DE1208743B - Process for the production of a sinterable uranium dioxide - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Int. α .:

COIg

German class: 12 η -43/02

Number; 1 208 743

File number: N18537IV a / 12 η

Filing date: June 27, 1960

Opened on: January 13, 1966

The invention relates to a process for preparing a sinterable Urandioxyds from prepared by reduction of uranium compounds at about 700 to 1000 ⁰ C uranium dioxide.

Uranium dioxide is used as a raw material for fissile elements in nuclear reactors. These fissile material elements, which in connection with the process in the nuclear reactor preferably consist of stoichiometric uranium dioxide, are produced by sintering uranium dioxide powder. It is already known that a small deviation from the stoichiometry, with an excess of oxygen in the uranium dioxide lattice, is advantageous in order to facilitate the sintering process. This excess of oxygen naturally has to be removed again afterwards. The sintering process is further promoted by starting from a fine powder. A problem that arises is that the uranium dioxide, in the form of a finely divided powder, is pyrophoric, so that it is easily oxidized in air to a compound with a higher oxygen content. The excess oxygen that occurs is greater than is desirable with regard to good sinterability, since cracks occur in such a product during sintering. It is also already known to carry out the sintering of stoichiometric uranium dioxide in a steam ^{atmosphere at 1400 to 1500 °} C., with excess oxygen atoms being formed. However, it is necessary to leave the product in an inert or reducing atmosphere both during heating to the treatment temperature and during cooling in order to avoid the formation of higher oxides at low temperatures. The sensitivity of uranium dioxide to oxygen can furthermore be reduced by reduction at a temperature above 100 ° C., which, however, reduces the sinterability. It is also possible to temporarily store the uranium dioxide in a carbonic acid atmosphere. After this treatment, when exposed to air, the uranium dioxide continues to _{oxidize slowly until the composition UO 2j25 is} reached.

According to the invention, a sinterable uranium dioxide is now produced from by reducing uranium compounds at about 700 to 1000 ^c C! Immediately after its production, uranium dioxide is subjected to an oxidation treatment at about 700 to 1000 C in an oxygen-free atmosphere containing water vapor until a product with a composition between UO _{2> 02} and UO _{2j0S is} obtained.

This product is not pyrophoric and is a good sintering process for making a sinterable one
Uranium dioxide

Applicant:

N.V. Philips' Gloeilampenfabrieken, Eindhoven

(Netherlands)

Representative:

Dr. rer. nat. H. Schüler, patent attorney,

Munich 12, Ridlerstr. 37

Named as inventor:

Barend Verkerk, Eindhoven (Netherlands)

Claimed priority:

Netherlands of June 30, 1959 (240 719)

bar, and it retains its composition even when stored in air.

In addition, it has been found that when dry pressing to form lozenges with that produced according to the invention Uranium dioxide has a higher density than with the known way from the same raw material achieved uranium dioxide. It should also be noted that the sinterability of the powder by changing the Temperature can be influenced, in the sense that when a lower temperature is used, the The sinterability of the product becomes greater, while when a higher temperature is used, the sinterability of the product decreases as a result of a certain pre-sintering.

The uranium dioxide used as the starting material can be produced in a known manner by reduction at about 700 to 1000 C, for example starting from uranium trioxide hydrate, uranium trioxide (UO ₃ ), uranium oxide (U ₃ O ₈ ), uranium peroxide (UO ₄ ) and non-stoichiometric uranium dioxide. The uranium dioxide is preferably produced by the decomposition and reduction of ammonium diuranate at about 700 to 1000 ^° C., since this results in a fine powder. The reduction can take place in hydrogen, in a hydrogen-containing, otherwise neutral gas or in carbon monoxide.

According to a further preferred embodiment, the oxidation temperature is equal to the reduction temperature chosen because this is technologically easy to achieve.

509 778/239

The oxidation is particularly in a water vapor containing, otherwise oxygen-free argon atmosphere or in a water vapor-containing, im remaining oxygen-free nitrogen atmosphere carried out. For this purpose the argon or the nitrogen is used first deoxygenated by passing the gas through a copper furnace.

Example I.

35 g of ammonium diuranate, which was obtained from a solution of uranyl nitrate by precipitation with 25% strength ^e m NH ₄ OH at 58 to 62 ° C., were placed in an oven and passed over an oxygen-free mixture of 76 volume percent N ₂ and 24 volume percent H ₂ heated to 800 ⁰ C. After this temperature was maintained for 1 hour, the gas flow was replaced by a flow of pure argon that has been passed through water of about 8O ⁰ C prior to entering into the oven and thus containing water vapor. This gas mixture was passed for 1 hour through the powder, while the temperature was maintained at 800 ⁰ C. The resulting product was then cooled and was found to be non-pyrophoric at room temperature. The composition of the product was UO _{2> 0} 4 immediately after manufacture.The product was stored in the air for 26 days and then also had the composition UO _{2 (04} .

B e i s ρ i e 1 II

25 g ammonium diuranate were treated in the manner described in Example I, with the difference that the temperature at which the reduction and followed by the oxidation was 900 ⁰ C. The product was not pyrophoric and the composition shortly after manufacture was UO _2j05 . It was kept 25 days in the air and then also had the composition UO _{2, 05th}

Example III

24 g of uranium oxide U ₃ O ₈ were treated at a temperature of 800 ⁰ C in the manner described in Example I. The product was not pyrophoric and had the composition UO _{2, 04th}

Example IV

Uranium dioxide was produced by reduction in hydrogen at 900 ^° C. and then exposed to air for 2 days. The composition was then UO _{2 # 12} . This powder mixed with an organic binder was placed in a die with a diameter of 12 mm under a pressure of

S 2 t / cm ² pressed pastilles. The density of the pressed products, measured after removal of the binder, averaged 4.57 g / cm ³ . In the same way pastilles of uranium dioxide were pressed, which had been made from the same raw material as the above-mentioned oxide, but according to the method according to the invention, the uranium dioxide is formed by reduction at 800 ° C in hydrogen and then at 800 ° C in an atmosphere of purified Argon and water vapor had been oxidized. The composition of this oxide was UO _2j04 . The densities of the pressed bodies after removal of the binder were 5.22 to 5.33 g / cm ³ .

Claims (4)

Patent claims: 1. A process for the production of a sinterable uranium dioxide from uranium dioxide produced by reducing uranium compounds at about 700 to 1000 ° C, characterized in that the uranium dioxide is subjected to an oxidation ^{treatment at about 700 to 1000 0} C in an oxygen-free atmosphere containing water vapor immediately after production, until a product of the composition between UO _2, UO 2, and ₀ is obtained _2i08. 2. The method according to claim 1, characterized in that the oxidation treatment by a Decomposition and reduction of ammonium diuranate at about 700 to 1000 ° C obtained uranium dioxide is subjected. 3. The method according to claim 1 or 2, characterized in that at an oxidation temperature is worked equal to the reduction temperature. 4. Process according to claims 1 to 3, characterized in that the oxidation in one steam containing argon or nitrogen atmosphere is carried out. Considered publications:
Nuclear Engineering, August 1958, pp. 327, 328.