This is the first in a two-part exchange between Amory Lovins and A. De Volpi about thorium cycles and nuclear proliferation. In this piece, Lovins connects the use of uranium-233 and nuclear proliferation. He analyzes misconceptions about nuclear fuel cycles that breed fissile uranium-233 from thorium and the differences in the use of thorium and plutonium cycles. Lovins concludes that uranium-233 is an attractive material for making fission bombs; pure thorium cycles would take many decades and much uranium to establish and offer no significant safeguards advantage over plutonium cycles; and while thorium cycles have some potential technical advantages, including flexibility, they cannot provide major savings in nuclear fuel resources compared to simpler ways of saving neutrons and uranium.