Molten Uranium Research Articles

Heat Content of Molten Uranium

The heat contents of γ-phase uranium from 1205° to 1394°K and of molten uranium from 1415° to 1579°K were measured using a drop calorimeter.

Treat Study of the Penetration of Molten Uranium and U/5 wt% Fs Alloy through Type 304 Stainless Steel

Penetration rates of uranium and uranium 5 wt% fissium fuels through Type 304 stainless steel cladding were measured in the TREAT reactor using a new electrical failure-detection method. Penetration through a 0.009 in. clad takes about 1 sec in the 1100 to 1200 deg C temperature range. These results agree very well with out-of-pile laboratory experiments performed earlier on the same materials. This agreement indicates that the idealized, basic laboratory experiments can give reliable safety information, but that they should be substantiated by the more realistic in-pile experiments for specific applications. (auth)

Penetration rate studies of stainless steel by molten uranium and uranium-fissium alloy

The rate of penetration of Type 304 stainless steel by molten uranium and uranium-5 wt % fissium alloy was investigated by a dip method in the range 1100 to 1350° C. For the uranium-5 wt % fissium alloy the rate was found to increase rapidly from 0.6 mils/sec ( 1.5 × 10 −3 cm/sec ) at 1100° C to 12 mils/sec ( 3 × 10 −2 cm/sec ) at 1150° C. It then sharply reversed, decreasing to 2.5 mils/sec ( 6.3 × 10 −3 cm/sec ) at 1187° C following which it gradually increased to 5 mils/sec ( 1.3 × 10 −2 cm/sec ) at 1350° C. Molten uranium was found to be somewhat more aggressive than molten uranium-5 wt % fissium alloy. The rates to penetrate 304 stainless steel were 15 mils/sec ( 3.8 × 10 −2 cm/sec ) at 1150° C, 4 mils/sec ( 1 × 10 −2 cm/sec ) at 1187° C and 6.5 mils/sec ( 1.65 × 10 −2 cm/sec at 1350° C. The unexpected reversal in penetration rate with temperature was attributed to the formation of an intermetallic compound which retards the reaction. It was found that surface film formation and phase transformation in the stainless steel were not the cause of this reversal.

The use of tantalum borides for the contalnment of molten uranium and calcium

Tests with molten U and Ca were made on Ta crucibles coated with TaB or Ta/sub 2/B. Results showed that, while in the absence of thermal cycling, coated crucibles lasted longer than uncoated ones, a bond is formed between solidified U and the boride coat with consequent crucible failure on thermal cycling. High B contents of 25 to 1000 ppm were found in the solidified U and Ca after melting in coated crucibles. It is concluded that boride coatings cannot be recommended for Ta cracibles for containing molten U and Ca. (D.L.C.)

Diffusion of Cerium and Zirconium in Molten Uranium

Coefficients for the diffusion of cerium in molten uranium have been measured over the temperature range 1170°–1480°C. An equation relating the diffusion coefficient with temperature is: . At 1200°C the diffusion coefficient for cerium in uranium is . An estimate of the coefficient of diffusion for zirconium in uranium at 1270°C is . A discussion of experimental errors involved in measuring diffusion coefficients at high temperatures is given.

Molten Fluorides as Power Reactor Fuels

A high-temperature reactor using molten uranium salts (Aircraft Reactor Experiment) was operated for a short time at the Oak Ridge National Laboratory. The reactor was of the circulating-fuel type, with a BeO moderator. The maximum outlet temperature achieved was greater than 1500°F (1100 K). It is believed that with further development the ARE could be a prototype for an economical uranium burner. Two very different schools of reactor design have emerged since the first reactors were built. One approach, exemplified by solid fuel reactors, holds that a reactor is basically a mechanical plant; the ultimate rationalization is to be sought in simplifying the heat transfer machinery. The other approach, exemplified by liquid fuel reactors, holds that a reactor is basically a chemical plant; the ultimate rationalization is to be sought in simplifying the handling and reprocessing of fuel. At the Oak Ridge National Laboratory we have chosen to explore the second approach to reactor development. The ORNL aqueous homogeneous reactor is the best-known embodiment of the liquid reactor approach; in a sense it represents the natural culmination of the aqueous reactor systems.

Experimental Estimate of the Free Energy of Formation of Plutonium Trifluoride

A study involving equilibration at 1573°K of fused uranium tetrafluoride and molten irradiated uranium has permitted calculation of the free energy of formation of plutonium trifluoride at 1573°K. During equilibration it is assumed that plutonium is extracted into molten uranium fluoride as represented by one of the following equations:Free energy values for the formation of plutonium trifluoride are calculated from experimentally determined equilibrium constants and the free energy of formation of uranium tetrafluoride, using the expression: The free energy of formation at 1573°K for PuF3 was found to be 93 ± 1.5 kcal/equivalent as compared to an estimated value of 94 kcal/equivalent at 1500°K based on earlier work by Brewer, Bromley, Gilles, and Lofgren.

The distribution of plutonium and fission products between molten uranium and molten uranium trifluoride-barium halide mixtures

The distribution of plutonium between molten uranium and mixtures of uranium trifluoride with barium chloride or fluoride has been measured at temperatures of 1200–1400°C. The equilibrium constant for the reaction Pu + UF 3 = PuF 3 + U is found to be 72 ± 50%, calculated on a mole fraction basis. This corresponds to a standard free energy change for the reaction at 1200°C of approximately −13 kcals, which agrees well with the estimated value. On the 20-g-of-uranium scale, at least 60-min contact between phases is required to establish equilibrium. Fission-product removals from the metal are greater than 99% under a variety of conditions, but owing to the complications of self-slagging effects, the results cannot be interpreted in terms of equilibrium constants. About 80% of fission-product caesium and about 20% strontium volatilizes under these conditions. The same final equilibrium is achieved if the salt mixtures are initially made up with uranium tetrafluoride instead of the trifluoride, reduction by the metallic phase being substantially complete.