JPS6064295A - 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 of the Invention] The present invention relates to a fuel assembly capable of capturing and retaining radioactive corrosion products contained in the coolant of a nuclear reactor in a reactor core.

[Prior art and its problems]

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

By the way, in the case of fast breeder reactors, the cladding tubes and core structures of the nuclear fuel elements are usually made of stainless steel, but when these constituent materials are irradiated with neutrons, they are Iron, cobalt, etc. cause a nuclear reaction, and a large amount of radionuclides such as manganese-54, cobalt-60, cobalt-58, etc. are produced. This constituent material is corroded by the above-mentioned alkaline earth metal used as a coolant and released into the coolant. At this time, the aforementioned radionuclides are also released into the coolant, and so-called radioactive corrosive acids are 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 the radioactive corrosion products deposited on the walls of the primary cooling system can be absorbed by a number of devices such as pumps, heat exchangers, valves, and flow meters, as well as piping connected to these devices. Failure to do so may impede maintenance, repair work, etc. In particular, there are many production residues such as manganese-54, cobal-1-60, cobalt-58, etc.
It has a long half-life, so the effect is significant.

Therefore, in order to eliminate such problems.

Recently, a J-injection corrosion product capture device has been developed that utilizes the property of nickel to efficiently capture radionuclides such as manganese-54 and cobalt-60 in high-temperature liquid metal sodium. It is considered to be installed inside the reactor vessel.This radioactive corrosion product capture device has a number of elements containing the capture material such as nickel placed above the reactor core, facing the coolant outlet of the reactor core. The radioactive nuclides are captured by bringing the extra coolant flowing out from the core into direct contact with the capture material.

The efficiency of the above-mentioned equipment is limited (in order to capture radionuclides, the contact area between the capture material and the cooling chest needs to be at least 6°C, and there is a concern that the equipment itself will become larger). That is, in order to actually install the above-mentioned device, the upper core mechanism and the reactor vessel must be enlarged, which poses the problem of increasing the construction cost of the reactor plant.

[Purpose of the invention]

The present invention was made in view of the above circumstances, and its purpose is to perform a radionuclide capture function on the fuel assembly itself forming the reactor core without increasing the size of the fuel assembly. It is an object of the present invention to provide a fuel assembly that can contribute to downsizing of the upper core mechanism and reactor vessel and to a reduction in the construction cost of a nuclear reactor plant.

[Summary of the invention]

In the present invention, nine of the grid spacers installed to maintain the spacing between a plurality of fuel elements, for example, the grid spacer on the downstream side with respect to the flow of coolant, that is, on the upper part of the reactor core, are made of metal plates such as nickel or mesh. This is a fuel assembly equipped with a radionuclide trap consisting of:

〔Effect of the invention〕

The coolant that flows into the fuel assembly from the entrance nozzle flows along the fuel elements through the gaps between the fuel elements and flows out from the handling head, so the grid spacer is placed in the coolant flow path within the fuel assembly. It takes shape. Therefore, in the above-mentioned (R configuration), when the coolant containing radionuclides flows through a part of the grid spacer on the downstream side, that is, the upper part of the reactor core, the radionuclide trap reduces the cross-sectional area of the flow path and cools the coolant. The flow rate of the material increases and the flow is disturbed.As a result, the boundary layer formed on the surface of the trap becomes thinner, making it easier for radionuclides to diffuse in the boundary I meat, resulting in a large amount of radionuclides being released. It comes into contact with the trap and is captured.Therefore, the radionuclides contained in the cooling phase can be prevented from flowing out of the reactor vessel.

In the present invention, since the grid spacer is equipped with the radionuclide trap, a mechanism for supporting the trap on the fuel assembly is required (the trap is installed in the gap between the fuel elements. .

There is no need to increase the size of the fuel assembly (radioactive nuclides can be captured, and therefore the reactor vessel does not need to be enlarged, which ultimately contributes to preventing the plant from becoming more expensive).

[Embodiments of the invention]

FIG. 1 is a cross-sectional view showing a schematic configuration of a fuel assembly according to an embodiment of the present invention, in which a fuel element 1 is placed in a trumpet tube 2 with a grid spacer 3, which has a function of restraining the fuel element group on the outside.
Therefore, the fuel elements are housed with a constant distance ζ maintained between them. FIG. 2 is a perspective view of the radionuclide trap 4 and part of the fuel element 1 attached to the grid spacer 3. The radionuclide trap is a nickel plate, and the stainless steel grid spacer 3 installed downstream of the coolant flow.

With such a configuration, when the coolant flowing through the gap 5 between the fuel elements flows through a portion of the grid spacer,
Since the cross-sectional area of the flow path is narrowed by the radionuclide trap 4, the flow rate of the coolant increases and the flow is disturbed. For this reason, the boundary layer formed on the surface of the trap becomes thin, making it easier for radionuclides mixed in the coolant to diffuse within the boundary layer. The length of the trap (approximately 1m)! Because there is a strain "C", the 1χ contact volume between this trap and the coolant is large.As a result, the radionuclides mixed in the coolant are transferred to the trap. on the surface
contact easily and reliably. Since the above trapping device is made of highly active nickel, the radioactive nuclei [1] that come into contact with it are exposed to the cape of the trapping device, and the above-mentioned effect is obtained.

[Spiritual oil seed fili1911] The present invention is not limited to the above-mentioned '-q bs example. In the actual example, a nickel plate was used for the radionuclide trap, but a mesh plate may also be used. ? f. It may be a plate with an uneven surface, and the shape may be cylindrical. Further, the material may be stainless steel with nickel plating on 1 surface of nickel alloy or nickel alloy with nickel plating on 8 surfaces.

[Brief explanation of the drawing]

FIG. 1 is a cross section U4 showing a schematic configuration of a fuel assembly according to an embodiment of the present invention, and FIG. 2 is a perspective view. DESCRIPTION OF SYMBOLS 1...Fuel element, 2...Trumpet pipe, 3...Grid spacer, 4...Radioactive nuclear capture device, 5...Gap between fuel elements, L...Cooling material. Representative Patent Attorney Kensuke Chika (and 1 other person) Figure 1 Figure 2

Claims (3)

[Claims] (1) In a fuel assembly comprising a grid spacer that holds a plurality of fuel elements at predetermined intervals, a radionuclide capture device consisting of a metal plate or metal mesh for capturing radionuclides is attached to the grid spacer. A fuel assembly characterized by comprising: (2) A patent claim characterized in that the radionuclide trap is formed of at least one of nickel, stainless steel with nickel plating on the surface of the nickel alloy, and nickel alloy with the surface of the nickel plating. Range 1
Fuel assembly as described in section. (3) The fuel assembly according to claim 1, characterized in that the radionuclide trap is provided downstream with respect to the flow of coolant for cooling the fuel elements.