Steam continued oxidation effects

According to the thermodynamic calculations performed by Besmann and Lin-demer (1978), the presence of pure H2O vapor in the gap does not effect an oxidation of UO2+X to U4O9 (UO2.25). This oxidation step, which is accompanied by a phase transformation of the uranium oxide, should only be possible in the presence of oxygen in the steam. However, as a consequence of radiolytic reactions the steam in the gap will contain oxygen in any case so that continued oxidation of the UO2-1-X should be possible. Under such conditions, the Csl assumed to be present as the most stable iodine compound in the gap of an intact fuel rod will become thermodynamically unstable in favor of elemental I2 and, in contact with zirconium metal, of Zrh or Zrh, with the rate of oxidation and its extent depending on the concentration of oxygen present in the steam. These oxidized iodine species have a measurable vapor pressure under the prevailing conditions. 

Morita et al. [222] compared bismuth molybdate (1/1) with U—Sb oxides (1 2) at 400°C in a continuous flow system. The methacrolein selectivity for U—Sb is significantly higher than in the case of Bi—Mo (see Table 20). These values increase slightly with increasing conversion of isobutene. Isobutene itself retards the oxidation. In contrast to the pro-pene oxidation, addition of steam accelerates the reaction up to a factor 4 with U—Sb and to a smaller degree with Bi—Mo. With the first catalyst, the activation energy decreases from 27 to 18 kcal mol-1 (0.23 atm steam). U—Sb seems to be less stable than Bi—Mo, but steam has a beneficial effect here too (Table 20). 

An emulsion is an intimate mixture of oil and water, generally of a milky or cloudy appearance. Emulsions may be of two types oil-in-water (where water is the continuous phase) and water-in-oil (where water is the discontinuous phase). Oil-in-water emulsions are used as cutting fluids because of the need for the cooling effect of the water. Water-in-oil emulsions are used where the oil, not the water, must contact a surface-as in rust preventives, non-flammable hydraulic fluids, and compounded steam cylinder oils such emulsions are sometimes referred to as inverse emulsions. Emulsions are produced by adding an emulsifier. Emulsibility is not a desirable characteristic in certain lubricating oils, such as crankcase or turbine oils, that must separate from water readily. Unwanted emulsification can occur as a result of oxidation products--which are usually polar compounds—or other contaminants in the oil. 

---