JPH03255990A - Plant operation monitoring system - Google Patents

Abstract

PURPOSE:To obtain an extremely small electrode which is usable in high- temperature, high-pressure running water by bending an electrode material in a U shape and sealing it at plural positions, and thus increasing the number of fulcra of the electrode material. CONSTITUTION:The electrode part 15 of the operating electrode of an electrochemical sensor 1 is made of a platinum thin wire of 50mum in diameter and curved in the U shape. Four leg parts are fixed and sealed with a seal part 16 made of ceramic. A lead wire 17 is embedded in the seal part 16 and put in electric contact with the leg part of the four electrode parts. Further, a protection jig 18 made of ceramic is provided surrounding the electrode part 15. Then the sensor 1 is inserted into an in-reactor instrumentation pipe 2, a pulse signal is sent to the operating electrode of the sensor 1 by using a potentiostat 3, a pulse generator 4, and a pulse response analyzer 5, and its response signal is analyzed to perform five kinds of pulse voltammetry or random pulse voltammetry.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a structure of a working electrode in an apparatus for electrochemical quantitative analysis of chemical species dissolved in a nuclear power plant cooling water system, and a working electrode of this structure. Water quality sensor using
The present invention also relates to a plant operating status monitoring system that controls water quality using water quality sensors.

[Conventional technology]

Conventionally, regarding electrochemical measurements using microelectrodes, electrochemistry and industrial physical chemistry 56 (1988) No. 608
It is generally discussed on pages 612 to 612. The structure and manufacturing method of the microelectrode are discussed in this document, and the structure is such that a thin metal wire or carbon fiber is sealed at one sealing point using an epoxy resin.

For the basic logic underlying quantitative analysis using microelectrodes as working electrodes, see Journal of Electroanalytical Chemistry 186 (1985) No. 79.
Pages 89 to 89 (J, Electroanal.

Che+m, 186 (1984), pp79-86)
, and the same magazine 230 (1987) pp. 61-6.
7 pages (ibid, 230 (1987), Pp61
-67) and the same magazine 250 (1988) No. 269
pages to 276 (ibid, 250 (1988), p.
p269-276), and the same magazine 171 (1984), pages 219 to 230 (ibid, 171
(1984).

pp219-230), and the same magazine 182 (198
5th year) pages 267 to 279 (ibid, 18
2 (1985), pp267-279), and
Same magazine 237 (1987) pp. 163 to 170 (ibid, 237 (1987) *pp163
-170).

A quantitative analysis method for simultaneously quantitatively analyzing a plurality of substances to be measured dissolved in a test liquid using a plurality of pulse voltammetries is discussed in Japanese Patent Application No. 311969/1982.

The conventional plant control system is disclosed in Japanese Patent Application Laid-Open No. 58-51312.
Publication and U, S, patent No. 45
No. 52718, it was a control system for machines and equipment that corresponded to plant quantities or state quantities.

A quantitative analysis method for simultaneously quantitatively analyzing multiple types of analyte dissolved in a test liquid using random pulse voltammetry is discussed in Bunseki (1988), pages 280 to 285.

[Problem to be solved by the invention]

The above-mentioned microelectrodes do not take into account the high-temperature durability of the sealing material and the mechanical durability of the electrode material, and are not suitable for quantitative analysis of chemical species dissolved in flowing high-temperature, high-pressure water from nuclear power plants, thermal power plants, etc. There was a problem that it could not be used.

An object of the present invention is to provide a microelectrode structure that can withstand use in high-temperature, high-pressure flowing water.

Plant control systems do not take into account the sensor technology that monitors water quality and feeds back water quality data to the control system to control water quality. There was a practical problem that the monitoring system and control system themselves were not practical.

A second object of the present invention is to provide a water quality monitoring system and control system by providing a durable and reliable water quality sensor.

[Means to solve the problem]

In order to achieve the above object, the present invention increases the number of fulcrums of the electrode material by bending the electrode material into a U-shape or the like and sealing it at multiple locations. In addition, a structure was adopted in which the tip or midway portion of the electrode material was supported by a support jig. In addition, a structure was adopted in which the electrode body was surrounded by a protective jig. Furthermore, ceramics or metal coated with ceramics was used as the material for sealing the electrode body.

[Effect]

By adopting a structure that seals the electrode material at multiple locations and a support jig, the strength of the electrode body against external forces is increased.
By employing the protective jig, the external force applied to the electrode body is alleviated. By using ceramic as the material of the sealing material, a durable seal can be achieved in high temperature and high pressure water.

This makes the working electrode less likely to be mechanically damaged.

By establishing a means to obtain highly reliable water quality information from sensors, high-level plant operation management becomes possible.

〔Example〕

<Example 1> In this example, an electrochemical sensor having a working electrode of the structure shown in Fig. 2 is installed in the operating status monitoring system of a BWR plant shown in Fig. 1 through an instrumentation pipe inside a nuclear reactor. This is an example of an attempt to measure dissolved oxygen concentration under this water quality environment.

In FIG. 1, an electrochemical sensor 1 is inserted into an in-furnace instrumentation tube 2. In FIG. Potentiostat electrochemical interface 3. Pulse generator 4. By sending a pulse signal to the working electrode of the electrochemical sensor using the pulse response analyzer 5 and analyzing the response signal, a reverse pulse,
Five types of pulse voltammetry or random pulse voltammetry are performed: normal pulse, differential pulse, square wave, and normal differential pulse. The computer 6 has functions such as storing reference data and measured data, comparing measured data with reference data, and issuing water quality control commands based on the comparison results. The display device 7 displays water quality data, plant operating status, safety or warnings, etc. 8 is a gas injection device, which operates according to water quality control instructions from the computer.

9 is a dryer, 10 is a reactor core, 11 is a reactor water supply pipe, 1
2 is a reactor recirculation system, 13 is a reactor pressure vessel, and 14 is a turbine.

FIG. 2 shows the structure of the working electrode of the electrochemical sensor of the present invention. The electrode part 15 is made of a thin platinum wire with a diameter of 50 μm.
It is assembled into the shape shown in the figure. The four leg portions are fixedly sealed by seal portions 16 made of ceramics. A lead wire 17 is embedded inside the seal part and makes electrical contact with one of the four legs of the electrode part. Furthermore, a ceramic protection jig 18 is provided to surround the electrode section. The protective jig has several small holes for water passage.

FIG. 3 shows the structure of an electrochemical sensor including the working electrode shown in FIG. 2 as a component. This sensor has a working electrode 19. shown in FIG. This is a three-electrode sensor consisting of three types of electrodes: a reference electrode 20 whose surface is a silver/silver chloride electrode coated with ceramics, and a counter electrode 21 made of platinum. This sensor is tightened by the metal fitting 22 and the metal fitting holder 2.
3, it is stably supported by the structural material and immersed in the water 24 to be monitored.

A in FIG. 4 shows the measurement of the change over time in the dissolved oxygen concentration in the water to be monitored using the sensor shown in FIG.

Here, the water to be monitored is air-saturated water, and the dissolved oxygen concentration should always be constant. As shown in the figure, the measured dissolved oxygen concentration is always constant, indicating that the sensor is operating stably. B in FIG. 4 shows the measurement results when a platinum wire with a diameter of 50 μm was fixed and sealed at only one point at the sealing portion as the 5 working electrodes. In this case, the measured values are not stable for the first month, and after that the measured values become significantly smaller. This is because the support of the electrode material was unstable and broke and broke.

Embodiment 2 This embodiment is an example in which an electrochemical sensor having a working electrode having the structure shown in FIG. 6 is installed in the operating status monitoring system of a once-through thermal power plant shown in FIG.

In FIG. 5, the electrochemical sensor 1 includes a condensate pump 26
, upstream of the deaerator 27 , and upstream of the two downstream economizers 28 . Potentiostat electrochemical interface 3. Pulse generator 4. Pulse response analyzer 5
and a memory 29 is installed for each electrochemical sensor. The memory stores water quality data at each location and predetermined reference water quality data.

The computer 6 reads the data corresponding to each location from the memory, compares the reference data and the measured data,
It has functions such as issuing water quality control commands based on comparison results.

Display bags w7 are prepared as many as the number of installed electrochemical sensors, and display water quality data, plant operating status, safety, warning, etc. corresponding to each location. 30 is a condensate desalination device, 31 is a low pressure feed water heater, 32 is a high pressure feed water heater, 33 is an ice wall, 34 is a superheater, 35 is a reheater, 36 is a high pressure turbine, and 37 is a low pressure turbine.

FIG. 6 shows the structure of the working electrode of an electrochemical sensor. The electrode part 15 is made of a thin gold wire with a diameter of 100 μm, and as shown in the figure, the tip part is fixed with a ceramic support jig 38, and the leg part is fixedly sealed by a seal portion 16 made of ceramics. Furthermore, a ceramic-coated stainless steel protective jig 18 is provided to surround the electrode section. The protective jig has several small holes for water passage.

FIG. 7 shows the structure of an electrochemical sensor including the working electrode shown in FIG. 6 as a component. This sensor is a two-electrode system sensor consisting of a working electrode 19 shown in FIG. 6, and a reference electrode 20 whose surface is a silver/silver sulfate electrode coated with ceramics. The reference electrode also serves as a counter electrode. This sensor is tightened by the metal fitting 22 and the metal fitting holder 2.
3, the water to be monitored 2 is stably supported by the structural member 24.
5.

<Example 3> In this example, the working electrode shown in FIG. 2 or FIG. An example of measuring the number of reaction electrons and diffusion coefficient of dissolved oxygen by normal pulse voltammetry using two types of working electrodes will be described with reference to the flowchart in FIG.

■ Now apply a normal pulse potential signal to the working electrode,
At that time, the change in current value over time is measured.

FIG. 9(A) is a normal pulse potential signal.

The initial potential Eo is the potential at which the oxygen reduction reaction does not proceed at all.
The electrolytic potential Ei is set to a potential at which the oxygen diffusion limiting current is obtained. FIG. 9(B) shows the change in current value over time. If the time at which the potential changes from Eo to El is O, then the change over time of the current value in the microelectrode and the plate electrode is 1n(
t)+ip (t) is expressed by equations (1) and (4).

xwac t) = 2 n F tc b CD f
(θ) ・−(1) Here, f(θ)=1/,/1(300.422−0.0675
Q■θ10.0058 (Mu area θ-1,47)! ...
(2) θ=Dt/a”...
・(3) i p (t) = n F A CJ "7
11-(4). Where, n is the number of reactive electrons in the oxygen reduction reaction, C is the dissolved oxygen concentration, D is the diffusion coefficient of dissolved oxygen, a is the radius of the thin electrode wire of the microelectrode, b is the length of the exposed part of the thin electrode wire, It is assumed that A is the area of the flat electrode, F is a Faraday constant, and values other than n and D are known.

In (1) to (2), n and D are calculated by combining equations (1) and (4).

First, assume the value of n to be an appropriate value in (■). Then, in step 2, the value of D is found from equation (4), and in step 2, the value of D is calculated from equation (1).

The method for calculating the value of D in (2) is shown below.

By eliminating D from equations (1) and (3), equation (5) is obtained.

1jt)・t/2nFπbCa”=of (θ)...
(5) When the left side of equation (5) is set as ξ(n) and the inverse function of of(θ) is set as g, equation (6) is obtained.

θ=gCξ(n)] ・
(6) Furthermore, by substituting and transforming equation (6) into equation (3), equation (7) is obtained.

D=a”g (ξ(n))/t
−= (7) That is, the value of D was calculated from equation (1) in ■ based on the assumption of the value of n in ■.

In (2), the values of D calculated in (2) and (2) are compared. If the two values are different, it means that the value of n assumed in (■) is incorrect. In that case, reset the assumed amount of n and re-execute the processes ① to ②. If the two values match, the assumed amount n in (1) and the calculated values in (2) and (2) become the number of reaction electrons and the diffusion coefficient, respectively.

<Example 4> This example shows an example in which dissolved oxygen, hydrogen peroxide, and hydrogen were simultaneously quantitatively analyzed using random pulse voltammetry using the working electrode shown in FIG. 2 or FIG. 6.

A in FIG. 10 is a current i-potential E curve in a ternary mixed system of oxygen, hydrogen peroxide, and hydrogen. Oxidation currents of hydrogen peroxide and hydrogen are observed in the high potential region, and reduction currents of oxygen and hydrogen peroxide are observed in the low potential region. Arbitrary potentials in the potential region where the oxidation current and reduction current rise are defined as El and El, and are divided and quantized into eight levels from 0 to 7.

FIG. 10B shows a random pulse potential signal applied to the working electrode. The combination of potentials (El, El) is
There are 8×8=64 types. At the end point S of El,
The current values are sampled and the current values corresponding to each (E 1 + E z) set are expanded into an 8×8 data matrix X.

It is converted into a data matrix or a matrix Y using equation (8).

Y=HXH...(8) However, these are. Here, a suitable one out of the 64 components of Y is extracted to create a vector of 2.

Z"(y02t'/20e'104+ V40+
yoat y80)...(11) Let 2 measured in water where oxygen, hydrogen peroxide, and hydrogen exist alone be Zl, Zx, and Za, respectively.

Here, a vector Wl that satisfies equations (12) and (13) is introduced.

<Zz, Wt>= O...(12)<Z a,
Wz>=O (13) where 〉 represents an inner product operation. Here, C1=< Z 1 t W
Wl is determined in advance so that the amount of i > (14) is the amount of dissolved oxygen in water.

Similarly, satisfy <Zl, Ws>=O, <Zz, W3>=0, and CZ=<ZI Wl># C3:<ZJII VJs>
Wz*Ws is predetermined so that the amounts -(16) are the amount of dissolved hydrogen peroxide and the amount of dissolved hydrogen, respectively.

For the vector Z measured in a mixed system of three types of oxygen, hydrogen peroxide, and hydrogen, <Z, Wl>, <Z
.

When Wx>, <Z, Ws> are calculated, these amounts become the amount of dissolved oxygen, the amount of dissolved hydrogen peroxide, and the amount of dissolved hydrogen.

FIG. 11 shows the simultaneous determination of dissolved oxygen, hydrogen peroxide, and hydrogen amounts in the nuclear reactor using random pulse voltammetry, and their respective changes over time. 1st
When the concentration of dissolved oxygen and hydrogen peroxide increases due to the operation of the system shown in the figure, the computer issues a command to inject hydrogen. It can be seen that dissolved oxygen and hydrogen peroxide concentrations tend to decrease with hydrogen injection.

Embodiment 5 In FIG. 12, a three-electrode sensor is constructed using a structural member 24 as a counter electrode, together with a reference electrode 20 and a working electrode 19 shown in FIG. 2 or 6. This electrochemical sensor is compact compared to the one in FIG.

Embodiment 6 In FIG. 13, a two-electrode sensor is constructed using the structural material 24 as a counter electrode and a reference electrode together with the working electrode 19 shown in FIG. 2 or 6. This electrochemical sensor is shown in Figs. 3 and 7.

It is more compact than the one in FIG.

〔Effect of the invention〕

According to the present invention, the working electrode, which is an important part of a water quality sensor, can have a longer lifespan and be highly stable, so the monitoring system and, by extension, the control system can be made highly reliable and maintenance-free, resulting in high economic efficiency. It can be realized.

[Brief explanation of drawings]

Figure 1 is a system diagram of a plant water quality control system for a BWR nuclear reactor that has sensors in the BWR in-reactor instrumentation pipe according to an embodiment of the present invention, and Figure 2 shows a plant water quality control system that is reinforced with four-point support for the electrode part and a protective jig. Figure 3 is a cross-sectional view of an electrochemical sensor consisting of a three-electrode system consisting of a working electrode, a reference electrode, and a counter electrode; Figure 4 is an explanatory diagram of changes in dissolved oxygen concentration over time; Figure 5
The figure is a system diagram of a water quality monitoring system for a once-through thermal power plant.
Fig. 6 is a cross-sectional view of a working electrode reinforced with a support jig and a protective jig, Fig. 7 is a cross-sectional view of an electrochemical sensor consisting of a two-electrode system of a reference electrode and a working electrode, and Fig. 8 is Flowchart for determining the number of reaction electrons and diffusion coefficient, Figure 9 is a normal pulse potential signal and current response diagram, and Figure 10 is for oxygen and hydrogen peroxide. Current-potential curve and random pulse potential signal characteristic diagram in a three-component hydrogen mixture system; Figure 11 is an explanatory diagram of the temporal changes in dissolved oxygen, hydrogen peroxide, and hydrogen concentrations in reactor water and the hydrogen injection effect;
FIG. 12 shows the working electrode of structural material 9. FIG. 13 is a cross-sectional view of an electrochemical sensor configured with a three-electrode system including a reference electrode, and FIG. 13 is a cross-sectional view of an electrochemical sensor configured with a two-electrode system including two structural members and a working electrode. 1... Electrochemical sensor, 2... In-furnace instrumentation tube, 3...
... Potentiostat, 4... Pulse generator, 5.
...Pulse response analyzer, 6...Computer, 7...
・Display device, 8... Gas injection device, 9... Dryer, 10... Reactor core, 11... Reactor water supply piping, 12.
・Reactor recirculation system, 1---1 disaster L 16 呵 7t=
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Claims (1)

[Claims] 1. Means for continuously extracting information directly related to the water quality of the monitored area for a certain period of time using an electrochemical water quality sensor installed in the monitored area of the plant; Equipped with means for evaluating water quality based on information, means for comparing the obtained water quality evaluation results with predetermined reference values for plant operation, and means for displaying or recording necessary parts of the comparison results. In the method for monitoring plant operating conditions, the working electrode of the electrochemical water quality sensor includes an electrode part and a seal part of an insulator for electrically insulating the electrode part and a structural material as minimum components. . A plant operating state monitoring system, characterized in that the electrode part is fixedly supported at two or more points of the seal part by bending the electrode part. 2. Means for continuously extracting information directly related to the water quality of the monitored part of the plant using an electrochemical water quality sensor installed in the monitored part of the plant containing high-temperature water during the period from plant inspection to the next inspection; , a means for evaluating water quality based on this extracted information, a means for comparing the obtained water quality evaluation result with a predetermined reference value for plant operation, and a means for displaying and displaying necessary parts of the comparison result. A method for monitoring plant operating conditions, comprising: a means for recording; and a means for generating a necessary control signal according to the operating state of the plant; A sealing part of an insulator for electrically insulating the insulator and a support jig for the insulator are the minimum components, and the electrode part is fixed at one or more points of the sealing part,
A plant operating state monitoring system characterized by having a structure in which the other end or other portion of the electrode part is supported by the support jig. 3. The plant operating state monitoring system according to claim 1 or 2, wherein any one of the square root of the area, radius, and width of the exposed portion where the electrode portion contacts the water to be monitored is shorter than 5 mm. 4. In claim 1, 2 or 3, the electrochemical water quality sensor comprises a three-electrode system each consisting of at least one working electrode, a reference electrode and a counter electrode, or a two-electrode system using two electrodes thereof. Plant operating status monitoring system. 5. In claim 4, the reference electrode is made of a ceramic material having a porosity sufficient to be impregnated with water to be monitored by plasma spraying or other methods, and is directly attached to the surface of the silver/silver halide or silver/silver sulfate electrode. A plant operating status monitoring system that has a coated structure and indicates a reference potential by means of not immersing silver halide or silver sulfate in a halide ion or sulfate ion solution. 6. In claim 1, 2, 3, 4 or 5, the means for extracting information directly related to the water quality of the monitored area by the electrochemical water quality sensor includes water quality analysis using one or more types of voltammetry. A plant operating status monitoring system that performs 7. The plant operating state monitoring system according to claim 6, wherein the voltammetry is one or more of reverse pulse, normal pulse, differential pulse, square wave, normal differential pulse, and pulse voltammetry. . 8. The plant operating status monitoring system according to claim 6, wherein the voltammetry is random pulse voltammetry. 9. Claim 1, 2, 3, 4, 5, 6, 7 or 8, wherein the means for extracting information directly related to the water quality of the monitored area by the electrochemical water quality sensor is dissolved in the monitored water. A plant operating status monitoring system that simultaneously measures oxygen, hydrogen peroxide, and hydrogen. 10.Claim 1, 2, 3, 4, 5, 6, 7, 8 or 9
In the plant operating state monitoring system, the electrochemical water quality sensor is installed in a reactor core of a nuclear power plant, near an instrumentation pipe, in or near a separator, in a lower plenum or near a cooling piping system. 11.Claim 1, 2, 3, 4, 5, 6, 7, 8 or 9
In the plant operating state monitoring system, the electrochemical water quality sensor is installed downstream of a condensate pump, upstream and downstream of a deaerator, and upstream of a energy saver of a thermal power plant. 12.Claims 1, 2, 3, 4, 5, 6, 7, 8, 9, 1
0 or 11, the means for generating the control signal generates hydrogen gas based on measurement data of one or more of dissolved oxygen concentration, dissolved hydrogen peroxide concentration, and dissolved hydrogen concentration measured at one or more locations. A plant operating status monitoring system that controls the amount of injection.