JPS5925452B2 - Hydrogen concentration measurement device in liquid metal - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device for measuring hydrogen concentration in a liquid metal, such as liquid sodium.

Liquid metals, especially liquid sodium, are used as coolants in fast breeder reactors, etc., and devices that measure the hydrogen concentration in them are used for leak detection to detect sodium-water reactions at an early stage, for example in steam generators. It is also important as a vessel. Conventional hydrogen meters collect hydrogen that diffuses and permeates from liquid metal through a thin bellows or hemispherical diffusion membrane made of nickel, etc., using an ion pump connected via an isolation valve, a vacuum gauge, a mass spectrometer, etc. It is measured by the output of

For example, the measurement method is to
of liquid sodium is poured into the membrane, the inside is made into a high vacuum using an ion pump, and hydrogen is passed through the diffusion membrane, either by opening the isolation valve and operating the ion pump, or by closing the isolation valve and passing through the diffusion membrane. This can be done by equilibrating the chlorohydrogen and measuring the hydrogen partial pressure with a vacuum gauge, mass spectrometer, or ion pump output. However, such conventional hydrogen meters have the following problems. 0) The ion pump may change over time due to excessive absorption of hydrogen.
It is necessary to correct the hydrogen partial pressure due to the temperature difference from 00'C), and measurement accuracy decreases due to fluctuations in these temperatures. (→ Because the vacuum gauge output depends on the type of gas being measured. , correction for hydrogen is required;
2) The vacuum gauge itself has a hydrogen exhaust effect, which deteriorates the measurement accuracy of low hydrogen concentrations,... Problems with gas release from the vacuum wall or leaks from the outside, Θ The diffusion membrane increases the amount of hydrogen permeation as much as possible. Therefore, it requires a thin and wide area, but since the interior is in a high vacuum state, the diffusion membrane is always under pressure of 1 atm or more from the sodium side, and moreover, the diffusion membrane is exposed to sodium for a long time at high temperatures. This may be due to problems with the mechanical strength and durability of the diffusion membrane due to exposure to water.

As described above, conventional hydrogen meters have many problems that need to be solved and are not practical. The present invention has been made in view of the various problems in the prior art as described above, and its purpose is to have a simple structure, excellent durability, and highly accurate determination of the hydrogen concentration in liquid metal. The objective is to provide a device capable of measuring.

In order to achieve this object, the present invention uses a thin-walled tube type, preferably a thin-walled coiled tube type, as the diffusion membrane instead of the conventional hemispherical or tongue-shaped type, and furthermore, in the conventional hydrogen meter, the inside of the diffusion membrane is Whereas a vacuum was created and the partial pressure of hydrogen diffused in the vacuum was measured, the present invention introduces an inert gas such as nitrogen or argon into the diffusion membrane, and introduces hydrogen that diffuses into this inert gas. The inert gas is introduced into a gas analyzer such as a gas chromatograph, and the absolute amount (number of moles) of hydrogen contained in the inert gas is measured.

That is, the present invention provides a diffusion membrane in the form of a metal capillary tube immersed in a liquid metal, an inert carrier gas supply section connected to the inlet portion thereof via a first on-off valve, and an outlet portion of the diffusion membrane capillary tube. a gas analyzer connected to the third on-off valve via a second on-off valve;
a bypass pipe interconnecting the outlet side of the inert carrier gas supply section and the inlet side of the gas analyzer, and a standard gas container containing a known amount of hydrogen attached to the gas analyzer. , is an apparatus for measuring hydrogen concentration in a liquid metal, in which the hydrogen diffused and permeated through the diffusion membrane is guided to a gas analyzer together with an inert carrier gas to quantify the amount of hydrogen in the inert gas. An embodiment of the present invention will be described in detail below based on the drawings.

As shown in FIG. 1, the hydrogen concentration measuring device consists of a diffusion membrane hydrogen detection section a, a gas introduction section b, and a gas analysis section c. The diffusion membrane hydrogen detection section a is constructed by attaching a metal tube diffusion membrane 2 to a bypass line 1 provided in a part of the liquid sodium loop. Metal tube 2 has an inner diameter of 2.0 m, 71 L, and a wall thickness of 0.1 mm.
It is made of nickel and has an internal volume of about 15 m1, and is inserted into a coil. Next, the gas introduction part b is for introducing an inert gas (in this example, pure argon gas) into the metal capillary tube 2 and guiding the diffused and permeated hydrogen to the gas analyzer part c. Consists of a .0mm thick stainless steel tube and multiple valves. That is, the inlet section 3 of the diffusion membrane metal capillary tube 2 is connected to the argon gas supply device 5 via the first on-off valve 4, and the outlet section 6 of the diffusion membrane metal capillary tube 2 is connected to the second on-off valve 7. The gas analyzer section Ci is connected through the gas analyzer section Ci. Further, the argon gas supply device 5 and the gas analyzer section c are connected to a bypass pipe 9 equipped with a third on-off valve 8.
are mutually connected. The pressure at which argon gas is introduced into the diffusion membrane metal capillary tube 2 varies depending on the gas flow resistance of the capillary tube 2, but it is the pressure required to introduce argon gas into the gas analyzer section c at a rate of 15 to 25 m1/min. pressure, i.e. 0.
Approximately 5 to 3.0 atmospheres is preferable. This carrier gas not only functions as a carrier to introduce hydrogen diffusing from the liquid metal into the gas analyzer, but also functions to reduce the load pressure on the diffusion membrane by adjusting the gas pressure. . In this embodiment, the gas analyzer section c is a commercially available gas chromatograph 10 equipped with a thermal conductivity detector (TCD).
The trace amount of hydrogen contained in argon is PF
Detection is possible by order, and the results are recorded by a recorder 11. The gas chromatograph 10 is equipped with an argon standard gas container 12 containing a known amount of hydrogen in order to obtain a TCD calibration curve. The hydrogen content of the standard gas is about the same as the hydrogen content in the argon gas introduced from the metal capillary tube 2, that is, 10 to 100PF.
About 1 is good. There are two measurement methods using the hydrogen concentration measuring device configured as described above: the equilibrium method and the continuous method. (1) Equilibrium method The third on-off valve 8 is opened, the first and second on-off valves 4 and 7 are closed, and argon gas is confined within the metal capillary tube 2.

Hydrogen is diffused and permeated from the liquid sodium for a certain period of time, and when equilibrium is sufficiently reached, the third on-off valve 8 is closed, and the first,
The second on-off valves 4 and 7 are opened to guide hydrogen in the thin tube 2 together with argon gas to the gas chromatograph 10 for measurement. Next, each on-off valve 4, 7, 8 is returned to its original state. FIG. 2 shows an example of the hydrogen concentration measurement results in argon obtained in this way, where the vertical axis shows the gas chromatograph output and the horizontal axis shows time.

Curves A and B correspond to the case where the hydrogen concentration in sodium is changed by the cold trap method (the lowest cold trap temperature for A is 250°C and for B 150°C). A, B
By determining the peak area of each curve, the amount of hydrogen (number of moles) in the argon gas can be determined. In the case of an ideal gas, the following Paul-Charles law holds.

P=NRT・・・・・・・・・(1) Here, P is the hydrogen partial pressure inside the metal tube, is the volume inside the metal tube, n is the amount of hydrogen in the metal tube (number of moles), R is the gas constant, T is the absolute temperature inside the metal tube It is.

From the hydrogen amount n, the hydrogen partial pressure inside the metal capillary 2, that is, the hydrogen partial pressure P in the equilibrium sodium can be determined.

In addition, the hydrogen partial pressure P in sodium is Siverts (Si
Everts' law, the following relationship exists between the hydrogen concentration in sodium and the hydrogen concentration in sodium.

ClI-K-'V (2) Here, CH is the hydrogen concentration in sodium, K is Sievert's constant, and P is the hydrogen partial pressure in sodium.

From the above equations (1) and (2), it becomes as follows, and the hydrogen concentration CH in sodium can be determined.

Hydrogen concentration in sodium determined in this way (p)
The relationship between cold trap temperature and cold trap temperature is shown in Figure 3 for reference. In this equilibrium measurement method, the temperature of the diffusion membrane tube section 2 is 3
It has the characteristic that the measured value of hydrogen concentration hardly changes even if it fluctuates from 50 to 600°C or even if the argon gas pressure inside the thin tube 2 is changed (even if it is evacuated). The time required to reach equilibrium depends on the sodium temperature in the capillary section, but a few minutes was found to be sufficient even at low temperatures (350 C). This measurement method does not require correction for temperature differences between the diffusion membrane part and the measurement part as in conventional hydrogen meters, and data analysis is extremely easy, so it is useful for accurately detecting the hydrogen concentration in sodium. Are suitable. A measurement time interval of about 10 minutes is sufficient and satisfies the frequency required for normal sodium-based hydrogen concentration measurements. (11) In the continuous method shown in Fig. 1, close the on-off valve 8 shown in Fig. 3, and
The on-off valves 4 and 7 are opened, argon gas is constantly flowed through the diffusion membrane metal capillary tube 2, and the amount of hydrogen diffused and permeated is continuously introduced into the gas chromatograph 10 and quantified.

An example of the measurement results is shown in FIG. The vertical axis is the gas chromatograph output, and the horizontal axis is time, or the diffusion membrane temperature is 350°C. In FIG. 4, parts A and B correspond to the hydrogen concentrations at the cold trap temperatures of 250° C. and 1500° C., respectively. The amount of hydrogen that diffuses and permeates depends on the hydrogen concentration in sodium, but is also easily influenced by the diffusion membrane temperature.
Therefore, in order to accurately quantify the hydrogen concentration in sodium using this continuous method, it is necessary to maintain the sodium temperature in the diffusion membrane constant and to perform the equilibrium method in (1) in advance to adjust the gas chromatograph output. It is necessary to find the relational expression for the concentration of hydrogen in sodium. The characteristics of this continuous measurement method are that an output corresponding to the hydrogen concentration in sodium can be obtained continuously, and that the hydrogen meter can quickly follow changes in the sodium hydrogen concentration.For this reason, in actual liquid sodium systems, for example, It is effective as a so-called leak detector that detects an increase in the amount of hydrogen due to a sodium-water reaction when the secondary steam generation part of a nuclear reactor is damaged. Further, by using the above two measurement methods, that is, the equilibrium method and the continuous method, it is possible to measure the hydrogen concentration continuously and with high accuracy.

As described above, in the present invention, since the diffusion membrane is made into a tubular shape with a fine diameter, the mechanical strength is improved, and the diffusion membrane area per unit volume is large, so that it can be used at a low liquid metal temperature of about 350 C. In addition, since a positive pressure inert gas is introduced into the interior of the diffusion membrane, the pressure applied to the membrane is reduced, and these factors combine to significantly improve durability b≦. Even if the diffusion membrane capillary is damaged, the liquid metal is unlikely to leak to the outside, and even if it leaks, it will solidify immediately within the gas introduction tube, resulting in an extremely safe product.

In addition, the present invention has an extremely simple configuration, can control the hydrogen concentration in liquid metal with high accuracy, and can use either the C equilibrium measurement method or the continuous measurement method depending on the measurement conditions. They can be selected as appropriate, or both can be used in combination, resulting in a number of excellent effects.

[Brief explanation of the drawing]

Figure 1 is a schematic explanatory diagram of an embodiment of the hydrogen concentration measuring device according to the present invention, Figure 2 is a diagram showing an example of measurement results by the equilibrium method, and Figure 3 is an example of measurement data of hydrogen concentration in sodium. FIG. 4 is a diagram showing an example of measurement results by the continuous method. DESCRIPTION OF SYMBOLS 1... Bypass line, 2... Diffusion membrane metal tube, 3... Inlet part, 6... Outlet part, 4, 7, 8... ...Opening/closing valve, 5...Argon gas supply device, 10...Gas chromatograph.

Claims (1)

[Claims] 1. A diffusion membrane in the form of a metal capillary tube immersed in a liquid metal, an inert carrier gas supply section connected to its inlet via a first on-off valve, and a diffusion membrane tube-shaped diffusion membrane immersed in a liquid metal. a gas analyzer connected to the outlet via a second on-off valve; and a bypass pipe that includes a third on-off valve and interconnects the inert carrier gas supply section outlet side and the gas analyzer inlet side. , a standard gas container containing a known amount of hydrogen attached to the gas analyzer, and the hydrogen diffused and permeated through the diffusion membrane is guided to the gas analyzer together with an inert carrier gas, and the hydrogen in the inert gas is A device for measuring the concentration of hydrogen in liquid metal. 2. The device according to claim 1, wherein the metal capillary tube constituting the diffusion membrane is coiled.