Interaction of uranium-molybdenum fuel with an aluminum matrix with deep burnup

Abstract

A thermodynamic analysis is used to calculate the phase and component composition of uraniummolybdenum fuel with burnup 200 GW·days/ton. The equilibrium composition of the gas phase, consisting mainly of gaseous cesium whose pressure reaches 30 kPa, is determined more accurately. The quantitative composition of the phase of solid solutions of tellurides, whose formation degrades the structure of a fuel granule, is presented. Thermal tests of the fuel composition (U-Mo)-Al were performed. The investigation was performed in the presence of simulators of the chemically active fission products of cesium and iodine at different temperature. The interaction zone of (U-Mo)-Al is investigated by means of metallography and scanning electron microscopy. The data obtained on the composition of the indicated zone made it possible to conjecture the character of interaction between the fuel material and the aluminum matrix.The world is showing heightened interest in power reactor facilities of low and ultralow power and research nuclear reactors. These facilities use dispersion compositions in the form of UO 2 , UAl x , U 3 Si 2 , uniformly distributed in an aluminum matrix, as nuclear fuel. The 235 U enrichment often reaches >90% [1].When low (to 20%) enrichment fuel is used, the burnup decreases because of the lower volume content of 235 U [2]. As compensation it is suggested that fuel granules consisting of U-9%Mo (density 17.2 g/cm 3 ) in a matrix consisting of an aluminum alloy be used [3,4]. For example, if in the composition UO 2 -Al the uranium content is 3-3.5 g/cm 3 , then in the composition (U−9Mo)-Al it increases by a factor of 2. However, the use of the composition (U-Mo)-Al is held back by the interaction between uranium-molybdenum granules and an aluminum matrix with burnup 150-200 GW·days/ton [5]. This interaction is complicated. On the one hand, a chemical interaction is observed in the system U-Al at a temperature close to the melting temperature of aluminum. On the other hand, the effect of the fission products on the physicochemical and physical-mechanical characteristics of uranium-molybdenum alloy must be taken into account.The compatibility of the fuel with the matrix can be improved by introducing into the alloy a component, for example, silicon, that substantially lowers the interaction rate as well as by depositing a coating on the surface of the fuel particles [5][6][7][8].Even though from the technological point of view alloying with silicon is considered to be optimal, one should take note of the decrease of the stability of the γ-U-Mo phase. The introduction of silicon into an intermetallide does not exclude the focal interaction with aluminum; in addition, it can increase the temperature gradient at the boundary between a fuel granule and an aluminum matrix [6].Of special interest is the appearance of barrier coatings on the surface of uranium-molybdenum granules. Specifically, it is proposed that a layer of pure molybdenum be deposited on the fuel granules, which would then be protected from int...

Atomistic modeling of the self-diffusion in γ-U and γ-U-Mo

“…Alloys based on the disordered solid solution of molybdenum in γ U (containing from 7 to 12 wt % molybdenum, which corresponds to 15.1-21.6 at %) have high indices of density, thermal conductivity, and increased corrosion and radiation resistance [14][15][16]. However, to reliably evaluate the efficiency of using this alloy in nuclear power engineering, detailed information on a large set of mechanical and thermal properties is nec essary; in addition, we should know how these prop erties vary under intense thermal and radiation effects.…”

Location preferences of fission products in high density U(Mo) dispersion fuel element

“…The aim is to replace high enriched fuel by low enriched one with relative 235 U/U tot contents less than 0.2. Experimental evidence of U(Mo) under irradiation [1][2][3][4] show the existence of an interaction layer (IL) between UMo and the Al matrix. The IL growth influences the mechanical integrity of the plates, generating a structural weakness.…”

A ternary EAM interatomic potential for U–Mo alloys with xenon

“…Alloying pure high-temperature bcc γ -uranium with 5-20 wt% molybdenum with the following quenching produces dense γ -U-Mo structure that can be retained as metastable at T = 300-900 K, and then returns to a stable state with a rise in temperature (T 900 K). Nevertheless, in both metastable and stable states the structure has appropriate mechanical and thermophysical properties [11][12][13][14][15][16] along with a heightened uranium density: 8-9 gU cm −3 for dispersion-type fuels and 15-18 gU cm −3 for monolithic fuel [17][18][19][20]. The last fact is important because it compensates for the low content of enriched uranium in the fuel.…”