JPS609522Y2 - Liquid sodium heating steam generator - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a liquid sodium heating steam generator, and more particularly to the material of the heat exchanger tube of the superheater of the steam generator.

Sodium has a high thermal conductivity, a boiling point as high as 880°C, and is advantageous as a heat medium because it can obtain high temperatures without pressurization.

However, spouting of water vapor into sodium causes a sodium-water reaction, leading to a serious accident.

Liquid sodium heated steam generators are used in fast breeder nuclear power plants and the like.

The heat transfer tubes of the superheater of conventional sodium-heated steam generators are all made of a single material such as stainless steel or high chromium steel, but austenitic stainless steel has a temperature of approximately 420℃. Stress corrosion is likely to occur in the temperature range below ℃.

The development of cracks, which can be seen as stress corrosion, leads to the ejection of steam into the sodium, resulting in a serious accident due to the sodium-water reaction.

Even if a single material is used that can prevent stress corrosion at low temperatures, it cannot prevent stress corrosion at high temperatures.
It is not possible to generate high-temperature steam.

Furthermore, in order to prevent wet steam from entering the superheater and increase the steam inlet temperature, a complicated system is required for installing a separator and controlling the temperature of the steam generator.

The purpose of the present invention is to provide a high-performance liquid sodium heated steam generator that eliminates the above-mentioned drawbacks of the prior art, prevents stress corrosion from occurring in superheater heat transfer tubes, and can raise the superheater outlet steam temperature to a high temperature. There is something to do.

In short, the present invention uses ferritic steel such as 21/4Cr-IMo steel or high chromium steel for the temperature range of the superheater heat exchanger tube below about 420°C, and uses austenitic stainless steel for the temperature range above this temperature. This is a liquid sodium heating steam generator characterized by the following.

Hereinafter, a superheater for a steam generator according to the present invention will be explained based on the drawings.

FIG. 1 schematically shows an embodiment of a coil boiler type superheater of a steam generator according to the present invention, in which steam passes through heat exchanger tubes 2 and 3 in a container 1 containing liquid sodium 5. It is flowing in the direction of the arrow.

The inlet and outlet for liquid sodium are omitted.

In the superheater of the present invention, the water vapor temperature is approximately 42Cf'
21/4Cr-IMo in the heat exchanger tube 2 in the temperature range below C
Alternatively, ferritic steel such as high chromium steel is used, and austenitic stainless steel is used for the heat exchanger tubes 3 in the temperature range above this temperature, and the heat exchanger tubes 2 and 3 are connected by a dissimilar metal joint 4.

FIG. 2 schematically shows a modular type superheater according to another embodiment of the present invention.

The same reference numerals as in FIG. 1 indicate the same parts.

In FIG. 2, the sodium supply pipe 6 is also shown.

Sodium is circulated in the direction of the arrow.

When using this method, the material of the heat exchanger tubes can be changed for each unit.

As described above, the steam generator of the present invention uses ferrite-based steels such as 21/4Cr-IMo steel and high chromium steel, which have low stress corrosion susceptibility, in the region below about 420°C where stress corrosion of SUS heat exchanger tubes tends to occur. , it is possible to prevent stress corrosion from occurring, and moist steam can flow into the superheater regardless of humidity, making it possible to use a moisture separation device and a superheater inlet steam temperature control device. becomes unnecessary.

Furthermore, since austenitic stainless steel is used in the high temperature range of approximately 420° C. or higher, the superheater outlet temperature can be increased.

Furthermore, since a material cheaper than austenitic stainless steel is used in the low temperature region, there is also the advantage that the device is inexpensive.

[Brief explanation of the drawing]

The drawings are schematic diagrams of embodiments of the superheater of the liquid sodium heated steam generator of the present invention; FIG. 1 shows a coil boiler type, and FIG. 2 shows a modular type. 1... Container, 2, 3... Heat exchanger tube, 4.
...Dissimilar material joint, 5...Sodium, 6.
...Sodium supply pipe.

Claims (1)

[Scope of utility model registration request] The temperature range of the superheater heat exchanger tube below approximately 420℃ is 21/4C.
A liquid sodium heated steam generator characterized in that it is made of ferritic steel such as r-IMo steel or high chromium steel, and austenitic stainless steel is used in the temperature range above the above temperature range.