DE2063720C3 - Oxidic nuclear fuel or nuclear fuel for fuel and / or breeding elements - Google Patents

Description

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The invention is based on the surprising finding from the fact that some metal oxides such as aluminum oxide or niobium oxide. The like. With uniform distribution in the fuel and / or breeding material have the property of the solid split products formed during nuclear fission to form stable and non-volatile complex metal oxides and thus the cleavage products in the Hold back fuel and / or breeding material.

On the basis of this knowledge, the object of the invention is achieved in the case of a nuclear fuel or granular material of the type mentioned above according to the invention in that the nuclear fuel or nuclear fuel up to 10 atomic percent differs from those formed during nuclear fission solid fission products at temperatures above 800 ° C to form complex metal oxides, which are non-volatile up to a temperature of 1500 ° C, binding metal oxides with low Neutron capture cross-section - such as aluminum oxide, niobium oxide or the like - added in finely divided form

By using finely divided metal oxides in the nuclear fuel or nuclear fuel according to the invention it is achieved that the solid fission products formed during the fission process are bound within the fuel and / or debris particles. Is z. If, for example, aluminum oxide is used as the metal oxide, complex metal oxides such as SrAl ₂ O ₄ , SrAl ₄ O ₇ , SrAl ₁₂ O ₁₉ , BaAl ₂ O ₄ , BaAl ₁₂ O ₁₉ , whose melting points are between 1800 ° C and 1900 ° C are formed. In the same way as with aluminum oxide, the desired binding of the solid cleavage products can also be achieved with finely divided niobium oxide. For example, silicon oxide can also be used, in particular for binding the cesium isotopes. Mixtures of metal oxides, e.g. B. a mixture containing silicon oxide and aluminum oxide can be used, the advantageous properties of the individual metal oxides for binding the solid cleavage products being used for themselves.

The metal oxides can be powdered or powdered Fuel and / or breeding material are added, but it is of course also possible in those cases in which the fuel and / or breeding material is produced from an aqueous solution is to add the material used to bind the solid fission products as an aqueous solution, during the sintering process in a uniformly distributed in the fuel and / or breeding material Oxide passes over.

An embodiment for the production of a fuel and breeding material according to the invention, in which an aqueous solution is assumed in the preparation is described in more detail below.

Embodiment

A solution of 256 g of (TH) (NO ₃ J ₄ 5H ₂ O and 28.5 g of UO ₂ (NO ₃ ) ₂ · 6H ₂ O in 500 ml of water was added to 500 ml of 25% ammonia solution with stirring The resulting precipitate was separated from the supernatant solution by suction and washed free of ions with a total of 10 1 of water

The precipitate was stirred up with 1.5 l of water and, after addition of 9.4 g of A1 (NO ₃ ) ₃ 9H ₂ O and 125 ml of IMHNO _3, heated to the boil. The resulting colloidal solution (sol) was evaporated to 167 ml, a concentration of about 600 g Th / 1 being reached. _{The sol was then mixed with 1M (CH 2} ) ₆ N ₄ solution (0.5 to 1 ml / 10 g sol) at 10 ° C. and added dropwise to paraffin oil at 90 to 95 ° C. The particles formed in the process were freed from the paraffin oil adhering to them with petroleum ether. _{In order to remove the NH 4} NO ₃ formed during the gelation of the sol droplets, the particles were kept in a glass vessel under concentrated ammonia solution for 5 hours. The solution was then suctioned off and the particles were predried in air at 50 to 70 ° C. until they rolled freely. After this treatment, the particles were sintered in a hydrogen-flushed tubular furnace with silicon rod heating for 5 hours at 1300 ° C to form dense fuel cores. The fuel cores were then encased in a fluidized bed made of graphite at 1550 "C by decomposing acetylene with a porous pyrocarbon layer and at 1300 ° C by decomposing propylene with a dense pyrocarbon layer.

ίο A comparative study of the release of the important fission products Sr-90 and Ba-140 from such coated particles under reactor conditions showed that, in contrast to particles with Al ₂ O ₃ -free fuel cores from the here described

beneath particles after 21 days at 1200 ° C no release of Sr-90 and Ba-140 took place.

Claims (1)

Claim: Oxidic nuclear fuel or nuclear fuel for fuel and / or breeding elements in graphite embedded, spherical, heatable up to temperatures of over 1000 ° C, with gas impermeable Contain pyrocarbon-coated fuel or fuel particles, characterized in that that the nuclear fuel is up to 10 atomic percent with the Nuclear fission forming solid fission products at temperatures above 800 ° C to complex Metal oxides which are not volatile up to a temperature of 1500 ° C, connecting metal oxides with a low neutron capture cross-section - such as aluminum oxide, niobium oxide or the like - in fine distributed form are added. 20th The invention relates to an oxidic nuclear fuel or nuclear fuel for fuel and / or Brood elements, which are embedded in graphite, can be heated up to temperatures of over 1000 ° C, spherical, contain fuel or debris particles coated with gas-impermeable pyrocarbon. In the fission process taking place in the nuclear reactor, gaseous and solid fission products are formed not from the fuel and / or breeding element into the coolant because of their high specific radioactivity should arrive. Various measures are known to hold back the gaseous fission products. So you have the fuel and / or breeding material with ceramic or metallic casings surround. In the case of metal-clad fuel elements filled with helium, with operating temperatures below 500 ° C it is known to add metal oxides to the nuclear fuel (DT-OS 1962764). The fission gases such as xenon and krypton are supposed to be present in the additives as gas bubbles be attached and fixed. Is known fcuch, fuel and / or Biutstoffteilchen, their Diameter is below 1 mm, with gas-impermeable pyrocarbon and / or suitable carbides how to coat silicon carbide. Fuel assemblies with coated fuel and / or debris particles are particularly suitable for high-temperature reactors. The coating of the Brennimd / or Brutstoffpartehen with gas-impermeable pyrocarbon holds the resulting gaseous Fission products back. The disadvantage of these fuel assemblies, however, is that when they are heated in the High-temperature reactor up to temperatures above 1000 ° C through an undesired solid diffusion «Let the pyrocarbon layer and the graphite matrix embedding the fuel or tirut elements through occurs. The most important fission products involved in this solid diffusion are the isotopes Sr-89, 90, Bal40 and Cs-134, 137. The object of the invention is at up to temperatures fuel or breeding elements heated to over 1000 ° C to prevent the solid diffusion of fission products with oxidic nuclear fuel or nuclear fuel, without the production of fuel and / or breeding material as well as the production of fuel and / or affect breeding elements. Also the reprocessing of the fuel and / or breeding elements after their use in the high-temperature reactor