KR100314901B1 - Self powered neutron detector for atomic power plant - Google Patents

Abstract

PURPOSE: A self powered neutron detector for an atomic power plant is provided to variously select a material of an emitter to design the self powered neutron detector and increase a life and a detecting efficiency. CONSTITUTION: A self powered neutron detector has a multiple tube shape. The self powered neutron detector is formed by an assembly of an order of an external accumulating member(51), an external insulator(52), a hollow emitter element(53), an internal insulator(54), and an internal accumulating member(55). The hollow emitter element(53) increase an escape probability of a beta particle. The internal insulator(54) is formed by an aluminum oxide. The beta particle is transferred to the internal insulator(54). The hollow emitter element(53) includes one of a silver(Ag), a platinum(Pt), or a cobalt(Co).

Description

Magnetic output neutron detector for nuclear power plant and its manufacturing method

The present invention relates to the design and manufacturing technology of a magnetic output neutron monitoring device for a nuclear power plant, and more particularly, to a magnetic output neutron detector for a nuclear power plant, an algorithm for designing the detector, a characteristic test method and a manufacturing security of the detector will be.

At present, a self-powered neutron detector is used as a device to measure the output distribution and the combustion degree according to the total power, position, and combustion in a nuclear power plant. However, due to the low current value, long response time, and short life, it should be replaced frequently. There is a disadvantage.

Self-powered neutron detectors using rhodium (Rh), which are conventionally used, are operated by the principle of neutron capture reaction of rhodium emitter material. The neutrons that enter the rhodium are trapped and undergo a beta decay, releasing high-energy electrons with enough energy to leave the emitter. The emitted electrons are collected in a charge collector through an aluminum oxide (Al ₂ O ₃ ) insulator, and a positive charge is generated in an electric conductor attached to the emitter. The resulting positive charge produces a current proportional to the neutron absorption in the emitter. The current signal is generated about 6% by photoelectron absorption, compton scattering, and dipole formation, 87% by beta decay of rhodium 104, and about 7% by double decay of rhodium 104m. . Beta decay eventually leads to combustion of rhodium over time, which in turn causes a decrease in the sensitivity of the instrument.

Conventional emitters, insulators, and detectors with integrated solids have the advantage of ease of manufacture, but the escape probability that electrons generated by neutron particles are transferred to the aggregates is not absorbed by the rhodium. There is a disadvantage that the generated current value is small due to the small number of.

Therefore, the present inventors have improved the magnetic output type neutron detector that can obtain a relatively short response time and a large current value by changing the element used for detection and the shape of the detector to improve the disadvantages of the existing detector. We tried to develop a design method and a method to economically manufacture a miniaturized detector.

It is a first object of the present invention to provide an algorithm capable of designing a magnetic output neutron detector by selecting various materials of an emitter.

A second object of the present invention is to provide a characteristic test method according to a beta particle non-absorption (leaving) probability calculation algorithm and neutron detector shape in the emitter.

It is a third object of the present invention to provide an ultra-small detector and a method of manufacturing the same, which can increase the lifespan, increase the detection efficiency, and simplify the peripheral electronic circuit for signal amplification.

1 is an overall configuration diagram of the monitoring system,

2A and 2B are a schematic diagram of a magnetic output neutron detector and a detection principle thereof;

3a and 3b is a structural diagram and characteristic comparison table of an improved shape according to the present invention,

Figure 4 is a micro detector continuous manufacturing apparatus having a multi-tube shape.

※ Explanation of drawing code ※

50... Detector. 51... External aggregates. 52... External insulator.

53... Emitter. 54... Internal insulator. 55... Internal aggregate.

100... Emitter outlet. 101... Lower Fixture. 102... Pressurization.

103... Lever 104.. Cylinder 105.. Powder of aluminum oxide.

106... Main body of the manufacturing apparatus. 107... Emitter fixture.

108... electrode. 109... Tube fixing. 110... Emitter Protection.

In order to achieve the above object, the present invention is a detector of a magnetic output neutron monitoring device for a nuclear power plant, the detector is made of a multi-tube shape, and the outer integrated body (in the direction of the inner center from the outside of the tube shape) 51), an outer insulator 52, an emitter 53, an inner insulator 54, and an inner aggregate 55, in which the emitter has its center velocity in order to increase the probability of release of the beta particles. It is made of a hollow form, the inner insulator is made of aluminum oxide, the beta particles are to be delivered to the inner aggregate structure.

In addition, the emitter element includes any one of silver (Ag), platinum (Pt), and cobalt (Co).

In order to achieve the above object, the present invention provides a fixing part for fixing the emitter and the electrode of the detector, a filler for filling the insulator material into the microcavity to form an insulator surrounding the emitter and the emitter and And a transfer unit for continuously transferring a detector formed of an insulator, wherein the detector is formed in a multi-tube shape.

In addition, the filling part was formed by a pressure filling method by the weight of the material itself.

First, the outline of the present invention will be described before explaining the embodiments of the present invention.

The present inventors introduced the design method of the magnetic output type neutron detector using Monte Carlo method to confirm the adequacy of the emitter through the performance evaluation before the actual production of the emitter material of various materials and to make the detector with a long life. We developed an algorithm that calculates the amount of sensitivity change as a device reacts with a neutron and burns.

We also developed an algorithm that calculates the amount of beta gamma rays generated by decay and reacts with neutrons using numerical integration.

In addition, new methods and new materials have been developed to overcome the short response time and short life of the magnetic output neutron detector.

In addition, in order to generate a large current, a method of designing and manufacturing by changing a shape from a conventional adhesive method of a detector type to a tube type detector was also developed.

Self-powered neutron detectors using rhodium (Rh), which are conventionally used, are operated by the neutron capture reaction principle of rhodium emitter materials.

The generated current signal is generated about 6% by photoelectron absorption reaction, gompton scattering reaction and dipole formation, 87% by beta decay of rhodium 104, and about 7% by double decay of rhodium 104m. Is generated.

Beta decay eventually leads to combustion of rhodium over time, which in turn causes a decrease in the sensitivity of the instrument. Therefore, if silver (Ag ¹⁰⁹ ) is used instead of the existing materials such as rhodium and vanadium, the cross-sectional area of the thermal neutron reaction can be reduced and gamma-sensitive materials such as platinum (Pt) and cobalt (Co) can be used. Likewise, a detector with a long life can be manufactured. However, when these materials are used, the current generation value per unit area decreases, which reduces the detection efficiency. The current value is proportional to how effectively the electrons generated in proportion to the neutron or gamma radiation dose are delivered to the collector rather than absorbed by the emitter.

The probability of electron departure is dependent on the critical distance between the emitter and the integrated body. Therefore, if the tube type of the detector is changed, the current increases by about 38%, increasing the detection efficiency and improving the electronic circuit for signal amplification. There is a simple advantage.

In addition, in order to use a variety of materials as the detector material, the sensitivity and electrons, the amount of generation of the audit line, and the location of the radiation described above must be calculated. As a method for calculating such a design variable, the present inventors have developed an algorithm using the Monte Carlo probability method.

The total diameter of the unit detector used in the nuclear power plant is 0.076cm, which is manufactured in a very small size such as an insulator thickness of 0.0254cm and an emitter thickness of 0.0253cm and a relatively high current value has to be obtained. That is, in the structure where the emitter, the insulator, and the integrated body are distributed, a method of forming a hollow cylindrical shape of the emitter by forming an insulating layer and a secondary collecting electrode has been developed.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

1 is an overall configuration diagram of a furnace neutron flux monitoring system used in a commercial nuclear power plant. In Fig. 1, reference numeral 1 denotes a reactor in which nuclear fuel 2 is embedded, numeral 3 denotes a detector assembly in a nuclear fuel, numeral 4 denotes a wall of a containment vessel containing nuclear reactor 1, and numeral 5 denotes a nuclear fuel ( 2 is a signal line for transmitting a detection signal from the detector assembly 3 embedded in 2), (6) is a detection signal data collecting device for receiving a detection signal transmitted through the signal line 5, and (7) a data collecting device ( A computer that reads and processes data from 6).

The configuration of FIG. 1 functions as follows. That is, the detector assembly 3 of the neutrons installed in the guide tube located in the center of the nuclear fuel 2 is connected as an input variable to the plant monitoring system via a signal line 5 through a sealing device which is a pressure boundary as a neutron resource. . The data collection device 6 and the computer 7, which are the on-site monitoring system computers, receive 45 detector signals, for example, installed in a nuclear reactor, and undergo signal processing by an internal detector signal processing program. This signal is used in the core operation limit monitoring system to calculate the linear thermal output margin and the radial neutron flux distribution and use it for reactor operation.

FIG. 2A shows a structure diagram of a magnetic output neutron detector in the detector assembly 3 shown in FIG. 1, and FIG. 2B shows a detection principle.

In Fig. 2A, reference numeral 21 denotes a sealing device, 22 a rhodium detector, 23 a signal cable, 24 a background neutron detector, 25 a terminator, 26 a thermocouple, and 27 ) Denotes a calibration guide tube, 28 denotes an aggregate outer tube, and 29 denotes an insulator.

In Fig. 2B, reference numeral 30 denotes an emitter, 31 denotes an insulator, and 32 denotes an integrated body. That is, in FIG. 2, it is composed of five rhodium detectors 22, a background detector 24, a core outlet thermocouple 26, a sealing device 21, and the like, and a neutron of 10% to 90% of the nuclear fuel length. The core and fuel outlet temperatures are measured. The rhodium detector 22 is composed of an emitter 30, an insulator 31, and an integrated body 32, and the emitter 30 and the integrated device 32 are connected by a signal line 5 to be proportional to the neutron flux. A current signal is output.

3A is a structural diagram of a detector according to the present invention, and FIG. 3B is a characteristic comparison diagram when Ag ¹⁰⁹ and Rh103 are used as emitters.

In Fig. 3A, reference numeral 50 denotes a detector according to the present invention, 51 denotes an external collector, 52 denotes an external insulator, 53 denotes an emitter, 54 denotes an internal insulator, and 55 denotes an internal collection. It is backlog.

As can be seen in Figure 3b, the tube-type detector 50 according to the present invention has a small change in the probability of departure even when moving from the center direction of the emitter 53 up and down, but the existing method in the axial direction Up to 11 times of deviation probability occurs when the position is changed, indicating relatively less accuracy in detecting axial neutron flux of the fuel.

4 is a view showing a micro detector continuous manufacturing apparatus having a multi-tube shape of the present invention.

In Fig. 4, reference numeral 100 denotes an emitter extractor as a detector continuous manufacturing apparatus according to the present invention, a lower fixture of an emitter extractor of 101, 102 a presser, 103 a lever, 104 ) Is cylinder, 105 is aluminum oxide powder, 106 is main body of manufacturing apparatus, 107 is emitter fixing part, 108 is electrode, 109 is tube fixing part, 110 is Emmy Protector.

In FIG. 4, the multi-tube shaped micro detector 50 according to the present invention is composed of an Inconel tube, an emitter element, and an insulator of aluminum oxide. However, since the thickness between the raw material and the raw material is about 0.25 mm, the alignment between the emitter 53, the insulator, and the tube is difficult by the conventional method. The apparatus of FIG. 4 in accordance with the present invention continuously comprises an emitter fixing part 107 for fixing the emitter 53 and an electrode 108 and a filling part and an electric field detector for filling the aluminum oxide powder 105 in the microcavity. Can be divided largely into a manual feed for manufacturing.

Hereinafter, a method of manufacturing the detector 50 of the present invention according to FIG. 4 will be described. First, the emitter element is made of an electrode by using the instantaneous welding method on the front, rear, and enters the process for manufacturing in the form of a tube by the detector continuous manufacturing apparatus. Aluminum oxide automatic filling part of the manufacturing apparatus according to the present invention is composed of a pressing portion 102, the lever 103, the cylinder 104, and the inner body 55 must be located in the center of the emitter tube volume reduction method Instead, the filling method of the lever method by the heavy material (structure in which the weight is applied to the powder in proportion to the weight of the precision weight and the force point and the length of the action point) is mixed with the aluminum oxide powder 105 and the zinc sterite powder in a certain ratio. Then, the cylinder is filled into the tube by applying the pressure using the lever principle to a mixture of aluminum oxide powder and zinc sterite powder in a proportion. In addition, when receiving heat according to the present invention, the volatile zinc stellite component is decomposed and evaporated during sintering of the insulating layer, and thus beta emission by the iodine component of the material of the detector 50 does not occur. The emitter filled with the aluminum oxide powder 105 is connected to the Inconel tube at the tube fixing part 109 and is provided with a detector shape of full length and then enters the sintering process.

The detector filled with the insulator is completely sintered in an electric furnace in which the eddy current generating coil is wound in a spiral form, and then enters a process for attaching a sealing connection connector.

Next, the development of computational algorithms for designing detectors using emitters of various materials will be described.

In order to easily change the emitter, which is the core material of the magnetic output neutron detector, from the existing rhodium to the new material, calculate the change in sensitivity as the neutron initial sensitivity for the emitter material to be used and the reaction with the neutron are burned. The inventors have developed an algorithm using a personal computer, the contents of which are as follows.

If the detector has a cylindrical shape and is used for the purpose of measuring thermal neutrons (energy: 0.024ev), Equation 1 representing the detector's output is as follows.

[Equation 1]

Where I is the detector output by thermal neutron, V is the volume of emitter (πR ² L),

E _Β : energy of the beta particles released by the collapse of the emitter,

ε (E _Β , r): probability of escape of beta particle energy proportional to the position (r) of the detector,

P (E _Β ): Normal distribution of beta energy, N _Rb (r): Emitter density.

In addition, the general formula for calculating the sensitivity of the detector is as follows.

[Equation 2]

Where S: sensitivity of detector [A / nv-cm], Φ ₀ : thermal neutron flux near detector

f _n (r): Neutron flux distribution normalized to Φ ₀

In addition, if the density and initial value are proportional to the position variable and the diameter of the emitter, respectively, the sensitivity calculation of the detector is simplified by dividing the time-dependent beta particle production rate term and the time-independent beta non-absorption probability term as follows. Can be displayed.

[Equation 3]

In addition, in order to calculate the beta production rate that is dependent on time and location, the distribution of time-dependent neutron flux must be calculated. The neutron absorption cross-sectional area of the material used in the emitter is relatively large compared to the scattering cross-sectional area, so neutron diffusion does not need to be considered. In the present invention, a beta production rate calculation algorithm was developed using the following Equation 4.

[Equation 4]

Where Ø (r, 0): beta particle production rate, Φ ₀ : thermal neutron flux in the vicinity of the detector,

x: thermal neutron transport path from the cylindrical emitter surface to the local position r,

∑ macroscopic neutron absorption cross section

Next, a beta particle non-absorption (departure) probability calculation algorithm and a characteristic test method according to the detector shape will be described.

Emitters absorbing neutrons generate energy by the Coulomb reaction, and the trajectory of energy loses energy by zigzag movement as it moves away from the emitter in a straight line. When energy is lost completely, the final stop position can be divided into three areas: the emitter interior, the integrated body, and the insulating layer. The stop position must be calculated for optimal detector shape design. When beta energy is stopped in a thin electrically insulating layer, the energy accumulates space charge in the insulating layer and generates an electrostatic field and potential. Since the charge accumulated after a certain time is finite in the electrical resistivity of the detector, the accumulated charge is saturated, and after saturation, the beta particles are returned to the emitter or transferred to the integrated body. Therefore, the non-absorption (deletion) probability of the beta particles can be defined as the probability of exiting the critical distance of the insulating layer before the beta particles stop, and this probability calculation needs to calculate the paths of various beta particles stochastically. Algorithm according to the calculation using the Monte Carlo neutron and particle transport calculation code. The calculation results allow the design and characterization of the beta particle formation position and the shape of the insulator and the integrated body, and the performance can be verified before the detector is manufactured without performing the characteristic test by neutron irradiation of the detector.

As described above, according to the present invention, in the magnetic output neutron monitoring device for nuclear power plants, emitters of various materials can be used, and the service life thereof can be extended, the detection efficiency can be increased, and the signal amplification can be used. Peripheral electronic circuits can be simplified.

In addition, according to the present invention, it is possible to continuously manufacture a microminiature neutron detector.

As mentioned above, although the invention made by this inventor was demonstrated concretely according to the said Example, this invention is not limited to the said Example and can be variously changed in the range which does not deviate from the summary.

Claims (2)

In the detector of the magnetic output neutron monitoring device for nuclear power plants, The detector has a multi-tubular shape and is formed from an outer integrator 51, an outer insulator 52, an emitter 53, an inner insulator 54, and an inner collector 55 from the outside of the tubular shape to the inner center direction. Made up of a sequence of The emitter is hollow in its center to increase the probability of release of beta particles, The internal insulator is made of aluminum oxide, The beta particles are detectors, characterized in that delivered to the internal aggregate. The method of claim 1, And the emitter element comprises one of silver (Ag), platinum (Pt) or cobalt (Co).

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