve 14, the gas in the reactor containment vessel 2 is processed by the emergency gas processing system (SGTS) 11 and released from the exhaust tower 15, so that the inside of the reactor containment vessel 2 and the exhaust pipe 13 The pressure is reduced and the leakage of radioactive material from the stop valves 18a and 18b is suppressed.

  The stop valves 18a and 18b of the pressure reduction device for the containment vessel of the present invention are used as follows.

  For example, when the pressure in the reactor containment vessel 2 rises above a predetermined pressure, such as when the residual heat removal system does not function properly after a pipe breakage accident, the first isolation valves 12a and 12b and the second isolation valve 14 is opened, and the gas containing the radioactive substance released from the exhaust pipes 13a, 13b, etc. is sent to the emergency gas processing system (SGTS) 11, where the gas from which the harmful radioactive substance has been removed is sent from the exhaust tower 15. Released into the atmosphere. As a result, the reactor containment vessel 2 is depressurized to maintain its soundness.

By the way, when the pressure and temperature in the reactor containment vessel 2 are suddenly increased by a gas containing a large amount of water vapor as in a breakage accident of a circulation pipe or the like, this gas is directly used as an emergency gas treatment system (SGTS) 11. Can not be sent to. The emergency gas treatment system (SGTS) 11 is configured to adsorb even low-concentration radioactive material by a specially processed charcoal filter to ensure high removal efficiency. When a gas containing a large amount of water vapor is allowed to flow through the system, the adsorption performance deteriorates rapidly, and the pressure resistance of the filter itself is small, which may cause damage due to the impact of the gas flow.
Therefore, in such a case, the stop valves 18a and 18b are opened, and the following measures are taken according to the degree of urgency, the gas pressure level, and the like.
First, if the gas pressure is too high to be processed only by the emergency gas processing system (SGTS) 11, but can be processed by lowering the pressure level a little, depressurization by opening the stop valves 18a and 18b, The processing by the emergency gas processing system (SGTS) 11 can be performed while performing the two-stage pressure reduction by the second isolation valve 14.
In this case, the radioactive substance is not removed from the gas discharged from the stop valves 18a and 18b, but the gas processed by the emergency gas processing system (SGTS) 11 does not contain the radioactive substance. It is possible to reduce the total amount of radioactive material released into the chamber.
When several accidents overlap and the pressure in the reactor containment vessel 2 exceeds a predetermined set pressure and the reactor containment vessel 2 may be damaged, the stop valves 18a and 18b are fully opened. The
Also, as in the case of the loss of reactor coolant accident (LOCA), it is necessary to perform urgent and large-scale injection of water into the reactor pressure vessel. However, if sufficient water injection cannot be performed with a high pump alone, the opening pressure of the stop valves 18a and 18b can be lowered to enable water injection with a pump with a low discharge pressure. (LOCA) can be avoided.
In the above embodiment, the rupture disk is not used. However, the present invention is not limited to this embodiment. For example, the second emergency exhaust is provided in the exhaust pipe 13 in parallel with the emergency exhaust pipe 13c. It is also possible to provide a pipe and provide an emergency pressure relief system comprising a stop valve and a rupture disk similar to the conventional one on the exhaust pipe.

  In the above embodiment, the case where the present invention is applied to the Mark-I type BWR has been described. However, the present invention is not limited to such an embodiment, and the Mark-II type BWR and Mark-III type are not limited thereto. The same can be applied to the reactor containment pressure reducing device of BWR or ABWR.

1 ... Reactor pressure vessel 2 ... Reactor containment vessel 3 ... Dry well 4 ... Suppression chamber 5 ... Vent pipe 6 ... Vent header 7 ... Downcomer pipe 8 ... Main steam system pipe 9 ... Relief safety valve 10 …… Exhaust pipe 11 …… Emergency gas treatment system (SGTS)
12a, 12b ...... First isolation valve 13, 13a, 13b ... Exhaust pipe 13c ... Emergency exhaust pipe 14 ... Second isolation valve 15 ... Exhaust tower 16 ... Motor valve 17 ... Rupture disk 18a, 18b ... ... Stop valve 19 ... Radiation monitor 20 ... Control device

Claims (4)

An exhaust pipe connected to the reactor containment vessel via a first isolation valve for transferring the gas generated in the reactor containment vessel to the exhaust tower;
An emergency gas treatment system connected via a second isolation valve in the middle of the exhaust pipe;
An emergency exhaust pipe branched from the upstream side of the second isolation valve of the exhaust pipe;
A plurality of stop valves arranged in series with the emergency exhaust pipe;
A radiation monitor disposed downstream of the plurality of stop valves of the emergency exhaust pipe;
Control means for opening the second isolation valve by the output of the radiation monitor and activating the emergency gas processing system;
A depressurizing device for a reactor containment vessel, comprising:   2. The atom according to claim 1, wherein the reactor containment side of the exhaust pipe includes a branch pipe connected to a dry well and a suppression chamber of the reactor containment vessel through separate first isolation valves. Pressure reducing device for reactor containment vessel.   3. The reactor containment vessel decompression device according to claim 2, wherein the first isolation valve of the exhaust pipe connected to the suppression chamber side of the reactor containment vessel is closed when the suppression chamber is full.   The reactor containment vessel decompression device according to any one of claims 1 to 3, wherein the gas treated in the emergency gas treatment system is transferred to an exhaust tower through an exhaust pipe.

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