What they failed to appreciate, and what the company failed to tell them, was that a fast-breeder uses fuel that has a 19% concentration of the fissileisotope of uranium, 235U. Ordinary nuclear reactors use fuel containing around 3% of the fissileisotope.
Their work there was aimed at separating the light, fissileisotope of uranium (useful for making bombs and reactors), from its more abundant, but less useful, heavy cousin.