Equipment atmosphere monitoring device and method

Abstract

To make it possible to prevent radioactive contamination caused by atmosphere gas inside the equipment when replacing an oxygen concentration sensor.SOLUTION: A device is configured to have a sampling line 11 for sampling atmosphere gas within a nuclear reactor containment 1, a galvanic cell type oxygen concentration sensor 17 for detecting the oxygen concentration in the atmosphere gas flowing through the sampling line, an inert gas supply line 25 connected upstream of the galvanic cell type oxygen concentration sensor in the sampling line and capable of supplying nitrogen gas to the sampling line, a bypass line 26 connected to the sampling line in bypass of the galvanic cell type oxygen concentration sensor, and a control device 27 that controls the galvanic cell type oxygen concentration sensor by closing the upstream and downstream sides of the galvanic cell type oxygen concentration sensor to a state where the galvanic cell type oxygen concentration sensor can be replaced, after supplying nitrogen gas from the inert gas supply line to the galvanic cell type oxygen concentration sensor for a certain period of time, and simultaneously supplying nitrogen gas to the bypass line.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] An embodiment of the present invention relates to an apparatus and a method for monitoring an atmosphere inside a facility. [Background technology]

[0002] 2. Description of the Related Art Nuclear power plants are equipped with containment vessel atmosphere monitoring devices that sample atmospheric gas within a reactor containment vessel that contains a reactor pressure vessel and monitor the concentration of oxygen and other such atmospheric gas. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2018-124230 A [Patent Document 2] JP 2000-2784 A [Patent Document 3] Japanese Patent Application Publication No. 10-311819 Summary of the Invention [Problem to be solved by the invention]

[0004] A magnetic wind oxygen concentration sensor is generally used to detect the oxygen concentration in the atmospheric gas in the reactor containment vessel, but this magnetic wind oxygen concentration sensor may deteriorate when the atmospheric gas contains a high concentration of hydrogen. In addition, when a galvanic cell oxygen concentration sensor is used as the oxygen concentration sensor, although this galvanic cell oxygen concentration sensor has hydrogen resistance characteristics, its oxygen concentration detection characteristics deteriorate in 1 to 2 years. Therefore, the galvanic cell oxygen concentration sensor needs to be frequently replaced, but there is a risk that the atmospheric gas will be released during the replacement and the surrounding environment of the sensor will be radioactively contaminated. Furthermore, since the galvanic cell oxygen concentration sensor needs to be replaced frequently as described above, it is necessary to always accurately diagnose the characteristics (deterioration) of the sensor. In addition, there is also a demand for reducing the replacement frequency of the galvanic cell oxygen concentration sensor as much as possible.

[0005] The embodiments of the present invention have been made in consideration of the above-mentioned circumstances, and an object of the present invention is to provide an atmosphere monitoring device and an atmosphere monitoring method within a facility that can prevent radioactive contamination caused by atmospheric gas within the facility when replacing an oxygen concentration sensor.

[0006] Another object of the embodiments of the present invention is to provide an apparatus and method for monitoring the atmosphere within a facility that can suitably calibrate an oxygen concentration sensor at necessary times, including when the galvanic battery type oxygen concentration sensor is replaced.

[0007] A further object of the present invention is to provide an apparatus and method for monitoring the atmosphere inside a facility that can prevent deterioration of a magnetic wind type oxygen concentration sensor due to hydrogen gas. [Means for solving the problem]

[0008] An embodiment of the present invention provides an atmosphere monitoring device within a facility, comprising: a sampling line for sampling atmospheric gas within the facility; an oxygen concentration sensor disposed in the sampling line for detecting the oxygen concentration in the atmospheric gas flowing through the sampling line; an inert gas supply line connected to the upstream side of the oxygen concentration sensor in the sampling line and capable of supplying inert gas to the sampling line; a bypass line connected to the sampling line, bypassing the oxygen concentration sensor; and a control device that supplies inert gas from the inert gas supply line through the sampling line to the oxygen concentration sensor for a certain period of time, and then supplies inert gas to the bypass line and closes the upstream and downstream sides of the oxygen concentration sensor to control the oxygen concentration sensor to a replaceable state.

[0009] Moreover, an atmosphere monitoring device within a facility in an embodiment of the present invention is characterized in that it is configured to include a sampling line that samples atmospheric gas within the facility, a galvanic cell type oxygen concentration sensor that is disposed in the sampling line and detects the oxygen concentration in the atmospheric gas flowing through the sampling line, an inert gas supply line that is connected to the upstream side of the galvanic cell type oxygen concentration sensor in the sampling line and is capable of supplying an inert gas to the sampling line, an oxygen gas supply line that is connected to the upstream side of the galvanic cell type oxygen concentration sensor in the sampling line and is capable of supplying oxygen gas of a predetermined concentration to the sampling line, and a control device that controls the galvanic cell type oxygen concentration sensor to be calibrated by supplying inert gas from the inert gas supply line via the sampling line to the galvanic cell type oxygen concentration sensor for a certain period of time, and then supplying oxygen gas of the predetermined concentration from the oxygen gas supply line to the galvanic cell type oxygen concentration sensor.

[0010] Furthermore, the atmosphere monitoring device within the facility in an embodiment of the present invention is characterized in that it is configured with a sampling line for sampling the atmospheric gas within the facility, a magnetic wind type oxygen concentration sensor arranged in parallel to the sampling line and detecting the oxygen concentration in the atmospheric gas flowing through the sampling line, and an oxygen concentration sensor of a different type than the oxygen concentration sensor, a hydrogen concentration sensor arranged in the sampling line and detecting the hydrogen concentration in the atmospheric gas flowing through the sampling line, an inert gas supply line connected upstream of each of the oxygen concentration sensors and the hydrogen concentration sensor in the sampling line and capable of supplying inert gas to the sampling line, and a control device that keeps the magnetic wind type oxygen concentration sensor in an operating state during normal operation of the facility, and controls the magnetic wind type oxygen concentration sensor to switch to the different type of oxygen concentration sensor when an event occurs in which the hydrogen concentration detected by the hydrogen concentration sensor is equal to or exceeds a specified value, and after inert gas has been supplied from the inert gas supply line for a certain period of time.

[0011] A method for monitoring the atmosphere within a facility in an embodiment of the present invention is a method for monitoring the oxygen concentration of atmospheric gas within the facility, wherein when replacing a galvanic cell type oxygen concentration sensor provided in a sampling line that samples atmospheric gas within the facility, the following steps are sequentially performed: cutting off the supply of atmospheric gas to the galvanic cell type oxygen concentration sensor; supplying inert gas from an inert gas supply line connected to the sampling line via the sampling line to the galvanic cell type oxygen concentration sensor for a fixed period of time; supplying inert gas to a bypass line connected to the sampling line, bypassing the galvanic cell type oxygen concentration sensor, and closing the upstream and downstream sides of the galvanic cell type oxygen concentration sensor; and replacing the galvanic cell type oxygen concentration sensor.

[0012] In addition, in an embodiment of the present invention, a method for monitoring the atmosphere within a facility is a method for monitoring the oxygen concentration of atmospheric gas within the facility, wherein calibration of a galvanic cell type oxygen concentration sensor provided in a sampling line that samples atmospheric gas within the facility is performed by sequentially performing the steps of cutting off the supply of atmospheric gas to the galvanic cell type oxygen concentration sensor, supplying inert gas from an inert gas supply line connected to the sampling line via the sampling line to the galvanic cell type oxygen concentration sensor for a fixed period of time, and supplying oxygen gas of a predetermined concentration from an oxygen gas supply line connected to the sampling line to the galvanic cell type oxygen concentration sensor via the sampling line.

[0013] Furthermore, in an embodiment of the present invention, a method for monitoring the atmosphere within a facility for monitoring the oxygen concentration and hydrogen concentration of the atmospheric gas within the facility includes preparing a magnetic wind type oxygen concentration sensor and a galvanic cell type oxygen concentration sensor arranged in parallel in a sampling line that samples the atmospheric gas within the facility, and performing a step of detecting the oxygen concentration in the atmospheric gas using the magnetic wind type oxygen concentration sensor during normal times when the hydrogen concentration in the atmospheric gas flowing through the sampling line is less than a specified value, and when the hydrogen concentration in the atmospheric gas flowing through the sampling line is equal to or greater than a specified value or when an event occurs in which the hydrogen concentration in the atmospheric gas flowing through the sampling line is equal to or greater than this specified value, supplying inert gas from an inert gas supply line to the magnetic wind type oxygen concentration sensor via the sampling line for a certain period of time, closing the upstream and downstream sides of the magnetic wind type oxygen concentration sensor after the supply of inert gas to the magnetic wind type oxygen concentration sensor is stopped, and switching to the galvanic cell type oxygen concentration sensor after closing the upstream and downstream sides of the magnetic wind type oxygen concentration sensor to detect the oxygen concentration in the atmospheric gas flowing through the sampling line, sequentially performing the following steps. Effect of the Invention

[0014] According to the embodiment of the present invention, radioactive contamination caused by the atmospheric gas in the facility can be prevented when replacing the oxygen concentration sensor. Also, according to the embodiment of the present invention, the oxygen concentration sensor can be suitably calibrated at the necessary time including when replacing the galvanic cell type oxygen concentration sensor. Furthermore, according to the embodiment of the present invention, deterioration of the magnetic wind type oxygen concentration sensor due to hydrogen gas can be avoided. [Brief description of the drawings]

[0015] [Figure 1] 1 is a piping diagram showing the configuration of an internal atmosphere monitoring device according to a first embodiment. [Diagram 2] 4 is a flowchart showing a procedure for replacing a galvanic cell type oxygen concentration sensor in the facility atmosphere monitoring device of FIG. 1. [Diagram 3] FIG. 11 is a piping diagram showing the configuration of a facility interior atmosphere monitoring device according to a second embodiment. [Figure 4] 4 is a flowchart showing a procedure for calibrating the galvanic cell type oxygen concentration sensor in the facility atmosphere monitoring device of FIG. 3. [Diagram 5] 4 is a piping diagram showing a configuration of a modified embodiment of the facility internal atmosphere monitoring device of FIG. 3. [Figure 6] FIG. 11 is a piping diagram showing the configuration of a facility interior atmosphere monitoring device according to a third embodiment. [Figure 7] 4 is a flowchart showing a switching procedure of the oxygen concentration sensor in the facility atmosphere monitoring device of FIG. 3 . [Figure 8] FIG. 11 is a piping diagram showing the configuration of a facility atmosphere monitoring device according to a fourth embodiment. [Figure 9] 9 is a flowchart showing a switching procedure of the oxygen concentration sensor in the facility atmosphere monitoring device of FIG. 8 . DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. [A] First embodiment (Figs. 1 and 2) Fig. 1 is a piping diagram showing the configuration of an atmosphere monitoring device in a facility according to a first embodiment. The atmosphere monitoring device in a facility 10 shown in Fig. 1 samples an atmosphere gas G in a reactor containment vessel 1 as a facility using a sampling line 11 to monitor the concentration of oxygen contained in the atmosphere gas G. The sampling line 11 has an intake side end 11A and an exhaust side end 11B both connected to the reactor containment vessel 1, and circulates and distributes the atmosphere gas G by an intake pump 15 and an exhaust pump 19 described below.

[0017] In the sampling line 11, from the suction end 11A side, a cooler 12, a dehumidifier 13, a filter 14, a suction pump 15, a pressure reducing valve 16, a measuring section 17M of a galvanic cell type oxygen concentration sensor 17, a flow controller 18, and an exhaust pump 19 are sequentially arranged. In addition, in the sampling line 11, a first switching valve 21 is arranged between the filter 14 and the suction pump 15, an upstream gate valve 23 is arranged between the suction pump 15 and the pressure reducing valve 16, and a downstream gate valve 24 is arranged between the measuring section 17M of the galvanic cell type oxygen concentration sensor 17 and the flow controller 18.

[0018] The suction pump 15 draws the ambient gas G in the reactor containment vessel 1 into the sampling line 11. The exhaust pump 19 exhausts the ambient gas G in the sampling line 11 into the reactor containment vessel 1. The cooler 12 cools the ambient gas G drawn into the sampling line 11 to approximately the ambient temperature of the cooler 12 (e.g., room temperature) or the cooling water temperature. The dehumidifier 13 dehumidifies the ambient gas G cooled by the cooler 12, for example, to prevent condensation on the filter 14. The pressure reducing valve 16 reduces the pressure of the ambient gas G in the sampling line 11 to a predetermined pressure.

[0019] The galvanic cell oxygen concentration sensor 17 detects the oxygen concentration in the atmospheric gas G flowing through the sampling line 11, and includes a measurement unit 17M and a preamplifier unit 17N. The preamplifier unit 17N is housed in a shield 20 made of lead, for example, to eliminate the effects of radiation. Although not shown, the measurement unit 17M of this galvanic cell oxygen concentration sensor 17 comprises an anode and a cathode that constitute a pair of electrodes, and the anode and cathode are disposed in a container filled with an electrolyte and provided with a diaphragm, and when oxygen passes through the diaphragm and diffuses into the container, the oxygen concentration is detected based on the current generated between the anode and cathode.

[0020] The filter 14 removes poisonous substances (iodine, etc.) in the ambient gas G flowing through the sampling line 11. For example, it is assumed that a part of the diaphragm of the measuring section 17M of the galvanic cell type oxygen concentration sensor 17 is blocked by iodine, which reduces the surface area and gradually reduces the output of the galvanic cell type oxygen concentration sensor 17. Therefore, the filter 14 is used to remove iodine in the ambient gas G in order to maintain the soundness of the galvanic cell type oxygen concentration sensor 17. In addition, in order to prevent condensation on the filter 14, the dehumidifier 13 removes moisture from the ambient gas G, and the filter 14 is heated to, for example, about 80° C. by a heater disposed inside the filter 14. A plurality of filters 14 may be disposed in series in the sampling line 11 in order to remove a plurality of poisonous substances.

[0021] In the galvanic cell type oxygen concentration sensor 17, the electrolyte and the diaphragm in the measuring part 17M need to be replaced every one to two years due to the detection of the oxygen concentration. For this reason, the facility internal atmosphere monitoring device 10 is provided with an inert gas supply line 25 and a bypass line 26, and further has a control device 27.

[0022] The inert gas supply line 25 has at one end a nitrogen gas cylinder 28 filled with nitrogen gas as an inert gas, and further has a pressure reducing valve 29 and a second switching valve 22. The other end of this inert gas supply line 25 is connected to the upstream side of the measurement unit 17M of the galvanic cell type oxygen concentration sensor 17 in the sampling line 11, specifically, between the first switching valve 21 and the suction pump 15 in the sampling line 11. The inert gas supply line 25 supplies nitrogen gas from the nitrogen gas cylinder 28 to the sampling line 11 by closing the first switching valve 21 and opening the second switching valve 22.

[0023] The bypass line 26 has a bypass valve 30, and is connected to the sampling line 11, bypassing the upstream gate valve 23, the pressure reducing valve 16, the measuring section 17M of the galvanic cell type oxygen concentration sensor 17, and the downstream gate valve 24. This bypass line 26 bypasses the nitrogen gas supplied from the inert gas supply line 25 into the sampling line 11 when the galvanic cell type oxygen concentration sensor 17 is replaced.

[0024] The control device 27 inputs a plurality of signals including the oxygen concentration signal from the preamplifier unit 17N of the galvanic cell type oxygen concentration sensor 17, and controls various devices, such as the suction pump 15 and the exhaust pump 19, based on these signals to introduce the atmospheric gas G in the reactor containment vessel 1 into the sampling line 11 and circulate it.

[0025] Furthermore, when replacing the galvanic cell type oxygen concentration sensor 17, the control device 27 closes the first selector valve 21 and opens the second selector valve 22 for a fixed time to supply nitrogen gas from the nitrogen gas cylinder 28 of the inert gas supply line 25 through the sampling line 11 to the measurement unit 17M of the galvanic cell type oxygen concentration sensor 17 for a fixed time, and then opens the bypass valve 30 to supply nitrogen gas to the bypass line 26, and further closes the upstream gate valve 23 and the downstream gate valve 24 to control the galvanic cell type oxygen concentration sensor 17 to a replaceable state. By supplying nitrogen gas to the measurement unit 17M of the galvanic cell type oxygen concentration sensor 17 for a fixed time, the atmospheric gas G in the measurement unit 17M is replaced with nitrogen gas.

[0026] Next, a procedure for replacing the galvanic cell type oxygen concentration sensor 17 based on the control of the above-mentioned control device 27 will be described with reference to FIG. First, the first switching valve 21 of the sampling line 11 is closed to cut off the supply of the atmospheric gas G to the measurement unit 17M of the galvanic cell type oxygen concentration sensor 17 (S11). Next, the second switching valve 22 is opened to supply nitrogen gas from the nitrogen gas cylinder 28 of the inert gas supply line 25 through the sampling line 11 to the measurement unit 17M of the galvanic cell type oxygen concentration sensor 17 for a certain period of time, thereby replacing the atmospheric gas G in this measurement unit 17M with nitrogen gas (S12).

[0027] After supplying nitrogen gas to the measurement section 17M of the galvanic cell type oxygen concentration sensor 17 for a fixed period of time, the bypass valve 30 is opened to supply nitrogen gas from the inert gas supply line 25 to the bypass line 26, and the upstream gate valve 23 and downstream gate valve 24 for the measurement section 17M of the galvanic cell type oxygen concentration sensor 17 are closed (S13). In this state, the galvanic cell type oxygen concentration sensor 17 becomes replaceable (S14).

[0028] As configured as above, the first embodiment provides the following effect (1). (1) When replacing the galvanic cell type oxygen concentration sensor 17 provided in the sampling line 11, nitrogen gas is supplied from the inert gas supply line 25 to the measurement unit 17M of the galvanic cell type oxygen concentration sensor 17 in advance for a certain period of time via the sampling line 11. Therefore, the atmospheric gas G is replaced with nitrogen gas in the measurement unit 17M of the galvanic cell type oxygen concentration sensor 17, so that the atmospheric gas G containing radioactive substances does not diffuse to the periphery of the measurement unit 17M from the open portion of the measurement unit 17M of the galvanic cell type oxygen concentration sensor 17 when replacing the galvanic cell type oxygen concentration sensor 17. As a result, radioactive contamination caused by the atmospheric gas G in the reactor containment vessel 1 can be prevented when replacing the galvanic cell type oxygen concentration sensor 17.

[0029] [B] Second embodiment (Figs. 3 to 5) 3 is a piping diagram showing the configuration of the facility atmosphere monitoring device according to the second embodiment. In the second embodiment, the same parts as those in the first embodiment are given the same reference numerals as those in the first embodiment, and the description thereof will be simplified or omitted.

[0030] The facility atmosphere monitoring device 40 of the second embodiment differs from the first embodiment in that it has an oxygen gas supply line 41 and a control device 42 in which control for calibrating the galvanic cell type oxygen concentration sensor 17 is added to the control contents of the control device 27. In addition, the facility atmosphere monitoring device 40 has a nitrogen side switching valve 43 provided between the pressure reducing valve 29 and the second switching valve 22 in the inert gas supply line 25.

[0031] The oxygen gas supply line 41 has an oxygen gas cylinder 44 filled with oxygen gas of a predetermined concentration at one end, and further has a pressure reducing valve 45 and an oxygen side switching valve 46. The lower end of the oxygen gas supply line 41 is connected to the upstream side of the measurement unit 17M of the galvanic cell type oxygen concentration sensor 17 in the sampling line 11, specifically, between the nitrogen side switching valve 43 and the second switching valve 22 in the inert gas supply line 25. When the oxygen side switching valve 46 and the second switching valve 22 are opened with the first switching valve 21 and the nitrogen side switching valve 43 closed, oxygen gas of a predetermined concentration in the oxygen gas cylinder 44 is supplied to the measurement unit 17M of the galvanic cell type oxygen concentration sensor 17 via the sampling line 11.

[0032] When calibrating the galvanic cell type oxygen concentration sensor 17, the control device 42 closes the first switching valve 21 and opens the second switching valve 22 and the nitrogen side switching valve 43 for a certain period of time, thereby supplying nitrogen gas from the nitrogen gas cylinder 28 in the inert gas supply line 25 via the sampling line 11 to the measurement unit 17M of the galvanic cell type oxygen concentration sensor 17 for a certain period of time, and then closes the nitrogen side switching valve 43 and opens the oxygen side switching valve 46, thereby supplying oxygen gas in the oxygen gas cylinder 44 in the oxygen gas supply line 41 via the sampling line 11 to the measurement unit 17M of the galvanic cell type oxygen concentration sensor 17 to calibrate the galvanic cell type oxygen concentration sensor 17.

[0033] The calibration of the above-mentioned galvanic cell type oxygen concentration sensor 17 is necessary to diagnose the characteristics (deterioration) of the galvanic cell type oxygen concentration sensor 17 because the electrolyte and diaphragm in the measuring section 17M of the galvanic cell type oxygen concentration sensor 17 need to be replaced every one to two years and the galvanic cell type oxygen concentration sensor 17 is replaced frequently. Therefore, the calibration of the galvanic cell type oxygen concentration sensor 17 is performed, for example, once a month or every time the galvanic cell type oxygen concentration sensor 17 is replaced. It is not necessary to use the bypass line 26 when calibrating the galvanic cell type oxygen concentration sensor.

[0034] Next, a procedure for calibrating the galvanic cell type oxygen concentration sensor 17 under the control of the control device 42 will be described with reference to FIG. First, the first switching valve 21 of the sampling line 11 is closed to cut off the supply of the atmospheric gas G to the measurement section 17M of the galvanic cell type oxygen concentration sensor 17 (S21). Next, the second switching valve 22 and the nitrogen side switching valve 43 are opened to supply nitrogen gas from the nitrogen gas cylinder 28 of the inert gas supply line 25 through the sampling line 11 to the measurement section 17M of the galvanic cell type oxygen concentration sensor 17 for a certain period of time, thereby replacing the atmospheric gas G in this measurement section 17M with nitrogen gas (S22).

[0035] Thereafter, with the second switching valve 22 open, the nitrogen side switching valve 43 is closed and the oxygen side switching valve 46 is opened, thereby supplying oxygen gas of a predetermined concentration from the oxygen gas cylinder 44 in the oxygen gas supply line 41 via the sampling line 11 to the measurement section 17M of the galvanic cell type oxygen concentration sensor 17 (S23), and calibration (deterioration diagnosis) of the galvanic cell type oxygen concentration sensor 17 is performed (S24).

[0036] As configured as above, the second embodiment provides the following effect (2) in addition to the effect (1) of the first embodiment.

[0037] (2) Before oxygen gas of a predetermined concentration is supplied from the oxygen gas supply line 41 to the measurement unit 17M of the galvanic cell type oxygen concentration sensor 17, nitrogen gas from the inert gas supply line 25 is supplied to the measurement unit 17M of the galvanic cell type oxygen concentration sensor 17 for a certain period of time, and the atmospheric gas G is replaced with nitrogen gas inside this measurement unit 17M. Therefore, calibration of the galvanic cell type oxygen concentration sensor 17 using oxygen gas of a predetermined concentration from the oxygen gas supply line 41 can be suitably performed at any time necessary, including when replacing the galvanic cell type oxygen concentration sensor.

[0038] Here, Fig. 5 is a piping diagram showing the configuration of a modified form of the facility internal atmosphere monitor of Fig. 3. The facility internal atmosphere monitor 47 of this modified form does not have the inert gas supply line 25 and the oxygen gas supply line 41 separately provided as shown in Fig. 3, but has a mixer 48 equipped with a nitrogen gas cylinder 28 and an oxygen gas cylinder 44.

[0039] That is, the mixer 48 is configured to supply nitrogen gas from the nitrogen gas cylinder 28 through the pressure reducing valve 29, pressure gauge 49, nitrogen gas mass flow controller 50, and check valve 51, and oxygen gas from the oxygen gas cylinder 44 through the pressure reducing valve 45, pressure gauge 52, oxygen gas mass flow controller 53, and check valve 54 to the mixer 55, respectively, to be mixed, and to supply the mixed gas to the sampling line 11 through the second switching valve 22. Under the control of the control device 42, the mixer 48 changes the flow rates of the nitrogen gas by the nitrogen gas mass flow controller 50 and the oxygen gas by the oxygen gas mass flow controller 53, thereby adjusting the mixture ratio of the nitrogen gas and the oxygen gas, and supplies only the nitrogen gas, or a plurality of oxygen gases of predetermined concentrations set by arbitrarily changing the flow rates, to the sampling line 11.

[0040] By using the above-mentioned mixer 48, it becomes possible to supply nitrogen gas for a fixed period of time to the measurement unit 17M of the galvanic cell type oxygen concentration sensor 17, thereby replacing the atmospheric gas G in the measurement unit 17M with nitrogen gas. Furthermore, by using the mixer 48, it becomes possible to supply oxygen gas of a different predetermined concentration that is arbitrarily set to the measurement unit 17M of the galvanic cell type oxygen concentration sensor 17, thereby performing characteristic (performance) diagnosis, including deterioration diagnosis, of the galvanic cell type oxygen concentration sensor 17. As a result, it is possible to perform more suitable calibration of the galvanic cell type oxygen concentration sensor 17.

[0041] [C] Third embodiment (FIGS. 6 and 7) 6 is a piping diagram showing the configuration of the facility atmosphere monitoring device of the third embodiment. In the third embodiment, the same parts as those in the first embodiment are given the same reference numerals as those in the first embodiment, and the description thereof will be simplified or omitted.

[0042] The third embodiment of the facility interior atmosphere monitoring device 60 differs from the first embodiment in that the galvanic cell type oxygen concentration sensor 17 provided in the sampling line 11 is replaced with a magnetic wind type oxygen concentration sensor 61, the bypass line 26 is replaced with a sensor switching line 62 equipped with the galvanic cell type oxygen concentration sensor 17, a hydrogen concentration sensor 63 is installed in the sampling line 11, and a control device 64 is further installed, so that oxygen concentration sensors with different measurement (detection) principles can be switched and used depending on the usage conditions.

[0043] The magnetic wind type oxygen concentration sensor 61 detects the oxygen concentration in the atmospheric gas G flowing through the sampling line 11, and includes a measurement unit 61M and a preamplifier unit 61N. The measurement unit 61M is disposed in the sampling line 11. In order to eliminate the effects of radiation, the preamplifier unit 61N is housed in the same shield 20, which is made of, for example, lead, together with the preamplifier unit 17N of the galvanic cell type oxygen concentration sensor 17 and a preamplifier unit 63N (described later) of the hydrogen concentration sensor 63.

[0044] Although not shown, the measurement unit 61M of the magnetic wind type oxygen concentration sensor 61 is configured by installing a thermistor whose resistance changes with temperature in a cell in which a non-uniform magnetic field is generated. When a detection gas containing oxygen flows into this cell, the oxygen in the detection gas is attracted to the magnetic field, but when heated by the thermistor, the magnetism weakens and the oxygen in the detection gas that has newly flowed into the cell pushes the oxygen, generating a magnetic wind in the cell. Since the strength of this magnetic wind is proportional to the amount of oxygen, the measurement unit 61M detects the oxygen concentration in the detection gas by measuring the strength of the magnetic wind from the temperature change (resistance change) of the thermistor.

[0045] The hydrogen concentration sensor 63 detects the hydrogen concentration in the atmospheric gas G flowing through the sampling line 11, and includes a measurement unit 63M and a preamplifier unit 63N. The measurement unit 63M is disposed in the sampling line 11, for example, downstream of the downstream gate valve 24 and upstream of the flow controller 18. The preamplifier unit 63N is housed within the shield 20 as described above.

[0046] The sensor switching line 62 is configured by arranging a pressure reducing valve 65 and an upstream gate valve 66 upstream of the measurement section 17M of the galvanic cell type oxygen concentration sensor 17, and a downstream gate valve 67 downstream. The sensor switching line 62 is provided in parallel with the upstream gate valve 23, pressure reducing valve 16, measurement section 61M of the magnetic wind type oxygen concentration sensor 61, and downstream gate valve 24 in the sampling line 11, and introduces atmospheric gas G flowing through the sampling line 11 when the magnetic wind type oxygen concentration sensor 61 is not in use, and allows the galvanic cell type oxygen concentration sensor 17 to detect the oxygen concentration in this atmospheric gas G.

[0047] Here, the magnetic wind type oxygen concentration sensor 61 on the sampling line 11 and the galvanic cell type oxygen concentration sensor 17 on the sensor switching line 62 are different types of oxygen concentration sensors with different measurement (detection) principles as described above. For this reason, the magnetic wind type oxygen concentration sensor 61 has a characteristic that the thermistor, which is the sensor element, deteriorates when exposed to hydrogen with a high concentration above a specified value. In contrast, the galvanic cell type oxygen concentration sensor 17 is not likely to deteriorate even when exposed to hydrogen with a concentration above a specified value, but the electrolyte and diaphragm of the measuring section 17M require replacement every 1 to 2 years depending on the oxygen measurement.

[0048] The control device 64 inputs a number of signals including an oxygen concentration signal from the preamplifier section 61N of the magnetic wind type oxygen concentration sensor 61 and the preamplifier section 17N of the galvanic battery type oxygen concentration sensor 17, and a hydrogen concentration signal from the preamplifier section 63N of the hydrogen concentration sensor 63, and controls various devices, such as the suction pump 15 and the exhaust pump 19, based on these signals to introduce the atmospheric gas G inside the reactor containment vessel 1 into the sampling line 11 and circulate it.

[0049] Furthermore, during normal operation of the reactor containment vessel 1 when the hydrogen concentration in the atmospheric gas G flowing through the sampling line 11 is below a predetermined value, the control device 64 opens the first changeover valve 21, the upstream gate valve 23, and the downstream gate valve 24, and closes the second changeover valve 22, the upstream gate valve 66, and the downstream gate valve 67. As a result, the control device 64 causes the atmospheric gas G to flow through the measuring section 61M of the magnetic wind type oxygen concentration sensor 61, setting it to an operating state, and causes the magnetic wind type oxygen concentration sensor 61 to detect the oxygen concentration in the atmospheric gas G flowing through the sampling line 11.

[0050] Furthermore, when the hydrogen concentration sensor 63 detects that the hydrogen concentration in the atmospheric gas G flowing through the sampling line 11 is equal to or higher than a specified value, or when a severe event occurs in the containment vessel 1 in which the hydrogen concentration becomes equal to or higher than a specified value, the control device 64 closes the first changeover valve 21 and opens the second changeover valve 22 for a fixed time. As a result, the control device 64 supplies nitrogen gas from the nitrogen gas cylinder 28 in the inert gas supply line 25 to the measuring unit 61M of the magnetic wind type oxygen concentration sensor 61 in the sampling line 11 for a fixed time. After supplying nitrogen gas to the measuring section 61M of this magnetic wind type oxygen concentration sensor 61 for a certain period of time, the control device 64 closes the second switching valve 22, the upstream gate valve 23, and the downstream gate valve 24, then opens the upstream gate valve 66 and the downstream gate valve 67, and then opens the first switching valve 21 to introduce atmospheric gas G into the sensor switching line 62, and switch the detection of the oxygen concentration in the atmospheric gas G from the magnetic wind type oxygen concentration sensor 61 to the galvanic battery type oxygen concentration sensor 17.

[0051] Next, a procedure for switching between the magnetic wind type oxygen concentration sensor 61 and the galvanic cell type oxygen concentration sensor 17 based on the control of the above-mentioned control device 64 will be described with reference to FIG. The first switching valve 21, the upstream gate valve 23, and the downstream gate valve 24 of the sampling line 11 are opened to detect the oxygen concentration of the atmospheric gas G flowing through the sampling line 11 by the magnetic wind type oxygen concentration sensor 61 (S31). In this state, the hydrogen concentration in the atmospheric gas G flowing through the sampling line 11 is detected by the hydrogen concentration sensor 63 (S32). If the hydrogen concentration in the atmospheric gas G flowing through the sampling line 11 detected by the hydrogen concentration sensor 63 is less than a specified value, steps S31 and S32 are continued (S33).

[0052] When the hydrogen concentration sensor 63 detects that the hydrogen concentration in the atmospheric gas G is above a specified value, or when a severe event occurs in the reactor containment vessel 1 in which the hydrogen concentration in the atmospheric gas G becomes above a specified value, the first switching valve 21 is closed to cut off the supply of atmospheric gas G to the measurement unit 61M of the magnetic wind type oxygen concentration sensor 61, and the second switching valve 22 is opened for a certain period of time to supply nitrogen gas from the nitrogen gas cylinder 28 in the inert gas supply line 25 to the measurement unit 61M of the magnetic wind type oxygen concentration sensor 61 via the sampling line 11 for a certain period of time (S34).

[0053] After nitrogen gas has been supplied to the measuring section 61M of the magnetic wind type oxygen concentration sensor 61 for a certain period of time, the second switching valve 22, the upstream gate valve 23, and the downstream gate valve 24 are closed (S35). Thereafter, the upstream gate valve 66 and the downstream gate valve 67 are opened, and further the first switching valve 21 is opened to introduce the atmospheric gas G in the sampling line 11 into the sensor switching line 62, and the oxygen concentration in the atmospheric gas G is detected by the galvanic cell type oxygen concentration sensor 17 of this sensor switching line 62, switching from the magnetic wind type oxygen concentration sensor 61 (S36).

[0054] As configured as above, the third embodiment provides the following advantages (3) to (5). (3) When the hydrogen concentration detected by the hydrogen concentration sensor 63 is equal to or exceeds a specified value or a severe event occurs that exceeds the specified value, and after nitrogen gas has been supplied from the nitrogen gas cylinder 28 of the inert gas supply line 25 for a certain period of time, the upstream gate valve 23 and downstream gate valve 24 for the measurement unit 61M of the magnetic wind type oxygen concentration sensor 61 are closed and the magnetic wind type oxygen concentration sensor 61 is switched to the galvanic cell type oxygen concentration sensor 17. As a result, the inside of the measurement unit 61M of the magnetic wind type oxygen concentration sensor 61 in the stopped state is maintained by replacing the atmospheric gas G, whose hydrogen concentration is equal to or exceeds the specified value, with nitrogen gas. As a result, the magnetic wind type oxygen concentration sensor 61 can avoid the risk of being exposed to high-concentration hydrogen gas and deteriorating.

[0055] (4) The magnetic wind type oxygen concentration sensor 61 is used during normal operation of the reactor containment vessel 1, and is switched to the galvanic cell type oxygen concentration sensor 17 when the hydrogen concentration in the atmospheric gas G of the reactor containment vessel 1 exceeds a specified value, or when a severe event occurs in which the hydrogen concentration exceeds the specified value. Therefore, the operating time of the galvanic cell type oxygen concentration sensor 17 is shortened, and the frequency of replacement can be reduced.

[0056] (5) During normal operation of the reactor containment vessel 1, the magnetic wind type oxygen concentration sensor 61 detects the oxygen concentration in the atmospheric gas G, and when the hydrogen concentration in the atmospheric gas G reaches or exceeds a specified value or when a severe event occurs in which the hydrogen concentration in the atmospheric gas G exceeds this specified value, the galvanic cell type oxygen concentration sensor 17 detects the oxygen concentration in the atmospheric gas G. Therefore, the oxygen concentration in the atmospheric gas G can be detected continuously without missing measurements.

[0057] [D] Fourth embodiment (FIGS. 8 and 9) 8 is a piping diagram showing the configuration of a facility atmosphere monitoring device according to the fourth embodiment. In the fourth embodiment, the same parts as those in the first and third embodiments are denoted by the same reference numerals as those in the first and third embodiments, and the description thereof will be simplified or omitted.

[0058] The fourth embodiment of the facility atmosphere monitoring device 70 differs from the third embodiment in that a sensor switching line 72 equipped with a magnetic oxygen concentration sensor 71 is provided in place of the sensor switching line 62, an auxiliary gas supply line 73 capable of supplying auxiliary gas J to the magnetic oxygen concentration sensor 71 is newly provided, a control device 74 is further provided, and the filter 14 is eliminated.

[0059] The sensor switching line 72 is arranged in parallel to the upstream gate valve 23, pressure reducing valve 16, measuring section 61M of the magnetic wind type oxygen concentration sensor 61, and downstream gate valve 24 in the sampling line 11, and when the magnetic wind type oxygen concentration sensor 61 is not in use, atmospheric gas G flowing through the sampling line 11 is introduced and the oxygen concentration in this atmospheric gas G is detected by the magnetic force type oxygen concentration sensor 71.

[0060] The magnetic force type oxygen concentration sensor 71 detects the oxygen concentration in the atmospheric gas G flowing in the sensor switching line 72, and includes a measurement unit 71M and a preamplifier unit 71N. The measurement unit 71M is disposed in the sensor switching line 72. In order to eliminate the effects of radiation, the preamplifier unit 71N is housed in the same lead shield 20 together with the preamplifier unit 61N of the magnetic wind type oxygen concentration sensor 61 and the preamplifier unit 63N of the hydrogen concentration sensor 63.

[0061] Although not shown, measuring unit 71M of magnetic force oxygen concentration sensor 71 causes auxiliary gas to flow into a flow path of oxygen-containing detection gas from two directions and applies a magnetic field to only one of the auxiliary gas inlets. Then, oxygen in the detection gas is attracted to the magnetic field and blocks one of the auxiliary gas inlets, and measuring unit 71M detects the oxygen concentration in the detection gas based on the pressure difference generated between the two auxiliary gas inlets.

[0062] Here, the magnetic wind type oxygen concentration sensor 61 on the sampling line 11 and the magnetic force type oxygen concentration sensor 71 on the sensor switching line 72 are different types of oxygen concentration sensors with different measurement (detection) principles. For this reason, the magnetic wind type oxygen concentration sensor 61 has the characteristic of deteriorating when exposed to hydrogen with a high concentration above a specified value, whereas the magnetic force type oxygen concentration sensor 71 is not likely to deteriorate even when exposed to hydrogen with a concentration above a specified value. However, the magnetic force type oxygen concentration sensor 71 requires an auxiliary gas J when detecting the oxygen concentration.

[0063] The auxiliary gas supply line 73 is equipped with a third switching valve 75, and its upstream end is connected between the pressure reducing valve 29 and the second switching line 22 of the inert gas supply line 25, and its downstream end is connected to the measurement unit 71M of the magnetic oxygen concentration sensor 71. When the third switching valve 75 is open, this auxiliary gas supply line 73 supplies nitrogen gas from the nitrogen gas cylinder 28 of the inert gas supply line 25 as auxiliary gas J to the measurement unit 71M of the magnetic oxygen concentration sensor 71.

[0064] The control device 74 has the functions of the control device 64 of the third embodiment, and in addition, after the second switching valve 22 of the inert gas supply line 25 is closed, it closes the upstream gate valve 23 and the downstream gate valve 24, and opens the first switching valve 21, the upstream gate valve 66, and the downstream gate valve 67 to supply the ambient gas G in the sampling line 11 to the measurement unit 71M of the magnetic force type oxygen concentration sensor 71. At this time, the control device 74 opens the third switching valve 75 to supply nitrogen gas from the nitrogen gas cylinder 28 of the inert gas supply line 25 as auxiliary gas J to the measurement unit 71M of the magnetic force type oxygen concentration sensor 71, and switches the magnetic force type oxygen concentration sensor 71 to detect the oxygen concentration in the ambient gas G by switching to the magnetic wind type oxygen concentration sensor 61.

[0065] Next, a procedure for switching between the magnetic wind type oxygen concentration sensor 61 and the magnetic force type oxygen concentration sensor 71 based on the control of the above-mentioned control device 74 will be described with reference to FIG. The first switching valve 21, the upstream gate valve 23, and the downstream gate valve 24 of the sampling line 11 are opened to detect the oxygen concentration of the atmospheric gas G flowing through the sampling line 11 by the magnetic wind type oxygen concentration sensor 61 (S41). In this state, the hydrogen concentration in the atmospheric gas G flowing through the sampling line 11 is detected by the hydrogen concentration sensor 63 (S42). If the hydrogen concentration in the atmospheric gas G flowing through the sampling line 11 detected by the hydrogen concentration sensor 63 is less than a specified value, steps S41 and S42 are continued (S43).

[0066] When the hydrogen concentration sensor 63 detects that the hydrogen concentration in the atmospheric gas G is above a specified value, or when a severe event occurs in the reactor containment vessel 1 in which the hydrogen concentration in the atmospheric gas G becomes above a specified value, the first switching valve 21 is closed to cut off the supply of atmospheric gas G to the measurement unit 61M of the magnetic wind type oxygen concentration sensor 61, and the second switching valve 22 is opened for a certain period of time to supply nitrogen gas from the nitrogen gas cylinder 28 in the inert gas supply line 25 to the measurement unit 61M of the magnetic wind type oxygen concentration sensor 61 via the sampling line 11 for a certain period of time (S44).

[0067] After nitrogen gas has been supplied to the measurement section 61M of the magnetic wind type oxygen concentration sensor 61 for a certain period of time, the second switching valve 22, the upstream gate valve 23, and the downstream gate valve 24 are closed (S45). Next, the upstream gate valve 66 and the downstream gate valve 67 of the sensor switching line 72 are opened, and further the third switching valve 75 of the auxiliary gas supply line 73 is opened to supply nitrogen gas from the nitrogen gas cylinder 28 of the inert gas supply line 25 as the auxiliary gas J to the measurement section 71M of the magnetic force type oxygen concentration sensor 71. Thereafter, the first switching valve 21 is opened to introduce the atmospheric gas G in the sampling line 11 into the sensor switching line 72, and the magnetic force type oxygen concentration sensor 71 of this sensor switching line 72 is switched from the magnetic wind type oxygen concentration sensor 61 to detect the oxygen concentration in the atmospheric gas G (S46).

[0068] As configured as above, the fourth embodiment provides the following effect (6) in addition to the effects (3) and (5) of the third embodiment.

[0069] (6) The magnetic wind type oxygen concentration sensor 61 is used during normal operation of the reactor containment vessel 1, and is switched to the magnetic force type oxygen concentration sensor 71 when the hydrogen concentration in the atmospheric gas G exceeds a specified value or when a severe event occurs in which the hydrogen concentration exceeds the specified value. Therefore, the operating period of the magnetic force type oxygen concentration sensor 71 is shortened, and the consumption of the auxiliary gas J required for the magnetic force type oxygen concentration sensor can be reduced.

[0070] Although several embodiments of the present invention have been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, changes, and combinations can be made without departing from the spirit of the invention. Furthermore, these substitutions, changes, and combinations are included in the scope and spirit of the invention, and are included in the scope of the invention and its equivalents described in the claims. [Explanation of symbols]

[0071] 1... reactor containment vessel (facility), 10... facility atmosphere monitoring device, 11... sampling line, 17... galvanic cell type oxygen concentration sensor, 21... first switching valve, 22... second switching valve, 23... upstream gate valve, 24... downstream gate valve, 25... inert gas supply line, 26... bypass line, 27... control device, 28... nitrogen gas cylinder, 30... bypass valve, 40... facility atmosphere monitoring device, 41... oxygen gas supply line, 42... control device, 43... nitrogen side switching valve, 44... oxygen gas cylinder, 46... oxygen side switching valve, 47... setting In-facility atmosphere monitoring device, 48...mixing device, 50...nitrogen gas mass flow controller, 53...oxygen gas mass flow controller, 60...facility atmosphere monitoring device, 61...magnetic wind type oxygen concentration sensor, 62...sensor switching line, 63...hydrogen concentration sensor, 64...control device, 66...upstream gate valve, 67...downstream gate valve, 70...facility atmosphere monitoring device, 71...magnetic force type oxygen concentration sensor, 72...sensor switching line, 73...auxiliary gas supply line, 74...control device, 75...third switching valve, G...atmospheric gas, J...auxiliary gas

Claims

1. A sampling line for sampling atmospheric gas within the facility; an oxygen concentration sensor disposed in the sampling line for detecting an oxygen concentration in the atmospheric gas flowing through the sampling line; an inert gas supply line connected to the sampling line upstream of the oxygen concentration sensor and capable of supplying an inert gas to the sampling line; a bypass line connected to the sampling line, bypassing the oxygen concentration sensor; a control device that supplies inert gas from the inert gas supply line through the sampling line to the oxygen concentration sensor for a certain period of time, and then supplies inert gas to the bypass line and closes the upstream and downstream sides of the oxygen concentration sensor to make the oxygen concentration sensor replaceable.

2. 2. The equipment for monitoring an atmosphere within a facility according to claim 1, wherein the oxygen concentration sensor is a galvanic cell type oxygen concentration sensor.

3. A sampling line for sampling atmospheric gas within the facility; a galvanic cell type oxygen concentration sensor disposed in the sampling line for detecting an oxygen concentration in the atmospheric gas flowing through the sampling line; an inert gas supply line connected to the upstream side of the galvanic cell type oxygen concentration sensor in the sampling line and capable of supplying an inert gas to the sampling line; an oxygen gas supply line connected to the upstream side of the galvanic cell type oxygen concentration sensor in the sampling line, capable of supplying a predetermined concentration of oxygen gas to the sampling line; a control device that controls the galvanic cell type oxygen concentration sensor to be calibrated by supplying inert gas from the inert gas supply line via the sampling line to the galvanic cell type oxygen concentration sensor for a certain period of time, and then supplying oxygen gas of a predetermined concentration from the oxygen gas supply line to the galvanic cell type oxygen concentration sensor.

4. 4. The equipment for monitoring an atmosphere inside a facility according to claim 3, wherein the predetermined concentration of the oxygen gas supplied through the oxygen gas supply line is variable.

5. A sampling line for sampling atmospheric gas within the facility; a magnetic wind type oxygen concentration sensor arranged in parallel with the sampling line for detecting the oxygen concentration in the atmospheric gas flowing through the sampling line, and an oxygen concentration sensor of a different type to the oxygen concentration sensor; a hydrogen concentration sensor disposed in the sampling line for detecting a hydrogen concentration in the atmospheric gas flowing through the sampling line; an inert gas supply line connected to the upstream side of each of the oxygen concentration sensors and the hydrogen concentration sensor in the sampling line, and capable of supplying an inert gas to the sampling line; an oxygen concentration sensor that detects the hydrogen concentration of a hydrogen gas contained in the hydrogen gas and detects the hydrogen concentration of the hydrogen gas contained in the hydrogen gas;

6. 6. The facility internal atmosphere monitoring device according to claim 5, wherein the different type of oxygen concentration sensor is a galvanic cell type oxygen concentration sensor.

7. The atmosphere monitoring device within a facility as described in claim 5, characterized in that the different type of oxygen concentration sensor is a magnetic force type oxygen concentration sensor, and is configured so that an inert gas from an inert gas supply line is supplied to this magnetic force type oxygen concentration sensor as an auxiliary gas.

8. 8. The facility internal atmosphere monitoring device according to claim 1, wherein the facility is a nuclear reactor containment vessel.

9. 1. A method for monitoring an oxygen concentration in an atmosphere in a facility, comprising: When replacing a galvanic cell type oxygen concentration sensor provided in a sampling line for sampling the atmospheric gas in the facility, cutting off the supply of atmospheric gas to the galvanic cell type oxygen concentration sensor; supplying an inert gas from an inert gas supply line connected to the sampling line to the galvanic cell type oxygen concentration sensor through the sampling line for a certain period of time; supplying an inert gas to a bypass line connected to the sampling line, bypassing the galvanic cell type oxygen concentration sensor, and closing the upstream side and downstream side of the galvanic cell type oxygen concentration sensor; and replacing the galvanic cell type oxygen concentration sensor.

10. 1. A method for monitoring an oxygen concentration in an atmosphere in a facility, comprising: The calibration of the galvanic cell type oxygen concentration sensor provided in the sampling line for sampling the atmospheric gas in the facility is performed by: cutting off the supply of atmospheric gas to the galvanic cell type oxygen concentration sensor; supplying an inert gas from an inert gas supply line connected to the sampling line to the galvanic cell type oxygen concentration sensor through the sampling line for a certain period of time; supplying oxygen gas of a predetermined concentration from an oxygen gas supply line connected to the sampling line to the galvanic cell type oxygen concentration sensor via the sampling line.

11. A method for monitoring an atmosphere in a facility, comprising: A magnetic wind type oxygen concentration sensor and a galvanic cell type oxygen concentration sensor are provided in parallel on a sampling line for sampling the atmospheric gas in the facility, When the hydrogen concentration in the atmospheric gas flowing through the sampling line is normally less than a specified value, a step of detecting the oxygen concentration in the atmospheric gas by the magnetic wind type oxygen concentration sensor is carried out; supplying inert gas from an inert gas supply line to the magnetic wind type oxygen concentration sensor through the sampling line for a certain period of time when the hydrogen concentration in the atmospheric gas flowing through the sampling line is equal to or greater than a specified value or when an event occurs in which the hydrogen concentration in the atmospheric gas flowing through the sampling line is equal to or greater than the specified value; after stopping the supply of the inert gas to the magnetic wind type oxygen concentration sensor, closing the upstream side and the downstream side of the magnetic wind type oxygen concentration sensor; and after closing the upstream and downstream sides of the magnetic wind type oxygen concentration sensor, switching to the galvanic battery type oxygen concentration sensor to detect the oxygen concentration in the ambient gas flowing through the sampling line.

12. A method for monitoring an atmosphere in a facility, comprising: A magnetic wind type oxygen concentration sensor and a magnetic force type oxygen concentration sensor are provided in parallel on a sampling line for sampling the atmospheric gas in the facility, When the hydrogen concentration in the atmospheric gas flowing through the sampling line is normally less than a specified value, a step of detecting the oxygen concentration in the atmospheric gas by the magnetic wind type oxygen concentration sensor is carried out; supplying inert gas from an inert gas supply line to the magnetic wind type oxygen concentration sensor through the sampling line for a certain period of time when the hydrogen concentration in the atmospheric gas flowing through the sampling line is equal to or greater than a specified value or when an event occurs in which the hydrogen concentration in the atmospheric gas flowing through the sampling line is equal to or greater than the specified value; after stopping the supply of the inert gas to the magnetic wind type oxygen concentration sensor, closing the upstream side and the downstream side of the magnetic wind type oxygen concentration sensor; and after closing the upstream and downstream sides of the magnetic wind type oxygen concentration sensor, supplying inert gas from the inert gas supply line to the magnetic force type oxygen concentration sensor as an auxiliary gas while switching to the magnetic force type oxygen concentration sensor to detect the oxygen concentration in the ambient gas flowing through the sampling line.

13. The method for monitoring an atmosphere inside a facility according to any one of claims 9 to 12, wherein the facility is a nuclear reactor containment vessel.

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