JP2008202972A - Waste disposal container corrosion monitoring device and monitoring method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a waste disposal container corrosion monitoring device and a monitoring method, capable of collecting corrosion data in an actual environment by utilizing a buried body. <P>SOLUTION: This device is such that a metal electrode 2 used as an electrochemical sensor is installed on the outer surface of a waste disposal container 1 in the insulated state 3 with a container body; an electrochemical signal between the metal electrode and the waste disposal container is detected; and a corrosion environment of the outside of the waste disposal container and corrosion speed of the container are monitored. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a waste disposal container corrosion monitoring apparatus and monitoring method used in the disposal of radioactive waste generated from nuclear facilities.

Radioactive waste has different disposal methods depending on its radioactivity level, but low-level waste is decided to be stored in a container such as carbon steel and buried in the ground. Radionuclides are isolated from the living sphere by barriers such as containers, concrete, bentonite, and bedrock, but after a long period of time, it is assumed that a trace amount of radioactivity after attenuation may pass through these barriers and reach the living sphere. To evaluate safety. Safety is evaluated for each case, but all of them are not expected to protect the container so much, and it is assumed that the corrosion hole penetrates at the same time as the groundwater is submerged.
JP 2003-344586 A

  Even in the case of carbon steel, the corrosion rate is extremely low and long-term protection can be expected in a reducing atmosphere in which high saturated pH cement saturated water or oxygen is consumed. It is necessary to raise the expectation for other barriers if the evaluation is made by estimating the corrosion resistance of the disposal container under excessive maintainability. For disposal containers, it is possible to design a rational waste burying system by evaluating the corrosion rate in the buried environment and assuming appropriate protection performance. However, there is no corrosion data in the actual environment, and the actual situation is to design based on the evaluation based on laboratory test data.

In view of the above problems, an object of the present invention is to provide a waste disposal container corrosion monitoring apparatus and monitoring method capable of collecting corrosion data in an actual environment using an initial buried body.

  The waste disposal container corrosion monitoring apparatus according to the present invention is a metal electrode that is disposed on the outer surface of a waste disposal container, insulated from the container body, and serves as an electrochemical sensor, and the electrochemical between the metal electrode and the waste disposal container. And a monitoring device for detecting a signal and monitoring a corrosive environment outside the waste disposal container and a corrosion rate of the waste disposal container.

  Further, the waste disposal container corrosion monitoring method according to the present invention includes an electrochemical signal between a metal electrode serving as an electrochemical sensor installed on the outer surface of the waste disposal container and insulated from the container body, and the waste disposal container. And the corrosive environment outside the waste disposal container and the corrosion rate of the container are monitored.

  In the present invention, the form of corrosion can be known from the form of potential fluctuation. Further, the corrosion resistance, that is, the corrosion rate can be estimated by simultaneously measuring the potential and the current.

(First embodiment)
A first embodiment of the invention will be described with reference to FIG. In FIG. 1, when the measurement is started when the outer surface of the waste disposal container 1, for example, the entire container is submerged, a carbon steel electrode 2 made of the same material as the container 1 is attached to the upper part 1 a of the container 1 via an insulating member 3. Is. The electrical conductivity is measured by measuring the electrical resistance between the carbon steel electrode 2 and the waste disposal container 1 through the lead wires 4 and 5.

By measuring the electrical conductivity around the disposal container 1, it is possible to know when the groundwater has been submerged after the disposal container 1 is buried. The conductivity is obtained by measuring the electrical resistance between the two electrodes. Before inundation, since it is in the atmosphere, the resistance between the two insulated electrodes can be considered almost infinite. After the immersion, the two electrodes are immersed in the electrolyte solution, that is, the electric resistance becomes a predetermined value or less. There are ions (a cation with positive electricity and an anion with negative electricity) in the electrolyte solution. When a pair of metal plates is placed in the electrolyte solution and the battery is connected, the positive ions move to the negative side of the battery, the negative ions move to the positive side of the battery, and an electric current is generated in the solution. It is done.

Conductivity = (Current / Voltage) x (Distance between electrodes / Area) ... (1)
By using the disposal container 1 as one electrode 5 and the electrode 4 installed in the present invention as a counter electrode, and continuously measuring the resistance between them, it becomes possible to know the timing of flooding.

  In this case, the area effect between the electrode and the counter electrode container cannot be expressed in a simple form as shown in Formula 1, but it is not necessary to measure the exact conductivity, and it is detected that water has been submerged from a sudden drop in resistance. Therefore, it is sufficient not to make the electrodes face each other but to arrange them in a plane.

  FIG. 2 shows an overall view of the waste disposal facility 10. The disposal container 1 is surrounded by barriers such as a filler 15, concrete pit 16, bentonite 16, and the like. It is unthinkable to flood in

  Electrochemical signals between the disposal container 1 and the electrode 2 shown in FIG. 1 are sent from the lead wires 4 and 5 through the signal cable 19 to the measuring instrument 11 and the data collection computer installed in the disposal body management building 18 and the like. 12 and sent to a remote management center (not shown) or the like as necessary.

  By measuring the electrical conductivity around the disposal container 1, it is possible to know at what point the groundwater has been submerged after the disposal container is buried. After the immersion, the corrosion potential of the container can be known by measuring the relative potential between the carbon steel electrode 2 and the disposal container 1 and the current between the carbon steel electrode 2 and the disposal container 1.

  Here, the measurement of the relative potential between the carbon steel electrode 2 and the disposal container 1 will be described.

When the surface of the corroding metal is microscopically captured, it can be divided into an anode part that locally contributes to the dissolution reaction and a cathode part that contributes to the reaction in which the oxidizing agent is reduced to capture electrons. Since the anode / cathode pair always fluctuates, the potential of the corroding material fluctuates microscopically, and the state of corrosion can be estimated by analyzing this fluctuation as electrochemical noise. it can. FIG. 3 shows an example of the change in corrosion potential (mVSCE) in which the time of the SUS304 steel immersed in a 3.5% NaCl solution at a temperature of 80 ° C. is shown on the horizontal axis. As shown in FIG. 3, the acute-angled potential oscillation in the base direction captures the occurrence of minute damage, and the rapid potential drop indicates that the damage is steadily progressing. By observing the potential oscillation in this way, it is possible to estimate the form and progress of corrosion and the elution rate of the disposal container.

  From the shape of the potential fluctuation, the form of corrosion can be known as shown in FIG. Further, the corrosion resistance, that is, the corrosion rate can be estimated by simultaneously measuring the potential and the current.

  Next, the measurement of the current between the carbon steel electrode 2 and the disposal container 1 will be described.

  As described in the measurement of the electric potential, since the local anode / cathode pair always fluctuates, current noise is obtained when the corrosion current flowing between the carbon steel electrode 2 and the disposal container 1 is measured. By analyzing this variation as electrochemical noise, the state of corrosion can be estimated. Further, by simultaneously measuring the potential fluctuation and the current fluctuation, the corrosion resistance Rp can be obtained by two formulas.

Rp = DE / Di (2)
Here, DE: deviation value of potential fluctuation, Di: deviation value of current fluctuation.

As shown above, by knowing the timing of inundation and the corrosion rate of the container in the actual environment or the dissolution rate of the disposal container, the elution and diffusion of the radionuclide can be estimated without excessive maintainability, A reasonable waste burial system can be designed.

  The measurement interval of the potential or current is 10 seconds or less. This is because by setting the measurement interval to 10 seconds or less, it is possible to accurately measure the potential vibration or current vibration, which is an electrochemical noise shown as a form of corrosion of the disposal container.

  Further, the detected electrochemical signal is taken into the data collection computer 12 which is a computer in the disposal site, and transmitted from the data collection computer 12 to the remote monitoring facility by wire or wirelessly, so that it is always easily discarded at the remote monitoring facility. Corrosion of material disposal containers can be monitored.

(Second Embodiment)
A second embodiment of the present invention is shown in FIG. In FIG. 4, the same parts as those in FIG.

  In the second embodiment of the present invention shown in FIG. 4, an inactive metal electrode, for example, a platinum electrode 6 is insulated and attached to the upper portion 1a of the waste disposal container 1, and the other configuration is the first embodiment. It is the same as the form.

  By using, for example, platinum, which is an inert metal, as an electrode, stable information can be acquired over a long period of time without corrosion even in a high temperature environment or a submerged environment.

In this embodiment, platinum is shown as an inactive metal, but it is needless to say that it may be made of gold.

  Therefore, in the second embodiment of the present invention, even if submerged, there is no risk of corrosion, and it is possible to know the timing of inundation and the corrosion rate of the container in the actual environment, and the elution and diffusion of radionuclides are excessively maintainable. This makes it possible to design a rational waste burying system.

The perspective view which shows the waste disposal container used for the 1st Embodiment of this invention. Schematic which shows the waste disposal container corrosion monitoring apparatus and monitoring method which concern on embodiment of this invention. The characteristic figure which shows the fluctuation | variation of the corrosion potential of stainless steel in a 3.5% NaCl solution. The perspective view which shows the waste disposal container used for the 2nd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Waste disposal container 2 ... Carbon steel electrode 3 ... Insulating member 4, 5 ... Lead wire 6 ... Platinum electrode 10 ... Waste disposal facility 11 ... Measuring instrument 12 ... Data collection computer 13 ... Concrete pit 14 ... Rock 15 ... Filler 16 ... Bentonite 17 ... Disposal cavity construction 18 ... Management building 19 ... Signal cable

Claims (11)

  A metal electrode that is insulated from the container body on the outer surface of the waste disposal container and serves as an electrochemical sensor, and detects an electrochemical signal between the metal electrode and the waste disposal container to detect the corrosive environment outside the waste disposal container and A waste disposal container corrosion monitoring device comprising: a monitoring device for monitoring a corrosion rate of the waste disposal container.   2. The waste disposal container corrosion monitoring apparatus according to claim 1, wherein the electrode material installed in the waste disposal container is an inert metal.   2. The waste disposal container corrosion monitoring apparatus according to claim 1, wherein the electrode material installed in the waste disposal container is the same material as the waste disposal container.   4. The waste disposal container corrosion monitoring apparatus according to claim 1, wherein the detected electrochemical signal is taken into a computer in a disposal site and remotely monitored by wire or wirelessly. 5.   The electrochemical signal between the metal electrode, which is an electrochemical sensor installed on the outer surface of the waste disposal container and insulated from the container body, and the waste disposal container is detected, and the corrosive environment outside the waste disposal container and the container A waste disposal container corrosion monitoring method characterized by monitoring the corrosion rate.   The electrochemical signal to be detected is an electrical resistance between the waste disposal container and the metal electrode, and when the value of the electrical resistance to be detected is a predetermined value or less, it is detected that the periphery of the container has been submerged. The waste disposal container corrosion monitoring method according to claim 5.   The detected electrochemical signal is a potential difference between a waste disposal container and a metal electrode and / or the detected electrochemical signal is a current flowing between the waste disposal container and the metal electrode or both. 5. The waste disposal container corrosion monitoring method according to 5.   The waste disposal container corrosion monitoring method according to claim 7, wherein the electrochemical signal to be detected detects the vibration of the potential or current as potential or current noise, and estimates the corrosion rate.   9. The waste disposal container corrosion monitoring method according to claim 8, wherein corrosion resistance is calculated from values of the potential vibration and current vibration, and a corrosion rate is estimated.   The waste disposal container corrosion monitoring method according to any one of claims 5 to 9, wherein a measurement interval of the potential or current is set to 10 seconds or less.   11. The waste disposal container corrosion monitoring method according to claim 5, wherein the detected electrochemical signal is taken into a computer in a disposal site and remotely monitored by wire or wirelessly. 11.

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