JPH0639351Y2 - Self-powered neutron detector - Google Patents

Description

[Detailed description of the device]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a self-powered neutron detector used for detecting neutrons, and more particularly to a detector capable of easily confirming disconnection.

[0002]

2. Description of the Related Art In recent years, a large number of large-scale power generation reactors have been constructed, and along with this, safe and economical operation of the reactors is carried out to obtain local neutron flux data in the core, or In order to enhance the fuel combustion and operate a nuclear reactor with high economic efficiency, a detector is placed inside the core instead of the out-of-core measurement to obtain an accurate reactor output.

As such detectors for in-reactor measurement, conventionally, for example, a small fission ionization chamber, a B ionization chamber, a neutron thermocouple, a self-powered neutron detector, etc. can be mentioned.
At present, the fission ionization chamber is often used for this purpose. However, in place of this fission ionization chamber, self-powered neutron detectors are attracting attention because of their small size, robustness, high reliability and economic efficiency due to their simple structure.

An example of the structure of a conventional self-powered neutron detector is shown in the attached FIG. In this figure, a self-powered neutron detector is provided at the tip of a so-called MI cable 4 in which an insulator 2 such as alumina or magnesia is filled around a central core wire 1 and the outer periphery is covered with an outer cover 3 such as stainless steel. 5 is attached. The detector 5 is composed of an emitter 6 made of rhodium or the like, a ceramic insulating material 7 attached around the emitter 6, and a collector 8 made of stainless steel or the like covering the emitter and the insulating material. The emitter 6 serving as the sensor unit is the M
The I-cable 4 and the core wire 1 are generally joined to each other by welding.

[0005]

However, in the above-mentioned prior art self-powered neutron detector, the junction between the emitter and the cable serving as the lead wire, for example, the nickel core wire is called rhodium or nickel. Since it is a joining of dissimilar materials, there is a possibility that cracks or disconnections may occur at this joining site due to thermal strain etc.
There was a problem with the reliability of the self-powered neutron detector. Especially, the self-powered neutron detector cannot be easily checked once it is loaded into the reactor for the purpose of use.
In addition, there was a weak point that the defect was not found until the output did not appear even if irradiated with neutrons and the behavior was strange.

In view of the above-mentioned problems in the self-powered neutron detector of the prior art, the present invention particularly checks the connection between the emitter of the neutron detector and the core wire of the cable that serves as the lead wire, and checks the disconnection state. It is an object of the present invention to provide a self-powered neutron detector capable of detecting neutrons even if the junction is broken.

[0007]

In order to achieve the above object, the present invention comprises an emitter, an insulating material arranged so as to surround the emitter, and a collector covering the emitter and the insulating material. A self-powered neutron detector in which the emitter is joined to a core of a cable and the collector is joined to a conductive outer skin of the cable, wherein the emitter is formed by bending it into a U shape, and Provided is a self-powered neutron detector in which two core wires are arranged inside a cable and the two core wires of the cable are joined to two ends of the U-shaped emitter.

[0008]

According to the self-powered neutron detector of the present invention, a U-shaped bent emitter is used, and two cores of the cable are respectively joined to the two ends of the emitter. It is possible to electrically confirm the disconnection state of the emitter and the core wire through these two core wires.
Even if one of the joints is broken, the output can be reliably taken out through the other joint.

[0009]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. First, in the attached Figure 1,
A cross-sectional structure of a self-powered neutron detector according to an embodiment of the present invention is shown. In this figure, the emitter 10 as a neutron sensor unit is made of a rod-shaped or flat-shaped metal such as rhodium (Rh) in a U-shape. It is formed by bending into a shape. A ceramic insulating material 20 is arranged around the U-shaped emitter 10 so as to surround the emitter in conformity with the shape of the emitter. A circular tubular collector 30 made of, for example, a stainless material is provided so as to surround the emitter 10 and the ceramic insulating material 20 around the emitter 10 from the outside.

On the other hand, a so-called MI cable 40 is attached to one end (the right end in this embodiment) of the above-mentioned detecting portion, and this MI cable 40 is made of stainless steel as shown in the drawing. An insulator 42 such as alumina or magnesia is filled in the interior of 41, and two nickel core wires (lead wires) 43 and 44 are housed in an independent and insulated state. And MI cable 40
The outer cover 41 is welded and fixed to the open end of the collector 30 of the detection unit, and the two core wires 43 and 44 in the MI cable 40 are formed by bending the U-shape. The two ends of the emitter 10 are joined by welding. Of these joining states, MI
Since the outer cover 41 of the cable 40 and the collector 30 of the detection unit are both formed of stainless steel, even if they are welded and joined, they are relatively stable because cracks are unlikely to occur because they are joined by similar materials. On the other hand, 2 in MI cable 40
Since the welded portions between the core wires 43 and 44 of the book and the two ends of the emitter 10 are joined by different materials, disconnection may occur at these portions.

By the way, when detecting neutrons in a nuclear reactor by the self-powered neutron detector of the present invention, as shown in FIG. 2 attached, two core wires 43 taken out from the MI cable 40 are used. , 44 are connected in parallel (short-circuited), and the ammeter 100 is inserted between this and the outer cover 41 of the MI cable 40. As the ammeter 100, for example, a vibration capacitance type electrometer or the like is used.

That is, when the self-powered neutron detector is placed in a nuclear reactor, the neutrons incident on the detector pass through the collector 30 and the insulating material 20 and are absorbed by the emitter 10 to emit β rays. A nuclide is generated. In general,
Since the emitted β-rays have large energy, the β-rays escape from the emitter 10, pass through the insulator 20, and stop in the collector 30 on the outer circumference. Therefore, electrons are deficient in the emitter 10, and positive charges are induced in the core wires 43 and 44 of the MI cable 40, that is, a current flows between the collector 30 and the emitter 10. Therefore, the neutron flux is detected by detecting this current.

By the way, according to the structure of the emitter 10 of the self-powered neutron detector which is the embodiment of the present invention as described above, the core wire 4 which is the lead wire is provided at the two ends of the U-shape.
Since 3 and 44 are joined, the wiring of the measurement circuit is switched as shown in the attached FIG. 3, and the power source 60 and the ammeter 70 are inserted between these two core wires 43 and 44, and the flowing current By checking (1), it is possible to easily confirm the joining state between the two U-shaped ends of the emitter 10 and the core wires 43 and 44 that are the lead wires, that is, the function check. That is, when a crack is generated in these joints and the wires are broken, it is determined that no current flows and a defect occurs in these joints.

When neutrons are measured in the core, as shown in FIG. 2, these two core wires 43, 4 are used.
Since 4 is connected to each other, even if one of the two joints between the two ends of the U-shaped emitter 10 and the core wires 43, 44 is broken, either of the two core wires 43, 44 is broken. It is possible to extract the detection current from the core wire of the neutron detector, which makes it possible to further improve the reliability of the self-powered neutron detector.

Further, in the above-mentioned embodiment, the current caused by β-rays is measured to detect the neutron flux, but the response speed is relatively slow, and therefore, for example, cobalt (Co ) Emitter, and adopt a method to measure the current caused by secondary electrons generated when the captured γ-rays emitted by absorbing and emitting neutrons cause photoelectric effect or Compton effect inside the emitter. Is also possible.

FIG. 5 attached herewith shows another embodiment of the present invention.
In this embodiment, the emitter 10 is formed into a pipe shape, a pipe-shaped insulating material 20 having a smaller diameter is inserted into the inside of the emitter 10, and one core wire 43 is further penetrated into the insulating material 20. At the left end. Also,
The other core wire 44 is connected to the right end of the emitter 10 in FIG. It is clear that this embodiment can also obtain the same operation and effect as the above-mentioned embodiment.

[0017]

As is apparent from the above detailed description of the present invention, according to the self-powered neutron detector of the present invention,
From its improved structure, it is possible to check its function regularly by switching the measuring circuit,
And, since it is possible to reliably detect neutrons even if one of them is broken, it is possible to provide a highly reliable and excellent self-powered neutron detector with a practically excellent effect. Demonstrate.

[Brief description of drawings]

FIG. 1 is a sectional view illustrating a detailed internal structure of a self-powered neutron detector according to an embodiment of the present invention.

FIG. 2 is an operation explanatory diagram for explaining a neutron detection operation of the self-powered neutron detector.

FIG. 3 is an operation explanatory diagram for explaining a disconnection check operation of the self-powered neutron detector.

FIG. 4 is a sectional view showing an example of a self-powered neutron detector according to the prior art.

FIG. 5 is a sectional view illustrating a detailed internal structure of a self-powered neutron detector according to another embodiment of the present invention.

[Explanation of symbols]

 10 Emitter 20 Insulating Material 30 Collector 40 MI Cable 41 Cable Outer 42 Insulator 43, 44 Core Wire (Lead Wire)

[Others] There is no change in the substance of the description.

Claims (1)

[Scope of utility model registration request] 1. An emitter, an insulating material arranged so as to surround the emitter, and a collector covering the emitter and the insulating material, the emitter being joined to a core wire of a cable, and the collector being a conductive member of the cable. In a self-powered neutron detector joined to a flexible outer skin, the emitter is formed by bending it into a U shape, and two core wires are arranged inside the cable, A self-powered neutron detector, wherein a core wire is joined to two ends of the U-shaped emitter.