JPS582617B2 - sodium ionization detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a sodium ionization detector, and particularly to a sodium ionization detector with improved detection accuracy.

In fast breeder reactors, it is necessary to detect sodium contained in the piping in order to ensure safety and prevent corrosion of the piping.

Traditionally, sodium detection has been performed with a sodium ionization detector.

This sodium ionization detector (So-dium Io
Detector (abbreviated as SID) is a device that utilizes physical phenomena, and was developed in Japanese Patent Application Laid-open No. 5
This is a well-known technique as disclosed in Publication No. 0-104989 and the like.

FIG. 1 shows the circuit configuration of the SID disclosed in the above publication.

That is, the AC power source 3 is applied to the primary side of the transformer 1.

Therefore, an AC voltage is applied to the filament 4 connected to the secondary side of the transformer 1, and the temperature of the filament 4 becomes high.

A collector 5 is arranged opposite to the filament 4.

A DC power source 2 is applied to the filament 4 and the collector 5.

With this configuration, if sodium is present in the gas, the sodium is heated by the filament 4 and ionized.

The generated sodium ions are caused by the electric field formed by the DC power supply 2 between the filament 4 and the collector 5.
It is collected by the collector 5 and detected by the ammeter 6 as a DC output.

The output waveform from the ammeter 6 at this time is shown in FIG.

The horizontal axis shows time (min), and the vertical axis shows ion current value (mA).

As is clear from the figure, the output of the SID has a DC component,
It is characterized by a temporal fluctuation component of about several Hz, and this temporal fluctuation component is SAS (Sodium A
It is called erosol (abbreviation of Sp-ike).

What defines the detection limit of such conventional SIDs is dark current.

There are three types of dark current. The first is leakage current flowing through the insulator between the electrodes, the second is ionic current caused by dirt on the filament surface, alkali metals contained inside the filament material during the manufacturing process, and the third is is the dark current due to radiation.

The first leakage current can be reduced to 10-12 A or less by increasing the insulation resistance.

However, for the second ion current, the lower melting point (approximately 25
In the case of metals (below 00°C), there is no essential solution.

In particular, this type of dark current has the property of increasing over time, and when a filament is exposed to a sodium-containing gas for several hours, the magnitude of the dark current increases from 1 to 3 mA in the case of platinum, for example. It also increases to 5 to 20 mA.

Therefore, the detection ability deteriorates over time.

Furthermore, regarding the third dark current, an increase in dark current is unavoidable unless radioactivity is attenuated.

Next, FIG. 3 shows the relationship between the various types of dark current, SID output, and sodium concentration described above.

The horizontal axis shows the sodium concentration, and the vertical axis shows the ionic current (mA).

The error at each measurement point represents the width of the temporal fluctuation shown in FIG.

In the case of this figure, the dark current is 10 mA, and considering the ratio of the SID output to the dark current, the sodium concentration is 1 to 100 ×
In the range of 10-9 g/cm3, it only increases from 12 to 4.

In addition, in the case of IX10-9g/cm3 and 100X10
The output level only increases about three times compared to the case of -9 g/cm3, and it is difficult to correlate the sodium concentration in the gas with the ion current value.

In particular, the lower the concentration, the more difficult it is to determine sodium leakage.

The present invention eliminates the above drawbacks and provides a sodium ionization detector with improved detection accuracy.

The gist of the present invention is to extract the alternating current component (fluctuation width) of the ion current and provide it as a detection signal.

FIG. 4 is a diagram showing the variation width of the ion current, that is, the width of the alternating current component.

The horizontal axis shows the sodium concentration.

As is clear from this figure, when looking at the fluctuation range of the ion current, IX10"-9g/cm3 and 100X10-9g/cm3
There is a difference in output of about 6 times compared to the case of cm3, and the linearity is much better than when looking at the current output.

Therefore, in the present invention, only the fluctuation range is extracted from the ion current as shown in FIG.

FIG. 5 is a diagram showing an embodiment of the present invention.

The difference from FIG. 1 is that a load resistor 7 is provided between the collector 5 and the negative side of the high voltage DC power supply 2, and the resistor 7
This is because a high-pass filter 8, an RMS (effective value) calculator 9, and a display section 10 are provided in series on the output side.

In the above configuration, the output voltage across the load resistor 7 is
First, filter 2 extracts only the variation.

Next, the RMS calculator 9 obtains the average value of the amplitude of fluctuations within a certain time T as a DC output.

The content of the calculation in the RMS calculator 9 is defined by the following equation.

Here, ΔERMS: RMS value of the amplitude of the variation ΔE: Amplitude of the variation The thus obtained DC outputs obtained by the RMS calculator 9 are compared and processed by the display unit 10, and can be displayed directly or as an alarm. conduct.

A, B, and C in Fig. 6 are input, output, and RMS of filter 8.
The outputs of the arithmetic unit 9 are shown respectively.

According to this embodiment, detection without the influence of dark current becomes possible.

FIG. 7 is a diagram showing another embodiment of the present invention.

The difference from FIG. 5 is that a peak hold circuit 20 is provided on the output side of the filter 8.

This peak hold circuit 20 includes a comparator 21 and a counter 2.
2. Consists of a DA converter 23.

First, only the variation is extracted by the filter 8 and input to the plus input side of the comparator 21.

The comparator 21 compares the negative input and the positive input, and generates an output only when the positive input is larger.

Therefore, when the output of the filter 8 is greater than the output of the DA converter 23, the output of the comparator 21 is generated and the counter 2
Open the passenger gate 2 and input the clock CL to the counter 22.

In the counter 22, the gate is opened while the output of the comparator 22 is present, and the input clock CL is counted during that time.

The count value of the counter 22 is outputted to the outside as a digital output, and is also inputted to the DA converter 23 and converted into an analog signal.

This analog output is also output to the outside, and the comparator 2
Input to the minus input side of 1.

According to the above configuration, the output of the filter 8 is transmitted to the DA converter 2.
3, the counter 22 is incremented until it becomes equal to the maximum value of the amplitude value, and S
This means that the maximum value of the ID fluctuation component can be detected.

Note that digital output and analog output are substantially the same, but are utilized when the external processing system is separated into an analog system and a digital system.

According to the above embodiment, the following effects can be obtained.

(1) Because the dark current component with little fluctuation is cut,
Deterioration of SID detection ability over time is eliminated.

(2) The above advantages also mean that pre-treatments such as baking out the alkali metal (a cause of dark current) in the filament material are no longer necessary.

In particular, since such pretreatment is not possible for metals with a low melting point of 2500° C. or lower, the effects of the present invention are significant.

(3) The dark current caused by radiation in the furnace also has little temporal variation, so it does not affect the SID output of the present invention as in (1) above.

(4) Since stable DC output can be obtained, it becomes easy to determine whether there is a sodium leak or not and to set the alarm level.

(5) The frequency band of SID output fluctuation is 0.1 to 4.
Since the frequency is approximately 0 Hz, the influence of electromagnetic noise within the plant can be reduced using a filter or the like.

In addition, as a method for extracting only the fluctuation component, RMS
There are various other possibilities besides calculations.

For example, sampling is also possible.

At this time, the sampling period needs to be shorter than the period of the fluctuation component.

According to the present invention as described above, it is possible to eliminate errors in detection accuracy due to dark current, and thus it is possible to achieve an improvement in detection accuracy compared to the conventional method.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing a conventional example, Fig. 2 is a diagram showing SID output, Fig. 3 is a diagram showing the relationship with dark current, Fig. 4 is an explanatory diagram of the present invention, and Fig. 5 is a diagram showing the present invention. FIG. 6 is a waveform diagram of each part, and FIG. 7 is a diagram of another embodiment of the present invention. 4...Filament, 5...Correction, 8...High pass filter, 9...R
MS calculator.

Claims (1)

[Scope of Claims] 1. A sodium ionization electrode that ionizes sodium by heating, a collector disposed opposite to the sodium ionization electrode to collect sodium ions, and a sodium ionization electrode that collects sodium ions collected by the collector. A sodium ionization detector comprising means for extracting an alternating current component from a current and detecting the amplitude value of this alternating current component. 2. The sodium ionization detector according to claim 1, wherein the amplitude value is an effective value of the AC component. 3. The sodium ionization detector according to claim 1, wherein the amplitude value is a peak hold value on a time series of the alternating current component.