JP6825992B2 - Oxygen measurement method in the reactor containment vessel - Google Patents

Description

Embodiments of the present invention relates to a nuclear reactor containment vessel oximetry method.

The power reactor facility has equipment to ensure the safety of the reactor and related facilities in the event of a severe accident, and has a mechanism to grasp the situation of the accident and take measures to resolve it.

In particular, the gas phase state in the reactor containment vessel is important information for detecting abnormalities during normal operation and grasping the situation at the time of a severe accident, and constant monitoring is required.

In a conventional reactor facility, hydrogen and oxygen concentrations in the gas phase are measured by a containment vessel atmosphere monitor. The equipment is installed outside the containment vessel, and the gas phase inside the containment vessel is transferred to the equipment by a blower, and the humidity, temperature, pressure, etc. are adjusted and measured using a cooler or the like. ing.

Japanese Unexamined Patent Publication No. 2016-532079 JP-A-2015-125138 Japanese Unexamined Patent Publication No. 60-042690

However, as the severe accident at the Fukushima Daiichi Nuclear Power Station caused by the Great East Japan Earthquake occurred, it has become clear that the existing facilities alone cannot take sufficient measures to deal with the severe accident. In a conventional nuclear reactor facility, if the AC power supply is lost in the event of a severe accident, the containment vessel atmosphere monitor cannot be operated, and continuous monitoring cannot be achieved at present. In particular, in the severe accident at the Fukushima Daiichi Nuclear Power Station, a hydrogen explosion caused by the reaction of hydrogen and oxygen has caused an event that damages the reactor facilities, and it is important to monitor the gas phase concentration to prevent the hydrogen explosion.

Therefore, there is a demand for a system for measuring the gas phase composition at the time of a severe accident without performing adjustments such as transfer of gas requiring an AC power source, dehumidification, cooling, and step-down.

In particular, oxygen coexists with hydrogen to cause combustion and explosion, so its concentration measurement is an important position in accident management.

As a prior art for dealing with such a situation, a method of measuring the oxygen concentration from the combustion reaction of hydrogen and oxygen has been proposed. When such a technique was used, it was possible to measure the oxygen concentration in the presence of hydrogen, but it was not possible to measure it in an environment where hydrogen did not coexist.

In addition, it is desirable to calibrate the oxygen sensor regularly, but when it is installed in the reactor containment vessel, which has a complicated shape, it is difficult to route the piping for supplying the calibration gas to the oxygen sensor from the viewpoint of installation space. is there.

An object to be solved by the embodiment of the present invention is to make it possible to measure the oxygen concentration or the oxygen partial pressure in the reactor containment vessel when the AC power source is lost.

According to one aspect of the present invention, the method for measuring oxygen in the containment vessel is to use a blower through an air supply pipe connected to a sample gas take-out portion of the containment vessel to use a blower in the containment vessel. The sample gas is taken out, passed through an oxygen measuring device outside the containment vessel arranged outside the containment vessel, and the sample gas after passing through the oxygen measuring device outside the containment vessel is used as a sample of the reactor containment vessel. Sample gas oxygen partial pressure for measuring the oxygen partial pressure of the sample gas taken out through the air supply pipe by the sample gas circulation step of returning to the inside of the reactor containment vessel through the gas return unit and the oxygen measuring device outside the containment vessel. A measurement step, an oxygen partial pressure measurement step in the containment vessel for measuring the oxygen partial pressure in the reactor containment vessel by an oxygen measuring device in the containment vessel arranged in the reactor containment vessel, and a sample gas oxygen partial pressure. Having a modification step of modifying the oxygen partial pressure in the reactor containment vessel obtained from the containment vessel oxygen partial pressure measurement step based on the oxygen partial pressure of the sample gas obtained from the measurement step. It is characterized by.

According to another aspect of the present invention, the method for measuring oxygen in the containment vessel is described by the step of carrying the portable oxygen measuring device into the containment vessel and the step of carrying in the portable oxygen measuring device. Based on the portable oxygen partial pressure measurement step for measuring the oxygen partial pressure in the containment vessel and the output of the oxygen measurement device in the containment vessel fixed in the reactor containment vessel, the inside of the reactor containment vessel. From the fixed oxygen partial pressure measurement step based on the fixed oxygen partial pressure measurement step for measuring the oxygen partial pressure and the oxygen partial pressure in the reactor containment vessel obtained from the portable oxygen partial pressure measurement step. It is characterized by having a modification step for modifying the oxygen partial pressure in the obtained containment vessel.

According to the embodiment of the present invention, the oxygen concentration or oxygen partial pressure in the reactor containment vessel can be measured at the time of loss of AC power supply without major remodeling work on the existing reactor facility.

It is a schematic vertical sectional view which shows one Embodiment of the nuclear reactor facility which concerns on this invention. It is a graph which shows an example of the characteristic of the critical current type oxygen sensor which can be used in one Embodiment of the nuclear reactor facility which concerns on this invention, and is the graph which shows the relationship between oxygen partial pressure and output voltage. It is a flow chart which shows the procedure of 1st Embodiment of the oxygen measurement method in a reactor containment vessel which concerns on this invention. It is a flow chart which shows the procedure of the 2nd Embodiment of the oxygen measurement method in a reactor containment vessel which concerns on this invention.

Hereinafter, embodiments will be described with reference to the drawings. Here, the same or similar parts are designated by a common reference numeral, and duplicate description will be omitted.

[First Embodiment]
FIG. 1 is a schematic vertical sectional view showing an embodiment of a nuclear reactor facility according to the present invention. Here, a boiling water reactor is shown as an example of a nuclear reactor facility. The reactor containment vessel 12 is housed inside the reactor building 11, and the reactor pressure vessel 13 containing nuclear fuel is installed in the reactor containment vessel 12. The reactor containment vessel 12 is divided into a dry well 21 and a wet well 22, and the reactor pressure vessel 13 is arranged in the dry well 21.

A containment vessel atmosphere monitor 14 is installed outside the reactor containment vessel 12 in order to constantly analyze and monitor the atmosphere composition of the dry well 21 and the wet well 22. A dry well gas phase air supply pipe (air supply pipe) 41 for sending gas in the gas phase portion from the dry well 21 to the storage container atmosphere monitor 14 is connected, and the wet well 22 connects the vapor phase portion to the storage container atmosphere monitor 14. A wet well gas phase air supply pipe (air supply pipe) 42 for sending gas is connected. Further, a return pipe 43 for returning the gas measured by the containment vessel atmosphere monitor 14 to the dry well 21 is connected.

The containment vessel atmosphere monitor 14 includes a blower 31, a cooler (heat exchanger) 32, and an oxygen concentration detector (oxygen measuring device outside the containment vessel) 33. The gas sent from the dry well gas phase air supply pipe 41 and the wet well gas phase air supply pipe 42 is boosted by the blower 31, cooled by the cooler 32, and then sent to the oxygen concentration detector 33. The gas discharged from the oxygen concentration detector 33 is returned to the dry well 21 (reactor containment vessel 12) through the return pipe 43.

Since the oxygen concentration detector 33 included in the containment vessel atmosphere monitor 14 is installed outside the reactor containment vessel 12, calibration can be appropriately performed during periodic inspections or normal operation of the reactor.

A pressure gauge 35 is installed in the reactor containment vessel 12. Although FIG. 1 shows an example in which the pressure gauge 35 is installed in the dry well 21, the pressure gauge may be installed in both the dry well 21 and the wet well 22. Further, a pressure gauge may be installed in the containment vessel atmosphere monitor 14.

The dry well gas phase air supply pipe 41 and the wet well gas phase air supply pipe 42 are connected to the reactor containment vessel 12, that is, in the reactor containment vessel 12 in the vicinity of the sample gas extraction units 36 and 37. , The containment vessel oxygen sensors (containment vessel oxygen measuring instruments) 15a and 15b are arranged. Further, the oxygen sensor 15c in the containment vessel (oxygen measuring device in the containment vessel) is located in the reactor containment vessel 12 where the return pipe 43 is connected to the reactor containment vessel 12, that is, in the vicinity of the sample gas return unit 38. Is placed.

In addition, instruments such as pipes and pressure gauges, electric wires for extracting their signals (not shown), and equipment for responding to a severe accident (not shown) are arranged.

The oxygen sensors 15a, 15b, and 15c in the containment vessel are, for example, a limit current type using a solid oxide fuel cell.

The atmosphere inside the reactor containment vessel 12 at the time of a severe accident can be a temperature of about 300 ° C., a pressure of 1 MPa or less, a high dose atmosphere, and a steam atmosphere equivalent to saturated vapor pressure due to damage to the reactor pressure vessel 13. In addition, depending on the degree of severe accident and the progress, there is a possibility that incidental equipment will not function due to the loss of AC power.

By the way, the limit current type oxygen sensor selectively transmits oxygen ions by applying a voltage to a solid oxide type oxygen ion conductor such as Itria stabilized zirconia using an electrode made of a metal or a metal oxide. The oxygen partial pressure is measured by measuring the current value associated with the ion permeation. In order to make the solid oxide oxygen ion conductor function, the solid oxide oxygen ion conductor portion is used by heating it to about 300 to 800 ° C. Therefore, it is possible to maintain the function even when the gas phase at the temperature assumed at the time of a severe accident flows into the critical current type oxygen sensor.

Further, the configuration of the critical current type oxygen sensor has a structure in which there is no closed portion that causes a pressure difference from the external pressure, and the structure is destroyed even when the pressure in the reactor containment vessel 12 rises. There is no such thing.

In addition, the faradaic current oxygen sensor can be composed of an inorganic substance, and its function can be maintained even in a high-dose atmosphere at the time of a severe accident.

Since the limit current type oxygen sensor causes electrolysis of water depending on the applied voltage, it is desirable to use the sensor at a potential below the potential at which water electrolysis occurs when it is used in the reactor containment vessel 12. Since the electrolysis temperature of water depends on the solid oxide oxygen ion conductor and the electrode temperature, the recommended operating potential cannot be unconditionally defined, but it is 2.0 V or less with respect to the potential of the standard hydrogen electrode. It is desirable to operate at potential. In principle, the faradaic current oxygen sensor operates only with a DC power supply, is installed directly inside the reactor containment vessel, and does not perform pretreatment of the gas phase that requires an AC power supply such as cooling and dehumidification. It can operate even in an environment where power is lost.

As described above, the critical current type oxygen sensor can respond to the atmosphere inside the reactor containment vessel 12 at the time of a severe accident by operating within the predetermined operating conditions, and the oxygen sensors 15a and 15b in the containment vessel can be used. , 15c can be used.

The characteristics of the faradaic current oxygen sensor using the solid oxide oxygen ion conductor will be described with reference to FIG. FIG. 2 is a graph showing an example of the characteristics of the critical current type oxygen sensor that can be used in one embodiment of the nuclear reactor facility according to the present invention, and is a graph showing the relationship between the oxygen partial pressure and the output voltage. As shown in FIG. 2, the critical current type oxygen sensor exhibits a behavior in which the response current linearly increases according to the oxygen partial pressure. By acquiring the response straight line according to the oxygen partial pressure in advance, one-point calibration or two-point calibration in an atmosphere with a known oxygen concentration is possible.

Since the characteristics of the oxygen sensors 15a, 15b, and 15c in the containment vessel may change due to irradiation and the passage of time, it is necessary to appropriately calibrate after installation. However, since these sensors are installed inside the reactor containment vessel 12, it is difficult to take the sensors out of the reactor containment vessel 12 and perform calibration work. Therefore, in this embodiment, measurement is performed using the containment vessel atmosphere monitor 14 with a gas substantially equivalent to the measurement target of the containment vessel oxygen sensors 15a, 15b, 15c as the measurement target, and the containment vessel oxygen sensors 15a, 15b, Calibrate 15c. Since the containment vessel atmosphere monitor 14 is arranged outside the reactor containment vessel 12, detailed description thereof will be omitted, but calibration can be performed as appropriate.

According to the present embodiment, during normal operation and periodic inspection of the reactor, the oxygen concentration or oxygen content of the gas in the containment vessel 12 is determined by the containment vessel atmosphere monitor 14 and the oxygen sensors 15a, 15b, 15c in the containment vessel. The pressure can be measured. Further, since the gas in the reactor containment vessel 12 at the positions corresponding to each other is measured by the containment vessel atmosphere monitor 14 and the containment vessel oxygen sensors 15a, 15b, 15c, the containment vessel oxygen sensors 15a, 15b, 15c Can be calibrated by the output of the containment atmosphere monitor 14. Further, even if the gas in the reactor containment vessel 12 cannot be measured by the containment vessel atmosphere monitor 14 in the event of a power loss accident, the gas in the reactor containment vessel 12 by the oxygen sensors 15a, 15b, 15c in the containment vessel The oxygen partial pressure can be measured.

Moreover, by using the existing containment vessel atmosphere monitor 14, dry well gas phase air supply pipe 41, wet well gas phase air supply pipe 42, and return pipe 43, oxygen sensors 15a, 15b, 15c in the containment vessel are newly used. It can be realized just by adding.

FIG. 3 is a flow chart showing the procedure of the first embodiment of the oxygen measurement method in the reactor containment vessel according to the present invention.

With the configuration shown in FIG. 1, first, the blower 31 is driven to circulate the gas (sample gas) in the reactor containment vessel 12 (step S11). That is, the gas in the reactor containment vessel 12 is sent to the containment vessel atmosphere monitor 14 through the drywell gas phase air supply pipe 41 and the wetwell gas phase air supply pipe 42. The sample gas exiting the blower 31 in the containment vessel atmosphere monitor 14 is cooled by the cooler 32 and then sent to the oxygen concentration detector 33. The sample gas that has passed through the oxygen concentration detector 33 is returned to the reactor containment vessel 12 through the return pipe 43.

Next, the oxygen concentration of the sample gas is detected by the oxygen concentration detector 33 in the containment vessel atmosphere monitor 14 (step S12). At the same time, the pressure in the reactor containment vessel 12 is measured by the pressure gauge 35 (step S13). This pressure may be measured by a pressure gauge (not shown) in the containment atmosphere monitor 14.

Next, the oxygen partial pressure in the reactor containment vessel 12 is calculated based on the oxygen concentration indicated value obtained from the containment vessel atmosphere monitor 14 and the pressure measurement result obtained from the pressure gauge in the reactor containment vessel 12. (1st oxygen partial pressure calculation step S14).

On the other hand, the output currents of the oxygen sensors 15a, 15b, and 15c in the containment vessel are detected (step S15). Next, the oxygen partial pressure in the reactor containment vessel 12 is calculated based on the output currents of the oxygen sensors 15a, 15b, and 15c in the containment vessel (second oxygen partial pressure calculation step S16).

Next, the result of the first oxygen partial pressure calculation step S14 is compared with the result of the second oxygen partial pressure calculation step S16 (step S17), and when these results do not match within a predetermined range (in step S17). In the case of No), the current values of the oxygen sensors 15a, 15b, and 15c in the containment vessel are calibrated (step S18). That is, the conversion formula for calculating the oxygen partial pressure from the output currents of the oxygen sensors 15a, 15b, and 15c in the containment vessel is adjusted.

In step S17, if the result of the first oxygen partial pressure calculation step S14 and the result of the second oxygen partial pressure calculation step S16 match within a predetermined range (yes in step S17), the calibration is completed.

By adopting this embodiment, the inside of the containment vessel 12 is not newly installed with piping or equipment for calibrating the oxygen sensors 15a, 15b, 15c in the containment vessel, and even during the normal operation of the reactor. The health of the oxygen sensor can be confirmed and calibrated.

[Second Embodiment]
FIG. 4 is a flow chart showing the procedure of the second embodiment of the oxygen measurement method in the reactor containment vessel according to the present invention.

In this second embodiment, the oxygen sensors 15a, 15b, and 15c in the containment vessel are installed in the reactor containment vessel 12 as in the first embodiment described above. The oxygen sensors 15a, 15b, and 15c in the containment vessel are, for example, a limit current type using a solid oxide fuel cell. As a result, the oxygen concentration in the reactor containment vessel 12 can be measured even in the event of a power loss accident.

In the first embodiment, the data of the containment vessel atmosphere monitor 14 is used for calibrating the containment oxygen sensors 15a, 15b, 15c, but in the second embodiment, for the calibration of the containment oxygen sensor 15. The difference is that the data from the portable oxygen sensor (not shown) is used.

It is assumed that the oxygen sensors 15a, 15b, and 15c in the containment vessel are fixedly installed in the reactor containment vessel 12 in advance. The oxygen sensors 15a, 15b, and 15c in the containment vessel are calibrated, for example, at the time of periodic inspection when the reactor is stopped. As shown in FIG. 4, during the periodic inspection, the portable oxygen sensor is carried into the vicinity of the oxygen sensors 15a, 15b, and 15c in the containment vessel 12 in the reactor containment vessel 12 and temporarily installed (step S21). At this time, a portable pressure gauge (not shown) may be carried in the vicinity of the portable oxygen sensor together with the portable oxygen sensor and temporarily installed.

Next, the oxygen concentration at that position is detected by the portable oxygen sensor carried into the reactor containment vessel 12 (step S22). At this time, the pressure in the reactor containment vessel 12 is measured by an existing pressure gauge or a portable pressure gauge carried in at this time (step S23).

Next, the oxygen partial pressure at that position is calculated based on the oxygen concentration obtained in step S22 and the pressure obtained in step S23 (first oxygen partial pressure calculation step S24).

On the other hand, similarly to step S15 of the first embodiment, the output currents of the oxygen sensors 15a, 15b, and 15c in the containment vessel are detected (step S25). Next, as in step S16 of the first embodiment, the oxygen partial pressure in the reactor containment vessel 12 is calculated based on the output currents of the oxygen sensors 15a, 15b, and 15c in the containment vessel (second oxygen). Pressure division calculation step S26).

Next, the result of the first oxygen partial pressure calculation step S24 is compared with the result of the second oxygen partial pressure calculation step S26 (step S27), and when these results do not match within a predetermined range (in step S27). In the case of No), the current values of the oxygen sensors 15a, 15b, and 15c in the containment vessel are calibrated (step S28). That is, the conversion formula for calculating the oxygen partial pressure from the output currents of the oxygen sensors 15a, 15b, and 15c in the containment vessel is adjusted.

In step S27, if the result of the first oxygen partial pressure calculation step S24 and the result of the second oxygen partial pressure calculation step S26 match within a predetermined range (if Yes in step S27), the calibration is completed.

By adopting this second embodiment, the oxygen sensor 15 in the containment vessel 12 is sound without laying piping for calibration or newly installing equipment for calibrating the oxygen sensors 15a, 15b, 15c in the containment vessel 12. It is possible to confirm the sex and calibrate.

[Other Embodiments]
The above embodiments are presented as examples and are not intended to limit the scope of the invention. This novel embodiment can be implemented in various other embodiments, and various omissions, replacements, and changes can be made without departing from the gist of the invention. This embodiment and its modifications are included in the scope and gist of the invention, and are also included in the scope of the invention described in the claims and the equivalent scope thereof.

11 ... Reactor building, 12 ... Reactor containment vessel, 13 ... Reactor pressure vessel, 14 ... Containment vessel atmosphere monitor, 15a, 15b, 15c ... Containment vessel oxygen sensor (containment vessel oxygen measuring instrument), 21 ... Dry Well, 22 ... Wet well, 31 ... Blower, 32 ... Cooler (heat exchanger), 33 ... Oxygen concentration detector (Oxygen measuring device outside containment vessel), 35 ... Pressure gauge, 36, 37 ... Sample gas extraction unit, 38 ... Sample gas return section, 41 ... Drywell gas phase air supply pipe (air supply pipe), 42 ... Wetwell gas phase air supply pipe (air supply pipe), 43 ... Return pipe

Claims (5)

Using a blower, the sample gas in the containment vessel is taken out through the air supply pipe connected to the sample gas take-out portion of the containment vessel, and the outside of the containment vessel arranged outside the containment vessel is taken out. A sample gas circulation step of passing the sample gas through the oxygen measuring device and returning the sample gas after passing through the oxygen measuring device outside the containment vessel to the inside of the reactor containment vessel through the sample gas return unit of the reactor containment vessel.
A sample gas oxygen partial pressure measurement step for measuring the oxygen partial pressure of the sample gas taken out through the air supply pipe by the oxygen measuring device outside the storage container, and
An oxygen partial pressure measurement step in the containment vessel for measuring the oxygen partial pressure in the reactor containment vessel by an oxygen measuring device in the containment vessel arranged in the containment vessel.
Modification to modify the oxygen partial pressure in the reactor containment vessel obtained from the containment oxygen partial pressure measurement step based on the oxygen partial pressure of the sample gas obtained from the sample gas oxygen partial pressure measurement step. Steps and
A method for measuring oxygen in a reactor containment vessel, which comprises. The containment vessel oxygen measuring device includes an oxygen concentration measuring device.
The sample gas oxygen partial pressure measurement step
An oxygen concentration measuring step of measuring the oxygen concentration of the sample gas by the oxygen measuring device outside the containment vessel,
A pressure measurement step for measuring the pressure inside the reactor containment vessel, and
A first oxygen partial pressure calculation step for calculating the oxygen partial pressure based on the oxygen concentration obtained from the oxygen concentration measurement step and the pressure in the reactor containment vessel obtained from the pressure measurement step.
Including
The containment oxygen measuring instrument includes an oxygen sensor that outputs an output current corresponding to the oxygen partial pressure in the reactor containment vessel.
The step of measuring the partial pressure of oxygen in the containment vessel is
Including a second oxygen partial pressure calculation step of calculating the oxygen partial pressure in the reactor containment vessel based on the output current of the oxygen sensor.
The method for measuring oxygen in a reactor containment vessel according to claim 1. A measuring instrument loading step for loading a portable oxygen measuring instrument into the reactor containment vessel,
A portable oxygen partial pressure measuring step for measuring the oxygen partial pressure in the reactor containment vessel by the portable oxygen measuring device, and a portable oxygen partial pressure measuring step.
A fixed oxygen partial pressure measuring step for measuring the oxygen partial pressure in the reactor containment vessel based on the output of the oxygen measuring device in the containment vessel fixed in the reactor containment vessel.
Based on the oxygen partial pressure in the reactor containment vessel obtained from the portable oxygen partial pressure measurement step, the oxygen partial pressure in the reactor containment vessel obtained from the fixed oxygen partial pressure measurement step is modified. Correction steps to be done and
A method for measuring oxygen in a reactor containment vessel, which comprises. The portable oxygen measuring device includes an oxygen concentration measuring device.
The portable oxygen partial pressure measurement step
An oxygen concentration measuring step of measuring the oxygen concentration in the reactor containment vessel by the portable oxygen measuring device, and
A pressure measurement step for measuring the pressure inside the reactor containment vessel, and
A first oxygen partial pressure calculation step for calculating the oxygen partial pressure based on the oxygen concentration obtained from the oxygen concentration measurement step and the pressure in the reactor containment vessel obtained from the pressure measurement step.
Including
The containment oxygen measuring instrument includes an oxygen sensor that outputs an output current corresponding to the oxygen partial pressure in the reactor containment vessel.
The fixed oxygen partial pressure measurement step
Including a second oxygen partial pressure calculation step of calculating the oxygen partial pressure in the reactor containment vessel based on the output current of the oxygen sensor.
The method for measuring oxygen in a reactor containment vessel according to claim 3. The reactor according to any one of claims 1 to 4, wherein the containment oxygen measuring instrument includes a critical current type oxygen sensor using a solid oxide type oxygen ion conductor. Oxygen measurement method in the containment vessel.

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