JPS59115998A - Condenser in atomic power plant - Google Patents

Abstract

PURPOSE:To obtain a condenser having improved corrosion resistance for lessening the amount of Fe to be released in the hot well portion for atomic power plants by forming black iron oxide film having excellent corrosion resistance on the surface to be brought in contact with liquid of the main condenser. CONSTITUTION:A black iron oxide film 3 is provided on the inner surface of the hot well 2 of a condenser 1 by contacting the inner surface of the hot well 2 of the main condenser 1 made of a carbon steel or low-alloy steel with oxygen- containing steam (5-10kg/cm<2>) of 100 deg.C or higher, e.g., of 140-170 deg.C, for 100- 500hr, usually for 200-400hr. Since the portion other than the hot well 2 of the main condenser 1, e.g., the cooling tube 4, outer surface of a support plate 5, and inner surface of the body cylinder 6, is touched by usual high-temperature steam during the operation of unclear reactor, no pretreatment with steam is needed for the portion.

Description

[Detailed description of the invention] [Technical field of invention] The present invention 8 relates to a condensing device in a nuclear power plant.

[Technical Background of the Invention] In nuclear power plants that use light water as a coolant, such as boiling water nuclear power plants, light water is directly heated in the reactor pressure vessel to generate steam, and this steam is used to drive a steam turbine. After operation, the discharged steam is converted into condensate in the main condenser, and is sent to the reactor pressure vessel again by a water suction pump via a feed water heater.

However, during the lever cycle, the iron-based metals that make up the equipment, piping, etc. are gradually oxidized by the oxygen contained in the light water, and some of them are released into the coolant in the form of fine iron oxides and ions. It becomes like this.

If such fine iron oxides and ions are released into the coolant, they become radioactive in the reactor core, so conventionally a condensate purification system has been placed after the main condenser where a particularly large amount of iron is released. Efforts are being made to remove the released iron.

[Problems with backlash technology]However, even if iron oxide released into the coolant is removed using a condensate purification system, it will not suppress backlash, so It is not a solution.

Furthermore, when a large amount of iron is released, the burden on the condensate purification system increases, and there are also disadvantages in that a large amount of solid waste must be suspended.

[Purpose of the Invention] The inventors of the present invention conducted intensive research in order to resolve these conventional difficulties, and found that d3
In the case of I-C, a black iron oxide film (Fe3O4) with excellent corrosion resistance is formed on the parts that come in contact with high-temperature steam, reducing the amount of iron released. The surface that comes into contact with water contains black iron oxide (Fe304) and red iron oxide (α-Fe2), which have poor corrosion resistance.
03) was formed, and it was found that a small portion of the total amount of iron released was released here.

The present invention has been made based on this knowledge, and is a condensing device for a nuclear power plant with a low amount of iron, in which the corrosion resistance of the hot well portion is particularly improved. Both pipes are collectively referred to as a condensate device).

[Summary of the Invention] In order to achieve the above object, the present invention includes a main condenser whose wetted surface is made of an iron-based alloy, which condenses steam generated in a reactor pressure vessel and passed through a steam turbine. The condenser device is characterized in that a black iron oxide coating with excellent corrosion resistance is formed on the liquid contact surface of the main condenser.

[Embodiments of the invention] An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a side sectional view schematically showing a condensing device of the present invention. A black iron oxide coating 3 is provided on the inner surface of the hot well 2 of this condensing device 1.

This black iron oxide coating 3 coats the inner surface of the main condenser 1 and hot well 2 made of carbon steel or low alloy steel.
It can be formed by contacting with oxygen-containing steam (5 to 10 hg/c+/) at a temperature of 1°C or higher, for example 140 to 17°C, for 1° to 500 hours, usually 200 to 400 hours. Hole of the main condenser 1 [portions other than the spatula 1, e.g.
Since the inner surface of the reactor is always in contact with high-temperature steam during operation of the nuclear reactor, it is not necessarily necessary to pre-treat the steam, but it is of course possible to pre-treat the inner surface if necessary. In the figure, C code 7.8 is the water chamber, 9 is the cooling water inlet, 10 is the cooling water outlet, 11 is the steam inlet, and 12 is the condensate water 1.
It is Ko.

To perform oxidation treatment only on the inner surface of Botwell 2,
Before installing the main condenser 1, the cooling envelope 4 may be directly introduced into the hot well 2 at a temperature of 100° C. or higher by covering the cooling envelope 4 with a shielding plate, for example, or after the installation. The steam used for this oxidation treatment may be introduced by connecting a bypass pipe to the main steam pipe, or may be introduced from the house boiler using a steam pipe.

The main condenser with the black iron oxide film formed in this way has extremely excellent corrosion resistance, as is clear from the following simulation experiment.

(Corrosion Resistance Test) Carbon m(38-41) of 34 mm x 46 mm x 2 mm was coated with D lN5095-1592 (
The surface was finished with emery paper of No. 120 or finer, and after ultrasonic cleaning in alcohol for 15 minutes, it was heated and pressurized at 150℃ for 340 hours in an O-1-crepe tube containing 20mJ2 of pure water. A black iron oxide film was formed on the surface.

When this carbon steel having a black iron oxide coating was analyzed using an X-ray analyzer, it was confirmed that Fe3O4 was formed.

Next, the sample on which this black iron oxide film was formed and a comparison sample that had not been formed with a black iron oxide film through ultrasonic cleaning were exposed to the condensate conditions of a nuclear reactor, and regular sampling was performed to release iron. The rate was calculated. In addition, to quantify the amount released, periodically sample the loop water from the outlet side of the corrosion test tank (with one 0.4 μm Nuclepore filter).
Ion exchange filter (2 cations, 2 anions)
Use) Iron was determined by atomic absorption d1.

The measurement results are shown in the graph of FIG. As is clear from Figure 2, the iron release rate of the sample with a black oxide film gradually increased, and after 550 hours, the iron release rate was 40MDM (11,
(/dm2/month), and it gradually decreases from then on to about 30 M D M after U300 to 900 hours have elapsed.
T" was stable. In addition, most of the released iron was in ionic form, and cladding was below the detection limit. In contrast, the iron release rate of the sample without the °C black iron oxide film is clear from Figure 2. As such, it was approximately 65MDM.

[Brief explanation of drawings]

FIG. 1 schematically shows the condensing device of the present invention, a J-side sectional view,
Figure 2 shows a mock experiment to confirm the effects of the present invention.
5 is a graph showing the iron release rate of 5 L. 1... Main condenser 2... Howell] Hewell 3...
・・・・・・・・・Black iron oxide coating 4・・・・・・・・・
...Cooling pipe 5...Pipe support plate 6...
・・・・・・Patent attorney representing the main body: Satoshi Suyama −

Claims (3)

[Claims] (1) In a condensing device equipped with a main condenser whose wetted surface is made of an iron-based alloy, the steam that is generated in the reactor j pressure vessel and passed through the steam turbine is condensed. A condensing device for a nuclear power plant characterized by forming a black iron oxide film on the liquid surface. (2) The condensing device in a nuclear power plant according to claim 1, wherein the iron-based alloy is made of carbon steel or low alloy steel. (3) A condensing device in a nuclear power plant according to claim 1 or 2, wherein the black iron oxide film is made of Fe3O4.