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Kovarex enrichment process
Kovarex enrichment process 
Recipe 

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Total raw 

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Prototype type 
recipe 
Internal name 
kovarexenrichmentprocess 
Required technologies 

Produced by 

The Kovarex enrichment process is a method for reprocessing uranium in a centrifuge. Although the process requires a large amount of the much rarer uranium235 to start, it can be a good way to get more use out of the available uranium ore.
Contents
Purpose
Uranium processing takes 10 uranium ore and returns 1 uranium235 with 0.007 (0.7%) probability, or 1 uranium238 with 0.993 (99.3%) probability, leading to an expected (though not guaranteed) 1 unit of uranium235 per approximately 143 processing cycles (or about a 1:142 ratio of U235 to U238). This is currently the only probabilitybased crafting recipe in the game.
Uranium235 is necessary to create uranium fuel cells and atomic bombs, in considerable quantities for the latter, but the probability distribution of uranium processing leads to it being produced slowly and creating large stockpiles of U238 as a byproduct. The Kovarex process thus provides the player with a considerably faster (and deterministic) method of producing U235, as well as a use for the surplus U238.
It should be noted that U238 is not useless; it is necessary (and sufficient) to manufacture uranium rounds magazines, uranium cannon shells, and explosive uranium cannon shells, and is required as a secondary ingredient in uranium fuel cells. Therefore, it is not advisable to use the Kovarex process to convert all stockpiled U238 into U235. (Although, in case of shortage, Used up uranium fuel cells can be reprocessed into a modest amount of U238.)
Requirements for initiation (uranium processing)
Unlike all other crafting processes in the game, uranium processing creates U235 and U238 based on probability, rather than in guaranteed deterministic amounts. Additionally, the Kovarex process requires a bulk stockpile of 40 units of the rare uranium235 isotope to initiate in a single centrifuge. Therefore, planning uranium mining and processing for the Kovarex process takes certain considerations not encountered elsewhere in the game.
Expected value
As U235 is created in centrifuges running uranium processing with p = 0.007, the expected number of processing cycles to gain a single unit is E(1,p) = 1 ÷ p = ~143. The expected number of cycles to gain 40 units is then E(40,p) = 40 × E(1,p) = ~5,714 cycles. Note that running this many cycles requires mining 57,140 uranium ore, a nontrivial task.
However, given the nature of probability, it is impossible to guarantee that 40 units will be reached in this number of cycles; as a matter of fact, some mathematics yields that the probability that 5,714 cycles will produce at least 40 units of U235 is only about 52%.
Confidence levels
Some further mathematics enables one to calculate the number of uranium processing cycles one must run to obtain at least 40 units of U235 (given p = 0.007) with a given level of confidence (probability of achieving the set goal).
As discussed in the previous section, the level of confidence corresponding to 5,714 cycles (for which the expected value of U235 gained is 40) happens to be about 52% (or, in other words, with this number of cycles, one can expect to fail to reach 40 U235 a bit less than once out of every 2 tries).
Some further example confidence levels that may be of interest to players are given in the table below. Consult the chart to the right for custom values.
Confidence level  Failures  Cycles required 

10%  9 out of 10  4,595 
50%  1 out of 2  5,667 
90%  1 out of 10  6,894 
95%  1 out of 20  7,272 
99%  1 out of 100  8,015 
Trivia
 The Kovarex enrichment process is named after Michal Kovařík, lead designer of Factorio and coowner of Wube, whose online nick is kovarex (which he usually spells lowercase). [1]
 In the real world, uranium235 is the only fissile isotope of uranium and makes up approximately 0.72% of naturallyoccurring uranium, with the other 99.28% being uranium238. The ingame representation is thus highly accurate in this regard. Uranium is commonly enriched in centrifuges to increase the percentage of ^{235}U for use in fission reactions.
 Uranium munitions are made from depleted uranium, a byproduct of uranium enrichment, which is mostly ^{238}U whose natural admixture of the ^{235}U isotope has been lowered even further through the enrichment process. Depleted uranium is minimally radioactive and the reason for its use in munitions is its very high density and other mechanical properties, not radioactivity/toxicity.
History
 0.17.0:
 Can be used with productivity modules once again.
 Use with productivity modules now gives correct amount of bonus items.
 0.15.2:
 No longer usable with productivity modules.
 0.15.0:
 Introduced