JP2019132685A - Oxygen measurement device for storage container and oxygen sensor thereof - Google Patents

Abstract

To allow a measurement of the concentration of oxygen regardless of the presence or absence of hydrogen in a nuclear reactor storage container.SOLUTION: According to an embodiment, an oxygen sensor 12 includes: a barrier film 15 of a solid electrolyte which presents an oxygen ion conductivity at a temperature of 525°C or less; and a pair of electrodes 16, 17 set on the barrier film 15 across the barrier film 15. The oxygen sensor is set in the nuclear reactor storage container 11 and measures the concentration of oxygen in the measurement target gas within the nuclear reactor storage container 11. The electrodes 16, 17 include a material of which heat of generation per an oxygen atom in the metal oxide is 80 kJ at highest or 150 kJ at lowest. The oxygen sensor 12 may be a limiting current oxygen sensor or a contrasting density oxygen sensor.SELECTED DRAWING: Figure 1

Description

  Embodiments described herein relate generally to a reactor containment vessel oxygen measuring device and an oxygen sensor used therefor.

  The nuclear power generation facility has equipment for ensuring the safety of the nuclear reactor and the facility in the event of a severe accident, and has a mechanism for grasping the situation of the accident and taking measures for convergence. In particular, in the severe accident at the Fukushima Daiichi Nuclear Power Station following the Great East Japan Earthquake, there was an event that damaged the reactor facility due to a hydrogen explosion caused by the reaction of hydrogen and oxygen, and gas phase concentration monitoring was required to prevent hydrogen explosions. It has been.

  In a conventional nuclear 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, the gas phase inside the containment vessel is transferred to the equipment by a blower, and humidity, temperature, pressure, etc. are adjusted and measured using a cooler. ing.

Japanese Patent Laying-Open No. 2006-532079 JP2015-125138A

Masaaki Kasuga, “Combustion Catalyst of Hydrogen and Carbon Monoxide”, Catalyst, 1987, Vol. 29, No. 4, p. 299-304

  However, as is clear from the fact that a severe accident occurred at the Fukushima Daiichi Nuclear Power Station, the existing facilities alone cannot take sufficient measures to respond to the severe accident. In a conventional nuclear reactor facility, when AC power is lost when a severe accident occurs, the containment vessel atmosphere monitor cannot be operated, and at present, constant monitoring cannot be achieved. In particular, in severe accidents at the Fukushima Daiichi Nuclear Power Station, an event that damages the reactor facility due to a hydrogen explosion caused by the reaction of hydrogen and oxygen has occurred, and it is important to monitor the gas phase concentration to prevent hydrogen explosions.

  Therefore, there is a need for a system that directly measures the gas phase composition in the containment vessel at the time of a severe accident without adjusting gas transfer, dehumidification, cooling, pressure reduction, or the like that requires an AC power supply. In particular, because oxygen coexists with hydrogen, it can cause combustion and explosion, and can cause events that have a major impact on the integrity of the containment vessel, so its measurement is an important part of accident management.

  However, in the current system, the measurement is performed only by the containment vessel atmosphere monitor that samples the gas inside the containment vessel with a blower from the inside of the containment vessel, and cannot be measured when the AC power source is lost.

  As a technique for coping with such a situation, a method of measuring the oxygen concentration from a combustion reaction of hydrogen and oxygen has been studied. However, when a known technique is used, measurement cannot be performed in an environment where hydrogen does not coexist, and even when hydrogen is present, an accurate oxygen concentration cannot be converted unless the hydrogen concentration is known. In addition, the combustion reaction of hydrogen and oxygen was used for the measurement, and the risk of hydrogen explosion starting from the measurement part could not be denied.

  The problem to be solved by the embodiment of the present invention is to make it possible to measure the oxygen concentration regardless of the presence or absence of hydrogen in the reactor containment vessel.

  In order to solve the above-described problem, an oxygen measuring device for a containment vessel according to an embodiment is provided in a reactor containment vessel, and includes a diaphragm containing a solid electrolyte having oxygen ion conductivity at 525 ° C. or less and the diaphragm. An oxygen sensor having a pair of electrodes disposed on the diaphragm so as to face each other, wherein the electrode includes a material having a heat of formation of 80 kJ or less or 150 kJ or more per oxygen atom in the metal oxide .

  Further, in order to solve the above-described problem, the oxygen measuring device for a containment vessel according to the embodiment is provided in the reactor containment vessel, and is disposed on the diaphragm so as to face the diaphragm across the diaphragm. An oxygen sensor comprising a pair of electrodes, wherein the diaphragm contains at least one of yttria-stabilized zirconia, scandia-stabilized zirconia, lanthanum strontium gallate and gadolinium-doped ceria, wherein the electrodes are gold, silver And at least one of copper, nickel and carbon.

  In addition, the oxygen sensor according to the embodiment is disposed on the diaphragm so as to be opposed to the diaphragm containing a solid electrolyte having oxygen ion conductivity at 525 ° C. or less provided in the reactor containment vessel. A pair of electrodes, the electrodes including a material having a heat of formation of 80 kJ or less or 150 kJ or more per oxygen atom in the metal oxide.

  The oxygen sensor according to the embodiment includes a diaphragm and a pair of electrodes disposed on the diaphragm so as to face each other with the diaphragm interposed therebetween, and the diaphragm includes: The electrode contains at least one of yttria stabilized zirconia, scandia stabilized zirconia, lanthanum strontium gallate and gadolinium doped ceria, and the electrode contains at least one of gold, silver, copper, nickel and carbon.

  According to the embodiment of the present invention, the oxygen concentration can be measured regardless of the presence or absence of hydrogen in the reactor containment vessel.

It is a typical lineblock diagram showing a 1st embodiment of an oxygen measuring device for containment vessels concerning the present invention. It is a typical elevation sectional view of a boiling water nuclear facility which shows the installation situation of a 1st embodiment of the oxygen measuring device for containment vessels concerning the present invention. It is a figure for demonstrating the effect of the oxygen measuring device for containment vessels which concerns on embodiment of this invention, Comprising: It is a graph which shows the relationship between the production | generation heat | fever per metal oxide oxygen atom, and hydrogen oxidation activity. It is a graph which shows an example of the characteristic of 1st Embodiment of the oxygen measuring device for containment vessels which concerns on this invention, Comprising: It is a graph which shows the relationship between oxygen partial pressure and output current. It is a typical block diagram which shows 2nd Embodiment of the oxygen measuring device for containment vessels which concerns on this invention.

  Hereinafter, embodiments will be described with reference to the drawings. Here, the same or similar parts are denoted by common reference numerals, and redundant description is omitted.

[First Embodiment]
FIG. 1 is a schematic configuration diagram showing a first embodiment of an oxygen measuring device for a containment vessel according to the present invention. FIG. 2 is a schematic sectional elevation view of the boiling water nuclear facility showing the installation state of the containment vessel oxygen measuring device of the first embodiment.

  The oxygen measuring device for a containment vessel (oxygen measuring device) of the first embodiment has substantially the same configuration as a generally known limit current type oxygen measuring device, and is an oxygen measuring device using oxygen pumping. is there.

  This oxygen measuring device includes an oxygen sensor (container oxygen sensor) 12 installed in the reactor containment vessel 11 and a control / monitoring device installed in a control room (not shown) outside the reactor containment vessel 11. Part 13.

  As shown in FIG. 2, in the boiling water nuclear facility, the reactor containment vessel 11 has a dry well 40 and a wet well 41. The dry well 40 and the wet well 41 are connected by a vent pipe 42. A reactor pressure vessel 43 is arranged in the dry well 40. A pressure suppression pool 44 is accommodated in the wet well 41.

  The oxygen sensors 12 are preferably arranged at a plurality of locations in the reactor containment vessel 11. When hydrogen is generated in the reactor containment vessel 11, since hydrogen has a small specific gravity, the hydrogen is likely to accumulate in the upper portions of the dry well 40 and the wet well 41. Therefore, it is preferable to dispose the oxygen sensor 12 at least above each of the dry well 40 and the wet well 41 in order to predict the reaction between hydrogen and oxygen. More specifically, the oxygen sensor 12 is preferably disposed at a position above the reactor pressure vessel 43 in the dry well 40 and at a position above the pressure suppression pool 44 in the wet well 41.

  As shown in FIG. 1, the oxygen sensor 12 includes an oxygen ion conductive diaphragm 15, a positive electrode (electrode) 16 and a negative electrode (electrode) 17 disposed in contact with the diaphragm 15 across the diaphragm 15, And a laboratory cover 18 arranged to cover the negative electrode 17.

  The examination room cover 18 forms a gas examination room 20 together with the diaphragm 15 and the negative electrode 17. The positive electrode 16 is outside the gas inspection chamber 20. A diffusion hole 21 is formed in the examination room cover 18. The diffusion hole 21 allows the measurement target gas G in the reactor containment vessel 11 to flow into the gas inspection chamber 20 by diffusion, and a hole having a small diameter or a porous material is used.

  The control / monitoring unit 13 includes a DC power supply 25 with adjustable voltage, an ammeter 26, and a voltmeter 27. The positive side of the DC power supply 25 is connected to the positive electrode 16 by a lead wire 30, and the negative side of the DC power supply 25 is connected to the negative electrode 17 by a lead wire 31. The lead wires 30 and 31 extend through the wall of the reactor containment vessel 11. The voltmeter 27 is connected so that the voltage applied between the positive electrode 16 and the negative electrode 17 can be measured. The ammeter 26 is connected so as to measure the current flowing through the positive electrode 16 and the negative electrode 17, that is, the current supplied from the DC power supply 25. Based on the output of the voltmeter 27, the voltage of the DC power source 25 can be controlled so that the voltage applied between the positive electrode 16 and the negative electrode 17 is maintained at a predetermined value.

  The diaphragm 15 is made of a solid electrolyte and has oxygen ion conductivity at least at 525 ° C. or less. Here, 525 ° C. is a natural combustion start temperature of hydrogen at atmospheric pressure and in an air environment (oxygen concentration of about 20%). Examples of the material of the diaphragm 15 include zirconia-based materials such as yttria-stabilized zirconia (YSZ) and scandia-stabilized zirconia (ScSZ), perovskite-type oxygen ion conductors such as lanthanum strontium gallate, gadolinium-doped ceria ( Ceria-based materials such as GDC).

  When the oxygen gas in the gas inspection chamber 20 comes into contact with the negative electrode 17, the oxygen gas changes to oxygen ions, and the oxygen ions move in the direction of the arrow a shown in FIG. It changes again from oxygen ions to oxygen gas. At this time, by appropriately setting the voltage between the positive electrode 16 and the negative electrode 17 so that sufficient oxygen ions flow through the diaphragm 15, the flow of the target gas G is caused by the diffusion process of the diffusion hole 21. It becomes rate-limiting. By measuring the electric signal (current) generated at this time with the ammeter 26, it is possible to measure the oxygen concentration or the oxygen partial pressure.

  The material constituting the positive electrode 16 and the negative electrode 17 is a conductor, and the generated heat per oxygen atom in the oxide generated when the material is oxidized is 80 kJ or less, or 150 kJ or more. Examples of materials having a generated heat of 80 kJ or less include gold and silver, and examples of materials having a generated heat of 150 kJ or higher include copper, nickel, and carbon. These materials can be used directly as electrodes, but can also be used as plating materials or alloy materials.

  When the heat of formation per oxygen atom in the oxide is 80 kJ or less, it is difficult to generate an intermediate product in which the metal material and oxygen are chemically adsorbed, and when the heat of formation per oxygen atom in the oxide is 150 kJ or more, It is considered that the reaction in which the intermediate product is reduced to the metal is difficult to proceed, and is considered to be an effective range for preventing the combustion reaction of hydrogen and oxygen.

Here, the reaction in which the intermediate product is generated and the reaction in which the intermediate product is reduced to the metal are as follows.
O ₂ + 2M → 2M-O
2M-O + H ₂ → M + H ₂ O
However, M represents a metal material, and “MO” represents an example in which the metal material and oxygen are chemically adsorbed.

  Here, the reason why the material constituting the positive electrode 16 and the negative electrode 17 has a heat of formation per oxygen atom in the oxide generated when the material is oxidized is 80 kJ or less, or 150 kJ or more is further illustrated in FIG. This will be described with reference to FIG.

FIG. 3 is a graph for explaining the effect of the containment vessel oxygen measuring device according to the embodiment of the present invention, and is a graph showing the relationship between the heat generated per one metal oxide oxygen atom and the hydrogen oxidation activity. . FIG. 3 is FIG. 1 of Non-Patent Document 1. The vertical axis T _1/2 [H ₂ ] (° C.) in this figure represents the H ₂ 50% oxidation rate temperature, and the smaller this value, the higher the hydrogen oxidation activity. The horizontal axis represents the heat of formation per atom of metal oxide oxygen (kcal / g · atom oxygen). In this figure, when the value on the horizontal axis is about 22 kcal / g · atom oxygen (92 kJ / g · atom oxygen), the value on the vertical axis is the smallest, the hydrogen oxidation activity is high, and the heat of formation per atom of metal oxide oxygen is high. Whether it is smaller or larger than this, the value on the vertical axis is large and the hydrogen oxidation activity is low.

  In the embodiment of the present invention, it is preferable to suppress the reaction between hydrogen and oxygen on the surface of the negative electrode 17. That is, when the value on the horizontal axis in FIG. 3 is within a predetermined range sandwiching about 22 kcal / g · atom oxygen (92 kJ / g · atom oxygen), the reaction between hydrogen and oxygen easily occurs on the surface of the negative electrode 17. It is better to avoid it and make it out of the range. Therefore, in the embodiment of the present invention, the value of the horizontal axis is 80 kJ / g / atom oxygen (19 kcal / g / atom oxygen) or less, or 150 kJ / g / atom oxygen (36 kcal / g / atom oxygen) or more. Range.

  FIG. 4 is a graph showing an example of the characteristics of the first embodiment of the containment vessel oxygen measuring device according to the present invention, showing the relationship between the oxygen partial pressure and the output current.

  As shown in FIG. 4, the output current value increases as the oxygen partial pressure increases, that is, as the oxygen concentration increases. As an operating condition for obtaining the result, the oxygen sensor 12 is operated under a condition in which the temperature and the externally applied voltage are constant. In this case, the upper temperature limit is 525 ° C. from the viewpoint of preventing hydrogen combustion.

  The operating temperature of the oxygen sensor 12 is preferably 300 ° C. or higher. The reason is as follows. Although the temperature in the reactor containment vessel 11 at the time of the nuclear reactor accident changes according to the accident progress situation, it is expected to change transiently with an upper limit of about 200 ° C. in general. Since the output of the oxygen sensor 12 of this embodiment changes depending on the temperature, it is necessary to operate under a temperature condition that is not affected by the outside air temperature. As an example for reducing the influence of the outside air temperature as much as possible, the temperature of the oxygen sensor 12 is set higher than the temperature in the reactor containment vessel 11, and the oxygen sensor 12 is heated by the temperature in the reactor containment vessel 11. It is preferable not to be done. Therefore, it is preferable to operate the oxygen sensor 12 at a temperature of 300 ° C. or higher.

  Further, when the detection method of monitoring the oxygen concentration by applying a constant voltage to the oxygen sensor 12, the voltage applied to the oxygen sensor 12 is lower than the theoretical voltage at which the solid electrolyte decomposes in an environment where oxygen does not coexist, more preferably the operation. It is desirable to operate below the theoretical voltage at which water vapor electrolysis occurs at temperature.

  According to the first embodiment described above, the reactor containment vessel oxygen sensor 12 is not accompanied by reaction with hydrogen, and the oxygen concentration or oxygen in the reactor containment vessel 11 is determined by an electrical signal according to the oxygen concentration. The partial pressure can be measured. Further, even when hydrogen and oxygen coexist, it is possible to avoid the hydrogen combustion reaction.

[Second Embodiment]
FIG. 5 is a schematic configuration diagram showing a second embodiment of the oxygen measuring device for a containment vessel according to the present invention.

  The containment vessel oxygen measuring device (oxygen measuring device) of the second embodiment has substantially the same configuration as a generally known concentration-type oxygen measuring device. As shown in FIG. 5, the oxygen measuring device according to the second embodiment includes an oxygen sensor (container oxygen sensor) 12 installed in the reactor containment vessel 11 and a control outside the reactor containment vessel 11. And a control / monitoring unit 13 installed in a chamber (not shown).

  The oxygen sensor 12 includes an oxygen ion conductive diaphragm 15, and a positive electrode 16 and a negative electrode 17 disposed in contact with the diaphragm 15 across the diaphragm 15. The reference gas chamber cover 51 is disposed so that the surfaces of the positive electrode 16 and the diaphragm 15 on the positive electrode 16 side are in contact with the reference gas chamber 50. The negative electrode 17 is outside the reference gas chamber 50. The reference gas chamber 50 is filled with a reference gas having a known oxygen concentration. The reference gas is, for example, 100% oxygen gas. In the example shown in FIG. 5, the reference gas chamber 50 is a pipe through which the reference gas flows.

  The control / monitoring unit 13 includes a voltmeter 52. The voltmeter 52 is connected to the positive electrode 16 and the negative electrode 17 by lead wires 53 and 54, respectively. The lead wires 53 and 54 extend through the wall of the reactor containment vessel 11.

  The material of the diaphragm 15, the positive electrode 16, and the negative electrode 17 may be the same as in the first embodiment.

  Due to the difference in oxygen concentration between the positive electrode 16 and the negative electrode 17 disposed in contact with the diaphragm 15 across the diaphragm 15, an electromotive force corresponding to the difference in oxygen concentration is generated between the positive electrode 16 and the negative electrode 17. Occur. By measuring this electromotive force with the voltmeter 52, the oxygen concentration of the measurement target gas in the reactor containment vessel 11 on the negative electrode 17 side can be measured.

  The reference gas chamber cover 51 is not necessarily a pipe through which the reference gas flows, and may be a sealed container in which the reference gas is stored.

[Other Embodiments]
Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

DESCRIPTION OF SYMBOLS 11 ... Reactor containment vessel, 12 ... Oxygen sensor (oxygen sensor for containment vessel), 13 ... Control / monitoring part, 15 ... Diaphragm, 16 ... Positive electrode (electrode), 17 ... Negative electrode (electrode), 18 ... Inspection room Cover: 20 ... Gas inspection room, 21 ... Diffusion hole, 25 ... DC power supply, 26 ... Ammeter, 27 ... Voltmeter, 30, 31 ... Lead wire, 40 ... Dry well, 41 ... Wet well, 42 ... Vent tube, 43 ... Reactor pressure vessel, 44 ... Pressure suppression pool, 50 ... Reference gas chamber, 51 ... Reference gas chamber cover, 52 ... Voltmeter, 53, 54 ... Lead wire

Claims (9)

An oxygen sensor provided in a reactor containment vessel, and comprising a pair of electrodes disposed on the diaphragm so as to face each other across the diaphragm with a diaphragm containing a solid electrolyte having oxygen ion conductivity at 525 ° C. or lower;
With
The said electrode is an oxygen measuring device for containment vessels containing the material whose production | generation heat | fever per oxygen atom in a metal oxide is 80 kJ or less or 150 kJ or more. An oxygen sensor provided in a nuclear reactor containment vessel, comprising: a diaphragm; and a pair of electrodes disposed on the diaphragm so as to face each other with the diaphragm interposed therebetween,
With
The diaphragm contains at least one of yttria stabilized zirconia, scandia stabilized zirconia, lanthanum strontium gallate and gadolinium doped ceria,
The said electrode is an oxygen measuring device for containment vessels containing at least 1 among gold | metal | money, silver, copper, nickel, and carbon. A DC power source for applying a voltage between the pair of electrodes;
An ammeter for measuring a current value between the pair of electrodes;
Further comprising
The pair of electrodes is a positive electrode and a negative electrode;
The oxygen sensor further includes an inspection chamber cover in which a diffusion hole communicating with the measurement target gas is formed, and a gas inspection chamber that surrounds the negative electrode together with the diaphragm and does not contact the positive electrode in the reactor containment vessel. The containment vessel oxygen measuring device according to claim 1 or 2.   The oxygen measuring device for a containment vessel according to claim 3, wherein a voltage applied to the positive electrode with respect to the negative electrode is equal to or lower than a theoretical voltage at which the solid electrolyte is decomposed when there is no oxygen.   4. The containment vessel oxygen measuring device according to claim 3, wherein a voltage applied to the positive electrode with respect to the negative electrode is equal to or lower than a theoretical voltage at which electrolysis of water vapor occurs at an operating temperature. A reference gas chamber filled with a reference gas that is a gas with a controlled oxygen concentration;
The reference gas and the gas outside the reference gas chamber are separated by a reference gas chamber cover and the diaphragm,
The containment vessel oxygen measuring device according to claim 1 or 2, wherein one of the pair of electrodes is provided in the reference gas chamber, and the other electrode of the pair of electrodes is provided outside the reference gas chamber. . The reactor containment vessel includes a dry well that accommodates a reactor pressure vessel, and a wet well that is connected to the dry well via a vent pipe and accommodates a pressure suppression pool therein.
The oxygen sensor is provided in plurality, and is disposed at least at a position above the reactor pressure vessel in the dry well and at a position above the pressure suppression pool in the wet well. The containment vessel oxygen measuring device according to any one of 1 to 6. A pair of electrodes arranged in the reactor containment vessel and disposed on the diaphragm so as to face each other across the diaphragm with a diaphragm containing a solid electrolyte having oxygen ion conductivity at 525 ° C. or lower;
The said electrode is an oxygen sensor containing the material whose production | generation heat | fever per oxygen atom in a metal oxide is 80 kJ or less or 150 kJ or more. Provided in a nuclear reactor containment vessel, comprising a diaphragm and a pair of electrodes disposed on the diaphragm so as to face each other with the diaphragm interposed therebetween;
The diaphragm contains at least one of yttria stabilized zirconia, scandia stabilized zirconia, lanthanum strontium gallate and gadolinium doped ceria,
The electrode is an oxygen sensor containing at least one of gold, silver, copper, nickel, and carbon.

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