Oxygen overpressure

Assessing Distillate Fuel Storage Stability by Oxygen Overpressure... 

To compensate for the low efficiency of gaseous oxygen as an oxidant, mediimi temperatures (150-160°C) and oxygen overpressures are required (1). 

The pressure leaching autoclave is continuously operating autoclave. The autoclave is divided in several compartments and the slurry flows inside the autoclave from compartment to compartment as overflow. Every compartment is equipped with an agitator. Oxygen is fed into the slurry, under the agitator. The oxygen overpressure in the autoclave is about 7 bar. The results from existing operations and laboratory test work show total matte to final product recoveries of over 98%. 

Solution from the atmospheric leaching thickener overflow and leach filtrate tank is pumped to the iron autoclave feed tank. From the autoclave feed tank, the solution is pumped through iron removal autoclave. The optimum operating temperature in the autoclave is 85-120 The temperature is controlled with steam (steam coils) depending on situation. The oxygen overpressure in the autoclave is 1-2 bar. 

Chemical stability of uranium oxides. Both the early Manhattan Project work [9] and the ORNL work [10] indicated that uranium trioxide would be the probable stable form of uranium oxide under the radiolytic gas formed by the radiation-induced decomposition of water in a reactor. Uranium dioxide in an aqueous slurry at 250°C was oxidized to uranium trioxide in the presence of oxygen overpressure and even in the presence of excess hydrogen gas. The extent of this oxidation depended on the oxygen pressure, and seemed to be independent of the partial pressure of hydrogen (Table 4-1). The extent of oxidation of U3O8 to uranium trioxide depended on both temperature and oxygen pressure. The presence... 

Other tests [158,159] carried out in autoclaves with oxygen overpressure have indicated that chloride concentrations as low as 5 to 10 ppm can cause stress-corrosion cracking of vapor phase specimens at temperatures of 100 and 250°C. Similar specimens exposed in the solution phase suffered no comparable attack even with chloride concentrations ranging up to 90 ppm. The quite different results obtained with changes in test condi-... 

Of the wide range of possible combinations of uranium oxide, phosphoric acid, and water, two systems appear to be of special interest. The first, which consists of UO3 dissolved in an aqueous solution containing between 30 and CO w/o of phosphoric acid and pressurized with an oxygen overpressure, was used for the first Los Alamos Power Reactor Experiment (LAPRE-1). The properties of this solution are given in Chapter 3 and summarized in Table 7-8. The vapor pressure of this solution at the design operating temperature of LAPRE-1 (430 C) is 3600 psi. 

---