What law was it that Jimmy Carter passed about nuclear energy?

I need to know the name of it and more of the story would be nice. Does anyone have any references? As well as the name of the law? Thanks!

It was less of a law and more of a presidential directive that prevented the US government from allowing the recycling of spent nuclear fuel in the US. This was intended to be a way of reducing the probability that spent nuclear fuel could be used to produce plutonium-239. The plutonium-239 could be used for nuclear weapons. It results from the irradiation (neutron absorption) of the uranium-238 in a reactor core.

Uranium-238 does not fission, but it is the dominant isotope in a reactor fuel. The uranium-235 is normally 3 to 5 percent of the reactor fuel, but it fissions to get the energy that comes from the reactor. The rest is uranium-238, which unavoidably gets to absorb neutrons and get converted into plutonium-239. After the uranium-235 is depleted enough such that the reactor no longer can have its chain reaction, the fuel has to be replaced. This "spent" fuel is replaced with new fuel, but the spent fuel still has a lot of uranium-235 and, also, the newly produced plutonium-239, both of which are fissionable and useful for either nuclear weapons or nuclear reactors.

Chemically reprocessing the spent fuel (which is highly radioactive) recovers a lot of fissionable materials and, also, helps remove some of the highly radioactive "fission products" that are really what inhibits using spent reactor fuel in a nuclear weapons program. The fear was that having a lot of reprocessing plants would eventually lead to further proliferation of nuclear weapon technology.