JPH0139544B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a pretreatment method for a radioactive sample water device.

Automatic analysis of radionuclides in water is necessary for operational management and release radioactivity management of facilities that handle radioactive materials, such as nuclear power plants and nuclear fuel reprocessing facilities. For this analysis, it is necessary to prepare a measurement sample in advance. This advance preparation is called pretreatment.

A conventional radioactive sample water device is shown in Figure 1. A fixed amount of radioactive sample water is collected from a collection tube 1 via a valve 2 into a collection and quantitative tank 3. Next, the sample water is transferred to the filtration tank 4 via the valve 2, and water is simultaneously passed through the filter 5 and the ion exchange resin column 6. The waste water is temporarily stored in the waste water tank 22 via the valve 40 and then exhausted via the exhaust pipe 8. The purpose of the filter 5 is to remove crud (powdery corrosive products) that are not the object of analysis, and the ion exchange resin column 6 collects the radionuclides that are the object of analysis. The collection efficiency of an ion exchange resin largely depends on the water flow rate at which sample water passes through the ion exchange resin. Naturally, when the water flow rate is low, a constant collection efficiency can always be maintained. On the other hand, the time required for processing becomes longer.

For this reason, conventional water flow control employs a pressurization process in which the water is pressurized to a constant pressure from the pressurizing pipe 7. The water flow rate takes the maximum allowable value from the point of view of collection efficiency after the water flow starts, and thereafter gradually decreases as the filter becomes clogged. After all the sample water has been passed through, the microcomputer 9 automatically performs a series of processes in which the ion exchange column 6 is removed from the apparatus and transferred to the radioactivity analyzer.

Now, when passing the last sample water through the filter,
In addition to a constant filtration pressure, an additional pressure of several atmospheres is required. This phenomenon will be explained in FIG. This is because when purging the last sample water 12 in the filter 5 sealed by the upper and lower holders 10 and gaskets 11 with air, a pressure greater than the interfacial tension (capillary phenomenon) generated in the capillary tubes 13 in the filter is required. .

This pressure is generally called the bubble point.
In response to the existence of such bubble points, if the pressurizing pressure is simply increased, the sample water will pass through the column at high speed after passing through the filter 5, and the sample water from the filter 5 to the column will be Ion exchange becomes impossible with a certain collection efficiency.

The above-described fluctuations in ion exchange collection efficiency directly affect the final analysis accuracy and become an important problem in terms of performance.

The purpose of the present invention is to provide a pretreatment method for a radioactive sample water device that detects that the final amount of water cannot pass through a filter due to the presence of a bubble point, and greatly improves the stability of the final sample water collection efficiency. It's about doing.

Detection that no further final amount of sample water can pass is performed using a liquid level switch that is activated when a predetermined amount of sample water has passed. Before applying pressure equivalent to the bubble point, a small amount of pure water is added to the filtration tank, and the remaining sample water is passed through the filter at a constant speed. This additional pure water (additional clean water) also
In the case of the last amount, a situation arises in which the bubble point cannot be passed any further due to the existence of the bubble point. Therefore, even in the case of additional clean water, the time point at which the effect of the bubble point appears is detected, and the final pressurization is performed based on this detection. In this way, it is possible to prevent a decrease in collection efficiency due to excessive flow velocity when exceeding the bubble point.

The present invention will be explained below using examples.

FIG. 3 shows an embodiment of the radioactive sample water apparatus of the present invention. This embodiment has a collection pipe 1, a valve 2, a collection/quantification tank 3, a filtration tank 4, a filter 5, an ion exchange resin column 6, a drainage tank 22, an exhaust pipe 8, and a microcomputer 9. These components are the same as the conventional example shown in FIG. What is new in this embodiment is that a low pressure system 21 and a high pressure system 25 are provided on the pipe 7A, and a pressure gauge 26 is provided to detect the pressure on this system, and feedback is provided. For control purposes, a flow meter 20 is installed on the drain outlet side of the ion exchange resin column 6 via a valve 40, and the detection of the point in time when the final amount cannot pass through due to the presence of a bubble point in the drain tank 22 ( The main features are that a level meter 23 (to be described in detail later) and a clean water supply pipe 24 are provided. Furthermore, the microcomputer 9 is set to perform overall control.

A fixed amount of sample water is collected from a collection tube 1 via a valve 2 into a collection and quantitative tank 3. Next, the sample water is transferred to the filtration tank 4 via the valve 2, and is simultaneously passed through the filter 5 and the ion exchange resin column 6.

To control the flow rate of water, the suction pressure from the exhaust pipe 8 by the vacuum pump is kept constant, and the valve of the low pressure system 21 is controlled so as to keep the signal of the flowmeter 20 at a constant value. With this feedback control, a constant collection efficiency can be maintained until the filter 5 becomes unable to pass due to the existence of a bubble point. Naturally, the flow rate can also be controlled in accordance with the amount of crud accumulated in the filter 5. The pressure control range at this time is approximately 0.5 Kg/cm ² with Clad 10 ³ ppm and 500 ml of water flowing.
The pressure is lower than the bubble point pressure, which will be described later.

Next is the detection of the fact that it is no longer possible to pass the final amount due to the presence of the bubble point.
This is possible by adjusting the liquid level in the drainage tank 22 in advance so that it can be detected by a level meter 23 that is adjusted to the amount of water passing through. As another method, it can also be detected from the integrated value of the flowmeter 20 and the water flow stop signal.
In other words, since the effect of the bubble point occurs in the last part of the sample water, the amount of sample water is known in advance, so the effect of the bubble point can be known as soon as nearly the entire amount of sample water can be detected to have passed. . Therefore, a detection method that looks at the liquid level in the drain tank 22 and a detection method that looks at the integrated value of the total flow rate of the flow meter 20 were adopted.

By the above method, approximately 100 c.c. of clean water is supplied from the clean water supply pipe 24 after detecting the point in time when the last amount cannot pass through due to the presence of the bubble point. This clean water is used to push out sample water remaining in the column 6 from the filter 5 at a constant flow rate. Feedback control using the flow meter 20 may also be performed at this constant flow rate. In this case, another level meter is provided in the drainage tank 22 in addition to the level meter 23, and this level meter is used to control the bubbles. Point pressure may be detected.

Here, even in this additional clean water, the last amount cannot pass any further due to the existence of the bubble point at the end. In other words, the effect of bubble points appears. Therefore, in order to purge this additional clean water, pressurized air is supplied as described below. The point at which the pressurized air is supplied depends on the detection of the point at which the last amount of air can no longer pass due to the presence of the bubble point. Therefore, as in the case of sample water, the amount of additional clean water is known in advance, so when the level meter 23 in the drainage tank 22 detects an amount close to the amount of additional clean water, it is assumed that the effect of bubble point pressure has appeared. supply pressurized air. As mentioned above, in addition to the level meter 23, the flow meter 20 or another level meter 23 can also be used for detection.

Next, the high pressure system 25 is activated to purge clean water remaining in the column 6 from the filter with air. Generally, the bubble point pressure is around 2 kg/cm ² and is adjusted according to the filter used. Apply pressurized air gradually. And the air pressure is filter 5
When the bubble point is exceeded, a pressure drop occurs within the system (internal pressure of the filtration tank 4). This pressure drop is detected by the pressure gauge 26, and the high pressurization system 25 is stopped. Detection of passage of this bubble point is done by flow meter 2.
It can also be obtained from 0. That is, the time when a flow rate instruction is given again after the start of pressurization is the time when the bubble point is passed. The above control is automatically performed by the microcomputer 9.

FIG. 4 shows a time chart of the control sequence of the embodiment shown in FIG. P indicates a signal from the pressure gauge 26, and F indicates a signal from the flowmeter 20. Initially, a constant flow rate is maintained, but the flow rate F stops in the pressurizing range of the low pressurization system 21 and the point at which the level meter 23 is activated is the point at which the effect of the bubble point appears (shown in Figure 4). . Next, the flow rate signal when additional clean water is added is the point. This drop in the flow rate signal is detected and the high pressurization system 25 is activated.
Next, it is confirmed that the influence of the bubble point has disappeared due to the pressure drop in the system (in FIG. 4 and the flow rate instruction value during purging), and the high pressurization system 25 is stopped.

FIG. 5 shows a modification of the above embodiment. In this example, only the high pressure system 30 for the bubble point is provided,
Orifice 3 with different flow resistance at the outlet of column 6
Two systems will be provided for 1 and 32. The flow velocity control until the effect of the bubble point appears is performed by the orifice 31 and valve 33, which have large flow resistance. When the effect of the bubble point appears, the valve 34 is opened to allow water to flow in parallel to the orifice 32 side, which has a lower flow resistance. In this modification, the third
As in the figure, the differential pressure between the filter 5 and the column 6 outlet can be changed depending on the purpose.

FIG. 6 is a control signal time chart of a modification of FIG. 5. The figure shows the point at which the effect of the bubble point appears, and indicates the point at which clean water is additionally supplied, and the point at which the effect of the bubble point disappears.

According to this embodiment, it is possible to keep the ion exchange collection efficiency constant during the water flow process in series between the filter and the ion exchange column, and to complete the water flow process in the shortest possible time. This processing time is 500 times longer than the conventional processing amount.
Quick processing is possible within 10 minutes compared to 15 minutes per ml. This has sufficient performance to mechanize fuel inspection (shipping) work during periodic reactor inspections. Furthermore, the fluctuation in ion exchange collection efficiency due to the influence of bubble points is removed, reducing the collection efficiency of all treatments by ±4%.
It can be stabilized within.

In addition to the above performance improvements, it is possible to realize a practical radioactive sample water pretreatment device that improves the reliability of the device by simplifying the device.

Next, another example of operation control in the embodiment corresponding to FIG. 3 will be explained. FIG. 7 is a processing flowchart, and FIG. 8 is an explanatory diagram of a control sequence. In Figure 7, low pressure system 2 is activated by starting control (START).
1 valve Vl is open for a time τ ₀ . Next, check whether the detected value F of the flowmeter 20 is the set maximum value (MAX), and if F=MAX, the flowmeter 20
It monitors whether the detected value F reaches the set minimum value (MIN), and when F=MIN, the level meter 23
Check whether this is the point at which the effect of the bubble point appears. Level meter 23
If the value is on, it is assumed that the effect of the bubble point has appeared, and clean water is injected onto the filter 5 from the pipe 24 (for example, 50 ml). Note that the set maximum value MAX is a value set for optimal control based on the flow rate dependence of the collection efficiency of the ion exchange resin. The set minimum value MIN is a value set to minimize the processing time from collection of sample water to completion of filtration ion exchange.

Next, the valve V _L of the low pressurization system 21 is turned on for a period of τ.
Open. This τ time means the time until the influence of the next bubble point appears. Next, the valve V _h of the high pressure system 25 is opened, and during this time the state of the pressure switch 26 is monitored to check whether the pressure switch 26 is off. The pressure switch 26 is configured to turn on ("1") when the pressure is above a predetermined set pressure value, and turn off ("0") when it is below. If the pressure switch 26 is off, the low pressure system 21 and the high pressure system 25
Close valves Vl and Vh. The above control sequence is shown in FIG.

As described above, according to the present invention, the stability of ion exchange collection efficiency is also improved when the final sample water is air purged below the filter. Especially when preparing the final sample water quickly.
Moreover, it achieves the effect of being able to pass over the filter accurately. Therefore, high-speed and highly accurate pretreatment of radioactivity analysis samples can be achieved.

[Brief explanation of drawings]

Fig. 1 is a block diagram of a conventional radioactive sample water device, Fig. 2 is a sectional view of a filtration section, Fig. 3 is a block diagram of an embodiment of the present invention, and Fig. 4 is a control time chart of the embodiment.
FIG. 5 is a block diagram of a modification of the present invention, FIG. 6 is a control time chart of the modification, FIG. 7 is another control flow chart, and FIG. 8 is a control time chart. 1... Collection pipe, 2... Valve, 3... Collection quantitative tank, 4... Filtration tank, 5... Filter, 6... Ion exchange resin column, 7... Pressure piping, 8... Exhaust pipe, 9
...microcomputer, 10...filtration holder,
11...Putkin, 12...Sample water, 13...Capillary tube,
20...Flow meter, 21...Low pressure system, 22...Drain tank, 23...Liquid level meter, 24...Clean water supply piping, 25...High pressure system, 26...Pressure gauge, 30...High pressure system, 31, 32... Orifice, 33, 34... Valve.

Claims (1)

[Claims] 1. A tank for quantitatively collecting sample water, a filtration tank for storing sample water obtained by the tank, a filter provided on the sample water detection outlet side of the filtration tank, and a filter for the filter. In a radioactive sample water device having an exchangeable ion exchange resin column installed on the sample water outlet side, the point at which the last amount of the sample water cannot pass through the filter any more due to the presence of a bubble point unique to the filter. a first step of detecting the amount of sample water after passing through the column; a second step of adding additional clean water onto the filter at the time of detection in the first step; and a second step of adding additional clean water onto the filter; a third step of detecting, by the amount of additional clean water after passing through the column, a point at which the final amount of additional clean water cannot pass through the filter any further due to the presence of a bubble point; a fourth step of applying pressurized gas to release clean water remaining between the filter and the column during detection;