JP4759755B2 - Device for measuring solid uranium in equipment - Google Patents

Description

  The present invention relates to a small measuring apparatus that can easily measure the amount of solid uranium present in a device such as a centrifuge from the outside.

  In a uranium enrichment facility using gas centrifugation, a large number of centrifuges are arranged at narrow intervals and interconnected by pipes to form a cascade. In such facilities, if you can monitor the amount and amount of solid uranium present in each centrifuge as the centrifuges operate, it will be useful information in terms of system safety and operational efficiency. Will be obtained. However, the amount of solid uranium present in this type of centrifuge is generally quite small, and there is almost no extra space around the centrifuge for installing a large sensitive detector.

By the way, for gamma ray measurement for the purpose of nuclide identification and dosimetry under the condition of extremely low dose and existence of multiple nuclides, a conventional Ge crystal detector with high energy resolution and high counting efficiency is used. A semiconductor detector as a base material is used. However, since a detector using a Ge crystal needs to be measured while cooling the Ge crystal by liquid nitrogen or electrical means, the Ge crystal must be coupled to a cooling device at the time of measurement. The necessity of cooling the Ge detector and the cooling facility using liquid nitrogen are described in Patent Document 1, for example. As described above, the γ-ray detection device is increased in size due to the attached cooling mechanism, and the installation space of the detection device may not be secured at the measurement site. In particular, in a uranium enrichment facility using a gas centrifuge, a large number of centrifuges are arranged at narrow intervals and interconnected by piping, etc., so if the γ-ray detector is large, the installation space can be secured. There was a problem that could not be done.
JP-A-11-153672

  The problem to be solved by the present invention is to identify and detect the dose of uranium 235 present in a device such as a centrifuge under the condition that a plurality of nuclides exist at an extremely low dose even if the detector installation space is narrow. It is to make it easy to measure from outside.

  The present invention comprises a γ-ray detector installed in the vicinity of a device under test, a cable for transmitting the detection signal, and a signal processing device for analyzing and calculating the transmitted detection signal, A line detector is made by laminating a plurality of thin plate-shaped detector base materials made of compound semiconductor sandwiched between electrodes to form a detection element for one system, and a plurality of detection elements are juxtaposed to form a plurality of detection elements. In addition, a preamplifier is installed for each system of the detection elements and a detection signal is output independently, and the signal processing device includes a main amplifier that amplifies the detection signal for each system independently, and each main amplifier A pulse height analysis unit for measuring the γ-rays caused by uranium 235 by independently performing pulse height analysis processing on each of the pulse signals amplified in step 1, an addition processing unit for adding the respective measurement results and converting the signal intensity into a uranium amount, Display the result A solid uranium measuring device in the device, characterized in that it consists of a radical 113.

  Here, the γ-ray detector is formed by stacking 3 to 7 thin plate-like detector base materials made of CdTe sandwiched between a Pt electrode and an In electrode to form a detection element for one system. The detection elements of the number of systems corresponding to the number of juxtapositions are formed side by side, and the detector base material overlapping surface of the detection elements is incorporated in the detector housing together with the preamplifier so that the γ-ray flying direction is parallel. If the number of detection elements is too large, the apparatus becomes complicated and the cost is increased. Therefore, the number is preferably about 3 to 4. A structure in which an electromagnetic shield is provided between the preamplifiers is preferable. Note that the wave height analysis unit obtains the measured values of the 185.7 keV central channel and its upper and lower channels in order to remove the background corresponding to 185.7 keV gamma rays caused by uranium 235. It is.

  The device to be measured by the measuring apparatus according to the present invention is typically a centrifuge in a gas uranium enrichment facility, but solid uranium may be accumulated or accumulated in other nuclear facilities. There are also equipment and piping.

  The gamma ray detector used in the present invention uses a compound semiconductor having a large band gap, a high density and a high atomic number as a detector base material, and the detector base material between the electrodes is made into a thin plate shape, so that it is measured at room temperature. Since it is possible, a cooling device is unnecessary, and both downsizing and high energy resolution can be achieved. In addition, by stacking a plurality of thin detector base materials through the electrodes, the γ-ray incident area is increased, and electrons and holes generated by reaction with γ-rays reach the electrodes at a high rate. Therefore, high energy resolution can be maintained. Furthermore, the present invention has a structure in which a plurality of detector elements in which a plurality of detector base materials are stacked are juxtaposed to form a plurality of detection elements, and a preamplifier is installed for each system to output detection signals independently. Capacitance can be limited to suppress the noise level, and a sufficiently large γ-ray incident area can be obtained.

  In addition, since the detection signals for each system are independently amplified and subjected to the pulse height analysis process, the respective pulse height analysis processing results are added, so that the S / N is also improved. Since the wave height processing unit does not measure the entire spectrum but specializes in the measurement of γ rays caused by uranium 235, the circuit configuration is simplified and can be manufactured at low cost.

  As a result, the solid uranium measuring device in the apparatus according to the present invention can reduce the size of the γ-ray detector, so that γ-ray measurement can be performed in a narrow measurement site that cannot be measured by a conventional large Ge detector. It becomes possible to identify and measure the dose of uranium 235 even under conditions in which multiple nuclides are present at extremely low doses such as solid uranium present in a centrifuge at a uranium enrichment facility using the centrifuge method.

  In addition, since the γ-ray detector is small, it is possible to move the γ-ray detector with respect to the device under test or to change the measurement direction, and it is also possible to measure a plurality of arrays, It can also be used for visualization of γ-ray sources.

  FIG. 1 is a block diagram showing an embodiment of a solid uranium measuring apparatus in an apparatus according to the present invention. This measuring apparatus is installed in the vicinity of the device under test (for example, in the case of a centrifuge, it is preferable to install the gamma ray detector 10 on the diagonally upper side of the end plate toward the centrifuge) and its It comprises an optical cable 12 that transmits a detection signal by optical communication, and a signal processing device 14 that analyzes and computes the transmitted detection signal.

  The detail of the principal part of a gamma ray detector is shown in FIG. A is a detection element, and B represents a cross section of the detection element. Five detector base materials 24 made of CdTe sandwiched between the Pt electrode 20 and the In electrode 22 are laminated to form a detection element 26 for one system. Four such detection elements 26 are juxtaposed to form four detection elements 28. This detection element 28 is incorporated in the detector housing together with the preamplifier so that the detector base material overlapping surface is parallel to the γ-ray flying direction.

  Here, each of the thin plate-shaped detector base materials has a size of 10 mm × 10 mm × 0.5 mm (thickness), and a stack of five of them becomes one line, and 10 mm is obtained by juxtaposing four lines. The effective volume is × 10 mm × 10 mm. Considering the absorption length (absorption ratio of γ rays with respect to the length of the detector base material), the detection element size (depth size) in the γ ray incident direction is set to about 10 mm, resulting in 185. By making the absorption ratio of 7 keV γ rays 90% or more and reducing the thickness of the detector base material (typically about 0.5 mm), it reacts with γ rays in the detector base material. The generated electrons and holes reach the electrode at a high rate, and thereby, high energy resolution can be obtained, and appropriate counting efficiency can be obtained. In addition, by stacking and juxtaposing detector base materials, a sufficiently large γ-ray incident area of about 10 mm × 10 mm is secured to improve sensitivity.

  Furthermore, by using a compound semiconductor with a large band gap as the detector base material, measurement at room temperature is possible (no cooling device is required), and the total length of the detector housing is reduced to about 15 cm with a built-in preamplifier. Since it can be reduced in size, it can be installed around a centrifuge, which is a device to be measured.

The outputs of the detection elements 26 of each system are individually input to the corresponding preamplifiers 30 to perform signal amplification, S / N improvement, impedance matching, and the like. In order to suppress signal attenuation and S / N degradation at the detection element, the preamplifier 30 is disposed in the immediate vicinity of the detection element 26, and they are housed in the detector housing. In the present invention, a semiconductor is used as a detector base material. In the semiconductor detector, since the capacitance of the detection element varies depending on the applied voltage, a charge-sensitive preamplifier (charge Sensitive amplifier). With such a configuration, each preamplifier outputs a detection signal independently for each corresponding system. By configuring the detection signals to be output independently for each corresponding system, the number of detector base materials stacked in each detection element is made appropriate to limit the capacitance and suppress the noise level.
In order to prevent crosstalk between systems, an electromagnetic shield 31 is provided between the preamplifiers 30.

  As described above, signal transmission between the γ-ray detector 10 and the signal processing device 14 is performed by optical communication using the optical fiber cable 12 in order to suppress electromagnetic disturbance.

  The signal processing apparatus 14 includes a main amplifier 32 that independently amplifies the detection signal for each system, and a pulse height that is obtained by independently analyzing the pulse signal amplified by each main amplifier and measuring γ-rays caused by uranium 235. It comprises an analysis unit 34, an addition processing unit 36 for adding the respective measurement results to convert the signal intensity into a uranium amount, and a display unit 38 for displaying the results.

  Each main amplifier 32 individually performs pulse processing on the preamplifier output for each system. Specifically, processing such as pulse wave height amplification and S / N improvement is performed, and a linear amplifier (spectroscopy amplifier) having excellent linearity is used. The pulse signal amplified by each main amplifier 32 is subjected to a pulse height analysis process independently by the corresponding pulse height analysis unit 34. The pulse height analysis unit 34 converts the peak value (analog amount) of the pulse signal from the main amplifier 32 into a digital amount (ch unit) at high speed by an ADC (analog-digital converter). Here, the wave height analysis unit 34 obtains a count value corresponding to 185.7 keV γ-rays caused by uranium 235, and the data of the lower channel and upper channel with respect to the central channel of 185.7 keV. The count value is accumulated in the memory. The count values of the lower channel and the upper channel are used for background calculation and the like. Thus, the device of the present invention only needs to have a measurement function for only solid uranium, and it is not necessary to measure the spectrum. Therefore, the signal processing apparatus can be greatly simplified.

  The addition processing unit 36 finally adds the accumulated count values in the four channels of the three channels (the center channel of 185.7 keV, its lower channel and the upper channel). As a result, the signal intensity of the 185.7 keV gamma rays resulting from uranium 235 is obtained by removing the background. Since the signal intensity obtained in this way has a correlation (linearity in a log-log graph) with the amount of uranium, it is converted to the amount of uranium using that and the uranium amount is displayed on the display unit 38. . The signal intensity may be calibrated separately using a high sensitivity Ge detector or the like.

  In order to confirm the effectiveness of the γ-ray detector (for one system) used in the present invention, the results (energy spectrum: pulse wave height distribution) of the amount of uranium source in the centrifuge are shown in FIG. The measurement target nuclide is uranium 235, and the energy of the γ-ray is 185.7 keV. Here, in order to show the effectiveness as a gamma ray detector, the measured spectrum is shown. A is when the amount of uranium in the centrifuge is small, and B is when the amount of uranium in the centrifuge is large. From FIG. 3, a signal of 185.7 keV, which is a gamma ray of uranium 235, is obtained (gamma ray of uranium 235 can be measured by being distinguished from the background), and an intensity corresponding to the amount of solid uranium contained in the device is obtained. It was confirmed that

  FIG. 4 is a graph showing the correlation between the amount of natural uranium and the signal intensity. When plotted in a log-log graph, the amount of uranium and the signal intensity are linear. The present invention utilizes this correlation, thereby obtaining the amount of uranium from the signal intensity.

  As described above, the measurement of solid uranium existing in the centrifuge has been described as an example. However, it goes without saying that the present invention can be used for measuring the amount of solid uranium contained in equipment and piping in a nuclear facility. . In addition, since the detector can be reduced in size, it is possible to visualize the distribution state of solid uranium by arranging and measuring a plurality of detectors or moving and measuring.

The block diagram which shows one Example of the solid uranium measuring device in the apparatus which concerns on this invention. The detail drawing of the principal part of the gamma ray detector. Explanatory drawing which shows the example of the spectrum acquired with the gamma ray detector. Explanatory drawing which shows the correlation with signal strength and the amount of natural uranium.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 γ-ray detector 12 Optical fiber 14 Signal processing apparatus 20 Pt electrode 22 In electrode 24 Detector base material 26 Detection element 28 Detection element 30 Preamplifier 32 Main amplifier 34 Wave height analysis part 36 Addition processing part 38 Display part

Claims (4)

A γ-ray detector installed in the vicinity of the device under measurement, a cable for transmitting the detection signal, and a signal processing device for analyzing and calculating the transmitted detection signal;
The γ-ray detector is formed by stacking a plurality of thin plate-like detector base materials made of a compound semiconductor sandwiched between electrodes to form a detection element for one system, and a plurality of detection elements are juxtaposed to form a plurality of detection elements Is formed, and a preamplifier is installed for each system of the detection elements to independently output a detection signal, the signal processing device includes a main amplifier that independently amplifies the detection signal for each system, and each A pulse height analysis unit for measuring the γ-rays caused by uranium 235 by independently performing pulse height analysis processing on the pulse signals amplified by the main amplifier, and an addition processing unit for adding the respective measurement results to convert the signal intensity into a uranium amount And a display unit for displaying the result, a solid uranium measuring device in equipment.   The γ-ray detector is composed of 3 to 7 thin plate-like detector base materials made of CdTe sandwiched between Pt electrodes and In electrodes to form a detection element for one system, and 2 to 6 detection elements are juxtaposed. The number of detection elements corresponding to the number of juxtaposed elements is formed, and the detector base material overlapping surface of the detection elements is incorporated in the detector housing together with the preamplifier so that the detector base material overlapping surface is parallel to the γ-ray flying direction. The apparatus for measuring solid uranium in an apparatus according to claim 1, wherein an electromagnetic shield is provided therebetween.   The wave height analysis unit obtains the measurement values of the central channel of 185.7 keV and its upper and lower channels in order to deal with 185.7 keV gamma rays caused by uranium 235 and to remove the background. The apparatus for measuring solid uranium in an apparatus according to claim 1 or 2.   4. The apparatus for measuring solid uranium in an instrument according to claim 3, wherein the device to be measured is a centrifuge in a uranium enrichment facility using gas centrifugation.

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