JP3801532B2 - α radioactivity identification device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to α radioactivity measurement of radioactive waste, and more particularly to an α radioactivity identification device that measures α radioactivity emitted from radioactive waste after solidification treatment.
[0002]
[Prior art]
With the operation of a nuclear fuel cycle facility such as a spent fuel reprocessing plant, TRU (a super uranium element; an artificial radioactive element whose mass is larger than uranium) containing α radionuclides is generated as high-level radioactive waste. For example, it has been studied that plutonium generated by reprocessing is finally solidified with a solidifying agent such as glass and sealed in a container for long-term storage.
[0003]
By the way, if all TRU waste generated from facilities handling radioactive materials such as reprocessing factories is handled in the same way, the disposal cost becomes enormous. For this reason, by measuring the radioactivity concentration of TRU wastes accurately, those having a low radioactivity level can be treated in a simple disposal form, and the overall disposal cost can be reduced. In this way, timely measurement and evaluation of α-activity of radioactive waste is an important task for radioactive waste and radioactivity management.
[0004]
Regarding the evaluation of α radioactivity of radioactive waste (glass solidified), which has been vitrified from high-level radioactive waste, etc., the radioactive waste is sampled before solidifying the radioactive waste, and α-ray spectrum measurement and chemical analysis are performed. Etc. have been implemented.
[0005]
However, this is a measurement of α radioactivity performed before the production of the vitrified body. After producing high-level radioactive waste into a vitrified body or when measuring the α radioactivity during storage, After cutting a part of the solidified body and pretreating it, the α radioactivity must be evaluated by so-called destructive analysis, which is measured by the above-mentioned α-ray spectrum measurement or chemical analysis method.
[0006]
When α radioactivity is measured after the production of high-level radioactive waste vitrified material, the radioactive waste solidified material will be subjected to a destructive analysis. It is necessary to break the containment of the radioactive material and extract the sample.
[0007]
Furthermore, solidified radioactive waste after sample extraction and samples used for analysis are generated as new radioactive waste, and complicated work including prevention of radioactive contamination is required for the treatment of these wastes. Is required.
[0008]
Since the method of measuring the radioactivity by destroying the measurement object in this way causes many problems, an α radioactivity identification device that can measure the radioactivity concentration of TRU waste in a non-destructive manner has been proposed. .
[0009]
As shown in FIG. 5, in the conventional α radioactivity identification device 100, an ionization chamber 102, an ionization chamber 103, a HEPA filter 105, and a blower 106 are arranged in this order between the upstream line 101 and the downstream line 107. Yes. TRU waste is placed in the ionization chamber 102. The ionization chamber 102 is filled with a measurement gas (ionized gas) containing a substance that is ionized by α rays via a line 101. The α rays react with the ionizing measurement gas filled in the ionization chamber 102 to generate ionized ions. As the measurement gas, for example, air, helium He, argon Ar gas alone or a mixture thereof is used. Since these gases have high ionization efficiency by α rays, it is possible to accurately measure α radioactivity.
[0010]
The measurement gas is sent to the ionization chamber 103 after being exposed to TRU waste radiation in the ionization chamber 102. When high-speed charged particles pass through the measurement gas, excited molecules and ionized molecules are generated along the passage. Cations and free electrons generated by separating neutron molecules are called ion pairs. This ion pair is detected by the ionization chamber 103 as an ionization current. In the ionization chamber 103, the electric signal detected by the electrode is input to the ionization current measuring device 104. The ionization current measuring device 104 converts the input electric signal into a pulse signal, counts it, and outputs the counting result to the data processing computer. The data processing computer displays the counted number of pulses on the display device and calculates the α radioactivity based on the number of pulses. This calculation result is also displayed on the display device as necessary.
[0011]
[Problems to be solved by the invention]
However, in the conventional apparatus, since the lines 101 and 107 through which the measurement gas flows are of the once-through method (one-through method), the amount of gas discharged by the end of the measurement is large, and the burden on the exhaust treatment facility becomes excessive.
[0012]
Moreover, in the conventional apparatus, it is necessary to enlarge the ionization chamber 103 according to the size of TRU waste, and as a result, the amount of lead shielding material covering the ionization chamber 103 increases. Large and heavy.
[0013]
Moreover, in the conventional apparatus, the measurement gas is easily affected by the surrounding environment, and when the moisture contained in the measurement gas increases or decreases, the sensitivity becomes unstable and the detection value varies accordingly. Measurement accuracy decreases.
[0014]
Furthermore, in conventional devices, the flow of measurement gas partially stagnates and stagnates in wastes with complicated shapes such as valves, and there is a part that does not directly touch the attached radioactive material. There is a possibility of causing shading (non-uniformity) and reducing measurement accuracy.
[0015]
The present invention has been made to solve the above-mentioned problems, is less susceptible to the background, can accurately measure the radioactivity concentration of TRU waste, and contributes to the reduction of disposal costs. An object of the present invention is to provide an α radioactivity identification device capable of
[0016]
[Means for Solving the Problems]
The measurement principle of α radioactivity is to measure the radioactivity concentration of waste by ionizing the measurement gas with radiation emitted from the radioactive waste and measuring this ionization current.
[0017]
The apparatus of the present invention has various functions (1) to (4) listed below as compared with the conventional apparatus in order to improve the measurement accuracy.
[0018]
(1) In the conventional device, the measurement gas is a once-through method, and the amount of gas discharged during measurement is large, which increases the burden on the exhaust treatment system of the facility. A circulation system is used to minimize the amount of exhaust gas.
[0019]
(2) In the conventional one-through type apparatus, the amount of measurement gas increases according to the size of the waste to be measured, so that the ionization chamber needs to be enlarged. In contrast, in the apparatus of the present invention, a part of the measurement gas is bypassed, and the ionization current in this bypass flow is measured, thereby avoiding an increase in the size of the ionization chamber. The miniaturization of the ionization chamber contributes to the reduction of the amount of lead shielding material used for shielding the ionization chamber and the weight of the apparatus.
[0020]
(3) It has been found that the humidity of the measurement gas affects the measurement accuracy, and performing humidity management is an important factor for stabilizing the measurement accuracy. In this device, a regenerative dryer is provided, and the humidity of the measurement gas is controlled to stabilize the measurement accuracy.
[0021]
(4) In the conventional apparatus, the flow of the measurement gas in the ionization chamber 2 into which the waste is introduced is a simple once-through method that flows from one side to the other side. However, for wastes with complicated shapes such as valves, the flow of the measurement gas is partially stagnated, or there is a part that does not directly touch the attached radioactive material, which can cause uneven ionization of the gas, degrading measurement accuracy. there is a possibility. On the other hand, in the apparatus of the present invention, the side surface (upper surface / rear surface) of the chamber is generated in order to generate a flow in which the waste material is blown from all directions so that it can be effectively measured corresponding to the waste having a complicated shape. A plurality of spray nozzles are installed on the bottom surface.
[0022]
An α radioactivity identification device according to the present invention is an α radioactivity identification device that measures α radioactivity radiated from radioactive waste, and an ionization chamber in which the radioactive waste to be measured is charged, and this A gas introduction part provided on the upstream side of the ionization chamber, a gas supply means for supplying a measurement gas into the ionization chamber via the gas introduction part, and a gas discharge part provided on the downstream side of the ionization chamber; A measurement gas exposed to α-rays radiated from radioactive waste in the ionization chamber is introduced through the gas discharge unit, and an ionization chamber that generates an ionization current from ion pairs and a gas generated in the ionization chamber An ionization current measuring unit that converts the ionization current generated into an electrical signal, and the gas discharge unit and the gas introduction unit both communicate with each other so that the measurement gas discharged from the gas discharge unit is returned to the gas introduction unit. In the measurement A gas circulation passage for circulating the scan in the ionization chamber, it includes a.
[0023]
Then, that having a first bypass passage merging into the gas circulation flow path after passing through the ionization chamber branched from the gas circulating passage. The ionization chamber can be reduced in size by covering most of the measurement gas through the circulation flow path and a part (very small amount) of the measurement gas flowing through the first bypass flow path. The amount of lead shielding is reduced, and the overall size and weight of the apparatus can be reduced.
[0024]
Furthermore, branches from the gas circulation flow path is removed and the second bypass passage back to the gas circulation flow path, the moisture from the measurement gas flowing through the second bypass passage on the downstream side of the ionization chamber Te that having a dryer to adjust the humidity of the measurement gas. The measurement accuracy is improved and the detection sensitivity is stabilized by adjusting the humidity of the measurement gas that circulates with a dryer. The dryer is preferably a regenerative type equipped with a heater that regenerates the hygroscopic material made of zeolite or the like.
[0025]
Furthermore, communication with the side periphery of the ionization chamber branched from the gas circulating flow path, that having a plurality of dispersion channels which blows from the various fields of the measurement gas to radioactive waste ionization chamber. When the measurement gas is introduced into the ionization chamber from all directions through the plurality of dispersion channels, the measurement gas is uniformly sprayed to every corner of each part (upper surface / rear surface / lower surface) of the complex shape TRU waste. Thus, it becomes possible to measure a complicated shape TRU waste such as a valve, which has been difficult to measure accurately, with high accuracy.
[0026]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. As shown in FIG. 1, the α radioactivity identification device 1 includes a loop-shaped gas circulation passage L2 and two bypass passages L3 and L4 (“first bypass passage”, “second passage” of the present invention). a bypass flow path "), and a circuit of three distributed passage L21 strains, L22, measurement gas consisting of L23 Prefecture.
[0027]
In the gas circulation flow path L2, an ionization chamber 2, a valve V1, a HEPA filter 5, a blower 6, a valve V5, a dew point meter (humidity meter) D1, a valve V7, and a flow meter F3 are provided in this order. The measurement gas is circulated and supplied to the ionization chamber 2 through the gas circulation flow path L2 by discharge.
[0028]
The measurement gas is a gas composed of a single substance or a mixture of air, helium He, and argon Ar gas having the property of ionizing when reacting with α rays, and gas is circulated from the gas supply source 8 shown in FIG. 2 through the flow path L1. After being introduced into the flow path L2 and circulated through the gas circulation flow path L2 for a predetermined period, it passes through the flow path L7 from the gas circulation flow path L2 through the factory building duct to the collective exhaust treatment device (not shown). It is supposed to be discharged. When the measurement gas is circulated in the gas circulation channel L2, both the valve V6 of the channel L1 and the valve V4 of the channel L7 are closed.
[0029]
The first bypass flow path L3 branches from the gas circulation flow path L2 between the outlet side of the ionization chamber 2 and the valve V1 and flows through the inside of the ionization chamber 3, and then the valve V1 and the HEPA filter 5 are connected to each other. In the meantime, it merges again with the gas circulation channel L2.
[0030]
An electrode is provided inside the ionization chamber 3. The electric signal collected at this electrode is input to the ionization current measuring device 4. The ionization current measuring device 4 converts the inputted electric signal into a pulse signal and counts it, and outputs the counting result to a data processing computer (not shown). Further, the data processing computer displays the counted number of pulses on a screen of a display device (not shown), and calculates α radioactivity based on the number of pulses. This calculation result is also displayed on the screen of the display device as necessary.
[0031]
As shown in FIGS. 3 and 4, the entire periphery of the box body 31 of the ionization chamber 3 is covered with a lead shield 32. The size of the ionization chamber body 31 is 86 mmφ in diameter × 110 mmH in height, and the thickness of the lead shield 32 is about 100 mm. The device 1 of the present invention is designed so that the total weight does not exceed 1 ton. For example, the total weight of one device is reduced to about 750 kg. Incidentally, the size of the ionization chamber 103 of the conventional apparatus shown in FIG. 5 is a diameter of 124 mmφ × a height of 151 mmH, and the total weight of the apparatus 100 is about 150 kg.
[0032]
The ionization chamber 2 includes a gas inlet portion 21, a chamber body 22, a gas outlet portion 23, an opening / closing window 24, a pressure gauge P1, and a thermometer T1. The chamber body 22 has a rectangular shape, and a gas inlet portion 21 and a gas outlet portion 23 are detachably attached to the chamber body 22 by a flange joint. The open / close window 24 is provided for easily taking in and out a small-size object to be measured in and out of the ionization chamber 2, and is movably supported on the side surface of the ionization chamber 2 by a hinge joint. When a large object to be measured is inserted into the ionization chamber 2, a large open / close window that opens the entire front surface of the chamber is used. The maximum size of the object to be measured in this apparatus is 350 mm × 450 mm.
[0033]
Three systems of distributed flow paths L21, L22, and L23 branched from the gas circulation flow path L2 communicate with the upper surface portion, the side surface portion, and the lower surface portion of the ionization chamber 2, respectively, toward the object to be measured in the ionization chamber 2. Measurement gas is sprayed from above, from the side and from below.
[0034]
The first dispersion flow path L21 is further branched into three via the valve V11 and the flow meter F5. Each branch passage communicates with the upper surface portion, the side surface portion, and the lower surface portion of the ionization chamber 2 via valves V12, V13, and V14.
[0035]
The second dispersion flow path L22 is further branched into three via the valve V15 and the flow meter F6. Each branch passage communicates with the upper surface portion, the side surface portion, and the lower surface portion of the ionization chamber 2 via valves V16, V17, and V18.
[0036]
The third dispersion flow path L23 is further branched into three via the valve V19 and the flow meter F7. Each branch passage communicates with the upper surface portion, the side surface portion, and the lower surface portion of the ionization chamber 2 via valves V20, V21, and V22.
[0037]
The second bypass flow path L4 branches off from the gas circulation flow path L2 on the downstream side of the blower 6, flows through the interior of the dryer 7 of the dryer unit 70, and then flows on the upstream side of the dew point meter D1. It merges again on the road L2. The dryer 7 is filled with an adsorbent 72, and a regenerative heater 71 is provided so as to penetrate the center of the filled adsorbent 72. The adsorbent 72 absorbed by the regeneration heater 71 is periodically heated and regenerated. A zeolite-based compound was used for the adsorbent 72 in this example.
[0038]
The second bypass flow path L4 further branches into two via the valve V9 and the flow meter F4. One branch passage communicates with the upper portion of the main body of the dryer 7 via a four-way valve V31. The other branch passage communicates with the upper end of the regeneration heater 71 of the dryer 7 via a four-way valve V32. The gas is introduced into the upper part of the main body of the dryer 7 and descends, the moisture is absorbed and removed by the adsorbent 72, rises through the hollow part of the central regenerative heater 71, and comes out of the dryer 7. Yes.
[0039]
The dew point meter (humidity meter) D1 detects moisture in the measurement gas flowing through the gas circulation passage L2, and sends a detection signal to the operation panel 41 (see FIG. 3) for display. When the measured value of humidity exceeds the reference value, the valve V5 is closed and the valve 9 is opened, and the hygroscopic gas is introduced into the dryer 7. The hygroscopic gas is continuously sent to the dryer 7 until the actual measurement value measured by the dew point meter D1 falls below the set reference value. Further, the dryer control panel 73 supplies power to the regeneration heater 71 from a power source (not shown) by a timer operation, and heats and regenerates the adsorbent 72 in the dryer 7. The flow path L9 is a line for exhausting the inside of the dryer 7 during the heat regeneration of the adsorbent.
[0040]
The flow meter F <b> 2 is provided between the HEPA filter 55 and the blower 6 and measures the flow rate of gas passing through the chamber 2.
[0041]
The flow path L5 joins the gas circulation flow path L2 between the flow meter F2 and the blower 6. When the valve V2 is opened, outside air is introduced into the gas circulation passage L2 through the passage L5 and functions to absorb pressure fluctuations in the system.
[0042]
The flow path L6 branches from the gas circulation flow path L2 on the downstream side of the blower 6, and joins the gas circulation flow path L2 immediately downstream of the flow path L5. When the valve V3 is opened, the gas circulation passage L2 is bypassed to the blower 6 through the passage L6, and the circulation flow rate of the gas circulation passage L2 is adjusted.
[0043]
The flow path L7 branches off from the gas circulation flow path L2 on the downstream side of the blower 6, and communicates with a collective exhaust treatment apparatus (not shown) in the factory. When the valve V4 is opened, the gas in the gas circulation flow path L2 is discharged to the collective exhaust treatment device through the flow path L7.
[0044]
The flow path L10 communicates with the gas circulation flow path L2 on the upstream side of the ionization chamber 2. When the valve V7 is closed and the valves V8 and V4 are opened, a one-through channel is formed through the channels L10 and L7.
[0045]
Next, a specific structure of the α radioactivity identification device 1 of the present embodiment will be described with reference to FIGS. 3 and 4.
[0046]
The entire α radioactivity identification device 1 is attached to the frames 11 and 15 and the post 14 as a skeleton. A plurality of wheels 13 are attached to the base frame 11 so that the apparatus 1 can be transported. A plurality of screw-type level adjusting members 12 are attached to the base frame 11 so that the horizontal level of the apparatus 1 can be finely adjusted. The overall size of the apparatus is approximately 2500 mm long × 1400 mm wide × 1745 mm high.
[0047]
The plurality of posts 14 rise from the base frame 11 and support the upper frame 15. The upper frame 15 is equipped with an ionization chamber 2, an ionization chamber 3, an ionization current measuring device 4, an operation panel 41 and various pipes and instruments.
[0048]
The operation panel 41 is for comprehensively controlling the entire apparatus 1 and includes a main power supply, a main switch, a plurality of sub switches, a switchboard, various display meters, and various display lamps.
[0049]
The dryer 7 has a vertically long cylindrical shape and is supported by a plurality of dedicated posts standing on the base frame 11. The dryer 7 is provided with a dedicated operation panel 73. A dryer operation panel 73 is used when the measurement gas is dehumidified or when the adsorbent 72 is regenerated and heated.
[0050]
Next, a case where α radioactivity radiated from TRU waste is measured using the above apparatus will be described.
[0051]
First, the open / close window 24 of the ionization chamber 2 or a large open / close window (the front of the chamber is opened / closed) is opened, and TRU waste as an object to be measured is inserted into the ionization chamber 2. When the opening / closing window 24 or the large opening / closing window (the front of the chamber is opened / closed) is closed, the inside of the ionization chamber 2 is kept airtight.
[0052]
An electrode is provided inside the ionization chamber 3. The electric signal collected at this electrode is input to the ionization current measuring device 4. The ionization current measuring device 4 converts the inputted electric signal into a pulse signal and counts it, and outputs the counting result to a data processing computer (not shown). Further, the data processing computer displays the counted number of pulses on a screen of a display device (not shown), and calculates α radioactivity based on the number of pulses. This calculation result is also displayed on the screen of the display device as necessary.
[0053]
According to the present embodiment, when the majority of the measurement gas is caused to flow in the circulation flow path and a part (very small amount) of the measurement gas is caused to flow in the bypass flow path, the ionization chamber can be reduced in size. The amount of lead shielding covering the ionization chamber is reduced, and the overall size and weight of the apparatus can be reduced.
[0054]
In addition, according to the present embodiment, the measurement accuracy is improved and the detection sensitivity is stabilized by adjusting the humidity of the measurement gas that circulates through the dryer.
[0055]
In addition, according to the present embodiment, when the measurement gas is introduced into the ionization chamber from a plurality of directions through the plurality of dispersion channels, it reaches every corner of each part (upper surface / rear surface / lower surface) of the complex shape TRU waste. The measurement gas is sprayed evenly, and it becomes possible to measure a complicated shape TRU waste such as a valve, which has conventionally been difficult to measure accurately, with high accuracy.
[0056]
【The invention's effect】
As described above in detail, according to the present invention, the measurement gas supply path to the ionization chamber is changed from the conventional one-through method to the circulation method, thereby making it less susceptible to the influence of the background and enabling highly accurate measurement. Become.
[0057]
In addition, according to the present invention, since the ionization chamber is smaller than the conventional product, the amount of shielding material used can be greatly reduced.
[0058]
Furthermore, according to the present invention, the moisture in the measurement gas is managed with high accuracy, so that the measurement accuracy is stabilized.
[0059]
Furthermore, according to the present invention, the measurement gas is introduced into the chamber from all directions on the side peripheral surface of the ionization chamber 2 through the plurality of branch channels, and the measurement gas is uniformly applied to the waste having a complicated shape. Since it is sprayed, the measurement accuracy of wastes with complex shapes is dramatically improved compared to the conventional case.
[Brief description of the drawings]
FIG. 1 is a schematic system diagram showing an α radioactivity identification device according to an embodiment of the present invention.
FIG. 2 is a detailed system diagram showing an α radioactivity identification device according to an embodiment of the present invention.
FIG. 3 is a front external view showing an α radioactivity identification device according to an embodiment of the present invention.
4 is a side external view showing the device as viewed from the direction of arrows IV-IV in FIG. 3;
FIG. 5 is a schematic system diagram showing a conventional apparatus.
[Explanation of symbols]
1 ... α radioactivity identification device,
2 ... Ionization chamber 2,
21 ... Gas inlet, 22 ... Chamber body, 23 ... Gas outlet, 24 ... Opening / closing window,
3 ... Ionization chamber,
31 ... Box body, 32 ... Lead shield,
4 ... Ionization current measuring instrument,
41 ... Control panel,
5 ... HEPA filter,
6 ... Blower,
7 ... Dryer,
70 ... dryer unit,
71 ... Regenerative heater, 72 ... Adsorbent,
73 ... dryer control panel,
8 ... Gas supply source,
11 ... Base frame,
14 ... Post,
15 ... Upper frame,
12 ... Level adjustment member,
13 ... wheels,
L2: Gas circulation channel,
L3, L4 ... Bypass flow path,
L21, L22, L23 ... dispersion flow path,
P1 ... Pressure gauge,
T1 ... thermometer,
D1 ... dew point meter (hygrometer),
F1-F7 ... flow meter,
V1-V32 ... Valve.

Claims (1)

An α radioactivity identification device for measuring α radioactivity radiated from radioactive waste, an ionization chamber in which the radioactive waste to be measured is charged, and gas introduction provided upstream of the ionization chamber A gas supply means for supplying a measurement gas into the ionization chamber via the gas introduction section, a gas discharge section provided downstream of the ionization chamber, and radiation from radioactive waste in the ionization chamber An ionization chamber that introduces an ionization current from an ion pair, and an ionization current that converts the ionization current generated in the ionization chamber into an electrical signal The measurement gas communicates with both the gas discharge unit and the gas introduction unit, and the measurement gas is circulated through the ionization chamber so that the measurement gas discharged from the gas discharge unit is returned to the gas introduction unit. A gas circulation flow path, as well as anda first bypass passage merging into the gas circulation flow path after passing through the ionization chamber branched from the gas circulating flow path, downstream of the ionization chamber A second bypass flow path that branches off from the gas circulation flow path and returns to the gas circulation flow path, and a humidity of the measurement gas by removing moisture from the measurement gas flowing through the second bypass flow path And a plurality of dispersion flow paths that branch from the gas circulation flow path and communicate with the side periphery of the ionization chamber, and spray measurement gas from various directions against the radioactive waste in the ionization chamber. α radioactivity identification equipment characterized by having a.

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