JPS59160794A - Nuclear fuel rod - 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 relates to a nuclear fuel rod that is capable of capturing and retaining radionuclides in a coolant in a reactor core. [Prior art and its problems] ] In fast breeder reactors, an alkaline liquid metal, typically liquid sodium, is generally used as a coolant. After being heated in the reactor core installed inside the reactor vessel, such liquid metal coolant is guided to a rigorous intermediate heat exchanger installed outside the vessel, and then returned to the reactor vessel. and circulate.

By the way, in fast breeder reactors, the cladding tubes and core structures of the nuclear fuel rods are usually made of stainless steel, which has high corrosion resistance. However, stainless steel can still be corroded by liquid sodium. Since the constituent materials of the cladding and core structure are radioactive, if they are corroded as described above, radioactive corrosion products will be mixed into the coolant. The radioactive corrosion products mixed into the coolant are carried by the coolant to the intermediate heat exchanger system, and are deposited on the pipe walls of the intermediate heat exchanger system. In this way, radiation from radionuclides deposited on the walls of the intermediate heat exchanger system can be used to maintain equipment such as pumps, heat exchangers, pulp, flowmeters, and the piping connected to these equipment.

Obstructing repair work. Among radionuclides, manganese-54, Kobal)-60, Kobal)-58, etc. are produced in large quantities and have long half-lives, so their effects are large.

Therefore, in order to eliminate such problems, recently it has been considered to install a radioactive nucleation product extraction device using a radionuclide capture material such as nickel inside the reactor reactor. . This radioactive corrosion product capture device has a plurality of elements containing the capture material arranged opposite to the coolant outlet of the reactor core, that is, above the core, and in which the capture material is brought into direct contact with the coolant flowing out from the core. By doing so, radionuclides are captured.

In order to efficiently capture radionuclides in such a device as described above, it is necessary to increase the contact area between the capture material and the coolant to a certain extent, and there is a concern that the device itself will become larger.

That is, to actually install the above device, a space with a height of about 30 cr/L is required above the reactor core. therefore,
In order to install the above-mentioned device, it is necessary to increase the size of the upper core mechanism and the reactor vessel, which poses the problem of increasing the construction cost of the reactor plant.

OBJECT OF THE INVENTION] The present invention was made in view of the above circumstances, and its purpose is to provide radionuclide capture action to the nuclear fuel rod itself without increasing the size of the nuclear fuel rod. It is an object of the present invention to provide a nuclear fuel rod that can contribute to the miniaturization of the upper core mechanism and reactor vessel and to the reduction of the construction cost of a nuclear reactor plant.

[Structure of the invention]

The present invention provides that a gas plenum portion on the outer circumferential surface of a nuclear fuel rod body and at the most downstream end with respect to the flow direction of the coolant that contacts the nuclear fuel rod body has a larger outer diameter than other nuclear fuel rod bodies;
It is a nuclear fuel rod whose surface is nickel-plated to form a radionuclide trap.

〔Effect of the invention〕

With the above configuration, radionuclides mixed into the coolant are captured by the radionuclide trap formed at the downstream end of the nuclear fuel rod body as the coolant flows along the nuclear fuel rod. In this case, as is well known, the number of nuclear fuel rod bodies loaded into the reactor core is large, ranging from tens to hundreds of rods per assembly, and if traps are attached to these nuclear fuel rod bodies, the total surface area will be It will be very large. In addition, the nuclear fuel rod bodies are generally arranged at intervals of several thousand seven hundred and elevenths, and the shape of the catcher portion is different from that of other fuel portions, and the flow is disturbed.

In addition, the flow velocity of the trap portion is increased by increasing the outer diameter and narrowing the flow path. Therefore, the coolant whose flow is disturbed in the trap part can be brought into contact with the trap which has a wide surface area M, and the rate of diffusion of radionuclides increases through the thinner boundary layer due to the increased flow velocity. It is possible to have Usai capture the radioactive nuclides that are mixed in with Shiko's coolant.

Therefore, radioactive nuclides can be prevented from flowing out to the intermediate heat exchanger system, which contributes to facilitating maintenance, repair, etc. of this system.

Further, a gas blemish portion is generally formed within the aforementioned most downstream end of the nuclear fuel rod body. Even if the shape of this gas blemish part is made different from other parts, it will not affect the performance as a nuclear fuel rod. In other words, providing a radionuclide capture function does not make the nuclear fuel rod itself particularly large. Therefore, it is possible to perform the trapping action of radionuclides without increasing the size of the upper core mechanism or the reactor vessel, which ultimately contributes to preventing the cost of nuclear reactor plants from increasing.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to the drawings.

The figure is a longitudinal cross-sectional view showing the main parts of a nuclear fuel rod according to an embodiment of the present invention. Reference numeral 1 denotes a nuclear fuel rod body 2 and a radionuclide trap formed on the outer peripheral surface of the nuclear fuel rod body 2 and at the most downstream end with reference to the flow direction of the coolant P that contacts the nuclear fuel rod body 2. It consists of a container 4.

The nuclear fuel rod body 2 includes a cladding tube 5 formed of a thin stainless steel tube, an upper end plug 6 for closing the upper opening of the cladding tube 5, and a lower end plug (not shown) for closing the lower opening of the cladding tube 5.
It consists of a fuel pellet 7 housed in a cladding tube 5, a spring 10 and a plate 8 forming a gas plenum 9 between the fuel pellet 7, the upper end plug 6, and the fuel pellet 7. A radionuclide trap 4 is formed in a portion of the cladding tube 5 where the gas blemish 9 is provided.
Its outer diameter is larger than that of other parts, and the surface is plated with nickel, for example. The nuclear fuel rods 1 configured as O above are assembled into the reactor core such that the trap 4 side is located at the most downstream side with respect to the flow direction of the coolant p flowing while contacting the nuclear fuel rod body 2. loaded.

With such a configuration, during reactor operation, the coolant p
As shown by the arrow in the figure, the coolant p flows while contacting the nuclear fuel rods 1, and this coolant p has a radionuclide trap 4.
When flowing through part □, the flow is disturbed because the shape of the door in the catcher part is different from that in other parts. In addition, the expanded diameter of the trap section 4 is larger than the outer diameter of the other fuel section main body 2, resulting in a narrow flow path and a high flow velocity, allowing radionuclides to diffuse through the thinned boundary layer at a high speed. Can be done. This ensures that the radionuclides mixed in the coolant come into contact with the surface of the trap 4. Since the trap 4 is plated with highly active nickel of, for example, 10μ or more, the radioactive nuclides that come into contact with it are captured by this trap and diffuse into the plating layer, resulting in the above-mentioned effect. You will get it.

[Other embodiments of the invention]

The invention is not limited to the embodiments described above.

In the example, two ? Although Kel plating is applied, the trap and the casplenum part may be made of a nickel material or a nickel alloy, or may be made of another metal material having the function of capturing radionuclides. It is also possible to further improve the trapping efficiency by making the surface of the trap uneven.

[Brief explanation of drawings]

FIG. 1 is a longitudinal internal view showing the essential parts of a nuclear fuel rod according to an embodiment of the present invention. 1...Nuclear fuel rod 2...Nuclear fuel rod body 3...
Gas plenum 4... Radionuclide trap 5... Cladding tube 6... Upper end plug 7... Fuel pellet 8... Plate 10... Spring p... Coolant Fig. 1

Claims (2)

[Claims] (1) On the outer peripheral surface of the nuclear fuel rod body,
A nuclear fuel rod further comprising a radionuclide trap having an outer diameter larger than that of the other fuel portion bodies at the most downstream end with respect to the flow direction of the coolant that contacts the nuclear fuel rod body. (2) Radionuclide traps include nickel, nickel alloy,
The nuclear fuel rod according to claim 1, characterized in that it is made of at least one piece of stainless steel whose surface is nickel-plated and a nickel alloy whose surface is nickel-plated.