RU2550745C2 - Fuel element of nuclear power reactor and method of making same - Google Patents

Abstract

FIELD: physics, atomic power.

SUBSTANCE: invention relates to nuclear physics, particularly to gas-filled fuel element structures for experimental, test and research reactors and methods of making same. The fuel element comprises an envelope filled with a gas of a given composition and pressure, a fuel column in the envelope and terminal elements sealed to the envelope by welded joints. Both terminal elements are connected to the envelope by welded joints made by multiple-pass electron-beam welding. At least one of the terminal elements has a cavity with an ampoule inside, the ampoule containing an inert gas of a given composition and pressure. The cavity is linked to the inner volume of the envelope, and the terminal element with the cavity has a thickness comparable with that of the wall of the envelope. The fuel element is made by first forming a cavity in the terminal element and placing an ampoule filled with a gas of a given composition and excess pressure. The ampoule is made of material with a melting point lower than that of the material of the terminal element. The fuel element is sealed by welded joints made by electron-beam welding, and the inner cavity of the envelope is filled with gas by opening the ampoule after sealing using thermal action on the terminal element.

EFFECT: obtaining a fuel element with high-quality, corrosion-resistant and low-stress joints.

3 cl, 4 dwg

Description

The invention relates to nuclear energy, in particular to the design of gas-filled fuel rods for experimental, test and research reactors and methods for their manufacture.

Known designs of gas-filled fuel rods, which are used in experimental (prototype energy), test and research reactors, including a shell filled with gas of a given composition and pressure with a fuel core placed in it, as well as end elements hermetically connected to the shell by welds (Reshetnikov F .G. Et al. Development, production and operation of fuel elements of power reactors. - M .: Energoatomizdat, 1995, kN.2, p.158-159).

In the manufacture of gas-filled fuel rods, end elements are first produced, the cladding is prepared by welding one end element and placing a fuel core in it, and the internal volume of the fuel rod is filled after evacuation in a chamber with excessive gas pressure (helium), and then the second end element is welded with a shell (Reshetnikov F.G. et al. Development, production and operation of fuel elements of power reactors. - M .: Energoatomizdat, 1995, kN.2, p.177-178, pat nt RU №2355533, IPC G21C 3/10, publ. 20.05.2009, patent RU №2065213, IPC G21C 21/00, publ. 08.10.1996 et al.), which is associated with an excessive flow of inert gas caused by the volume of the chamber.

The operational reliability of fuel elements is largely determined by the quality of the welded joints. It is known that a welded joint (seam) made by multi-pass electron beam welding (ELS) provides corrosion and erosion resistance, mechanical strength without breaking the seal. However, the implementation of the welded joints of the ELS fuel rods filled with inert gas necessitates a significant complication of the design of the fuel rod due to the need to perform additional operation of the fuel elements of power reactors. - M .: Energoatomizdat, 1995, kN.2, p.181, p.210, p.213, p.217).

A known method of manufacturing a gas-filled fuel rod, in which the shell is connected to the second end element using gas arc welding (GDS). Despite the fact that only two welds are present in the fuel rod structure, a layer is formed on their surface and in the heat affected zone of the joints, which arises as a result of the interaction of the metal with the atmosphere - oxygen and nitrogen, which worsens the corrosion resistance of the joints (Reshetnikov F.G. et al. Development, production and operation of fuel elements of power reactors. - M .: Energoatomizdat, 1995, kN.2, p.177, p.192, p.213).

The closest known technical solution adopted for the prototype is a fuel element of a nuclear power reactor, including a shell filled with gas of a given composition and pressure, with a fuel core placed in it, end elements hermetically connected to the shell with welds (patent RU No. 2127457, IPC G21C 3/10, publ. 03/10/1999).

The connection of the second end element with the cladding (i.e., at the final sealing) of a fuel element equipped with fuel and filled with inert gas (helium) is performed by flash butt welding (KSS). A significant drawback of the joints made by KSS is a high level of residual post-welding stresses, leading to corrosion. Moreover, for each fuel rod two types of welding are used: ELS and KSS. Gas filling is carried out in a separate chamber, which is associated with its increased consumption.

The manufacture of a known fuel rod construction consists in preparing a cladding, placing a fuel core in it, evacuating it, filling the cladding with an inert gas with excess pressure and connecting it to the end elements using welds. In this case, one end element is welded using ELS, and after filling the fuel rod with gas, the second end element is welded using KSS.

This method also has disadvantages. When welding the second end element using KSS (final sealing), the quality of the welded joint decreases, since nitrogen and oxygen are present in the atmosphere under the shell and in the zone of the weld, which reduces the corrosion resistance, mechanical strength of the weld and, as a result, the reliability of the fuel rod . (Reshetnikov F.G. et al. Development, production and operation of fuel elements of power reactors. - M .: Energoatomizdat, 1995, kN.2, p.183). As already mentioned, in the manufacture of the known fuel rod there is an increased gas consumption.

The task at hand is to increase the reliability of the fuel rod and simplify its manufacture by providing the ability to connect the shell with two end elements using two seams made by multi-pass ELS.

The problem to be solved and the technical result are achieved due to the fact that in the design of a fuel rod including a shell filled with gas of a given composition and pressure with a fuel core placed in it, end elements hermetically connected to the shell by welds, according to the invention, both end elements are connected to the shell using welds made by electron-beam welding in at least one of the end elements, a cavity is made with an inert gas ampoule of a given composition inside and pressed iia, while the cavity is connected to the inner volume of the shell, and the end element with the cavity is made of a thickness commensurate with the wall thickness of the shell.

The specified task and the technical result are also achieved by the fact that in the method of manufacturing a fuel element, including preparing the shell with the placement of the fuel core, the manufacture of end elements, evacuation, filling the shell with inert gas with excess pressure, sealing the shell using welds, according to the invention, at least in one of the end elements, a cavity is preliminarily formed, connected to the internal volume of the shell, into which an ampoule filled with gas is placed a predetermined composition with excess pressure, made of a material with a melting point below the melting temperature of the material of the end element, and filling the inner cavity of the shell with gas is performed by opening the ampoule after sealing.

Opening the ampoule can be done by thermal exposure to the end element with the ampoule.

The essence of this technical solution is illustrated by drawings.

Figure 1 shows the design diagram of a fuel rod.

Figure 2 shows a diagram of the evacuation of the inner volume of the shell and welding in the chamber for ELS.

Figure 3 shows a diagram of a manufacturing option for a gas-filled ampoule.

Figure 4 (a, b, c, d) presents a fuel rod simulator with an ampoule in the end element and the results of opening the ampoule.

The fuel element (figure 1) consists of a shell 1 in which the fuel core 2 is placed. The shell 1 is connected to the end elements 3 and 4 by means of seams made of multi-pass ELS. In the end element 3, a cavity 5 is made, in which a gas-filled ampoule 6 is placed, fixed from axial displacement by a threaded plug 7 with an opening. The fuel core 2 is fixed by a coil spring 8. A heater 9 is located opposite the ampoule 6.

The manufacture of a fuel rod is as follows. First, the shell 1 is prepared and the fuel core 2 is placed in it. The end elements 3, 4 are made and a cavity 5 is formed in at least one of them, into which the ampoule 6 is filled, filled with gas of a given composition and pressure. A screw plug 7 with a hole fixes it from axial displacement. A spring 8 is installed in the end element. Then, in the evacuated chamber for ELS 10 (Fig. 2), a shell 1 with a fuel core 2, an end element 3 with an ampoule, a tube and a spring placed in the cavity 5 are placed, a second end element 4. End elements 3 and 4 are initially installed with clearance to the cladding of the fuel rod. The evacuated fuel rod is sealed with a multi-pass ELS of the end elements with the shell simultaneously or sequentially (Fig. 2, item 11 - the head of the electron-beam installation), after which the ampoule is opened by thermal exposure to the fusible shell and the gas inside it fills the internal cavity of the shell to set pressure value. It is possible to produce a thermal effect on the ampoule with an electron beam directly in the chamber (Fig. 2), directing it to the end element with the ampoule, or immediately before the leak test.

Thus, the design of the fuel rod is two-seam, and welded joints can be performed by one type of welding. This simplifies the manufacture of fuel rods. The implementation of the seams (joints) of multi-pass ELS increases the reliability of the fuel rods. The vacuum in the chamber (figure 2) of the shell with the fuel core in the presence of a gap between the end elements 3 and 4 and the cladding 1 of the fuel rod improves the vacuum conditions, which ultimately affects the quality of the atmosphere under the cladding.

The shell of a gas-filled ampoule is made of fusible or easily opened material. The manufacture of a gas-filled ampoule is possible, for example, from a tubular billet connected to a gas station (Fig. 3). The tubular billet 12 is clamped by the rollers 13, which ensures diffusion welding of the ampoule 6, while the ampoule volume 14 remains at the required pressure P, which is provided by the gas station. Such manufacture of the ampoule and the entire fuel rod allows to save inert gas, which is especially important when using expensive inert gases. Compared with the prototype, there are no operations of filling the chamber with gas, discharging gas from the welding chamber at KSS.

This embodiment of gas-filled fuel elements is advisable for experimental fuel elements with a low internal gas pressure in the range from 1 to 2 kg / cm ² . Using this technical solution allows you to apply one type of welding - ELS, which allows you to speed up and simplify the manufacture of fuel rods (especially small in the length range from 0.5 m to 2 m), reduce gas consumption, improve the vacuum conditions of the internal volume of the fuel rod.

Implementation example

For a fuel element with an internal volume of 1.5 cm ³ at a helium pressure of 1.2 kg / cm ² , an ampoule with a volume of 0.37 cm ³ and an internal helium pressure of 5 kg / cm ^{2 was used} . For the manufacture of the ampoule, a tubular, carefully cleaned blank of grade C0 lead was used. The inner diameter of the workpiece is 4 mm, the wall thickness is 0.8 mm. One end of the billet was connected to a gas station, which provided the required helium pressure of 5 kg / cm ² , the other end was cold-worked (diffusion welding) by compression by rollers 13 (Fig. 3). The rollers 13 (or tubular workpiece) were moved to the size of the ampoule (for a volume of 0.37 cm ^{3 the} length would be 30 mm), after squeezing the workpiece by the rollers 13, a finished ampoule with a cavity pressure of 15-5 kg / cm ^{2 was} obtained. The ampoule was tested for helium leakage through a leak detector. The ampoule was inserted into the cavity provided in the end element (plug) 3 (Fig. 1), then a threaded plug 7 was installed with an opening providing connection to the internal cavity of the shell 1 and a compression spring 8. The wall thickness of the plug made of stainless steel in the zone The placement of the ampoule was 0.8 mm. Next, the plug 3 assembly, the shell 1 with the fuel core 2 and the plug 4 were placed coaxially in the evacuated chamber 10, as shown in figure 2. The chamber was evacuated to a residual pressure of 10 ⁻⁵ mm Hg. Plugs (end elements) 3 and 4 were sent to the end at the ends of the shell 1, which were installed opposite the heads 11 ELS. The fuel rod was sealed with multi-pass welds during rotation of the product. In this case, the formation of welds can be performed both simultaneously and sequentially in one chamber. The opening of the gas-filled ampoule was carried out by heating through the wall of the end element 3, the thickness of which was 0.6 mm in the zone of the ampoule, by the heater 9 (Fig. 1). When the temperature on the wall of the cladding reaches (450-500) ° C, the ampoule opens and helium fills the entire volume of the fuel rod through the hole in the plug 7. The pressure in the fuel element P _{1 is} proportional to the pressure in the ampoule P, the volumes of the fuel rod V ₁ and the ampoule V (P × V = P ₁ × V ₁ ) and is (at P = 5 kg / cm ² , V = 0.37 cm 3, V, = 1.5 cm ³ ) a value of 1.2 kg / cm ² .

The proposed technical solution was tested on a fuel rod simulator (Fig. 4a) with an end element 3 in which an ampoule 5 was placed (Fig. 4b is an x-ray of the simulator of Fig. 4a). The internal cavity of the simulator was pumped out to a pressure of 10 ^-3 mm Hg. The outer surface of the end element 3, the wall thickness of which was 0.6 mm, was heated to a temperature of 500 ° C. The ampoule was opened, which was confirmed by x-ray (pigv), and the internal volume was filled with gas to a pressure of 1.2 kg / cm ² , which was determined by the pressure gauge. On Figg presents a photograph of the ampoule, extracted after testing, which shows the opening and melting of the lead shell of the ampoule.

Thus, due to the absence of inert gas losses, its consumption for the production of one fuel element is minimal. The introduction of a gas-filled ampoule being opened into the fuel element construction made it possible to obtain a two-seam fuel element design with two welds made of multi-pass ELS. This type of welding allows to obtain better, corrosion-resistant, less stressed welds, which increases the reliability of the fuel rod. Also, the use of ELS for both sealing welded joints simplifies the fuel rod sealing process, increases productivity, and reduces the amount of equipment required for sealing (welding). Evacuation of the shell with the fuel core with free access to both ends of the shell improves the vacuum conditions of the internal volume of the fuel rod, and then, after sealing and opening the ampoule, it improves the composition of the atmosphere under the shell, which also affects the reliability of the fuel rod. Compared with the prototype, the invention allows to abandon the manufacture, and then the fusion of the "flat" on one of the end elements. The manufacture of a gas-filled ampoule, in turn, does not require complicated, expensive equipment.

Claims (3)

1. The fuel element of an energy nuclear reactor, including a shell filled with gas of a given composition and pressure, with a fuel core placed therein, end elements hermetically connected to the shell by welds, characterized in that both end elements are connected to the shell by welds, made by electron beam welding, in at least one of the end elements a cavity is made with an inert gas ampoule placed inside of a given composition and pressure, while the cavity is connected and with the internal volume of the shell, and the end element with the cavity is made of a thickness commensurate with the thickness of the shell wall. 2. A method of manufacturing a fuel element, including the preparation of the shell with the placement of the fuel core, the manufacture of end elements, evacuation, filling the shell with inert gas with overpressure, sealing the shell using welds, characterized in that in at least one of end elements pre-form a cavity connected to the internal volume of the shell, into which is placed an ampoule filled with gas of a given composition and with excess pressure made of material with a melting point below the melting temperature of the material of the end element, and filling the inner cavity of the shell with gas is done by opening the ampoule after sealing the shell. 3. The method according to claim 2, characterized in that the opening of the ampoule is performed by thermal exposure to the end element with the ampoule.

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