JPS6064294A - Fuel aggregate - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] [Technical field to which the invention pertains] The present invention is capable of capturing and retaining radioactive corrosion products contained in liquid metal used as a coolant in a fast breeder reactor in a reactor core. The present invention relates to a fuel assembly l having the following structure.

[Prior art and its problems]

In fast breeder reactors, an alkaline liquid metal represented by liquid sodium is generally used as a coolant. After being heated in the reactor core installed inside the reactor vessel, such static metal coolant is guided to the primary cooling system installed outside the reactor vessel, and then returned to the inside of the reactor vessel. is returned and circulated.

By the way, in the case of a fast breeder reactor, the fuel element summer tube, the wrapper tube that functions as an outer restraint for the fuel element group, and the core structure are usually made of stainless steel, but these components are different from each other. When the material is irradiated with neutrons, the iron contained in the constituent material is removed.

Cobalt and the like cause a nuclear reaction, and a large amount of radionuclides such as manganese-54, cobalt-60, and cobalt-58 are produced. The side slopes of this configuration are corroded by the aforementioned alkaline earth metals used in the design and are released into the coolant. At this time, the aforementioned radionuclides are also released into the coolant,
So-called radioactive corrosion products will be mixed into the coolant.

The radioactive corrosion products mixed into the coolant are carried to the primary cooling system according to the flow of the coolant, and are deposited on the walls of the piping of primary cooling system equipment such as intermediate heat exchangers.

In this way, the radioactivity of radioactive corrosion products deposited on the walls of the cooling system can be used for maintenance, repair, etc. of equipment such as pumps, heat exchangers, pulp, mud gauges, and piping connected to these equipment. impede the work of・Especially manganese-54, Kobal 1
--6o, cobalt-58, etc. have a large number of formation layers and a long half-life, so their effects are large.

Therefore, in order to eliminate such problems, recently it has been considered to install a radionuclide capture device using a radionuclide capture material such as nickel inside the reactor vessel. This radioactive corrosion generation J snout capture device has a plurality of elements containing capture material arranged opposite to the coolant outlet of the reactor core, that is, at the top of the core, and brings the capture material into direct contact with the coolant flowing out from the core. This allows radioactive corrosion products to be captured.

Some conventional capture devices, such as those described above, require space above the core when installed. The space is said to be approximately 30 cm in order to efficiently capture radioactive corrosion products. Therefore, in order to install the above capture device,
The reactor vessel must be made larger. As a result, the reactor building also needs to be larger, resulting in the problem of increased construction costs for the reactor plant.

Furthermore, in order to avoid the above-mentioned problems, it has been considered to install a capture device above the fuel rods in the fuel assembly. However, in this case, there is a problem in that the outer circumferential surface of the trumpet tube of the fuel assembly corrodes, making it impossible to capture radioactive corrosion products released into the coolant.

[Purpose of the invention]

The present invention has been made in view of the above circumstances, and its purpose is to provide a trapping effect for radioactive corrosion products on the outer circumferential surface of a fuel assembly without increasing the size of the fuel assembly. It is an object of the present invention to provide a fuel assembly that can prevent the reactor vessel from becoming too large and contribute to reducing the construction cost of a nuclear reactor plant.

[4th Summary of the Invention] The present invention provides a fuel assembly consisting of a handling head, a trumpet pipe, an entrance nozzle, a fuel element, and a fuel element support assembly (1?). Nickel plating is applied to the surface.1.
This is a fuel assembly equipped with a radioactive 1i''i eclipse trapping device made of stainless steel or nickel alloy wire with nickel plating and holes on the surface.

〔Effect of the invention〕

With the above configuration, the radioactive corrosion products contained in the coolant flowing through the gaps between the fuel assemblies flow along the outer peripheral surface of the fuel assemblies, and in the process of flowing out to the upper part of the reactor core, the radioactive corrosion products reach the handling head of the fuel assemblies. The radioactive corrosion products are captured by a capture device formed on the outer circumferential surface. In this case, the fuel assemblies to be unloaded into the reactor are core fuel assemblies in large reactors,
There were approximately 600 radial planfoot fuel assemblies in total, and capture devices were attached to these fuel assemblies. The surface area can be made very large. And, because the above-mentioned capture device is formed by wire, it is only 3%.

Its surface is more uneven than that of the fuel assembly's trumpet tube, which disrupts the flow of coolant. As a result, the so-called boundary JZ is created in the trapping device portion, and the radioactive corrosion products can be easily diffused within the boundary layer, so that a large amount of the radioactive corrosion products can be reliably captured.

Therefore, the radioactive corrosion products contained in the coolant that fills the gap between the fuel assemblies can be prevented from flowing out of the reactor vessel. Incidentally, the radioactive corrosion products contained in the coolant flowing through the fuel assembly can be captured by installing a capture device on the upper part of the fuel rod as in the conventional method. In the present invention, radioactive corrosion products can be captured without the need to make the fuel assembly particularly large, and therefore the reactor vessel does not need to be enlarged, which ultimately contributes to preventing the high cost of nuclear reactor plants. .

[Embodiments of the invention]

FIG. 1 is a perspective view showing a schematic configuration of a fuel assembly according to an embodiment of the present invention.

A handling head 1, an internal fuel element (not shown), a fuel element support mechanism, a wrapper tube 2 having functions such as external restraint, and a coolant are introduced into the fuel assembly (
It consists of an entrance nozzle 3 having multiple layers, and a radioactive corrosion product capture device 4 made of a 21 tsukel wire wound multiple times around the outer peripheral surface of the handling head.

A spacer pad 5 for maintaining a gap between the fuel assemblies is attached to the outer periphery of the handling head 1 and the trumpet tube 2, and the entrance nozzle 3
An orifice hole 6 is provided in the fuel assembly for introducing coolant into the fuel assembly.

The thickness of the wire wound around the handling head 1 is smaller than the thickness of the spacer pad 5.

With this configuration, the coolant that has not flowed into the fuel assembly through the orifice hole 6 of the entrance nozzle 3 flows through the gap between the fuel assemblies.

Then, when flowing through the radioactive corrosion product capture device section,
Since the flow path of the capture device section is narrow, the cooling 1'
Since the flow velocity of L becomes faster (and its shape is different from that of the wrapper tube part), the flow n is disturbed. Therefore, in the radioactive corrosion product capture device part, the boundary layer formed on the surface becomes thinner,
The outer periphery of the wrapper tube 2 is corroded, and radioactive corrosion products mixed into the coolant can easily diffuse within the boundary layer. Also,
Since the radioactive corrosion product trapping device is formed by winding the wire many times, the contact area between the trapping device and the coolant is large. As a result, the radioactive corrosion products mixed in the coolant can easily and reliably come into contact with the surface of the capture device. Since the trapping device is made of highly active nickel, the radioactive corrosion products that come into contact with it are captured by the trapping device17, thereby providing the above-mentioned effect.

[Other embodiments of the invention]

The invention is not limited to the embodiments described above. In the embodiment, a wire made of nickel was used for the capture device, but a wire made of stainless steel with nickel plating on the surface of nickel alloy 1 or a wire made of nickel alloy with nickel plating on the surface may also be used.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing a schematic structure of a fuel assembly according to a first embodiment of the present invention. 1... Handling head, 2... Trumpet tube, 3.
... Entrance nozzle, 4... Radioactive corrosion product capture device, 5... Spacer bud, 6... Orifice hole, L... Coolant. Representative Patent Attorney Noriyuki Chika (and 1 other person) Figure 1

Claims (1)

[Claims] (11) In a fuel assembly consisting of a handling head, a rattank pipe, an entrance nozzle, a fuel element, and a fuel element support mechanism, a radioactive corrosion product capture device is provided around the outer periphery of the link head. A fuel assembly characterized by: (2) A fuel assembly as described in claim 1, characterized in that the radioactive corrosion product capturing device is a metal wire for capturing radioactive corrosion products. . (3) The fuel assembly according to claim 2, wherein the wire is made of nickel, nickel alloy, nickel-plated stainless steel, or nickel-plated Ni-Nokel alloy.