JPH051904B2 - - Google Patents

Description

Detailed Description of the Invention [Field of Application of the Invention] The present invention relates to a high-temperature, high-pressure water reference electrode body used for measuring the corrosion potential of a nuclear reactor structure under a high-temperature, high-pressure environment, and particularly relates to an internal reference electrode method. The present invention relates to a high-temperature, high-pressure water reference electrode body having a structure suitable for use in the present invention.

[Background of the invention]

Conventional reference electrodes used for electrochemical testing of metal materials in high-temperature, high-pressure water include the external reference electrode method, in which a reference electrode installed under atmospheric pressure and a sample electrode in high-temperature water are connected, and the reference electrode method. There is an internal reference electrode method in which the electrode is placed directly in high-temperature, high-pressure water. Since it is difficult to convert the potential measured by the external reference electrode method into a thermodynamically meaningful potential, it is preferable to use the internal reference electrode method. This internal reference electrode method requires the use of an electrode that can stably measure corrosion potential over a long period of time in a high-temperature, high-pressure environment. However, conventional electrodes have a problem in that it is difficult to perform stable measurements over a long period of time due to a decrease in the electrode liquid due to leakage from the liquid junction. The present invention relates to an improvement in the structure of this internal reference electrode body.

In the internal reference electrode method, the pressure and temperature inside the pressure vessel are maintained at reactor water conditions of approximately 70 to 80 kg/cm ² g and 250 to 300°C. The electrode solution in the electrode chamber is also pressurized and heated to the same extent, the volume of the electrode solution expands, and the increased amount of electrode solution leaks out of the electrode chamber through the liquid junction member. On the other hand, when the pressure and temperature are lowered, the volume of the electrode solution contracts, so the test water flows into the electrode chamber through the liquid junction member, reducing the concentration of the electrode solution and making stable measurements over a long period of time difficult. . Therefore, in order to measure corrosion potential stably over a long period of time, the structure of the electrode chamber must be such that the electrode solution does not leak even under high temperature and high pressure environments.

Conventional reference electrode body for high temperature and high pressure
108949 (reference electrode body for high-temperature, high-pressure water) will be explained using FIG.

The reference electrode body 1 is tightly fixed to the pressure vessel lid plate 2, and its lower half is in the test water 3 and its upper half is in the atmosphere. The reference electrode body 1 is a cylindrical body made of stainless steel, and an electrode chamber 4 containing an electrode liquid 5 of KCl solution and a reference electrode 6 made of a silver chloride electrode is formed in the lower part of the body, and the electrode chamber 4 is sealed with a sealing material 7. It's stopped.
Asbestos string is inserted into the hole provided in the sealing material 7 to form a liquid junction member 8. A passage 9 provided above the electrode chamber 4 is bent at the upper part of the electrode chamber 4 and communicates with the test water 3 via a pressure transmission hole 10 . The pressure transmission hole 10 and the passage 9 maintain the pressure balance between the test water 3 and the electrode liquid 5.
In addition, a small cylindrical piston 11 made of corrosion-resistant synthetic rubber is movable in the passage 9, and an electrode liquid 5
and test water 3 with both ends in contact with each other.
The platinum wire connected to the reference electrode 6 is insulated with a tube 12 of a fluorine resin such as Teflon (trade name of Dupont Co., the same hereinafter), enters the rising part of the passage 9, and is further sealed with a pressure seal part 13. The lead wire 15 is passed through the material 14 airtight and drawn out into the atmosphere.
is connected to. This lead wire 15 is connected to the test material immersed in the test water 3 via a voltmeter.

When this pressure vessel is heated to raise the temperature of the test water 3 to about 300°C, the electrode solution 5 is also heated to the same degree.
Therefore, the volume of the electrode liquid 5 expands, but the increased volume pushes down the piston 11 in the passage 9, and stops when the pressure of the test water 3 and the pressure of the electrode liquid 5 are in equilibrium. On the other hand, when the heating of the pressure vessel is stopped and the temperature of the test water 3 is lowered, the temperature of the electrode solution 5 is also lowered and the volume contracts. Along with this, the piston 11 moves up the passage 9 and the electrode solution 5 and the test water 3 are removed.
Move to a place where the pressure is balanced. That is, the volume change due to the temperature change of the electrode liquid 5 causes the piston 11 to
The structure is such that most of it is absorbed by the movement of

However, this structure had the following drawbacks.

(1) Since the piston 11 has a movable part that moves up and down the passage 9, the electrode liquid 5 gradually leaks from the gap between the piston and the passage, making long-term stable use impossible.

(2) Since it has the above-mentioned movable part, high precision is required in manufacturing the part where the piston 11 and the passage 9 come into contact. In addition, synthetic rubber piston 11 and
It is necessary to design and manufacture the device by fully considering the difference in volumetric expansion due to the difference in material between the channel of the reference electrode body made of SUS304, and this point leads to a major drawback (increased cost, etc.) in device manufacturing. Furthermore, having such a movable part may impair the reliability of the electrode for long-term use.

Next, a conventional reference electrode body for high-temperature, high-pressure water (internal reference electrode body for a corrosion test tank in a high-temperature, high-pressure environment according to JP-A-57-125841) will be explained with reference to FIG.

As the liquid junction member 8 between the reference electrode body 1 and the test water 3, a liquid junction plug 16 made of porous zirconia is installed at the tip of the electrode protection tube to prevent leakage of the electrode liquid 5 and to form a liquid junction with the test water 3. ing. This liquid junction plug 16
is fixed to the electrode container 23. The electrode body 1 is
It is an insulator such as zirconium oxide, and has an insulating resin piston 11 therein. An Ag/AgCl electrode rod 17 is inserted into this piston 11, and an electrode liquid 5 such as a KCl solution is filled between the piston 11 and the liquid junction plug 16. The space between the test water 3 and the electrode liquid 5 is sealed by a packing 19 on the outer surface of the piston 11 and a packing 20 on the inner surface. The piston 11 has an insulating tube 22 that electrically insulates the inner surface of the electrode body 1 and the Ag electrode rod 21.
attached so that it can slide over the surface of the Between the piston 11 and the seal plug 18, the piston 1
The pressure in the pressure vessel is applied through the hole 24 of the electrode body located above the electrode body 1, and the pressure is the same as that of the outer and inner surfaces of the electrode vessel 23, and equilibrium is maintained.
Therefore, the electrode liquid 5 is less likely to leak from the liquid junction member 8.

However, since the electrode body also has a movable piston 11, there is a risk that the electrode liquid 5 may leak from the gap between the piston and the inner surface of the electrode body and the surface of the insulating tube 22 (hereinafter referred to as the sliding surface), similar to the electrode body. There are problems such as difficulty in manufacturing the piston 11 and the sliding surface, and the possibility that movement of the piston will be inhibited due to the difference in coefficient of thermal expansion caused by the difference in the materials of the piston and the sliding surface. The structure is not yet optimal for stable long-term measurements.

On the other hand, Utility Model Publication No. 46-29673 discloses a reference electrode for high-pressure water that is equipped with an electrode chamber, a pressure absorption mechanism, a liquid junction member, and the like. In this case, a spring is used to pressurize the piston, and the pressure of the electrode liquid, that is, the internal liquid, is maintained at a more positive pressure than the pressure of the measurement liquid tank. Because the electrode liquid is constantly pressurized, the fiber type liquid This is in a direction that encourages leakage of the electrode solution from the area. This is not suitable for long-term use on the order of several years.

Further, it cannot be used in a high-temperature, high-pressure environment like the present invention. When the gas phase part suppresses the rise in the level of the measured liquid that has entered the protection tube, the pressure in the measured liquid tank does not rise significantly after the level of the measured liquid rises. The assumption that the exposed mating surface of the piston is never immersed in the measuring liquid does not hold true in the case of nuclear power plants, and the pressure rises from atmospheric pressure to approximately 80 kg/cm ² g. This is because the liquid level will rise accordingly, and there is a possibility that the measuring liquid may enter from the upper part of the outer cylinder.

Furthermore, Utility Model Publication No. 52-14476 proposes a reference electrode that is suitable for measurements in places with high external pressure, such as pH measurement in seawater.

However, there is no description suggesting use in a high-temperature environment, and there are no plans to use it in a high-temperature, high-pressure environment like a nuclear reactor, and the device was developed on the premise that the entire device would be immersed in the measurement liquid. Such a structure cannot withstand the reactor water environment (approximately 280°C, approximately 80 kg/cm ² g).

Next, the internal liquid, that is, the electrode liquid, is allowed to flow out, and a method is adopted in which the bellows is provided with a contraction force to promote the outflow of the internal liquid. Therefore, in order to eliminate the instability of the reference electrode potential due to the intrusion of seawater, we aim only in the direction of the outflow of the electrode solution, and the reduced electrode solution is removed each time the reference electrode is brought up to a ship at sea. This is a replenishment method.

In this case, as in Utility Model Publication No. 46-29673, the method is to apply pressure in a direction that actively promotes leakage of the electrode solution, so the electrode solution has to be replenished in a relatively short period of time. It is not suitable for applications where the purpose is to use it for several years without replenishing the liquid.

[Purpose of the invention]

The purpose of the present invention is to:
An object of the present invention is to provide a reference electrode body for high-temperature, high-pressure water having a structure that prevents leakage and suppresses diffusion of an electrode liquid in order to stably measure the corrosion potential of various structural materials over a long period of time.

[Summary of the invention]

The main points of the invention will be explained below using FIG.

(1) Electrode liquid leakage prevention structure The reference electrode body 1 with the protective tube 1A fixed to the pressure vessel cover plate 2 is heated and pressurized by high temperature and high pressure test water 3. Therefore, the electrode liquid 5 filled in the electrode chamber 4 is also heated to the same extent and causes volume expansion. Due to this volumetric expansion of the electrode solution 5, the electrode chamber 4
The internal pressure P _i0 inside increases to become P _i . If the electrode chamber pressure P _i becomes considerably larger than the leakage pressure P _l of the liquid junction member 8, the electrode liquid 5 will leak through the liquid junction member 8 into the test water 3 at a leakage rate R _i , and as shown in FIG. The performance as an electrode will deteriorate. Electrode chamber pressure P _i
and the leakage pressure P _l of the liquid junction member 8,
Reducing the leakage rate R _i of the electrode solution 5 into the test water as low as possible is a condition for maintaining the performance of the reference electrode over a long period of time.

Here, the dilution rate of the electrode solution 5 to maintain the performance of the reference electrode varies depending on the accuracy required for measurement, but from experience, the leakage rate R of the electrode solution 5 is usually about 1/10. _c is determined by the frequency of replacing the electrode solution 5. If the frequency of replacing the electrode solution 5 is n years due to design requirements, the concentration of the electrode solution 5 should be set to A.
[N], the allowable leakage rate R _c is R _c =
0.1A/n [N/year]. Therefore, R _i <R _c
(See Figure 2) If the relationship between the electrode chamber pressure P _i and the leakage pressure P _l of the liquid junction member 8 is demonstrated, the electrode liquid 5 can be used for a long period of time (N years or more) without being replaced. becomes possible.

To do this, a pressure absorption mechanism is provided in a part of the electrode chamber 4 to absorb the increase in internal pressure due to thermal expansion of the electrode liquid 5, suppressing the increase in the electrode chamber pressure P _i , and reducing the leakage pressure P _l of P _i and the liquid junction member 8. It is necessary to reduce the pressure difference between

To summarize the above conditions, in order to suppress the increase in electrode chamber pressure P _i due to volumetric expansion of the electrode liquid 5 at high temperatures, a flexible bellows or diaphragm without sliding parts is installed in a part of the electrode chamber 4 to suppress the increase in electrode chamber pressure P i due to volumetric expansion of the electrode solution 5 at high temperatures. The absorption mechanism 26 is provided to reduce the differential pressure between this and the leakage pressure P _l of the liquid junction member 8, so that R _i (leakage rate of the electrode liquid 5 from the liquid junction member 8) < R _c (liquid junction member 8 The first key point of the present invention is to maintain the performance of the reference electrode over a long period of time by achieving a permissible leakage rate of the electrode solution 5 from the electrode.

(2) Electrode liquid diffusion suppression structure Electrode liquid 5 leaking from the liquid junction member 8 at high temperatures
has conventionally been directly diffused into the test water 3. Conversely, when the temperature drops, the test water 3 flows into the electrode chamber 4 through the liquid junction member 8, diluting the electrode solution and contributing to deterioration of electrode performance. Therefore, as shown in FIG. 1, a liquid junction cover 25 is provided to cover the liquid junction member 8, and a concentration buffer area is provided between the liquid junction member 8 and the test water 3 to prevent leakage from the liquid junction member 8. The electrode liquid 5 is retained in the liquid tank cover 25,
Improvements were made to suppress diffusion into Test Water 3.
Further, when the temperature is lowered, the structure is such that the stagnant electrode liquid flows into the electrode chamber 4 through the liquid junction. The liquid junction with the test water is performed through the pores 27 of the liquid junction cover 25.

Thus, the second point of the present invention is to improve the conventional drawback that the electrode solution was diluted when the temperature of the electrode body was lowered, making it impossible to stably measure the corrosion potential over a long period of time.

Note that although the concentration buffer region has been described here as being provided between the liquid junction member and the test water, the same effect can be obtained even if it is provided between the electrode chamber and the liquid junction member.

[Embodiments of the invention]

FIG. 3 is a vertical cross-sectional view showing a state in which a high-temperature, high-pressure water reference electrode body according to a preferred embodiment of the present invention is attached.

The protection tube 1A of the reference electrode body 1 is connected to the pressure vessel lid plate 2.
The lower half is in the test water 3, and the upper half is in the atmosphere. The protection tube 1A of this reference electrode body 1 is a cylindrical body made of stainless steel.
A fin 29 is provided on the outside for air cooling. On the other hand, inside there is an electrode chamber 4 having a reference electrode 6 and an electrode solution (KCl solution, etc.) 5, which is sealed with a Teflon holder 28. This Teflon holder 28
A liquid junction member 8 made of porous Teflon (or ceramic) is attached to the holder 28, and a liquid junction cover 25 having pores 27 for forming a liquid junction with the test water 3 is provided on the outside of the Teflon holder 28. installed.

Further, a diaphragm 26 is provided above the electrode chamber 4 as one of the pressure absorption mechanisms. The pressure of the test water 3 is transmitted to the outside of the diaphragm 26 through the pressure transmission hole 10 and the pressure transmission passage 9. The diaphragm 26 absorbs an increase in internal pressure due to volumetric expansion of the electrode liquid 5 at high temperatures.

Next, a method of testing the corrosion resistance of a nuclear reactor structural material using the reference electrode body 1 configured in this manner will be described.

The pressure vessel is filled with test water 3, the material to be tested is immersed and sealed, and the pressure vessel is heated under pressure (for example, under reactor water environmental conditions, 70 to 80 kg/cm ² g and 250
~300℃). The electrode liquid 5 in the electrode chamber 4 is also heated to the same extent, expands in volume, and the internal pressure P _i in the electrode chamber 4 increases. This internal pressure increase ΔP _i is caused by the diaphragm 26 which is a pressure absorption mechanism provided at the upper part of the electrode chamber 4.
(the volumetric expansion of the electrode liquid 5 is absorbed by the deformation of the diaphragm 26 without a sliding part), and the internal pressure P _i is kept lower than the allowable leakage pressure P _lc of the liquid junction member 8. Thereby, the leakage rate R _i of the electrode liquid 5 from the liquid junction member 8 becomes smaller than the permissible rate R _c , and the performance of the reference electrode body 1 can be stably maintained over a long period of time.

Further, in order to prevent the electrode solution 5 from directly diffusing into the test water 3 from the liquid junction member 8 of the Teflon holder 28, a liquid junction cover 25 is provided on the outside of the Teflon holder 28. The diffused electrode solution 5 is retained in this liquid junction cover 25, suppressing diffusion into the test water 3, and preventing deterioration of the electrode solution 5.

As a result of the above, stable measurement of corrosion potential over a long period of time has become possible.

〔Effect of the invention〕

According to the present invention, the following effects can be obtained.

(1) In a high-temperature, high-pressure water environment, the increase in pressure within the electrode chamber due to volumetric expansion of the electrode liquid is absorbed by a pressure absorption mechanism (diaphragm, etc.) with no sliding parts provided in a part of the electrode chamber, and (Electrode chamber pressure P _i )<
(Leakage rate from liquid junction member _{R i )} <
(allowable leakage rate R _c from the liquid junction member) and suppressed the leakage of the electrode liquid from the liquid junction member to below the allowable value, preventing deterioration of the electrode liquid and even under high temperature and high pressure. , corrosion potential can be measured stably over a long period of time.

(2) Attach a liquid junction cover to the outside of the Teflon holder to create a concentration buffer area between the liquid junction member and the test water, suppress the diffusion of the electrode liquid from the electrode chamber into the test water, and prevent the electrode inside the electrode chamber from spreading. Since dilution of the liquid is prevented, corrosion potential can be measured stably over a long period of time.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram of a reference electrode body for high-temperature, high-pressure water according to the present invention, Fig. 2 is a graph showing the relationship between elapsed years and allowable leakage amount of electrode liquid, and Fig. 3 is a reference electrode body for high-temperature and high-pressure water to which the present invention is applied. Cross-sectional view of the electrode body, Figures 4 and 5
The figure is a cross-sectional view of a conventional reference electrode body for high-temperature, high-pressure water. DESCRIPTION OF SYMBOLS 1... Reference electrode body, 1A... Protection tube, 2... Pressure vessel cover plate, 3... Test water, 4... Electrode chamber, 5...
... Electrode liquid, 6 ... Reference electrode, 7 ... Sealing material, 8 ...
... Liquid junction member, 9 ... Passage, 10 ... Pressure transmission hole,
11...Piston, 12...Teflon tube,
13... Pressure seal portion, 14... Sealing material, 15...
...Lead wire, 16...Liquid junction plug, 17...
Ag/AgCl electrode rod, 18... Seal plug, 19
...Patsukin, 20...Patsukin, 21...Ag
Electrode rod, 22... Insulating tube, 23... Electrode container, 24... Hole, 25... Liquid junction cover, 26...
...diaphragm, 27...pore, 28...Teflon holder, 29...fin.

Claims (1)

[Scope of Claims] 1. A high-temperature, high-pressure water reference electrode body for measuring the potential of a test material immersed in test water, which houses a reference electrode and an electrode solution inside, and is flexible and has no sliding parts. an electrode chamber having a pressure absorption mechanism in the upper part and a liquid junction member having an allowable leakage pressure Plc greater than the internal pressure Pi of the electrode chamber itself arranged in the lower part; a protection tube having a transmission hole and a pressure transmission passage and guiding the pressure of the test water to a pressure absorption mechanism in the upper part of the electrode chamber; and a protection tube having a pore in liquid contact with the test water and connecting the lower part of the electrode chamber A reference electrode body for high-temperature, high-pressure water, characterized in that it comprises a liquid junction member and a liquid droplet cover that forms a concentration buffer region around the liquid junction member. 2. In the reference electrode body for high-temperature and high-pressure water according to claim 1, a concentration buffering area between the electrode solution and the test water inside the liquid droplet cover is arranged between the liquid junction member and the test water. A reference electrode body for high-temperature, high-pressure water, characterized by being formed in. 3. In the reference electrode body for high-temperature and high-pressure water according to claim 1, a concentration buffering area between the electrode solution and the test water inside the liquid chamber cover is located between the electrode chamber and the liquid junction member. A reference electrode body for high-temperature, high-pressure water, characterized by being formed in. 4. In the reference electrode body for high-temperature, high-pressure water according to any one of claims 1 to 3, the protective tube in at least a portion of the electrode chamber containing a built-in pressure absorption mechanism is filled with the test water. 1. A reference electrode body for high-temperature, high-pressure water, characterized in that the reference electrode body for high-temperature and high-pressure water is provided with a means for cooling the pressure absorption mechanism, which is made to protrude outside the container in which it is housed, and is provided outside the protection tube.