DE1592468B2 - PROCESS FOR MANUFACTURING A BINDER-FREE, DIRECTLY COMPRESSIBLE, GRAINABLE URANDIUM DIOXIDE GRANULATE WITH GOOD SINTERABILITY - Google Patents

Description

The invention relates to a method of manufacture a binder-free, directly compressible, free-flowing uranium dioxide granulate with good sinterability, that can be further processed into dense nuclear fuel pellets.

It is well known that uranium dioxide is concentrated in various degrees, mainly in the form of sintered bodies (Pellets) versatile use as nuclear fuel.

The production of uranium dioxide sintered bodies presupposes that the uranium dioxide powder is active, i. H. sinterable is, well compressible, so has certain sliding properties and is easy to pour, so that when Pressing a constant die filling is guaranteed.

The requirements in terms of dimensional accuracy, density and structure of the uranium dioxide sintered body are very high; therefore these properties must be used in a production process can be set or checked very precisely. It is extremely difficult. Because batch effects The uranium dioxide is normally with the addition of a binding agent and is particularly important Compressed lubricant as granules.

To do this, the uranium dioxide powder is first mixed with water, binding agent and lubricant (e.g. stearic acid) added and then granulated.

The granulate is then dried and the desired grain fraction is sieved out. This is then pressed into pellets, which are then carefully dewaxed and sintered.

In another process, uranium dioxide powder is first turned into water, a binding agent and a lubricant Slurry is produced, which is then dried and broken into irregular granules.

These wet granulation processes have the following disadvantages:

1. Due to the water moderation, enriched Uranium dioxide significantly reduces the critical amount and thus the permissible batch size.

2. The granulation process is very cumbersome and labor-intensive, especially because of the upper and lower grain of the granulate must be fed back into the granulation process.

3. The pressed pellet must first be carefully dewaxed and only then can it be sintered. That requires dewaxing, for example

and a sintering furnace.

4. Due to the relatively high density of the granulate after drying, the sintered pellet shows in many cases unwanted textures.

It is known that uranium dioxide powder has good sintering properties by chemical precipitation and subsequent temperature treatment under precisely adhered to reaction and temperature conditions to produce from uranium salt solutions, directly or via a corresponding Granules can be processed into nuclear fuel pellets (DT-AS 1173 885). That generated However, uranium dioxide powder has the disadvantage that the manufacturing process is required by the exact

! 5 Compliance with the reaction parameters is quite complex and the powder has a large open pore system as a result of these process conditions, the considerable Includes water and gas quantities, which can lead to malfunctions in the subsequent operation of the pellets in the reactor can lead.

It was therefore an object of the present invention to find a method that allows a sinter-inactive, gas- and moisture-free uranium dioxide powder produced in any way binder-free, directly compressible, free-flowing uranium dioxide granulate with good sintering properties as simple as possible to generate.

This object is achieved according to the invention in that the sinter-inactive uranium dioxide powder by Fine grinding to a grain size of <1 μm to 5 μm activated and then rounded dry Particles is granulated.

Fine grinding can be done, for example, in an air jet or steam jet mill (also called micronizer or jetonizer) take place, the granulation on a Granulating plates or in a dragee drum. These granulates can then be pressed directly into pellets and be sintered.

The fine grinding is preferably carried out up to grain sizes in the range = 1 μ.

Under sintering inactive one understands the property of a ceramic material to become only very difficult to have a dense and solid ceramic body processed.

The following examples are intended to explain the process according to the invention in more detail:

example 1

In an air jet mill with a 200 mm chamber 5 "diameter, UO ₂ powder with an initial particle size between 20 and 60 μ was finely ground (particle size is 1 μ) with an hourly throughput of 25 or 40 kg / h 10 1 dragee drum dry granulated for 30 minutes. The granules (particles from 0.5 to 1 mm 0) were then pressed into pellets 12 mm 0 and 15 mm high and sintered directly. The pellets were of excellent quality and had sintered densities of 10.6 g / cm ³ .

Example 2

_{The fine UO 2} powder obtained according to Example 1

was continuously granulated on a granulating plate. The granules were compressed as in Example 1 and sintered. As in Example 1, good pellets were made

obtained with densities of 10.6 g / cm ³ .

Claims (2)

Patent claims: 1. Process for the production of a binder-free, directly compressible, free-flowing uranium dioxide granulate with good sintering properties from a sinter-inactive uranium dioxide powder, thereby characterized in that the uranium dioxide powder by fine grinding to a grain size of <1 μτη to 5 μπι activated and then dry is granulated into round particles. 2. The method according to claim 1, characterized in that the fine grinding up to grain sizes is carried out in the range ai 1 μπι.