JPS60168080A - 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 in which radioactive corrosion products contained in the coolant of a nuclear reactor are captured and retained in the reactor core. .

[Prior art and its problems]

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

By the way, in the case of fast breeder reactors, the fuel element cladding and core structure 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 material is corroded by the aforementioned alkaline earth metal used as a coolant and is released into the coolant. At this time, the aforementioned radionuclides are also released into the coolant, and so-called radioactive corrosion products 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 radioactive corrosion products deposited on the walls of the primary cooling system can be removed by maintenance and repair of equipment such as pumps, heat exchangers, valves, flowmeters, and the piping connected to these equipment. or other work. Special ζotmangan-54. this(
Luto 60. Konoku Cito-58 and the like have many production connections and a long half-life, so this has a large effect.

Therefore, in order to solve this problem, recently, nickel has been treated with temanganese in high-temperature liquid metal sodium.
54. It is being considered to install a radioactive corrosion product capture device inside the reactor vessel that takes advantage of the property of Kono (Luto 60) to efficiently capture radionuclides. The product capture device has a plurality of elements containing the capture material such as nickel arranged opposite to the coolant outlet of the reactor core, that is, above the core, and brings the coolant flowing out from the core into direct contact with the capture material. This allows radionuclides to be captured.

When installing such a capture device, a space above the reactor core is required. The space is said to be approximately 30 cm in order to efficiently capture radioactive corrosion products. Therefore, in order to install the above-mentioned capture device, the reactor vessel must be made thicker. There is a problem in that the vessel becomes larger and the construction cost of the nuclear reactor plant increases.

[Purpose of the invention]

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

[Summary of the invention]

The present invention relates to a trumpet tube, a handling head, and an entrance nozzle each having a regular hexagonal cross-sectional shape.

In a fuel assembly consisting of a fuel element and a fuel element support mechanism, the handling head has an outer facing distance greater than the outer facing distance of the wrapper tube within a range that does not contact an adjacent fuel assembly, and the surface thereof is coated with nickel. It is a fuel assembly characterized by a plating treatment that gives the handling head the ability to capture radioactive nuclides.

〔Effect of the invention〕

According to the present invention, the coolant that does not flow into the fuel assembly through the entrance nozzle flows through the gap between adjacent fuel assemblies. Then, the hand IJ flows through the trumpet pipe section.
When the coolant reaches the 7th head section, the flow velocity becomes faster because the flow path cross-sectional area of the handling head section is smaller than that of the wrapper tube section.Therefore, the so-called boundary 1 threat formed on the surface of the handling head section As the wrapper tube becomes thinner and the outer periphery corrodes, it becomes easier for radionuclides mixed in the coolant to diffuse within the boundary 1. Therefore, a large amount of radionuclides is ensured in contact with the nickel-plated handling head. , is captured by the highly active nickel.As a result, it is possible to prevent the radionuclides contained in the coolant flowing through the gaps between the fuel assemblies from leaking out of the reactor vessel. The radionuclides contained therein can be captured by installing a capture device on top of the fuel element as in the conventional method.In the present invention, the radionuclides can be captured without the need to make the fuel assembly particularly large. Therefore, without increasing the size of the nuclear reactor, it is possible to prevent the cost of the nuclear reactor plant from increasing.

[Funny example of invention]

FIG. 1 is a perspective view showing the schematic structure of a fuel assembly according to an embodiment of the present invention, and this fuel assembly includes a handling head I (!: an internal fuel element and a fuel element support mechanism (not shown), It consists of a trumpet tube 2 that has functions such as external restraint, and an entrance nozzle 3 that has a function of introducing coolant into the fuel assembly.The above-mentioned handling head 1
A spacer pad 4 is attached to the outer peripheral surface of the wrapper tube 2 to maintain a gap between the fuel bundles, and an orifice hole is provided in the entrance nozzle 3 to introduce coolant into the fuel bundle. 5 is provided.

The cross section of the trumpet tube 2 and the handling head 1 is a regular hexagon, and the distance between the outer facing sides of the central part of the handling head 1 is smaller than the facing distance between the outer sides of the trumpet tube 2 by several mm than the facing distance of the spacer pad 4. It's a big deal. This part of the handling head 1 is nickel plated.

With such a configuration, when a large number of fuel assemblies are arranged, the coolant that has not flowed into the fuel assemblies through the orifice hole 5 of the entrance nozzle 3 flows through the gaps between the fuel assemblies. At this time, the activated outer circumferential surface of the trumpet tube corrodes, and radioactive nuclides such as Mn, Co, and Co are mixed into the coolant.When this coolant flows through the handling head, , handling head 1
Since the outer facing distance of the trumpet tube 2 is larger than the outer facing distance of the trumpet tube 2, the flow path cross section of the handling head becomes small.
The flow velocity of the coolant increases and the flow is disturbed.

For this reason, the boundary layer formed on the surface of the handling head becomes thin, making it easier for radionuclides mixed in the coolant to diffuse in the boundary layer. Contaminated radionuclides easily and reliably come into contact with the surface of the handling head.This part is coated with highly active nickel plating, so the radionuclides that come into contact are captured, producing the effect described above. .

[Other embodiments of the invention]

The invention is not limited to the embodiments described above. For example, it is better to make the distance between the handling head and the outside facing each other larger than the distance between the outside facing the trumpet tube (and it is even better if the surface is made uneven).

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing a schematic structure of a material assembly according to an embodiment of the present invention. 1... Handling head, 2... Trumpet tube, 3.
... Entrance nozzle, 4... Spacer pad,
5... Orifice hole, L... Coolant. Representative Patent Attorney Noriyuki Chika (and 1 other person) No. 1

Claims (1)

[Claims] A trumpet tube with a regular hexagonal cross-sectional shape, a handling head, an entrance nozzle, a fuel element, and a fuel g:
2. The handling head has an outer facing distance larger than the outer facing distance of the wrapper tube, and 11 the surface of the link head is nickel plated, and the outer peripheral surface of the handling head is coated with radioactive material. A fuel assembly characterized by being used as a nuclide trap.