JPS6152379A - Method and device for corrosion prevention of wetting metallic material - Google Patents

Abstract

PURPOSE:To prevent the corrosion of the wetting metallic material of a boiling water reactor (BWR) during the shutdown of the BWR by measuring the specific conductivity of the water to be used and controlling the concn. of the dissolved oxygen in the water or the pH thereof from the measured value. CONSTITUTION:The conductivity of the water is measured by a detector 16 and the concn. of the dissolved oxygen in the water is measured by a dissolved oxygen meter 17 in order to prevent the corrosion of condensate and feed water pipings by the water in the shutdown stage of the BWR plant for the purpose of making a periodic inspection of the BWR10. The oxygen conc. is adjusted by an oxygen feeder 18 so as to attain 40ppb-40ppm when the specific conductivity is <=0.1muS/cm to decrease considerably the corrosion rate of the piping of the wetting metallic material. An inert gas is fed from the feeder 18 to deaerate the water until the concn. of the dissolved oxygen is brought to <=40ppb or ammonia or the like is fed to the water to maintain the pH at 7.5-10 passive region to prevent the corrosion of the metallic pipings if the specific conductivity exceeds 0.1muS/cm.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a method and apparatus for preventing corrosion of a metal material in contact with water in a system where water containing dissolved oxygen and a metal material come into contact.

[Background of the invention]

In a system where water containing dissolved oxygen contacts a metal material, the metal material in contact with the water is corroded. The degree of corrosion increases as the dissolved oxygen concentration increases, especially when water contains oxygen at a concentration of approximately 40 ppb.
~40P is dissolved, corrosion occurs on metal materials in contact with water,
Corrosion prevention measures are required.

In particular, in BWR (boiling water reactor) plants, during operational shutdowns such as periodic inspections, condensate and water supply system piping is exposed to water with a dissolved oxygen concentration as high as 5 to 8 P when exposed to the atmosphere. Metal materials, especially carbon steel, are severely corroded. Corrosion products (mainly iron oxides and called cladding) generated by corrosion are brought into the reactor at plant start-up and adhere to the fuel rods, reducing thermal efficiency or damaging the fuel rods. There is a risk. Furthermore, the crud attached to the fuel rods is activated and then peeled off and reattached to the reactor recirculation system piping, etc., increasing the surface dose rate of the piping, etc. There is also the risk of causing an increase in For these reasons, when a BWR plant is shut down, corrosion prevention measures for condensate and water supply system piping have become an important issue.

Conventionally, a water draining drying method called ``Honto Drain Off'' has been adopted in some plants for corrosion protection during shutdown of systems where water containing dissolved oxygen and metal materials come into contact, especially BWR plants. This method involves draining the water supply before it has completely cooled down after plant operation is stopped, and drying the piping surface using residual heat. However, there are variations in plant structures, and this method cannot be applied to all plants, and there are also problems in processing the large amount of radioactive waste fluid that is generated when water is drained. Furthermore, this draining and drying method is complicated to operate and is not suitable for short-term shutdowns.

As another corrosion prevention method, in thermal power plants, when the operation is stopped for a short period of time, a full water storage method by adding hydrazine is adopted. When this method is applied to a BWR plant, there are problems in post-processing, such as the added hydrazine having to be removed until later startup and nitrogen gas also having to be degassed.

It is difficult to apply these methods to corrosion protection in BWFL plants.

In response to this problem, the present inventors previously proposed a corrosion prevention method that focuses on the specific conductivity and flow velocity of water (Japanese Patent Laid-Open No. 55-16
No. 4081). The key point of this invention is to reduce the specific conductivity of water to 0.
The purpose was to keep the temperature below 5 μS/cm and allow the water to flow.

Although the above method was somewhat effective, further detailed study revealed that there are differences in corrosion behavior around a certain value of the specific conductivity of water.

[Purpose of the invention]

It is an object of the present invention to provide a simple method and apparatus for preventing corrosion of metal materials in contact with water when a BW furnace plant is stopped at a rate of 9%.

[Summary of the invention]

The corrosion prevention method for metal materials in contact with water of the present invention is characterized by detecting the specific conductivity of water in a system where water containing dissolved oxygen and metal materials are in contact with each other, and controlling the dissolved oxygen concentration or pH based on the detected value. In particular, it has been discovered that there is a difference in corrosion behavior when the specific conductivity reaches a boundary of 0.1 μS/lYn, and this is utilized to prevent corrosion.

The concentration of dissolved oxygen in water in the system to which the present invention is applied is within a range where metal materials are corroded when in contact with oxygen-dissolved water and corrosion prevention becomes a problem. It depends on the type of metal material.

Specifically, it is about 40 ppb to about 40 p. When the BWR plant is shut down, the condensate and water supply system piping is exposed to the atmosphere and comes into contact with water with a dissolved oxygen concentration of 5 to 8, so the present invention is particularly suitable for preventing corrosion of the metal materials of this piping. It is.

In the present invention, the metal material to be subjected to corrosion protection may be any rice variety as long as it comes in contact with water containing dissolved oxygen, especially water with a dissolved oxygen concentration of 4.0 ppb - about 40 P. , in particular carbon steel, low alloy steel, stainless steel tl/At and alloys thereof. BWR
Plant condensate.

Carbon steel, which is the material for water supply piping, is effectively protected against corrosion by the present invention.

When the BWR plant is stopped, is the specific conductivity of water in the condensate and water supply systems kept low? This protects the materials in the system from corrosion. Various means for lowering the specific conductivity can be considered, but usually, for example, water may be passed through a demineralizer filled with a granular positive/porous ion exchange resin. In the present invention, the specific conductivity of water is detected, and if it is 0.1 μs/- or less, the dissolved oxygen concentration is maintained at about 4 opI)b to about 40F, and the corrosion rate of metal materials in contact with water is significantly reduced. , effectively prevent corrosion. On the other hand,
If the specific conductivity exceeds 0.1 μS/cm due to sodium leaks due to problems such as demineralizer performance, dissolved oxygen promotes corrosion, so deaeration should be performed to reduce the dissolved oxygen concentration to 40 ppb or less. Corrosion is prevented by keeping the pH at 7.5 to 10, or by injecting an alkaline agent.
To carry out the method of the present invention, a combination system of a conductivity detector, a dissolved oxygen concentration meter, an oxygen injection device and a deaerator linked to the conductivity detector, or an alkaline agent injection device and a pH measuring device is required. It is.

Note that deaeration is performed by injecting nitrogen, argon, and hydrogen, and pHv4 adjustment is performed by injecting ammonia).

The temperature at which the anticorrosion method of the present invention is carried out is usually 20 to 40C, and the time is determined as appropriate depending on the mode of implementation.

[Embodiments of the invention]

Next, examples of the present invention will be described.

Example 1 Corrosion loss was measured by immersing the test piece.

The carbon steel used in the experiment was 884 having the chemical composition shown in Table 1.
1, processed into a plate shape of 5 x 50 x 0.5 m was used. The surface of the test piece was polished with No. 600 emery paper, degreased with Triclean, and stored in a desiccator until immediately before immersion.

Table 1 (Part 1) The dissolved oxygen concentration of the immersed water was adjusted to <5 ppb-8F using an oxygen-nitrogen mixed gas. In addition, the specific conductivity was determined by adding sodium sulfate and sodium chloride (0,1-1
It was adjusted to 0.ca8/cm. The test piece was immersed in zsh,
The corrosion weight loss was determined by the difference between the weight before immersion and the weight after removing the corrosion products attached after immersion. In addition, the temperature is 25
±2Cs flow rate was 0.3 cm/s.

Figure 1 is a diagram showing the results of investigating the effect of dissolved oxygen concentration on corrosion loss when IJium is present as an impurity in pure water and the specific conductivity of water is different. . When the specific conductivity is 0.1 μS/cm or less, the dissolved oxygen concentration is 40
Corrosion was suppressed with ppb-40F. On the other hand, 0.1μS
/cm, reducing the dissolved oxygen concentration from the atmospheric saturated state of 8-cm will reduce the corrosion loss, especially at 40-cm.
When the amount was lower than ppb, the effect was remarkable. Note that degassing is achieved by blowing an inert gas such as nitrogen or argon or hydrogen gas into the system, or by vacuum degassing.

Similar results were also obtained when the specific conductivity was adjusted using sodium chloride. .

Example 2 Table 2 shows dissolved oxygen concentration 8F, specific conductivity 1.0μS/a
This is a change in corrosion weight loss of carbon steel when the pH of water of n is changed. pH was adjusted with ammonia. Other test conditions are the same as in Example 1.

Table 2 (mg/ze) Under neutral conditions of pH 7.0, the corrosion loss increases in proportion to the immersion time, and after 75 hours, the surface of the test piece becomes r-Fe203.
It was covered with a thick film of HzO (outer layer) and peso4 (inner layer). On the other hand, under alkaline conditions of pH 7, 5, and 8.4, corrosion was significantly suppressed, and the corrosion rate showed a tendency to decrease with time.

FIG. 2 is a diagram showing changes in corrosion potential over time.

Note that the potential is shown on a saturated end electrode (SCE) basis. p
In the case of pH 7.0, it took a low value of -210 mV after 75 hours, which was in the corrosion range for carbon steel, but at pH 7.5, it took a negative value of -80 mV, and at pH 8.4, it took a negative value of 10 mV, and under alkaline conditions. Below, the carbon steel was in a stable passive region and protected against corrosion.

Embodiment 3 FIG. 3 is a schematic diagram of a BWR plant equipped with a corrosion protection device for metal materials in contact with water according to the present invention.

In the figure, 10 is a nuclear reactor, 11 is a turbine, 12 is a condenser, 13 is a condensate demineralizer, 14 is a condensate low pressure pump, 15
is a feed water recirculation line, 16 is a conductivity detector, 17 is a dissolved oxygen concentration meter, 18 is an oxygen, inert gas, or alkaline agent injection device, 19 is a pH meter, 20 is a feed water heater, and 21 is a reactor water It is a purification system. Parts 16 to 19 are the corrosion protection device for metal materials in contact with water according to the present invention.

In such a system configuration, for example, when the plant is stopped for periodic inspection, the specific conductivity is measured by the conductivity detector 16 and the dissolved oxygen concentration meter 17 is measured by the conductivity detector 16. When the specific conductivity is 0.1 μS/cm or less, the dissolved oxygen concentration is maintained at about 40 I) pb to about 40 F, and the corrosion rate of the metal material in contact with water is significantly reduced, making it possible to effectively prevent corrosion. Oxygen is controlled by an oxygen injection device 18. Specific conductivity is 0.1μS/
If Crn is exceeded, dissolved oxygen promotes corrosion, so either deaerate with an inert gas injection device and keep the dissolved oxygen concentration preferably below 40 ppb, or inject ammonia etc. with an alkaline agent injection device to adjust the pH. preferably 7.5~
10 to prevent corrosion. I) This range of H is the passive region.

Although a BWR plant has been described here as an example, it is clear that the present invention can be applied to all other plants where dissolved oxygen affects corrosion of metal materials.

〔Effect of the invention〕

According to the present invention, it is possible to obtain a simple method and apparatus for preventing corrosion of metal materials in contact with water, especially metal materials in contact with water when a KBWR plant is stopped.

[Brief explanation of drawings]

Figure 1 is a diagram showing the relationship between corrosion loss and dissolved oxygen concentration in carbon steel, Figure 2 is a diagram showing changes over time in the corrosion potential of carbon steel,
FIG. 3 is a schematic diagram of a BWR plant equipped with a corrosion protection device for metal materials in contact with water according to the present invention. l...Curve with specific conductivity of 0.1ttS/cm or less, 2.
...Curve of 0.15ttS/crs, 3...0.
30 pS/cm curve, 4-... 0.50 a 8/
cm curve, 5... same 1.00 μS/an curve'-
6-...Curve of 101iS/m, 7...pH7,
0 curve, 8... pH 7, 5 curve, 9... pH
8, 4 curves, 10... Nuclear reactor, 11... Turbine, 12... Condenser, 13... Condensate demineralizer, 14...
・Condensate low pressure pump, 1t・・Feed water recirculation line, 16・
... Conductivity detector, 17... Dissolved oxygen concentration meter, 18.
... Injection device, 19... pH measuring device.

Claims (1)

[Claims] 1. The specific conductivity of the cooling water in contact with the carbon steel piping of the water supply system of the BWR power plant was measured, and the specific conductivity was found to be 0.1 μS/
cm or less, reduce the dissolved oxygen concentration to 40 ppb to 40 ppb
A method for preventing corrosion of metal materials in contact with water, characterized in that the dissolved oxygen concentration is maintained at 0.1 μS/cm, while reducing the dissolved oxygen concentration to 40 ppb or less by degassing if it exceeds 0.1 μS/cm, thereby preventing corrosion of piping during a power plant shutdown period. 2. In claim 1, nitrogen, argon,
A method for preventing corrosion of metal materials in contact with water, characterized by injecting at least one type of hydrogen into cooling water and degassing it. 3. Measure the specific conductivity of the cooling water in contact with the carbon steel piping of the BWR power plant, and find that the specific conductivity is 0.1μS/
cm or less, reduce the dissolved oxygen concentration to 40 ppb to 40 ppb
A water-contact metal material characterized by maintaining the pH at 7.5 to 10 by injecting an alkaline agent if the pH exceeds 0.1 μS/cm, thereby preventing corrosion of piping during power plant shutdown periods. Corrosion prevention method. 4. A method for preventing corrosion of metal materials in contact with water according to claim 3, characterized in that the alkaline agent to be injected is ammonia. 5. In a power generation plant that includes a nuclear reactor, a turbine, a condenser, a condensate demineralizer, and piping that connects these, conductivity detection is installed in the piping downstream of the condensate demineralizer to measure the specific conductivity of the cooling water. and a dissolved oxygen concentration meter that measures the dissolved oxygen concentration in the cooling water.
A device for injecting oxygen or dissolved oxygen degassing gas is arranged according to the measured values of each of these parameters, and when the specific conductivity is 0.1 μS/cm or less, the dissolved oxygen concentration is
While maintaining the dissolved oxygen concentration between 0 ppb and 40 ppm, if it exceeds 0.1 μS/cm, reduce the dissolved oxygen concentration by injecting degassing gas.
A corrosion protection device for metal materials in contact with water, characterized in that it reduces corrosion to 0 ppb or less and protects piping during a power plant shutdown period. 6. In a power generation plant that includes a nuclear reactor, a turbine, a condenser, a condensate demineralizer, and piping that connects these, conductivity detection is installed in the piping downstream of the condensate demineralizer to measure the specific conductivity of the cooling water. and a dissolved oxygen concentration meter that measures the dissolved oxygen concentration in the cooling water.
It is equipped with a pH measuring device that measures the pH of the cooling water and a device that injects oxygen or alkaline agent according to the measured values of each parameter.If the specific conductivity is 0.1μS/cm or less, dissolved oxygen is detected. It is characterized by maintaining the concentration at 40 ppb to 40 ppm, and if it exceeds 0.1 μS/cm, adjusting the pH to 7.5 to 10 by injecting an alkaline agent to prevent corrosion of the piping during the power plant shutdown period. Corrosion prevention equipment for metal materials in contact with water.