The Manhattan Project: Making the Atomic Bomb
Part IV: The Manhattan Engineer District in Operation
In late summer 1943 it was decided that K-25 would play a lesser role than originally intended. Instead of producing fully enriched uranium-235, the gaseous diffusion plant would now provide around fifty percent enrichment for use as feed material in Y-12. This would be accomplished by eliminating the more troublesome upper part of the cascade. Even this level of enrichment was not assured since a barrier for the diffusion plant still did not exist. The decision to downgrade K-25 was part of the larger decision to double Y-12 capacity and fit with Groves' new strategy of utilizing a combination of methods to produce enough fissionable material for bombs as soon as possible.
There was no doubt in Groves' mind that gaseous diffusion still had to be pursued vigorously. Not only had major resources already been expended on the program, but there was also the possibility that it might yet prove successful. Y-12 was in trouble as 1944 began, and the plutonium pile projects were just getting underway. A workable barrier design might put K-25 ahead in the race for the bomb. Unfortunately, no one had been able to fabricate barrier of sufficient quality. The only alternative remaining was to increase production enough to compensate for the low percentage of barrier that met specifications. As Lawrence prepared to throw everything he had into a thirty-beam source for Y-12, Groves ordered a crash barrier program, hoping to prevent K-25 from standing idle as the race for the bomb continued.