The "Atomic Piles" which were used in the 1950's and 60's to produce plutonium from uranium for use in nuclear weapons produced a lot of waste heat. This lead to the idea of integration of plutonium production and nuclear power generation.
"Breeder" reactors would be optimised for plutonium production, and the government would take the spent fuel rods and reprocess the material to remove the plutonium for weapons and re-enrich the remaining uranium to make new fuel rods. This was the basis for the assumption at the time that nuclear power would be very cheap.
By the late 1960's the assumption that more plutonium would be needed indefinitely because we would use up nuclear weapons in wars was shown to be incorrect. Meanwhile the nuclear power industry was not doing so well because the government was not producing new fuel rods for next to nothing, as had been assumed.
The justification for breeder reactors was shifted to using the plutonium in power reactors. This would make nuclear power cheaper, and solve the problem of accumulating spent fuel rods at the reactor sites. The slogan was that the breeder reactors would "produce more fuel than they consumed".
President Nixon (1969 t0 1973) was a proponent of this idea. but it went no where as there were many problems with the plan relating to safety and proliferation. When the price of oil quadrupled in 1973 -74, the price of all other fuels went up (I think that coal went up to 7 times its 1972 price).
Companies like GE which had sold nuclear reactors to electric utilities with 20 and 30 year fixed price contracts for fuel rods found themselves in a bind. The courts ended up voiding most if not all of these contracts, and nuclear power got a lot more expensive to produce.
This and other problems caused the electrical power industry to fall out of love with nuclear reactors, and none have been built for several decades. Nuclear power is now being advocated again, but as far as I know the cost and waste disposal problems are stil unsolved.