The internal gelation process and a suitable broth formulation with an uranium concentration of 1.3 M was used to produce air-dried uranium trioxide dihydrate (UO3'2H2O) and carbon microspheres with crush strengths greater than 600 g per microsphere. The addition of carbon lowered the slow-pour densities of the air-dried microspheres by a minimum of 9% if all other conditions were held constant. The crush strengths of the air-dried microspheres with and without carbon remained very good. These microspheres were not prone to leach when they were washed with ammonium hydroxide, and they did not have the tendency to crack during subsequent heat treatments. For the UOr2H2O microspheres with and without carbon, dehydration occurred at the same rate. The dehydration was accompanied by spontaneous reduction of the urania to UO2.67- In the same temperature range, hydrogen and carbon can be used to further reduce the urania to uranium dioxide. Therefore, the loss of carbon during calcination appears to be unavoidable. The current recommendation on calcinations is to use a temperature of 600 °C or higher to minimize the loss of carbon. Dense and strong uranium fuel kernels with carbon were produced in argon at 1680 °C.
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