JP6526587B2 - Hydrogen sensor system - Google Patents

Description

  Embodiments of the present invention relate to a hydrogen sensor system.

  At the time of a severe accident in a nuclear reactor, hydrogen is generated by the reaction between water and zirconium which has become hot. In an environment with oxygen, hydrogen reacts explosively if there is an ignition source or if the temperature rises to a temperature at which self-ignition occurs. The explosion may cause damage to safety related equipment including the pressure vessel and containment vessel of the reactor.

  In order to measure hydrogen at the time of severe accident, a method of installing a hydrogen sensor in a building such as a nuclear power plant can be considered. As a conventional hydrogen sensor, there is a thermoelectric conversion type that measures a temperature change generated by an exothermic reaction using a noble metal catalyst (Pt, Pd, etc.) that promotes the combustion of hydrogen and oxygen (for example, patent documents 1, 2). Further, as a conventional hydrogen sensor, there is one which makes a noble metal wire (Pd-Ag or the like) as a hydrogen storage alloy absorb hydrogen and measures the amount of change in resistance value (for example, Patent Document 3).

Patent No. 4430844 Patent No. 3226923 Japanese Examined Patent Publication 2-24460

  Even if you try to install a conventional hydrogen sensor in a building such as a nuclear power plant, the hydrogen sensor may be affected by the air flow at the time of a severe accident, or the hydrogen sensor may be damaged by falling objects at the severe accident. There is a risk of

  Further, the surface of the hydrogen sensor containing a noble metal is easily covered with iodine generated at the time of a severe accident, so there is a problem that the above-mentioned catalytic reaction and hydrogen storage reaction are easily inhibited.

  The hydrogen sensor system according to the present embodiment includes a hydrogen sensor containing a noble metal, a case enclosing the hydrogen sensor and having an opening at a part thereof, and an iodine removing unit for removing iodine in gas. .

  According to the hydrogen sensor system according to the present embodiment, the hydrogen sensor can be protected from the environment at the time of an accident, and the influence of iodine in the catalytic reaction of a noble metal and the hydrogen storage reaction can be removed.

Schematic which shows the environment where a hydrogen concentration measuring apparatus is installed. The figure which shows the structural example of a hydrogen sensor system. The external view which shows the structure of a hydrogen sensor. (A), (B) is a figure which shows the 1st example of the arrangement | positioning method of the sintered metal (or stainless steel lump) to an opening part. The figure which shows the 2nd example of the arrangement | positioning method of the sintered metal (or stainless steel lump) to an opening part. The figure which shows the relationship between the thickness of an iodine removal part, and an iodine concentration. The figure which shows the 1st modification of a structure of a hydrogen sensor system. The figure which shows the 2nd modification of a structure of a hydrogen sensor system. The figure which shows arrangement | positioning of a hydrogen sensor and an iodine removal part. The figure which shows the 3rd modification of a structure of a hydrogen sensor system.

  The hydrogen sensor system according to the present embodiment will be described with reference to the attached drawings.

  FIG. 1 is a schematic view showing an environment in which a hydrogen concentration measuring device is installed.

  FIG. 1 shows a place where measurement (monitoring) of hydrogen concentration is performed, for example, a reactor containment vessel 1 in a nuclear power plant, and a hydrogen concentration measurement device 10 for measuring the hydrogen concentration in the reactor containment vessel 1. Measurement of hydrogen concentration is mainly aimed at dealing with severe accidents at nuclear power plants.

  The reactor containment vessel 1 stores all facilities of a nuclear reactor (not shown) and a primary cooling system (not shown). When an accident such as pipe breakage occurs, the reactor containment vessel 1 automatically shuts a pipe (not shown) passing therethrough.

  The hydrogen concentration measurement device 10 includes the hydrogen sensor system 11 according to the present embodiment, a resistor (tester) 12, and a control unit 13. The configuration of the hydrogen sensor system 11 will be described later with reference to FIG.

  The resistor 12 measures the electric resistance value of the noble metal wire by supplying a current to the noble metal wire 31 (shown in FIG. 3) of the hydrogen sensor system 11. Although a well-known thing is applied as the resistor 12, when the measurement system (for example, two-terminal method, a Wheatstone bridge) other than the 4-wire method is employ | adopted as the resistor 12, each measurement system is taken. The appropriate ones apply.

  The control unit 13 includes a central processing unit (CPU), a memory, and the like. The control unit 13 calculates the hydrogen concentration based on the electrical resistance value measured by the resistor 12. For example, the control unit 13 calculates the hydrogen concentration corresponding to the electric resistance value measured by the resistor 12 based on the previously obtained correlation equation between the hydrogen concentration and the electric resistance value.

  FIG. 2 is a view showing a configuration example of the hydrogen sensor system 11.

  As shown in FIG. 2, the hydrogen sensor system 11 includes a hydrogen sensor 111 and a case 112 enclosing the hydrogen sensor 111 and provided with one or more openings B, and an iodine removing unit 113 for removing iodine in gas. And. In FIG. 2, the iodine removing portion 113 is disposed at the opening B of the housing 112. In the present embodiment, the case where the housing 112 of the hydrogen sensor system 11 is provided with one opening B will be described.

  The hydrogen sensor system 11 operates not only during steady-state operation of the reactor but also during a severe accident. The gas G outside the housing 112 reaches the hydrogen sensor 111 via the iodine removing unit 113 disposed in the opening B. The gas G outside the housing 112 passes through the opening B. For this reason, by disposing the iodine removing portion 113 in the opening portion B, the contact probability between the gas G containing iodine generated at the time of severe accident and the iodine removing portion 113 becomes large, and the gas G in the small amount iodine removing portion 113 It is possible to adsorb the iodine contained in

  FIG. 3 is an external view showing the structure of the hydrogen sensor 111. As shown in FIG.

  As shown in FIG. 3, the hydrogen sensor 111 includes a noble metal wire 31, a fixing portion 32, and a connection portion 33.

  The noble metal wire 31 is disposed so as to be spirally wound on the outer surface of the fixing portion 32. The noble metal wire 31 is formed of a hydrogen storage alloy (Pd-Ag or the like) having a hydrogen storage ability whose electric resistance value changes due to hydrogen storage.

  The fixing portion 32 is made of an insulating material such as ceramic or glass, and is used for fixing and insulating the noble metal wire 31. Although FIG. 3 illustrates the case where the fixing portion 32 has a cylindrical shape, the fixing portion 32 does not have to have a cylindrical shape. That is, the entire fixing portion 32 does not have to be made of the same material. When the fixing portion 32 has a cylindrical shape, the fixing portion 32 can adopt a structure in which a heater is included in the inner space thereof. In addition, when the fixing portion 32 has a cylindrical shape, the fixing portion 32 can adopt a structure in which an electrical wiring is included in the internal space thereof.

  The connecting portion 33 fixes the noble metal wire 31 to the fixing portion 32 and functions as a terminal for measuring the electric resistance value of the noble metal wire 31. Moreover, although the example in which the connection part 33 is installed in the outer surface of the side surface of the fixing part 32 is shown in FIG. 3, the connection part 33 may be installed in the inner surface of the side surface of the fixing part 32.

  Returning to the description of FIG. 2, the housing 112 encloses the hydrogen sensor 111. The material of the housing 112 is preferably stainless steel. The housing 112 prevents the hydrogen sensor 111 from being affected by air flow at the time of a severe accident, and protects the hydrogen sensor 111 from falling objects at the time of a severe accident.

  In addition, it is thought that a large amount of hydrogen and a small amount of oxygen exist in the gas at the time of a severe accident. When all around the hydrogen sensor 111 is enclosed, the gas G can not be exchanged between the inside and the outside of the housing 112, so an opening B for diffusing the gas G is formed in a part of the housing 112. Provided.

  The iodine removing unit 113 is provided at the opening B of the housing 112. Here, materials suitable for the iodine removing unit 113 will be described.

It is known that stainless steel is corroded by iodine (Dainari Engineering Center, "Fabrication of surface corrosion behavior of ferritic stainless steel", MFR, March 1987). Iodine causes the following reaction on the surface of stainless steel to corrode stainless steel. That is, iodine is trapped on the surface of stainless steel, reacts with metal atoms, and becomes stable. Therefore, stainless steel is an excellent capture material of iodine contained in the gas G.
M (s) + I ₂ (g) → MI ₂ (s)
M (s) + 2I (g) → MI ₂ (s)

  When the material of the iodine removing portion 113 is stainless steel, the iodine removing portion 113 is a sintered metal of stainless steel obtained by sintering a powder made of stainless steel at a temperature around the melting point. In sintered metal, the size of the powder can adjust the size of the void in the element.

  Alternatively, when the material of the iodine removing unit 113 is stainless steel, the iodine removing unit 113 is a stainless steel block formed by adding a crease that curls by rolling a stainless steel wire. When the iodine removing unit 113 is a sintered metal or a stainless steel block, the hydrogen sensor system 11 holds the sintered metal or the stainless steel block, and holds the holding plate S1 for fixing itself to the opening B of the housing 112 ( It has FIG. 4 (A), (B) or holding container S2 (it shows in figure in FIG. 5).

  Alternatively, when the material of the iodine removing portion 113 is stainless steel, it is one stainless steel wire mesh (stainless plain woven wire mesh or stainless steel woven wire mesh). Alternatively, the iodine removing unit 113 is a plurality of stainless steel wire nets stacked in the normal direction of the stainless steel wire net surface. In the case of the latter, the iodine removing unit 113 may be a plurality of stainless steel mesh in which the positions of the openings of the adjacent stainless steel meshs are shifted. The open eye is the space between the lines making up the stainless steel wire mesh.

  FIGS. 4A and 4B show a first example of the method of arranging the sintered metal (or stainless steel block) in the opening B. FIG.

  FIG. 4A shows a holding plate S <b> 1 for placing sintered metal in the opening B of the housing 112. The holding plate S1 has a mesh-shaped portion having an opening through which gas can enter and exit. The sizes (dimensions) of the plurality of openings may or may not be uniform. The holding plate S1 is fixed to the inner wall of the housing 112 by screwing (FIG. 4 (B)). Alternatively, the holding plate S1 is fixed to the inner wall of the housing 112 by adhesion or welding. In the opening B shown in FIG. 4B, in the upper part of the holding plate S1 fixed to the inner wall of the housing 112, a space in which the sintered metal can be disposed is formed.

  The net of the holding plate S1 can also be a stainless steel wire which is a capturing material of iodine.

  FIG. 5 is a view showing a second example of the method of arranging the sintered metal (or stainless steel block) in the opening B. As shown in FIG.

  FIG. 5 shows a holding container S2 for placing sintered metal in the opening B of the housing 112. The holding container S2 is provided with a bottom surface having a mesh-shaped portion having an opening through which gas can enter and leave, and forms a space in which a sintered metal can be disposed. The sizes of the plurality of openings may or may not be uniform. The holding container S2 is fixed to the outer wall of the housing 112 by screwing. Alternatively, the holding container S2 is fixed to the inner wall of the housing 112 by adhesion or welding. Inside the holding container S2 fixed to the outer wall of the housing 112, a space in which the sintered metal can be disposed is formed.

  The net on the bottom of the holding container S2 may be a stainless steel wire as a capturing material of iodine.

  Returning to the explanation of FIG. 2, zeolite and activated carbon are known as materials which adsorb various substances having large surface area. Therefore, zeolite or activated carbon can be used as an adsorbent for iodine contained in the gas G. When the material of the iodine removing unit 113 is zeolite or activated carbon, the hydrogen sensor system 11 holds the zeolite or activated carbon, and a holder for fixing itself to the opening B of the housing 112 (FIG. 4 (A), It has holding plate S1 shown to (B), or holding container S2 shown in FIG.

Thirdly, in silver zeolite, H ⁺ and Ag ^{+ in the} vicinity of Al atoms in the zeolite are ion-exchanged, and Ag ⁺ is attached in the vicinity of Al atoms by ionic bonding. Silver and iodine can easily cause the following reaction, so that silver zeolite can firmly capture iodine contained in gas G.
2Ag (s) + I ₂ (g) → 2AgI
Ag (s) + I (g) → AgI

  When the material of the iodine removing unit 113 is silver zeolite, the hydrogen sensor system 11 holds the silver zeolite and fixes the holder to the opening B of the housing 112 (FIGS. 4A and 4B). Or a holding container S2 shown in FIG. 5).

  The material of the iodine removing unit 113 may be made of at least one of the above-described stainless steel, zeolite, activated carbon, and silver zeolite.

  Subsequently, the thickness of the iodine removing portion 113 will be described.

  The gas G containing iodine enters the inside of the housing 112 through the opening B of the housing 112. When the iodine removing portion 113 is disposed at the opening B, the iodine contained in the gas G is gradually adsorbed by the iodine removing portion 113 according to the distance (thickness) to the iodine removing portion 113, so the iodine concentration is The distribution is as shown in FIG. 6 in relation to the thickness.

  FIG. 6 is a view showing the relationship between the thickness of the iodine removing portion 113 and the iodine concentration.

As shown in FIG. 6, the iodine concentration in the thickness of the iodine removing portion 113 is C, the iodine concentration contained in the gas is C0, the adsorption coefficient is a, and the thickness (the distance from the outer wall of the iodine removing portion 113) Assuming that x is, the iodine concentration C is expressed by the following equation.
C = C0 exp (-ax)

Among stainless steels, zeolites, activated carbons, and silver zeolites, the adsorption coefficient a of stainless steels is the smallest, and the porosity is about 2 [cm ⁻¹ ] or more at about 0.3. Therefore, assuming that the adsorption coefficient a of stainless steel is 2 cm ^-1 , the iodine concentration C is 0.022 C0 when the thickness x is 1.9 cm, and the thickness is 2.0 When it is [cm], it will be 0.018 C0. That is, when the material of the iodine removing portion 113 is stainless steel, if the thickness x of the stainless steel is 2 cm or more, the concentration C of iodine reaching the hydrogen sensor 111 is 2% of the outside of the casing 112 It can be reduced to the following. In view of the iodine concentration based on the severest scenario expected in a severe accident, it is sufficient to reduce the concentration C of iodine reaching the hydrogen sensor 111 to 2% or less. The upper limit of the thickness x of stainless steel may be appropriately determined from the response time of the target hydrogen sensor 111.

  When the thickness x of the iodine removing portion 113 is 2 cm, in FIG. 4B, the thickness of the upper wall of the housing may be 2 cm or more. When the thickness x of the iodine removing portion 113 is 2 cm, in FIG. 5, the depth of the holding container S2 may be 2 cm or more.

  In addition, although iodine will be adsorbed to the stainless steel as the iodine removal part 113 at the time of a severe accident, replacement | exchange of stainless steel can not be performed about two weeks after a severe accident occurrence. However, even if the thickness x of the stainless steel as the iodine removing portion 113 is 2 cm or more, the iodine removing portion 113 is sufficiently Can continue to adsorb iodine.

  The system for storing hydrogen by the noble metal wire of the hydrogen sensor 111 has been described. However, the technical concept of the present embodiment is not limited to a system that occludes hydrogen by a noble metal wire. The technical concept of the present embodiment can be applied as long as the hydrogen sensor 111 contains a noble metal. For example, the technical concept of the present embodiment can be applied to a thermoelectric conversion system that measures temperature change caused by an exothermic reaction using a noble metal catalyst (Pt, Pd, etc.) that promotes combustion of hydrogen and oxygen. is there.

  According to the hydrogen sensor system 11, iodine contained in the gas is brought into contact with the iodine removing portion 113, and iodine is removed from the gas reaching the hydrogen sensor 111. Therefore, iodine in the gas reaches the surface of the hydrogen sensor 111 There is almost nothing, and the oxygen-hydrogen reaction which is the surface reaction of the noble metal of the hydrogen sensor 111 and the hydrogen storage reaction of the noble metal are not inhibited. Therefore, according to the hydrogen sensor system 11, the influence of iodine in the catalytic reaction of the noble metal and the hydrogen storage reaction can be removed. Further, according to the hydrogen sensor system 11, the case 112 can protect the hydrogen sensor from the environment at the time of an accident.

(First modification)
FIG. 7 is a view showing a first modified example of the configuration of the hydrogen sensor system 11.

  As shown in FIG. 7, the hydrogen sensor system 11 includes a hydrogen sensor 111, a housing 112, an iodine removing unit 113, and iodine removing units 114 and 115 disposed inside the housing 112. The iodine removing unit 113 is not an essential component. Either of the iodine removing units 114 and 115 may be provided. Hereinafter, the case where all the iodine removal parts 113-115 are provided is demonstrated.

  The iodine removing unit 114 is installed on the inner side wall of the housing 112, and the iodine removing unit 115 is installed on the inner upper wall of the housing 112. The gas G outside the housing 112 reaches the hydrogen sensor 111 via the iodine removing unit 113 disposed in the opening B.

  In FIG. 7, the same components as those shown in FIG.

  The iodine contained in the gas G that has entered the inside of the housing 112 does not inhibit the function of the hydrogen sensor 111 unless it adheres to the hydrogen sensor 111. Therefore, as shown in FIG. 7, iodine removing portions 114 and 115 are disposed in the vicinity of the hydrogen sensor 111. As a result, a part of iodine that has entered the inside of the housing 112 is removed by the iodine removing portions 114 and 115, so that iodine hardly adheres to the surface of the hydrogen sensor 111.

  According to the first modification of the hydrogen sensor system 11, by providing the iodine removing portions 114 and 115 in addition to the iodine removing portion 113, the catalytic reaction or reaction of the noble metal is more sufficient than in the case of the hydrogen sensor system 11 shown in FIG. The influence of iodine in the hydrogen storage reaction can be removed.

(Second modification)
FIG. 8 is a view showing a second modified example of the configuration of the hydrogen sensor system 11.

  As shown in FIG. 8, the hydrogen sensor system 11 includes a hydrogen sensor 111, a housing 112, an iodine removing unit 113, and an iodine removing unit 116 disposed inside the housing 112. The iodine removing unit 113 is not an essential component. Hereinafter, the case where all the iodine removal parts 113 and 116 are provided is demonstrated.

  The iodine removing unit 116 is provided on the outer periphery of the hydrogen sensor 111 without contacting the hydrogen sensor 111. The gas G outside the housing 112 reaches the hydrogen sensor 111 via the iodine removing unit 113 disposed in the opening B.

  In FIG. 8, the same components as those shown in FIG. 2 will be assigned the same reference numerals and explanation thereof will be omitted.

  FIG. 9 is a view showing the arrangement of the hydrogen sensor 111 and the iodine removing unit 116. As shown in FIG.

As shown in FIG. 9, the iodine removing unit 116 is held by the holding container S <b> 3 on the outer periphery of the hydrogen sensor 111. The holding container S3 has a mesh-shaped outer surface and an inner surface having an opening through which gas can enter and leave. The sizes of the plurality of openings may or may not be uniform. The iodine removing unit 116 is sandwiched between the outer surface and the inner surface of the holding container S3. The hydrogen sensor 111 and the iodine removing unit 116 are supported on the housing 112 (shown in FIG. 8) by a support (not shown) so that they do not contact each other. The net of the holding container S3 can also be a stainless steel wire which is a capturing material of iodine.

  The iodine removing unit 116 may have a plate-like shape, and may be provided on the upper part or the lower part of the hydrogen sensor 111 without contacting the hydrogen sensor 111.

  Returning to the explanation of FIG. 8, iodine contained in the gas G which has entered the inside of the housing 112 does not inhibit the function of the hydrogen sensor 111 unless it adheres to the hydrogen sensor 111. Therefore, as shown in FIG. 8, the iodine removing unit 116 is disposed on the outer periphery of the hydrogen sensor 111 without contacting the hydrogen sensor 111. As a result, a part of iodine that has entered the inside of the housing 112 is removed by the iodine removing unit 116, so that iodine hardly adheres to the surface of the hydrogen sensor 111.

  The hydrogen sensor system 11 shown in FIG. 8 may include the iodine removing portions 114 and 115 shown in FIG. 7 in addition to the iodine removing portions 113 and 116.

  According to the second modification of the hydrogen sensor system 11, by providing the iodine removing unit 113 in addition to the iodine removing unit 113, the catalytic reaction or the hydrogen storage of the noble metal is more sufficient than in the case of the hydrogen sensor system 11 shown in FIG. The effect of iodine in the reaction can be removed.

(Third modification)
FIG. 10 is a diagram showing a third modification of the configuration of the hydrogen sensor system 11. As shown in FIG.

  As shown in FIG. 10, the hydrogen sensor system 11 includes a hydrogen sensor 111, a housing 112, an iodine removing unit 113, and a heater 117 disposed inside the housing 112. The iodine removing unit 113 is not an essential component. Hereinafter, the case where the iodine removing unit 113 and the heater 117 are provided will be described.

  The heater 117 is provided in the vicinity of the hydrogen sensor 111, for example, below the hydrogen sensor 111 without contacting the hydrogen sensor 111. The gas G outside the housing 112 reaches the hydrogen sensor 111 via the iodine removing unit 113 disposed in the opening B.

Iodine evaporates when it gets hot. Therefore, in order to remove iodine attached to the surface of the hydrogen sensor 111 (the surface of the noble metal), it is effective to heat the surface of the hydrogen sensor 111 to a high temperature. Therefore, the heater 117 is disposed in the vicinity of the hydrogen sensor 111. The hydrogen sensor 111 is supported by the housing 112 by a support (not shown) so as not to contact the heater 117. The elemental iodine evaporates at 184.3 ° C. However, on the surface of the noble metal, the noble metal atom and the iodine atom are bonded by a weak covalent bond. Therefore, in order to remove iodine from the surface of the noble metal, it is necessary to apply a temperature beyond the barrier to the surface of the noble metal.

  Therefore, the heater 117 is controlled by the control unit 13 (shown in FIG. 1) such that the temperature of the surface of the hydrogen sensor 111 is 300 ° C. or more, more preferably 500 ° C. or more. The heater 117 may be provided inside the cylindrical fixing portion 32 (shown in FIG. 3) or may be provided around the hydrogen sensor 111 without contacting the hydrogen sensor 111. Further, the heater 117 may be provided above the hydrogen sensor 111 without being in contact with the hydrogen sensor 111.

  In addition, the hydrogen concentration measured in the scenario is controlled in a state where the heater 117 is controlled by the control unit 13 (shown in FIG. 1) so that the temperature of the surface of the hydrogen sensor 111 becomes a predetermined value (less than 500.degree. C.). The temperature of the surface of the hydrogen sensor 111 may be controlled to be 500 ° C. or higher when the temperature is significantly lower than the predicted value based on it. In that case, the control unit 13 may notify the operator that the measured hydrogen concentration is affected by iodine.

  The hydrogen sensor system 11 shown in FIG. 10 may include, in addition to the iodine removing unit 113, iodine removing units 114 and 115 shown in FIG. 7 and an iodine removing unit 116 shown in FIG.

  According to the third modification of the hydrogen sensor system 11, by providing the heater 117 in addition to the iodine removing unit 113, the catalytic reaction and the hydrogen storage reaction of the noble metal are more sufficient than in the case of the hydrogen sensor system 11 shown in FIG. The effect of iodine can be removed.

  According to the hydrogen sensor system according to the at least one embodiment and the modified example described above, the hydrogen sensor can be protected from the environment at the time of an accident, and the influence of iodine in the catalytic reaction and hydrogen storage reaction of noble metals can be removed.

  While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and the gist of the invention, and are included in the invention described in the claims and the equivalents thereof. For example, the hydrogen sensor of the embodiment can be installed at any of the nuclear facilities of a BWR plant and a PWR plant. In addition, the hydrogen sensor according to the embodiment can be installed at any facility other than a nuclear facility, as long as it is a facility that requires detection and measurement of hydrogen.

11 ... hydrogen sensor system, 111 ... hydrogen sensor, 112 ... housing, 113 to 116 ... iodine removal unit, 117 ... heater.

Claims (5)

A hydrogen sensor containing a noble metal,
An enclosure enclosing the hydrogen sensor and provided with an opening in part;
An iodine removing unit disposed on the outer periphery of the hydrogen sensor in the housing and removing iodine in gas;
Hydrogen sensor system equipped with   The hydrogen sensor system according to claim 1, wherein the material of the iodine removing unit is made of at least one of stainless steel, zeolite, activated carbon, and silver zeolite.   The hydrogen sensor system according to claim 1, wherein the iodine removing unit is disposed at the opening.   The hydrogen sensor system according to any one of claims 1 to 3, wherein the iodine removing unit is installed on an inner wall of the housing. The hydrogen sensor system according to any one of claims 1 to 4 , further comprising a heater in the housing.

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