JP3028904B2 - Glass level detection method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for detecting a glass level of a melter capable of accurately detecting a glass level irrespective of a glass composition and a temperature, and more particularly to a ceramic for treating a highly radioactive waste liquid by a vitrification method. Suitable for melters.

[0002]

2. Description of the Related Art For example, as a method of treating a highly radioactive waste liquid generated in a reprocessing plant, a technique has been developed in which the waste liquid and a glass raw material are melted at a high temperature and filled in a canister as a container and solidified.

That is, the highly radioactive liquid waste is subjected to an appropriate pretreatment, and is first supplied to a melter together with a glass raw material. Thus, the highly radioactive waste liquid becomes molten glass together with the glass raw material in the melter. This molten glass is regularly filled in the canister. The glass-filled canister is sealed and temporarily stored in a solidification facility.

[0004] In these steps, the glass melting furnace has been assigned the function of a first barrier for confining radioactive materials. Therefore, from the viewpoint of preventing the spread of contamination by radioactive substances, it is necessary to detect the glass level in the melting furnace in order to prevent the release of radioactive substances from the melting furnace due to excessive supply of raw materials. Further, from the viewpoint of protecting the electrode for direct current supply of the glass melting furnace, it is necessary to detect the glass level to prevent the glass from being excessively extracted.

Conventionally, to detect the above glass level,
Japanese Patent Publication No. 3-58649 discloses a method of detecting the rate of change of the electric resistance value between the electrodes installed in the molten glass via a differential operation circuit and detecting the glass level at the time when the rate of change shows the maximum value. No. 6,086,045.

[0006]

In the above conventional glass level detecting method, the rate of change of the electric resistance between the electrodes installed in the molten glass is detected via a differential operation circuit, and the rate of change of the rate of change is detected. It was a method of trying to detect the glass level when the maximum value was reached. However, the rise of the glass level in the molten state in the actual high-level radioactive liquid waste vitrification melter is very slow, and the resistance change rate is very slow due to the effect of the glass adhered to the level detection probe. Only change, so in the above method,
It has proven difficult to detect glass levels.
Also, erroneous operation of level detection due to glass level waving phenomenon and noise due to the input of raw materials was frequently observed.

The present invention has been proposed in view of the above-mentioned problems of the prior art, and has as its object to accurately measure the glass level regardless of the glass composition and temperature, even if the change is slow. An object of the present invention is to provide a glass level detecting method capable of detecting and preventing malfunction of level detection.

[0008]

In order to achieve the above object, the present invention provides a melter having one common electrode and a plurality of level detecting electrodes corresponding to each glass level. Is set to a predetermined constant multiple of the electric resistance value between the lower-level detection electrode and the common electrode, and the lower-level detection is performed among the above-described detection reference values for each level.
Set the reference value so that the glass level in the melter is
Lower limit level detection electrode and common electrode in stable state
The electrical resistance value between is stored and the predetermined constant
Was doubled, the detection of each level, and an electrical resistance value and the detection reference value for each level between the common electrode and the detection electrode of each level is compared, the electrical resistance value of the level detection reference value of the level And that the state has been continued for a predetermined time.

[0009]

According to the present invention, the detection reference value of each level is set to a predetermined constant times the electric resistance value between the lower-level electrode and the common electrode, so that the temperature of the molten glass in the melter can be reduced. Changes in composition between runs can be automatically canceled. Further, since the detection of each level is a method of detecting the electric resistance value between the electrode of the level and the common electrode by comparing with the detection reference value of the level, the change in the glass level is slow. Can also be detected accurately. Further, since each level is detected when the above state continues for a predetermined time, it is possible to prevent erroneous determination of the level detection due to temporary fluctuation of the liquid level due to the input of the raw material or the like and instantaneous noise. In addition, the electric resistance between the lower-level detection electrode and the common electrode in a state where the glass level in the melter is stabilized at a level equal to or higher than the lower-level level is stored, and a predetermined constant times the lower-limit level is used. , It is possible to omit one electrode for setting the lower limit detection reference value.

[0010]

FIG. 1 is an explanatory view showing an example of the arrangement of electrodes on a melter in the method of the present invention.
Is a molten glass, (3) is a control part, (4) is a common electrode, (5) is a lower limit level detecting electrode, (6) is an extraction start level detecting electrode, (7) is an upper limit level detecting electrode, ( 8) shows an upper limit backup electrode.

The melter (1) has a structure in which a glass raw material and a highly radioactive waste liquid are charged from an upper portion and a molten glass (2) is extracted from a lower portion. The melter (1) is housed in a cell strictly protected against radioactive contamination. .

Each electrode is arranged in a state as shown in FIG. 1 with respect to the melter (1). That is, the lower limit level detection electrode (5) is provided at the lower limit level of the molten glass (2) extracted from the melter (1).
The molten glass (2), which is necessary for melting the continuously supplied glass raw material by heat generation, is set to such a position that the minimum molten glass (2) remains in the melter (1). The installation position of the common electrode (4) depends on the lower-level detection electrode (5).
It is installed below. The extraction start level detecting electrode (6) is provided at a position of an appropriate level so that the molten glass (2) in the melter (1) reaches a predetermined amount and the extraction into the canister is started. The upper limit level detection electrode (7) is provided above the extraction start level detection electrode (6). The upper limit backup electrode (8)
It is installed further above the upper limit level detection electrode (7).

The detection of each level is performed by the molten glass (2) between the common electrode (4) and each of the electrodes (5) (6) (7) (8).
The detection is performed by detecting an electrical resistance value that changes depending on the presence or absence of the signal, comparing the detected value with a preset detection reference value of each level, and monitoring for a predetermined time. This electric resistance value is
The value is small when the molten glass (2) is full between the electrodes, and large when there is no molten glass (2) between the electrodes.

The detection reference value of each level is set to a predetermined constant times the electric resistance value between the lower-level detection electrode (5) and the common electrode (4), and the detection electrode (5) of each level is set.
(6) The electric resistance between the common electrode (4) and (7) is a predetermined constant times the electric resistance between the lower-level detection electrode (5) and the common electrode (4). , And the arrival of each level is detected when the state continues for a predetermined time. In addition, the electric resistance between the lower-level detection electrode (5) and the common electrode (4) in a state where the glass level in the melter (1) is stabilized at a level equal to or higher than the lower-limit level is stored. , A predetermined multiple of this value is used as the detection reference value of the lower limit level.

The method of setting the detection reference value of each level will be described in detail. The detection reference value (R2) of the extraction start level is set between the lower limit level detection electrode (5) and the common electrode (4). A predetermined magnification α of the electric resistance value (R1) is set. That is, R2 = R1 · α.

Further, the upper limit level detection reference value (R3)
Is set to a predetermined magnification β of the electric resistance value (R1) between the lower-level detection electrode (5) and the common electrode (4). That is, R3 = R1 · β.

The detection reference value (R4) of the upper-limit backup level is set to a predetermined magnification γ of the electric resistance (R1) between the lower-level detection electrode (5) and the common electrode (4). That is, R4 = R1 · γ.

Further, the lower limit level detection reference value (R5)
Is the electric resistance value between the lower limit level detecting electrode (5) and the common electrode (4) in a state where the glass level in the melter (1) is equal to or higher than the lower limit level and is stabilized at the level immediately before the extraction start level. (R1 ′) is stored, and a predetermined magnification δ of the stored electric resistance value (R1 ′) is stored.
Set to. That is, R5 = R1 ′ · δ. And
The detection reference value (R5) of this lower limit level is determined by the melter (1)
Each time the molten glass (2) is extracted from the apparatus, it is updated in response to the extraction start signal.

FIG. 2 shows a specific embodiment of the present invention. In FIG. 2, (9) is a changeover switch, (10)
Is a constant voltage power supply, (11) is a detection resistor, (12) (1
3) indicates an AC / DC converter, and (14) indicates a system computer.

The changeover switch (9) connects the electrodes (5), (6), (7) and (8) while switching them at predetermined time intervals (for example, every 5 seconds) by the system computer (14). Each connected electrode (5) (6) (7)
Between the electrode (8) and the common electrode (4), an interelectrode resistance exists through the molten glass (2), and the following closed circuit is configured including the resistance.

Constant voltage power supply (10) → detection resistor (11)
→ Each electrode (5) (6) (7) (8) → Molten glass (2)
→ Common electrode (4) → Constant voltage power supply (10)

The power supply voltage V2 and the terminal voltage V1 of the detection resistor (11) are measured from the closed circuit and input to the system computer (14) via the AC / DC converters (12) and (13), respectively. Computer (1
According to 4), the resistance value (Ri) between each of the electrodes (5), (6), (7), (8) and the common electrode (4) is obtained by the following equation.

(Ri) = (V2 / V1-1) × resistor for detection (11) In order to avoid interference with the heating current in the melter (1), the constant voltage power supply (10) Has changed,
In addition, a filter is provided in the circuit to separate signals. Each device such as a measurement and changeover switch (9) for each voltage is centrally managed and automatically controlled by a system computer (14). The system computer (14) takes in the voltage data while checking the connected circuit, calculates the resistance value (Ri) between each electrode (5) (6) (7) (8) and the common electrode (4), Each level is stored and stored in the control panel, and each level is detected by using a determination magnification (α, β, γ, δ) and a monitoring time set by a digital switch. The setting of the determination magnification and the monitoring time can be changed. Each measured resistance value (R
i) and each detected level signal are sent from the system computer (14) to a higher-level controller.

An embodiment of the present invention has the above-described configuration.
Next, the operation will be described. A glass raw material and a highly radioactive waste liquid are charged into the melter (1) from above, and a heating current is applied to a heating electrode to heat and melt the glass raw material to obtain a molten glass (2) mixed with the highly radioactive waste liquid. This molten glass (2)
Increases and approaches a predetermined amount, the resistance value (R6) between the extraction start level detecting electrode (6) and the common electrode (4) becomes as shown in FIG. When the extraction start level detection electrode (6) is completely immersed, the resistance value slightly decreases but hardly changes, and the electric resistance between the lower limit level detection electrode (5) and the common electrode (4). This is almost the same value as the value (R1). (The value is slightly larger due to the distance between the electrodes.)

Extraction start level detection reference value (R2)
Is set to R2 = R1 · α, and when the state of R2 or less continues for a predetermined time (for example, 20 seconds), an extraction start signal is output. If the state of R2 or less does not continue for a predetermined time, it is determined that the state is caused by a temporary fluctuation of the liquid level due to the input of the raw material or an instantaneous noise or the like, so that the extraction start signal is not output.

When the extraction start signal is output while the state below R2 continues for a predetermined time, the molten glass (2) is extracted from the lower part of the melter (1) into the canister. As a result, the level of the molten glass (2) in the melter (1) drops and drops below the extraction start level detecting electrode (6). Resistance (R6) between the extraction start level detection electrode (6) and the common electrode (4) when the level falls
Rises as shown in FIG.

Then, the molten glass (2) in the melter (1) is drawn out to the canister, the level of which is reduced, and the lower limit level detecting electrode (5) starts to be exposed. The change in the electric resistance value (R1) between the lower-level detection electrode (5) and the common electrode (4) during this time is a rising change similar to that shown in FIG. In the course of this change, the detection reference value R5 of the lower limit level exceeds R5 = R1 ′ · δ. Then, when the state of R5 = R1 ′ · δ or more continues for a predetermined time, the extraction end signal is output, and the extraction to the canister is ended. If the above state does not continue for a predetermined time, the extraction end signal is not output.

When the extraction completion signal is output, the extraction of the molten glass (2) from the lower portion of the melter (1) is stopped, and the input of the glass material and the like and the heating and melting are continued in the melter (1). . Thereby, the level of the molten glass (2) in the melter (1) starts to rise. Then, when reaching the installation position of the extraction start level detecting electrode (6), an extraction start signal is output under the same conditions as described above.

When the extraction start level detection circuit or the extraction start signal output circuit or the like is out of order, the level of the molten glass (2) in the melter (1) is changed to the upper limit level detection electrode (7). As a result, the electric resistance between the electrode (7) and the common electrode (4) decreases as in FIG. Then, the upper-level detection reference value R3 = R
When the state equal to or less than 1 · β continues for a predetermined time, a raw material charging stop signal is output, and the raw material charging to the melter (1) is stopped. If the state of R3 = R1.beta. Or less does not continue for a predetermined time, the material input stop signal is not output.

When the upper limit level detection circuit or the material input stop signal output circuit is out of order, the level of the molten glass (2) in the melter (1) reaches the upper limit backup electrode (8). The electric resistance between the electrode (8) and the common electrode (4) decreases as in FIG. Then, the detection reference value R of the upper limit backup level
If the condition of 4 = R1.γ or less continues for a predetermined time, an alarm is issued. If the condition of R4 = R1 · γ or less does not continue for a predetermined time, no alarm is issued.

The above is the operation in the embodiment of the present invention. After reaching the detection reference value of each level, it is monitored whether or not the state continues for a predetermined time, and then each signal is output. This can prevent a malfunction. The monitoring time is appropriately set in consideration of the capacity and capacity of the melter (1). When the changeover switch (9) is used as in the embodiment of FIG. 2, the monitoring time is changed by the number of times of switching. Set, but not restricted to this.

[0032]

According to the present invention, the detection reference value of each level is set to a predetermined constant times the electric resistance value between the lower-level electrode and the common electrode, so that the melting point in the melter can be improved. Changes in glass temperature and composition for each operation can be automatically canceled, and the glass level can be detected regardless of the glass composition and temperature. Further, since the detection of each level is a method of detecting the electric resistance value between the electrode of the level and the common electrode by comparing with the detection reference value of the level, the change in the glass level is slow. Can also be detected accurately. In addition, each level of detection
Since the detection is performed when the above state continues for a predetermined period of time, it is possible to prevent a temporary fluctuation of the liquid level due to the input of the raw material or the like and an erroneous operation of the level detection due to instantaneous noise. In addition, the electric resistance between the lower-level detection electrode and the common electrode in a state where the glass level in the melter is stabilized at a level equal to or higher than the lower-level level is stored, and a predetermined constant times the lower-limit level is used. , One electrode for setting the lower-level detection reference value can be omitted, the number of electrode mounting holes communicating with the molten glass in the melter can be reduced, and leakage can be reduced. It is possible to reduce the number of danger and leakage prevention work locations.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing an example of the arrangement of electrodes on a melter in the method of the present invention.

FIG. 2 is an explanatory view showing a specific embodiment of the present invention.

FIG. 3A is an explanatory diagram showing a change in electric resistance between an extraction start level detection electrode and a common electrode when the glass level in the melter rises, and FIG. FIG. 7 is an explanatory diagram showing a change in electric resistance between the extraction start level detection electrode and the common electrode.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Melter 2 Molten glass 3 Control part 4 Common electrode 5 Lower limit level detection electrode 6 Extraction start level detection electrode 7 Upper limit level detection electrode 8 Upper limit backup electrode

──────────────────────────────────────────────────続 き Continuing on the front page (72) Noboru Endo, No. 33, Muramatsu, Oji, Tokai-mura, Naka-gun, Ibaraki Prefecture Within the Tokai Works, Power Reactor and Nuclear Fuel Development Corp. 7-1 Japan Electric Glass Co., Ltd. (72) Inventor Toshio Nakamura 2-7-1 Hararashi, Otsu-shi, Shiga Japan Electric Glass Co., Ltd. (72) Hirokazu Takeuchi 2-7-1 Hararashi, Otsu-shi, Shiga No. 1 Inside Japan Electric Glass Co., Ltd. (72) Inventor Kazuya Noguchi 2-7-1 Hararashi, Otsu-shi, Shiga Prefecture Inside Japan Electric Glass Co., Ltd. (56) References JP-A-63-210628 (JP, A) 63-122237 (JP, U) JP-A-2-63424 (JP, U) JP-B 3-58649 (JP, B2) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01F 23 /twenty four

Claims (1)

(57) [Claims] 1. A single common electrode and a plurality of level detection electrodes corresponding to each glass level are provided in a melter, and a detection reference value of each level is determined by a lower limit level detection electrode and a common electrode. Of the lower limit level among the above-mentioned detection reference values for each level.
Set the reference value so that the glass level in the melter is
Lower limit level detection electrode and common electrode in stable state
The electrical resistance value between is stored and the predetermined constant
Was doubled, the detection of each level, and an electrical resistance value and the detection reference value for each level between the common electrode and the detection electrode of each level is compared, the electrical resistance value of the level detection reference value of the level A glass level detection method, wherein the method is performed after confirming that the state has passed for a predetermined time.