Method for producing a sintered nuclear fuel body

Details Method for producing a sintered nuclear fuel body Method for producing a sintered nuclear fuel body

1998-11-04

2001-05-22

Derrington, James (Department: 1731)

Plastic and nonmetallic article shaping or treating: processes

Shaping or treating radioactive material

C252S636000, C376S409000, C376S421000

Reexamination Certificate

active

06235223

ABSTRACT:

BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The invention relates to a sintered nuclear fuel body or compact that contains (U, Pu)O
2
mixed crystals.
The invention also relates to a method for producing a sintered nuclear fuel body that contains (U, Pu)O
2
mixed crystals from powdered starting materials of uranium dioxide UO
2+X
and plutonium dioxide PuO
2
, which are ground, compressed into bodies, and sintered as bodies in a hydrogen-containing sintering atmosphere. The variable X is in a range from 0 to 0.3.
One such sintered nuclear fuel body and one such method are known from German Published, Non-Prosecuted Patent Application DE 38 02 048 A1. In that known method, the powdered starting materials of uranium dioxide and plutonium dioxide are ground together with an additive, which is at least one powdered substance selected from the group consisting of ammonium uranyl carbonate, ammonium diuranate, ammonium bicarbonate, zinc stearate, zinc behenate, starch, cellulose, oxalic acid diamide and stearic acid diamide. The powder mixture can be ground and then compressed into tablet-like bodies, which are sintered in a sintering atmosphere of hydrogen.
The sintered nuclear fuel bodies that are obtained are dimensionally stable and also only have slight open porosity, so that gaseous nuclear fission products in a nuclear reactor can be trapped in the sintered nuclear fuel bodies
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a sintered nuclear fuel body and a method for producing a sintered nuclear fuel body, which overcome the hereinafore-mentioned disadvantages of the heretofore-known products and methods of this general type, which further improve retention of gaseous nuclear fission products and in particular assure the same even if the sintered nuclear fuel bodies are located in a nuclear reactor for long periods of time and output high power.
With the foregoing and other objects in view there is provided, in accordance with the invention, a sintered nuclear fuel body, comprising (U, Pu)O
2
mixed crystals having a mean particle size in a range from 7.5 &mgr;m to 50 &mgr;m.
In accordance with another feature of the invention, the (U, Pu)O
2
mixed crystals have a mean particle size in a range from 8 &mgr;m to 25 &mgr;m.
This relatively large mean particle size changes only insignificantly during the power output of the sintered nuclear fuel body in a nuclear reactor, so that the gaseous fission products that are produced remain at the site where they were created in the sintered nuclear fuel body and are not released.
The determination of the mean particle size is carried out in accordance with a book by H. Schumann entitled “Metallographie” [Metallography], 10th Edition, VEB Deutscher Verlag fur Grundstoffindustrie, Leipzig, Germany, pp. 51-57.
With the objects of the invention in view, there is also provided a method for producing a sintered nuclear fuel body containing (U, Pu)O
2
mixed crystals, which comprises adding at least one powdered substance selected from the group consisting of aluminum oxide, titanium oxide, niobium oxide, chromium oxide, vanadium oxide, aluminum hydroxide, chromium hydroxide, aluminum monostearate, aluminum distearate and aluminum tristearate as an additive to powdered starting materials of uranium dioxide UO
2+X
and plutonium dioxide PuO
2
at least one of before, during and after grinding the starting materials, compressing the ground starting materials into a body, and/or sintering the body during a holding time of 10 minutes to 8 hours at a sintering temperature in a range from 1400° C. to 1800° C. in a hydrogen-containing sintering atmosphere having an oxygen partial pressure of 10
−10
to 10
−20
bar during a first portion of the holding time and having an oxygen partial pressure of 10
−8
to 10
−10
bar during an ensuing second portion of the holding time, and then cooling down the body in a hydrogen-containing atmosphere with an oxygen partial pressure of 10
−10
to 10
−20
bar.
Both the additive and the oxygen partial pressure, especially during the second portion of the holding time, bring about high mobility on the part of uranium, plutonium and oxygen during sintering in the body, thus promoting a uniform, increased particle growth during the sintering of the body.
In accordance with another mode of the invention, there is provided a method which comprises maintaining the sintering temperature at an at least approximately constant value in a range from 1400° C. to 1800° C. This further increases the mobility of uranium, plutonium and oxygen atoms.
In accordance with a further mode of the invention, there is provided a method which comprises heating the body to the sintering temperature in the hydrogen-containing atmosphere having an oxygen partial pressure of 10
−10
to 10
−20
bar. This effects calcination of hydroxides of the additives into oxides, having a crystal lattice structure which is quite similar to the lattice structure of uranium oxide and plutonium oxide, that promotes the formation of (U, Pu)O
2
mixed crystals.
In accordance with an added mode of the invention, there is provided a method which comprises maintaining the sintering temperature in a range from 1600° C. to 1800° C. and preferably from 1650° C. to 1750° C.
In accordance with an additional mode of the invention, there is provided a method which comprises heating the body to the sintering temperature in temperature stages.
In accordance with yet another mode of the invention, there is provided a method which comprises providing the hydrogen-containing sintering atmosphere with from 2 to 10 volume % hydrogen and at least one gas selected from the group consisting of noble gas, nitrogen, CO
2
, CO, O
2
and water vapor. This brings about an especially high oxygen partial pressure during sintering.
In accordance with yet a further mode of the invention, there is provided a method which comprises selecting the first portion of the holding time to be in a range from 10 minutes to 4 hours.
In accordance with a concomitant mode of the invention, there is provided a method which comprises selecting the second portion of the holding time to be in a range from 10 minutes to 4 hours and preferably from 2 to 3 hours. These modes bring about a large proportion of the (U, Pu)O
2
mixed crystal in the sintered nuclear fuel body.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a sintered nuclear fuel body and a method for producing a sintered nuclear fuel body, it is nevertheless not intended to be limited to the details given, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific examples.


REFERENCES:
patent: 3375306 (1968-03-01), Russell
patent: 3504058 (1970-03-01), Masselot
patent: 3620720 (1971-11-01), Galmiche et al.
patent: 3872022 (1975-03-01), De Hollander
patent: 4060497 (1977-11-01), Huschka et al.
patent: 4119563 (1978-10-01), Kadner et al.
patent: 4235563 (1980-11-01), Druckenbrodt et al.
patent: 4676935 (1987-06-01), Funke et al.
patent: 38 02 048 A1 (1989-08-01), None
“Gmelin Manual for Inorganic Chemistry” (Assmann et al.), Springer-Verlag, Berlin-Heidelberg-New York, 1981, pp. 99-115.
“Metallographie” (Schumann), 10thEdition, VEB Deutscher Verlag für Grundstoffindustrie, Leipzig, Germayn, pp. 51-57.

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