JPS5965297A - Method of suppressing adhesion of radioactive material to atomic power plant - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a method for forming an oxide film to prevent the adhesion of radioactive ions, and in particular to piping for the primary cooling water system of a boiling water type atomic couplant. This invention relates to a method for forming an oxidation degree Jq for a metal member used in contact with a liquid in which a radioactive substance is dissolved.

Piping used in the primary cooling water system of the nuclear couplant)
Pumps, valves, etc. are made of stainless steel, stellite steel, etc. The metals that make up these structural materials are subject to corrosion damage when used for long periods of time. +, 5';
Elemental metals Elements are eluted into the cooling water and brought into the reactor. Most of the eluted gold and metal elements become oxides and adhere to the fuel rods, where they are exposed to neutron irradiation. The rice supply, “Co,”
Radionuclides with relatively long half-lives such as Co, Cr, and Mn are generated.These radionuclides are re-eluted into the primary cooling water and ions, or these ions are mainly oxidized and generated within the reactor. It floats as an insoluble solid component (hereinafter referred to as crud).The floating part is removed by a demineralizer for purifying the reactor water, but the remainder is mainly deposited in the stainless steel as it circulates throughout the primary cooling water system. It adheres to the surface of structural materials made of steel.For this reason, the dose rate on the surface of the structural materials increases, creating a problem of radiation blast exposure for workers when carrying out maintenance and inspections.

For this reason, as a method to prevent the surface dose rate of structural materials from increasing JA, methods of removing radioactive substances adhering to structural materials have been studied and implemented. Examples of removal methods include fil mechanical cleaning method (2) chemical cleaning method (3) 'rLj cleaning method using gas decomposition.

fil's mechanical cleaning method is mainly applied to parts, for example, cleaning the surface with high-pressure jet water. However, with this method, it is difficult to remove highly adhesive radioactive substances, and a wide area u1j cannot be systematically decontaminated. In fact, even if the dose rate is temporarily reduced by this method, the dose rate tends to increase again with subsequent long-term use.

The chemical cleaning method (2) uses a chemical such as an acidic solution to dissolve the oxide film on the steel surface that undergoes a chemical reaction, and removes the radioactive substances present in the film. The problem with this method is the corrosion damage to the 4N construction material caused by the chemicals. That is, when the coating is dissolved, the structural materials are also damaged by corrosion, and there is a risk that the small amount of chemicals remaining after the first decontamination may cause stress corrosion cracking in the 4ijj construction materials.

The cleaning method using '.d gas decomposition in (3) also has the same problems as the fil reconnaissance cleaning method.

Furthermore, in order to reduce the amount of radioactive substances, methods are being used to suppress the elution of the metal element itself, which is the source of radioactive substances. In other words, most of the impurities in the secondary cooling water are produced when the 4:,7 metals in the water supply system are eclipsed and brought into the reactor, so i'i '
Injecting two elements into the water supply system to suppress corrosion, suppress the inflow of corrosion products including iron into the reactor, and activate it]:
We have achieved some results in reducing the shrinkage rate by reducing the shrinkage rate. In order to suppress the ingress of radioactive ions into the oxide film at the initial stage, preliminary oxidation of the structurally controlled surface has been considered. This is done by focusing on the fact that the penetration rate is proportional to the rate of oxide film formation on the M-piece within the structure, and that the rate of oxide film formation increases significantly in the early stages of immersion in high-temperature water.

In this case, for preliminary oxidation, the inner surface of the structural material should be
It is necessary to immerse in high-temperature water with a temperature of C or higher, and for materials such as stainless steel, which have a low corrosion rate and therefore a relatively low rate of oxide film formation, pre-oxidation time of at least several hundred hours is required to prevent radioactive ions. There are problems in applying it to actual atomic couplants where plant operation cannot be interrupted for long periods of time, such as the inability to obtain the effect of suppressing the incorporation of into the oxide film.

[Purpose of the invention]

An object of the present invention is to provide a method for suppressing the adhesion of radioactive substances to an atomic couplant, which accelerates the formation of an oxide film on a structural material, shortens the pre-oxidation time on the structural material, and suppresses the incorporation of radioactive ions into the oxide film. Our goal is to provide the following.

[Summary of the invention]

In order to achieve the above object, the present invention aims at electrically accelerating the formation of an oxide film by anodically polarizing the target structural material in order to accelerate the formation of the film at the above oxidation level. This is what I did. More preferably, when forming an oxide film, even if oxide film-forming component elements such as nickel and chromium adhere to the surface of the horizontal G material after being irradiated in the reactor, due to their short half-life, the surface is line -
In order to increase the concentration of component elements that do not contribute to an increase in the E ratio in high-temperature water, 4 Mi of eluted gold pieces rich in the component elements are added to the anode, and the elution rate is increased.
It is designed to multiply by W.

That is, the first feature of the present invention is that radioactive substances or
J4 In a method for suppressing the adhesion of radioactive substances in an atomic couplant using a structural material made of metal that is used in contact with a liquid, the structural material is anodically polarized to electrically form an oxide film on the structural material. It is about forming.

The 2B2 feature of the present invention is that radioactive substances are dissolved in l
(In the method for suppressing the adhesion of radioactive substances in atomic couplants that use structural materials made of metal that are used in contact with
A reference electrode is provided in the liquid, and the potential difference between the reference electrode and the structural material is maintained at a potential within a range where a film is formed on the structural material. The object of the present invention is to form an oxide film on the structural material by adjusting the current flowing between the structural material and the cathode electrode so that the material serves as an anode and the cathode electrode serves as a cathode.

A third feature of the present invention is a method for suppressing the adhesion of radioactive substances in an atomic couplant using a structural material made of metal that is used in contact with a liquid in which radioactive substances are dissolved, in which a reference electrode is provided in the liquid. The potential difference between the reference electrode and the structural material is maintained at a potential in a range where an oxide film is formed on the structural material, and a metal piece containing a component element forming an oxide film, a reference electrode, and a first cathode electrode are is provided in the liquid, and the potential difference between the metal piece and the reference electrode is the total potential difference between the gold piece and the gold J'j.
The concentration of metal ions in the liquid is increased by adjusting the current flowing between the metal piece and the first cathode electrode while maintaining the potential within a range where three ions are eluted, and the second metal ion concentration in the liquid is increased. By providing a cathode electrode to make the structural material f positive (an enemy), and adjusting the current flowing between the structural material and the second cathode electrode so that the second cathode electrode serves as a cathode. , forming an oxide film of the eluted metal ions on the structural material.

The features of the present invention described above are based on the following findings.

] 1q Taking stainless steel made from 1q material as an example, it is known that the relationship between the electric potential and the current of stainless steel is as shown in FIG. Potential here is the potential of stainless steel relative to a standard hydrogen electrode. According to Fig. 1, there are two parts: a part where the absolute value of the potential is small (i.e., region B) and a part where the absolute value of the potential is small (i.e., region B).
There are points where the current flows. The absolute value of the potential is 2 x 1 J in region B, and the thick point of the flow corresponds to the elution of metal ions from the stainless steel. '-1.
The thick point of current in region A where the absolute value of potential is small is
This corresponds to the formation of an oxide film on stainless steel. When a structural material is forcibly energized from the outside to maintain the potential in area B in Figure 1, the inner surface of the structural material is forcibly corroded, and an oxide film is formed naturally or chemically. An oxide film can be formed in a shorter time than when an oxide film is formed by a method. By applying electricity so as to maintain the potential of the eluted gold piece at the potential in region A in FIG. 1, the leaching of the gold piece is accelerated and the concentration of metal ions in the solution is increased.

[Embodiments of the invention]

An embodiment of the present invention will be described based on FIG. 2.

Figure 2 shows an example in which a stainless steel pipe through which 6 iU of liquid passes as a structural material is set to V/Il, and an oxide film is accelerated and formed in a short period of time when forming an oxide film on the inner surface of this pipe. ing.

The pipe 2 through which the liquid containing all dissolved oxygen flows is provided with a circulation pump 4, a temperature raising device 6 for heating the liquid, and a pipe 8 on which an oxide film is formed, forming a circulation system. A pure water tank 10 and an injection pump 12 for supplying pure water into this circulation system are connected to the circulation system. The dissolved oxygen in the pure water was adjusted to 200 ppb by blowing nitrogen gas mixed with oxygen into the pure water tank 10.

The oxide film forming pipe 8 is provided with a cathode electrode 14 and a reference electrode 16, each of which is immersed in the liquid in the pipe 8.

The lead wire 18 of the cathode jL electrode 14 and the lead wire 20 of the reference 1 (and pole IG) are electrically insulated from the oxide film forming pipe 8 by electrode seals 22 and 24, respectively. A pipe electrode 26 is provided in the pipe 8,
This piping electrode 26 is connected to one terminal of the constant voltage follow-up current source 30 by a lead wire 28, and the other terminal is connected to the lead wire 18 of the cathode electrode 14.
Lead wire 28 of piping electrode 26 and lead 1 of reference electrode 16
120 is connected to the voltmeter 32.

In the above configuration, pure water containing oxygen in the pure water tank 10 is injected into the circulation system piping 2 via the injection pump 12 and circulated within the piping 2 by the circulation pump 4. Piping 2
The temperature of the liquid inside the reactor is raised to approximately 280C, which is the reactor water temperature of a boiling water reactor, by a temperature raising device 6. The heated liquid is further circulated and flows into the oxide film forming pipe 8. The potential difference between the reference electrode 16 and the pipe electrode 26 of the oxide film forming pipe 8 is measured by the blood pressure monitor 32, and the potential between the pipe electrode 28 of the oxide film forming pipe 8 and the cathode electrode 14 is determined by taking this potential difference into consideration. A current is passed through the oxide film forming pipe 8 from the constant voltage follow-up current source 30 so as to maintain the voltage at the potential in region A in FIG. In this case, the oxide film forming pipe 8 serves as an anode, the electrode 14 serves as a cathode, and the current flows from the oxide film forming pipe 8 through the high temperature liquid to the cathode 14. Iron, which is a main constituent element of the oxidation degree HU forming pipe 8, becomes ions through the following reaction. That is, in the pipe 8, which is the anode, the reaction pe-+pe'' + 2 e-''- (I) occurs, while the reaction at the @ electrode occurs, 9, fl) and (2). The following reaction occurred.

Fe+211++X02→Fe2++H20...
(3) The generated iron ions (Fe'') react with dissolved oxygen in the high temperature liquid, and an oxide film layer mainly composed of F'e304 is formed on the inner surface of the pipe 8 through iron hydroxide. .

At this time, 10 tt per unit area of the oxide film forming pipe 8
By forming an oxide film by passing a current of ampere/cytf, the oxide film is formed at a rate more than 10 times faster than when the oxide film is formed by natural corrosion in a high-temperature liquid without electricity. was completed. Therefore, in order to prevent radioactive substances from being taken into the inner surface of the piping of the atomic couplant, an effective piping preliminary i:i12 coating of 0.5μ
The time required to form an oxide film of nl to 1 μm can be shortened to several tens of hours.

[ - The electric bit was able to flow sufficiently.If the electrical conductivity of the high temperature liquid in the pipe 8 is extremely low, for example, 0.1 μs/cm or less, a solution such as sodium sulfate should be added to the pipe. It is necessary to increase the electrical conductivity of the liquid to an extent that does not adversely affect the base material.

Another embodiment will be described based on FIG. 81z3. In the example shown in FIG. 2, iron in the oxide film forming pipe 8 was eluted into the high temperature liquid, combined with oxygen in the liquid to form iron oxide, and an oxide film layer was formed on the inner surface of the pipe 8. However, in order to further speed up the formation of an oxide film, or to form an oxide film that is difficult to absorb radioactive substances such as 60Co, the degree of metal ion concentration in the high temperature liquid may be increased. FIG. 3 shows an example in which the metal ion concentration in the high temperature liquid is increased in the example shown in FIG. 2 in this way. In FIG. 3, the same parts are given the same reference numerals. An elution container 34 is installed in the circulation system between the temperature raising device 6 and the oxide film forming pipe 8. The elution container 34 contains an elution metal piece 36 containing metal ion elements to be eluted into the liquid and a cathode 38.
and the reference electrode 40 are installed so as to be immersed in the liquid. The lead wires 42, 44, 46 of the eluted metal piece 36, the cathode 38, and the reference electrode 40 are taken out of the elution container 34, and the lead wire 42 of the eluted metal piece 36 and the lead wire 4 of the reference electrode 40 are connected to each other.
6 are connected to both terminals of a voltmeter 48, respectively, and a lead wire 42 of the eluted metal piece 36 and a lead wire 44 of the cathode 38 are connected to both terminals of a constant voltage follow-up current source 50, respectively. Each lead 13142, 44°46 has electric 4 blood seals 52, 54
．． It is electrically insulated from the elution container 34 by 56.

In such a configuration, the eluted metal piece 36 and the reference electrode 40
The potential difference between the eluted gold pieces 36 and A current is passed through. In this case, the eluted metal piece 36 is not an anode, and the current flows from the eluted metal piece 36 to the cathode 38 through high temperature and night. The eluted metal pieces 36 are elements that have a small activation cross section and are difficult to activate even if irradiated in a nuclear reactor, or /J's that have a relatively short half-life or relatively high energy even if activated. Any element may be used as long as it is an element that generates a nuclide that generates radiation and can be a constituent element of the oxide film. For example, it may be a simple substance such as nickel, chromium, or titanium, or a metal containing these metal elements such as stainless steel or (-). The seismic intensity was maintained at approximately 10 ppb, and oxidation degree JIA with a high chromium content was formed on the stainless steel oxide film forming pipe 8.

Next, a system 'f for accelerated forming of an oxide film on the inner surface of the reactor-subcooling system piping is shown in FIG. In the boiling water reactor-subcooling system, steam generated in the reactor 58 passes through a main steam system piping 60, rotates a turbine 62, and generates electricity.

The steam is condensed into condensate in a condenser 64, a de-equalizer 66,
The water passes through the feed water heater 68 and returns to the reactor 58. On the other hand, most of the reactor water is recirculated through the li system 70, and a portion is returned to the water supply system piping 76 through the purifier 74 in the reactor water purification system 72, and enters the reactor 58. . In the recirculation system 70, similarly to the embodiment shown in FIG. 3, a metal elution section 78 for elution of metal ions into the reactor water and an oxide film accelerated formation section 80 are provided. The metal elution section 78 includes the elution metal piece 36 and the cathode 38.
, a reference electrode 40, a voltmeter 48, a constant voltage follow-up current source 50, and the like.
, reference electrode 16, piping electrode 26, voltmeter 32, constant voltage follow-up ammeter 30, etc. 4'1! j, and its operation is similar to the embodiment shown in FIG. Is the 7jf flow value used for oxide film formation based on the pipe inner surface area of 1n? Approximately 0.
1 ampere (A), the applied voltage is approximately 10 pol (V) including the electrical resistance of high temperature reactor water, and the power consumption (1
'L is 17? ? Approximately 1 Watt per unit.

The time required to form the oxide film is several tens of hours.

In this way, an oxide film is formed on the inner surface of the recirculation system piping before the reactor core is heated. After the oxide film is formed, the flow to the electric box may be stopped and the cathode and reference electrode may be left in the pipe until then, or there is no problem if they are pulled out and sealed for now.

Although this example focuses on the formation of an oxide film on the recirculation system 1a, it is not limited to the recirculation system, and can be applied to the reactor water purification system or the water supply system piping, which is a source of elution of corrosion products. The present invention can also be applied to the degree of oxidation and olfactory formation.

〔Effect of the invention〕

According to the present invention, since the structural material of the atomic couplant is anodically polarized to form an oxide film on the structural material from the oxide of metal ions in the liquid, it is approximately It can be formed in 1/10 of the time.

Therefore, when constructing a new plant, the start date of the reactor will be brought forward by more than 10 days, and in existing plants, the time required for oxidation treatment of the inner surface of the primary cooling system piping after system decontamination can be significantly shortened. be.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between potential and corresponding current between stainless steel piping and its internal fluid. FIG. 2 shows an embodiment of the present invention and is a system diagram having an oxide film forming part. FIG. 3 shows another embodiment of the present invention, and is a system diagram having a metal elution section and an oxide film forming section. FIG. 4 is a system diagram when the present invention is applied to a reactor water recirculation system. 8... Oxide film forming piping, 14.38... Cathode, 1
6゜40...Reference electrode, 26...Piping 7E pole, 32
．． j8°°. Voltage -1130,50...Constant'+Q pressure following current meter, 5
8... Nuclear reactor, 70... Recirculation system piping, 78...
Metal leaching area, Figure 2

Claims (1)

[Claims] In a method for suppressing the adhesion of radioactive substances in an atomic couplant using a structural material made of a metal that is used in contact with a liquid in which a radioactive material is dissolved, the structural material is anodically polarized. A method for suppressing the adhesion of radioactive substances to an atomic couplant, which is characterized by electrically forming an oxide film on a structural material. 2. In a method for suppressing the adhesion of radioactive substances to an atomic couplant using a structural material made of metal that is used in contact with a liquid in which radioactive substances are dissolved, (a) a reference electrode is provided in the liquid; (b) providing a cathode electrode in the liquid, using the structural material as an anode, and using the cathode electrode as a cathode; A method for suppressing adhesion of radioactive substances to an atomic couplant, characterized in that an oxide film is formed on the structural material by adjusting a current flowing between the structural material and the cathode electrode so as to: 3. A patent claim in which iron ions in the structural material are eluted into the liquid, and the iron ions react with dissolved oxygen ions in the liquid to form an oxide film containing iron oxide as a main component on the structural material. A method for suppressing adhesion of radioactive substances to an atomic cufflint according to item 2. 4. The method for suppressing the adhesion of radioactive substances to an atomic couplant according to claim 2 or 3, wherein the structural member is a water supply pipe for a sub-reactor cooling system. 5. In a method for suppressing the adhesion of radioactive substances to an atomic couplant using a 4i'M material made of gold L4 that is used in contact with a liquid in which radioactive substances are dissolved, (1) a reference electrode is placed in the liquid; (b) a metal piece containing a component element forming an oxidation degree j relation; A reference electrode and a first cathode electrode are both provided in the liquid, and the metal piece and the first cathode are connected to each other while maintaining the potential difference between the metal piece and the reference electrode within a potential range that allows metal ions to be eluted from the metal piece. (C) increasing the metal ion concentration in the liquid by adjusting the current flowing between the cathode electrodes; (C) providing a second cathode hole 4 in the liquid and using the structural material as an anode; Forming an oxide film of the metal ions on the structural material by adjusting the current flowing between the structural material and the second cathode electrode so that the second cathode electrode serves as a cathode. A method for suppressing the adhesion of radioactive substances to an atomic couplant characterized by: 6. The structural material is water supply piping for a reactor-subcooling system.
Agency n' ``Method for suppressing adhesion of radioactive substances to an atomic couplant according to claim 5.