JPS5892986A - 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 l) Technique of the Invention The present invention relates to a nuclear fuel rod capable of capturing and retaining radionuclides in a coolant in a reactor core.

2) Prior Art Fast breeder reactors generally use an alkaline liquid metal represented by liquid sodium as a coolant. After this liquid metal coolant is heated in the reactor core installed inside the reactor vessel, it is led to an 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 section are usually made of stainless steel, which is highly corrosion resistant. However, stainless steel can still be corroded by liquid sodium. Since the constituent materials of the cladding tube and core structure are radioactive, if they are corroded as described above, radioactive corrosion products may be mixed into the coolant. The radioactive corrosion products warmed to the coolant are carried by the coolant to the intermediate heat exchanger system and deposited on the pipe walls of the intermediate heat exchanger system. The radioactivity of radionuclides deposited on walls etc. is removed by pumps,
It may cause trouble in the maintenance and repair work of equipment such as heat exchangers, valves, flow meters, etc., and the piping connected to these equipment. Of the radionuclides, manganese-54,5-balt (io,
Since cobalt-58 and the like are produced in large amounts and have a long half-life, their influence is significant.

In order to eliminate such problems, recently, it has been considered to install a radioactive corrosion product capture device using a radionuclide capture material such as nickel inside the reactor vessel. 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 directly shakes the capture material into the coolant flowing out from the core. By doing so, radionuclides are captured.

3) Problems with the prior art In order to efficiently capture radionuclides with the above-mentioned device, it is necessary to increase the contact area between the capture material and the coolant to a certain extent, which increases the amount of the device itself. There are concerns.

That is, in order to actually install the above device, a space with a height of approximately 30,511 mm is required above the reactor core. Therefore, in order to install the above-mentioned device, it is necessary to increase the number of reactor core upper mechanisms and reactor vessels, which poses a problem of increasing the construction cost of the nuclear reactor plant.

4) Purpose of the Invention The present invention has been made in view of the above circumstances, and its purpose is to enable the nuclear fuel rods themselves to perform a radionuclide capture function without increasing the number of nuclear fuel rods. The object of the present invention is to provide a nuclear fuel rod that can contribute to downsizing of the upper core mechanism and reactor vessel and to reducing the construction cost of a nuclear reactor plant.

■Structure of the Invention The present invention provides a metal wire for capturing radionuclides that is wound around the outer peripheral surface of the nuclear fuel rod body and at the most downstream end with reference to the flow direction of the coolant that contacts the nuclear fuel rod body. It is characterized by

6) Effects of the invention With the above configuration, radionuclides added to the coolant are:
Coolant flows along the nuclear fuel rod body.

During the filtration process, it will be captured on the surface of the metal wire provided at the most downstream end of the nuclear fuel rod body. In this case, in the core #
As is well known, there are a large number of nuclear fuel rod bodies, ranging from 10 to several hundred rods, and each of these nuclear fuel bodies is wrapped with metal wire for capturing radionuclides. In this case, if a thin wire is used as the metal wire, the total surface area of the wound portion becomes very large. Further, the nuclear fuel rod bodies are generally arranged at intervals of several square meters, and the surface of the wound part of the metal wire is uneven. Therefore, since the coolant whose flow is disturbed by the unevenness is brought into contact with the metal wire winding portion having a large surface area, it is possible to reliably capture radionuclides mixed in the coolant. Therefore, it is possible to prevent radionuclides from flowing out to the intermediate heat exchanger system, which contributes to facilitating maintenance, repair, etc. of this system.

Additionally, a gas plenum is generally formed within the aforementioned most downstream end of the nuclear fuel rod body.

Even if the outer diameter of this gas plenum portion is made smaller than other portions, the performance as a nuclear fuel rod will not be affected in any way. Therefore, by forming the most downstream end part to have a smaller diameter than the deaf part, and by wrapping the aforementioned metal wire Ia times around the outer periphery of this small diameter part, the external dimensions as a nuclear fuel rod are exactly the same as conventional ones, and the flow rate is The radionuclide capture function can be achieved while the channel is secured in the same way as with conventional ones. In other words, adding a radionuclide capture function will not result in a significant increase in the number of nuclear fuel rods. Therefore, it is possible to perform the trapping action of radionuclides without increasing the number of core upper mechanisms and reactor vessels, which ultimately contributes to preventing the cost of nuclear reactor plants from increasing.

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

The figure is a vertical cross-sectional view showing the essential parts of a nuclear fuel rod according to an embodiment of the present invention, and this fueled rod l includes a nuclear fuel rod body and a nuclear fuel rod body! In the external aspect, and above the nuclear fuel rod body! It is composed of a winding layer 8r that is wound and attached to the most downstream end 1 based on the flow direction of the coolant P that comes into contact with the
I'm L.

The nuclear fuel rod body J includes a cladding tube 5 made of thin stainless steel or the like, an upper end 4&# which closes the upper opening of the cladding tube 5, and a lower end 1k (81!) which closes the lower opening of the cladding tube 5.
(not shown), a fuel pellet 7 housed in the cladding tube 1, and a plate 8 inserted between the fuel pellet 1 and the upper end J&C, and a plate member 8 inserted between the upper end member 6 and the fuel pellet 1.
and a spring 1o forming a gas plenum between them. The outer diameter of the portion of the cladding tube 5 where the gas plenum 9 is provided is set to a minimum diameter mIX that is smaller than the outer diameter of other portions.

However, the above-mentioned winding layer! is formed by wrapping, for example, a thin metal wire, such as a nickel wire, twice around the outer periphery of the small diameter portion 11 and having a function of capturing radioactive nuclides. The nuclear fuel rods configured as described above are assembled in such a way that the winding layer j 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. is 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 rod 1, but when the coolant P flows through the portion of the winding layer 1, the flow is disrupted by the irregularities on the surface of the winding layer 1. be done. Therefore, this turbulence ensures that the radionuclides mixed in the coolant P come into contact with the surface of the winding layer l. The winding layer A1 is made of a highly active nickel wire, and the radioactive nuclide that comes into contact with it is captured by this winding wire 1i and penetrates into the inside of the wire by diffusion. In the case of B, it is easy to increase the surface area of the winding 1 by making the wire thinner, and also to position the winding layer 1 at the most downstream end of the nuclear fuel rod body. Considering that it is easy to match the outer diameter of the winding layer ↓ to the outer diameter of the nuclear fuel rod body 1, the above-mentioned effect can be obtained after all.

8) Other embodiments The present invention is not limited to the embodiments described above. In Act IIag1, nickel wire was used as the metal wire to capture radionuclides, but nickel alloy wire, stainless steel wire with nickel plating on the surface, nickel alloy wire with nickel plating on the surface, or the like may also be used. It may be a combination, or it may be a diagonal line made of another metal material that has the function of capturing one radionuclide. Furthermore, if a sufficient flow path for the coolant can be ensured, the small diameter portion may not be provided.

[Brief explanation of drawings]

The figure is a vertical cross-sectional view showing a main part of a nuclear fuel rod according to an embodiment of the present invention. - Nuclear fuel rod, 1... Nuclear fuel rod body, l... Winding layer, 5... Cladding tube, 1... Fuel pellet, 9...
・Gas plenum, -10... Spring, 11...
Small diameter part, P...coolant.

Claims (2)

[Claims] (1) A nuclear fuel rod body, and a radionuclide trap wound around the outer peripheral surface of the 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. A nuclear fuel rod comprising a metal wire. (2) The nuclear fuel rod according to claim 11, wherein the metal wire is wound around a small diameter portion provided at the most downstream end of the nuclear fuel rod main body. Claims characterized in that the metal wire is made of at least one of nickel, nickel alloy, stainless steel with nickel plating on the surface, and nickel alloy with nickel plating on the surface. 1st (1st
) or (2). □