Seminar: Auf dem Weg zu hochdichten Uranbrennstoffen für Forschungsreaktoren I, Metallurgie hochdichter UMo Brennstoffe unter Bestrahlung
There are strong international efforts to reduce the enrichment of the nuclear fuel currently used in high performance research and test reactors. However, these efforts were hindered due to the fact that the most promising candidate for a new fuel – a Uranium-Molybdenum alloy (UMo) dispersed in an aluminium matrix – suffered from unforeseeable and unacceptable swelling during in-pile test irradiations. The main cause for this behaviour is the build-up of an Al rich diffusion layer at the interface between the UMo and the Al matrix during irradiation.
To overcome this problem, four different possibilities have been identified: (i) the modification of the Al matrix, e.g. by adding diffusion limiting elements (ii) the insertion of a diffusion barrier at the interface UMo-Al (iii) further alloying the UMo with a third element to stabilize the UMo gamma-phase (iv) a combination of means (i)-(iii). In consequence, 20 different UMoX/AlY (X=Si, Ti, Mg, Bi, with and without oxidation layer; Y=Nb, Ti, Pt) samples have been produced and examined before and after irradiation with Iodine at 80MeV from a tandem accelerator. Heavy ion irradiation is frequently used to cause similar radiation damage in samples that also occurs after in-pile irradiation without the drawback of strong activiation of the samples.
First it has been shown, that a protective oxidation layer on the UMo grains does not prevent the formation of a destructive interdiffusion layer. In contrast, it could be shown, that additions to the Al matrix and/or additions to the UMo can be reduced to the self-acting formation of a protective layer at the UMo/Al interface. These layers form already during the production process or latest during in-pile irradiation and prevent the undesired UMo/Al diffusion. On the other hand, ternary additions to the UMo in order to stabilize the gamma-UMo upon heating are of minor importance since irradiation with heavy ion or in-pile reverses the phase decomposition of UMo.
- Physics HS3
- Garching, Garching, Deutschland
- R. Jungwirth, Forschungs-Neutronenquelle Heinz Maier-Leibnitz (FRM II)
- TUM/FRM II