KR20010078579A - Measuring method for fissile content in nuclear fuel material using cadmium ratio of neutron counts and its equipment - Google Patents

Abstract

PURPOSE: A method and an apparatus for measuring fissionable materials of a nuclear fuel using a variation of a cadmium ratio of a neutron coefficient are provided to measure fissionable materials of a nuclear fuel by using a lead shielding body, a polyethylene reflective body, and a cadmium. CONSTITUTION: A lead shielding body(3,12) is installed within an outer tank(1) of a main body. The lead shielding body(3,12) protects a pre-amplifier(16) and a detection tube(17) from a gamma ray. A multitude of detection tube(17) connected with a neutron moderation body(2) and the pre-amplifier(16) is installed between the lead shielding body(3) and the outer tank(1) of the main body. A reflective body(5,11), a cadmium plate(7,8), a nuclear fuel loading case(6), and a neutron storage case(10) are installed at an inner face of the lead shielding body(3). An upper outer tank(18) is installed on an upper portion of the lead shielding body(3) and the outer tank(1) of the main body. An upper shielding body cover(21) including an upper neutron reflective body(19) and an upper lead shielding body(20) is installed on the lead shielding body(3).

Description

Measurement method and fissile content in nuclear fuel material using cadmium ratio of neutron counts and its equipment

The present invention relates to a method and apparatus for measuring fissile material of nuclear fuel using a change in the cadmium ratio value of the neutron coefficient, wherein the induced fission is induced by absorbing neutrons into new fuel, mixed fuel and spent fuel material. The present invention relates to a method for measuring fissile material of a nuclear fuel using a change in the cadmium ratio value of the neutron coefficient which measures the change in the number of neutrons and the fissile material contained in the fuel.

In general, various nuclear fuel materials contain fissile materials that can cause fission. In order to make fuel that can be burned in a reactor using such fuel material, the content of fissile material contained in the fuel material must be accurately measured. Two methods are used for this purpose. The first is a chemical analysis as a destruction method, and the second is a nondestructive method by measuring neutrons or gamma rays.

The chemical analysis method is not used because it takes a long time, and recently, non-destructive analysis method that can be analyzed in real time is preferred, but the conventional non-destructive analysis method has been used gamma ray spectrum analysis method only for new fuel, There was no clear measurement method for fissile material contained in spent fuel.

In the 1990s, neutron detection tubes with good detection efficiency have been developed, and neutron multiplication coefficients using these detection tubes have been mainly used in the technique of measuring the content of plutonium. In the late 1990s, the detection tube and preamplifier were found to be poor at measuring neutrons at high gamma-ray levels. This fact has a problem that the detection tube should be used only in nuclear fuel in which a small amount of gamma rays are released, that is, a new fuel and a mixed fuel.

In addition, U.S. Patent No. 4493810 (1985) for measuring only fissile material and reactivity characteristics of spent fuel assembly in water, and Japanese Patent 90-190241 for measuring fissile material by rotating a neutron source around a test material Although there is also a US patent, there is a restriction in the water, the Japanese patent is a device for measuring only the fissile material in the radioactive waste, there must be a number of problems, such as having a neutron source.

The present invention has been made in consideration of the above problems, and an object thereof is to use nuclear lead shield, polyethylene reflector, and cadmium, and nuclear fission such as uranium-235 and plutonium-239 isotopes included in new fuel, mixed fuel, and spent nuclear fuel. The present invention provides a method and apparatus for measuring fissile material of nuclear fuel using a change in the cadmium ratio value of the neutron coefficient, which can measure the content of a substance.

The present invention absorbs thermal neutrons in nuclear fuel to cause induced fission, and the first step of measuring the neutrons generated by the induced nuclear fission as a signal, and the thermal neutrons absorbed by the nuclear fuel to the cadmium plate to prevent induced fission And then measuring the concentration of fissile material in the nuclear fuel through the ratio of the neutron count without cadmium plate and the neutron count with cadmium plate measured by the first and second steps. Determination of fissile material of nuclear fuel using the change of cadmium ratio value of neutron coefficient to measure fissile material for fuel powder, sintered body and fuel rod in the process of processing new fuel, mixed fuel and spent fuel through 3 steps A method and apparatus are provided.

1 is a schematic diagram of an apparatus for measuring fissile material

2 is a cross-sectional view of the measuring device

3 is a measurement circuit diagram of a measuring device;

* Explanation of symbols for the main parts of the drawings

(1): main body outer cylinder (2): neutron deceleration body

(3): Side shielding (4): Lead shielding

(5): side reflector (6): nuclear fuel battleship

(7): side cadmium plate (8): lower cadmium plate

(9): Neutron source cylinder (10): Neutron source cylinder

(11): lower neutron reflector (12): lower lead shield

(13): Signal box (14): Signal terminal

(15): Signal line (16): Preamplifier

(17): detection tube (18): upper outer cylinder

(19): upper neutron reflector (20): upper lead shield

(21): upper shield lid (22): upper shield lid ring

In the present invention, a nuclear fuel specimen is placed in a nuclear fuel charge box (6), and the neutrons are absorbed into the nuclear fuel to cause induced fission. 235 and plutonium-239 isotopes).

1 shows a schematic diagram of an apparatus for measuring fissile material, and in the present invention, a lead shielding body 3 and 12 is installed in a main body outer cylinder 1, and a neutron is disposed between the lead shielding body 3 and the main body outer cylinder 1. A plurality of detection tubes 17 are installed and connected to the decelerator 2 and the preamplifier 16, respectively, and the reflectors 5, 11, cadmium plates 7, 8, on the inner side of the lead shielding body 3, A nuclear fuel loader (6) and a heavy source storage container (10) are installed, and an upper outer cylinder (18) is installed on the main body outer cylinder (1) and the lead shielding body (3), and on the upper shielding body (3). An upper shield lid 21 having an upper neutron semiconducting body 19 and an upper lead shielding body 20 is installed.

The lead shield is used to protect the preamplifier 16 and the detection tube 17 from the strong gamma rays emitted from the spent fuel when the spent fuel is used as a specimen. It is installed to be located in the center of the outer cylinder (1), the side shielding body (3) and the upper shielding lid (21) for separating the main body outer cylinder (1) into a portion into which the nuclear fuel specimen is inserted and the detection tube 17 is installed The lower lead shielding body 12 is formed by casting with lead in the lower portion of the main body outer cylinder 1 so as to be located at the rear of the upper lead shielding body 20 and the side lead shielding body 3 which are installed at the lower part.

The lead shielded outer cylinder (4) is made for the purpose of casting and storing lead, and is made of aluminum material that absorbs less neutrons.

The neutron deceleration body (2) is to reduce the speed of the neutron, is installed between the main body outer cylinder (1) and the side lead shield (3), made of high-density polyethylene, etc., the plurality of detection tubes 17 is a neutron It can make high speed neutron into thermal neutron so that it can be detected well.

The detection tube 17 captures the neutron decelerated by the neutron deceleration body 2, and is connected to and installed with the neutron deceleration body 2, and has two circles between the main body outer cylinder 1 and the lead shielded outer cylinder 4. A plurality of detection tubes 17 are provided in duplicate so as to be provided, and are connected to the preamplifier 16. That is, the detection tube 17 is configured in an inner and outer ring shape, the inner ring and the outer ring is composed of a predetermined number of detection tubes, respectively, as shown in FIG.

The preamplifier 16 amplifies a signal generated by the detected neutrons and is connected to each detection tube 17 and is connected to each other by a plurality of signal connection lines 15. That is, when 16 and 32 detection tubes 17 are installed in the inner and outer rings, respectively, the preamplifiers 16 connected to the detection tubes 17 are also 32 in total. As described above, all 32 preamplifiers 16 are divided into four groups, each grouped by eight, divided into A, B, C, and D, and the output signal values of A, B, C, and D are compared with each other. The abnormality of the signal connection line 15 is confirmed.

The reflector is a function of making a thermal neutron to cause induced fission, consisting of high-density polyethylene, the side reflector (5) connected to and installed in the side lead shield outer cylinder (4), and installed in the upper shield lid 21 The lower neutron reflector 11 is connected to and installed in the upper neutron reflector 19 and the lower lead shielding body 12.

The cadmium plate absorbs thermal neutrons, and the side cadmium plate (7) inserted between the reflector (5) and the nuclear fuel container (6), the reflector (5) and the heavy source storage container (10), and the nuclear fuel charge box (6) and the lower cadmium plate (8) inserted between the heavy source storage container (10).

The fuel charge box 6 is inserted to be positioned in the lead shields 3, 12, and 20 in which the reflectors 5, 11, and 19 are installed, and nuclear fuel specimens are loaded therein.

The neutron storage container 10 is to store the neutron beam cylinder 9 in which the neutron source is stored, is installed in the lead shield (3, 12, 20) provided with the reflectors (5, 11, 19). That is, the neutron source is loaded in the neutron cylinder 9, the neutron source cylinder 9 is loaded in the neutron storage cylinder (10).

The upper outer cylinder 18 is installed on the main body outer cylinder 1 and the side shielding body outer cylinder 4, the neutron reduction body 2, the detection tube 17 and the preamplifier 16 is installed.

The upper shield body 21 is installed so as to be positioned on the upper side of the lead shield (3) in which the nuclear fuel charge box (6), the neutron cylinder (9) and the cadmium plate (7,8) is inserted, the upper portion on the lower surface The lead shield 20 and the upper neutron reflector 19 are sequentially installed, and the upper shield lid 22 is installed at the top to facilitate the work in the hot cell.

That is, the upper lead shield 20 is cast by filling in the upper shield lid 21.

As described above, the present invention focuses on the cadmium plate (7,8), the reflector (5) and the upper neutron reflector (19), the side shielding (5) and the upper lead centering on the nuclear fuel charge box (6) and the neutron storage container (10). The shield 20 is provided in sequence.

In order to measure the fissile material of the new fuel and the mixed fuel using the present invention configured as described above, the neutron source is placed in the neutron source cylinder inside the neutron source container by inserting the nuclear fuel sample into the nuclear fuel container. Put it in. In this case, there is no need to use neutron sources when inserting spent fuel into the nuclear fuel loader. This is because spent neutrons generate many neutrons on their own. Fast neutrons from neutron sources or spent fuel collide in the ethylene material of the side reflectors, the bottom reflectors, and the upper reflectors, and then become thermal neutrons after they have slowed down. The thermal neutrons return to the nuclear fuel and are absorbed by the fissile material contained in the fuel to cause fission. This fission phenomenon is called induced fission. Due to the induced fission, neutrons are multiplied again, and the generated neutrons pass through the side lead shield and are decelerated in the neutron decelerator made of polyethylene, captured by the detection tube, and measured by a preamplifier as a signal.

The present invention measures the concentration of fissile material in nuclear fuel by measuring the rate at which induced fission occurs and the rate at which it does not occur using the above method.

In other words, as the concentration of fissile material in the fuel increases, the ratio of induced fission increases, so that when the side cadmium plate and the lower cadmium plate are placed inside, most of the thermal neutrons are absorbed by the cadmium plate so that induced fission does not occur. . When the cadmium plate is withdrawn, induced fission occurs again. This is summarized as a relational expression as follows.

Fissile content = experimental factor × neutron count without cadmium plate / neutron count with cadmium plate

As described above, the present invention measures the content of fissile materials such as uranium-235 and plutonium-239 isotopes contained in new fuels, mixed fuels, and spent fuels by introducing a new concept of changing the cadmium ratio in the neutron coefficient. It is suitable for handling neutron sources, handling new and mixed fuels, handling spent radioactive fuels, treating card mupans and neutron deceleration and measurement.

In addition, since the measurement of the content of fissile material of the spent fuel that emits high radiation has to be performed in the hot cell, the work in the hot cell requires the removal and insertion of the spent fuel specimen into the test apparatus and the installation and removal of the cadmium plate. It is configured to facilitate the measurement of the number of neutrons and to measure the outside of the hot cell through the signal line connected to the test equipment.

The present invention is not limited to the above-described specific preferred embodiments, and various modifications can be made by any person having ordinary skill in the art without departing from the gist of the present invention claimed in the claims. Of course, such changes will fall within the scope of the claims.

As described above, the present invention more precisely measures the change in the cadmium ratio value of the neutron coefficient caused by the induced fission according to the change in the content of the fissile material, and to measure the concentration of the fissile material contained in the nuclear fuel by using the same. And non-destructive analysis of the amount of fissile material contained in new fuels, mixed fuels, and spent fuels in a non-destructive manner, and the content of fissile material in all types of fuels, including fuel powders, sintered bodies, and fuel rods Can be measured.

In addition, the present invention is to be movable, can measure the fissile material of the nuclear fuel under various conditions, can measure the fissile material of the spent fuel without neutron source, using a fixed neutron source The content of fissile material can be measured.

As described above, the present invention is essential in a facility that needs to handle / process spent fuel, such as a new concept of fuel cycle technology (light and light water reactor-linked fuel cycle technology) cycle, which has recently been spotlighted worldwide. There are many effects, including the expectation of bringing new electricity.

Claims (5)

A first step of absorbing thermal neutrons into nuclear fuel to cause induced fission, and measuring the neutrons generated by the induced fission as signals; A second step of absorbing the thermal neutrons absorbed by the nuclear fuel into the cadmium plate to prevent induced fission and then measuring the neutrons as a signal; New fuel, mixed fuel and spent fuel through the third step of measuring the concentration of fissile material in the nuclear fuel by the ratio of the neutron count without cadmium plate and the neutron count with cadmium plate measured by the first and second steps Method for measuring fissile material of nuclear fuel using a cadmium ratio value change of the neutron coefficient, characterized in that to measure the fissile material for the fuel powder, the sintered body and the fuel rod during processing. The side lead shielding body installed by the lead shielding outer cylinder in the central part of the outer cylinder, A neutron reduction body installed between the main body outer cylinder and the side shielding body; A plurality of detection tubes connected to and installed with the neutron reduction body, A preamplifier connected to and installed with the detection tube; A signal terminal and a signal connection box connected by the plurality of preamplifiers and signal connection lines; The upper outer passage is installed on the outer body of the main body and the side shielding body is installed the neutron reduction body, the preamplifier and the signal connection line, An upper shielding body lid installed on the side shielding upper body, An upper lead shielding body connected to and installed on a lower end surface of the upper shielding body; A lower lead shielding body installed at a lower surface of the outer cylinder body so as to be positioned below the side shielding body; A side reflector, an upper neutron reflector, and a lower neutron reflector connected to and installed in the side shielding body, the upper shielding body, and the lower shielding body, respectively; A neutron beam through which the reflector is installed and inserted into a lead shield and loaded with a neutron source; A neutron source storage passage in which the neutron cylinder is loaded, A nuclear fuel charge box inserted into a lead shielding body in which the reflector is installed and loaded with a fuel sample; Nuclear fission of nuclear fuel using a change in the cadmium ratio value of the neutron coefficient, characterized in that it comprises a cadmium plate installed between the neutron source reservoir and the reflector, between the nuclear fuel charge box and the reflector, between the neutron source and the fuel advantage box Material measuring device. The method of claim 2; The detection tube is a nuclear fissile material measuring apparatus using a cadmium ratio value change of the neutron coefficient, characterized in that installed in a double ring arrangement. The method of claim 2; The side reflector, the lower neutron reflector, the upper neutron reflector is a nuclear fissile material measuring apparatus using a cadmium ratio value change of the neutron coefficient, characterized in that made of polyethylene. The method of claim 2; The lead shield extracorporeal tube is a fissile material measuring apparatus for nuclear fuel using a cadmium ratio value change of the neutron coefficient, characterized in that the aluminum material.