JPH0634075B2 - Irradiation assembly with instrumentation - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of Invention] (Field of Industrial Application) The present invention relates to an instrumented irradiation assembly.

(Prior Art) In order to elucidate the behavior of nuclear fuel and structural materials in a nuclear reactor, an instrumented irradiation assembly capable of online measurement is used. Usually, the irradiation assembly is provided with a flow meter for measuring the coolant flow rate. Thus, the signal line for transmitting the measurement output of the flow meter is drawn out via the environment of high temperature and high radioactivity. Therefore, a permanent magnet type that can obtain a stable output signal is often used as the flowmeter.

FIG. 7 is a transverse sectional view of an example thereof. In this figure,
A pair of permanent magnets 2 and 3 having a different diameter and facing each other are installed at a position where the flow rate of the coolant channel pipe 1 is to be measured. Further, the electrode 4 and the electrode 5 are arranged facing each other on a diameter orthogonal to the one diameter. In the figure, 6 is a casing surrounding and supporting the permanent magnets 2 and 3, 7 is a signal line connected to the electrode 4, 8
Indicates the signal lines connected to the electrodes 5, respectively.
Any material may be used as the material of each electrode 4 and 5 as long as it is a conductive material, but since it is welded to the flow path pipe 1, it is desirable to use the same material as this.
Further, since the signal lines 7 and 8 are used under high temperature and high radioactivity, they are inorganic insulated cables. Austenitic stainless steel, copper or copper alloy is used for the cable core wire, and magnesium oxide or aluminum oxide is used for the insulator. Austenitic stainless steel is used as the coating material. Further, the permanent magnets 2 and 3 are usually rare earth magnets (for example, SmCo ₅ ) having excellent high temperature characteristics. The core wire of each signal wire is connected to each corresponding electrode by welding or brazing, and the covering material is hermetically welded to the flow path pipe 1.

FIG. 8 is a diagram showing a magnetic field line distribution in the permanent magnet type flow meter having the above-mentioned configuration. As can be seen from this figure, most of the magnetic lines of force from the N pole of the permanent magnet 3 cross the coolant passage tube 1 and enter the S pole of the permanent magnet 2 and exit from the N pole of the permanent magnet 2. Most of the lines of magnetic force bypass the coolant channel pipe 1 casing 6 and enter the S pole of the permanent magnet 3.

In the flowmeter having the above structure, when the electromagnetic fluid flows in the flow path tube 1, an electromotive force in the direction perpendicular to the magnetic field lines is generated in proportion to the flow rate of the electromagnetic fluid. This electromotive force is taken out of the reactor by a signal line connected to the electrodes 4 and 5, and the flow rate is measured.

Thus, in order to maintain the insulation of the signal lines 4 and 5 and prevent the deterioration of the material, and also to prevent the deterioration of the material of the permanent magnet, both of them are kept in an inert gas or dry air by the casing 6. It is sealed. In order to form this closed structure, it is necessary to use a welded structure because the installation location of the flowmeter is a high temperature and high radioactivity environment. However, since the welding arc is a high-temperature plasma and is a flow of charged particles, it causes an electromagnetic interaction with the lines of magnetic force from the strong permanent magnets 2, 3.

That is, the welding for sealing the signal lines 7 and 8 and the permanent magnets 2 and 3 in the casing 6 is made around the casing 6, and the arc of the welding is performed while the welding is performed. It is bent under the influence of distribution. Therefore, the welding line is usually set at a position as far as possible from the permanent magnets 2 and 3. However, then the distribution of the lines of magnetic force becomes three-dimensional. Moreover, the effect of magnetic field lines cannot be completely escaped. Therefore, when welding is performed, it is necessary to consider the bending state of the welding arc due to the distribution of the magnetic force lines, and the welding operation is extremely difficult.

Actually, we try to carry out welding after making some trials and obtaining sufficient enthusiasm, but it is not possible to ignore the practice time and waste of practice materials for that, and it is sufficient. Even after practice, the yield of products was low, and the cost increase was inevitable.

(Problems to be Solved by the Invention) As described above, in the instrumentation irradiation assembly including the permanent magnet type flow meter of the conventional structure, the welding arc is generated during the welding operation for sealing the flow meter signal line and the permanent magnet. Since it bends under the influence of the distribution of magnetic field lines, welding work is extremely difficult, which not only increases the manufacturing cost of the flowmeter, but also requires a long time for manufacturing.

In order to avoid this, it is necessary to significantly reduce the magnetic field lines at the welding line. The simplest way is to keep the weld away from the permanent magnet sufficiently so that the lines of magnetic force do not reach the weld. However, since the instrumented irradiation assembly is mounted in the reactor core in the same manner as the fuel assembly and the control rod, its shape and dimensions cannot be arbitrarily set, and the fuel assembly, It is necessary to match the control rod and shape. Therefore, the flow meter must be made compact, and the welded part and the permanent magnet cannot be sufficiently separated from each other as described above.

The present invention has been made based on the above circumstances, has a compact structure and is not affected by the distribution of magnetic force lines.
It is an object of the present invention to provide an instrumentation irradiation assembly that can easily and easily perform welding for easily obtaining a signal line and a permanent magnet seal.

[Structure of the Invention] (Means for Solving the Problems) An instrumented irradiation assembly of the present invention is provided in a trumpet tube having a handling head at one end and an entrance nozzle at the other end, and in the trumpet tube. An irradiation sample part, a flow path pipe that is connected to the entrance nozzle opening at one end thereof and is connected to the irradiation sample part at the other end, and is installed at both ends of one diameter of the flow path pipe, and the different electrodes are opposed to each other.
A pair of permanent magnets and a permanent magnet type flow meter having a pair of electrodes mounted on the flow path tube and located on a diameter perpendicular to the one diameter, the circle between the pair of permanent magnets. A holding metal fitting made of a magnetic material is attached to the circumferential gap.

(Operation) In the instrumented irradiation assembly of the present invention having the above-mentioned configuration, since the holding metal fitting made of a magnetic material is mounted between the pair of permanent magnets constituting the flow meter, the leakage of the magnetic force lines is drastically reduced. It is possible to prevent bending of the welding arc during welding work. Therefore, the welding for forming the space for sealing the permanent magnets, the signal lines, etc. and isolating them from the reactor coolant becomes very easy. Further, since the welded part may be a part close to the permanent magnet, the axial dimension of the instrumented irradiation assembly can be easily matched with other core constituent elements.

(Embodiment) FIG. 1 is a longitudinal sectional view of an embodiment of the present invention, and FIG. 2 in which the same parts as those in FIGS. 7 and 8 are denoted by the same reference numerals is a transverse sectional view of a permanent magnet type flow meter. FIG. 3 is a vertical cross-sectional view showing at the same time a cross section of the flowmeter intersecting at 90 °. First, the details of the embodiment of the present invention will be described with reference to FIG. In this figure, an entrance nozzle 13 into which a coolant flows is provided at the other end of a trumpet tube 12 having a handling head 11 at one end, and a flow connecting an opening of the entrance nozzle 13 and an irradiation sample section 14 in the trumpet tube. A permanent magnet type flow system 15 is provided so as to surround the passage pipe 1. Reference numeral 16 in the drawing denotes an orifice provided at the entrance of the entrance nozzle.

In FIG. 2, a holding member 9 and a holding member 10 made of a magnetic material such as pure iron are attached between the permanent magnets 2 and 3. The holding metal fittings 9 and 10 form a yoke, and the leakage of magnetic force lines to the outside of the casing 6 is almost eliminated. Also,
Since the casing 6 is made of a non-magnetic material such as austenitic stainless steel, for example, SUS316, like the other core internal structures, the magnetic force lines passing through the inside can be ignored.

Therefore, even if welding is performed near the permanent magnets 2 and 3,
There is no influence of the magnetic field lines on the welding arc, and the welding can be performed simply and easily as in ordinary welding. In addition, the electrodes 4 and 5 and the flow path tube 1, the electrodes 4 and 5 and the signal lines 7 and 8
Needless to say, since welding with and is performed before assembling the permanent magnets 2 and 3 and the flow path pipe 1, these are easily welded.

As described above, since welding can be performed in the vicinity of the permanent magnet to seal the permanent magnet and the like, the permanent magnet type flow meter 15
Since the axial dimension thereof can be made small and compact, the instrumented irradiation assembly of the present invention can be matched in outer shape and size with other core mountings such as fuel assemblies.

Furthermore, in the above embodiment, since the two permanent magnets 2 and 3 are connected by the holding metal fittings 9 and 10, an efficient magnetic circuit is formed, and the permeance coefficient of the magnetic circuit increases, The magnetic flux density in the flow path tube 1 sandwiched between the permanent magnets 2 and 3 is increased. As a result, when the permanent magnets having the same performance are used, the obtained flow signal level becomes higher than that of the conventional flow meter, the S / N ratio is improved, and a high performance flow meter can be obtained.

FIG. 4 in which the same parts as those in the previous figures are denoted by the same reference numerals is a perspective view of the essential parts of a second embodiment of the present invention. In this embodiment, each of the holding fittings 9 and 10 is provided with a window hole (only the window hole 10a of the holding fitting 10 is shown in the figure) to increase the surface area of the holding fitting. If the material of the holding metal fitting is appropriately selected, even if the above-mentioned window is provided, magnetically sufficient characteristics are exhibited, and the same operation and effect as those of the above-mentioned embodiment can be obtained.
Further, by increasing the surface area as described above, the heat dissipation is improved, and the temperature rise can be suppressed by the irradiation of neutrons, gamma rays and the like.

FIG. 5 is a perspective view showing a third embodiment of the present invention. In this embodiment, the holding metal fittings 9 and 10 are composed of two arcuate members (only the members 10 ₁ and 10 ₂ forming the holding metal fitting 10 are shown in the figure) arranged apart from each other in the axial direction. It is configured. Also in this embodiment, the same operation and effect as those of the second embodiment can be obtained.

FIG. 6 is a cross-sectional view of the essential parts of a fourth embodiment of the present invention.
In this embodiment, the cylindrical magnetic path 20 having a two-divided structure is attached to the outer periphery of the casing 6 at positions corresponding to the permanent magnets 2 and 3 only during welding. Also in this embodiment, leakage of magnetic lines of force is prevented, and the welding arc is not bent even if welding work is performed near the permanent magnet.

[Advantages of the Invention] In the instrumentation irradiation assembly of the present invention having the above-mentioned configuration, since the holding metal fitting made of a magnetic material is mounted between the pair of permanent magnets constituting the flowmeter, leakage of magnetic field lines is prevented. It can be drastically reduced, and there is no risk of bending the welding arc during welding work. Therefore, the part to be welded to form a space for sealing the permanent magnets, signal lines, etc. and isolating them from the reactor coolant may be a part near the permanent magnets. The axial dimensions of the body can be easily matched with other core components. Further, since the holding metal member forms a magnetic path between the permanent magnets, the magnetic flux density in the flow passage tube can be increased, and the instrumentation irradiation assembly has high sensitivity and good S / N ratio. be able to.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view of an embodiment of the present invention, FIG. 2 is a horizontal cross-sectional view of the main part thereof, FIG. 3 is an enlarged cross-sectional view of the main part, and FIG. 4 is a modification of the main part. FIG. 5, FIG. 5 is a perspective view of another modification of the main part, FIG. 6 is a cross-sectional view of still another modification of the main part, and FIG. 7 is a conventional permanent magnet type flow meter. FIG. 8 is a schematic cross-sectional view showing the distribution of the lines of magnetic force. 1 ... flow path tube, 2, 3 ... permanent magnet, 4, 5 ... electrode,
6 ...... casing, 7,8 ...... signal line, 9,10 ...... holding metal fitting, 10a ...... window opening, 10 _1, 10 ₂ ...... member, 11
...... Handling head, 12 ...... Trumpet tube, 13 ......
Entrance nozzle, 14 ... Irradiation sample part, 15 ... Flowmeter, 16 ... Orifice, 20 ... Cylindrical magnetic path

Claims (1)

[Claims] 1. A trumpet tube having a handling head at one end and an entrance nozzle at the other end, an irradiation sample portion provided in the trumpet tube, and an irradiation sample connected to the entrance of the entrance nozzle at one end and the irradiation sample at the other end. Part of the flow path pipe, a pair of permanent magnets located at both ends of one diameter of the flow path pipe and having opposite poles facing each other, and a diameter of the permanent magnet attached to the flow path pipe and perpendicular to the one diameter. And a permanent magnet type flow meter having a pair of electrodes positioned in a pair of electrodes, a holding metal fitting made of a magnetic material is attached to a circumferential gap between the pair of permanent magnets. Irradiation assembly.