JPS62177427A - Leak detecting method for double heat conduction tube vapor generator - Google Patents

Abstract

PURPOSE:To detect damages to both internal and external tubes of a heat conduction tube with simple constitution by charging helium having pressure higher than the pressure in the internal tube between the internal and external tubes, and detecting variation in the pressure of the helium. CONSTITUTION:Helium He of about 160kg/cm<2> higher than the pressure in the internal tube 8 is charged in spaces 9 and 10 and the gap between the internal and external tubes which communicate with both spaces. A pressure gage 17 is linked with either of the spaces and analyzers 15 and 16 are linked with a vapor outlet passage 13 and an outlet flow passage 14 for liquid sodium respectively. For example, if the internal tube 8 cracks, the He leaks to the vapor side because the pressure of the He is higher than the vapor pressure and the leak is detected by the pressure gage 17 from a drop in He pressure. Further, the He concentration in vapor increases, so that damage to the internal tube 8 is found by the analyzer 15. If the external tube 7 cracks, on the other hand, the He leaks to the liquid sodium and the pressure drops. The leak is also detected in this case as well and the damage to the external tube 7 is known through the analyzer 16.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a leak detection method for a double heat exchanger tube steam generator in a fast breeder reactor nuclear power facility.

F. Conventional technology] Normally, in a fast breeder reactor, heat from nuclear fission generated in the reactor core is extracted using liquid sodium, which is the primary heat carrier.
Exchange heat with secondary liquid sodium in an intermediate heat exchanger,
Further, the secondary liquid sodium is led to a steam generator, where it exchanges heat with water, which is a working medium, to generate steam. Alternatively, in order to rationalize the plant, a system has been proposed in which the intermediate heat exchanger is omitted and primary liquid sodium is directly guided to a steam generator to generate steam.

In such a natural gas generator, heat is exchanged between liquid sodium and water via heat transfer tubes, so if a crack occurs in the heat transfer tube and water leaks into liquid sodium, liquid sodium and water will be exchanged. He reacted violently and caused a major accident. In particular, in equipment that does not have an intermediate heat exchanger, the influence of an accident is large because the liquid sodium has a radioactive capacity, and the steam generator is close to the reactor vessel, so the influence of an accident is It is extremely dangerous if it spreads all the way to the container.

Therefore, in order to improve the reliability and safety of the steam generator,
If the heat exchanger tube is a double heat exchanger tube and either the inner tube or the outer tube of the heat exchanger tube has a crack and leaks, the inner tube can be removed by detecting water leaking into the gap between the inner tube and the outer tube. ,
A system has been proposed that detects the occurrence of cracks in the outer pipe and repairs them before a major accident occurs.

FIG. 2 schematically shows a steam generator with double heat exchanger tubes. Outer tube plates 2 and 3 are installed at the upper and lower parts of the pressure vessel 1, respectively.
, inner tube tube sheets 4 and 5 are provided, and a double heat exchanger tube 6 is installed between these tube sheets.
It is set up by hanging it. The end of the outer tube 7 is welded to the outer tube sheet 2.3 as shown in FIG. 3, and the end of the inner tube 8 is welded to the inner tube sheet 4, 5.
Weld to. In addition, the heat exchanger tube is omitted in the figure and only one is shown. Here, the small gap between the inner tube 8 and the outer tube 7 is in communication with the space 9.10 defined by the outer tube plate and the inner tube plate.

One of the things currently being proposed is the spaces 9 and 10.
Helium gas (I-1c) at a pressure of about 20 K(]/Cm2 is passed through the gap between the inner tube 8 and the outer tube 7 through the analyzer 11 to detect moisture (H2O>) in He. There is also an attempt to detect He in liquid sodium using the analyzer 16.

Here, the pressure of steam flowing inside the inner pipe is approximately 130KMcm2.
, and the pressure of the liquid I/Rium flowing outside the outer tube is approximately 5
g/cm2.

However, the above method requires a circulation system 12 for circulating He, and an analyzer 11 for detecting H2O in He or an analysis device for detecting He in liquid sodium. requires 16 vessels,
The leak detection system is troublesome to equip.

In view of the above-mentioned circumstances, the present invention has a simple structure and an inner tube,
The present invention aims to provide a leak detection method that can detect ff1m even if any of the outer tubes is damaged.

[Means for Solving the Problems] The present invention provides a double-tube steam generator in which the heat exchanger tube is a double tube, liquid sodium flows outside the heat exchanger tube, and water flows inside the heat exchanger tube to generate steam. This is characterized in that helium at a high pressure within the inner tube is sealed between the inner tube and the outer tube of the heat transfer tube, and leakage detection is performed by detecting the pressure change of the helium.

[Function] The liquid sodium i-cum is lower than the internal pressure of the inner tube (water pressure), and the sealed helium is higher than the internal and external pressure of the heat transfer tube. Therefore, even if there are 11 scratches on either the inner tube or the outer tube, a leak will occur and the helium pressure will drop, and the leak can be detected by detecting the pressure.

[Example] The present invention will be described in detail below with reference to the drawings.

Components in FIG. 1 that are the same as those shown in FIG. 2 are given the same reference numerals.

Approximately 160 KMCm2 of He, which is higher than the internal pressure of the inner tube 8, is sealed in the gap between the inner and outer tubes communicating with the spaces 9 and 10 and the rain space. A pressure gauge 17 is connected to one side of the rain space (for example, the upper space 9). Further, analyzers 15 and 16 are connected to the vapor outlet channel 13 and the liquid solution outlet channels 14, respectively.

According to the above, if a crack occurs in the inner tube 8, the vapor pressure J: (He pressure is higher, so it goes to the natural gas side) (C leaks, the He pressure decreases, and the pressure gauge 17 shows relief. Further, the analyzer 15 detects that the He concentration in the vapor increases, indicating that damage has occurred to the inner tube 8.Furthermore, if the outer tube 7 is cracked, the He concentration increases. leaks into the liquid helium, and the He pressure decreases.Therefore, in this case as well, the pressure gauge 17 detects the leak, and the analyzer 16 detects that the outer tube 7 is damaged. .

In addition, in order to improve the responsiveness of pressure changes on the pressure gauge, grooves in the axial direction may be carved on the outer surface of the inner tube 8 or the inner surface of the outer tube 7, so that the gap between the inner tube and the outer tube can be improved. The gap may be actively enlarged.

In addition, in the conventional type, the inner tube needs to be thick enough to withstand steam pressure, and the outer tube needs to be strong enough to withstand even if the inner tube is damaged. Therefore, the heat transfer tube has a large diameter, but in the present invention, the pressure of He is increased, and when looking at the inner tube 8, the differential pressure between the inner and outer circumferences is several + KMccm2, and the inner tube has this differential pressure. withstands 1q
It is sufficient if the strength is as strong as the

In the above embodiment, if only leaks from the heat exchanger tubes are to be detected, the analyzers 15 and 16 can be omitted, leading to significant streamlining of the leak detection system.

[Effects of the Invention] As described above, according to the present invention, leaks in heat transfer tubes can be easily detected with a simple device, the wall thickness of the inner tube can be reduced, and the heat transfer coefficient can be improved. At the same time, the natural air generator can be made smaller.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of the present invention, FIG. 2 is an explanatory diagram of a conventional example, and FIG. 3 is an enlarged view of section A in FIG. 6 is a double heat exchanger tube, 7 is an outer tube, 8 is an inner tube, and 17 is a pressure gauge. Figure 3

Claims (1)

[Claims] 1) In a double-tube steam generator where the heat transfer tube is a double tube and liquid sodium is flowed outside the heat transfer tube and water is flowed inside the heat transfer tube to generate steam, there is a space between the inner and outer heat transfer tubes. A method for detecting leaks in a double heat exchanger tube steam generator, characterized in that helium is sealed at a pressure higher than the internal pressure of the inner tubes, and leaks are detected by detecting changes in the pressure of the helium.