KR20240077036A - Muon tomography system using muon detector based on plastic scintillator and wavelength shifting fiber for monitoring of spent fuel - Google Patents

Abstract

The present invention relates to a muon tomography system using a muon detector based on a plastic scintillator and wavelength shift fiber used for detection of unidentified nuclear materials, monitoring of spent nuclear fuel, monitoring of nuclear waste storage facilities, and container monitoring in airport bays, A plastic scintillator that converts muon charged particles into a flash signal and transmits the converted flash signal, a wavelength shift fiber that focuses the converted flash signal received from the plastic scintillator and transmits the focused flash signal, and the above A muon detector including a plurality of optical sensors each converting the absorbed scintillation signal transmitted from the wavelength shift fiber into an electric signal; an analog signal processing and acquisition unit that amplifies the output signals of the plurality of optical sensors and adjusts signal rise time, fall time, signal width, and offset voltage; Obtain signal response position, signal size, and signal measurement time information from the output signal of the analog signal processing and acquisition unit, and compare the signal measurement time for the charged particle acquired within a specific time to pass through the muon detector to determine whether the charged particle passed at the same time. A digital signal processing and acquisition unit that measures the simultaneous coefficient of counting signals; and a detection position determination algorithm unit that receives the output signal of the digital signal processing and acquisition unit and determines the X-axis detection position and Y-axis detection position of the muon, and detects the Based on the position and Y-axis detection position, the muon detector simultaneously determines the X-axis detection position and Y-axis detection position of the muon.

Description

Muon tomography system using a muon detector based on a plastic scintillator and a wavelength shift fiber {MUON TOMOGRAPHY SYSTEM USING MUON DETECTOR BASED ON PLASTIC SCINTILLATOR AND WAVELENGTH SHIFTING FIBER FOR MONITORING OF SPENT FUEL}

The present invention relates to a muon tomography system, and more specifically, to a plastic scintillator and wavelength-shifting fiber-based system used for detection of unidentified nuclear materials, monitoring of spent nuclear fuel, monitoring of nuclear waste storage facilities, and container monitoring in airport bays. This relates to a muon tomography system using a muon detector.

Recently, the use of radioactive materials is increasing in various fields. In this environment, risks such as theft, loss, and seizure of radioactive materials also increase. Among these, as the possibility of radioactive materials being misused in ways such as nuclear terrorism is emerging, the need to monitor radioactive materials is increasing.

For this reason, it is important to prevent the theft and illegal transfer of spent nuclear fuel, nuclear waste, and unidentified nuclear materials in advance. Therefore, it is necessary to develop a detection system that can detect the inside of the shield storing nuclear materials for the purpose of detecting unidentified nuclear materials, monitoring spent nuclear fuel, monitoring nuclear waste storage facilities, and monitoring containers in airport bays.

For this purpose, various X-ray, gamma-ray, and neutron counting-based technologies were used. These technologies have problems that make them difficult to apply in actual use due to limitations such as low detection efficiency and user exposure.

Research is being conducted worldwide on how to utilize a tomography system using muons to compensate for the above-mentioned limitations. These muons are created when protons or charged particles flying from space interact with the atmosphere, and have the characteristic of multiple Coulomb scattering while interacting with materials. A tomography system using muons has the advantage of being able to penetrate materials such as concrete and iron due to its good penetrating power due to the high energy of muons. Additionally, since the scattering angle increases when reacting with a material with a high atomic number (Z), it is possible to determine the atomic number (Z) of the material by calculating the scattering angle. Additionally, it has the advantage of using muons, a type of natural radiation, so there is no problem with user exposure.

Muon detection technologies currently used to construct spent nuclear fuel monitoring systems include gas-drift tubes and gas electron multiplier detectors.

However, gas muon detectors have the advantage of high spatial resolution and fast response time, but have the problem of low detection efficiency due to the use of gas-based muon detectors. In addition, there is a problem that the muon detector must be manufactured in a double structure because the part that detects the X-axis position and the part that detects the Y-axis position must be separately configured to determine the two-dimensional detection position of the measured muon.

In addition, the gas electron-amplified muon detector has the advantage of high spatial resolution, fast response time, and the ability to simultaneously determine the detection location of the muon on the X and Y axes with a single-structure muon detector. There is a problem that causes an increase in detection time due to low detection efficiency.

Therefore, the purpose of the present invention was to solve the above problems, and to provide a muon tomography system using a muon detector based on a plastic scintillator and a wavelength shift fiber for monitoring materials with high atomic numbers such as uranium and plutonium. This is what I want to do.

The muon tomography system using a muon detector based on a plastic scintillator and a wavelength shift fiber according to the present invention includes a plastic scintillator that converts charged particles of muons into a scintillation signal and transmits the converted scintillation signal, and the above received from the plastic scintillator. A muon detector including a wavelength shift fiber that focuses the converted scintillation signal and transmits the focused scintillation signal, and a plurality of optical sensors that each convert the absorbed scintillation signal transmitted from the wavelength shift fiber into an electrical signal; an analog signal processing and acquisition unit that amplifies the output signals of the plurality of optical sensors and adjusts signal rise time, fall time, signal width, and offset voltage; Obtain signal response position, signal size, and signal measurement time information from the output signal of the analog signal processing and acquisition unit, and compare the signal measurement time for the charged particle acquired within a specific time to pass through the muon detector to determine whether the charged particle passed at the same time. A digital signal processing and acquisition unit that measures the simultaneous coefficient of counting signals; and a detection position determination algorithm unit that receives the output signal of the digital signal processing and acquisition unit and determines the X-axis detection position and Y-axis detection position of the muon, and detects the Based on the position and Y-axis detection position, the X-axis detection position and Y-axis detection position of the muon charged particle are simultaneously determined.

In addition, the muon tomography system using a plastic scintillator and a muon detector based on a wavelength shift fiber according to the present invention includes a plastic scintillator that converts charged particles of muons into a scintillation signal and transmits the converted scintillation signal, and a plastic scintillator that transmits the converted scintillation signal from the plastic scintillator. A muon detector including a wavelength shift fiber that focuses the received converted scintillation signal and transmits the focused scintillation signal, and a plurality of optical sensors that each convert the absorbed scintillation signal transmitted from the wavelength shift fiber into an electrical signal. ; a spent nuclear fuel assembly fully loaded with spent nuclear fuel rods disposed between the muon detectors; an analog signal processing and acquisition unit that amplifies the output signals of the plurality of optical sensors and adjusts signal rise time, fall time, signal width, and offset voltage; Obtain signal response position, signal size, and signal measurement time information from the output signal of the analog signal processing and acquisition unit, and compare the signal measurement time for the charged particle acquired within a specific time to pass through the muon detector to determine whether the charged particle passed at the same time. A digital signal processing and acquisition unit that measures the simultaneous coefficient of counting signals; And a detection position determination algorithm unit that receives the output signal of the digital signal processing and acquisition unit and simultaneously determines the X-axis detection position and Y-axis detection position of the charged particle of the muon, wherein the detection position determination algorithm unit determines Based on the X-axis detection position and Y-axis detection position of the muon charged particle, the position of the spent nuclear fuel discharged from the spent nuclear fuel assembly is determined.

As described above, the muon tomography system using a muon detector based on a plastic scintillator and a wavelength shift fiber according to the present invention can simultaneously acquire the X and Y axis positions through a single muon detector composed of a single structure by design, It has the advantage of relatively low manufacturing costs.

Additionally, since a plastic scintillator with sufficient density for muon measurement is used, there is an advantage in that it can provide detection efficiency and short detection time.

In addition, because it uses a single muon detector composed of a single structure in design and a relatively inexpensive plastic scintillator, it has the advantage of being advantageous in constructing a large-area muon detector.

Figure 1 is a diagram schematically showing multiple Coulomb scattering of a typical muon.
Figure 2 is a diagram showing an example of an image restored using a typical PoCA algorithm.
Figure 3 is a diagram schematically showing a typical muon tomography system.
Figure 4 is a schematic block diagram of a muon tomography system using a muon detector based on a plastic scintillator and a wavelength shift fiber according to the present invention.
Figure 5 is a diagram schematically showing the implementation of a muon tomography system using a muon detector based on a plastic scintillator and a wavelength shift fiber according to the present invention.
Figure 6 is a diagram showing a spent nuclear fuel assembly simulated using a muon tomography system using a muon detector based on a plastic scintillator and a wavelength shift fiber according to the present invention.
7A-7C are diagrams illustrating simulated line profiles of a fully loaded spent nuclear fuel assembly.
8A to 8C are diagrams illustrating simulated line profiles of spent fuel assemblies with the second and fourth rows discharged.

Hereinafter, a muon tomography system using a muon detector based on a plastic scintillator and a wavelength shift fiber according to the present invention will be described in more detail through a detailed description of embodiments with reference to the drawings. In describing the present invention, if it is determined that a detailed description of related known technology or configuration may unnecessarily obscure the gist of the present invention, the detailed description will be omitted. In addition, the terms described below are terms defined in consideration of functions in the present invention, and may vary depending on the intention or custom of the client, operator, or user. Therefore, the definition should be made based on the contents throughout this specification.

Like reference numbers refer to like elements throughout the drawings.

Figure 1 is a diagram schematically showing multiple Coulomb scattering of a typical muon, Figure 2 is a diagram schematically showing an example of an image restored using a typical PoCA algorithm, and Figure 3 is a schematic diagram showing a typical image. It is a schematic diagram, Figure 4 is a schematic block diagram of according to the present invention, and Figure 5 is a schematic illustration of the implementation of a muon tomography system using a muon detector based on a plastic scintillator and wavelength shift fiber according to the present invention. Figure 6 is a diagram for spent nuclear fuel monitoring showing a spent nuclear fuel assembly simulated using a muon tomography system using a muon detector based on a plastic scintillator and a wavelength shift fiber according to the present invention, Figure 7a Figures 7c are diagrams showing simulated line profiles of fully loaded spent fuel assemblies, and Figures 8a - 8c are diagrams showing simulated line profiles of spent fuel assemblies with the second and fourth rows discharged. It is also a city.

Principles of muon tomography

Primary particles (mainly high-energy protons and heavy atomic nuclei), which are high-energy particles in the solar system, interact with the Earth's upper atmosphere to generate pions, and charged pions decay into charged muons.

The muon created in this way has a mass of 105.7 MeV/c2, which is 200 times heavier than the electron, and the charge ratio of positive to negative flux is about 1.3.

In addition, muons are highly penetrative particles with an average energy of 3 to 4 GeV at a flow rate of 1/cm2/min at sea level, so they are affected by the Coulomb force when muons pass through materials. When muons pass through atoms of materials. By attacking electrons, electrons can be removed from molecular orbitals, which is called ionization.

Hereinafter, we will look at the multiple Coulomb scattering of typical muons with reference to FIG. 1.

As shown in Figure 1, muons interact with the atomic nuclei of the material, resulting in many small angular deviations and losing energy through electromagnetic interactions, which causes multiple Coulomb scattering. In other words, muons interact with the nuclear charges of the material they pass through, causing multiple Coulomb scattering.

This multiple Coulomb scattering results in a scattering angle distribution between the incoming and outgoing trajectories of the muon, and the resulting scattering angle distribution can be expressed as Equation 1 below.

here and the velocity and momentum of the incoming muon, l/X ₀ is the thickness of the material expressed in terms of radiation length.

In general, high-energy charged particles lose energy in matter by bremsstrahlung, and high-energy photons are lost by pair creation, so the probability that bremsstrahlung and pair creation occur is expressed in the radial length. is defined by Equation 2 below.

Here, A is the atomic mass of the substance, ρ is the density of the substance, and Z is the atomic number of the substance.

Typically, the radiation length decreases as the atomic number of the material increases, so the scattering angle is proportional to the atomic number. Therefore, materials with higher atomic numbers cause more deflections in the trajectory.

Table 1 below shows the radial lengths of various materials.

matter Z# Radiation length (cm) water 36.08 polyethylene 47.9 shielding concrete 10.7 aluminum 13 8.9 steel 26 1.76 copper 29 1.43 tungsten 74 0.35 lead 82 0.56 uranium 92 0.32

Muon tomography

Muon tomography uses the scattering angle due to multiple Coulomb scattering of muons, which is proportional to the atomic number (Z) of the material. Muon tomography is very useful for detecting high-Z material, a process known as Z-discrimination, because the trajectory of the muon can be traced, the degree of deflection can be calculated, and then the material can be identified.

Reconstruction algorithm for muon tomography

Muon tomography determines the target location by the intersection point of the incoming and outgoing muon trajectories, and determines the atomic number of the material by the difference in degree between the trajectories.

Muons undergo a lot of small-angle scattering as they pass through matter, making it difficult to calculate the specific locations where muons interact. To solve this, the Point-of-Closest-Approach (PoCA) algorithm is used, which calculates the closest point of the skew line of two muon trajectories.

The PoCA algorithm approximates the nearest position obtained by least squares fitting of the interactions in the muon detector and calculates the scattering angle between the two mounted tracks. The shortest line between tracks is calculated by finding the closest pair of points between the two lines, and the midpoint of the line is taken as the scattering point of the muon.

Hereinafter, with reference to FIG. 2, we will look at an example of an image restored using a typical PoCA algorithm.

In an example of an image restored using a conventional PoCA algorithm as shown in Figure 2, the data points represent the positions where muons were scattered by interacting with the target. This position is estimated using the PoCA algorithm, the color of the point represents the calculated scattering angle, and the color bar on the right represents the distribution of scattering angles.

High-angle points are reconstructed from high-Z target materials such as Pb (lead) and U (uranium), and most muons that pass through the uranium target are scattered at 4 to 7°.

Muon tomography system modeling

Muon tomography system modeling was performed using GEANT4.

Hereinafter, we will look at a typical muon tomography system with reference to FIG. 3.

As shown in Figure 3, a typical muon tomography system requires at least four two-dimensional position-sensitive muon detectors. Two detectors on top of the material and two detectors on the bottom of the material measure the incoming and outgoing trajectories of the muon, respectively, so the scattering angle and interaction position of the muon can be calculated. However, in general dry storage container monitoring, the muon detector cannot be installed under the container.

Now, with reference to FIG. 4, we will look at the configuration of a muon tomography system using a muon detector based on a plastic scintillator and a wavelength shift fiber according to the present invention.

As shown in Figure 4, the muon tomography system using a muon detector based on a plastic scintillator and a wavelength shift fiber according to the present invention includes a muon detector 100, an analog signal processing and acquisition unit 200, and a digital signal processing and acquisition. It consists of a unit 300 and a detection position determination algorithm unit 400 for determining the detection position.

Here, the muon detector 100 includes a plastic scintillator (110) that converts the charged particles of the muon into scintillation signals (i.e. photons) when the charged particles of the muon pass through, and focuses the converted scintillation signal. A plurality of silicon photomultipliers (hereinafter collectively referred to as “SiPM”) are transmitted from the wavelength shifting fiber (WLS fiber, 130) transmitted to the optical sensor 150, and the wavelength shifting fiber 130. It consists of a SiPM optical sensor 150 that converts the flash signal into an electrical signal, and transmits the SiPM optical sensor output signal output from the SiPM optical sensor 150 to the analog signal processing and acquisition unit 200.

In addition, the analog signal processing and acquisition unit 200 amplifies the SiPM optical sensor output signal received from the SiPM optical sensor 150, adjusts the signal rise time, fall time, signal width, offset voltage, etc., and adjusts the adjusted signal. is transmitted to the digital signal processing and acquisition unit 300.

In addition, the digital signal processing and acquisition unit 300 processes the adjusted signal received from the analog signal processing and acquisition unit 200 through ADC, TDC, FPGA (Field-Programmable Gate Array), or ASICs (Application Specific Integrated Circuits). Through this, information on the signal reaction position, signal size, and signal measurement time is acquired, and the signal measurement time for the charged muon particles obtained within a specific time to pass through the muon detector 100 is compared to measure the simultaneous coefficient. Here, the simultaneous coefficient is a coefficient calculated by comparing the signal measurement time for the charged particle to pass through the muon detector and counting the signals that passed simultaneously.

In addition, the detection position determination algorithm unit 400 receives the digitized output signal from the digital signal processing and acquisition unit 300 into a computer and determines the X-axis detection position and Y-axis detection position of the muon. The detection position determination algorithm unit 400 uses signal measurement time information among the output signals of the SiPM optical sensor 150 to confirm through simultaneous coefficient discrimination that the output signal is generated by a single muon particle, and signal size information among the output signals. It removes noise by comparing the sum of the signal sizes of simultaneously generated output signals with the threshold value, and applies the X-axis detection position algorithm using the signal response position and signal size information among the output signals. By applying the Y-axis detection position algorithm using the signal response position and signal size information, the muon detection position (X, Y) is determined.

Meanwhile, the X-axis detection position algorithm is a method of obtaining the X-axis position by analyzing the output signal distribution between adjacent wavelength shift fibers 130 using Anger logic. In other words ^, _the The signals measured in (150) are respectively defined as SiPM _b ⁿ , and the total signal measured at the Nth wavelength shift fiber, which is the sum of the signals, is defined as SiPM _total ⁿ . SiPM _total ⁿ , which is the sum of the Nth wavelength shift fiber signals, and Anger logic are used to determine the X-axis position as shown in the formula below.

Here, X is the muon interaction in the X direction, and w is the weighting factor.

On the other hand, the Y-axis detection position algorithm calculates the signal size ratio between the two SiPM optical sensors 150 attached to one wavelength shift fiber 130 to obtain the Y-axis position. ^In the same way _as the The signals measured in (150) are respectively defined as SiPM _b ⁿ . The ratio of signals measured at the Nth wavelength shift fiber 130 is calculated and the Y-axis position is determined using the formula below.

Here Y is the muon interaction in the Y direction.

This algorithm can simultaneously acquire the Therefore, the number of channels required is reduced. Therefore, the analog signal processing and acquisition unit 200 and the digital signal processing and acquisition unit 300 can be simplified to reduce development costs.

The muon tomography system using a muon detector based on a plastic scintillator and a wavelength shift fiber according to the present invention can simultaneously acquire the Because it uses (110), it is advantageous for constructing a large-area muon detector. In addition, the plastic scintillator 110 has a sufficient density for muon measurement and has the advantage of relatively high detection efficiency.

In contrast, the conventional muon detector structure attempted to simultaneously acquire the X and Y axis positions through a single muon detector by arranging wavelength shift fibers above and below a plastic scintillator. Due to the nature of the muon detector using a plastic scintillator with such a large area, the spatial resolution must be measured uniformly over the entire area, but in the previous structure, the spatial resolution was not uniform and there were limitations in measuring the spatial resolution at a low level in areas far from the optical sensor.

Therefore, the muon tomography system using a muon detector based on a plastic scintillator and a wavelength shift fiber according to the present invention attaches a wavelength shift fiber only to the top surface of the plastic scintillator to compensate for the limitations of the typical muon detector structure and The positions were measured simultaneously using an algorithm.

The muon tomography system using a muon detector based on a plastic scintillator and a wavelength-shifting fiber according to the present invention has the advantage of being simple in construction because it does not require artificial sources and eliminating the problem of worker radiation exposure. The muon detector 100 for the muon tomography system is composed of a plastic scintillator 110 and has sufficient density for muon measurement, resulting in relatively high detection efficiency. In addition, due to the design of the muon detector, there is an advantage in that the X and Y axis positions can be acquired simultaneously through a single muon detector, and there is an economic advantage because a relatively inexpensive plastic scintillator is used. It is expected that the muon detector 100 according to the present invention can be used for the purposes of verifying the health of spent nuclear fuel, inspecting containers only at airports, and inspecting nuclear waste drums.

Now, with reference to FIG. 5, we will look at the implementation of a muon tomography system using a muon detector based on a plastic scintillator and a wavelength shift fiber according to the present invention.

As shown in FIG. 5, the implementation of the muon tomography system using a muon detector based on a plastic scintillator and a wavelength shift fiber according to the present invention is designed so that each pair of muon detectors 100 are arranged diagonally. A pair of muon detectors 100 for tracking incoming and outgoing muons are placed on opposite sides of a target with a height difference of 100 cm. Each muon detector 100 with a size of ²⁰⁰ ) Attached to the top, and connect SiPM optical sensors (150) to both ends of each wavelength shift fiber (110). In the muon detector 100, the Since it can be obtained by comparing the signal size between (150), the X and Y positions can be detected simultaneously with a single muon detector. The spatial resolution of the muon detector capable of detecting X and Y positions is evaluated, and the muon detector is divided into pixels based on the spatial resolution. A lead block measuring 20 x 20 x 10 cm ³ is located in the center of the FOV (Field Of View). The energy of the muon is set to 3 GeV and a physical list constructed with a cosmic ray shower generator is used.

Sensitivity and Z-discrimination are calculated to quantitatively evaluate the performance of the muon tomography system using the muon detector based on the plastic scintillator and wavelength shift fiber according to the present invention. Two characteristic factors for quantitatively evaluating the performance of a muon tomography system using a muon detector based on a plastic scintillator and a wavelength shift fiber are defined as Equations 3 and 4 below.

In equation 3, sensitivity is the ratio of the number of detected muons to the number of incident muons, i.e., the ratio of the number of reconstructed points to the number of incoming muons.

Z-discrimination is the ratio of the number of muons scattered to a certain extent on the target to the total number of muons detected. Z-discrimination provides information about the target's location and atomic number (Z). If both sensitivity and Z-discrimination are increased, the performance of the spent fuel monitoring system can be considered better.

Muon tomography system simulation monitoring for spent nuclear fuel

To detect the loss of spent nuclear fuel assemblies, Geant4 simulations were performed using a muon tomography system for spent nuclear fuel. A feasibility study was conducted by modeling spent fuel and analyzing line profiles, and the simulations considered a two-dimensional muon detector, spent fuel assembly, and external shielding.

Now, with reference to FIG. 6, we will look at a spent nuclear fuel assembly simulated using a muon tomography system using a muon detector based on a plastic scintillator and a wavelength shift fiber according to the present invention.

As shown in FIG. 6, the spent nuclear fuel assembly simulated using a muon tomography system using a muon detector based on a plastic scintillator and a wavelength shift fiber according to the present invention is 5 x 5 consisting of 8 x 8 spent nuclear fuel rods. The spent fuel assembly array is modeled inside the external shield.

Here, the length of the spent nuclear fuel rod is 82 cm and the diameter is 0.95 cm, and the external shielding is made of stainless steel (7.92 g/cm ³ ) and Holtite-A neutron shielding (1.61 g/cm ³ ).

In addition, the external dimensions are 4.5m in height and 2.4m in diameter, and the concentrations of spent nuclear fuel are U-234 (0.0442%), U-235 (5%), U-236 (0.023%), and U-238 (94.9328%). ), and the density of spent nuclear fuel is 10.4g/cm ³ . Muons are simulated using the Cosmic-Ray Shower Generator (CRY) library distributed by Lawrence Livermore National Laboratory (LLNL), and a physical list constructed from the osmic-ray shower generator is used.

Additionally, two cases are assumed. Firstly, it assumes the case where all fuel assemblies are present and secondly, the case where fuel assemblies in one row or column are lost, so the Geant4 simulation assumes the case of fully loaded spent fuel assemblies and a second row of discharged spent fuel assemblies. and 4th column.

We now turn to Figures 7A-7C to examine simulated line profiles of a fully loaded spent fuel assembly.

As shown in FIGS. 7A to 7C, it is shown that the position of the fuel assembly ejected from the fully loaded spent nuclear fuel assembly can be distinguished. Here, FIG. 7A shows a simulated spent fuel assembly and muon detector geometry, FIG. 7B shows a reconstructed X-Y image, and FIG. 7C shows a line profile.

Now, with reference to FIGS. 8A to 8C, we will look at the simulated line profiles of the spent fuel assemblies with the second and fourth rows discharged.

As shown in FIGS. 8A to 8C, the second and fourth rows show that the positions of the fuel assemblies ejected from the discharged spent nuclear fuel assemblies can be distinguished. Here, FIG. 8A shows a simulated spent fuel assembly and muon detector geometry, FIG. 8B shows a reconstructed X-Y image, and FIG. 8C shows a line profile.

The muon tomography system using a muon detector based on a plastic scintillator and a wavelength shift fiber used in the present invention is not intended to determine the material composition of spent nuclear fuel, but rather to detect the loss of spent nuclear fuel assemblies, so uranium and Although it is impossible to distinguish the material composition of spent nuclear fuel with similar atomic numbers, such as plutonium, it is possible to inspect the loss of spent nuclear fuel assemblies inside a dry storage container based on simulation results, and for this purpose, a diagonally arranged muon tomography system is used. You can utilize it.

As described above, the muon tomography system using a muon detector based on a plastic scintillator and a wavelength shift fiber according to the present invention can simultaneously acquire the The cost is relatively low, and by using a plastic scintillator with sufficient density for muon measurement, it can provide detection efficiency and short detection time. In addition, by design, it is a single muon detector composed of a single structure and a relative Because it uses an inexpensive plastic scintillator, it is advantageous for constructing a large-area muon detector.

In the present invention, appropriate geometric parameters for dry storage monitoring were derived based on simulation results, and it was confirmed that the muon tomography device according to the present invention has sufficient validity for monitoring spent nuclear fuel in dry storage containers.

As described above, the present invention has been described based on preferred embodiments, but these embodiments are not intended to limit the present invention but are intended to illustrate the present invention, so those skilled in the art to which the present invention pertains can carry out the above-mentioned embodiments without departing from the technical idea of the present invention. Various changes, changes, or adjustments to the example may be possible. Therefore, the protection scope of the present invention should be interpreted as including all changes, modifications, or adjustments that fall within the gist of the technical idea of the present invention.

100: muon detector 110: plastic scintillator
130: Wavelength shift fiber 150: SiPM optical sensor
200: Analog signal processing and acquisition unit
300: Digital signal processing and acquisition unit
400: Detection position determination algorithm unit

Claims (9)

A plastic scintillator that converts muon charged particles into a flash signal and transmits the converted flash signal, a wavelength shift fiber that focuses the converted flash signal received from the plastic scintillator and transmits the focused flash signal, and the above A muon detector including a plurality of optical sensors each converting the absorbed scintillation signal transmitted from the wavelength shift fiber into an electric signal;
an analog signal processing and acquisition unit that amplifies the output signals of the plurality of optical sensors and adjusts signal rise time, fall time, signal width, and offset voltage;
Obtain signal response position, signal size, and signal measurement time information from the output signal of the analog signal processing and acquisition unit, and compare the signal measurement time for the charged particle acquired within a specific time to pass through the muon detector to determine whether the charged particle passed at the same time. A digital signal processing and acquisition unit that measures the simultaneous coefficient of counting signals; and
Using a muon detector based on a plastic scintillator and a wavelength shift fiber, including a detection position determination algorithm unit that receives the output signal of the digital signal processing and acquisition unit and simultaneously determines the X-axis detection position and Y-axis detection position of the charged particle of the muon. Muon tomography system.
In claim 1,
The detection position determination algorithm unit,
Using signal measurement time information among the output signals of the plurality of optical sensors, it is confirmed through the simultaneous coefficient determination that the output signal is generated by a single muon particle,
Using signal size information among the output signals, noise is removed by comparing the sum of signal sizes of simultaneously generated output signals with a threshold value,
The X-axis detection position algorithm is applied using the signal response position and signal size information among the output signals,
A muon tomography system using a muon detector based on a plastic scintillator and wavelength shift fiber that determines the muon detection position by applying a Y-axis detection position algorithm using the signal response position and signal size information among the output signals.
In claim 2,
The X-axis detection position algorithm obtains the X-axis position by analyzing the center of the light spot using Anger logic for the output signal distribution between adjacent wavelength shift fibers. Tomography system.
In claim 2,
The Y-axis detection position algorithm calculates the signal size ratio between two optical sensors attached to one wavelength shift fiber to obtain the Y-axis position. A muon tomography system using a muon detector based on a plastic scintillator and a wavelength shift fiber.
In claim 1,
The spent nuclear fuel monitoring system optimizes parameters for the distance between the muon detectors, FOV (Field Of View), and pixel size of the muon detector through Geant4 simulation,
The pixel size of the muon detector and the distance between the muon detector are used for Z-discrimination,
The FOV size is a muon tomography system using a muon detector based on a plastic scintillator and wavelength shift fiber used for sensitivity.
In claim 1,
A muon tomography system using a plastic scintillator and a wavelength shift fiber-based muon detector, where the plurality of detectors are a plurality of silicon photomultiplier (SiPM) optical sensors.
In claim 1,
The digital signal processing and acquisition unit converts the adjusted signal received from the analog signal processing and acquisition unit into the signal response position and signal through ADC, TDC, FPGA (Field-Programmable Gate Array), or ASICs (Application Specific Integrated Circuits). A muon tomography system using a muon detector based on a plastic scintillator and wavelength shift fiber that acquires size and signal measurement time information.
In claim 1,
A muon tomography system using a muon detector based on a plastic scintillator and a wavelength shift fiber in which a spent nuclear fuel assembly fully loaded with spent nuclear fuel rods is placed between the muon detectors.
A plastic scintillator that converts muon charged particles into a flash signal and transmits the converted flash signal, a wavelength shift fiber that focuses the converted flash signal received from the plastic scintillator and transmits the focused flash signal, and the above A muon detector including a plurality of optical sensors each converting the absorbed scintillation signal transmitted from the wavelength shift fiber into an electric signal;
a spent nuclear fuel assembly fully loaded with spent nuclear fuel rods disposed between the muon detectors;
an analog signal processing and acquisition unit that amplifies the output signals of the plurality of optical sensors and adjusts signal rise time, fall time, signal width, and offset voltage;
Obtain signal response position, signal size, and signal measurement time information from the output signal of the analog signal processing and acquisition unit, and compare the signal measurement time for the charged particle acquired within a specific time to pass through the muon detector to determine whether the charged particle passed at the same time. A digital signal processing and acquisition unit that measures the simultaneous coefficient of counting signals; and
It includes a detection position determination algorithm unit that receives the output signal of the digital signal processing and acquisition unit and simultaneously determines the X-axis detection position and Y-axis detection position of the charged particle of the muon,
A plastic scintillator and a wavelength shift fiber that determine the location of spent nuclear fuel discharged from the spent nuclear fuel assembly based on the X-axis detection position and Y-axis detection position of the charged particle of the muon determined by the detection position determination algorithm unit. Muon tomography system using a muon-based muon detector.

Images