Corrosion of Uranium, Thorium, and Uranium Alloys in Sodium and Organics
- North American Aviation, Inc., Canoga Park, CA (United States). Atomics International Div.
Sodium and sodium-potassium alloys and the polyphenyl class of organic compounds possess certain advantages over water for use as reactor coolants. There are no reactions between uranium and the pure liquid metals; however, thermodynamic data predict that formation of uranium carbide and uranium hydride is possible in reactions with organics, and with their pyrolytic and radiolytic products. In this paper, available experimental data are reviewed for uranium and uranium alloys exposed both to sodium and sodium-potassium alloys in static and dynamic systems. Effects of irradiation on corrosion rate do not appear to be significant. The observed corrosion rate of uranium and uranium alloys depends very strongly on the impurity (especially oxygen) content of the liquid metal. In capsule-type static corrosion experiments, made with liquid metal with oxygen content near 0.01 weight percent (100 ppm), corrosion rates are of the order of 10 mg/cm2-mo, at temperatures up to 750°C. UO2 and UO have been identified as corrosion products. In dynamic systems, corrosion rates of more than 600 mg/cm2-mo have been observed at 500°C, with oxygen content ranging near 0.005 weight percent (50 ppm). Corrosion rates of uranium and uranium alloys in purified biphenyl are of the order of 1 mg/cm2-mo at temperatures up to 400 °C in static systems. Under dynamic conditions in loop experiments, rates are perhaps five times greater. Formation of uranium monocarbide, through UH3 as an inferred intermediary, has been observed in mono-isopropyl biphenyl under hydrogen gas pressures of the order of 100 psi. Impurities dissolved in the organic, such as air, oxygen, or water, greatly accelerate the corrosion rate. It is concluded that the corrosion rate of uranium and its alloys in liquid sodium and NaK is low enough to permit the use of a static liquid metal bond between the fuel and a cladding of some other metal. Exposure of relatively large surfaces of fuel to circulating liquid metal coolant appears to be not feasible because of the difficulty of adequate control of oxygen in a large volume liquid metal system. There would be no advantage in reactor performance in direct exposure of unclad fuel to an organic coolant, but in case of accidental exposure by way of a cladding failure, the corrosive attack would be relatively very slow.
- Research Organization:
- North American Aviation, Inc., Canoga Park, CA (United States). Atomics International Div.
- Sponsoring Organization:
- US Atomic Energy Commission (AEC)
- OSTI ID:
- 1962381
- Report Number(s):
- NAA-SR--2225
- Country of Publication:
- United States
- Language:
- English
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