RU2388081C2 - Method for hot isostatic pressing cermet rod of nuclear reactor fuel element - Google Patents

Abstract

FIELD: physics, nuclear.

SUBSTANCE: invention relates to nuclear power engineering and specifically to methods of making cermet rods of fuel cores of fuel elements of nuclear reactors for different purposes. A workpiece is put into a container. Working medium in form of solid glass is put into the container and the container with the workpiece and the working medium is heated to pressing temperature. The container is put into a press mould and moulding force is applied by increasing pressure of the working medium while moving the moulding die. In the proposed method the working medium is in form of a briquette. The briquette is placed at the bottom of the container. The workpiece is put on top of the briquette. The container with the workpiece and the working medium is heated outside the press mould until the workpiece is immersed in the working medium.

EFFECT: reduced probability of formation of voids, transfer of pressure onto the moulded workpiece becomes more uniform, increased output of the suitable products.

Description

1. The technical field to which the invention relates.

The invention relates to the field of nuclear energy, in particular, to methods for manufacturing cermet rods of fuel cores of fuel elements (fuel elements) of nuclear reactors for various purposes.

2. The level of technology

One of the directions in nuclear energy is the use of fuel rods in which fuel cores are drawn from cermet rods (see, for example, Fedik II, Gavrilin SS and others. A new generation of microfuel fuel rods for VVER, M .: Atomic energy, 2004, vol. 96, issue 4, p. 280), and the rods are encapsulated in a shell made of zirconium alloy (see, for example, Solonin MI, Bibilashvili Yu.K. et al. Zirconium-niobium alloys for cladding of fuel rods and fuel assemblies of power reactors and installations of the WWER and RBMK type, Selected Works of VNIINM, M .: FSUE VNIINM, t.1, p. 65-69 )

As a blank in the manufacture of such cermet rods, a zirconium tube filled with nuclear fuel powder and closed on both sides with plugs is used (see, for example, Gavrilin S.S., Deniskin V.P., Leonov A.V., Fedik I.I. Procurement of the core core of the cermet fuel element of a nuclear reactor, RF Patent No. 2305333 dated March 15, 2006, published on August 27, 2007, bull. No. 24). After encapsulation of the fuel in the zirconium shell, the blank is compressed and the fuel is compressed by isostatic pressing (see, for example, Gavrilin S.S., Permyakov L.N., Chernikov A.S. Composite material for fuel cores of dispersion fuel elements, RF Patent No. 2139581 dated June 23, 1998, published on October 10, 1999, Bulletin No. 28; Gavrilin SS, Deniskin VP, Leonov AV, Fedik II Method for the manufacture of a cermet rod of a fuel core of a fuel element of a nuclear reactor, RF patent No. 2305334 dated March 15, 2006, published on August 27, 2007, bull. No. 24).

Isostatic pressure transfer during pressing of objects of this type can be carried out in various ways. A known method of hot isostatic pressing of a workpiece of a core core of a cermet fuel rod of a nuclear reactor, in which the workpiece is placed in a container, a gas working medium is supplied to the container by means of which pressure is transmitted to the workpiece, the container and working medium are heated to the pressing temperature and the workpiece is kept under pressure for the required time (see, for example, Samoilov AG, Volkov BC, Solonin MN Fuel elements of nuclear reactors ", M .: Energoatomizdat, 1996, p. 220). of the preform at a temperature of about 1000 ° C, a gas pressure of at least 100 MPa with a pressing time of 1-1.5 hours is required.Providing such a gas pressure at a high temperature and at significant volumes of output is decided by the creation of complex production equipment, requires a lot of time and tough regulation of the work of staff in terms of compliance with safety regulations.

With the proposed method, this method coincides with the operation of placing the workpiece in the container, supplying the working medium to the container to transfer pressure to the workpiece, heating the container and the working medium to the pressing temperature and holding the workpiece under pressure for the required time.

There is also known a method for hot isostatic pressing of a blank of a core core of a cermet fuel rod of a nuclear reactor, in which the blank is heated to a pressing temperature, the blank is placed in a container, the gaps between the blank and the walls of the container are filled with a pre-molten working medium, which is used as glass, and the container is placed in a press -form of the press and apply the pressing force by increasing the pressure of the working medium when moving the press punch (see, for example, V.I. Ural sky, plakhotin VS et al. Deformation of high pressure liquid metals, M .: Metallurgy, 1976, s.390).

Since the molten glass has a high viscosity, in this method there is a high probability of formation of gas bubbles in the melt, which entails the unevenness of the applied pressure over the surface of the pressed billet and its curvature. As a result, the yield of billets is reduced.

With the proposed method, this method coincides with the following essential features:

- the workpiece is heated to a pressing temperature outside the press,

- place the workpiece in the container,

- fill the working medium, which is used as glass, the gaps between the workpiece and the walls of the container,

- install the container in the mold of the press,

- apply the pressing force by increasing the pressure of the working medium when moving the punch of the press.

There is also known a method for hot isostatic pressing of a blank of a core core of a cermet fuel rod of a nuclear reactor, in which the blank is placed in a container, the gaps between the blank and the walls of the container are filled with a working medium in the solid state, which is used as ground glass, the container with the workpiece and the working medium is degassed in vacuum, install the container in the mold of the press, heat the container in the mold to the pressing temperature and apply force I working fluid pressure is increased by moving the punch press (see., e.g., Karl M., Vincent C., Microstructurally toughened metal matrix composite article and method of making same, US Pat. № 4,885,212, Dec.5, 1989).

The disadvantage of this method, as well as the previous one, is the high probability of formation of closed cavities in the glass melt, the elimination of which is difficult due to the high viscosity of the melt. Such cavities, unpredictably combining with each other, lead to uneven distribution of the pressing pressure over the surface of the workpiece and, therefore, to its curvature. As a result, the yield of billets is reduced. In addition, since the shrinkage of the ground glass undergoes significant shrinkage, the implementation of this method requires a larger container, which, in turn, entails an increase in energy costs for heating the press.

With the proposed method, this method coincides with the following essential features:

- place the workpiece in the container,

- a working medium is placed in the container, in which quality glass is used in a solid state,

- install the container in the mold of the press,

- heat the container with the workpiece and the working medium to a pressing temperature,

- apply the pressing force by increasing the pressure of the working medium when moving the punch of the press.

The last method of hot isostatic pressing of the core rod of the cermet fuel rod of a nuclear reactor by the set of essential features is the closest to the claimed one and is selected as a prototype.

3. The invention

A method for hot hydro-pressing a blank of a core core of a cermet fuel rod of a nuclear reactor is proposed, namely, the blank is placed in a container, the working medium is made in the form of a glass briquette, the briquette is placed on the bottom of the container, the container with the workpiece and the working medium is heated until immersion billet in the working environment, install the container in the mold of the press and apply the pressing force by increasing the pressure of the working medium when moving the press punch. Unlike the prototype, in the proposed method, the working medium is made in the form of a briquette, it is placed on the bottom of the container, the workpiece is placed on top of the briquette, the container with the workpiece and working medium is heated outside the mold of the press until the workpiece is immersed in the working medium.

Due to this difference, the workpiece is immersed under its own weight in a homogeneous working environment, which significantly reduces the likelihood of voids and, consequently, the pressure transfer to the workpiece being pressed becomes more uniform in comparison with the prototype. Thus, the proposed method provides increased yield.

4. Information confirming the possibility of carrying out the invention

A pressing of the proposed method was subjected to a block of seven blanks of rods of the fuel core of the cermet fuel rod of a nuclear reactor. Each billet was a zirconium pipe with a diameter of 9.1 mm, a length of 60 mm and a wall thickness of 0.7 mm. The pipe was filled with fuel spheres made of uranium dioxide with a diameter of 500 μm and closed with plugs on both sides. As a matrix material, the fuel spheres were coated with a 35 μm thick zirconium alloy coating. The block of blanks was placed in a steel container with an inner diameter of 46 mm over a briquette weighing 320 g of sodium silicate, selected as the working medium. The container, together with the block of preforms and the briquette of the working medium, was heated in a separate furnace to a temperature of 1000 ° C for 30 minutes. After immersing the blank block in glass, the container was transferred to the hydraulic press mold and the blank block was pressed at a load of 120 tons and a machine time of 30 s. The deviation of the shape of the pressed blanks from the cylindrical did not exceed 100 μm, which is guaranteed to reduce the diameter of the rod during further machining (centerless grinding) to the required value of 7.6 mm without opening and destroying the fuel particles.

Claims (1)

A method of hot isostatic pressing of a blank of a core core of a cermet fuel rod of a nuclear reactor, which consists in placing the blank in a container, placing the working medium in the container, using glass in the solid state, heating the container with the blank and the working medium to the pressing temperature, and setting container into the mold of the press and apply the pressing force by increasing the pressure of the working medium when moving the press punch, characterized in that the working medium is They are molded in the form of a briquette, the briquette is placed on the bottom of the container, the workpiece is placed on top of the briquette, the container with the workpiece and the working medium is heated outside the mold of the press until the workpiece is immersed in the working medium.