JPS62197784A - Neutron detecting nuclear fission type ionization chamber - Google Patents

Abstract

PURPOSE:To ensure the electric connection between an outer electrode and an airtight casing and increasing a reliability by connecting the electric connection between the airtight casing connected to the outer conductor of a coaxial cable and the outer electrode to an electrode end plug by pressure welding through a connecting lead wire. CONSTITUTION:The air release pipe side end portion of an outer electrode 12 arranged inside an airtight casing 11 made of a conductor is fixedly adhered by welding to an electrode end plug 31 made of a conductor, said plug 31 being formed by the metallic material of the same kind as that of the outer electrode 12. An air release pipe 36 or the connecting lead wire 33 electrically connected to the casing 11 is fixedly adhered to the end plug 31 by pressure welding. The electrode 12 is electrically connected to the casing 11 via the outer electrode end plug 31 welded to the electrode 12, the lead wire 33 pressure-welded to the end plug 31 and a casing end plug 34 having an air release pipe portion, and the casing 11 is electrically connected to the outer conductor of a coaxial cable 22. In the electrically connecting path thus formed, since the metallic materials of the same kind are connected to each other by TIG welding and the metallic materials of different kinds by pressure welding, a good welding condition can be obtained in either weld.

Description

[Detailed Description of the Invention] [Object of the Invention] (Field of Industrial Application) This invention relates to a fission type ionization chamber for detecting neutrons in the local power range, which is used as a means of neutron instrumentation such as in power reactors. , especially regarding the connection structure of the electrodes.

(Prior Art) This type of ionization chamber has already been disclosed in Japanese Utility Model Application Publication No. 57-142374 and Japanese Patent Application Laid-open No. 60-121658 Tan.

Generally, the cylindrical outer electrode (cathode) is electrically connected to the outer conductor of the coaxial cable for signal derivation, and the cylindrical or cylindrical inner electrode (anode) is electrically connected to the inner conductor of the coaxial cable. In that case, The outer electrode is connected directly or via a relay conductor to the airtight case of the ionization chamber and also to the outer conductor of the coaxial cable.The conventional structure thereof will be explained with reference to FIGS. 6 and 7, respectively. 11 is a stainless steel!In! airtight case, 12 is a titanium cylindrical outer electrode disposed inside the case, 13 is a coating layer of a fissile material such as uranium-235 deposited on its inner surface, and 14 is an airtight case made of stainless steel! A cylindrical inner electrode, 15 a ceramic insulator spacer that holds the small diameter end of the inner electrode, 16 a similar insulating spacer forming a partition wall, and 17 a stainless steel case that closes the open end of the airtight space. Reference numeral 18 indicates an exhaust pipe portion integrally formed therein; 8 indicates a joint where the airtight case and the case end plug are airtightly welded over the entire circumference; 1
Reference numeral 9 designates a connecting ribbon, and 20 designates a gap (for example, about 0.25 mm) between the inner and outer electrodes, which is filled with an ionizing gas.

In the structure shown in FIG. 6, the outer electrode 12 is simply fitted inside the airtight case, and its open end is connected to the case end plug 17.
It is butted against and supported. Therefore, the outer electrode is only electrically connected to the airtight case through mechanical contact. However, although this has a simple structure, the electrical connection tends to be unstable. In other words, this ionization chamber is normally used in a vertical position, and in order to facilitate assembly, the outer dimensions of the outer electrode are made somewhat smaller than the inner diameter of the airtight case, and thermal expansion of the outer airtight case occurs. Therefore, the airtight case and the outer electrode may be in a non-contact state. In particular, a slight film called smut is formed on the surface of the outer electrode during the process of depositing each fissile substance or chemical treatment process, which tends to cause insufficient electrical contact with the airtight case, etc. . In this way, electrical contact between the outer electrode and the airtight case tends to be incomplete. In particular, this type of ionization chamber is unique in that the degree of electrical insulation between the inner and outer electrodes is extremely low, so it is impossible to detect from the outside whether or not the outer electrode and the airtight case are in a non-contact state. Close to. Therefore, it is difficult to judge whether the electrical connection is good or not, and even more so, it is impossible to detect unstable contact during actual use, so there is a possibility that reliability problems may remain.

Furthermore, for the purpose of improving this, a structure shown in FIG. 7 may be considered. This is the ribbon 1 for connecting the outer electrode and the airtight case.
9 for electrical connection. However, the joining is done by resistance welding, etc., and titanium, etc., which has good adhesion to the fissile material layer, is used for the vertical side electrode, while stainless steel, etc., which has good corrosion resistance and oxidation resistance, is used for the airtight case. What kind of metal is used for the connection ribbon?B Welding of dissimilar metals becomes difficult, making highly reliable welding difficult. In addition, it is possible that the molten metal that scatters as sparks during resistance welding cools and leaves behind fine lumps, which require a lot of effort to completely remove. If this splash remains inside the tube and enters the gap 20 between the inner and outer electrodes, it will cause an electrical short circuit, resulting in a fatal failure.

(Problems to be Solved by the Invention) According to the conventional structure as described above, there is a possibility that the electrical contact between the outer electrode and the airtight case becomes unstable. In particular, there remains a risk that the contact between the two may become unstable or the welded part may peel due to stress due to thermal cycles after being installed in a nuclear reactor, or mechanical external forces such as vibration and impact. Furthermore, if the splash remains inside the tube, there is a possibility that it will enter the gap between the two electrodes and cause a short circuit. Needless to say, this type of neutron detection 3 must have high reliability. Therefore, it is necessary to reliably prevent such unstable electrical contact between the outer electrode and the airtight case.

The object of the present invention is to ensure electrical connection between an outer electrode and an airtight case, and to obtain a highly reliable fission type ionization chamber for neutron detection.

[Structure of the Invention] (Means for Solving the Problems) This invention provides an electrode formed on the exhaust pipe side end of an outer electrode disposed inside an airtight case made of a conductor, preferably made of the same kind of metal material. This is a nuclear fission type ionization chamber for neutron detection, in which an electrode end plug made of a conductive material is fixed by welding, and an exhaust pipe or a connecting conductor electrically connected to an airtight case is fixed to the electrode end plug by pressure welding.

(Function) The present invention provides reliable welding between the outer electrode and the electrode end plug connected to the open end thereof, and a metal exhaust pipe or connection electrically connected to the electrode end plug and the airtight case. Since the conductive wire is firmly connected by pressure welding, a reliable electrical connection can be obtained. In addition, there is no occurrence of foreign objects in the tube such as splash! It is possible to obtain a fission-type ionization chamber for neutron detection with high performance.

(Example) An example will be described below with reference to the drawings. Identical parts are designated by the same reference numerals.

Figure 1 shows the main parts in the completed state. Cylindrical airtight case 1 made of a conductor such as ausbunite stainless steel
Inside 1, a cylindrical outer electrode (cathode) 12 made of titanium (Ti) is disposed along the inner wall.

A layer 13 of fissile material, such as uranium-235, is deposited on a predetermined area of the inner peripheral surface of the outer electrode 12.

A cylindrical inner electrode (anode) 14 is arranged inside the outer electrode 12 with a predetermined gap 20 in between. This inner electrode 14 has both end portions formed with a small diameter, and these small diameter end portions 14a and 14b are held by a ring-shaped ceramic insulating spacer 15.21 made of an alumina ceramic cap. A coaxial cable 22 is connected to one end of the airtight case 11, and its inner conductor 23 is connected to the small diameter end 14b of the inner electrode via an inner conductor lead wire 24, and its outer conductor 25 is connected to the tapered end of the airtight case 11. connected to the end. The minute gap 20 between the inner and outer electrodes is a gas space, which is filled with an ionizing gas such as argon. Note that a power source 26 and a display 27 are connected to the coaxial cable 22 for measurement.

Therefore, a cylindrical electrode end plug 31 made of the same material, that is, titanium, is fitted into the open end of the outer electrode 12, and several points on the outer periphery are joined at welded joints B. An insulating spacer 16 is provided in the space between this end plug and the small diameter end portion 14a of the inner electrode to ensure insulation between the two. Further, a protruding cylindrical part 32 is integrally formed in the center of the electrode end plug 31, and one end part of a thin stainless steel connecting lead wire 33 is inserted into the protruding cylindrical part 32 and connected at a pressure contact part C. Furthermore, by inserting these somewhere, the stainless steel case end plug 34 closes the open end of the airtight case 11 and
The entire circumference is hermetically sealed at the airtight welded part A.

The case end plug 34 integrally forms an exhaust pipe portion that communicates with the central through hole 35. The other end of the connecting conductor 33 is extended at least to the airtight sealing cut 37 of the exhaust pipe section,
They are sandwiched at the sealing cut portion of the exhaust pipe and integrally rounded and welded. Note that the center through hole 35 is connected to the case end plug 3.
The ventilation slit 34a formed in 4, the electrode end plug 31
It communicates with the gap 20 between the inner and outer electrodes via a flat cut surface 31a formed on a part of the outer periphery of the insulating spacer 15 and a flat portion 15a similarly formed on the insulating spacer 15.

Next, the main parts will be explained according to the preferred assembly order. First, a cylindrical outer electrode 12 made of titanium is subjected to the necessary chemical treatments, and then a layer 13 of fissile material is deposited on its inner surface. On the other hand, as shown in FIGS. 2 and 3, an electrode end plug 31 made of a conductor and made of the same material as the outer electrode is prepared. This electrode end plug 31 has a cylindrical portion 31b having an outer dimension approximately corresponding to the inner diameter of the outer electrode 12, and a large-diameter locking portion 31c having the same outer dimension as the outer diameter. Also, one end 33 of a connecting conductor 33 made of the same material as the metal exhaust pipe, that is, stainless steel, is attached to the protruding cylindrical portion 32.
Insert a and arrow ``as shown]] just (as shown)
The protruding cylindrical portion is pressed from the outside to mechanically and electrically press-contact it. The connecting conductor has a diameter of approximately 0.5 mm and has a length extending from this pressurized connection C to at least the sealing cut of the exhaust pipe. The electrode end plug 31 thus constructed is fitted to the end 12a of the outer electrode. Then, the two parts are joined together circumferentially, as indicated by arrow P, or at several locations as indicated by X marks, by edge arc TIG (TIG) welding. Since both are made of the same metal material, titanium, they can be easily connected by TIG welding with good welding conditions without splashing.

Next, a case end plug 34 having an exhaust pipe portion, which is a combination of internal electrodes, insulating spacers, etc., is fitted to the end portion 11a of the airtight case 11 while passing the connecting wire 33 through its center hole. Then, the entire circumference of the seam between the two is airtightly joined by dig welding. After assembling in this manner, the inside is evacuated from the exhaust pipe section 36, and ionizing gas at a predetermined pressure is filled. Finally, the exhaust pipe section 36 is crushed at a predetermined depth with the end 33b of the connecting conductor 33 sandwiched therein, sealed and cut, and then both are melted and rolled into a hemispherical shape and welded. Since both are of the same type of metal, electrical and vacuum-tight connection and closing of the sealing cut portion can be performed reliably and easily.

In this way, the outer electrode is electrically connected to the airtight case via the outer electrode end plug welded to the electrode, the conductor pressure-welded to the outer electrode end plug, and the case plug having the exhaust pipe section,
This is electrically connected to the outer conductor of the coaxial cable. In this electrical connection path, similar metal materials are connected by TIG welding, and dissimilar metals are connected by pressure welding, so all connections have a good connection condition.
It will be done.

In the embodiment shown in FIG. 4, a spiral portion 33c is formed in a part of the connecting conductor 33. Also, a relatively large-diameter recess 35a that surrounds this spiral portion in the case end plug 34 without contacting it.
It is formed.

According to this embodiment, since the spiral portion is formed in the connecting conductor, there is no risk of the connecting conductor being cut in the middle even when the exhaust pipe is crushed and sealed or there is a thermal expansion cycle during use. reliability is further improved.

In the embodiment shown in FIG. 5, the airtight case 11 includes a case 9J,
: The stopper 34 is integrally formed and the whole is made of stainless steel,
A pipe-shaped gold-bottomed exhaust pipe 36 made of the same type of stainless steel is hermetically joined to the welded portion of the small-diameter end 34b. A protruding cylindrical portion 32 is integrally formed on the titanium electrode end plug welded to the outer electrode, and the protruding cylindrical portion 32 extends from the extended open inner end 36a of the exhaust pipe 36.
2 and mechanically and electrically connected by pressure welding. A vent hole 36b is formed in a portion of the exhaust pipe 36 near the pressure contact portion, so that the inside of the pipe can be exhausted.

In the ionization chamber of this embodiment, a metal exhaust pipe is directly connected to the electrode end plug by pressure welding, and this exhaust pipe is electrically connected to the airtight case by TIG welding or the like in a vacuum-tight manner. In this way, the exhaust pipe itself is used as an electrical connection conductor for the outer electrode, so the number of parts is small.

A3: It is important to select the same type of metal material for both the outer electrode and the electrode end plug welded thereto, which have good weldability and do not cause splash during welding. For this purpose, it is preferable to use titanium or a titanium alloy for both, to which a fissile material layer can easily be attached, as in the above embodiment. However, it is not limited to this. In addition to TIG welding, welding methods include laser welding, electron beam welding, and hard soldering.

[Effects of the Invention] As explained above, according to the present invention, the electrical connection between the airtight case connected to the outer conductor of the coaxial cable and the outer electrode is achieved by connecting the metal exhaust pipe directly or by shorting it to the exhaust pipe. Since it is connected to the electrode end plug by pressure welding through the connecting conductor wire, the reliability of the electrical connection is significantly improved. By forming the outer electrode and the electrode end plug from the same type of metal material, there is no risk of splash occurring during welding, and there is no risk of splash entering the gap between both the inner and outer electrodes and causing a short circuit between the electrodes.

In this way, a highly reliable fission type ionization chamber for neutron detection can be obtained.

[Brief explanation of drawings]

FIG. 1 is a vertical cross-sectional view of a main part showing an embodiment of the present invention, FIG. 2 is an assembled perspective view thereof, FIG. 3 is an assembled cross-sectional view thereof, and FIGS. A sectional view of the main part showing the embodiment, and FIGS. 6 and 7 are longitudinal sectional views of the main part showing the conventional structure, respectively. 11... Airtight case, 12... Outer electrode, 14...
...Inner electrode, 20...Gap, 22...Coaxial cable, 31...Electrode end plug, 32...Protrusion part,
33... Connection conductor, 34... Case end plug, 37
...Sealing cut part, △, B...Welding part, C...Pressure welding part.

Claims (6)

[Claims] (1) A cylindrical outer electrode and an inner electrode are provided with a predetermined gap in an airtight case made of a conductor, this gap is filled with ionizing gas, a coaxial cable is connected to one end of the airtight case, and the other is In a fission type ionization chamber for neutron detection, in which a case end plug having a metal exhaust pipe sealed and cut at the end is joined, and the outer electrode is electrically short-circuited to the airtight case, the outer electrode has an exhaust pipe. An electrode end plug made of a conductor is fixed to the side end by welding, and an exhaust pipe or a connecting conductor electrically connected to the airtight case is fixed to the electrode end plug by pressure welding. Fission type ionization chamber for neutron detection. (2) The fission type ionization chamber for neutron detection according to claim 1, wherein the outer electrode and the electrode end plug are formed of the same kind of metal material. (3) The fission type ionization chamber for neutron detection according to claim 2, wherein the outer electrode and the electrode end plug are both made of titanium or a titanium alloy. (4) The fission type ionization chamber for neutron detection according to claim 1, wherein the metal exhaust pipe, the case end plug, and the airtight case are all made of the same kind of metal material. (5) The metal exhaust pipe, the case end plug, and the airtight case are all made of stainless steel.
Nuclear fission type ionization chamber for neutron detection as described in section. (6) The neutron detection device according to claim 1, wherein the connecting conductor and the exhaust pipe are made of the same kind of metal material, and the connecting conductor is sandwiched between the exhaust pipe, sealed, cut, and welded together. Fission type ionization chamber.