This wiki is about 0.17, the current experimental version of Factorio.
Information about 0.16, the current stable version of Factorio, can be found on stable.wiki.factorio.com.
Uranium processing
Uranium processing 
Recipe 

+ → +  
Total raw 

+ 
Prototype type 
recipe 
Internal name 
uraniumprocessing 
Required technologies 

Produced by 

Uranium processing is the only way to use uranium ore and the first source of uranium235 and uranium238 that is available to the player. The process has a 99.3% chance to produce 1 uranium238 and a 0.7% chance to produce 1 uranium235.
Initiating the kovarex enrichment process
The kovarex enrichment process acts as another source of uranium235, however 40 uranium235 are needed to initiate it. Due to the 0.7% probability of receiving 1 U235 per uranium processing cycle, it is expected that it takes 5714 uranium processing cycles to receive 40 U235. However, this is not guaranteed, and there is only a 52% probability to actually get 40 U235 after 5714 uranium processing cycles. Further mathematical exploration of this can be found here.
History
 0.15.0:
 Introduced