How could uranium be extracted from ore to be melt?
There is another process for extraction of Uranium from the uranium ore in the form of UO2(NO3)2 by dissolving the Uranium ore in nitric acid and extract of uranium  using 20% solution of Tributyl phosphate/dodecane. TBP form strong complex with uranium nitrate and thus you can easily remove uranium from other impurities. Obtained UO2(NO3)2 can easily be converted to (NH4)2U2O7 by reacting with ammonia and finally reduction with hydrogen gave you UO2. 
You can't obtained pure Uranium because it is susceptible to oxidation easily.